- Email: [email protected]
Parallel Control for Hybrid Propulsion of Multifunction Ships*
Proceedings of the 20th World Congress Proceedings of 20th The International Federation of Congress Automatic Control Proceedings of the the 20th World World Congress Proceedings of the 20th World Congress Control The of Toulouse, France,Federation July 9-14, 2017 Available online at www.sciencedirect.com The International International Federation of Automatic Automatic Control The International Federation of Automatic Control Toulouse, Toulouse, France, France, July July 9-14, 9-14, 2017 2017 Toulouse, France, July 9-14, 2017
ScienceDirect
IFAC PapersOnLine 50-1 (2017) 2296–2303
Parallel Parallel Parallel Parallel R. R. R. R.
D. D. D. D.
Control for Hybrid Propulsion Control for Hybrid Propulsion Control for Hybrid Propulsion Control for Hybrid Propulsion Multifunction Ships Multifunction Ships Multifunction Ships Multifunction Ships ∗,∗∗ ∗∗ ∗∗
of of of of
Geertsma ∗,∗∗ R. R. Negenborn ∗∗ K. Visser ∗∗ ∗,∗∗ R. R. Negenborn ∗∗ K. Visser ∗∗ Geertsma ∗∗ Geertsma R. ∗∗ K. Visser ∗∗ J. R. J. Hopman ∗∗ Geertsma ∗,∗∗ R. R. Negenborn Negenborn K. Visser ∗∗ J. J. Hopman J. J. Hopman ∗∗ J. J. Hopman ∗ ∗ Netherlands Defence Academy, 1780 CA Den Helder, The ∗ Netherlands Defence Academy, 1780 CA Den Helder, The Defence Academy, 1780 ∗ Netherlands Netherlands, (e-mail: [email protected]). Netherlands Defence Academy, 1780 CA CA Den Den Helder, Helder, The The Netherlands, (e-mail: [email protected]). ∗∗ Netherlands, (e-mail: [email protected]). of Technology, 2628CD Delft, The Netherlands. ∗∗ Delft University Netherlands, (e-mail: [email protected]). ∗∗ Delft University of Technology, 2628CD Delft, The Netherlands. ∗∗ Delft University of Technology, 2628CD Delft, The Netherlands. Delft University of Technology, 2628CD Delft, The Netherlands. Abstract: Multifunction ships, naval vessels in particular, need to reduce fuel consumption Abstract: Multifunction ships, naval vessels in particular, need to reduce fuel consumption Abstract: Multifunction ships, vessels in need to fuel while maintaining manoeuvrability. Hybrid propulsion that runs a main diesel engine and electric Abstract: Multifunction ships, naval naval vessels in particular, particular, need to reduce reduce fuel consumption consumption while maintaining manoeuvrability. Hybrid propulsion that runs a main diesel engine and electric while maintaining manoeuvrability. Hybrid propulsion that runs a main diesel engine and drive in parallel can achieve this. However, a parallel control strategy needs to be developed. In while maintaining manoeuvrability. Hybrid propulsion that runs a mainneeds dieselto engine and electric electric drive in parallel can achieve this. However, a parallel control strategy be developed. In drive in parallel can achieve this. However, a parallel control strategy needs to be developed. In this paper, we use a simulation model of a hybrid propulsion system to investigate two parallel drive in parallel cana achieve this.model However, a parallel control strategy needs to be developed. In this paper, we use simulation of aa hybrid propulsion system to investigate two parallel this paper, we use a simulation model of hybrid propulsion system to investigate two parallel control strategies for diesel mechanical and electrical propulsion on multifunction ships. For the this paper, we usefor a simulation model of a hybrid propulsion system to investigateships. two parallel control strategies diesel mechanical and electrical propulsion on multifunction For the control strategies diesel mechanical and propulsion on multifunction ships. the case study frigate,for parallel can increase the ship top speed 3 kts when usingFor two 4 control strategies for diesel control mechanical and electrical electrical propulsion on with multifunction ships. For the case study frigate, parallel control can increase the ship top speed with 33 kts when using two 4 case study frigate, parallel control can increase the ship top speed with kts when using two MW electric drives and two 10 MW main diesel engines, compared with the same baseline hybrid case study frigate, parallel control can increase the shipcompared top speedwith withthe 3 kts when usinghybrid two 44 MW electric drives and two 10 MW main diesel engines, same baseline MW electric drives and two 10 MW main diesel engines, compared with the same baseline hybrid propulsion parallel control. The diesel dieselengines, engine speed control with electric drive hybrid torque MW electricwithout drives and two 10 MW main compared withwith the same baseline propulsion without parallel control. The diesel speed electric drive torque propulsion without parallel control. The diesel engine speed control with electric drive torque control strategy increases ship acceleration rateengine with 17% andcontrol reduces average engine thermal propulsion without parallel control. The diesel engine speed control with electric drive torque control strategy ship acceleration rate with 17% and reduces average control strategy increases ship acceleration rate with and reduces average engine thermal loading with 150 increases K. Moreover, electric drive control diesel engineengine torquethermal control control strategy increases ship the acceleration rate speed with 17% 17% andwith reduces average engine thermal loading with 150 K. Moreover, the electric drive speed control with diesel engine torque control loading with 150 K. Moreover, the electric drive speed control with diesel engine torque strategy can improve acceleration rate by 40%, while eliminating thermal loading fluctuation due loading with 150 K. Moreover, therate electric drive speed control with dieselloading enginefluctuation torque control control strategy can improve acceleration by 40%, while eliminating thermal due strategy can improve acceleration rate by 40%, while eliminating thermal loading fluctuation due to heavy can seas,improve and also reducing engine average thermal loading with 150 loading K. Future combination strategy acceleration rate by 40%, while eliminating thermal fluctuation due to heavy seas, and also reducing engine average thermal loading with 150 K. Future combination to heavy seas, also engine average thermal loading with K. Future of the proposed electric drive speed control strategy with an adaptive pitch and optimal to heavy seas, and and also reducing reducing engine average thermal loading with 150 150 K. control Future combination combination of the proposed electric drive speed control strategy with an adaptive pitch control and optimal of the proposed electric drive speed control strategy with an adaptive pitch control and power split strategy can potentially further increase hybrid propulsion plant performance. of the proposed electric drive speed control strategy with an propulsion adaptive pitch control and optimal optimal power split strategy can potentially further increase hybrid plant performance. power split strategy can potentially further increase hybrid propulsion plant performance. power split strategy can potentially further increase hybrid propulsion plant performance. © 2017, IFAC (International Federation of Automatic Control) Hosting by Elsevier Ltd. All rights reserved. Keywords: Marine Systems, Control architectures in marine systems, Nonlinear and optimal Keywords: Marine Systems, Control architectures in marine marine systems, Nonlineardrive and optimal optimal Keywords: Marine Systems, Control architectures in systems, Nonlinear and marine systems control, Engine modelling and control, Hybrid and alternative vehicles, Keywords: Marine Systems, Control architectures in marine systems, Nonlineardrive and optimal marine systems control, Engine modelling and control, Hybrid and alternative vehicles, marine systems control, Engine modelling and control, Hybrid and alternative drive vehicles, Dynamic interaction of power plants, Control system design, Energy systems. marine systems control, Engineplants, modelling andsystem control,design, HybridEnergy and alternative Dynamic interaction of power power Control systems. drive vehicles, Dynamic interaction of plants, Control system design, Energy systems. Dynamic interaction of power plants, Control system design, Energy systems. 1. INTRODUCTION is of the same magnitude as the ships services (de Waard, 1. INTRODUCTION INTRODUCTION is of the same magnitude the ships services Waard, 1. is of same magnitude as the (de Waard, 2015). For example, hybridas has been(de applied to 1. INTRODUCTION is of the the same magnitude aspropulsion the ships ships services services (de Waard, 2015). For example, hybrid propulsion has been applied to 2015). For example, hybrid propulsion has been applied to frigates and destroyers (Castles and Bendre, 2009), Electric propulsion has gained enormous interest in the naval 2015). For example, hybrid propulsion has been applied to naval frigates and destroyers (Castles and Bendre, 2009), Electric propulsion has gained enormous interest in the naval frigates and destroyers (Castles and Bendre, 2009), towing vessels (Breijs and Amam, 2016), offshore vessels Electric propulsion gained interest in cruise industryhas in the ‘90senormous (Vie, 1998), because it naval frigates and destroyers (Castles and Bendre, 2009), Electricship propulsion has gained enormous interest in the the towing vessels (Breijs and Amam, 2016), offshore vessels cruise ship industry in the ‘90s (Vie, 1998), because it towing vessels (Breijs Amam, 2013), andand yachts (van2016), Loon offshore and vanvessels Zon, cruise ship industry in (Vie, 1998), it allows to match the connected power capacity towing vessels (Breijs and Amam, 2016), offshore vessels cruise ship industry in the the ‘90s ‘90s (Vie,generating 1998), because because it (Barcellos, (Barcellos, 2013), and yachts (van Loon and van Zon, allowstotal to match the connected power generating capacity (Barcellos, 2013), and yachts (van Loon and van 2016). allows to match the connected power generating capacity with power demand of the vessel. Since then, electric (Barcellos, 2013), and yachts (van Loon and van Zon, Zon, allows to match the connected power generating capacity 2016). with total power demand of the vessel. Since then, electric 2016). with total power demand the vessel. Since then, propulsion has also beenof successfully applied in electric ferries, 2016). with total power demand of the vessel. Since then, electric In most current applications of hybrid propulsion, propulsion has alsocable been layers, successfully applied in capital ferries, In most current applications of hybrid propulsion, the propulsion also been successfully applied in ferries, DP drilling has vessels, icebreakers, tugs, propulsion has alsocable been layers, successfully applied in capital ferries, ship In most current applications hybrid the either operates in directof mode or the in DP drilling vessels, icebreakers, tugs, most current applications ofmechanical hybrid propulsion, propulsion, the DP drilling vessels, cable icebreakers, tugs, capital naval vessels, and even in layers, naval combatants (Moreno and In ship either operates in direct mechanical or in DP drilling vessels, cable layers, icebreakers, tugs, capital ship either operates in direct mechanical mode or in electrical mode. Thesein applications do not mode yet achieve naval vessels, and even in naval combatants (Moreno and ship either operates direct mechanical mode or in naval vessels, even in naval combatants Pigazo, 2007;and Hodge and Mattick, 2008; (Moreno Loyd et and al., electrical mode. These applications do not yet achieve naval vessels, and even in naval combatants (Moreno and electrical mode. These applications do not yet achieve the full potential of the hybrid propulsion concept. First, Pigazo, 2007; Hodge and Mattick, 