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photovoltaic hybrid power source for plug-in hybrid electric vehicles
Solar Energy 159 (2018) 243–250
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Novel battery/photovoltaic hybrid power source for plug-in hybrid electric vehicles
MARK
Hassan Fathabadi School of Electrical and Computer Engineering, National Technical University of Athens (NTUA), Athens, Greece
A R T I C L E I N F O
A B S T R A C T
Keywords: Plug-in hybrid electric vehicle Photovoltaic Lithium-ion battery Vehicle-to-grid (V2G)
A plug-in hybrid electric vehicle (PHEV) uses an internal combustion engine to extend its cruising range, and to produce the electric power needed to be supplied to its electric motor when the charge level of the vehicle’s battery becomes low and reaches a predetermined state of charge (SOC). Because of environmental issues, utilizing a gasoline-powered internal combustion engine in a PHEV is not an optimal solution. This paper provides a better solution by replacing the internal combustion engine with a small-size photovoltaic (PV) module mounted horizontally on the roof of the PHEV, and so this study proposes a novel battery/PV hybrid power source to be utilized in PHEVs. The proposed power source equipped with vehicle-to-grid (V2G) technology utilizes a 19.2 kWh Lithium (Li)-ion battery as the main energy storage device and a 200 W PV module as the clean and renewable energy based auxiliary power source. A prototype of the battery/PV hybrid power source has been constructed, and experimental verifications are presented that explicitly demonstrate utilizing the PV module adds 13.4 km to the cruising range of a PHEV with the weight of 1880 kg in a normal operation of the PHEV during two sunny days, and provides higher power efficiency (91.1%) and speed (121 km/h). Highly accurate DC-link voltage regulation and producing an appropriate three-phase stator current for the traction motor by using PWM technique are the other contributions of this work.
1. Introduction Because of environmental issues and economic considerations, there is an upward trend in developing the usage of electric vehicles (EVs), hybrid electric vehicle (HEV) and PHEVs rather than the vehicles with internal combustion engines (Adnan et al., 2017; Fathabadi, 2015), so that there is an ascending demand for different types of EV charging stations in some countries (Kim et al., 2017; Fathabadi, 2017a). A PHEV utilizes its electric motor to provide the power needed for propulsion, and is more efficient compared to a traditional HEV that mainly uses an internal combustion engine (Dong et al., 2016). The V2G technology implemented in PHEVs is the other benefit that makes them more advantageous and popular (Fathabadi, 2017b,c). In particular, the advantage of a PHEV is highlighted when it is connected to a microgrid or a smart grid to manage and balance load demand (Hota et al., 2014; Mou et al., 2015). A through survey of the current literature shows that the research works concerning PHEVs can be classified into the three categories. The first category includes the researches performed to improve the performance of the batteries used in PHEVs. For instance, an analysis about the battery aging in a PHEV by using the experimental data about the voltage recovery and internal resistance of the battery was reported in Canals Casals et al. (2016). Some other related works
are analyzing the effect of V2G connection on PHEVs’ batteries (Bishop et al., 2013), determining a suitable Li-ion battery pack for a PHEV (Xue et al., 2014), evaluating the impact of ultracapacitors on degradation of the performance of a Li-ion battery used in a PHEV (Hochgraf et al., 2014), and maximization of the income of charging the batteries of PHEVs (Zhao et al., 2014). The second category is composed of the research works that have proposed some peripheral devices and facilities for PHEVs such as the wireless charging mechanism applicable to PHEVs (Zeng et al., 2017), and the resonant converter based battery charger suitable for a PHEV (Deng et al., 2015). Finally, the third category comprises the articles that propose different strategies to combine the charging and discharging process of PHEVs with other power sources such as renewable energy resources to satisfy load demand in a grid (Peng et al., 2012). Some examples are utilizing PHEVs in a smart grid to optimize the electrical parameters of the grid by providing distributed demand response (Fan, 2012), and the energy management scheme proposed for an integrated energy system including PHEVs (ElZonkoly, 2014). A solar car is powered just by a PV array composed of many PV cells distributed on the external surface of the car. The literature survey shows that five solar cars have been designed and manufactured since 2006 (Gören, 2017). The experiences of the five solar cars demonstrated that a solar car cannot be used in practical
E-mail address: [email protected]. http://dx.doi.org/10.1016/j.solener.2017.10.071 Received 17 June 2017; Received in revised form 23 October 2017; Accepted 25 October 2017 0038-092X/ © 2017 Elsevier Ltd. All rights reserved.
