- Email: [email protected]
supercapacitor hybrid power source for fuel cell hybrid electric vehicles
Accepted Manuscript Novel fuel cell/battery/supercapacitor hybrid power source for fuel cell hybrid electric vehicles
Hassan Fathabadi PII:
S0360-5442(17)31812-1
DOI:
10.1016/j.energy.2017.10.107
Reference:
EGY 11751
To appear in:
Energy
Received Date:
27 May 2017
Revised Date:
21 October 2017
Accepted Date:
23 October 2017
Please cite this article as: Hassan Fathabadi, Novel fuel cell/battery/supercapacitor hybrid power source for fuel cell hybrid electric vehicles, Energy (2017), doi: 10.1016/j.energy.2017.10.107
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ACCEPTED MANUSCRIPT
Highlights Novel PEMFC/battery/SC hybrid power source proposed to be utilized in FCHEVs Higher efficiency (96.2%) compared to the state-of-the-art power sources of FCHEVs Highly accurate DC-link voltage regulation Providing higher speed (161km/h) compared to the state-of-the-art power sources Providing 0-100 km/h acceleration in 12.2 sec and significant cruising range (545km)
ACCEPTED MANUSCRIPT
Novel fuel cell/battery/supercapacitor hybrid power source for fuel cell hybrid electric vehicles Hassan Fathabadi School of Electrical and Computer Engineering, National Technical University of Athens (NTUA), Athens, Greece. Email: [email protected]
Abstract A fuel cell hybrid electric vehicle (FCHEV) is more advantageous compared to a gasoline-powered internal combustion engine based vehicle or a traditional hybrid electric vehicle (HEV) because of using only one electric motor instead of an internal combustion engine or an electric motor in combination with an internal combustion engine. This study proposes a novel fuel cell (FC)/battery/ supercapacitor (SC) hybrid power source to be utilized in FCHEVs. The power source includes a 90 kW proton exchange membrane fuel cell (PEMFC) stack used as the main power source and a 19.2 kW Lithium (Li)-ion battery together with a 600 F SC bank used as the auxiliary energy storage devices. A prototype of the FC/battery/SC hybrid power source has been constructed, and experimental verifications are presented that explicitly substantiate having a power efficiency of 96.2% around the rated power, highly accurate DC-link voltage regulation and producing an appropriate three-phase stator current for the traction motor by using PWM technique are the main contributions of this work. Providing a maximum speed of 161 km/h, 0-100 km/h acceleration in 12.2 sec and a cruising range of 545 km are the other advantages. The proposed FC/battery/SC hybrid power source is also compared to the state of the art of all kinds of power sources used in FCHEVs and reported in the literature that clearly demonstrates its better performance such as higher speed and acceleration.
Keywords Fuel cell hybrid electric vehicle; fuel cell; Lithium- ion battery; supercapacitor; power source. 1
ACCEPTED MANUSCRIPT Nomenclature C
Capacitance occurring between the anode and cathode of the fuel cell (F).
Cstack
Total capacitance of fuel cell stack (F).
C1
Parasitic capacitance of the N-MOSFET switch of the converter connected to the PEMFC stack (F).
C2
Secondary-side serial capacitor of the converter connected to the PEMFC stack (F).
C dc
DC-link capacitor (F).
C fc
Input capacitor of the converter connected to the PEMFC stack (F).
Cout
Output capacitor of the converter connected to the PEMFC stack (F).
D
Diffusion constant ( m 2 s 1 ).
D1 & D2
Diodes of the converter connected to the PEMFC stack.
Dbat char
Duty cycle of the switching pulse supplied to the converter connected to the Li-ion battery in charging mode.
Dbat disc
Duty cycle of the switching pulse supplied to the converter connected to the Li-ion battery in discharging mode.
Dscchar
Duty cycle of the switching pulse supplied to the converter connected to the SC bank in charging mode.
Dsc disc
Duty cycle of the switching pulse supplied to the converter connected to the SC bank in discharging mode.
D fc
Duty cycle of the converter connected to the PEMFC stack.
fs
Constant switching frequency of the converter connected to the PEMFC stack (Hz).
F
Faraday’s constant (96485.3 C mol1 ).
2
ACCEPTED MANUSCRIPT i (t )
Fuel cell current (A).
i0
Exchange current (A).
iL
Limiting current (A).
I bat
Li-ion battery output current (A).
I sc
SC bank output current (A).
I fc
PEMFC stack output current (A).
I load
Load current supplied to the three-phase inverter and traction motor (A).
Llk1
Primary-side leakage inductor of the transformer of the converter connected to the PEMFC stack (H).
Llk 2
Secondary-side leakage inductor of the transformer of the converter connected to the PEMFC stack (H). Equivalent magnetizing inductor of the transformer of the converter connected to the
Lm
PEMFC stack (H). N2
N1
Turns ratio of the transformer of the converter connected to the PEMFC stack.
n
Number of electrons involved in the fuel cell reaction.
N cell
Fuel cells number in the FC stack.
Pbat char
Charging power of the Li-ion battery (W).
Pbat disc
Discharging power of the Li-ion battery (W).
Pfc
PEMFC stack output power (W).
Pscchar
Charging power of the SC bank (W).
Psc disc
Discharging power of the SC bank (W).
3
ACCEPTED MANUSCRIPT
Pload
Total electric power supplied to the three-phase inverter and traction motor (W).
R
Gas constant (8.314 J mol1K 1 ).
Ract
Activation resistance associated with act ( ).
Rconc
Concentration resistance of the fuel cell associated with conc ( ).
Rbat esr
Equivalent series resistance (ESR) of the Li-ion battery ( ).
Resr
ESR of the DC-link capacitor ( ).
Rsc esr
ESR of the SC bank ( ).
Ri
Internal resistance of the fuel cell ( ).
Rin
Input resistance of the converter connected to the PEMFC stack ( ).
RL
Equivalent load resistance observed from the output terminal of the converter connected to the PEMFC stack ( ).
Rload
Load resistance connected to the fuel cell ( ).
R Lbat
Resistance of the inductance Lbat of the bidirectional boost-buck converter connected to the Li-ion battery ( ).
RLsc
Resistance of the inductance Lsc of the bidirectional boost-buck converter connected to the supercapacitor bank ( ).
Rohm
Ohmic resistance of the fuel cell associated with ohm ( ).
S fc
N-MOSFET switch used in the converter connected to the PEMFC stack.
ti
Transference number.
T
Fuel cell temperature (K).
Ts
Switching period of the converter connected to the PEMFC stack (sec).
4
ACCEPTED MANUSCRIPT
Tsc
Switching period of the control signal supplied to the converter connected to the SC bank (sec).
Vbat
Li-ion battery output voltage (V).
Vdc
DC-link voltage (V).
V fc (t )
FC stack output voltage (V).
Voc (t ) E cell Open-circuit voltage of the fuel cell (V). Vout (t )
Fuel cell voltage under load (V).
Vsc
SC bank output voltage (V).
Activity coefficient; 0 1 .
conc
Concentration polarization of the fuel cell (V).
act
Activation polarization of the fuel cell (V).
ohm
Ohmic polarization of the fuel cell (V).
Equivalent conductance of reacting ion ( m 2 Ω 1 equiv 1 or m 2 Ω 1 mol1 ).
1. Introduction Nowadays, environmental problems and economic considerations cause an upward trend in developing electric vehicles (EVs) rather than the vehicles with internal combustion engines [1]. In particular, a traditional HEV consists of an internal combustion engine used as the main power source and an auxiliary energy storage device with the capability of storing energy such as a battery. The auxiliary energy storage device is mainly used to extend the cruising range of the vehicle, to provide the extra energy needed whenever the vehicle accelerates, and to store the regenerative energy produced during braking. A FCHEV is a type of HEV that utilizes a FC stack as the main power source combined with a SC and/or battery used as the auxiliary energy storage device to power the vehicle’s traction motor 5
ACCEPTED MANUSCRIPT which is an electric motor, not an internal combustion engine [2]. A FCHEV is more advantageous compared to a traditional HEV or an internal combustion engine based vehicle because as mentioned it uses an electric motor instead of a gasoline-powered internal combustion engine, so it not only satisfies the environmental issues but also is more efficient [3-4]. It is reminded that even a plug-in hybrid electric vehicle (PHEV) uses an internal combustion engine to extend its cruising range [5], and to produce the electric power needed to be supplied to the vehicle’s electric motor when the level of the vehicle’s battery becomes low and gets to a predetermined state of charge (SOC) [6]. A FC stack produces electric power through the chemical reaction basically occurs in the presence of hydrogen, oxygen and an electrolyte. Compared to an internal combustion engine based power source, relatively higher efficiency [7], lower pollution, the usage of clean energy resources with lower price such as methanol [8], and being appropriate for various industrial applications [9] such as distributed power generations [10] and vehicular systems [11-12] are some benefits of utilizing FC stacks. Among the different FC systems available in the market, the PEMFC technology is more appropriate to be utilized in vehicles because of higher density in electric power production along with lower heat generation causing a lower temperature which is a necessity in a vehicle equipped with a FC stack [13-14]. The first drawback of utilizing a FC stack in a vehicle is that, the FC stack cannot provide appropriate responses to sudden variations in the load demand of the vehicle [15-17]. For instance, the FC stack cannot efficiently respond to the sudden upward and downward powers needed respectively during accelerating and decelerating, or the considerable initial electric power required to start up the vehicle [18-19]. The second drawback is that the FC stack cannot store the regenerative power produced during decelerating and braking, so an extra energy storage device such as a rechargeable battery or SC bank is also needed [20-21]. The two above-mentioned drawbacks demonstrate that an additional device with a suitable storage capacity and high-speed dynamic response should be utilized as an auxiliary energy storage device along with the FC stack.