2008; Loyd et al., electrical mode. These applications do not yet achieve Pigazo, 2007; and 2008; Loyd al., 2003). However, the significant conversion in the full potential of the ishybrid propulsion concept. Pigazo, 2007; Hodge Hodge and Mattick, Mattick, 2008; losses Loyd et et al., the the full potential of propulsion concept. First, when main engine running, the electric driveFirst, can 2003). However, However, the significant significant conversion losses in the the the fullthe potential of the the ishybrid hybrid propulsion concept. First, 2003). the conversion losses in generators, transformers, frequency converters and electric when the main engine running, the electric drive can 2003). However, the significant conversion losses in the very when the main engine is running, the electric drive can efficiently generate electric power, and the diesel generators, transformers, frequency converters and electric the main engine is electric running,power, the electric drivediesel can generators, transformers, frequency converters and electric machines lead to poor propulsion efficiency at full load. when very efficiently generate and the generators, transformers, frequency converters and electric very efficiently generate electric power, and the diesel generators can thus be shut down.power, Secondly, the electric machines lead to poor propulsion efficiency at full load. very efficiently generate electric and the diesel machines lead to poor propulsion efficiency at full load. Thus, electric propulsion has only been applied on ships generators can thus be shut down. Secondly, the electric machines lead propulsion to poor propulsion efficiency at full load. motor generators thus shut down. Secondly, the can can assist thebe for example to Thus, aelectric electric has only only beenand applied on ships ships generators can thus bemain shutdiesel down.engine, Secondly, the electric electric Thus, propulsion has been applied on with very broad operating profile a significant motor can assist the main diesel engine, for example to Thus, electric propulsion has only been applied on ships motor can assist the main diesel engine, for example to improve acceleration performance, reduce thermal loading with aa of very broad operating profile and aa significant significant motor can assist the performance, main diesel engine, for example to with very broad profile and portion hotel load operating compared to the propulsion load. improve acceleration reduce thermal loading with a very broad operating profile and a significant improve acceleration performance, reduce thermal loading of the main engine or increase top speed. However, to run portion of hotel load compared to the propulsion load. improve acceleration performance, reduce However, thermal loading portion of hotel load compared to the propulsion load. of the main engine or increase top speed. to run portion of hotel load compared the propulsion load. of main engine increase top speed. However, to thethe main engine andor drive parallel, an advanced Alternatively, hybrid propulsiontoachieves high efficiencies of the main engine orelectric increase top in speed. However, to run run the main engine and electric drive in parallel, an advanced Alternatively, hybrid propulsion achieves high efficiencies the main engine and electric drive in parallel, an advanced control strategy is required. Alternatively, hybrid propulsion achieves high efficiencies with direct drive diesel engines achieves or gas turbines at high the main engine and electric drive in parallel, an advanced Alternatively, hybrid propulsion high efficiencies control strategy required. with direct direct drive diesel engines orflexibility gas turbines turbines at high high strategy is is with diesel gas at speed, while drive allowing for engines a similaror to select the control control is required. required. with direct drive diesel engines orflexibility gas turbines at high Parallel strategy control of the main engine and electric drive to speed, while allowing for a similar to select the speed, while for aacapacity similar flexibility select the electric powerallowing generating for electricto propulsion Parallel control of the main engine and electric drive to speed, while allowing for similar flexibility to select the Parallel control of the main and electric drive to date has hardly been (Geertsma al., 2017; electric power generating capacity for electric propulsion Parallel control of thestudied main engine engine and et electric driveSulto electric power generating capacity for electric propulsion and hotel load at low ship speeds (Geertsma et al., 2017). date has hardly been studied (Geertsma et al., 2017; Sulelectric power generating capacity for electric propulsion date has hardly been studied (Geertsma et al., 2017; Sulligoi et al., 2012; Topaloglou et al., 2016). Sulligoi et al. and hotel load at low ship speeds (Geertsma et al., 2017). date has hardly been studied (Geertsma et al., 2017; Suland hotel load at low ship speeds (Geertsma et al., 2017). This concept particularly suitable for vessels in ligoi et have al., 2012; Topaloglou et al., 2016). Sulligoi et al. and load is low ship speeds (Geertsma et al.,that 2017). ligoi al., Topaloglou et 2016). Sulligoi et investigated running a shaft generator Thishotel concept isat particularly suitable for vessels vessels that in (2012) ligoi et et have al., 2012; 2012; Topaloglou et al., al., 2016). Sulligoidriven et al. al. This concept particularly for that in some operatingis modes require suitable a large propulsion load and (2012) investigated running a shaft generator driven This concept is particularly suitable for vessels that in (2012) have investigated running a shaft generator driven by the have maininvestigated gas turbine running of a FREMM However, some operating modes require a large large propulsionload load that and (2012) a shaft frigate. generator driven some operating modes require a propulsion load and in other operating modes require a propulsion by the main gas turbine of a FREMM frigate. However, some operating modes require a large propulsionload load that and their by main gas of frigate. However, on parallel speed and voltage droop in other other operating modes require a propulsion by the thestudy mainfocussed gas turbine turbine of aa FREMM FREMM frigate. However, in study focussed on parallel speed and voltage droop in other operating operating modes modes require require aa propulsion propulsion load load that that their their study focussed on parallel speed and voltage control of the electric drive and the diesel generator. Betheir study focussed ondrive parallel speed and generator. voltage droop droop This project is partially supported by the project ‘ShipDrive: A control of the electric and the diesel Becontrol of the electric drive and the diesel generator. Be cause the gas turbine main drive has a very wide operating This project is partially supported by the project ‘ShipDrive: A control of gas theturbine electricmain drivedrive and has the adiesel generator. Be ThisMethodology Novel for Integrated Modelling, Optimizais partially supported by theControl, project and ‘ShipDrive: A cause the very wide operating This project cause the gas turbine main drive has a very wide operating project is partially supported by the project ‘ShipDrive: A envelope that is insensitive to the relatively small dynamNovel for and Optimizacause the that gas turbine main drive has a very wide operating tion ofMethodology Hybrid Ship Systems’(project 13276) ofControl, the Dutch Novel Methodology for Integrated Integrated Modelling, Modelling, Control, andTechnology Optimizaenvelope is insensitive to the relatively small dynamNovel Methodology for Integrated Modelling, Control, and Optimizaenvelope is relatively small ics of thethat shaft generator, to thethe did tion Ship Systems’(project 13276) Dutch envelope that is insensitive insensitive to thepropulsion relatively dynamics small dynamdynamFoundation STW by the Royal Netherlands tion of of Hybrid Hybrid Shipand Systems’(project 13276) of of the theNavy. Dutch Technology Technology ics of the shaft generator, the propulsion dynamics did tion of Hybrid Shipand Systems’(project 13276) of theNavy. Dutch Technology ics of the shaft generator, the propulsion dynamics Foundation STW by the Royal Netherlands Foundation STW and by the Royal Netherlands Navy. ics of the shaft generator, the propulsion dynamics did did Foundation STW and by the Royal Netherlands Navy. Copyright 2332Hosting by Elsevier Ltd. All rights reserved. 2405-8963 © © 2017 2017, IFAC IFAC (International Federation of Automatic Control) Copyright © 2017 2332 Copyright © under 2017 IFAC IFAC 2332Control. Peer review responsibility of International Federation of Automatic Copyright © 2017 IFAC 2332 10.1016/j.ifacol.2017.08.229
Proceedings of the 20th IFAC World Congress R.D. Geertsma et al. / IFAC PapersOnLine 50-1 (2017) 2296–2303 Toulouse, France, July 9-14, 2017
Legend: (1) Hull (2) Diesel generator (3) Electric drive (4) Main diesel (5) Gearbox (6) Shaft (7) Controllable pitch propeller (8) Waves
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(1) G
(2)
(7)
(4)
(2)
(6) (3)
G G
(3)
(2)
MG
(5) (7)
MG
(6)
(4)
(8)
(5)
Fig. 2. Typical hybrid propulsion system layout for a naval vessel. Fig. 1. Artist impression of notional future frigate for the Royal Netherlands Navy, case study in this paper. not have to be considered in detail. Moreover, Topaloglou et al. (2016) investigate electric motor assist with a control strategy aimed at reducing engine thermal loading with a power split controller for the electric machine and speed control for the main engine. The work demonstrates the potential to reduce fuel consumption and emissions, while maintaining engine speed control. However, in this study we investigate parallel control of main diesel engines and electric drives. Although diesel engines have been the working horse for most ship propulsion systems, they can be prone to overloading, particularly for high performance applications such as naval vessels (Van Spronsen and Toussain, 2001; Guillemette and Bussi`eres, 1997). Furthermore, diesel engines on commercial vessels increasingly risk overloading in adverse weather, due to the trend to reduce engine rating to meet EEDI guidelines and their fixed pitch propellers (Kouroutzis and Visser, 2016; Dedes et al., 2012). Moreover, the limited operating envelope of diesel engines can limit the acceleration performance, of particular interest for multifunction ships such as naval vessels, offshore vessels and ferries. In this study, we use simulation models, most of which have been introduced in (Geertsma et al., 2016), to investigate performance of parallel control of hybrid propulsion. We compare two strategies: speed control of diesel engines in parallel with torque control of electric drives and speed control of electric drives in parallel with torque control of diesel engines. We assess engine thermal loading and acceleration performance of these control strategies using a frigate case study, shown in Figure 1, against the same baseline hybrid propulsion without parallel control. Because the static combinator curve mainly determines the amount of fuel to be consumed, fuel consumption is not considered in this paper. The paper is organised as follows: In the first section we describe the hybrid propulsion system of the frigate and introduce the dynamic model. In the second section we describe the baseline strategy and two proposed control strategies. In the third section we present the comparison of these strategies with the baseline strategy. In the final section, we summarise conclusions and propose further research into an adaptive control strategy. 2. SYSTEM DESCRIPTION In this paper, we consider hybrid propulsion that propels a frigate with two shafts, each consisting of one diesel engine, one electric drive, a gearbox, a shaft and a controllable