Solar Energy 159 (2018) 243–250
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Nomenclature
C1 C2
Cpv Cdc D1 & D2 Dchar Ddisc
Dpv fs G Ibat Iload
Ipv Ipv − mpp Llk1
Llk2 Lm
n = N2/ N1 turns ratio of the transformer of the converter connected to the PV module. PV module output power (W). Ppv Pchar charging power of the Li-ion battery (W). Pdischar discharging power of the Li-ion battery (W). Pload total electric power supplied to the three-phase inverter and traction motor (W). Ppv − mpp PV module output power at maximum power point (W). Rbat − esr equivalent series resistance (ESR) of the Li-ion battery (Ω). R esr ESR of the DC-link capacitor (Ω). input resistance of the converter connected to the PV Rin module (Ω). RL equivalent load resistance observed from the output terminal of the converter connected to the PV module (Ω). R Lbat resistance of the inductance Lbat of the bidirectional boostbuck converter connected to the Li-ion battery (Ω). N-MOSFET switch used in the converter connected to the Spv PV module. T PV module temperature (°C). switching period of the converter connected to the PV Ts module (sec). Tb switching period of the control signal supplied to the converter connected to the Li-ion battery (sec). Vbat Li-ion battery output voltage (V). Vdc DC-link voltage (V). PV module output voltage (V). Vpv Vpv − mpp PV module output voltage at maximum power point (V).
parasitic capacitance of the N-MOSFET switch of the converter connected to the PV module (F). secondary-side capacitor of the converter connected to the PV module (F). input capacitor of the converter connected to the PV module (F). DC-link capacitor (F). diodes of the converter connected to the PV module. duty cycle of the control signal supplied to the converter connected to the Li-ion battery in charging mode. duty cycle of the control signal supplied to the converter connected to the Li-ion battery in discharging mode. duty cycle of the converter connected to the PV module. constant switching frequency of the converter connected to the PV module (Hz). solar irradiance on the PV module surface (Wm−2 ). Li-ion battery output current (A). load current supplied to the three-phase inverter and traction motor (A). PV module output current (A). PV module output current at maximum power point (A). primary-side leakage inductor of the transformer of the converter connected to the PV module (H). secondary-side leakage inductor of the transformer of the converter connected to the PV module (H). equivalent magnetizing inductor of the transformer of the converter connected to the PV module (H).
as follows. The proposed battery/PV hybrid power source is designed and implemented in Section 2. Details about the constructed hybrid power source and experimental verifications are given in Section 3, and the paper is concluded in Section 4.
applications because of its limitations in design and implementation. For instance, a solar car should be lightweight, and this enforces the manufacturers to use polymer composites in manufacturing process that makes a solar car unsafe in practical applications such as daily trips, traveling abroad, etc (Gören, 2017). A few research works addressing solar energy harvesting in EVs and HEVs are also available that all are simulation based works (models) Ezzat and Dincer, 2016. Modeling and simulation of utilizing a PV power source in a fuel cell hybrid electric vehicle (FCHEV) with a small-scale 3 kW electric motor was performed in Matlab/Simulink environment (Mokrani et al., 2014). Similarly, a mathematical model implemented in Matlab/Simulink environment theoretically showed that a PV based power generation system can be used in small-scale HEVs (Chowdhury et al., 2016). The main drawback of a PHEV is that it uses an internal combustion engine to extend its cruising range, and to produce the electric power needed to be supplied to its electric motor when the charge level of the vehicle’s battery becomes low and gets to a predetermined SOC. It is clear that utilizing a gasoline-powered internal combustion engine in a PHEV cannot be considered as an optimal solution because of environmental issues. A detailed overview in the literature demonstrates that there is not any research work giving a solution. This study addresses this problem by presenting a novel battery/PV hybrid power source to be utilized in PHEVs. In the proposed hybrid power source, the internal combustion engine has been replaced with a small-size PV module located on the roof of the PHEV, and solar energy has been utilized as a clean and renewable energy to extend the cruising range of the PHEV. A prototype of the battery/PV hybrid power source has been built, and experimental verifications are given that explicitly substantiate utilizing the PV module adds 13.4 km to the cruising range of a PHEV with the weight of 1880 kg during a sunny day, and provides higher power efficiency (91.1%) and speed (121 km/h). Highly accurate DC-link voltage regulation and producing an appropriate threephase stator current for the traction motor by using PWM technique are the other contributions of this work. The rest of this paper is organized