6
ACCEPTED MANUSCRIPT Because of the advantages of FCHEVs explained in detail, this study focuses on this type of HEV, and proposes a novel FC/battery/SC hybrid power source to be utilized in FCHEVs. The power source includes a 90 kW PEMFC stack used as the main power source and a 19.2 kW Li-ion battery together with a 600 F SC bank used as the auxiliary energy storage devices. A prototype of the FC/battery/SC hybrid power source has been built, and experimental verifications are presented that demonstrate having a power efficiency of more than 96% around the rated power, highly accurate DC-link voltage regulation, and producing an appropriate three-phase current using pulse-width modulation (PWM) technique which is supplied to the traction motor are some contributions of this work. The power source presented in this study is also compared to the state-of-the-art power sources used in FCHEVs that demonstrates the better capability of the proposed power source. The rest of this paper is organized as follows. The behavior of a FC stack in response to sudden variations in load demand is presented in Section 2. The proposed FC/battery/SC hybrid power source is designed and implemented in Section 3. Details about the constructed power source, experimental verifications and comparing the proposed power source to the state-of-the-art power sources used in FCHEVs are given in Section 4. Finally, the paper is concluded in Section 5.
2. Behavior of a FC stack in response to sudden variations in load demand Fig. 1 shows a simple schematic diagram of a typical FCHEV in which a PEMFC stack has been used as the main power source to supply the power needs of the FCHEV, in particular, its traction motor which is an electric motor. Electric power is produced in a PEMFC via a set of the chemical reactions which can be expressed and summarized as [22]:
At Anode :
2H 2 4H 4e
At Cathode : O 2 4H 4e 2H 2 O
(1)
Over all : 2H 2 O 2 2H 2 O
7
ACCEPTED MANUSCRIPT At steady state, the output voltage of a FC is expressed as [23]:
Vout (t ) E cell conc act ohm Ri i (t )
(2)
where Ri represents the internal resistance of the fuel cell consisting of the resistances of the electrolyte, anode, cathode and any diaphragms available between the anode and cathode that the electrons pass through them. Concentration polarization conc is caused by changing in the concentration gradients at the surface of the two electrodes resulting from the continuous chemical reactions, and activation polarization act is due to the slowness of the individual chemical reactions performed at the two electrodes. Ohmic polarization ohm shows the voltage drop caused by the change in specific conductivity resulted from the electro-chemical reactions occurring inside the fuel cell. To formulize the three mentioned polarizations, the activation polarization act of a fuel cell is expressed using Tofel equation as [24]:
act
RT RT ln(i0 ) 2.303 ln[i (t )] nF nF
(3)
The concentration polarization conc of the same fuel cell can be formulized as:
conc
RT i L i (t ) ln n F iL
(4)
Similarly, the ohmic polarization ohm of the fuel cell is obtained as:
ohm
i i (t ) nFD ln L (1 t i ) i L
(5)
Using linearization at a given fuel cell current such as i (t ) in and by defining the three resistances
Ract (T ) , Rconc (T ) and Rohm (T ) , Eqs. (3)-(5) are rewritten as:
conc conc i (t ) Rconc (T ) i (t ) Eq. i i(6) Substituting in in Eq. (2) results that: act i (t ) Ract (T ) i (t ) act i i in ohm i (t ) Rohm (T ) i (t ) ohm i i i n
(6)
8
ACCEPTED MANUSCRIPT Vout (t ) E cell Rconc (T ) i (t ) Ract (T ) i (t ) Rohm (T ) i (t ) Ri i (t )
(7)
Noting Eq. (7) and adding the effect of the electric field appearing between the two electrodes of the FC (cathode and anode), a FC can be modeled as the electric circuit shown in Fig. 2, where the capacitor C with a large capacity at the level of 1-9 Farad represents the electric capacity resulted from the electric field occurring between the cathode and anode. The model is in fact a first-order circuit with the time constant of oc ( Rconc Ract Rohm ) C . As shown in Fig. 3, under loading condition, the electric power produced by the FC is supplied to a load ( Rload ), so the time constant is expressed as:
( Rconc Ract Rohm )( Ri Rload ) C Rconc Ract Rohm Rload Ri
(8)
Eq. (8) demonstrates that a time delay of 2.2 appears when the FC responds to sudden variations in load demand. In industrial applications, a FC stack with the required rated power and voltage is constructed by connecting in series an appropriate number ( N cell ) of FCs, so under steady state condition, the output voltage of a FC stack is found by using Eq. (7) as:
V fc (t ) N cell Vout (t ) N cell E cell N cell Rconc (T ) i (t ) N cell Ract (T ) i (t ) N cell Rohm (T ) i (t ) N cell Ri i (t )
(9)
On the one hand, Eq. (1) substantiates that the electric power production in a PEMFC stack is resulted from a set of the low-speed chemical reactions. On the other hand, the time constant ( ) of a FC given in Eq. (8), and hence, the associated time delay ( 2.2 ) occurring in the response of a FC to sudden variations in load demand explicitly demonstrates that a FC stack is actually a power source with a low-speed dynamic response. To provide experimental evidence, a PEMFC stack H-1000 manufactured by Horizon company has been used [25], the dynamic response of the stack obtained experimentally by varying the resistive load connected to the stack is shown in Fig. 4. The dynamic response simulated by using the proposed model depicted in Fig. 2 is also shown as blue curve in Fig. 9
ACCEPTED MANUSCRIPT 4. The model parameters obtained from Eq. (6) at the stack operating point ( in 35 A , T=300 K) and the technical specification of the H-1000 PEM fuel cell stack reported in its user manual [25] are presented in Table 1. The experimental and simulation results shown in Fig. 4 explicitly verify that a FC stack really has a low-speed dynamic response. This point demonstrates that a PEMFC stack cannot respond to sudden variations in the load demand of an EV such as sudden upward and downward powers needed during transient states such as acceleration and deceleration, or the considerable initial electric power required to start up the EV. As another important point, it is reminded that a FC stack cannot store the regenerative power produced during decelerating and braking, so an additional device such as a rechargeable battery or a SC bank with appropriate capacity is also needed. It can be summarized that an additional device with high-speed dynamic response is also needed to be utilized as an auxiliary power source in a FCHEV to assist the FC stack in providing effective responses to different instant load demands and also saving the regenerative power.
3. Implementation of the FC/battery/SC hybrid power source proposed for FCHEVs The configuration of the FC/battery/SC hybrid power source proposed to be utilized in FCHEVs is shown in Fig. 5. It is composed of a PEMFC stack used as the main power source, a Li-ion battery together with a SC bank used as the auxiliary energy storage devices, a unidirectional DC/DC boost converter connected to the PEMFC stack, two similar bidirectional DC/DC boost-buck converters connected to the battery and SC bank, a three-phase bidirectional PWM DC/AC inverter connected the traction motor which is a three-phase induction motor, in practice, a three-phase permanent magnet synchronous motor (PMSM), and a power control unit. The DC-link voltage is continually regulated to a specific constant value by the power control unit. Fig. 6 shows the electric circuit of the unidirectional DC/DC boost converter connected to the PEMFC stack. The average power efficiency of the converter is 98% and its gain is given as [26]:
10
ACCEPTED MANUSCRIPT
Vdc n V fc 1 D fc
(10)
The DC-link voltage can be obtained from Eq. (10) as:
Vdc (
n ) V fc 1 D fc
(11)
Eq. (11) demonstrates that when the PEMFC stack output voltage varies over time the DC-link voltage can be continuously regulated to a specific value by changing the duty cycle D fc . When D fc is changed by the power control unit to regulate the DC-link voltage, the available output power of the PEMFC stack also varies in accordance with the following power equation: Pfc V fc I fc
V fc 2 Rin
V fc 2 (1 D fc ) 2 n2
(12) RL
where Rin and RL introduced in Nomenclature section are shown in Figs. 5-6. As shown in Fig. 5, the PEMFC stack output current and voltage, and hence, the stack output power is continuously measured by the power control unit. The electric circuit of the bidirectional DC/DC boost-buck converter with the average power efficiency of 90% connected to the SC bank is shown in Fig. 7. The discharging power of the SC bank is given as:
Pscdisc Vsc I sc
(13)
The SC bank output voltage and current ( Vsc and I sc ), and hence, the discharging and charging powers of the SC bank are continuously measured by the power control unit as shown in Fig. 5. Noting Fig. 7 demonstrates that in discharging mode, the converter operates as a boost converter, and the discharging power of the SC bank is expressed as:
11
ACCEPTED MANUSCRIPT
Psc disc
1 ) Vsc Vdc ( 1 Dsc disc 1 1 ( ) Vsc 0.9 1 Dsc disc 0.001 Resr
(14)
where Dsc disc is the duty cycle of the control signal supplied to the gate of the insulated gate bipolar transistor (IGBT) Q1 (SC discharge switch) as shown in Fig. 7. It is deduced from Eq. (14) that the discharging power can be regulated to a required rated power by varying the duty cycle Dsc disc . In charging mode, the direction of the SC bank current becomes reverse, the converter operates as a buck converter, and the charging power is found as:
Dsc char Vdc Vsc Psc char Dsc char Vdc 0.001 Rsc esr R L sc
(15)
