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wind system with quinary asymmetric inverter without increasing DC-link number
Ain Shams Engineering Journal (2015) xxx, xxx–xxx
Ain Shams University
Ain Shams Engineering Journal www.elsevier.com/locate/asej www.sciencedirect.com
ELECTRICAL ENGINEERING
Hybrid PV/wind system with quinary asymmetric inverter without increasing DC-link numberq Aida Baghbany Oskouei a b
a,*
, Mohamad Reza Banaei a, Mehran Sabahi
b
Department of Electrical Engineering, Azarbaijan Shahid Madani University, Tabriz, Iran Faculty of Electrical and Computer Engineering, University of Tabriz, Tabriz, Iran
Received 1 November 2014; revised 26 April 2015; accepted 19 June 2015
KEYWORDS Hybrid photovoltaic (PV)/wind system; Quinary asymmetric inverter; Coupled inductors; Battery system; Boost converter
Abstract This paper suggests quinary asymmetric inverter with coupled inductors and transformer, and uses it in hybrid system including photovoltaic (PV) and wind. This inverter produces twenty-five-level voltage in addition to merits of multilevel inverter, has only one DC source. Then, it is adequate for hybrid systems, which prevents increasing DC-link and makes control of system easy. Proposed structure also provides isolation in the system and the switch numbers are reduced in this topology compared with other multilevel structures. In this system, battery is used as backup, where PV and wind have complementary nature. The performance of proposed inverter and hybrid system is validated with simulation results using MATLAB/SIMULINK software and experimental results based PCI-1716 data acquisition system. 2015 Faculty of Engineering, Ain Shams University. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
1. Introduction In recent years, renewable energies were expanded because of fossil fuel consumption and greenhouse-effect gas emission q
This research has been supported by Azarbaijan Shahid Madani University. Abbreviations: MPP, maximum power point; MPPT, maximum power point tracking; P&O, perturbation and observation algorithm; PMSG, permanent magnet synchronous generator; PV, photovoltaic; PWM, pulse width modulation; V–I, voltage–current; V–P, voltage–power * Corresponding author. Tel.: +98 9141186476. E-mail addresses: [email protected] (A. Baghbany Oskouei), [email protected] (M.R. Banaei). Peer review under responsibility of Ain Shams University.
Production and hosting by Elsevier
[1–3]. Research and development efforts in renewable energies are required to accurately predict their output reliably assembling them with other conventional sources. So, use of battery in such systems is beneficial solution for increase of reliability and better operation of those systems. Meanwhile, hybrid system including different types of renewable energies was proposed [4,5]. Hybrid system in addition to advantages of renewable energies, causes reduction in battery size and increase in reliability of system [6,7]. The renewable energies in hybrid system can be photovoltaic (PV), wind, fuel cell, etc. In this paper, PV and wind systems are used because of complementary operation. In hybrid systems, an inverter between DC link and load provides ac voltage demand of load, which may have various types. Nowadays, multilevel inverters receive more attention [8–10], which include some power semiconductors and DC voltage sources. The most common multilevel inverter topologies are the cascaded, diode-clamped, and capacitor-clamped
http://dx.doi.org/10.1016/j.asej.2015.06.008 2090-4479 2015 Faculty of Engineering, Ain Shams University. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Please cite this article in press as: Baghbany Oskouei A et al., Hybrid PV/wind system with quinary asymmetric inverter without increasing DC-link number, Ain Shams Eng J (2015), http://dx.doi.org/10.1016/j.asej.2015.06.008
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Nomenclature IPV VPV Iph Io T K q A RSmod G Gr Iscrcell Tr ki NP NS q
current of PV cell voltage of PV cell photocurrent diode saturation current cell temperature Boltzmann’s constant coulomb constant P–N junction ideality factor series resistance real solar radiation solar radiation photocurrent standard test conditions cell absolute temperature temperature coefficient number of parallel PV cell number of series PV cell air density
types [11–13]. Multilevel inverters with only one DC source may be the most desirable topology. Recently [14] presented an inverter called a five-level-active-neutral-point-clamped with coupled inductor, which uses split of the DC-link capacitor. In [8] inverter was proposed using coupled inductors. This inverter can output a novel, single phase, five-level voltage with only one DC source. Meanwhile, asymmetric structures use geometric progression for voltage of DC sources to increase the output levels. Then, it is desirable to use of new inverters in asymmetric structures for producing more voltage levels in output. But increasing DC source numbers in asymmetric structures causes cost increase; also control of system with more DC links is more complex.
At Vx CP k b R x L11 L12 M Tdwell Vi NML Vout_max
area swept out by the turbine blades wind velocity power coefficient tip speed ratio blade pitch angel blade radius rotational speed first coupled inductor second coupled inductor mutual inductance of coupled inductors dwelling time of switch voltage of DC sources in quinary asymmetric inverter maximum levels number in quinary asymmetric inverter maximum generated voltage of quinary asymmetric inverter
This paper proposes quinary asymmetric inverter with coupled inductors and transformer, and uses it in hybrid system including PV and wind systems. This inverter has one DC source which makes it easy and usable in hybrid system. Theoretical analysis and simulation and experimental results are presented to show the validity of the proposed inverter and proposed hybrid system. 2. Renewable energy systems 2.1. PV system PV system is based on solar energy, where PV cell is the most basic generation part in PV. As Fig. 1(a) shows, the PV cell is formed from a diode and a current source was connected antiparallel with a series resistance [15–17]. The relation of the current and voltage in the single-diode cell can be written as follows: qðVPV þ RSmod IPV Þ 1 ð1Þ IPV ¼ Iph IO exp AKT
(a)
(b) Figure 1
Electrical model of PV; (a) PV cell; (b) solar module.
Figure 2 Characteristic curves of a typical PV module in certain solar irradiance and temperature.
Please cite this article in press as: Baghbany Oskouei A et al., Hybrid PV/wind system with quinary asymmetric inverter without increasing DC-link number, Ain Shams Eng J (2015), http://dx.doi.org/10.1016/j.asej.2015.06.008
Hybrid PV/wind system with quinary asymmetric inverter
Figure 3
3
A typical turbine output power versus rotor speed with the wind speed as a parameter.
Figure 5
Generation of the dwelling time.
Figure 4 Structures of single-phase five-level inverter with coupled inductors.
where IPV and VPV are the current and voltage of PV cell respectively. And, Iph is photocurrent, Io is diode saturation current, T is cell temperature, K is Boltzmann’s constant, q is coulomb constant, A is P–N junction ideality factor, and RSmod is series resistance. Photocurrent is directly proportional to solar irradiation and cell temperature, which is described as Iph ¼ Iscrcell þ ki ðT Tr Þ ðG=Gr Þ ð2Þ
Table 1
Figure 6
Asymmetric inverter structure (V1 „ V2 „ „Vn).
where G is the real solar radiation, Gr, Iscrcell , Tr, and ki are the solar radiation, photocurrent standard test conditions, cell absolute temperature, and the temperature coefficient, respectively.