2. Implementation of the battery/PV hybrid power source proposed for PHEVs The configuration of the battery/PV hybrid power source proposed to be utilized in PHEVs is shown in Fig. 1. It is composed of a Li-ion rechargeable battery used as the main energy storage device, a bidirectional DC/DC boost-buck converter connected to the Li-ion battery, a single-phase bidirectional DC/AC inverter connected between the battery and grid to provide V2G operation, a PV module used as the auxiliary power source, a unidirectional DC/DC boost converter connected to the PV module, a three-phase bidirectional PWM DC/AC inverter connected the traction motor which is practically a three-phase permanent magnet synchronous motor (PMSM), and a combined power control and maximum power point tracking (MPPT) unit. It is reminded that in a PV system, the MPPT unit tracks the maximum power point (MPP) of the PV module connected to the system (Fathabadi, 2016a). The DC-link voltage is continuously regulated to a designated constant value. Fig. 2 shows the electric circuit of the unidirectional DC/DC boost converter connected to the PV module. The average power efficiency of the converter is 98% and its gain is given as (Fathabadi, 2016b):
Vdc n = Vpv 1−Dpv
(1)
so, the PV voltage is given as:
Vpv =
(1−Dpv ) Vdc n
(2)
As mentioned the DC link voltage is a constant value, so in 244
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accordance with Eq. (2), the MPPT unit continuously tunes the duty cycle Dpv to regulate the voltage of the PV module (Vpv ) to the voltage at MPP (Vpv − mpp ). In detail, when Vpv is less than Vpv − mpp , the MPPT unit decreases the duty cycle Dpv , and contrarily, the duty cycle Dpv is increased by the MPPT unit when Vpv is more than Vpv − mpp . The other way to clearly explain the theoretical concept of the MPPT process is the functional association between the output power of the PV module and the duty cycle Dpv that is formulized in detail as:
Ppv = Vpv Ipv =
2 Vpv
Rin
≈
2 Vpv (1 − Dpv )2 n2
RL
(3)
where Rin and RL introduced in Nomenclature section are shown in Figs. 1–2. Eq. (3) explicitly demonstrates that the PV output power can be regulated to its maximum amount, i.e., the PV power at MPP (Ppv − mpp ) by varying the duty cycle Dpv . As shown in Fig. 1, the PV module output current and voltage, and hence, the PV output power is continually measured by the power control unit. In each step, the measured power is compared to the previous amount to find the maximum available power by varying the duty cycle Dpv . The electric circuit of the bidirectional DC/DC boost-buck converter with the average power efficiency of 90% connected to the Li-ion battery is shown in Fig. 3. The discharging power of the Li-ion battery is given as: (4)
Pdischar = Vbat Ibat
The Li-ion battery output voltage and current (Vbat and Ibat ), and hence, the discharging and charging powers of the Li-ion battery are continuously measured by the power control unit as shown in Fig. 1. Noting Fig. 3 demonstrates that in discharging mode, the converter operates as a boost converter, and the discharging power of the Li-ion battery is expressed as:
Pdischar
⎡ ⎛ 1 ⎢⎛ 1 ⎞ Vbat ⎜ = 0.9 ⎢ ⎝ 1−Ddisc ⎠ ⎜ ⎢ ⎝ ⎣ ⎜
(
1 1 − Ddisc
)V
bat −Vdc ⎞ ⎤
⎟
0.001 + R esr
⎟⎥ ⎟⎥ ⎠⎥ ⎦
(5)
where Ddisc is the duty cycle of the control signal supplied to the gate of the insulated gate bipolar transistor (IGBT) Q1 (discharge switch) as shown in Fig. 3. It is deduced from Eq. (5) that the discharging power can be regulated to a required power rate by varying the duty cycle Ddisc . In charging mode, the direction of the battery current becomes reverse, the converter operates as a buck converter, and the charging power is found as:
Dchar Vdc−Vbat ⎞⎟ Pchar = Dchar Vdc ⎛⎜ + Rbat − esr + R Lbat ⎠ 0.001 ⎝
Fig. 1. Configuration of the battery/PV hybrid power source proposed to be utilized in PHEVs.
(6)
where Dchar is the duty cycle of the switching pulse supplied to the gate of the IGBT Q2 (charge switch) as shown in Fig. 3. Thus, in a similar Fig. 2. Unidirectional DC/DC boost converter connected to the PV module.