where Dscchar is the duty cycle of the switching pulse supplied to the gate of the IGBT Q2 (SC charge switch) as shown in Fig. 7. Thus, the charging power is regulated to a required power rate by varying the duty cycle Dscchar . The discharging power of the Li-ion battery is obtained as:
Pbat disc Vbat I bat
(16)
Similar to SC bank, a bidirectional DC/DC boost-buck converter has been also connected to the Li-ion battery, so similar to the SC bank, the battery discharging power is expressed as:
Pbat disc
1 ) Vbat Vdc ( 1 Dbat disc 1 1 ( ) Vbat 0.9 1 Dbat disc 0.001 Resr
(17)
Similarly, the battery charging power is given as:
Dbat char Vdc Vbat Pbat char Dbat char Vdc 0.001 Rbat esr R L bat
(18)
12
ACCEPTED MANUSCRIPT
As shown in Fig. 5, the power control unit also measures the DC-link voltage ( Vdc ) and load current (
I load ), and then computes the total electric power ( Pload ) supplied to the three-phase bidirectional PWM DC/AC inverter connected to the three-phase traction motor as:
Pload Vdc I load
(19)
The power control in the FC/battery/SC hybrid power source proposed for FCHEVs is performed by the power control unit as below: Case 1 (charging mode): If 0.98 Pfc Pload , then the power control sets the Li-ion battery and SC bank in charging mode by activating the switching pulses with the duty cycles Dbat char and Dscchar as shown in Figs. 5 and 7. In this case, the power balance in the hybrid power source is expressed as: 0.98 Pfc Pload
1 Psc char 0.9
(20)
So, the electric power consumed to charge the SC bank is given as:
Psc char 0.9 0.98 Pfc Pload
(21)
It is derived from comparing Eq. (10) with Eq. (16) that:
Dsc char Vdc Vsc Dsc char Vdc 0.001 Rsc esr R L sc
0.9 0.98 Pfc Pload
(22)
Eq. (22) explicitly demonstrates that in this case (charging mode), the power control unit measures Pfc and Pload , and then regulates the charging power of the SC bank to the required amount specified in Eq. (21) by varying Dscchar . When the charging current of the SC bank reaches below 0.5 A, the SC bank becomes fully charged. Then, the control unit stops charging the SC bank, and sets the Li-ion battery in charging mode, so the power balance is expressed as: 0.98 Pfc Pload
1 Pbat char 0.9
(23)
The electric power required to charge the battery is obtained as: 13
ACCEPTED MANUSCRIPT
Pbat char 0.9 0.98 Pfc Pload
(24)
It is deduced from substituting Eq. (18) in Eq. (24) that:
Dbat char Vdc Vbat Dbat char Vdc 0.001 Rbat esr R L bat
0.9 0.98 Pfc Pload
(25)
Similar to the SC bank, Eq. (25) demonstrates that the charging power of the battery is regulated to the amount demanded in Eq. (24) by varying Dbat char . Case 2 (discharging mode): If 0.98 Pfc Pload , then the power control unit sets the SC bank in discharging mode by activating the duty cycle Ddisc as shown in Fig. 5 to provide the additional electric power needed. In this case, the power balance in the hybrid power source is expressed as:
0.98 Pfc 0.9 Psc disc Pload
(26)
In this case, the amount of the supplementary electric power that should be provided by discharging the SC bank is found from Eq. (26) as: Psc disc
1 Pload 0.98 Pfc 0.9
(27)
By replacing Psc disc from Eq. (14) in Eq. (27), it is found that: 1 ) Vsc Vdc ( 1 Dsc disc 1 ( ) Vsc 1 Dsc disc 0.001 Resr
P 0.98 P fc load
14
(28)
ACCEPTED MANUSCRIPT
It is deduced from Eq. (28) that in this case (discharging mode), the power control unit measures Pfc and Pload , and then regulates the discharging power of the SC bank to the amount demanded in Eq. (27) by varying Dsc disc . When the discharging current of the SC bank reaches below 0.5 A, the SC bank becomes fully discharged, the control unit stops discharging the SC bank, and sets the Li-ion battery in discharging mode, so the power balance is expressed as:
0.98 Pfc 0.9 Pbat disc Pload
(29)
The supplementary electric power that should be provided by discharging the battery is found from Eq. (29) as: Pbat disc
1 Pload 0.98 Pfc 0.9
(30)
By substituting Pbat disc from Eq. (17) in Eq. (30), it is found that: 1 ) Vbat Vdc ( 1 Dbat disc 1 ( ) Vbat 1 Dbat disc 0.001 Resr
P 0.98 P fc load
(31)
It is deduced from Eq. (31) that the power control unit measures Pfc and Pload , and regulates the discharging power of the Li-ion battery to the required amount specified in Eq. (30) by varying Dbat disc . The electric circuit of the proposed three-phase bidirectional PWM six-switch DC/AC inverter connected the traction motor is shown in Fig. 8. It comprises the six IGBTs that convert the DC-link voltage into a three-phase three-level PWM AC voltage supplied to the stator of the traction motor which is in practice a three-phase PMSM. Since the traction motor acts as a three-phase inductive load, the current delivered to the stator is the integral of the three-level PWM AC voltage, and so the current waveform is close to a sinusoidal form. As shown in Fig. 8, each IGBT itself includes an emitter-tocollector connected diode, the six diodes operate as a three-phase rectifier to convert the three-phase 15
ACCEPTED MANUSCRIPT AC voltage resulted from the regenerative power produced by the traction motor during decelerating and braking into the DC-link voltage which is used to charge the SC bank and battery. Thus, the proposed three-phase PWM six-switch DC/AC inverter is a bidirectional inverter.
4. Construction of the FC/battery/SC hybrid power source and experimental verifications The detailed specifications of all the components used to construct the FC/battery/SC hybrid power source proposed to be utilized in FCHEVs are listed in Table 2. As reported in Table 2, an 80 kW three-phase PMSM used as the traction motor, a 90 kW PEMFC stack, a 19.2 kW Li-ion battery and a SC bank with the rated capacitance of 600 F composed of the four parallel-connected blocks that each block itself consists of 20 series-connected SC cells ESHSR-3000C0-002R7A5T have been utilized. The waveforms of the line voltages ( V AB and VBC ) supplied to the PMSM and the DC-link voltage are shown in Fig. 9. The waveforms of the line voltages show that they are the three-level AC voltages with correct magnitude and phase produced using PWM technique by the three-phase bidirectional DC/AC inverter. This point explicitly verifies the correct operation of the three-phase bidirectional PWM six-switch DC/AC inverter connected to the traction motor. Similarly, the waveform of the DC-link voltage explicitly demonstrates that the DC-link voltage is exactly regulated to the appointed value (400 V) by the unidirectional DC/DC boost converter connected to the PEMFC stack in accordance with Eq. (10). The waveforms of the currents ( I A and I B ) supplied to the stator of the PMSM are shown in Fig. 10. The periodic switching pulse with the switching frequency of 25 kHz and the duty cycle D fc determined according to Eq. (10) to regulate the DClink voltage along with the regulated DC-link voltage is also shown in Fig. 11. As mentioned, the periodic switching pulse is supplied to the switch S fc of the unidirectional DC/DC boost converter connected to the PEMFC stack. The electric power supplied to the traction motor (output power), and the total of the electric power provided by the PEMFC stack power production, discharging the 16
ACCEPTED MANUSCRIPT SC bank and Li-ion battery (input power) were measured point by point. Then, the power efficiency of the proposed FC/battery/SC hybrid power source was computed point by point as: Power efficiency
Output power 100 Input power
(32)
The power efficiency curve resulted from the point by point computing is shown in Fig. 12. The following points which are the main contributions of this study are deduced from the experimental results shown in Figs. 9-12: ● The power efficiency curve explicitly demonstrates that the proposed FC/battery/SC hybrid power source provides a power efficiency of 96.2% around the rated power. ● The DC-link voltage is high accurately regulated to the appointed value (400 V). ● The traction motor is well supplied by the sinusoidal currents resulted from the three-level AC voltages produced by using PWM technique. The other benefit of the FC/battery/SC hybrid power source presented in this study is its flexibility, so that, it can be also utilized as a FC/battery or FC/SC power source. In detail, on the request, the power control unit disables the switching pulses with the duty cycles Dscchar and Dsc disc supplied to the converter connected to the SC bank, so the SC bank is isolated from the system, and the system changes into a FC/battery power source. Similarly, the proposed power source operates as a FC/SC hybrid power source by disabling the switching pulses with the duty cycles Dbat char and Dbat disc supplied to the converter connected to the Li-ion battery. Thus, the power source can be utilized in the three modes; FC/battery/SC, FC/battery and FC/SC. The technical parameters of the power source in the three modes are summarized and compared in Table 3. The comparison demonstrates that utilizing the SC bank mainly improves the acceleration of the vehicle, while the Li-ion battery provides longer cruising range, so that, a FCHEV with the weight of 1880 kg equipped with the proposed FC/battery/SC hybrid power source has a maximum speed of 161 km/h, 0-100 km/h acceleration in 12.2 sec, and a cruising range of 435 km on one 17
ACCEPTED MANUSCRIPT tank of hydrogen with the fuel capacity/tank pressure of 5.4 kg/5000 psi and 110 km on the 19.2 kWh Li-ion battery (totally, 545 km). As another attempt to prove the contributions of this work, a comparison between the proposed FC/battery/SC hybrid power source and the state of the art of all kinds of power sources reported in the literature to be used in FCHEVs is performed in Table 4 [15], [27-63]. It is worthwhile to note that while the majority of the other works are only simulated models, the comparison explicitly demonstrates the excellent performance of the proposed FC/battery/SC hybrid power source such as higher speed and acceleration.