Output voltage of five-level inverter with coupled inductors.
v12
+2E
+E
+E
0
0
E
E
2E
On switches
S1, S4, S6
S1, S4, S5
S1, S3, S6
S1, S3, S5
S2, S4, S6
S2, S4, S5
S2, S3, S6
S2, S3, S5
Please cite this article in press as: Baghbany Oskouei A et al., Hybrid PV/wind system with quinary asymmetric inverter without increasing DC-link number, Ain Shams Eng J (2015), http://dx.doi.org/10.1016/j.asej.2015.06.008
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A. Baghbany Oskouei et al.
Figure 7
Figure 8
Proposed quinary asymmetric inverter structure.
Proposed configuration of hybrid system with battery.
Several same PV cells are arranged together in parallel and series to form PV modules. This work is performed in order to increase output voltage and current of PV system. The current versus voltage of the PV module can be formulated as qðVPV þ RSmod IPV Þ 1 ð3Þ IPV ¼ Np Iph Np IO exp Ns AKT
there is one point with specific voltage and current which produced maximum power [15]. This point is known as maximum power point (MPP), and operation in it is known as maximum power point tracking (MPPT).
Fig. 1(b) shows PV modeling of module, where NP and NS are number of the parallel and series PV cell, respectively. For each module, two characteristic curves are defined: voltage–current (V–I) and voltage–power (V–P). These curves are plotted based on solar irradiance and temperature. Fig. 2 shows such curves for typical PV module. From Fig. 2, it is obvious that in each solar irradiance and temperature, the voltage, current, and power can have different mounts. But
The mechanical power of a wind turbine is expressed as fol-
2.2. Wind system
lows [18–20]: 1 Pmech ¼ qAt CP V3x 2
ð4Þ
where q is the air density, At is the area swept out by the turbine blades, Vx is the wind velocity, and CP is the power
Please cite this article in press as: Baghbany Oskouei A et al., Hybrid PV/wind system with quinary asymmetric inverter without increasing DC-link number, Ain Shams Eng J (2015), http://dx.doi.org/10.1016/j.asej.2015.06.008
Hybrid PV/wind system with quinary asymmetric inverter
Figure 9
Table 2
5
Control loop of load voltage in hybrid system.
Inverter parameters. 100 V 3.1 mH 3 mH 50 Hz 20 O 8.3 mH
VDC L11 = L12 = L M Nominal frequency Load resistance Load inductance
(a)
(b)
(c) Figure 10
Output voltage of proposed inverter with respect to time(s); (a) upper unit; (b) lower unit; (c) total.
Please cite this article in press as: Baghbany Oskouei A et al., Hybrid PV/wind system with quinary asymmetric inverter without increasing DC-link number, Ain Shams Eng J (2015), http://dx.doi.org/10.1016/j.asej.2015.06.008
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A. Baghbany Oskouei et al.
(a)
(b) Figure 11
Stepped variation of (a) solar irradiance; (b) temperature, with respect to time(s).
Figure 12
Output power of PV system and DC–DC converter with respect to time(s).
coefficient and represents the efficiency of the wind turbine which is expressed as 21 116 ð5Þ CP ðk; bÞ ¼ 0:5176 0:4b 5 e ki þ 0:006k ki 1 1 0:035 ¼ ki k þ 0:08b b3 þ 1
ð6Þ
where k is tip speed ratio, b is blade pitch angel (deg), R is the blade radius (m), and x is the rotational speed (rad/s). The torque obtained from wind energy is transferred via the turbine/generator shaft to the rotor of the generator and drives the electrical generator, and in this paper the permanent magnet synchronous generator (PMSG) is used in the output of wind turbine.
Please cite this article in press as: Baghbany Oskouei A et al., Hybrid PV/wind system with quinary asymmetric inverter without increasing DC-link number, Ain Shams Eng J (2015), http://dx.doi.org/10.1016/j.asej.2015.06.008
Hybrid PV/wind system with quinary asymmetric inverter
Figure 13
7
MPPT operation of each PV module in hybrid system.
(a)
(b) Figure 14 time(s).
Wind system characteristics; (a) power characteristic curve of the wind turbine; (b) wind speed variation with respect to
Please cite this article in press as: Baghbany Oskouei A et al., Hybrid PV/wind system with quinary asymmetric inverter without increasing DC-link number, Ain Shams Eng J (2015), http://dx.doi.org/10.1016/j.asej.2015.06.008
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A. Baghbany Oskouei et al.
(a)
(b)
(c) Figure 15
Results of wind system with respect to time(s); (a) rotor speed; (b) output power of turbine; (c) delivered power to DC link.
The power characteristic curve of a typical wind turbine is shown in Fig. 3. It is observed that the maximum power output occurs at different turbine speeds for different wind velocities. 3. Proposed hybrid system 3.1. Proposed quinary asymmetric inverter with coupled inductors and transformer Single-phase five-level inverter with coupled inductors and one DC source was first proposed in [6], which is presented in Fig. 4. In this structure no split of the DC capacitor is needed, avoiding the voltage balancing. The level of the output voltage is half of the DC voltage in all switching conditions, causing
Table 3
much reduced dv/dt. In this inverter, the voltage stresses on all the switches are the same. So, construction of it is easy. In Fig. 4, 2E is the DC source voltage and L11 and L12 are the two coupled inductors. Two coupled inductors have the same number of turns and the mutual inductance of them is M. With attention to Fig. 4 and assuming L11 = L12 = L, the voltage of coupled inductors can be derived as follows: L
dib dic M ¼ vbn v2n dt dt
ð7Þ
L
dic dib M ¼ vcn v2n dt dt
ð8Þ
And according to Kirchhoff’s current law, the following is obtained:
Hybrid system parameters.
Load voltage Load amount
Nominal frequency Filter capacitance Filter inductance
220 V Z1 = 35 + 5j Z1 = 30 + 20j Z1 = 26 + 25j 50 Hz 30 lF 0.5 mH
Please cite this article in press as: Baghbany Oskouei A et al., Hybrid PV/wind system with quinary asymmetric inverter without increasing DC-link number, Ain Shams Eng J (2015), http://dx.doi.org/10.1016/j.asej.2015.06.008
Hybrid PV/wind system with quinary asymmetric inverter
Figure 16
Figure 17
9
DC-link voltage of hybrid system with respect to time(s).
Exchanged power between system and battery in proposed system with respect to time(s).
ib þ ic þ iL ¼ 0
ð9Þ
From 7–9, v2n can be expressed as v2n ¼
vbn þ vcn þ ðL MÞ didtL 2
ð10Þ
The leakage inductance can be designed to be near to mutual inductance of two inductors. Therefore, (10) can be rewritten as v2n ¼
vbn þ vcn 2
ð11Þ
Please cite this article in press as: Baghbany Oskouei A et al., Hybrid PV/wind system with quinary asymmetric inverter without increasing DC-link number, Ain Shams Eng J (2015), http://dx.doi.org/10.1016/j.asej.2015.06.008
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A. Baghbany Oskouei et al.
(a)
(b)
(c) Figure 18
The phase voltage of proposed inverter in hybrid system with respect to time(s); (a) upper unit; (b) lower unit; (c) total.