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Fig. 3. Bidirectional DC/DC boost-buck converter connected to the Li-ion battery.
manner, the charging power is regulated to a required power rate by varying the duty cycle Dchar . As shown in Fig. 1, the power control unit also measures the DC-link voltage (Vdc ) and load current (Iload ), and then computes the total electric power (Pload ) supplied to the three-phase bidirectional PWM DC/AC inverter and the three-phase traction motor connected to the inverter as:
Ddisc as shown in Fig. 1 and Fig. 3 to provide the additional electric power needed. In this case, the power balance in the hybrid power source is expressed as:
0.98Ppv + 0.9Pdischar = Pload
In this case, the amount of the supplementary electric power that should be provided by discharging the Li-ion battery is found from Eq. (11) as:
(7)
Pload = Vdc Iload
The power control in the battery/PV hybrid power source is performed by the power control unit as below:
Pdischar =
Case 1 (charging mode). If 0.98Ppv ⩾ Pload , then the power control unit sets the Li-ion battery in charging mode by activating the duty cycle Dchar as shown in Fig. 1 and Fig. 3. In this case, the power balance in the hybrid power source is expressed as:
1 Pchar 0.9
1
(8)
⎟
(13)
It is deduced from Eq. (13) that in this case (discharging mode), the power control unit measures Ppv and Pload , and then regulates the discharging power of the Li-ion battery to the amount demanded in Eq. (12) by varying Ddisc .
(9)
The electric circuit of the proposed three-phase bidirectional PWM six-switch DC/AC inverter connected the traction motor is shown in Fig. 4. 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. 4, each IGBT itself includes an emitter-to-collector connected diode, the six diodes operate as a three-phase rectifier to convert the three-phase AC voltage resulted from the regenerative power produced
It is derived from comparing Eq. (6) with Eq. (9) that:
Dchar Vdc−Vbat ⎞ Dchar Vdc ⎛⎜ ⎟ = 0.9(0.98Ppv−Pload ) ⎝ 0.001 + Rbat − esr + R Lbat ⎠
(12)
) Vbat −Vdc ⎞ ⎛( ⎛ 1 ⎞ Vbat 1 − Ddisc = Pload−0.98Ppv ⎜ ⎜ 0.001 + R esr ⎟⎟ ⎝ 1−Ddisc ⎠ ⎝ ⎠
So, the electric power consumed to charge the Li-ion battery is obtained as:
Pchar = 0.9(0.98Ppv−Pload )
1 (Pload−0.98Ppv ) 0.9
By replacing Pdischar from Eq. (5) in Eq. (12), it is found that:
⎜
0.98Ppv = Pload +
(11)
(10)
Eq. (10) explicitly demonstrates that in this case (charging mode), the power control unit measures Ppv and Pload , and then regulates the charging power of the Li-ion battery to the required amount specified in Eq. (9) by varying Dchar . Case 2 (discharging mode). If 0.98Ppv < Pload , then the power control unit sets the Li-ion battery in discharging mode by activating the duty cycle
Fig. 4. Three-phase bidirectional PWM six-switch DC/AC inverter.
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Fig. 5. Electric circuit of the constructed battery/PV hybrid power source proposed to be utilized in PHEVs.
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by the traction motor during decelerating and braking into the DC-link voltage to be used to charge the Li-ion battery. Thus, the proposed three-phase PWM six-switch DC/AC inverter is bidirectional type. 3. Construction of the battery/PV hybrid power source and experimental verifications The configuration of the proposed battery/PV hybrid power source was shown in Fig. 1, based on which the power source has been constructed to provide experimental verifications. The electric circuit of the constructed battery/PV hybrid power source is shown in Fig. 5. As shown in Fig. 5, the microcontroller MC68HC11E9 has been used as the power control and MPPT unit. The PV module output current (Ipv ) is measured by an INA 168, and is supplied to the pin AN2 which is an analog pin of the microcontroller. The PV module output voltage (Vpv ) is first scaled by the potentiometer RV2, and then is supplied to the other analog pin (AN3). In similar manner, the load current (Iload ), DC-link voltage (Vdc ), Li-ion battery output current (Ibat ) and voltage (Vbat ) are measured and respectively supplied to the analog pins AN0, AN1, AN4 and AN5. The duty cycle Dpv is varied by the microcontroller to regulate the DC-link voltage to the appointed value (400 V) according to Eq. (1). The periodic switching pulse with the duty cycle Dpv is then supplied to the switch Spv via the two buffers interconnected in series. The powers Pload , Ppv , Pchar (in charging mode) and Pdischar (in discharging mode) are measured by the microcontroller, and the charging or discharging power of the Li-ion battery is regulated to the required amount respectively specified in Eq. (9) or Eq. (12) by varying Dchar or Ddisc in accordance with Eq. (10) or Eq. (13). The detailed specifications of all the components used to construct the battery/PV hybrid power source proposed to be utilized in PHEVs are listed in Table 1. As reported in Table 1, an 80 kW three-phase PMSM used as the traction motor, a 19.2 kWh Li-ion battery and a PV module KC200GT have been utilized. The waveforms of the line voltages (VAB and VBC ) supplied to the PMSM and the DC-link voltage are shown in Fig. 6. The waveforms of the line
Fig. 6. Experimental results: the waveforms of the line voltages (VAB and VBC ) supplied to the PMSM, and the regulated DC-link voltage.