5. Conclusion In this paper, a novel FC/battery/SC hybrid power source was proposed to be used in FCHEVs. A 90 kW PEMFC stack, a 600 F SC bank and a 19.2 kW Li-ion battery were used to construct a prototype of the FC/battery/SC hybrid power source. The experimental results demonstrated that the power efficiency of 96.2% around the rated power, highly accurate DC-link voltage regulation and providing a suitable three-phase current by using PWM technique that is supplied to the stator of the traction motor are the main contributions of this work. For a FCHEV with the weight of 1880 kg, the proposed power source provides a total cruising range of 545 km on one tank of hydrogen with the fuel capacity/tank pressure of 5.4 kg/5000 psi, a maximum speed of 161 km/h and 0-100 km/h acceleration in 12.2 sec. The proposed hybrid power source was also compared to the state-of-the-art power sources used in FCHEVs and reported in the literature that clearly substantiated its better parameters such as higher speed and acceleration, while most of the other works were simulated models. References [1] H. Fathabadi, Utilization of electric vehicles and renewable energy sources used as distributed generators for improving characteristics of electric power distribution systems, Energy 90 (2015) 1100-1110. 18
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[41] A. Benrabeh, F. Khoucha, O. Herizi, M. Benbouzid, A. Kheloui, FC/battery power management for electric vehicle based interleaved DC-DC boost converter topology, Proceedings of 15th European Conference on Power Electronics and Applications (EPE) IEEE (2013) 1-9. [42] M. Uzunoglu, M. Alam, Modeling and analysis of an FC/UC hybrid vehicular power system using a novel-wavelet-based load sharing algorithm, IEEE Transactions on Energy Conversion 23 (2008) 263-272. [43] P. Rodatz, G. Paganelli, A. Sciarretta, L. Guzzella, Optimal power management of an experimental fuel cell/supercapacitor-powered hybrid vehicle, Control Engineering Practice 13 (2005) 41-53. [44] M. Kisacikoglu, M. Uzunoglu, M. Alam, Load sharing using fuzzy logic control in a fuel cell/ultracapacitor hybrid vehicle, International Journal of Hydrogen Energy 34 (2009) 1497-1507. [45] J.S. Martínez, D. Hissel, M.-C. Péra, M. Amiet, Practical control structure and energy management of a testbed hybrid electric vehicle, IEEE Transactions on Vehicular Technology 60 (2011) 4139-4152. [46] Q. Li, W. Chen, Y. Li, S. Liu, J. Huang, Energy management strategy for fuel cell/battery/ultracapacitor hybrid vehicle based on fuzzy logic, International Journal of Electrical Power & Energy Systems 43 (1) (2012) 514-525. [47] D. Gao, Z. Jin, Q. Lu, Energy management strategy based on fuzzy logic for a fuel cell hybrid bus, Journal of Power Sources 185 (2008) 311–317. [48] M. Hannan, F. Azidin, A. Mohamed, Multi-sources model and control algorithm of an energy management system for light electric vehicles, Energy Conversion and Management 62 (2012) 123130. 23
ACCEPTED MANUSCRIPT [49] P. García, J.P. Torreglosa, L.M. Fernández, F. Jurado, Control strategies for high-power electric vehicles powered by hydrogen fuel cell, battery and supercapacitor, Expert Systems with Applications 40 (12) (2013) 4791-4804. [50] Z. Yu, D. Zinger, A. Bose, An innovative optimal power allocation strategy for fuel cell, battery and supercapacitor hybrid electric vehicle, Journal of Power Sources 196 (2011) 2351-2359. [51] X. Liu, D. Diallo, C. Marchand, Design methodology of fuel cell electric vehicle power system, Proceedings of 18th IEEE International Conference on Electrical Machines (ICEM) (2008) 1-6. [52] A. Melero-Pérez, W. Gao, I.J. Fernández-Lozano, Fuzzy logic energy management strategy for Fuel Cell/Ultracapacitor/Battery hybrid vehicle with multiple-input DC/DC converter, Proceedings of Vehicle Power and Propulsion Conference (VPPC'09 IEEE) (2009) 199-206.
24
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Fig.1. Schematic diagram of a typical FCHEV.
25
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Fig. 2. Electric circuit representing the behavior of a FC.
Fig. 3. Electric circuit representing the behavior of a FC under loading condition.
26
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Fig. 4. Dynamic response of a PEMFC stack H-1000.
27
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Fig. 5. Configuration of the FC/battery/SC hybrid power source proposed to be utilized in FCHEVs. 28
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Fig. 6. Unidirectional DC/DC boost converter connected to the PEMFC stack.
Fig. 7. Bidirectional DC/DC boost-buck converter connected to the SC bank.
29
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Fig. 8. Three-phase bidirectional PWM six-switch DC/AC inverter.
30
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Fig. 9. Experimental results: The waveforms of the line voltages ( V AB and VBC ) supplied to the PMSM, and the regulated DC-link voltage.
31
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Fig. 10. Experimental results: The waveforms of the currents ( I A and I B ) supplied to the stator of the PMSM.
32
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Fig. 11. Experimental results: The periodic switching pulse supplied to the switch S fc of the DC/DC boost converter connected to the PEMFC stack, and the regulated DC-link voltage.
33
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Fig. 12. Experimental results: Point by point measured power efficiency of the FC/battery/SC hybrid power source.
34
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Table 1. Technical specification of the PEM fuel cell stack H-1000 [25] and model parameters obtained from Eq. (6) at the stack operating point ( in 35 A ) and T=300 K. Technical specification of the PEM fuel cell stack H-1000 48 N cell
Model parameters obtained from Eq. (6) at the stack operating point ( in 35 A ) and T=300 K
E0 (V)
46
Stack efficiency
40% @ 28.8 V
Rconc ()
0.0374
Rated power (W)
1000
Ract ()
0.1092
Operating point
28.8 V @ 35 A
Rohm ()
0.0637
Max. stack temperature ( C )
65
Ri ()
0.1224
Over current shut down (A)
42
C (F)
4.8623
H 2 pressure (bar)
0.45-0.55
Cstack (F)
0.1013
Flow rate at max. output power (lit/min)
13
35
ACCEPTED MANUSCRIPT Table 2. Technical specification of the components used in the constructed FC/battery/SC hybrid power source. Traction motor Product name
DC/DC boost converter connected to PEMFC stack
C fc ( μ F )-Aluminum
LSRPM 200 L
electrolytic capacitor/400 V Converter switching frequency: f s (kHz)
470
Made by
Leroy-Somer Co.
Type
3-phase, permanent magnet synchronous motor (PMSM)
electrolytic capacitor/600 V
220
Nominal line voltage (V)
400
DC-link voltage Vdc (V)
400
Rated power (kW)
80
C2 ( μ F )-Premium metallized
Rated torque (Nm)
170
Rated current (A)
157
Speed range (rpm)
0-4500
Efficiency (%)
95.7
MOSFET switch S fc
IRFPS40N60K
Maximum torque/Rated torque Magnet material
1.4
Diodes: D1 - D2
15ETH06S
Cout ( μ F )-Aluminum
polypropylene capacitor/600 V C1 ( n F )-Parasitic capacitance of IRFPS40N60K Type of transformer T
N2
NdFeB
Maximum current/Rated current Moment of inertia ( kg.m 2 ) Weight (kg)
N1
25
22 15.6 Pulse
11 10 13
PEMFC stack
1.5
Product name
HD-90
0.15 145
Made by
Hydrogenics Co.
Peak efficiency
55%
Rated power (kW)
90
Supercapacitor cell Product name
ESHSR-3000C0002R7A5T
Maximum power (kW)
99
Made by
Nesscap Co.
Stack operating pressure (kPa)
<120
Rated voltage (V)
2.7
Operating current (A)
0-500
Surge voltage (V)
2.85
Operating voltage (V)
180-360
Rated capacitance (F)
3000
Average capacitance tolerance (%)
5
Maximum continuous current (A)
148
DC/DC converter connected to the supercapacitor bank Type Bidirectional boost-buck IGBT switches: SW, Q1-Q2 STGY40NC60VD
6
36
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Maximum leakage current (mA)
5.2
Average ESR ( mΩ )
0.14
Maximum stored energy (Wh) Maximum specific energy (Wh/kg)
3.03
Parallel-connected blocks
4
5.67
20
Usable specific power (kW/kg) Nominal weight (g)
6.28
Series-connected supercapacitor cells in each block Rated capacitance (F)
600
535
Rated voltage (V)
54
Maximum continuous current (A) Maximum stored energy (Wh)
592 242.4
Average ESR ( Rsc esr ( mΩ ))
0.7
RLsc ( mΩ ) Supercapacitor bank
Three-phase bidirectional PWM six-switch DC/AC inverter IGBT switches: Q9-Q14
13.3
STGY40NC60VD
5
C dc ( μ F )-Aluminum
220
electrolytic capacitor/600 V DC/DC converter connected to the Li-ion battery bank Type IGBT switches: SW, Q1Q2
R Lbat ( mΩ )
Battery bank: Sixteen 12 V/100 Ah Li-ion batteries Rated voltage (V) 48
Bidirectional boost-buck STGY40NC60VD
Current capacity (Ah)
400
Capacity (kWh)
19.2
Series-connected batteries
4
Parallel-connected sets
4
Average ESR ( Rbat esr ( mΩ ))
2.9
8 10.8
Table 3. Comparison between the technical parameters of the hybrid power source in different modes. Mode of the power source
Analysis type
FC/Battery/SC FC/SC FC/Battery
Experiment Experiment Experiment
Cruising range (km) 545 435 530
Max. speed ( km/h) 161 158 155
37
0-100 km/h Max. Fuel Tank Vehicle acceleration efficiency capacity Pressure weight (sec) (%) (kg) (psi) (kg) 12.2 96.2 5.4 5000 1880 12.2 96.2 5.4 5000 1880 13.4 96.1 5.4 5000 1880
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Table 4. Comparison between the proposed FC/battery/SC hybrid power source and the state-of-the-art power sources used in FCHEVs and reported in the literature. Power source type
DC-link Max. speed Analysis type voltage (V) ( km/h)
PEMFC/battery/SC Experiment PEMFC/Battery Simulation& experiment PEMFC/Battery Simulation PEMFC/Battery Simulation PEMFC/Battery Simulation PEMFC/Battery Simulation & experiment PEMFC/Battery Simulation PEMFC/Battery Simulation PEMFC/Battery Simulation PEMFC/Battery Simulation PEMFC/Battery Simulation PEMFC/Battery Simulation PEMFC/Battery Simulation PEMFC/Battery Simulation PEMFC/Battery Simulation PEMFC/Battery Simulation PEMFC/SC Simulation PEMFC/SC Simulation PEMFC/SC Simulation PEMFC/SC Simulation PEMFC/Battery/SC Experiment PEMFC/Battery/SC Simulation PEMFC/Battery/SC Experiment PEMFC/Battery/SC Simulation PEMFC/Battery/SC Simulation & experiment PEMFC/Battery/SC Simulation PEMFC/Battery/SC Simulation PEMFC/Battery/SC Simulation & experiment
545 400
161 –
0-100 km/h acceleration (sec) 12.2 –
– – 300 450
– 108 80 90
– – – –
62 30 40 40
[28] [29] [30] [31]
– – – – 60 – – 400 – – 400 188 340 206 560 – 400 120 750