Xact
V, f
Control actions
Xact
V, f
Diesel engine
Mde
Electric drive
Mem
Gearbox ne and np shaftline
Diesel engine
Mem Mde
Mp T
vw y waves vw
P Electric drive
Propeller
Gearbox np and shaftline n e
Hull
vs
T Propeller
Mp
Fig. 3. Schematic presentation of direct drive propulsion system for naval vessel showing coupling between models. pitch propeller (CPP), as illustrated in Figure 2. Figure 2 also shows the electrical network that feeds the electrical drive, but the electrical network dynamics are not considered in this paper. The model representation of the hybrid propulsion components and their interaction are shown in Figure 3. In order to investigate the performance of the propulsion plant in adverse weather conditions, the influence of waves on the advance speed of the propeller is modelled as a disturbance. The models of the diesel engine, gearbox, shaft-line, propeller, hull and waves have been described in Geertsma et al. (2016). This paper introduces the model that represents the induction machine and its frequency converter to complete the hybrid propulsion model. 2.1 Induction machine model Induction machine models can be categorised in three categories: equivalent circuit models, state-space models and partial or complete finite element models (Singh et al., 2016). Because we are interested in the control of the induction machine, including the transients in machine field and torque, we use a fifth-order state-space induction machine model as proposed in (Ong, 1998). Furthermore, we assume balanced supply voltage and thus neglect the zero sequence current. In order to reduce the simulation time, we model the flux equations in the synchronously rotating reference frame aligned with the rotor flux, leading to stationary flux vectors and a zero q component of the rotor field, while Ong (1998) uses the stationary reference frame. First, the following state equations represent the dynamic behaviour of the stator and rotor flux linkages:
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Proceedings of the 20th IFAC World Congress 2298 R.D. Geertsma et al. / IFAC PapersOnLine 50-1 (2017) 2296–2303 Toulouse, France, July 9-14, 2017
t
rs e Ψmq (t) − Ψeqs (t) xs 0 ωe (t) e − Ψds (t) dt ωb t rs uds (t) + (Ψemd (t) − Ψeds (t)) Ψeds (t) = ωb xs 0 ωe (t) e Ψqs (t) dt + ωb t rr e Ψmq (t) − Ψeqr (t) Ψeqr (t) = ωb x r 0 ωe (t) − ωr (t) e Ψdr (t) dt − ωb t rr (Ψemd (t) − Ψedr (t)) Ψedr (t) = ωb x r 0 ωe (t) − ωr (t) e + Ψqr (t) dt, ωb rr ωb ieqr (t) ωe (t) = ωr (t) − Ψedr (t) t ρe (t) = ωe (t)dt, Ψeqs (t) = ωb
uqs (t) +
(1)
(2)
(3)
(4)
(5) (6)
0
where Ψeqs is the quadrature component of the stator flux linkage per second in the rotating reference frame in V, ωb is the base frequency in rad/s, uqs is the quadrature component of the stator voltage in V, rs is the stator resistance in Ω, xs is the stator self-inductance in Ω, Ψemq is the quadrature component of the mutual flux linkage per second in the rotating reference frame in V, ωe is the frequency of the rotating reference frame in rad/s, Ψeds is the direct component of the stator flux linkage per second in the rotating reference frame in V, uds is the direct component of the stator voltage in V, Ψemd is the direct component of the mutual flux linkage per second in the rotating reference frame in V, Ψeqr is the quadrature component of the rotor flux linkage per second in the rotating reference frame in V, rr is the rotor resistance in Ω, xr is the rotor self-inductance in Ω, ωr is the electrical rotor speed in rad/s, Ψedr is the direct component of the rotor flux linkage per second in the rotating reference frame in V and ρe is the angle of the rotating reference frame relative to the a phase of the stator. The electrical rotor speed ωr is determined by the induction machine shaft speed ωi , as follows: ωr = Pp ωi ,
(7)
where Pp is the number of pole pairs of the electric machine. Second, the relationship between the mutual flux and the stator and rotor flux can be represented, as follows: e Ψqs (t) Ψeqr (t) (8) Ψemq (t) = xM + x xlr e ls Ψds (t) Ψedr (t) Ψemd (t) = xM + (9) xls xlr 1 1 1 1 = + + , (10) xM xm xls xlr where xM is the equivalent inductance in Ω and xm is the mutual inductance in Ω.
Third, the quadrature and direct stator and rotor current in the synchronously rotating reference frame ieqs , ieds , ieqr and iedr can be represented by the following equations: Ψeqs (t) − Ψemq (t) ieqs (t) = (11) xls Ψe (t) − Ψemd (t) ieds (t) = ds (12) xls Ψeqr (t) − Ψemq (t) ieqr (t) = (13) xlr Ψe (t) − Ψemd (t) iedr (t) = dr . (14) xlr The phase values of the currents can then be obtained using Park’s transformation (Ong, 1998, Ch. 5 p. 142). These current values are used as feedback for the controller. Finally, the electromagnetic torque Tem produced in the induction machine can be described as follows: 3Pp e Ψds (t)ieqs (t) − Ψeqs (t)ieds (t) . (15) Tem (t) = 2ωb
2.2 Frequency converter model
This study investigates the mechanical dynamics of parallel control of hybrid propulsion. This study does not intend to study the dynamics of the electrical network. Because the response time of modern frequency drives is in the order of ms and the mechanical dynamic responsi is in the order of 0.1 s, we assume the induction machine is fed with an ideal voltage source. The frequency converter is thus modelled as an ideal voltage source providing the requested voltage and frequency to the induction machine. The control strategy to provide the voltage and frequency reference is discussed in Section 3. 3. CONTROL STRATEGIES 3.1 Baseline control strategy In the baseline control strategy the main diesel engine provides propulsion at high ship speeds. The primary control objective is to provide propulsion at the requested virtual shaft speed nvirt in rpm, which is the product of pitch ratio P and shaft speed ns in rpm as introduced in (Vrijdag et al., 2008), as follows: P (t) − P0 nvirt (t) = ns (t), (16) Pnom − P0 where P0 is the pitch ratio at which the propeller delivers zero thrust and Pnom is the nominal pitch ratio. The relationship between the virtual shaft speed setpoint, the engine speed setpoint and pitch ratio setpoint is determined in the combinator curve as discussed in Martelli (2014) and Geertsma et al. (2016). This combinator curve should ensure the static operating points of the engine in design conditions have sufficient margin to the engine operating envelope. The combinator curve used in the baseline control strategy is illustrated in Figure 4. Please note that the nominal pitch ratio Pnom for the baseline control strategy is lower (1.48) than the pitch ratio for the parallel control strategies (1.8), because the total available power at maximum shaft speed is reduced. Moreover, the matching of the propeller with the hybrid propulsion plant
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shaft speed [%] and relative pitch setpoint [%]
100
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Table 1. Speed and torque control parameters
80 60
proportional gain speed KP S reset rate speed KIS proportional gain torque KP T reset rate torque KIT proportional gain field KP D reset rate field KID acceleration rate dnmax
40 20 0 -20
induction machine 10 0.02 1 0.2 1 0.5 1.5 rev/s
diesel engine 2 0.5 0.1 2
0.75 rev/s
-40 -60 -80 -100
iqse* idse*
shaft speed for speed control relative pitch setpoint relative torque setpoint for torque control
-80
-60
-40
-20
0
20
40
60
80
100
ωr iqss iqss
Fig. 4. Combinator curve for diesel mechanical and hybrid propulsion for baseline and parallel control strategies. Speed control Equation (17) ne
Figure 3
Torque control Xset,1
nref Equation (34) Me
Q* D*
Voltage Decomposition Equation 23-26
vqss* vdss*
120
virtual shaft speed setpoint [rpm]
nref
PID control Equation 21-22
Current transformation Equation 17-20
iqse idse
Fig. 6. Schematic representation of indirect field oriented control strategy.
Xset,2
proposed in Wesselink et al. (2006), Martelli (2014) and Martelli et al. (2014).
Figure 3
Fig. 5. Control loop for mechanical propulsion for speed control and torque control. was performed with total available power of the diesel engine and the electric drive according to the matching procedure proposed in Stapersma (2005). The primary control strategy for the baseline controller is engine speed control, using the speed setpoint from the combinator curve. The schematic representation of diesel engine speed control is shown in Figure 5. The controller algorithm is defined as follows: ne (t) nref (t) + − Xset (t) = KP S 100 nnom t ne (t) nref (t) KIS − dt, (17) 100 nnom 0
where Xset is the fuel pump setpoint in %, KP S is the proportional gain for speed control, KIS is the reset rate for speed control, nref is the reference speed in % and nnom is the nominal engine speed in rev/s.
In order to prevent thermal overloading of the diesel engine, the acceleration rate can be limited as proposed in Vrijdag et al. (2010). With a virtual shaft speed acceleration rate of 0.75 rev/s, engine loading is retained within the operating envelope, as will be shown in Section 4. The resulting speed control parameters are listed in Table 1. In all control strategies the behaviour of the pitch controller and the associated hydraulic circuit is simplified with a first order time delay as described in Geertsma et al. (2016). Alternative modelling strategies that account for the delays due to the non-linearities in CPP system behaviour, as discussed in Godjevac et al. (2009), are
3.2 Engine speed control parallel with electric drive torque control In this control strategy, the secondary control objective is to assist diesel engine main propulsion to allow higher ship speeds and increase acceleration, while maintaining the primary objective to provide the requested virtual shaft speed. We maintain engine speed control and provide additional torque to the shaft line with the electric motor. The electric motor torque is controlled with direct field oriented control as proposed by Blaschke (1974) and Hasse (1969) and covered in depth in Sudhoff et al. (1998), Trzynadlowski (2001) and Ong (1998). Figure 6 illustrates the schematic representation of the field oriented control strategy used in this study. The quadrature and direct current references in the syne chronously rotating reference frame ie∗ qs and ids ∗ in A are determined from the torque and direct rotor flux references ∗ Tem in N m and Ψe∗ dr in V , as follows: ∗ 2 (xlr + xm ) Tem (t)ωb e∗ 3P xm Ψdr (t) 1 e∗ e∗ Ψ (t). ids (t) = xm dr
ie∗ qs (t) =
(18) (19)
The actual quadrature and direct current in the syne∗ chronously rotating reference frame ie∗ qs and ids in A can be determined from the measured stator current and mutual flux ωslip in rad/s, as follows: xr + xm s Ψsqr (t) = Ψmq (t) − xr isqs (t) (20) xm xr + xm s Ψmd (t) − xr isds (t) (21) Ψsdr (t) = xm
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|Ψsr (t)| =
2 2 Ψsdr (t) + Ψsqr (t)
Ψsdr (t) |Ψsr (t)| Ψsqr (t) sin ρe (t) = s |Ψr (t)| ieqs (t) = isqs (t) cos (ρe (t)) − isds (t) sin (ρe (t)) ieds (t) = isqs (t) sin (ρe (t)) − isds (t) cos (ρe (t)).
cos ρe (t) =
(23) (24) (25) (26)
Subsequently, PID control is applied to obtain the quadrature and direct references Q∗ and D∗ , as follows: e (27) Q∗ (t) = KP T ie∗ qs (t) − iqs (t) + t e∗ iqs (t) − ieqs (t) dt KIT 0
e D∗ (t) = KP D (ie∗ ds (t) − ids (t)) + t e KID (ie∗ ds (t) − ids (t)) dt,
• Increase acceleration by fully utilising electric motor torque, because the electric motor runs most efficiently at rated torque. • Reduce engine thermal loading and thermal loading fluctuation by running the engine at constant torque. The maximum cylinder temperature is used as an indicator for the thermal loading.