voltages show that they are the three-level AC voltages with correct magnitude and phase produced using PWM technique by the threephase bidirectional DC/AC inverter, and this 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). The waveforms of the currents (IA and IB ) supplied to the stator of the PMSM are shown in Fig. 7. The periodic switching pulse with the switching frequency of 25 kHz and the duty cycle Dpv and the regulated DC-link voltage are also shown in Fig. 8. As mentioned, the periodic switching pulse is produced by the microcontroller, and then, is supplied to the switch Spv of the unidirectional DC/DC boost converter connected to the PV module. Fig. 8 shows that the duty cycle of the switching pulse supplied
Table 1 Technical specification of the components used in the constructed battery/PV hybrid power source proposed to be utilized in PHEVs. Traction motor
DC/DC boost converter connected to PV module
Model
LSRPM 200 L
Cpv (μF )-Aluminum electrolytic capacitor/400 V
470
Made by
Leroy-Somer Co.
25
Type Phase number Nominal line voltage (V) Rated power (kW) Rated torque (Nm) Rated current (A) Speed range (rpm) Efficiency (%)
Permanent magnet synchronous motor (PMSM) 3 400 80 170 157 0–4500 95.7
Converter switching frequency: fs (kHz) DC-link voltage Vdc (V) DC-link capacitor Cdc (μF )-Aluminum electrolytic capacitor/600 V Average ESR of Cdc : R esr (mΩ ) C2 (μF )-Premium metallized polypropylene capacitor/600 V C1 (nF )-Parasitic capacitance of IRFPS40N60K Type of transformer T n = N2/ N1 MOSFET switch Spv
Maximum torque/rated torque Magnet material
1.4 NdFeB
Diodes: D1 - D2 PV module KC200GT
Maximum current/rated current
1.5
7.61
Moment of inertia (kgm2 ) Weight (kg)
0.15
(G = 1000 Wm−2 , T = 25 °C ) Current at MPP Ipv − mpp (A) Voltage at MPP Vpv − mpp (V)
145
Output power at MPP Ppv − mpp (W)
200.1430
Battery bank: Sixteen 12 V/100 Ah Li-ion batteries Type Li-ion Voltage (V) 48 Current capacity (Ah) 400
Short-circuit current Isc (A)
8.21
Open-circuit voltage Voc (V) DC/DC converter connected to the Li-ion battery bank Type
32.9
Capacity (kWh) Series-connected batteries
19.2 4
IGBT switches: SW, Q1-Q2 R Lbat (mΩ )
Bidirectional boost-buck STGY40NC60VD × 40 10.8
Parallel-connected sets
4
Single-phase inverter (V2G connection) (Single-phase grid voltage: ∼110 VAC, 60 Hz) IGBT switches: Q9-Q12 N4/ N3 Lg (μH )
STGY40NC60VD × 8 39/12 68
Cg (μF )
8.2
2.9 Average ESR (Rbat − esr (mΩ )) Three-phase bidirectional PWM six-switch DC/AC inverter IGBT switches: Q3-Q8 STGY40NC60VD × 5
248
400 680 109 22 1.2 Pulse 20/3 IRFPS40N60K 15ETH06S
26.3
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Fig. 7. Experimental results: the waveforms of the currents (IA and IB ) supplied to the stator of the PMSM. Fig. 10. Power extracted from the PV module KC200GT from hour to hour in daylight (5:00–21:00) during a sunny day.