60 88.5 – 120 – 129 – 50 144 120 120 91 120 91 20 160 23.4 47 50
– – – – – – – – – – 12.5 – – – – – – – –
130 75 – 80 2 80 2 8 4 60 48 60 60 40 40 40 120 3 400
[32] [33] [34] [35] [36] [37] [38] [39] [40] [41] [15] [42] [43] [44] [45] [46] [47] [48] [49]
300 300 400
128 120 –
– – –
100 58 38.5
[50] [51] [52]
38
Max. power (kW)
Reference
99 30
This work [27]
Hassan Fathabadi PII:
S0360-5442(17)31812-1
DOI:
10.1016/j.energy.2017.10.107
Reference:
EGY 11751
To appear in:
Energy
Received Date:
27 May 2017
Revised Date:
21 October 2017
Accepted Date:
23 October 2017
Please cite this article as: Hassan Fathabadi, Novel fuel cell/battery/supercapacitor hybrid power source for fuel cell hybrid electric vehicles, Energy (2017), doi: 10.1016/j.energy.2017.10.107
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT
Highlights Novel PEMFC/battery/SC hybrid power source proposed to be utilized in FCHEVs Higher efficiency (96.2%) compared to the state-of-the-art power sources of FCHEVs Highly accurate DC-link voltage regulation Providing higher speed (161km/h) compared to the state-of-the-art power sources Providing 0-100 km/h acceleration in 12.2 sec and significant cruising range (545km)
ACCEPTED MANUSCRIPT
Novel fuel cell/battery/supercapacitor hybrid power source for fuel cell hybrid electric vehicles Hassan Fathabadi School of Electrical and Computer Engineering, National Technical University of Athens (NTUA), Athens, Greece. Email: [email protected]
Abstract A fuel cell hybrid electric vehicle (FCHEV) is more advantageous compared to a gasoline-powered internal combustion engine based vehicle or a traditional hybrid electric vehicle (HEV) because of using only one electric motor instead of an internal combustion engine or an electric motor in combination with an internal combustion engine. This study proposes a novel fuel cell (FC)/battery/ supercapacitor (SC) hybrid power source to be utilized in FCHEVs. The power source includes a 90 kW proton exchange membrane fuel cell (PEMFC) stack used as the main power source and a 19.2 kW Lithium (Li)-ion battery together with a 600 F SC bank used as the auxiliary energy storage devices. A prototype of the FC/battery/SC hybrid power source has been constructed, and experimental verifications are presented that explicitly substantiate having a power efficiency of 96.2% around the rated power, highly accurate DC-link voltage regulation and producing an appropriate three-phase stator current for the traction motor by using PWM technique are the main contributions of this work. Providing a maximum speed of 161 km/h, 0-100 km/h acceleration in 12.2 sec and a cruising range of 545 km are the other advantages. The proposed FC/battery/SC hybrid power source is also compared to the state of the art of all kinds of power sources used in FCHEVs and reported in the literature that clearly demonstrates its better performance such as higher speed and acceleration.
Keywords Fuel cell hybrid electric vehicle; fuel cell; Lithium- ion battery; supercapacitor; power source. 1
ACCEPTED MANUSCRIPT Nomenclature C
Capacitance occurring between the anode and cathode of the fuel cell (F).
Cstack
Total capacitance of fuel cell stack (F).
C1
Parasitic capacitance of the N-MOSFET switch of the converter connected to the PEMFC stack (F).
C2
Secondary-side serial capacitor of the converter connected to the PEMFC stack (F).
C dc
DC-link capacitor (F).
C fc
Input capacitor of the converter connected to the PEMFC stack (F).
Cout
Output capacitor of the converter connected to the PEMFC stack (F).
D
Diffusion constant ( m 2 s 1 ).
D1 & D2
Diodes of the converter connected to the PEMFC stack.
Dbat char
Duty cycle of the switching pulse supplied to the converter connected to the Li-ion battery in charging mode.
Dbat disc
Duty cycle of the switching pulse supplied to the converter connected to the Li-ion battery in discharging mode.
Dscchar
Duty cycle of the switching pulse supplied to the converter connected to the SC bank in charging mode.
Dsc disc
Duty cycle of the switching pulse supplied to the converter connected to the SC bank in discharging mode.
D fc
Duty cycle of the converter connected to the PEMFC stack.
fs
Constant switching frequency of the converter connected to the PEMFC stack (Hz).
F
Faraday’s constant (96485.3 C mol1 ).
2
ACCEPTED MANUSCRIPT i (t )
Fuel cell current (A).
i0
Exchange current (A).
iL
Limiting current (A).
I bat
Li-ion battery output current (A).
I sc
SC bank output current (A).
I fc
PEMFC stack output current (A).
I load
Load current supplied to the three-phase inverter and traction motor (A).
Llk1
Primary-side leakage inductor of the transformer of the converter connected to the PEMFC stack (H).
Llk 2
Secondary-side leakage inductor of the transformer of the converter connected to the PEMFC stack (H). Equivalent magnetizing inductor of the transformer of the converter connected to the
Lm
PEMFC stack (H). N2
N1
Turns ratio of the transformer of the converter connected to the PEMFC stack.
n
Number of electrons involved in the fuel cell reaction.
N cell
Fuel cells number in the FC stack.
Pbat char
Charging power of the Li-ion battery (W).
Pbat disc
Discharging power of the Li-ion battery (W).
Pfc
PEMFC stack output power (W).
Pscchar
Charging power of the SC bank (W).
Psc disc
Discharging power of the SC bank (W).
3
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Pload
Total electric power supplied to the three-phase inverter and traction motor (W).
R
Gas constant (8.314 J mol1K 1 ).
Ract
Activation resistance associated with act ( ).
Rconc
Concentration resistance of the fuel cell associated with conc ( ).
Rbat esr
Equivalent series resistance (ESR) of the Li-ion battery ( ).
Resr
ESR of the DC-link capacitor ( ).
Rsc esr
ESR of the SC bank ( ).
Ri
Internal resistance of the fuel cell ( ).
Rin
Input resistance of the converter connected to the PEMFC stack ( ).
RL
Equivalent load resistance observed from the output terminal of the converter connected to the PEMFC stack ( ).
Rload
Load resistance connected to the fuel cell ( ).
R Lbat
Resistance of the inductance Lbat of the bidirectional boost-buck converter connected to the Li-ion battery ( ).
RLsc
Resistance of the inductance Lsc of the bidirectional boost-buck converter connected to the supercapacitor bank ( ).
Rohm
Ohmic resistance of the fuel cell associated with ohm ( ).
S fc
N-MOSFET switch used in the converter connected to the PEMFC stack.
ti
Transference number.
T
Fuel cell temperature (K).
Ts
Switching period of the converter connected to the PEMFC stack (sec).
4
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Tsc
Switching period of the control signal supplied to the converter connected to the SC bank (sec).
Vbat
Li-ion battery output voltage (V).
Vdc
DC-link voltage (V).
V fc (t )
FC stack output voltage (V).
Voc (t ) E cell Open-circuit voltage of the fuel cell (V). Vout (t )
Fuel cell voltage under load (V).
Vsc
SC bank output voltage (V).
Activity coefficient; 0 1 .
conc
Concentration polarization of the fuel cell (V).
act
Activation polarization of the fuel cell (V).
ohm
Ohmic polarization of the fuel cell (V).
Equivalent conductance of reacting ion ( m 2 Ω 1 equiv 1 or m 2 Ω 1 mol1 ).
1. Introduction Nowadays, environmental problems and economic considerations cause an upward trend in developing electric vehicles (EVs) rather than the vehicles with internal combustion engines [1]. In particular, a traditional HEV consists of an internal combustion engine used as the main power source and an auxiliary energy storage device with the capability of storing energy such as a battery. The auxiliary energy storage device is mainly used to extend the cruising range of the vehicle, to provide the extra energy needed whenever the vehicle accelerates, and to store the regenerative energy produced during braking. A FCHEV is a type of HEV that utilizes a FC stack as the main power source combined with a SC and/or battery used as the auxiliary energy storage device to power the vehicle’s traction motor 5
ACCEPTED MANUSCRIPT which is an electric motor, not an internal combustion engine [2]. A FCHEV is more advantageous compared to a traditional HEV or an internal combustion engine based vehicle because as mentioned it uses an electric motor instead of a gasoline-powered internal combustion engine, so it not only satisfies the environmental issues but also is more efficient [3-4]. It is reminded that even a plug-in hybrid electric vehicle (PHEV) uses an internal combustion engine to extend its cruising range [5], and to produce the electric power needed to be supplied to the vehicle’s electric motor when the level of the vehicle’s battery becomes low and gets to a predetermined state of charge (SOC) [6]. A FC stack produces electric power through the chemical reaction basically occurs in the presence of hydrogen, oxygen and an electrolyte. Compared to an internal combustion engine based power source, relatively higher efficiency [7], lower pollution, the usage of clean energy resources with lower price such as methanol [8], and being appropriate for various industrial applications [9] such as distributed power generations [10] and vehicular systems [11-12] are some benefits of utilizing FC stacks. Among the different FC systems available in the market, the PEMFC technology is more appropriate to be utilized in vehicles because of higher density in electric power production along with lower heat generation causing a lower temperature which is a necessity in a vehicle equipped with a FC stack [13-14]. The first drawback of utilizing a FC stack in a vehicle is that, the FC stack cannot provide appropriate responses to sudden variations in the load demand of the vehicle [15-17]. For instance, the FC stack cannot efficiently respond to the sudden upward and downward powers needed respectively during accelerating and decelerating, or the considerable initial electric power required to start up the vehicle [18-19]. The second drawback is that the FC stack cannot store the regenerative power produced during decelerating and braking, so an extra energy storage device such as a rechargeable battery or SC bank is also needed [20-21]. The two above-mentioned drawbacks demonstrate that an additional device with a suitable storage capacity and high-speed dynamic response should be utilized as an auxiliary energy storage device along with the FC stack.