From Fig. 4 and (11), the output voltage of the inverter is obtained: v12 ¼ v1n v2n ¼ v1n
ðvbn þ vcn Þ 2
ð12Þ
So, the output voltage can have five levels, which are summarized in Table 1. Then, it is obvious that the switching state of S1 is decided by the sign of v12-ref (the reference of v12): S1 is 1 if v12-ref P 0 and S1 is 0 if v12-ref 6 0, which is very easy to implement. However, the switching states of S3 and S5 cannot be selected without careful study [8]. To decide the switching states of (S3, S5), the following PWM algorithm is presented: The dwelling time for the switch switches within every sample time, and Ts is defined as follows: jv12-ref j Kvi Tdwell ¼ ð13Þ vi where the integer K is calculated by jv12-ref j K¼ vi
ð14Þ
The function [x] rounds x to the nearest integer less than x. Obviously, the dwelling time in (13) can be generated using the conventional triangle wave which is shown in Fig. 5. Asymmetric structures use geometric progression for DC source voltages to increase the output levels. Such a structure produces output voltage with summation of series structures voltages with different DC sources, which is displayed in Fig. 6.
Progression factor in quinary asymmetric structure is 5. So, the voltage of DC sources can be written as follows: Vi ¼ 5i1 VDC ; i ¼ 1; 2; 3; . . . ; n ð15Þ Then, maximum levels number which inverter can be generated is NML ¼ 5n
ð16Þ
and, the maximum generated voltage of inverter can be obtained as Vout
max
1 VDC ¼ ð5n 1Þ 2 2
ð17Þ
According to a bow description, it is obtained that two series five-level inverter with quinary asymmetric structure creates twenty-five-level inverter. But, increasing DC sources number in quinary structure causes cost increase, also control of system with more DC links is more complex. Then use of transformer in the proposed structure is the solution of represented drawbacks. New proposed structure is shown in Fig. 7. From Fig. 7, two transformers have different turn ratios according to (15). Then, the turn ratio of first transformer is 1:1, and the turn ratio of second transformer is 1:5. Use of transformer in this structure, in addition to decreasing DC source number to one, causes reliability increase and isolation. Using coupled inductor in this structure causes switches number to reduce. Also, the voltage stresses on all the switches on each inverter section are the same. Then, the switching of two blocks of
Please cite this article in press as: Baghbany Oskouei A et al., Hybrid PV/wind system with quinary asymmetric inverter without increasing DC-link number, Ain Shams Eng J (2015), http://dx.doi.org/10.1016/j.asej.2015.06.008
Hybrid PV/wind system with quinary asymmetric inverter
11
(a)
(b) Figure 19
Output parameters of the load with respect to time(s); (a) load voltage; (b) load power.
proposed inverter is based on PWM, which is explained later, where each block is switched independently and based on output level. 3.2. Proposed hybrid system with proposed inverter The configuration of hybrid system is shown in Fig. 8, where PV connected to the DC-link through the DC–DC converter
and PMSG wind turbine is connected to the same DC-link through the diode rectifier and DC–DC converter, and also, battery is connected to it by DC–DC converter. Because of low voltage generated from PV and wind systems, the boost DC–DC converter is preferred. The boost converter of PV section does MPPT of PV system and, in wind section, the diode rectifier acts as the DC source, and its output is controlled by boost converter to apply MPPT of wind system. The battery
Please cite this article in press as: Baghbany Oskouei A et al., Hybrid PV/wind system with quinary asymmetric inverter without increasing DC-link number, Ain Shams Eng J (2015), http://dx.doi.org/10.1016/j.asej.2015.06.008
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Figure 20
MPPT operation of wind system.
system is used as backup for unpredictable nature of PV and wind. But, in high DC-link voltage, it is necessary to series connection of multiple batteries and connecting them to DC-link. The other solution is use of bidirectional boost converter. This battery with its converter momentarily absorbs or injects excess power corresponding to abrupt change in the PV and wind systems. Then, an inverter between DC-link and load provides ac voltage demand of load. The inverter may have various types. In this paper, it is used from proposed 25-level inverter, where because of its multilevel nature, it has merits of multilevel inverter. Also, the presence of one DC source is very suitable for this hybrid system, where control of one capacitor voltage is very easy and does not have complexity of several capacitors voltage as source of multilevel inverter. This structure also provides isolation in the system. The control loop of hybrid system is presented in Fig. 9.
4.1.2.1. PV system. In this paper, 10 numbers of 250 W PV module (in nominal condition of G = 1000 W/m2 and T = 25 C) are paralleled, where it is considered stepped variation for solar irradiance and temperature in Fig. 11. The output powers of PV system and DC–DC converter are shown in Fig. 12. From Fig. 12, it can be seen that there is difference between those powers, which is because of system losses. The boost converter increases PV voltage up to DC link level. MPPT operation of each PV module is presented in Fig. 13, where it is obvious that utilization of each PV module is almost in MPPT points. 4.1.2.2. Wind system. In this paper, the power characteristic curve of the wind turbine is shown in Fig. 14(a). The wind speed variation is assumed stepped according to Fig. 14(b). The rotor speed, output power of turbine, and delivered power to DC link are presented in Fig. 15.
4. Simulation and experimental results For investigating the proposed structure, results of system are studied. In this paper, the results include two sections: simulation and experimental as follows. 4.1. Simulation results 4.1.1. Proposed inverter Inverter shown in Fig. 7 has been simulated by MATLAB/SIMULINK to verify proposed topology. The system parameters with RL load are listed in Table 2. Fig. 10 presents output voltage of the inverter. 4.1.2. Hybrid system with proposed inverter The proposed hybrid system is simulated, and the results of it are expatiated as follows. Different MPPT algorithms have been developed. In this paper, the perturbation and observation (P&O) algorithm with the merit of simplicity is used.
4.1.2.3. Hybrid system. As represented, the output power of PV and wind systems is transferred to DC-link and then the DC-link power is delivered to load. The parameters of simulated system are listed in Table 3, where the load is unbalanced. Fig. 16 displays DC-link voltage which is fixed in 64 V, although unbalancing of the load causes little fluctuation in the voltage. In this system, the battery system is used and its voltage increases with bidirectional boost converter. The exchanged power between system and battery is shown in Fig. 17. If the exchanged power is positive, the battery system compensates deficiency of hybrid power, and if the exchanged power is negative, the excess power is stored in battery. Then, DC-link voltage is transmitted from inverter and delivered to ac load. The used inverter in this paper, as represented, is proposed quinary inverter with coupled inverters and transformer which generate 25-level voltage. Fig. 18 shows the phase voltage of proposed inverter in this system. The load voltage and power are displayed in Fig. 19. Also, Fig. 20 shows correct MPPT operation of wind system.
Please cite this article in press as: Baghbany Oskouei A et al., Hybrid PV/wind system with quinary asymmetric inverter without increasing DC-link number, Ain Shams Eng J (2015), http://dx.doi.org/10.1016/j.asej.2015.06.008
Hybrid PV/wind system with quinary asymmetric inverter
13
(a)
(b) Figure 21
Experimental results; (a) photograph of prototype; (b) load voltage.