to the converter connected to the PV module is about 0.562, Vdc = 400 V and Vpv = 26.25 V. Considering the parameters of the converter reported in Table 1 (n = 20/3), these values are exactly compatible with Eq. (1). Comparing the operating voltage of the PV module (26.25 V) to the MPP voltage of the PV module (Vpv − mpp = 26.3 V) under nominal condition (irradiance G = 1000 Wm−2 , temperature T = 25 °C) reported in Table 1 explicitly verifies that the MPPT unit high accurately tracks the MPP of the PV module. The electric power supplied to the traction motor (PMSM) and the total of the electric power produced by the PV module and discharging the Li-ion battery were measured point by point, and then, the power efficiency of the proposed battery/PV hybrid power source was obtained point by point as shown in Fig. 9. The following points which are the main contributions of this study are deduced from the experimental results shown in Figs. 6–9:
Fig. 8. Experimental results: the periodic switching pulse supplied to the switch Spv of the
• The power efficiency curve explicitly demonstrates that the pro-
DC/DC converter connected to the PV module, the DC-link voltage and the operating voltage of the PV module.
• •
posed battery/PV hybrid power source provides a power efficiency of about 91% around the rated power of the traction motor. 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.
Fig. 9. Experimental results: the power efficiency of the battery/PV hybrid power proposed to be utilized in PHEVs.
Fig. 11. Experimental results: power flow measured hour by hour.
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Table 2 Comparison between the technical parameters of the hybrid battery/PV power source in different modes. Mode of the power source
Analysis type
Cruising range (km)
Max. speed (km/h)
0–100 km/h acceleration (sec)
Max. efficiency (%)
PHEV weight (kg)
Battery/PV Battery
Experiment Experiment
123.4 110
121 120
13.4 13.4
91.1 90.2
1880 1880
References
To evaluate the impact of the PV module, three other tests were also performed by utilizing the hybrid power source in a PHEV with the weight of 1880 kg. The tests and measurements have been carried out in the geographic position of (37.9667°N, 23.7167°E) where is outside urban areas, and there is no traffic. In the first test, the power extracted from the PV module KC200GT mounted horizontally on the roof of the PHEV was measured from hour to hour in daylight (5:00–21:00) during a sunny day. The measured power curve is shown in Fig. 10 that explicitly demonstrates the PV module KC200GT produces a daily electric energy of about 1.33 kWh during a sunny day. In the second test, the PV module was in operation, so the power source was in battery/PV hybrid mode. The test was performed in a normal operation of the PHEV composed of working and parking during two sunny days. It is reminded that according to the automobile companies’ standard, a car normally travels about 20,000 km per year or about 110 km per two days. The test was started at 5:00 when the SOC of the Li-ion battery was one (SOC = 1), and was ended on the second day at 18:23 when the SOC reached zero (SOC = 0). The power flow measured hour by hour that represents the power portions provided by the battery and PV module is shown in detail in Fig. 11. In the third test, the PV module was isolated from the system, and so the power source was in battery mode. The results of the two last tests are summarized in Table 2, the experimental measurements and results demonstrate that utilizing the PV module adds 13.4 km to the cruising range in a normal operation of the PHEV during two sunny days, and provides higher power efficiency (91.1%) and speed (121 km/h). As reported in Table 2, a PHEV with the weight of 1880 kg equipped with the proposed battery/PV hybrid power source has a maximum speed of 121 km/h and a cruising range of 123.4 km.