(22)
(28)
0
where KP T , KIT , KP D and KID are the gains and reset rates, which have been determined by manual tuning, as defined in Table 1. Finally, the decoupling equations, as discussed in (Ong, 1998, Ch. 9, pp. 448), are used to obtain the direct and s∗ s∗ quadrature voltage references vqs and vqs , as follows: xs ωe (t) e xm ωe (t) e∗ ids (t) + Ψdr (t) ωb xr + x m ωb (29) e∗ x x ω (t) dΨ (t) s e m e∗ dr (t) = D∗ (t) + ieqs (t) + vds ωb (xr + xm ) ωb dt (30) e s∗ e (31) vqs (t) = vqs (t) cos (ρe (t)) + vds (t) sin (ρe (t)) e s∗ e vds (t) sin (ρe (t)) + vds (t) cos (ρe (t)). (32) (t) = − vqs The phase values of the voltage can then be obtained using Clarke’s transformation (Ong, 1998, Ch. 5 p. 142). These phase voltages serve as the reference values for the frequency converter, which is assumed to be an ideal voltage source. e∗ (t) = Q∗ (t) + vqs
∗ in N m The relative torque setpoint for torque control Tem is a function of the virtual shaft speed and is shown in the combinator curve in Figure 4. Because we intend to investigate the difference between engine speed control and electric drive speed control, we use an equal power split between the engine and electric drive, using the propeller law. Both proposed parallel control strategies could be combined with more advanced optimised power split control strategies as proposed for automotive applications in Sciarretta et al. (2014), Koot et al. (2005) and Silvas et al. (2015) and for ship application in Grimmelius et al. (2011) and Breijs and Amam (2016).The speed and pitch setting for this control strategy remain the same as in the baseline strategy and are also shown in Figure 4.
3.3 Electric drive speed control parallel with engine torque control In this control strategy the primary objective again is to propel the ship at the requested virtual shaft speed, with the following secondary objectives:
The electric drive now utilises speed control, by adding an extra speed control loop in front of the torque controller, as follows: ∗ ω (t) − ωr (t) ∗ + Tem (t) = KP S ωnom t ∗ ω (t) − ωr (t) dt, (33) KIS ωnom 0 where ω ∗ is the reference speed for the induction machine as defined in the combinator curve shown in Figure 4. Furthermore the diesel engine is controlled with a torque control loop, as previously proposed in Geertsma et al. (2016) and illustrated in Figure 5. The fuel pump setpoint Xset (t) is derived from the engine torque setpoint Me∗ , as follows: ∗ Me (t) Me (t) + − Xset (t) = KP T Menom Menom t ∗ Me (t) Me (t) KIT dt, (34) − Menom Menom 0 where Menom is the nominal engine torque in kNm and the engine torque setpoint Me∗ is a function of the virtual shaft speed and is shown in the combinator curve in Figure 4. 4. RESULTS 4.1 Simulation experiments In this paper, we consider a frigate as a case study with hybrid propulsion. The parameters of the hybrid propulsion plant, which are based on the parameters in Geertsma et al. (2016), are listed in Table 2. We investigate heavy weather condition in sea state 5. The MATLAB Simulink R2104b software has been used on a PC with Intel Core i5 processor and 8 GB memory to simulate the hybrid propulsion plant. In the simulation experiment we study an acceleration manoeuvre from 44 rpm to the maximum 134 rpm virtual shaft speed in design conditions, starting at t = 200s, as shown in Figure 7. The results in the phase plane in Figure 8 show that during the acceleration procedure the engine loading meets and slightly exceeds the temporary operation limit. Therefore, the acceleration rate limitation has been chosen at its limit for design conditions, for the chosen control strategy and combinator curve. 4.2 Engine speed control parallel with electric drive torque control The simulation results of engine speed control parallel with the electric drive in torque control in Figure 7 show that the ship accelerates to a 3 kts higher ship speed and at a faster rate of acceleration due to the additional torque of the electric drive: 60 s from 10 to 20 kts in stead of 70 s. Furthermore, the cylinder peak temperature, an indicator
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Table 2. Frigate case study model parameters. Hull ship mass m number of propellers kp thrust deduction factor t maximum ship speed vmax design resistance Rvmax nominal resistance factor c0 Propeller wake fraction w diameter D design pitch Pd nominal pitch Pnom relative rotative efficiency ηR Gearbox and shaftline reduction ratio i total moment of inertia Itot shaft efficiency ηs gearbox loss function parameter a agb gearbox loss function parameter b bgb gearbox loss function parameter c cgb Induction machine pole pairs P nominal voltage V base speed ωb mutual reactance xm stator self reactance xs rotor self reactance xr stator resistance rs rotor resistance rr nominal power Pnom
5200e3 kg 2 0.19 27 kts 1138 kN 5896 kg/m 0.09 4.8 m 1.4 1.48 and 1.8 1 7.463 12500 kgm2 0.99 0.0925 kNm 0.149 kNms 0.0088 3 3300 kV 2 π 50 rad/s 9.11 Ω 0.255 Ω 0.255 Ω 0.0083 Ω 0.0083 Ω 4000 kW
Diesel engine nominal power Pnom nominal speed nnom number of cylinders ie fuel injection constant CX fuel pump time delay τX heat release efficiency ηq effective compression ratio rc cylinder volume at state 1 V1 nominal pressure at state 1 p1nom temperature at state 1 T1 gas constant of air Ra specific heat at constant volume of air cv,a specific heat at constat pressure of air cp,a isentropic index of air κa polytropic exponent for expansion nexp nominal mechanical efficiency ηmnom nominal constant volume portion Xcv,nom constant volume portion gradient Xcv,grad
10000 kW 16.7 rev/s 20 2.7 g 0.02 s 0.78 12.5 0.0020 m3 4.1e5 Pa 328 K 287 J/kgK 717.5 J/kgK 1004.5 J/kgK 1.4 1.38 0.90 -0.169 -1
Sea state 5 wave amplitude ζ wave radial frequency ω wave number k water depth at propeller center z standard gravity g
1.75 m 0.74 rad/s 0.056 6.5 m 9.81 m/s2
20
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Fig. 7. Ship speed and cylinder peak temperature during acceleration manoeuvre of baseline, parallel diesel engine speed control and parallel electric drive speed control strategies. for engine thermal loading, has reduced by 150 K, which can lead to significantly less maintenance. Moreover, a reduced peak temperature, and the associated increased air excess ratio will lead to a reduction in NOx as discussed in Topaloglou et al. (2016). The simulation results in Figure 9 show that the electric motor torque increases with the engine speed. Although the electric drive could deliver full torque directly, the speed control strategy for the diesel engine would dras-
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Fig. 8. Phase plane presentation of acceleration manoeuvre from 44 rpm to 134 rpm in engine operating envelope for baseline control. tically reduce the diesel engine load, leading to a very low engine load, which is highly unfavourable. Furthermore, the engine loading during the manoeuvre, shown in Figure 10, has sufficient margin to the engines temporary operation limit. 4.3 Electric drive speed control parallel with engine torque control The simulation results of Figure 7 show that the ship accelerates even faster with electric drive speed control
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valves and turbochargers, again leading to a reduction in required maintenance.
40
electric motor torque [kNm]
35
5. CONCLUSION AND FUTURE RESEARCH
30
In this paper an electric drive model has been introduced and integrated in the mechanical propulsion model introduced in Geertsma et al. (2016). The combined hybrid propulsion model is used to investigate the dynamic performance of hybrid propulsion systems for multifunction ships. This model needs to be validated against real ship measurements in order to increase confidence in its results.
25 20 15 10 5 acceleration diesel engine speed control acceleration electric drive speed control
0 -5 300
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Fig. 9. Phase plane presentation of acceleration manoeuvre from 44 rpm to 134 rpm in electric drive operating envelope for parallel diesel engine speed control and parallel electric drive speed control strategies. 120
egine torque [kNm]
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engine envelope temporary operation limit acceleration engine speed control acceleration electric drive speed control
The simulation studies performed with this model show that parallel use of hybrid propulsion in the proposed configuration can lead to an increase of ship top speed with 3 kts. Moreover, diesel engine speed control parallel with electric drive torque control can improve the acceleration rate with 17% and reduce engine average thermal loading with 150 K. Even better, an electric drive speed control parallel with diesel engine torque control strategy can improve the acceleration rate by 40%, while eliminating thermal loading fluctuation, and also reducing engine average thermal loading with 150 K. The additional cost is limited to the cost of control strategy development and implementation, as these vessels require an electric drive for silent drive already. Future research should investigate what the impact of the electric drive load dynamics is on the electrical network and whether batteries can provide the load dynamics, thus preventing high load fluctuation on the diesel generators. Furthermore, the combination of parallel control and adaptive pitch control, as proposed in Geertsma et al. (2016), can potentially further improve performance of diesel engine driven hybrid propulsion plants.
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REFERENCES 400
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Fig. 10. Phase plane presentation of acceleration manoeuvre from 44 rpm to 134 rpm in engine operating envelope for parallel diesel engine speed control strategy. parallel with engine torque control, because the electric drive delivers full torque almost instantaneously as shown in Figure 9; the electric motor torque during the acceleration with electric drive speed control increases from a fluctuating value of -2 to 7 kNm to 37 kNm almost instantaneously, before the electric motor speed, which is increased at a limited rate, has accelerated. Moreover, the maximum cylinder peak temperature and rate of change of average peak temperature stay the same, as shown in Figure 7, leading to the same average thermal loading of the engine. However, the fluctuation of the cylinder peak temperature due to the wave disturbance, as extensively discussed in Geertsma et al. (2016) and validated with Van Spronsen and Toussain (2001), has disappeared, because the diesel engine runs at constant torque, as illustrated in Figure 10. This reduction of temperature fluctuation will significantly reduce thermal stresses in the hot diesel engine components such as cylinder head, inlet and outlet
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IFAC PapersOnLine 50-1 (2017) 2296–2303
Parallel Parallel Parallel Parallel R. R. R. R.