6
ACCEPTED MANUSCRIPT Because of the advantages of FCHEVs explained in detail, this study focuses on this type of HEV, and proposes a novel FC/battery/SC hybrid power source to be utilized in FCHEVs. The power source includes a 90 kW PEMFC stack used as the main power source and a 19.2 kW Li-ion battery together with a 600 F SC bank used as the auxiliary energy storage devices. A prototype of the FC/battery/SC hybrid power source has been built, and experimental verifications are presented that demonstrate having a power efficiency of more than 96% around the rated power, highly accurate DC-link voltage regulation, and producing an appropriate three-phase current using pulse-width modulation (PWM) technique which is supplied to the traction motor are some contributions of this work. The power source presented in this study is also compared to the state-of-the-art power sources used in FCHEVs that demonstrates the better capability of the proposed power source. The rest of this paper is organized as follows. The behavior of a FC stack in response to sudden variations in load demand is presented in Section 2. The proposed FC/battery/SC hybrid power source is designed and implemented in Section 3. Details about the constructed power source, experimental verifications and comparing the proposed power source to the state-of-the-art power sources used in FCHEVs are given in Section 4. Finally, the paper is concluded in Section 5.
2. Behavior of a FC stack in response to sudden variations in load demand Fig. 1 shows a simple schematic diagram of a typical FCHEV in which a PEMFC stack has been used as the main power source to supply the power needs of the FCHEV, in particular, its traction motor which is an electric motor. Electric power is produced in a PEMFC via a set of the chemical reactions which can be expressed and summarized as [22]:
At Anode :
2H 2 4H 4e
At Cathode : O 2 4H 4e 2H 2 O
(1)
Over all : 2H 2 O 2 2H 2 O
7
ACCEPTED MANUSCRIPT At steady state, the output voltage of a FC is expressed as [23]:
Vout (t ) E cell conc act ohm Ri i (t )
(2)
where Ri represents the internal resistance of the fuel cell consisting of the resistances of the electrolyte, anode, cathode and any diaphragms available between the anode and cathode that the electrons pass through them. Concentration polarization conc is caused by changing in the concentration gradients at the surface of the two electrodes resulting from the continuous chemical reactions, and activation polarization act is due to the slowness of the individual chemical reactions performed at the two electrodes. Ohmic polarization ohm shows the voltage drop caused by the change in specific conductivity resulted from the electro-chemical reactions occurring inside the fuel cell. To formulize the three mentioned polarizations, the activation polarization act of a fuel cell is expressed using Tofel equation as [24]:
act
RT RT ln(i0 ) 2.303 ln[i (t )] nF nF
(3)
The concentration polarization conc of the same fuel cell can be formulized as:
conc
RT i L i (t ) ln n F iL
(4)
Similarly, the ohmic polarization ohm of the fuel cell is obtained as:
ohm
i i (t ) nFD ln L (1 t i ) i L
(5)
Using linearization at a given fuel cell current such as i (t ) in and by defining the three resistances
Ract (T ) , Rconc (T ) and Rohm (T ) , Eqs. (3)-(5) are rewritten as:
conc conc i (t ) Rconc (T ) i (t ) Eq. i i(6) Substituting in in Eq. (2) results that: act i (t ) Ract (T ) i (t ) act i i in ohm i (t ) Rohm (T ) i (t ) ohm i i i n
(6)
8
ACCEPTED MANUSCRIPT Vout (t ) E cell Rconc (T ) i (t ) Ract (T ) i (t ) Rohm (T ) i (t ) Ri i (t )
(7)
Noting Eq. (7) and adding the effect of the electric field appearing between the two electrodes of the FC (cathode and anode), a FC can be modeled as the electric circuit shown in Fig. 2, where the capacitor C with a large capacity at the level of 1-9 Farad represents the electric capacity resulted from the electric field occurring between the cathode and anode. The model is in fact a first-order circuit with the time constant of oc ( Rconc Ract Rohm ) C . As shown in Fig. 3, under loading condition, the electric power produced by the FC is supplied to a load ( Rload ), so the time constant is expressed as:
( Rconc Ract Rohm )( Ri Rload ) C Rconc Ract Rohm Rload Ri
(8)
Eq. (8) demonstrates that a time delay of 2.2 appears when the FC responds to sudden variations in load demand. In industrial applications, a FC stack with the required rated power and voltage is constructed by connecting in series an appropriate number ( N cell ) of FCs, so under steady state condition, the output voltage of a FC stack is found by using Eq. (7) as:
V fc (t ) N cell Vout (t ) N cell E cell N cell Rconc (T ) i (t ) N cell Ract (T ) i (t ) N cell Rohm (T ) i (t ) N cell Ri i (t )
(9)
On the one hand, Eq. (1) substantiates that the electric power production in a PEMFC stack is resulted from a set of the low-speed chemical reactions. On the other hand, the time constant ( ) of a FC given in Eq. (8), and hence, the associated time delay ( 2.2 ) occurring in the response of a FC to sudden variations in load demand explicitly demonstrates that a FC stack is actually a power source with a low-speed dynamic response. To provide experimental evidence, a PEMFC stack H-1000 manufactured by Horizon company has been used [25], the dynamic response of the stack obtained experimentally by varying the resistive load connected to the stack is shown in Fig. 4. The dynamic response simulated by using the proposed model depicted in Fig. 2 is also shown as blue curve in Fig. 9
ACCEPTED MANUSCRIPT 4. The model parameters obtained from Eq. (6) at the stack operating point ( in 35 A , T=300 K) and the technical specification of the H-1000 PEM fuel cell stack reported in its user manual [25] are presented in Table 1. The experimental and simulation results shown in Fig. 4 explicitly verify that a FC stack really has a low-speed dynamic response. This point demonstrates that a PEMFC stack cannot respond to sudden variations in the load demand of an EV such as sudden upward and downward powers needed during transient states such as acceleration and deceleration, or the considerable initial electric power required to start up the EV. As another important point, it is reminded that a FC stack cannot store the regenerative power produced during decelerating and braking, so an additional device such as a rechargeable battery or a SC bank with appropriate capacity is also needed. It can be summarized that an additional device with high-speed dynamic response is also needed to be utilized as an auxiliary power source in a FCHEV to assist the FC stack in providing effective responses to different instant load demands and also saving the regenerative power.
3. Implementation of the FC/battery/SC hybrid power source proposed for FCHEVs The configuration of the FC/battery/SC hybrid power source proposed to be utilized in FCHEVs is shown in Fig. 5. It is composed of a PEMFC stack used as the main power source, a Li-ion battery together with a SC bank used as the auxiliary energy storage devices, a unidirectional DC/DC boost converter connected to the PEMFC stack, two similar bidirectional DC/DC boost-buck converters connected to the battery and SC bank, a three-phase bidirectional PWM DC/AC inverter connected the traction motor which is a three-phase induction motor, in practice, a three-phase permanent magnet synchronous motor (PMSM), and a power control unit. The DC-link voltage is continually regulated to a specific constant value by the power control unit. Fig. 6 shows the electric circuit of the unidirectional DC/DC boost converter connected to the PEMFC stack. The average power efficiency of the converter is 98% and its gain is given as [26]:
10
ACCEPTED MANUSCRIPT
Vdc n V fc 1 D fc
(10)
The DC-link voltage can be obtained from Eq. (10) as:
Vdc (
n ) V fc 1 D fc
(11)
Eq. (11) demonstrates that when the PEMFC stack output voltage varies over time the DC-link voltage can be continuously regulated to a specific value by changing the duty cycle D fc . When D fc is changed by the power control unit to regulate the DC-link voltage, the available output power of the PEMFC stack also varies in accordance with the following power equation: Pfc V fc I fc
V fc 2 Rin
V fc 2 (1 D fc ) 2 n2
(12) RL
where Rin and RL introduced in Nomenclature section are shown in Figs. 5-6. As shown in Fig. 5, the PEMFC stack output current and voltage, and hence, the stack output power is continuously measured by the power control unit. The electric circuit of the bidirectional DC/DC boost-buck converter with the average power efficiency of 90% connected to the SC bank is shown in Fig. 7. The discharging power of the SC bank is given as:
Pscdisc Vsc I sc
(13)
The SC bank output voltage and current ( Vsc and I sc ), and hence, the discharging and charging powers of the SC bank are continuously measured by the power control unit as shown in Fig. 5. Noting Fig. 7 demonstrates that in discharging mode, the converter operates as a boost converter, and the discharging power of the SC bank is expressed as:
11
ACCEPTED MANUSCRIPT
Psc disc
1 ) Vsc Vdc ( 1 Dsc disc 1 1 ( ) Vsc 0.9 1 Dsc disc 0.001 Resr
(14)
where Dsc disc is the duty cycle of the control signal supplied to the gate of the insulated gate bipolar transistor (IGBT) Q1 (SC discharge switch) as shown in Fig. 7. It is deduced from Eq. (14) that the discharging power can be regulated to a required rated power by varying the duty cycle Dsc disc . In charging mode, the direction of the SC bank current becomes reverse, the converter operates as a buck converter, and the charging power is found as:
Dsc char Vdc Vsc Psc char Dsc char Vdc 0.001 Rsc esr R L sc
(15)