4.2. Experimental results Base segment of proposed inverter according to Fig. 4 was built using IRFP460 MOSFETS as the switching devices and MUR820G as fast diodes in this topology. A DC voltage source with amplitude 12 (V) was used to individually supply the inverter. The switching signals that were obtained from PWM algorithm were produced with PCI-1716 DAQ. The switching signals were interfaced with the inverter power switches through driver TLP250. Fig. 21(a) shows photographs of the prototype. The load voltage of the inverter is shown in Fig. 21(b). Measured five levels are 0, ±6, ±12.
Load voltage total harmonic distortion (THD) was measured with power analyzer and it is about 38.2%. 5. Conclusion This paper proposes hybrid system including PV and wind systems suggested quinary asymmetric inverter with coupled inductors and transformer. This inverter outputs twenty-fivelevel voltage with only one DC source. This structure has such merits as easy control and isolation, and uses battery system backup, where PV and wind have complementary nature. The simulation results showed that the proposed inverter
Please cite this article in press as: Baghbany Oskouei A et al., Hybrid PV/wind system with quinary asymmetric inverter without increasing DC-link number, Ain Shams Eng J (2015), http://dx.doi.org/10.1016/j.asej.2015.06.008
14 produces a high-quality load voltage and it demonstrates its ability in hybrid system. Also, the experimental results verified the proportionality of proposed inverter. Acknowledgement This research has been supported by Azarbaijan Shahid Madani University. References [1] Morales R, Ordonez R, Morales MA, Flores V. Control system design and simulation of an AC/DC–DC/DC–DC/AC power converter for a permanent magnet wind power generator in rural power generation. In: International conference on electrical, communications, and computers, February/2009, Cholula/ Mexico. pp. 79–83. [2] Heier S. Grid integration of wind energy conversion system. Chichester: John Wiley & Sons, Ltd; 2006, ISBN 10: 0470868996. [3] Morales DS. Maximum power point tracking algorithms for photovoltaic applications. Thesis for the Degree of Master of Science. Finland: Alto University; 2010. [4] Zeng J, Qiao W, Qu L, Jiao Y. An isolated multiport DC–DC converter for simultaneous power management of multiple different renewable energy sources. IEEE J Emerg Select Top Power Electron 2014;2(1):70–8. [5] Wandhare RG, Agarwal V. Novel integration of a PV-wind energy system with enhanced efficiency. IEEE Trans Power Electron 2015;30(7):3638–49. [6] Keyrouz F, Hamad M, Georges S. Bayesian fusion for maximum power output in hybrid wind-solar systems. In: 3rd IEEE International symposium on power electronics for distributed generation systems (PEDG), June/2012, Jutland/Denmark. pp. 393–7. [7] Hui J, Bakhshai A, Jain PK. A hybrid wind-solar energy system: a new rectifier stage topology. In: Applied power electronics conference and exposition, February/2010, Palm Springs/USA. pp. 155–61. [8] Li Z, Wang P, Li Y, Gao F. A novel single-phase five-level inverter with coupled inductors. IEEE Trans Power Electron 2012;27(6):2716–25. [9] Banaei MR, Dehghanzadeh AR, Salary E, Khounjahan H, Alizadeh R. Z-source-based multilevel inverter with reduction of switches. IET Power Electron 2011;5(3):385–92. [10] Rodrı´ guez J, Mora´n L, Correa P, Silva C. A vector control technique for medium voltage multilevel inverters. IEEE Trans Ind Electron 2002;49(4):882–8. [11] Rodriguez J, Lai JS, Peng FZ. Multilevel inverters: a survey of topologies, controls, and applications. IEEE Trans Ind Electron 2002;49(4):724–38. [12] Malinowski M, Gopakumar K, Rodriguez J, Perez MA. A survey on cascaded multilevel inverters. IEEE Trans Ind Electron 2010;57(7):2197–206. [13] Rodriguez J, Bernet S, Steimer PK, Lizama IE. A survey on neutral-point-clamped inverters. IEEE Trans Ind Electron 2010;57(7):2219–30. [14] Floricau D, Floricau E, Gateau G. New multilevel converters with coupled inductors: properties and control. IEEE Trans Ind Electron 2011;58(12):5344–51. [15] Rekioua D, Magenta E. Optimization of photovoltaic power systems. Springer; 2012.
A. Baghbany Oskouei et al. [16] Poshtkouhi S, Palaniappan V, Fard M, Trescases O. A general approach for quantifying the benefit of distributed power electronics for fine grained MPPT in photovoltaic applications using 3D modeling. IEEE Trans Power Electron 2012;27(11): 4656–66. [17] Milosevic M. On the control of distributed generation in power systems. Thesis for the Degree of Doctor of Technical Science. Switzerland: Swiss Federal Institute of Technology; 2007. [18] Dehghan SM, Mohamadian M, Varjani AY. A new variablespeed wind energy conversion system using permanent-magnet synchronous generator and Z-source inverter. IEEE Trans Energy Convers 2009;24(3):714–24. [19] Nussbaumer T, Kolar JW. Improving mains current quality for three-phase three-switch buck-type PWM rectifiers. IEEE Trans Power Electron 2006;21(4):967–73. [20] Nedic V, Lipo TA. Low-cost current-fed PMSM drive system with sinusoidal input currents. IEEE Trans Ind Appl 2006;42(3): 753–62.
Aida Baghbany Oskouei was born in Tabriz, Iran, in 1988. She received the B.Sc. degree in electrical engineering from Azarbaijan Shahid Madani University, Tabriz, Iran, in 2010 and the M.Sc. degree in electrical engineering from the University of Tabriz, Tabriz, Iran, in 2012. She is currently working toward the Ph.D. degree in electrical engineering at Azarbaijan Shahid Madani University. Her current research interests include modeling and application of power electronic circuits in power systems and renewable energies. Mohamad Reza Banaei was born in Tabriz, Iran. He received his M.Sc. degree from the Poly Technique University of Tehran, Iran, in control engineering in 1999 and his Ph.D. degree from the electrical engineering faculty of Tabriz University in power engineering in 2005. He is an Associate Professor in the Electrical Engineering Department of Azarbaijan Shahid Madani University, Iran, which he joined in 2005. His main research interests include the modeling and controlling of power electronic converters, renewable energy, modeling and controlling of FACTS and Custom Power devices and power systems dynamics. Mehran Sabahi was born in Tabriz, Iran, in 1968. He received the B.S. degree in electronic engineering from the University of Tabriz, the M.S. degree in electrical engineering from Tehran University, Tehran, Iran, and the Ph.D. degree in electrical engineering from the University of Tabriz, in 1991, 1994, and 2009, respectively. In 2009, he joined the Faculty of Electrical and Computer Engineering, University of Tabriz, where he was an Assistant Professor from 2009 to 2013 and where he has been an Associate Professor since 2014. His current research interests include power electronic converters and renewable energy systems.