D. D. D. D.
Control for Hybrid Propulsion Control for Hybrid Propulsion Control for Hybrid Propulsion Control for Hybrid Propulsion Multifunction Ships Multifunction Ships Multifunction Ships Multifunction Ships ∗,∗∗ ∗∗ ∗∗
of of of of
Geertsma ∗,∗∗ R. R. Negenborn ∗∗ K. Visser ∗∗ ∗,∗∗ R. R. Negenborn ∗∗ K. Visser ∗∗ Geertsma ∗∗ Geertsma R. ∗∗ K. Visser ∗∗ J. R. J. Hopman ∗∗ Geertsma ∗,∗∗ R. R. Negenborn Negenborn K. Visser ∗∗ J. J. Hopman J. J. Hopman ∗∗ J. J. Hopman ∗ ∗ Netherlands Defence Academy, 1780 CA Den Helder, The ∗ Netherlands Defence Academy, 1780 CA Den Helder, The Defence Academy, 1780 ∗ Netherlands Netherlands, (e-mail: [email protected]). Netherlands Defence Academy, 1780 CA CA Den Den Helder, Helder, The The Netherlands, (e-mail: [email protected]). ∗∗ Netherlands, (e-mail: [email protected]). of Technology, 2628CD Delft, The Netherlands. ∗∗ Delft University Netherlands, (e-mail: [email protected]). ∗∗ Delft University of Technology, 2628CD Delft, The Netherlands. ∗∗ Delft University of Technology, 2628CD Delft, The Netherlands. Delft University of Technology, 2628CD Delft, The Netherlands. Abstract: Multifunction ships, naval vessels in particular, need to reduce fuel consumption Abstract: Multifunction ships, naval vessels in particular, need to reduce fuel consumption Abstract: Multifunction ships, vessels in need to fuel while maintaining manoeuvrability. Hybrid propulsion that runs a main diesel engine and electric Abstract: Multifunction ships, naval naval vessels in particular, particular, need to reduce reduce fuel consumption consumption while maintaining manoeuvrability. Hybrid propulsion that runs a main diesel engine and electric while maintaining manoeuvrability. Hybrid propulsion that runs a main diesel engine and drive in parallel can achieve this. However, a parallel control strategy needs to be developed. In while maintaining manoeuvrability. Hybrid propulsion that runs a mainneeds dieselto engine and electric electric drive in parallel can achieve this. However, a parallel control strategy be developed. In drive in parallel can achieve this. However, a parallel control strategy needs to be developed. In this paper, we use a simulation model of a hybrid propulsion system to investigate two parallel drive in parallel cana achieve this.model However, a parallel control strategy needs to be developed. In this paper, we use simulation of aa hybrid propulsion system to investigate two parallel this paper, we use a simulation model of hybrid propulsion system to investigate two parallel control strategies for diesel mechanical and electrical propulsion on multifunction ships. For the this paper, we usefor a simulation model of a hybrid propulsion system to investigateships. two parallel control strategies diesel mechanical and electrical propulsion on multifunction For the control strategies diesel mechanical and propulsion on multifunction ships. the case study frigate,for parallel can increase the ship top speed 3 kts when usingFor two 4 control strategies for diesel control mechanical and electrical electrical propulsion on with multifunction ships. For the case study frigate, parallel control can increase the ship top speed with 33 kts when using two 4 case study frigate, parallel control can increase the ship top speed with kts when using two MW electric drives and two 10 MW main diesel engines, compared with the same baseline hybrid case study frigate, parallel control can increase the shipcompared top speedwith withthe 3 kts when usinghybrid two 44 MW electric drives and two 10 MW main diesel engines, same baseline MW electric drives and two 10 MW main diesel engines, compared with the same baseline hybrid propulsion parallel control. The diesel dieselengines, engine speed control with electric drive hybrid torque MW electricwithout drives and two 10 MW main compared withwith the same baseline propulsion without parallel control. The diesel speed electric drive torque propulsion without parallel control. The diesel engine speed control with electric drive torque control strategy increases ship acceleration rateengine with 17% andcontrol reduces average engine thermal propulsion without parallel control. The diesel engine speed control with electric drive torque control strategy ship acceleration rate with 17% and reduces average control strategy increases ship acceleration rate with and reduces average engine thermal loading with 150 increases K. Moreover, electric drive control diesel engineengine torquethermal control control strategy increases ship the acceleration rate speed with 17% 17% andwith reduces average engine thermal loading with 150 K. Moreover, the electric drive speed control with diesel engine torque control loading with 150 K. Moreover, the electric drive speed control with diesel engine torque strategy can improve acceleration rate by 40%, while eliminating thermal loading fluctuation due loading with 150 K. Moreover, therate electric drive speed control with dieselloading enginefluctuation torque control control strategy can improve acceleration by 40%, while eliminating thermal due strategy can improve acceleration rate by 40%, while eliminating thermal loading fluctuation due to heavy can seas,improve and also reducing engine average thermal loading with 150 loading K. Future combination strategy acceleration rate by 40%, while eliminating thermal fluctuation due to heavy seas, and also reducing engine average thermal loading with 150 K. Future combination to heavy seas, also engine average thermal loading with K. Future of the proposed electric drive speed control strategy with an adaptive pitch and optimal to heavy seas, and and also reducing reducing engine average thermal loading with 150 150 K. control Future combination combination of the proposed electric drive speed control strategy with an adaptive pitch control and optimal of the proposed electric drive speed control strategy with an adaptive pitch control and power split strategy can potentially further increase hybrid propulsion plant performance. of the proposed electric drive speed control strategy with an propulsion adaptive pitch control and optimal optimal power split strategy can potentially further increase hybrid plant performance. power split strategy can potentially further increase hybrid propulsion plant performance. power split strategy can potentially further increase hybrid propulsion plant performance. © 2017, IFAC (International Federation of Automatic Control) Hosting by Elsevier Ltd. All rights reserved. Keywords: Marine Systems, Control architectures in marine systems, Nonlinear and optimal Keywords: Marine Systems, Control architectures in marine marine systems, Nonlineardrive and optimal optimal Keywords: Marine Systems, Control architectures in systems, Nonlinear and marine systems control, Engine modelling and control, Hybrid and alternative vehicles, Keywords: Marine Systems, Control architectures in marine systems, Nonlineardrive and optimal marine systems control, Engine modelling and control, Hybrid and alternative vehicles, marine systems control, Engine modelling and control, Hybrid and alternative drive vehicles, Dynamic interaction of power plants, Control system design, Energy systems. marine systems control, Engineplants, modelling andsystem control,design, HybridEnergy and alternative Dynamic interaction of power power Control systems. drive vehicles, Dynamic interaction of plants, Control system design, Energy systems. Dynamic interaction of power plants, Control system design, Energy systems. 1. INTRODUCTION is of the same magnitude as the ships services (de Waard, 1. INTRODUCTION INTRODUCTION is of the same magnitude the ships services Waard, 1. is of same magnitude as the (de Waard, 2015). For example, hybridas has been(de applied to 1. INTRODUCTION is of the the same magnitude aspropulsion the ships ships services services (de Waard, 2015). For example, hybrid propulsion has been applied to 2015). For example, hybrid propulsion has been applied to frigates and destroyers (Castles and Bendre, 2009), Electric propulsion has gained enormous interest in the naval 2015). For example, hybrid propulsion has been applied to naval frigates and destroyers (Castles and Bendre, 2009), Electric propulsion has gained enormous interest in the naval frigates and destroyers (Castles and Bendre, 2009), towing vessels (Breijs and Amam, 2016), offshore vessels Electric propulsion gained interest in cruise industryhas in the ‘90senormous (Vie, 1998), because it naval frigates and destroyers (Castles and Bendre, 2009), Electricship propulsion has gained enormous interest in the the towing vessels (Breijs and Amam, 2016), offshore vessels cruise ship industry in the ‘90s (Vie, 1998), because it towing vessels (Breijs Amam, 2013), andand yachts (van2016), Loon offshore and vanvessels Zon, cruise ship industry in (Vie, 1998), it allows to match the connected power capacity towing vessels (Breijs and Amam, 2016), offshore vessels cruise ship industry in the the ‘90s ‘90s (Vie,generating 1998), because because it (Barcellos, (Barcellos, 2013), and yachts (van Loon and van Zon, allowstotal to match the connected power generating capacity (Barcellos, 2013), and yachts (van Loon and van 2016). allows to match the connected power generating capacity with power demand of the vessel. Since then, electric (Barcellos, 2013), and yachts (van Loon and van Zon, Zon, allows to match the connected power generating capacity 2016). with total power demand of the vessel. Since then, electric 2016). with total power demand the vessel. Since then, propulsion has also beenof successfully applied in electric ferries, 2016). with total power demand of the vessel. Since then, electric In most current applications of hybrid propulsion, propulsion has alsocable been layers, successfully applied in capital ferries, In most current applications of hybrid propulsion, the propulsion also been successfully applied in ferries, DP drilling has vessels, icebreakers, tugs, propulsion has alsocable been layers, successfully applied in capital ferries, ship In most current applications hybrid the either operates in directof mode or the in DP drilling vessels, icebreakers, tugs, most current applications ofmechanical hybrid propulsion, propulsion, the DP drilling vessels, cable icebreakers, tugs, capital naval vessels, and even in layers, naval combatants (Moreno and In ship either operates in direct mechanical or in DP drilling vessels, cable layers, icebreakers, tugs, capital ship either operates in direct mechanical mode or in electrical mode. Thesein applications do not mode yet achieve naval vessels, and even in naval combatants (Moreno and ship either operates direct mechanical mode or in naval vessels, even in naval combatants Pigazo, 2007;and Hodge and Mattick, 2008; (Moreno Loyd et and al., electrical mode. These applications do not yet achieve naval vessels, and even in naval combatants (Moreno and electrical mode. These applications do not yet achieve the full potential of the hybrid propulsion concept. First, Pigazo, 2007; Hodge and Mattick, 2008; Loyd et al., electrical mode. These applications do not yet achieve Pigazo, 2007; and 2008; Loyd al., 2003). However, the significant conversion in the full potential of the ishybrid propulsion concept. Pigazo, 2007; Hodge Hodge and Mattick, Mattick, 2008; losses Loyd et et al., the the full potential of propulsion concept. First, when main engine running, the electric driveFirst, can 2003). However, However, the significant