where Dscchar is the duty cycle of the switching pulse supplied to the gate of the IGBT Q2 (SC charge switch) as shown in Fig. 7. Thus, the charging power is regulated to a required power rate by varying the duty cycle Dscchar . The discharging power of the Li-ion battery is obtained as:
Pbat disc Vbat I bat
(16)
Similar to SC bank, a bidirectional DC/DC boost-buck converter has been also connected to the Li-ion battery, so similar to the SC bank, the battery discharging power is expressed as:
Pbat disc
1 ) Vbat Vdc ( 1 Dbat disc 1 1 ( ) Vbat 0.9 1 Dbat disc 0.001 Resr
(17)
Similarly, the battery charging power is given as:
Dbat char Vdc Vbat Pbat char Dbat char Vdc 0.001 Rbat esr R L bat
(18)
12
ACCEPTED MANUSCRIPT
As shown in Fig. 5, the power control unit also measures the DC-link voltage ( Vdc ) and load current (
I load ), and then computes the total electric power ( Pload ) supplied to the three-phase bidirectional PWM DC/AC inverter connected to the three-phase traction motor as:
Pload Vdc I load
(19)
The power control in the FC/battery/SC hybrid power source proposed for FCHEVs is performed by the power control unit as below: Case 1 (charging mode): If 0.98 Pfc Pload , then the power control sets the Li-ion battery and SC bank in charging mode by activating the switching pulses with the duty cycles Dbat char and Dscchar as shown in Figs. 5 and 7. In this case, the power balance in the hybrid power source is expressed as: 0.98 Pfc Pload
1 Psc char 0.9
(20)
So, the electric power consumed to charge the SC bank is given as:
Psc char 0.9 0.98 Pfc Pload
(21)
It is derived from comparing Eq. (10) with Eq. (16) that:
Dsc char Vdc Vsc Dsc char Vdc 0.001 Rsc esr R L sc
0.9 0.98 Pfc Pload
(22)
Eq. (22) explicitly demonstrates that in this case (charging mode), the power control unit measures Pfc and Pload , and then regulates the charging power of the SC bank to the required amount specified in Eq. (21) by varying Dscchar . When the charging current of the SC bank reaches below 0.5 A, the SC bank becomes fully charged. Then, the control unit stops charging the SC bank, and sets the Li-ion battery in charging mode, so the power balance is expressed as: 0.98 Pfc Pload
1 Pbat char 0.9
(23)
The electric power required to charge the battery is obtained as: 13
ACCEPTED MANUSCRIPT
Pbat char 0.9 0.98 Pfc Pload
(24)
It is deduced from substituting Eq. (18) in Eq. (24) that:
Dbat char Vdc Vbat Dbat char Vdc 0.001 Rbat esr R L bat
0.9 0.98 Pfc Pload
(25)
Similar to the SC bank, Eq. (25) demonstrates that the charging power of the battery is regulated to the amount demanded in Eq. (24) by varying Dbat char . Case 2 (discharging mode): If 0.98 Pfc Pload , then the power control unit sets the SC bank in discharging mode by activating the duty cycle Ddisc as shown in Fig. 5 to provide the additional electric power needed. In this case, the power balance in the hybrid power source is expressed as:
0.98 Pfc 0.9 Psc disc Pload
(26)
In this case, the amount of the supplementary electric power that should be provided by discharging the SC bank is found from Eq. (26) as: Psc disc
1 Pload 0.98 Pfc 0.9
(27)
By replacing Psc disc from Eq. (14) in Eq. (27), it is found that: 1 ) Vsc Vdc ( 1 Dsc disc 1 ( ) Vsc 1 Dsc disc 0.001 Resr
P 0.98 P fc load
14
(28)
ACCEPTED MANUSCRIPT
It is deduced from Eq. (28) that in this case (discharging mode), the power control unit measures Pfc and Pload , and then regulates the discharging power of the SC bank to the amount demanded in Eq. (27) by varying Dsc disc . When the discharging current of the SC bank reaches below 0.5 A, the SC bank becomes fully discharged, the control unit stops discharging the SC bank, and sets the Li-ion battery in discharging mode, so the power balance is expressed as:
0.98 Pfc 0.9 Pbat disc Pload
(29)
The supplementary electric power that should be provided by discharging the battery is found from Eq. (29) as: Pbat disc
1 Pload 0.98 Pfc 0.9
(30)
By substituting Pbat disc from Eq. (17) in Eq. (30), it is found that: 1 ) Vbat Vdc ( 1 Dbat disc 1 ( ) Vbat 1 Dbat disc 0.001 Resr
P 0.98 P fc load
(31)
It is deduced from Eq. (31) that the power control unit measures Pfc and Pload , and regulates the discharging power of the Li-ion battery to the required amount specified in Eq. (30) by varying Dbat disc . The electric circuit of the proposed three-phase bidirectional PWM six-switch DC/AC inverter connected the traction motor is shown in Fig. 8. It comprises the six IGBTs that convert the DC-link voltage into a three-phase three-level PWM AC voltage supplied to the stator of the traction motor which is in practice a three-phase PMSM. Since the traction motor acts as a three-phase inductive load, the current delivered to the stator is the integral of the three-level PWM AC voltage, and so the current waveform is close to a sinusoidal form. As shown in Fig. 8, each IGBT itself includes an emitter-tocollector connected diode, the six diodes operate as a three-phase rectifier to convert the three-phase 15
ACCEPTED MANUSCRIPT AC voltage resulted from the regenerative power produced by the traction motor during decelerating and braking into the DC-link voltage which is used to charge the SC bank and battery. Thus, the proposed three-phase PWM six-switch DC/AC inverter is a bidirectional inverter.
4. Construction of the FC/battery/SC hybrid power source and experimental verifications The detailed specifications of all the components used to construct the FC/battery/SC hybrid power source proposed to be utilized in FCHEVs are listed in Table 2. As reported in Table 2, an 80 kW three-phase PMSM used as the traction motor, a 90 kW PEMFC stack, a 19.2 kW Li-ion battery and a SC bank with the rated capacitance of 600 F composed of the four parallel-connected blocks that each block itself consists of 20 series-connected SC cells ESHSR-3000C0-002R7A5T have been utilized. The waveforms of the line voltages ( V AB and VBC ) supplied to the PMSM and the DC-link voltage are shown in Fig. 9. The waveforms of the line voltages show that they are the three-level AC voltages with correct magnitude and phase produced using PWM technique by the three-phase bidirectional DC/AC inverter. This point explicitly verifies the correct operation of the three-phase bidirectional PWM six-switch DC/AC inverter connected to the traction motor. Similarly, the waveform of the DC-link voltage explicitly demonstrates that the DC-link voltage is exactly regulated to the appointed value (400 V) by the unidirectional DC/DC boost converter connected to the PEMFC stack in accordance with Eq. (10). The waveforms of the currents ( I A and I B ) supplied to the stator of the PMSM are shown in Fig. 10. The periodic switching pulse with the switching frequency of 25 kHz and the duty cycle D fc determined according to Eq. (10) to regulate the DClink voltage along with the regulated DC-link voltage is also shown in Fig. 11. As mentioned, the periodic switching pulse is supplied to the switch S fc of the unidirectional DC/DC boost converter connected to the PEMFC stack. The electric power supplied to the traction motor (output power), and the total of the electric power provided by the PEMFC stack power production, discharging the 16
ACCEPTED MANUSCRIPT SC bank and Li-ion battery (input power) were measured point by point. Then, the power efficiency of the proposed FC/battery/SC hybrid power source was computed point by point as: Power efficiency
Output power 100 Input power
(32)
The power efficiency curve resulted from the point by point computing is shown in Fig. 12. The following points which are the main contributions of this study are deduced from the experimental results shown in Figs. 9-12: ● The power efficiency curve explicitly demonstrates that the proposed FC/battery/SC hybrid power source provides a power efficiency of 96.2% around the rated power. ● The DC-link voltage is high accurately regulated to the appointed value (400 V). ● The traction motor is well supplied by the sinusoidal currents resulted from the three-level AC voltages produced by using PWM technique. The other benefit of the FC/battery/SC hybrid power source presented in this study is its flexibility, so that, it can be also utilized as a FC/battery or FC/SC power source. In detail, on the request, the power control unit disables the switching pulses with the duty cycles Dscchar and Dsc disc supplied to the converter connected to the SC bank, so the SC bank is isolated from the system, and the system changes into a FC/battery power source. Similarly, the proposed power source operates as a FC/SC hybrid power source by disabling the switching pulses with the duty cycles Dbat char and Dbat disc supplied to the converter connected to the Li-ion battery. Thus, the power source can be utilized in the three modes; FC/battery/SC, FC/battery and FC/SC. The technical parameters of the power source in the three modes are summarized and compared in Table 3. The comparison demonstrates that utilizing the SC bank mainly improves the acceleration of the vehicle, while the Li-ion battery provides longer cruising range, so that, a FCHEV with the weight of 1880 kg equipped with the proposed FC/battery/SC hybrid power source has a maximum speed of 161 km/h, 0-100 km/h acceleration in 12.2 sec, and a cruising range of 435 km on one 17
ACCEPTED MANUSCRIPT tank of hydrogen with the fuel capacity/tank pressure of 5.4 kg/5000 psi and 110 km on the 19.2 kWh Li-ion battery (totally, 545 km). As another attempt to prove the contributions of this work, a comparison between the proposed FC/battery/SC hybrid power source and the state of the art of all kinds of power sources reported in the literature to be used in FCHEVs is performed in Table 4 [15], [27-63]. It is worthwhile to note that while the majority of the other works are only simulated models, the comparison explicitly demonstrates the excellent performance of the proposed FC/battery/SC hybrid power source such as higher speed and acceleration.