Please cite this article in press as: Baghbany Oskouei A et al., Hybrid PV/wind system with quinary asymmetric inverter without increasing DC-link number, Ain Shams Eng J (2015), http://dx.doi.org/10.1016/j.asej.2015.06.008
Ain Shams University
Ain Shams Engineering Journal www.elsevier.com/locate/asej www.sciencedirect.com
ELECTRICAL ENGINEERING
Hybrid PV/wind system with quinary asymmetric inverter without increasing DC-link numberq Aida Baghbany Oskouei a b
a,*
, Mohamad Reza Banaei a, Mehran Sabahi
b
Department of Electrical Engineering, Azarbaijan Shahid Madani University, Tabriz, Iran Faculty of Electrical and Computer Engineering, University of Tabriz, Tabriz, Iran
Received 1 November 2014; revised 26 April 2015; accepted 19 June 2015
KEYWORDS Hybrid photovoltaic (PV)/wind system; Quinary asymmetric inverter; Coupled inductors; Battery system; Boost converter
Abstract This paper suggests quinary asymmetric inverter with coupled inductors and transformer, and uses it in hybrid system including photovoltaic (PV) and wind. This inverter produces twenty-five-level voltage in addition to merits of multilevel inverter, has only one DC source. Then, it is adequate for hybrid systems, which prevents increasing DC-link and makes control of system easy. Proposed structure also provides isolation in the system and the switch numbers are reduced in this topology compared with other multilevel structures. In this system, battery is used as backup, where PV and wind have complementary nature. The performance of proposed inverter and hybrid system is validated with simulation results using MATLAB/SIMULINK software and experimental results based PCI-1716 data acquisition system. 2015 Faculty of Engineering, Ain Shams University. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
1. Introduction In recent years, renewable energies were expanded because of fossil fuel consumption and greenhouse-effect gas emission q
This research has been supported by Azarbaijan Shahid Madani University. Abbreviations: MPP, maximum power point; MPPT, maximum power point tracking; P&O, perturbation and observation algorithm; PMSG, permanent magnet synchronous generator; PV, photovoltaic; PWM, pulse width modulation; V–I, voltage–current; V–P, voltage–power * Corresponding author. Tel.: +98 9141186476. E-mail addresses: [email protected] (A. Baghbany Oskouei), [email protected] (M.R. Banaei). Peer review under responsibility of Ain Shams University.
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[1–3]. Research and development efforts in renewable energies are required to accurately predict their output reliably assembling them with other conventional sources. So, use of battery in such systems is beneficial solution for increase of reliability and better operation of those systems. Meanwhile, hybrid system including different types of renewable energies was proposed [4,5]. Hybrid system in addition to advantages of renewable energies, causes reduction in battery size and increase in reliability of system [6,7]. The renewable energies in hybrid system can be photovoltaic (PV), wind, fuel cell, etc. In this paper, PV and wind systems are used because of complementary operation. In hybrid systems, an inverter between DC link and load provides ac voltage demand of load, which may have various types. Nowadays, multilevel inverters receive more attention [8–10], which include some power semiconductors and DC voltage sources. The most common multilevel inverter topologies are the cascaded, diode-clamped, and capacitor-clamped
http://dx.doi.org/10.1016/j.asej.2015.06.008 2090-4479 2015 Faculty of Engineering, Ain Shams University. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Please cite this article in press as: Baghbany Oskouei A et al., Hybrid PV/wind system with quinary asymmetric inverter without increasing DC-link number, Ain Shams Eng J (2015), http://dx.doi.org/10.1016/j.asej.2015.06.008
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Nomenclature IPV VPV Iph Io T K q A RSmod G Gr Iscrcell Tr ki NP NS q
current of PV cell voltage of PV cell photocurrent diode saturation current cell temperature Boltzmann’s constant coulomb constant P–N junction ideality factor series resistance real solar radiation solar radiation photocurrent standard test conditions cell absolute temperature temperature coefficient number of parallel PV cell number of series PV cell air density
types [11–13]. Multilevel inverters with only one DC source may be the most desirable topology. Recently [14] presented an inverter called a five-level-active-neutral-point-clamped with coupled inductor, which uses split of the DC-link capacitor. In [8] inverter was proposed using coupled inductors. This inverter can output a novel, single phase, five-level voltage with only one DC source. Meanwhile, asymmetric structures use geometric progression for voltage of DC sources to increase the output levels. Then, it is desirable to use of new inverters in asymmetric structures for producing more voltage levels in output. But increasing DC source numbers in asymmetric structures causes cost increase; also control of system with more DC links is more complex.
At Vx CP k b R x L11 L12 M Tdwell Vi NML Vout_max
area swept out by the turbine blades wind velocity power coefficient tip speed ratio blade pitch angel blade radius rotational speed first coupled inductor second coupled inductor mutual inductance of coupled inductors dwelling time of switch voltage of DC sources in quinary asymmetric inverter maximum levels number in quinary asymmetric inverter maximum generated voltage of quinary asymmetric inverter
This paper proposes quinary asymmetric inverter with coupled inductors and transformer, and uses it in hybrid system including PV and wind systems. This inverter has one DC source which makes it easy and usable in hybrid system. Theoretical analysis and simulation and experimental results are presented to show the validity of the proposed inverter and proposed hybrid system. 2. Renewable energy systems 2.1. PV system PV system is based on solar energy, where PV cell is the most basic generation part in PV. As Fig. 1(a) shows, the PV cell is formed from a diode and a current source was connected antiparallel with a series resistance [15–17]. The relation of the current and voltage in the single-diode cell can be written as follows: qðVPV þ RSmod IPV Þ 1 ð1Þ IPV ¼ Iph IO exp AKT
(a)
(b) Figure 1
Electrical model of PV; (a) PV cell; (b) solar module.
Figure 2 Characteristic curves of a typical PV module in certain solar irradiance and temperature.
Please cite this article in press as: Baghbany Oskouei A et al., Hybrid PV/wind system with quinary asymmetric inverter without increasing DC-link number, Ain Shams Eng J (2015), http://dx.doi.org/10.1016/j.asej.2015.06.008
Hybrid PV/wind system with quinary asymmetric inverter
Figure 3
3
A typical turbine output power versus rotor speed with the wind speed as a parameter.
Figure 5
Generation of the dwelling time.
Figure 4 Structures of single-phase five-level inverter with coupled inductors.
where IPV and VPV are the current and voltage of PV cell respectively. And, Iph is photocurrent, Io is diode saturation current, T is cell temperature, K is Boltzmann’s constant, q is coulomb constant, A is P–N junction ideality factor, and RSmod is series resistance. Photocurrent is directly proportional to solar irradiation and cell temperature, which is described as Iph ¼ Iscrcell þ ki ðT Tr Þ ðG=Gr Þ ð2Þ
Table 1
Figure 6
Asymmetric inverter structure (V1 „ V2 „ „Vn).
where G is the real solar radiation, Gr, Iscrcell , Tr, and ki are the solar radiation, photocurrent standard test conditions, cell absolute temperature, and the temperature coefficient, respectively.