significant conversion losses in the the the fullthe potential of the the ishybrid hybrid propulsion concept. First, 2003). the conversion losses in generators, transformers, frequency converters and electric when the main engine running, the electric drive can 2003). However, the significant conversion losses in the very when the main engine is running, the electric drive can efficiently generate electric power, and the diesel generators, transformers, frequency converters and electric the main engine is electric running,power, the electric drivediesel can generators, transformers, frequency converters and electric machines lead to poor propulsion efficiency at full load. when very efficiently generate and the generators, transformers, frequency converters and electric very efficiently generate electric power, and the diesel generators can thus be shut down.power, Secondly, the electric machines lead to poor propulsion efficiency at full load. very efficiently generate electric and the diesel machines lead to poor propulsion efficiency at full load. Thus, electric propulsion has only been applied on ships generators can thus be shut down. Secondly, the electric machines lead propulsion to poor propulsion efficiency at full load. motor generators thus shut down. Secondly, the can can assist thebe for example to Thus, aelectric electric has only only beenand applied on ships ships generators can thus bemain shutdiesel down.engine, Secondly, the electric electric Thus, propulsion has been applied on with very broad operating profile a significant motor can assist the main diesel engine, for example to Thus, electric propulsion has only been applied on ships motor can assist the main diesel engine, for example to improve acceleration performance, reduce thermal loading with aa of very broad operating profile and aa significant significant motor can assist the performance, main diesel engine, for example to with very broad profile and portion hotel load operating compared to the propulsion load. improve acceleration reduce thermal loading with a very broad operating profile and a significant improve acceleration performance, reduce thermal loading of the main engine or increase top speed. However, to run portion of hotel load compared to the propulsion load. improve acceleration performance, reduce However, thermal loading portion of hotel load compared to the propulsion load. of the main engine or increase top speed. to run portion of hotel load compared the propulsion load. of main engine increase top speed. However, to thethe main engine andor drive parallel, an advanced Alternatively, hybrid propulsiontoachieves high efficiencies of the main engine orelectric increase top in speed. However, to run run the main engine and electric drive in parallel, an advanced Alternatively, hybrid propulsion achieves high efficiencies the main engine and electric drive in parallel, an advanced control strategy is required. Alternatively, hybrid propulsion achieves high efficiencies with direct drive diesel engines achieves or gas turbines at high the main engine and electric drive in parallel, an advanced Alternatively, hybrid propulsion high efficiencies control strategy required. with direct direct drive diesel engines orflexibility gas turbines turbines at high high strategy is is with diesel gas at speed, while drive allowing for engines a similaror to select the control control is required. required. with direct drive diesel engines orflexibility gas turbines at high Parallel strategy control of the main engine and electric drive to speed, while allowing for a similar to select the speed, while for aacapacity similar flexibility select the electric powerallowing generating for electricto propulsion Parallel control of the main engine and electric drive to speed, while allowing for similar flexibility to select the Parallel control of the main and electric drive to date has hardly been (Geertsma al., 2017; electric power generating capacity for electric propulsion Parallel control of thestudied main engine engine and et electric driveSulto electric power generating capacity for electric propulsion and hotel load at low ship speeds (Geertsma et al., 2017). date has hardly been studied (Geertsma et al., 2017; Sulelectric power generating capacity for electric propulsion date has hardly been studied (Geertsma et al., 2017; Sulligoi et al., 2012; Topaloglou et al., 2016). Sulligoi et al. and hotel load at low ship speeds (Geertsma et al., 2017). date has hardly been studied (Geertsma et al., 2017; Suland hotel load at low ship speeds (Geertsma et al., 2017). This concept particularly suitable for vessels in ligoi et have al., 2012; Topaloglou et al., 2016). Sulligoi et al. and load is low ship speeds (Geertsma et al.,that 2017). ligoi al., Topaloglou et 2016). Sulligoi et investigated running a shaft generator Thishotel concept isat particularly suitable for vessels vessels that in (2012) ligoi et et have al., 2012; 2012; Topaloglou et al., al., 2016). Sulligoidriven et al. al. This concept particularly for that in some operatingis modes require suitable a large propulsion load and (2012) investigated running a shaft generator driven This concept is particularly suitable for vessels that in (2012) have investigated running a shaft generator driven by the have maininvestigated gas turbine running of a FREMM However, some operating modes require a large large propulsionload load that and (2012) a shaft frigate. generator driven some operating modes require a propulsion load and in other operating modes require a propulsion by the main gas turbine of a FREMM frigate. However, some operating modes require a large propulsionload load that and their by main gas of frigate. However, on parallel speed and voltage droop in other other operating modes require a propulsion by the thestudy mainfocussed gas turbine turbine of aa FREMM FREMM frigate. However, in study focussed on parallel speed and voltage droop in other operating operating modes modes require require aa propulsion propulsion load load that that their their study focussed on parallel speed and voltage control of the electric drive and the diesel generator. Betheir study focussed ondrive parallel speed and generator. voltage droop droop This project is partially supported by the project ‘ShipDrive: A control of the electric and the diesel Becontrol of the electric drive and the diesel generator. Be cause the gas turbine main drive has a very wide operating This project is partially supported by the project ‘ShipDrive: A control of gas theturbine electricmain drivedrive and has the adiesel generator. Be ThisMethodology Novel for Integrated Modelling, Optimizais partially supported by theControl, project and ‘ShipDrive: A cause the very wide operating This project cause the gas turbine main drive has a very wide operating project is partially supported by the project ‘ShipDrive: A envelope that is insensitive to the relatively small dynamNovel for and Optimizacause the that gas turbine main drive has a very wide operating tion ofMethodology Hybrid Ship Systems’(project 13276) ofControl, the Dutch Novel Methodology for Integrated Integrated Modelling, Modelling, Control, andTechnology Optimizaenvelope is insensitive to the relatively small dynamNovel Methodology for Integrated Modelling, Control, and Optimizaenvelope is relatively small ics of thethat shaft generator, to thethe did tion Ship Systems’(project 13276) Dutch envelope that is insensitive insensitive to thepropulsion relatively dynamics small dynamdynamFoundation STW by the Royal Netherlands tion of of Hybrid Hybrid Shipand Systems’(project 13276) of of the theNavy. Dutch Technology Technology ics of the shaft generator, the propulsion dynamics did tion of Hybrid Shipand Systems’(project 13276) of theNavy. Dutch Technology ics of the shaft generator, the propulsion dynamics Foundation STW by the Royal Netherlands Foundation STW and by the Royal Netherlands Navy. ics of the shaft generator, the propulsion dynamics did did Foundation STW and by the Royal Netherlands Navy. Copyright 2332Hosting by Elsevier Ltd. All rights reserved. 2405-8963 © © 2017 2017, IFAC IFAC (International Federation of Automatic Control) Copyright © 2017 2332 Copyright © under 2017 IFAC IFAC 2332Control. Peer review responsibility of International Federation of Automatic Copyright © 2017 IFAC 2332 10.1016/j.ifacol.2017.08.229
Proceedings of the 20th IFAC World Congress R.D. Geertsma et al. / IFAC PapersOnLine 50-1 (2017) 2296–2303 Toulouse, France, July 9-14, 2017
Legend: (1) Hull (2) Diesel generator (3) Electric drive (4) Main diesel (5) Gearbox (6) Shaft (7) Controllable pitch propeller (8) Waves
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(1) G
(2)
(7)
(4)
(2)
(6) (3)
G G
(3)
(2)
MG
(5) (7)
MG
(6)
(4)
(8)
(5)
Fig. 2. Typical hybrid propulsion system layout for a naval vessel. Fig. 1. Artist impression of notional future frigate for the Royal Netherlands Navy, case study in this paper. not have to be considered in detail. Moreover, Topaloglou et al. (2016) investigate electric motor assist with a control strategy aimed at reducing engine thermal loading with a power split controller for the electric machine and speed control for the main engine. The work demonstrates the potential to reduce fuel consumption and emissions, while maintaining engine speed control. However, in this study we investigate parallel control of main diesel engines and electric drives. Although diesel engines have been the working horse for most ship propulsion systems, they can be prone to overloading, particularly for high performance applications such as naval vessels (Van Spronsen and Toussain, 2001; Guillemette and Bussi`eres, 1997). Furthermore, diesel engines on commercial vessels increasingly risk overloading in adverse weather, due to the trend to reduce engine rating to meet EEDI guidelines and their fixed pitch propellers (Kouroutzis and Visser, 2016; Dedes et al., 2012). Moreover, the limited operating envelope of diesel engines can limit the acceleration performance, of particular interest for multifunction ships such as naval vessels, offshore vessels and ferries. In this study, we use simulation models, most of which have been introduced in (Geertsma et al., 2016), to investigate performance of parallel control of hybrid propulsion. We compare two strategies: speed control of diesel engines in parallel with torque control of electric drives and speed control of electric drives in parallel with torque control of diesel engines. We assess engine thermal loading and acceleration performance of these control strategies using a frigate case study, shown in Figure 1, against the same baseline hybrid propulsion without parallel control. Because the static combinator curve mainly determines the amount of fuel to be consumed, fuel consumption is not considered in this paper. The paper is organised as follows: In the first section we describe the hybrid propulsion system of the frigate and introduce the dynamic model. In the second section we describe the baseline strategy and two proposed control strategies. In the third section we present the comparison of these strategies with the baseline strategy. In the final section, we summarise conclusions and propose further research into an adaptive control strategy. 2. SYSTEM DESCRIPTION In this paper, we consider hybrid propulsion that propels a frigate with two shafts, each consisting of one diesel engine, one electric drive, a gearbox, a shaft and a controllable
Xact