5. Conclusion In this paper, a novel FC/battery/SC hybrid power source was proposed to be used in FCHEVs. A 90 kW PEMFC stack, a 600 F SC bank and a 19.2 kW Li-ion battery were used to construct a prototype of the FC/battery/SC hybrid power source. The experimental results demonstrated that the power efficiency of 96.2% around the rated power, highly accurate DC-link voltage regulation and providing a suitable three-phase current by using PWM technique that is supplied to the stator of the traction motor are the main contributions of this work. For a FCHEV with the weight of 1880 kg, the proposed power source provides a total cruising range of 545 km on one tank of hydrogen with the fuel capacity/tank pressure of 5.4 kg/5000 psi, a maximum speed of 161 km/h and 0-100 km/h acceleration in 12.2 sec. The proposed hybrid power source was also compared to the state-of-the-art power sources used in FCHEVs and reported in the literature that clearly substantiated its better parameters such as higher speed and acceleration, while most of the other works were simulated models. References [1] H. Fathabadi, Utilization of electric vehicles and renewable energy sources used as distributed generators for improving characteristics of electric power distribution systems, Energy 90 (2015) 1100-1110. 18
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ACCEPTED MANUSCRIPT [49] P. García, J.P. Torreglosa, L.M. Fernández, F. Jurado, Control strategies for high-power electric vehicles powered by hydrogen fuel cell, battery and supercapacitor, Expert Systems with Applications 40 (12) (2013) 4791-4804. [50] Z. Yu, D. Zinger, A. Bose, An innovative optimal power allocation strategy for fuel cell, battery and supercapacitor hybrid electric vehicle, Journal of Power Sources 196 (2011) 2351-2359. [51] X. Liu, D. Diallo, C. Marchand, Design methodology of fuel cell electric vehicle power system, Proceedings of 18th IEEE International Conference on Electrical Machines (ICEM) (2008) 1-6. [52] A. Melero-Pérez, W. Gao, I.J. Fernández-Lozano, Fuzzy logic energy management strategy for Fuel Cell/Ultracapacitor/Battery hybrid vehicle with multiple-input DC/DC converter, Proceedings of Vehicle Power and Propulsion Conference (VPPC'09 IEEE) (2009) 199-206.
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Fig.1. Schematic diagram of a typical FCHEV.
25
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Fig. 2. Electric circuit representing the behavior of a FC.
Fig. 3. Electric circuit representing the behavior of a FC under loading condition.
26
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Fig. 4. Dynamic response of a PEMFC stack H-1000.
27
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Fig. 5. Configuration of the FC/battery/SC hybrid power source proposed to be utilized in FCHEVs. 28
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Fig. 6. Unidirectional DC/DC boost converter connected to the PEMFC stack.
Fig. 7. Bidirectional DC/DC boost-buck converter connected to the SC bank.
29
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Fig. 8. Three-phase bidirectional PWM six-switch DC/AC inverter.
30
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Fig. 9. Experimental results: The waveforms of the line voltages ( V AB and VBC ) supplied to the PMSM, and the regulated DC-link voltage.
31
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Fig. 10. Experimental results: The waveforms of the currents ( I A and I B ) supplied to the stator of the PMSM.
32
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Fig. 11. Experimental results: The periodic switching pulse supplied to the switch S fc of the DC/DC boost converter connected to the PEMFC stack, and the regulated DC-link voltage.
33
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Fig. 12. Experimental results: Point by point measured power efficiency of the FC/battery/SC hybrid power source.
34
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Table 1. Technical specification of the PEM fuel cell stack H-1000 [25] and model parameters obtained from Eq. (6) at the stack operating point ( in 35 A ) and T=300 K. Technical specification of the PEM fuel cell stack H-1000 48 N cell
Model parameters obtained from Eq. (6) at the stack operating point ( in 35 A ) and T=300 K
E0 (V)
46
Stack efficiency
40% @ 28.8 V
Rconc ()
0.0374
Rated power (W)
1000
Ract ()
0.1092
Operating point
28.8 V @ 35 A
Rohm ()
0.0637
Max. stack temperature ( C )
65
Ri ()
0.1224
Over current shut down (A)
42
C (F)
4.8623
H 2 pressure (bar)
0.45-0.55
Cstack (F)
0.1013
Flow rate at max. output power (lit/min)
13
35
ACCEPTED MANUSCRIPT Table 2. Technical specification of the components used in the constructed FC/battery/SC hybrid power source. Traction motor Product name
DC/DC boost converter connected to PEMFC stack
C fc ( μ F )-Aluminum
LSRPM 200 L
electrolytic capacitor/400 V Converter switching frequency: f s (kHz)
470
Made by
Leroy-Somer Co.
Type
3-phase, permanent magnet synchronous motor (PMSM)
electrolytic capacitor/600 V
220
Nominal line voltage (V)
400
DC-link voltage Vdc (V)
400
Rated power (kW)
80
C2 ( μ F )-Premium metallized
Rated torque (Nm)
170
Rated current (A)
157
Speed range (rpm)
0-4500
Efficiency (%)
95.7
MOSFET switch S fc
IRFPS40N60K
Maximum torque/Rated torque Magnet material
1.4
Diodes: D1 - D2
15ETH06S
Cout ( μ F )-Aluminum
polypropylene capacitor/600 V C1 ( n F )-Parasitic capacitance of IRFPS40N60K Type of transformer T
N2
NdFeB
Maximum current/Rated current Moment of inertia ( kg.m 2 ) Weight (kg)
N1
25
22 15.6 Pulse
11 10 13
PEMFC stack
1.5
Product name
HD-90
0.15 145
Made by
Hydrogenics Co.
Peak efficiency
55%
Rated power (kW)
90
Supercapacitor cell Product name
ESHSR-3000C0002R7A5T
Maximum power (kW)
99
Made by
Nesscap Co.
Stack operating pressure (kPa)
<120
Rated voltage (V)
2.7
Operating current (A)
0-500
Surge voltage (V)
2.85
Operating voltage (V)
180-360
Rated capacitance (F)
3000
Average capacitance tolerance (%)
5
Maximum continuous current (A)
148
DC/DC converter connected to the supercapacitor bank Type Bidirectional boost-buck IGBT switches: SW, Q1-Q2 STGY40NC60VD
6
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Maximum leakage current (mA)
5.2
Average ESR ( mΩ )
0.14
Maximum stored energy (Wh) Maximum specific energy (Wh/kg)
3.03
Parallel-connected blocks
4
5.67
20
Usable specific power (kW/kg) Nominal weight (g)
6.28
Series-connected supercapacitor cells in each block Rated capacitance (F)
600
535
Rated voltage (V)
54
Maximum continuous current (A) Maximum stored energy (Wh)
592 242.4
Average ESR ( Rsc esr ( mΩ ))
0.7
RLsc ( mΩ ) Supercapacitor bank
Three-phase bidirectional PWM six-switch DC/AC inverter IGBT switches: Q9-Q14
13.3
STGY40NC60VD
5
C dc ( μ F )-Aluminum
220
electrolytic capacitor/600 V DC/DC converter connected to the Li-ion battery bank Type IGBT switches: SW, Q1Q2
R Lbat ( mΩ )
Battery bank: Sixteen 12 V/100 Ah Li-ion batteries Rated voltage (V) 48
Bidirectional boost-buck STGY40NC60VD
Current capacity (Ah)
400
Capacity (kWh)
19.2
Series-connected batteries
4
Parallel-connected sets
4
Average ESR ( Rbat esr ( mΩ ))
2.9
8 10.8
Table 3. Comparison between the technical parameters of the hybrid power source in different modes. Mode of the power source
Analysis type
FC/Battery/SC FC/SC FC/Battery
Experiment Experiment Experiment
Cruising range (km) 545 435 530
Max. speed ( km/h) 161 158 155
37
0-100 km/h Max. Fuel Tank Vehicle acceleration efficiency capacity Pressure weight (sec) (%) (kg) (psi) (kg) 12.2 96.2 5.4 5000 1880 12.2 96.2 5.4 5000 1880 13.4 96.1 5.4 5000 1880
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Table 4. Comparison between the proposed FC/battery/SC hybrid power source and the state-of-the-art power sources used in FCHEVs and reported in the literature. Power source type
DC-link Max. speed Analysis type voltage (V) ( km/h)
PEMFC/battery/SC Experiment PEMFC/Battery Simulation& experiment PEMFC/Battery Simulation PEMFC/Battery Simulation PEMFC/Battery Simulation PEMFC/Battery Simulation & experiment PEMFC/Battery Simulation PEMFC/Battery Simulation PEMFC/Battery Simulation PEMFC/Battery Simulation PEMFC/Battery Simulation PEMFC/Battery Simulation PEMFC/Battery Simulation PEMFC/Battery Simulation PEMFC/Battery Simulation PEMFC/Battery Simulation PEMFC/SC Simulation PEMFC/SC Simulation PEMFC/SC Simulation PEMFC/SC Simulation PEMFC/Battery/SC Experiment PEMFC/Battery/SC Simulation PEMFC/Battery/SC Experiment PEMFC/Battery/SC Simulation PEMFC/Battery/SC Simulation & experiment PEMFC/Battery/SC Simulation PEMFC/Battery/SC Simulation PEMFC/Battery/SC Simulation & experiment
545 400
161 –
0-100 km/h acceleration (sec) 12.2 –
– – 300 450
– 108 80 90
– – – –
62 30 40 40
[28] [29] [30] [31]
– – – – 60 – – 400 – – 400 188 340 206 560 – 400 120 750
60 88.5 – 120 – 129 – 50 144 120 120 91 120 91 20 160 23.4 47 50
– – – – – – – – – – 12.5 – – – – – – – –
130 75 – 80 2 80 2 8 4 60 48 60 60 40 40 40 120 3 400
[32] [33] [34] [35] [36] [37] [38] [39] [40] [41] [15] [42] [43] [44] [45] [46] [47] [48] [49]
300 300 400
128 120 –
– – –
100 58 38.5
[50] [51] [52]
38
Max. power (kW)
Reference
99 30
This work [27]