Output voltage of five-level inverter with coupled inductors.
v12
+2E
+E
+E
0
0
E
E
2E
On switches
S1, S4, S6
S1, S4, S5
S1, S3, S6
S1, S3, S5
S2, S4, S6
S2, S4, S5
S2, S3, S6
S2, S3, S5
Please cite this article in press as: Baghbany Oskouei A et al., Hybrid PV/wind system with quinary asymmetric inverter without increasing DC-link number, Ain Shams Eng J (2015), http://dx.doi.org/10.1016/j.asej.2015.06.008
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Figure 7
Figure 8
Proposed quinary asymmetric inverter structure.
Proposed configuration of hybrid system with battery.
Several same PV cells are arranged together in parallel and series to form PV modules. This work is performed in order to increase output voltage and current of PV system. The current versus voltage of the PV module can be formulated as qðVPV þ RSmod IPV Þ 1 ð3Þ IPV ¼ Np Iph Np IO exp Ns AKT
there is one point with specific voltage and current which produced maximum power [15]. This point is known as maximum power point (MPP), and operation in it is known as maximum power point tracking (MPPT).
Fig. 1(b) shows PV modeling of module, where NP and NS are number of the parallel and series PV cell, respectively. For each module, two characteristic curves are defined: voltage–current (V–I) and voltage–power (V–P). These curves are plotted based on solar irradiance and temperature. Fig. 2 shows such curves for typical PV module. From Fig. 2, it is obvious that in each solar irradiance and temperature, the voltage, current, and power can have different mounts. But
The mechanical power of a wind turbine is expressed as fol-
2.2. Wind system
lows [18–20]: 1 Pmech ¼ qAt CP V3x 2
ð4Þ
where q is the air density, At is the area swept out by the turbine blades, Vx is the wind velocity, and CP is the power
Please cite this article in press as: Baghbany Oskouei A et al., Hybrid PV/wind system with quinary asymmetric inverter without increasing DC-link number, Ain Shams Eng J (2015), http://dx.doi.org/10.1016/j.asej.2015.06.008
Hybrid PV/wind system with quinary asymmetric inverter
Figure 9
Table 2
5
Control loop of load voltage in hybrid system.
Inverter parameters. 100 V 3.1 mH 3 mH 50 Hz 20 O 8.3 mH
VDC L11 = L12 = L M Nominal frequency Load resistance Load inductance
(a)
(b)
(c) Figure 10
Output voltage of proposed inverter with respect to time(s); (a) upper unit; (b) lower unit; (c) total.
Please cite this article in press as: Baghbany Oskouei A et al., Hybrid PV/wind system with quinary asymmetric inverter without increasing DC-link number, Ain Shams Eng J (2015), http://dx.doi.org/10.1016/j.asej.2015.06.008
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(a)
(b) Figure 11
Stepped variation of (a) solar irradiance; (b) temperature, with respect to time(s).
Figure 12
Output power of PV system and DC–DC converter with respect to time(s).
coefficient and represents the efficiency of the wind turbine which is expressed as 21 116 ð5Þ CP ðk; bÞ ¼ 0:5176 0:4b 5 e ki þ 0:006k ki 1 1 0:035 ¼ ki k þ 0:08b b3 þ 1
ð6Þ
where k is tip speed ratio, b is blade pitch angel (deg), R is the blade radius (m), and x is the rotational speed (rad/s). The torque obtained from wind energy is transferred via the turbine/generator shaft to the rotor of the generator and drives the electrical generator, and in this paper the permanent magnet synchronous generator (PMSG) is used in the output of wind turbine.
Please cite this article in press as: Baghbany Oskouei A et al., Hybrid PV/wind system with quinary asymmetric inverter without increasing DC-link number, Ain Shams Eng J (2015), http://dx.doi.org/10.1016/j.asej.2015.06.008
Hybrid PV/wind system with quinary asymmetric inverter
Figure 13
7
MPPT operation of each PV module in hybrid system.
(a)
(b) Figure 14 time(s).
Wind system characteristics; (a) power characteristic curve of the wind turbine; (b) wind speed variation with respect to
Please cite this article in press as: Baghbany Oskouei A et al., Hybrid PV/wind system with quinary asymmetric inverter without increasing DC-link number, Ain Shams Eng J (2015), http://dx.doi.org/10.1016/j.asej.2015.06.008
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(a)
(b)
(c) Figure 15
Results of wind system with respect to time(s); (a) rotor speed; (b) output power of turbine; (c) delivered power to DC link.
The power characteristic curve of a typical wind turbine is shown in Fig. 3. It is observed that the maximum power output occurs at different turbine speeds for different wind velocities. 3. Proposed hybrid system 3.1. Proposed quinary asymmetric inverter with coupled inductors and transformer Single-phase five-level inverter with coupled inductors and one DC source was first proposed in [6], which is presented in Fig. 4. In this structure no split of the DC capacitor is needed, avoiding the voltage balancing. The level of the output voltage is half of the DC voltage in all switching conditions, causing
Table 3
much reduced dv/dt. In this inverter, the voltage stresses on all the switches are the same. So, construction of it is easy. In Fig. 4, 2E is the DC source voltage and L11 and L12 are the two coupled inductors. Two coupled inductors have the same number of turns and the mutual inductance of them is M. With attention to Fig. 4 and assuming L11 = L12 = L, the voltage of coupled inductors can be derived as follows: L
dib dic M ¼ vbn v2n dt dt
ð7Þ
L
dic dib M ¼ vcn v2n dt dt
ð8Þ
And according to Kirchhoff’s current law, the following is obtained:
Hybrid system parameters.
Load voltage Load amount
Nominal frequency Filter capacitance Filter inductance
220 V Z1 = 35 + 5j Z1 = 30 + 20j Z1 = 26 + 25j 50 Hz 30 lF 0.5 mH
Please cite this article in press as: Baghbany Oskouei A et al., Hybrid PV/wind system with quinary asymmetric inverter without increasing DC-link number, Ain Shams Eng J (2015), http://dx.doi.org/10.1016/j.asej.2015.06.008
Hybrid PV/wind system with quinary asymmetric inverter
Figure 16
Figure 17
9
DC-link voltage of hybrid system with respect to time(s).
Exchanged power between system and battery in proposed system with respect to time(s).
ib þ ic þ iL ¼ 0
ð9Þ
From 7–9, v2n can be expressed as v2n ¼
vbn þ vcn þ ðL MÞ didtL 2
ð10Þ
The leakage inductance can be designed to be near to mutual inductance of two inductors. Therefore, (10) can be rewritten as v2n ¼
vbn þ vcn 2
ð11Þ
Please cite this article in press as: Baghbany Oskouei A et al., Hybrid PV/wind system with quinary asymmetric inverter without increasing DC-link number, Ain Shams Eng J (2015), http://dx.doi.org/10.1016/j.asej.2015.06.008
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(a)
(b)
(c) Figure 18
The phase voltage of proposed inverter in hybrid system with respect to time(s); (a) upper unit; (b) lower unit; (c) total.