Adnan, N., Nordin, S.M., Rahman, I., 2017. Adoption of PHEV/EV in Malaysia: a critical review on predicting consumer behaviour. Renew. Sustain. Energy Rev. 72, 849–862. Fathabadi, H., 2015. Utilization of electric vehicles and renewable energy sources used as distributed generators for improving characteristics of electric power distribution systems. Energy 90, 1100–1110. Kim, Y., Kwak, J., Chong, S., 2017. Dynamic pricing, scheduling, and energy management for profit maximization in PHEV charging stations. IEEE Trans. Veh. Technol. 66 (2), 1011–1026. Fathabadi, H., 2017a. Novel solar powered electric vehicle charging station with the capability of vehicle-to-grid. Sol. Energy 142, 136–143. Dong, Q., Niyato, D., Wang, P., Han, Z., 2016. The PHEV charging scheduling and power supply optimization for charging stations. IEEE Trans. Veh. Technol. 65 (2), 566–580. Fathabadi, H., 2017b. Novel grid-connected solar/wind powered electric vehicle charging station with vehicle-to-grid technology. Energy 132, 1–11. Fathabadi, H., 2017c. Novel wind powered electric vehicle charging station with vehicleto-grid (V2G) connection capability. Energy Convers. Manage. 136, 229–239. Hota, A.R., Juvvanapudi, M., Bajpai, P., 2014. Issues and solution approaches in PHEV integration to the smart grid. Renew. Sustain. Energy Rev. 30, 217–229. Mou, Y., Xing, H., Lin, Z., Fu, M., 2015. Decentralized optimal demand-side management for PHEV charging in a smart grid. IEEE Trans. Smart Grid 6 (2), 726–736. Canals Casals, L., Schiffer Gonzalez, A.M., Garcia, B., Llorca, J., 2016. PHEV battery aging study using voltage recovery and internal resistance from onboard data. IEEE Trans. Veh. Technol. 65 (6), 4209–4216. Bishop, J.D.K., Axon, C.J., Bonilla, D., Tran, M., Banister, D., McCulloch, M.D., 2013. Evaluating the impact of V2G services on the degradation of batteries in PHEV and EV. Appl. Energy 111, 206–218. Xue, N., Du, W., Greszler, T.A., Shyy, W., Martins, J.R.R.A., 2014. Design of a lithium-ion battery pack for PHEV using a hybrid optimization method. Appl. Energy 115, 591–602. Hochgraf, C.G., Basco, J.K., Bohn, T.P., Bloom, I., 2014. Effect of ultracapacitor-modified PHEV protocol on performance degradation in lithium-ion cells. J. Power Sources 246, 965–969. Zhao, B., Shi, Y., Dong, X., 2014. Pricing and revenue maximization for battery charging services in PHEV markets. IEEE Trans. Veh. Technol. 63 (4), 1987–1993. Zeng, H., Yang, S., Peng, F.Z., 2017. Design consideration and comparison of wireless power transfer via harmonic current. IEEE Trans. Power Electron. 32 (8), 5943–5952. Deng, J., Mi, C.C., Ma, R., Li, S., 2015. Design of LLC resonant converters based on operation-mode analysis for level two PHEV battery chargers. IEEE/ASME Trans. Mechatron. 20 (4), 1595–1606. Peng, M., Liu, L., Jiang, C., 2012. A review on the economic dispatch and risk management of the large-scale plug-in electric vehicles (PHEVs)-penetrated power systems. Renew. Sustain. Energy Rev. 16 (3), 1508–1515. Fan, Z., 2012. A distributed demand response algorithm and its application to PHEV charging in smart grids. IEEE Trans. Smart Grid 3 (3), 1280–1290. El-Zonkoly, A., 2014. Intelligent energy management of optimally located renewable energy systems incorporating PHEV. Energy Convers. Manage. 84, 427–435. Gören, A., 2017. Solar energy harvesting in electro mobility. Lecture Notes in Energy 37, 293–326. Ezzat, M.F., Dincer, I., 2016. Development, analysis and assessment of a fuel cell and solar photovoltaic system powered vehicle. Energy Convers. Manage. 129, 284–292. Mokrani, Z., Rekioua, D., Rekioua, T., 2014. Modeling, control and power management of hybrid photovoltaic fuel cells with battery bank supplying electric vehicle. Int. J. Hydrogen Energy 39 (27), 15178–15187. Chowdhury M.S.A., Mamun K.A.A., Rahman A.M. 2016. Modelling and simulation of power system of battery, solar and fuel cell powered hybrid electric vehicle. In: 3rd International Conference on Electrical Engineering and Information and Communication Technology, 7873126. Fathabadi, H., 2016a. Novel fast dynamic MPPT (maximum power point tracking) technique with the capability of very high accurate power tracking. Energy 94, 466–475. Fathabadi, H., 2016b. Novel high efficiency DC/DC boost converter for using in photovoltaic systems. Sol. Energy 125, 22–31.
4. Conclusion In this paper, a novel battery/PV hybrid power source was proposed to be utilized in PHEVs. In the hybrid power source, the gasolinepowered internal combustion engine of a PHEV has been replaced with a small-size PV module positioned horizontally on the roof of the PHEV, and solar energy has been utilized as a clean and renewable energy to extend the cruising range of the PHEV. The power source has the capability of V2G, and utilizes a 19.2 kWh Li-ion battery as the main energy storage device and a 200 W PV module as the auxiliary power source. A prototype of the battery/PV hybrid power source has been built, and experimental verifications were presented. It was demonstrated that utilizing the PV module adds 13.4 km to the cruising range of a PHEV with the weight of 1880 kg in a normal operation of it during two sunny days, and provides higher power efficiency (91.1%) and speed (121 km/h). It was also shown that the power source high accurately regulates the DC-link voltage, and produces suitable stator currents for the traction motor by using PWM technique.