V, f
Control actions
Xact
V, f
Diesel engine
Mde
Electric drive
Mem
Gearbox ne and np shaftline
Diesel engine
Mem Mde
Mp T
vw y waves vw
P Electric drive
Propeller
Gearbox np and shaftline n e
Hull
vs
T Propeller
Mp
Fig. 3. Schematic presentation of direct drive propulsion system for naval vessel showing coupling between models. pitch propeller (CPP), as illustrated in Figure 2. Figure 2 also shows the electrical network that feeds the electrical drive, but the electrical network dynamics are not considered in this paper. The model representation of the hybrid propulsion components and their interaction are shown in Figure 3. In order to investigate the performance of the propulsion plant in adverse weather conditions, the influence of waves on the advance speed of the propeller is modelled as a disturbance. The models of the diesel engine, gearbox, shaft-line, propeller, hull and waves have been described in Geertsma et al. (2016). This paper introduces the model that represents the induction machine and its frequency converter to complete the hybrid propulsion model. 2.1 Induction machine model Induction machine models can be categorised in three categories: equivalent circuit models, state-space models and partial or complete finite element models (Singh et al., 2016). Because we are interested in the control of the induction machine, including the transients in machine field and torque, we use a fifth-order state-space induction machine model as proposed in (Ong, 1998). Furthermore, we assume balanced supply voltage and thus neglect the zero sequence current. In order to reduce the simulation time, we model the flux equations in the synchronously rotating reference frame aligned with the rotor flux, leading to stationary flux vectors and a zero q component of the rotor field, while Ong (1998) uses the stationary reference frame. First, the following state equations represent the dynamic behaviour of the stator and rotor flux linkages:
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t
rs e Ψmq (t) − Ψeqs (t) xs 0 ωe (t) e − Ψds (t) dt ωb t rs uds (t) + (Ψemd (t) − Ψeds (t)) Ψeds (t) = ωb xs 0 ωe (t) e Ψqs (t) dt + ωb t rr e Ψmq (t) − Ψeqr (t) Ψeqr (t) = ωb x r 0 ωe (t) − ωr (t) e Ψdr (t) dt − ωb t rr (Ψemd (t) − Ψedr (t)) Ψedr (t) = ωb x r 0 ωe (t) − ωr (t) e + Ψqr (t) dt, ωb rr ωb ieqr (t) ωe (t) = ωr (t) − Ψedr (t) t ρe (t) = ωe (t)dt, Ψeqs (t) = ωb
uqs (t) +
(1)
(2)
(3)
(4)
(5) (6)
0
where Ψeqs is the quadrature component of the stator flux linkage per second in the rotating reference frame in V, ωb is the base frequency in rad/s, uqs is the quadrature component of the stator voltage in V, rs is the stator resistance in Ω, xs is the stator self-inductance in Ω, Ψemq is the quadrature component of the mutual flux linkage per second in the rotating reference frame in V, ωe is the frequency of the rotating reference frame in rad/s, Ψeds is the direct component of the stator flux linkage per second in the rotating reference frame in V, uds is the direct component of the stator voltage in V, Ψemd is the direct component of the mutual flux linkage per second in the rotating reference frame in V, Ψeqr is the quadrature component of the rotor flux linkage per second in the rotating reference frame in V, rr is the rotor resistance in Ω, xr is the rotor self-inductance in Ω, ωr is the electrical rotor speed in rad/s, Ψedr is the direct component of the rotor flux linkage per second in the rotating reference frame in V and ρe is the angle of the rotating reference frame relative to the a phase of the stator. The electrical rotor speed ωr is determined by the induction machine shaft speed ωi , as follows: ωr = Pp ωi ,
(7)
where Pp is the number of pole pairs of the electric machine. Second, the relationship between the mutual flux and the stator and rotor flux can be represented, as follows: e Ψqs (t) Ψeqr (t) (8) Ψemq (t) = xM + x xlr e ls Ψds (t) Ψedr (t) Ψemd (t) = xM + (9) xls xlr 1 1 1 1 = + + , (10) xM xm xls xlr where xM is the equivalent inductance in Ω and xm is the mutual inductance in Ω.
Third, the quadrature and direct stator and rotor current in the synchronously rotating reference frame ieqs , ieds , ieqr and iedr can be represented by the following equations: Ψeqs (t) − Ψemq (t) ieqs (t) = (11) xls Ψe (t) − Ψemd (t) ieds (t) = ds (12) xls Ψeqr (t) − Ψemq (t) ieqr (t) = (13) xlr Ψe (t) − Ψemd (t) iedr (t) = dr . (14) xlr The phase values of the currents can then be obtained using Park’s transformation (Ong, 1998, Ch. 5 p. 142). These current values are used as feedback for the controller. Finally, the electromagnetic torque Tem produced in the induction machine can be described as follows: 3Pp e Ψds (t)ieqs (t) − Ψeqs (t)ieds (t) . (15) Tem (t) = 2ωb
2.2 Frequency converter model
This study investigates the mechanical dynamics of parallel control of hybrid propulsion. This study does not intend to study the dynamics of the electrical network. Because the response time of modern frequency drives is in the order of ms and the mechanical dynamic responsi is in the order of 0.1 s, we assume the induction machine is fed with an ideal voltage source. The frequency converter is thus modelled as an ideal voltage source providing the requested voltage and frequency to the induction machine. The control strategy to provide the voltage and frequency reference is discussed in Section 3. 3. CONTROL STRATEGIES 3.1 Baseline control strategy In the baseline control strategy the main diesel engine provides propulsion at high ship speeds. The primary control objective is to provide propulsion at the requested virtual shaft speed nvirt in rpm, which is the product of pitch ratio P and shaft speed ns in rpm as introduced in (Vrijdag et al., 2008), as follows: P (t) − P0 nvirt (t) = ns (t), (16) Pnom − P0 where P0 is the pitch ratio at which the propeller delivers zero thrust and Pnom is the nominal pitch ratio. The relationship between the virtual shaft speed setpoint, the engine speed setpoint and pitch ratio setpoint is determined in the combinator curve as discussed in Martelli (2014) and Geertsma et al. (2016). This combinator curve should ensure the static operating points of the engine in design conditions have sufficient margin to the engine operating envelope. The combinator curve used in the baseline control strategy is illustrated in Figure 4. Please note that the nominal pitch ratio Pnom for the baseline control strategy is lower (1.48) than the pitch ratio for the parallel control strategies (1.8), because the total available power at maximum shaft speed is reduced. Moreover, the matching of the propeller with the hybrid propulsion plant
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shaft speed [%] and relative pitch setpoint [%]
100
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Table 1. Speed and torque control parameters
80 60
proportional gain speed KP S reset rate speed KIS proportional gain torque KP T reset rate torque KIT proportional gain field KP D reset rate field KID acceleration rate dnmax
40 20 0 -20
induction machine 10 0.02 1 0.2 1 0.5 1.5 rev/s
diesel engine 2 0.5 0.1 2
0.75 rev/s
-40 -60 -80 -100
iqse* idse*
shaft speed for speed control relative pitch setpoint relative torque setpoint for torque control
-80
-60
-40
-20
0
20
40
60
80
100
ωr iqss iqss
Fig. 4. Combinator curve for diesel mechanical and hybrid propulsion for baseline and parallel control strategies. Speed control Equation (17) ne
Figure 3
Torque control Xset,1
nref Equation (34) Me
Q* D*
Voltage Decomposition Equation 23-26
vqss* vdss*
120
virtual shaft speed setpoint [rpm]
nref
PID control Equation 21-22
Current transformation Equation 17-20
iqse idse
Fig. 6. Schematic representation of indirect field oriented control strategy.
Xset,2
proposed in Wesselink et al. (2006), Martelli (2014) and Martelli et al. (2014).
Figure 3
Fig. 5. Control loop for mechanical propulsion for speed control and torque control. was performed with total available power of the diesel engine and the electric drive according to the matching procedure proposed in Stapersma (2005). The primary control strategy for the baseline controller is engine speed control, using the speed setpoint from the combinator curve. The schematic representation of diesel engine speed control is shown in Figure 5. The controller algorithm is defined as follows: ne (t) nref (t) + − Xset (t) = KP S 100 nnom t ne (t) nref (t) KIS − dt, (17) 100 nnom 0
where Xset is the fuel pump setpoint in %, KP S is the proportional gain for speed control, KIS is the reset rate for speed control, nref is the reference speed in % and nnom is the nominal engine speed in rev/s.
In order to prevent thermal overloading of the diesel engine, the acceleration rate can be limited as proposed in Vrijdag et al. (2010). With a virtual shaft speed acceleration rate of 0.75 rev/s, engine loading is retained within the operating envelope, as will be shown in Section 4. The resulting speed control parameters are listed in Table 1. In all control strategies the behaviour of the pitch controller and the associated hydraulic circuit is simplified with a first order time delay as described in Geertsma et al. (2016). Alternative modelling strategies that account for the delays due to the non-linearities in CPP system behaviour, as discussed in Godjevac et al. (2009), are
3.2 Engine speed control parallel with electric drive torque control In this control strategy, the secondary control objective is to assist diesel engine main propulsion to allow higher ship speeds and increase acceleration, while maintaining the primary objective to provide the requested virtual shaft speed. We maintain engine speed control and provide additional torque to the shaft line with the electric motor. The electric motor torque is controlled with direct field oriented control as proposed by Blaschke (1974) and Hasse (1969) and covered in depth in Sudhoff et al. (1998), Trzynadlowski (2001) and Ong (1998). Figure 6 illustrates the schematic representation of the field oriented control strategy used in this study. The quadrature and direct current references in the syne chronously rotating reference frame ie∗ qs and ids ∗ in A are determined from the torque and direct rotor flux references ∗ Tem in N m and Ψe∗ dr in V , as follows: ∗ 2 (xlr + xm ) Tem (t)ωb e∗ 3P xm Ψdr (t) 1 e∗ e∗ Ψ (t). ids (t) = xm dr
ie∗ qs (t) =
(18) (19)
The actual quadrature and direct current in the syne∗ chronously rotating reference frame ie∗ qs and ids in A can be determined from the measured stator current and mutual flux ωslip in rad/s, as follows: xr + xm s Ψsqr (t) = Ψmq (t) − xr isqs (t) (20) xm xr + xm s Ψmd (t) − xr isds (t) (21) Ψsdr (t) = xm
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|Ψsr (t)| =
2 2 Ψsdr (t) + Ψsqr (t)
Ψsdr (t) |Ψsr (t)| Ψsqr (t) sin ρe (t) = s |Ψr (t)| ieqs (t) = isqs (t) cos (ρe (t)) − isds (t) sin (ρe (t)) ieds (t) = isqs (t) sin (ρe (t)) − isds (t) cos (ρe (t)).
cos ρe (t) =
(23) (24) (25) (26)
Subsequently, PID control is applied to obtain the quadrature and direct references Q∗ and D∗ , as follows: e (27) Q∗ (t) = KP T ie∗ qs (t) − iqs (t) + t e∗ iqs (t) − ieqs (t) dt KIT 0
e D∗ (t) = KP D (ie∗ ds (t) − ids (t)) + t e KID (ie∗ ds (t) − ids (t)) dt,
• Increase acceleration by fully utilising electric motor torque, because the electric motor runs most efficiently at rated torque. • Reduce engine thermal loading and thermal loading fluctuation by running the engine at constant torque. The maximum cylinder temperature is used as an indicator for the thermal loading.