From Fig. 4 and (11), the output voltage of the inverter is obtained: v12 ¼ v1n v2n ¼ v1n
ðvbn þ vcn Þ 2
ð12Þ
So, the output voltage can have five levels, which are summarized in Table 1. Then, it is obvious that the switching state of S1 is decided by the sign of v12-ref (the reference of v12): S1 is 1 if v12-ref P 0 and S1 is 0 if v12-ref 6 0, which is very easy to implement. However, the switching states of S3 and S5 cannot be selected without careful study [8]. To decide the switching states of (S3, S5), the following PWM algorithm is presented: The dwelling time for the switch switches within every sample time, and Ts is defined as follows: jv12-ref j Kvi Tdwell ¼ ð13Þ vi where the integer K is calculated by jv12-ref j K¼ vi
ð14Þ
The function [x] rounds x to the nearest integer less than x. Obviously, the dwelling time in (13) can be generated using the conventional triangle wave which is shown in Fig. 5. Asymmetric structures use geometric progression for DC source voltages to increase the output levels. Such a structure produces output voltage with summation of series structures voltages with different DC sources, which is displayed in Fig. 6.
Progression factor in quinary asymmetric structure is 5. So, the voltage of DC sources can be written as follows: Vi ¼ 5i1 VDC ; i ¼ 1; 2; 3; . . . ; n ð15Þ Then, maximum levels number which inverter can be generated is NML ¼ 5n
ð16Þ
and, the maximum generated voltage of inverter can be obtained as Vout
max
1 VDC ¼ ð5n 1Þ 2 2
ð17Þ
According to a bow description, it is obtained that two series five-level inverter with quinary asymmetric structure creates twenty-five-level inverter. But, increasing DC sources number in quinary structure causes cost increase, also control of system with more DC links is more complex. Then use of transformer in the proposed structure is the solution of represented drawbacks. New proposed structure is shown in Fig. 7. From Fig. 7, two transformers have different turn ratios according to (15). Then, the turn ratio of first transformer is 1:1, and the turn ratio of second transformer is 1:5. Use of transformer in this structure, in addition to decreasing DC source number to one, causes reliability increase and isolation. Using coupled inductor in this structure causes switches number to reduce. Also, the voltage stresses on all the switches on each inverter section are the same. Then, the switching of two blocks of
Please cite this article in press as: Baghbany Oskouei A et al., Hybrid PV/wind system with quinary asymmetric inverter without increasing DC-link number, Ain Shams Eng J (2015), http://dx.doi.org/10.1016/j.asej.2015.06.008
Hybrid PV/wind system with quinary asymmetric inverter
11
(a)
(b) Figure 19
Output parameters of the load with respect to time(s); (a) load voltage; (b) load power.
proposed inverter is based on PWM, which is explained later, where each block is switched independently and based on output level. 3.2. Proposed hybrid system with proposed inverter The configuration of hybrid system is shown in Fig. 8, where PV connected to the DC-link through the DC–DC converter
and PMSG wind turbine is connected to the same DC-link through the diode rectifier and DC–DC converter, and also, battery is connected to it by DC–DC converter. Because of low voltage generated from PV and wind systems, the boost DC–DC converter is preferred. The boost converter of PV section does MPPT of PV system and, in wind section, the diode rectifier acts as the DC source, and its output is controlled by boost converter to apply MPPT of wind system. The battery
Please cite this article in press as: Baghbany Oskouei A et al., Hybrid PV/wind system with quinary asymmetric inverter without increasing DC-link number, Ain Shams Eng J (2015), http://dx.doi.org/10.1016/j.asej.2015.06.008
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Figure 20
MPPT operation of wind system.
system is used as backup for unpredictable nature of PV and wind. But, in high DC-link voltage, it is necessary to series connection of multiple batteries and connecting them to DC-link. The other solution is use of bidirectional boost converter. This battery with its converter momentarily absorbs or injects excess power corresponding to abrupt change in the PV and wind systems. Then, an inverter between DC-link and load provides ac voltage demand of load. The inverter may have various types. In this paper, it is used from proposed 25-level inverter, where because of its multilevel nature, it has merits of multilevel inverter. Also, the presence of one DC source is very suitable for this hybrid system, where control of one capacitor voltage is very easy and does not have complexity of several capacitors voltage as source of multilevel inverter. This structure also provides isolation in the system. The control loop of hybrid system is presented in Fig. 9.
4.1.2.1. PV system. In this paper, 10 numbers of 250 W PV module (in nominal condition of G = 1000 W/m2 and T = 25 C) are paralleled, where it is considered stepped variation for solar irradiance and temperature in Fig. 11. The output powers of PV system and DC–DC converter are shown in Fig. 12. From Fig. 12, it can be seen that there is difference between those powers, which is because of system losses. The boost converter increases PV voltage up to DC link level. MPPT operation of each PV module is presented in Fig. 13, where it is obvious that utilization of each PV module is almost in MPPT points. 4.1.2.2. Wind system. In this paper, the power characteristic curve of the wind turbine is shown in Fig. 14(a). The wind speed variation is assumed stepped according to Fig. 14(b). The rotor speed, output power of turbine, and delivered power to DC link are presented in Fig. 15.
4. Simulation and experimental results For investigating the proposed structure, results of system are studied. In this paper, the results include two sections: simulation and experimental as follows. 4.1. Simulation results 4.1.1. Proposed inverter Inverter shown in Fig. 7 has been simulated by MATLAB/SIMULINK to verify proposed topology. The system parameters with RL load are listed in Table 2. Fig. 10 presents output voltage of the inverter. 4.1.2. Hybrid system with proposed inverter The proposed hybrid system is simulated, and the results of it are expatiated as follows. Different MPPT algorithms have been developed. In this paper, the perturbation and observation (P&O) algorithm with the merit of simplicity is used.
4.1.2.3. Hybrid system. As represented, the output power of PV and wind systems is transferred to DC-link and then the DC-link power is delivered to load. The parameters of simulated system are listed in Table 3, where the load is unbalanced. Fig. 16 displays DC-link voltage which is fixed in 64 V, although unbalancing of the load causes little fluctuation in the voltage. In this system, the battery system is used and its voltage increases with bidirectional boost converter. The exchanged power between system and battery is shown in Fig. 17. If the exchanged power is positive, the battery system compensates deficiency of hybrid power, and if the exchanged power is negative, the excess power is stored in battery. Then, DC-link voltage is transmitted from inverter and delivered to ac load. The used inverter in this paper, as represented, is proposed quinary inverter with coupled inverters and transformer which generate 25-level voltage. Fig. 18 shows the phase voltage of proposed inverter in this system. The load voltage and power are displayed in Fig. 19. Also, Fig. 20 shows correct MPPT operation of wind system.
Please cite this article in press as: Baghbany Oskouei A et al., Hybrid PV/wind system with quinary asymmetric inverter without increasing DC-link number, Ain Shams Eng J (2015), http://dx.doi.org/10.1016/j.asej.2015.06.008
Hybrid PV/wind system with quinary asymmetric inverter
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(a)
(b) Figure 21
Experimental results; (a) photograph of prototype; (b) load voltage.