(22)
(28)
0
where KP T , KIT , KP D and KID are the gains and reset rates, which have been determined by manual tuning, as defined in Table 1. Finally, the decoupling equations, as discussed in (Ong, 1998, Ch. 9, pp. 448), are used to obtain the direct and s∗ s∗ quadrature voltage references vqs and vqs , as follows: xs ωe (t) e xm ωe (t) e∗ ids (t) + Ψdr (t) ωb xr + x m ωb (29) e∗ x x ω (t) dΨ (t) s e m e∗ dr (t) = D∗ (t) + ieqs (t) + vds ωb (xr + xm ) ωb dt (30) e s∗ e (31) vqs (t) = vqs (t) cos (ρe (t)) + vds (t) sin (ρe (t)) e s∗ e vds (t) sin (ρe (t)) + vds (t) cos (ρe (t)). (32) (t) = − vqs The phase values of the voltage can then be obtained using Clarke’s transformation (Ong, 1998, Ch. 5 p. 142). These phase voltages serve as the reference values for the frequency converter, which is assumed to be an ideal voltage source. e∗ (t) = Q∗ (t) + vqs
∗ in N m The relative torque setpoint for torque control Tem is a function of the virtual shaft speed and is shown in the combinator curve in Figure 4. Because we intend to investigate the difference between engine speed control and electric drive speed control, we use an equal power split between the engine and electric drive, using the propeller law. Both proposed parallel control strategies could be combined with more advanced optimised power split control strategies as proposed for automotive applications in Sciarretta et al. (2014), Koot et al. (2005) and Silvas et al. (2015) and for ship application in Grimmelius et al. (2011) and Breijs and Amam (2016).The speed and pitch setting for this control strategy remain the same as in the baseline strategy and are also shown in Figure 4.
3.3 Electric drive speed control parallel with engine torque control In this control strategy the primary objective again is to propel the ship at the requested virtual shaft speed, with the following secondary objectives:
The electric drive now utilises speed control, by adding an extra speed control loop in front of the torque controller, as follows: ∗ ω (t) − ωr (t) ∗ + Tem (t) = KP S ωnom t ∗ ω (t) − ωr (t) dt, (33) KIS ωnom 0 where ω ∗ is the reference speed for the induction machine as defined in the combinator curve shown in Figure 4. Furthermore the diesel engine is controlled with a torque control loop, as previously proposed in Geertsma et al. (2016) and illustrated in Figure 5. The fuel pump setpoint Xset (t) is derived from the engine torque setpoint Me∗ , as follows: ∗ Me (t) Me (t) + − Xset (t) = KP T Menom Menom t ∗ Me (t) Me (t) KIT dt, (34) − Menom Menom 0 where Menom is the nominal engine torque in kNm and the engine torque setpoint Me∗ is a function of the virtual shaft speed and is shown in the combinator curve in Figure 4. 4. RESULTS 4.1 Simulation experiments In this paper, we consider a frigate as a case study with hybrid propulsion. The parameters of the hybrid propulsion plant, which are based on the parameters in Geertsma et al. (2016), are listed in Table 2. We investigate heavy weather condition in sea state 5. The MATLAB Simulink R2104b software has been used on a PC with Intel Core i5 processor and 8 GB memory to simulate the hybrid propulsion plant. In the simulation experiment we study an acceleration manoeuvre from 44 rpm to the maximum 134 rpm virtual shaft speed in design conditions, starting at t = 200s, as shown in Figure 7. The results in the phase plane in Figure 8 show that during the acceleration procedure the engine loading meets and slightly exceeds the temporary operation limit. Therefore, the acceleration rate limitation has been chosen at its limit for design conditions, for the chosen control strategy and combinator curve. 4.2 Engine speed control parallel with electric drive torque control The simulation results of engine speed control parallel with the electric drive in torque control in Figure 7 show that the ship accelerates to a 3 kts higher ship speed and at a faster rate of acceleration due to the additional torque of the electric drive: 60 s from 10 to 20 kts in stead of 70 s. Furthermore, the cylinder peak temperature, an indicator
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Table 2. Frigate case study model parameters. Hull ship mass m number of propellers kp thrust deduction factor t maximum ship speed vmax design resistance Rvmax nominal resistance factor c0 Propeller wake fraction w diameter D design pitch Pd nominal pitch Pnom relative rotative efficiency ηR Gearbox and shaftline reduction ratio i total moment of inertia Itot shaft efficiency ηs gearbox loss function parameter a agb gearbox loss function parameter b bgb gearbox loss function parameter c cgb Induction machine pole pairs P nominal voltage V base speed ωb mutual reactance xm stator self reactance xs rotor self reactance xr stator resistance rs rotor resistance rr nominal power Pnom
5200e3 kg 2 0.19 27 kts 1138 kN 5896 kg/m 0.09 4.8 m 1.4 1.48 and 1.8 1 7.463 12500 kgm2 0.99 0.0925 kNm 0.149 kNms 0.0088 3 3300 kV 2 π 50 rad/s 9.11 Ω 0.255 Ω 0.255 Ω 0.0083 Ω 0.0083 Ω 4000 kW
Diesel engine nominal power Pnom nominal speed nnom number of cylinders ie fuel injection constant CX fuel pump time delay τX heat release efficiency ηq effective compression ratio rc cylinder volume at state 1 V1 nominal pressure at state 1 p1nom temperature at state 1 T1 gas constant of air Ra specific heat at constant volume of air cv,a specific heat at constat pressure of air cp,a isentropic index of air κa polytropic exponent for expansion nexp nominal mechanical efficiency ηmnom nominal constant volume portion Xcv,nom constant volume portion gradient Xcv,grad
10000 kW 16.7 rev/s 20 2.7 g 0.02 s 0.78 12.5 0.0020 m3 4.1e5 Pa 328 K 287 J/kgK 717.5 J/kgK 1004.5 J/kgK 1.4 1.38 0.90 -0.169 -1
Sea state 5 wave amplitude ζ wave radial frequency ω wave number k water depth at propeller center z standard gravity g
1.75 m 0.74 rad/s 0.056 6.5 m 9.81 m/s2
20
100
15 10
baseline Diesel Engine speed control parallel Electric drive speed vontrol parallel
5 0 40
cylinder peak temperature [K]
120
25
60
80
100
4000
120
time [s]
140
160
180
egine torque [kNm]
ship speed [kts]
30
200
baseline Diesel Engine speed control parallel Electric drive speed control parallel
3500 3000 2500
engine envelope temporary operation limit acceleration manoeuvre basline
80
60
40
20
2000 1500 1000 40
60
80
100
120
time [s]
140
160
180
0 300
200
Fig. 7. Ship speed and cylinder peak temperature during acceleration manoeuvre of baseline, parallel diesel engine speed control and parallel electric drive speed control strategies. for engine thermal loading, has reduced by 150 K, which can lead to significantly less maintenance. Moreover, a reduced peak temperature, and the associated increased air excess ratio will lead to a reduction in NOx as discussed in Topaloglou et al. (2016). The simulation results in Figure 9 show that the electric motor torque increases with the engine speed. Although the electric drive could deliver full torque directly, the speed control strategy for the diesel engine would dras-
400
500
600
700
800
engine speed [rpm]
900
1000
1100
Fig. 8. Phase plane presentation of acceleration manoeuvre from 44 rpm to 134 rpm in engine operating envelope for baseline control. tically reduce the diesel engine load, leading to a very low engine load, which is highly unfavourable. Furthermore, the engine loading during the manoeuvre, shown in Figure 10, has sufficient margin to the engines temporary operation limit. 4.3 Electric drive speed control parallel with engine torque control The simulation results of Figure 7 show that the ship accelerates even faster with electric drive speed control
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valves and turbochargers, again leading to a reduction in required maintenance.
40
electric motor torque [kNm]
35
5. CONCLUSION AND FUTURE RESEARCH
30
In this paper an electric drive model has been introduced and integrated in the mechanical propulsion model introduced in Geertsma et al. (2016). The combined hybrid propulsion model is used to investigate the dynamic performance of hybrid propulsion systems for multifunction ships. This model needs to be validated against real ship measurements in order to increase confidence in its results.
25 20 15 10 5 acceleration diesel engine speed control acceleration electric drive speed control
0 -5 300
400
500
600
700
800
electric motor speed [rpm]
900
1000
1100
Fig. 9. Phase plane presentation of acceleration manoeuvre from 44 rpm to 134 rpm in electric drive operating envelope for parallel diesel engine speed control and parallel electric drive speed control strategies. 120
egine torque [kNm]
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engine envelope temporary operation limit acceleration engine speed control acceleration electric drive speed control
The simulation studies performed with this model show that parallel use of hybrid propulsion in the proposed configuration can lead to an increase of ship top speed with 3 kts. Moreover, diesel engine speed control parallel with electric drive torque control can improve the acceleration rate with 17% and reduce engine average thermal loading with 150 K. Even better, an electric drive speed control parallel with diesel engine torque control strategy can improve the acceleration rate by 40%, while eliminating thermal loading fluctuation, and also reducing engine average thermal loading with 150 K. The additional cost is limited to the cost of control strategy development and implementation, as these vessels require an electric drive for silent drive already. Future research should investigate what the impact of the electric drive load dynamics is on the electrical network and whether batteries can provide the load dynamics, thus preventing high load fluctuation on the diesel generators. Furthermore, the combination of parallel control and adaptive pitch control, as proposed in Geertsma et al. (2016), can potentially further improve performance of diesel engine driven hybrid propulsion plants.
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Fig. 10. Phase plane presentation of acceleration manoeuvre from 44 rpm to 134 rpm in engine operating envelope for parallel diesel engine speed control strategy. parallel with engine torque control, because the electric drive delivers full torque almost instantaneously as shown in Figure 9; the electric motor torque during the acceleration with electric drive speed control increases from a fluctuating value of -2 to 7 kNm to 37 kNm almost instantaneously, before the electric motor speed, which is increased at a limited rate, has accelerated. Moreover, the maximum cylinder peak temperature and rate of change of average peak temperature stay the same, as shown in Figure 7, leading to the same average thermal loading of the engine. However, the fluctuation of the cylinder peak temperature due to the wave disturbance, as extensively discussed in Geertsma et al. (2016) and validated with Van Spronsen and Toussain (2001), has disappeared, because the diesel engine runs at constant torque, as illustrated in Figure 10. This reduction of temperature fluctuation will significantly reduce thermal stresses in the hot diesel engine components such as cylinder head, inlet and outlet
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