4.2. Experimental results Base segment of proposed inverter according to Fig. 4 was built using IRFP460 MOSFETS as the switching devices and MUR820G as fast diodes in this topology. A DC voltage source with amplitude 12 (V) was used to individually supply the inverter. The switching signals that were obtained from PWM algorithm were produced with PCI-1716 DAQ. The switching signals were interfaced with the inverter power switches through driver TLP250. Fig. 21(a) shows photographs of the prototype. The load voltage of the inverter is shown in Fig. 21(b). Measured five levels are 0, ±6, ±12.
Load voltage total harmonic distortion (THD) was measured with power analyzer and it is about 38.2%. 5. Conclusion This paper proposes hybrid system including PV and wind systems suggested quinary asymmetric inverter with coupled inductors and transformer. This inverter outputs twenty-fivelevel voltage with only one DC source. This structure has such merits as easy control and isolation, and uses battery system backup, where PV and wind have complementary nature. The simulation results showed that the proposed inverter
Please cite this article in press as: Baghbany Oskouei A et al., Hybrid PV/wind system with quinary asymmetric inverter without increasing DC-link number, Ain Shams Eng J (2015), http://dx.doi.org/10.1016/j.asej.2015.06.008
14 produces a high-quality load voltage and it demonstrates its ability in hybrid system. Also, the experimental results verified the proportionality of proposed inverter. Acknowledgement This research has been supported by Azarbaijan Shahid Madani University. References [1] Morales R, Ordonez R, Morales MA, Flores V. Control system design and simulation of an AC/DC–DC/DC–DC/AC power converter for a permanent magnet wind power generator in rural power generation. In: International conference on electrical, communications, and computers, February/2009, Cholula/ Mexico. pp. 79–83. [2] Heier S. Grid integration of wind energy conversion system. Chichester: John Wiley & Sons, Ltd; 2006, ISBN 10: 0470868996. [3] Morales DS. Maximum power point tracking algorithms for photovoltaic applications. Thesis for the Degree of Master of Science. Finland: Alto University; 2010. [4] Zeng J, Qiao W, Qu L, Jiao Y. An isolated multiport DC–DC converter for simultaneous power management of multiple different renewable energy sources. IEEE J Emerg Select Top Power Electron 2014;2(1):70–8. [5] Wandhare RG, Agarwal V. Novel integration of a PV-wind energy system with enhanced efficiency. IEEE Trans Power Electron 2015;30(7):3638–49. [6] Keyrouz F, Hamad M, Georges S. Bayesian fusion for maximum power output in hybrid wind-solar systems. In: 3rd IEEE International symposium on power electronics for distributed generation systems (PEDG), June/2012, Jutland/Denmark. pp. 393–7. [7] Hui J, Bakhshai A, Jain PK. A hybrid wind-solar energy system: a new rectifier stage topology. In: Applied power electronics conference and exposition, February/2010, Palm Springs/USA. pp. 155–61. [8] Li Z, Wang P, Li Y, Gao F. A novel single-phase five-level inverter with coupled inductors. IEEE Trans Power Electron 2012;27(6):2716–25. [9] Banaei MR, Dehghanzadeh AR, Salary E, Khounjahan H, Alizadeh R. Z-source-based multilevel inverter with reduction of switches. IET Power Electron 2011;5(3):385–92. [10] Rodrı´ guez J, Mora´n L, Correa P, Silva C. A vector control technique for medium voltage multilevel inverters. IEEE Trans Ind Electron 2002;49(4):882–8. [11] Rodriguez J, Lai JS, Peng FZ. Multilevel inverters: a survey of topologies, controls, and applications. IEEE Trans Ind Electron 2002;49(4):724–38. [12] Malinowski M, Gopakumar K, Rodriguez J, Perez MA. A survey on cascaded multilevel inverters. IEEE Trans Ind Electron 2010;57(7):2197–206. [13] Rodriguez J, Bernet S, Steimer PK, Lizama IE. A survey on neutral-point-clamped inverters. IEEE Trans Ind Electron 2010;57(7):2219–30. [14] Floricau D, Floricau E, Gateau G. New multilevel converters with coupled inductors: properties and control. IEEE Trans Ind Electron 2011;58(12):5344–51. [15] Rekioua D, Magenta E. Optimization of photovoltaic power systems. Springer; 2012.
A. Baghbany Oskouei et al. [16] Poshtkouhi S, Palaniappan V, Fard M, Trescases O. A general approach for quantifying the benefit of distributed power electronics for fine grained MPPT in photovoltaic applications using 3D modeling. IEEE Trans Power Electron 2012;27(11): 4656–66. [17] Milosevic M. On the control of distributed generation in power systems. Thesis for the Degree of Doctor of Technical Science. Switzerland: Swiss Federal Institute of Technology; 2007. [18] Dehghan SM, Mohamadian M, Varjani AY. A new variablespeed wind energy conversion system using permanent-magnet synchronous generator and Z-source inverter. IEEE Trans Energy Convers 2009;24(3):714–24. [19] Nussbaumer T, Kolar JW. Improving mains current quality for three-phase three-switch buck-type PWM rectifiers. IEEE Trans Power Electron 2006;21(4):967–73. [20] Nedic V, Lipo TA. Low-cost current-fed PMSM drive system with sinusoidal input currents. IEEE Trans Ind Appl 2006;42(3): 753–62.
Aida Baghbany Oskouei was born in Tabriz, Iran, in 1988. She received the B.Sc. degree in electrical engineering from Azarbaijan Shahid Madani University, Tabriz, Iran, in 2010 and the M.Sc. degree in electrical engineering from the University of Tabriz, Tabriz, Iran, in 2012. She is currently working toward the Ph.D. degree in electrical engineering at Azarbaijan Shahid Madani University. Her current research interests include modeling and application of power electronic circuits in power systems and renewable energies. Mohamad Reza Banaei was born in Tabriz, Iran. He received his M.Sc. degree from the Poly Technique University of Tehran, Iran, in control engineering in 1999 and his Ph.D. degree from the electrical engineering faculty of Tabriz University in power engineering in 2005. He is an Associate Professor in the Electrical Engineering Department of Azarbaijan Shahid Madani University, Iran, which he joined in 2005. His main research interests include the modeling and controlling of power electronic converters, renewable energy, modeling and controlling of FACTS and Custom Power devices and power systems dynamics. Mehran Sabahi was born in Tabriz, Iran, in 1968. He received the B.S. degree in electronic engineering from the University of Tabriz, the M.S. degree in electrical engineering from Tehran University, Tehran, Iran, and the Ph.D. degree in electrical engineering from the University of Tabriz, in 1991, 1994, and 2009, respectively. In 2009, he joined the Faculty of Electrical and Computer Engineering, University of Tabriz, where he was an Assistant Professor from 2009 to 2013 and where he has been an Associate Professor since 2014. His current research interests include power electronic converters and renewable energy systems.
Please cite this article in press as: Baghbany Oskouei A et al., Hybrid PV/wind system with quinary asymmetric inverter without increasing DC-link number, Ain Shams Eng J (2015), http://dx.doi.org/10.1016/j.asej.2015.06.008