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Novel battery/photovoltaic hybrid power source for plug-in hybrid electric vehicles
MARK
Hassan Fathabadi School of Electrical and Computer Engineering, National Technical University of Athens (NTUA), Athens, Greece
A R T I C L E I N F O
A B S T R A C T
Keywords: Plug-in hybrid electric vehicle Photovoltaic Lithium-ion battery Vehicle-to-grid (V2G)
A plug-in hybrid electric vehicle (PHEV) uses an internal combustion engine to extend its cruising range, and to produce the electric power needed to be supplied to its electric motor when the charge level of the vehicle’s battery becomes low and reaches a predetermined state of charge (SOC). Because of environmental issues, utilizing a gasoline-powered internal combustion engine in a PHEV is not an optimal solution. This paper provides a better solution by replacing the internal combustion engine with a small-size photovoltaic (PV) module mounted horizontally on the roof of the PHEV, and so this study proposes a novel battery/PV hybrid power source to be utilized in PHEVs. The proposed power source equipped with vehicle-to-grid (V2G) technology utilizes a 19.2 kWh Lithium (Li)-ion battery as the main energy storage device and a 200 W PV module as the clean and renewable energy based auxiliary power source. A prototype of the battery/PV hybrid power source has been constructed, and experimental verifications are presented that explicitly demonstrate utilizing the PV module adds 13.4 km to the cruising range of a PHEV with the weight of 1880 kg in a normal operation of the PHEV during two sunny days, and provides higher power efficiency (91.1%) and speed (121 km/h). Highly accurate DC-link voltage regulation and producing an appropriate three-phase stator current for the traction motor by using PWM technique are the other contributions of this work.
1. Introduction Because of environmental issues and economic considerations, there is an upward trend in developing the usage of electric vehicles (EVs), hybrid electric vehicle (HEV) and PHEVs rather than the vehicles with internal combustion engines (Adnan et al., 2017; Fathabadi, 2015), so that there is an ascending demand for different types of EV charging stations in some countries (Kim et al., 2017; Fathabadi, 2017a). A PHEV utilizes its electric motor to provide the power needed for propulsion, and is more efficient compared to a traditional HEV that mainly uses an internal combustion engine (Dong et al., 2016). The V2G technology implemented in PHEVs is the other benefit that makes them more advantageous and popular (Fathabadi, 2017b,c). In particular, the advantage of a PHEV is highlighted when it is connected to a microgrid or a smart grid to manage and balance load demand (Hota et al., 2014; Mou et al., 2015). A through survey of the current literature shows that the research works concerning PHEVs can be classified into the three categories. The first category includes the researches performed to improve the performance of the batteries used in PHEVs. For instance, an analysis about the battery aging in a PHEV by using the experimental data about the voltage recovery and internal resistance of the battery was reported in Canals Casals et al. (2016). Some other related works
are analyzing the effect of V2G connection on PHEVs’ batteries (Bishop et al., 2013), determining a suitable Li-ion battery pack for a PHEV (Xue et al., 2014), evaluating the impact of ultracapacitors on degradation of the performance of a Li-ion battery used in a PHEV (Hochgraf et al., 2014), and maximization of the income of charging the batteries of PHEVs (Zhao et al., 2014). The second category is composed of the research works that have proposed some peripheral devices and facilities for PHEVs such as the wireless charging mechanism applicable to PHEVs (Zeng et al., 2017), and the resonant converter based battery charger suitable for a PHEV (Deng et al., 2015). Finally, the third category comprises the articles that propose different strategies to combine the charging and discharging process of PHEVs with other power sources such as renewable energy resources to satisfy load demand in a grid (Peng et al., 2012). Some examples are utilizing PHEVs in a smart grid to optimize the electrical parameters of the grid by providing distributed demand response (Fan, 2012), and the energy management scheme proposed for an integrated energy system including PHEVs (ElZonkoly, 2014). A solar car is powered just by a PV array composed of many PV cells distributed on the external surface of the car. The literature survey shows that five solar cars have been designed and manufactured since 2006 (Gören, 2017). The experiences of the five solar cars demonstrated that a solar car cannot be used in practical
E-mail address: [email protected]. http://dx.doi.org/10.1016/j.solener.2017.10.071 Received 17 June 2017; Received in revised form 23 October 2017; Accepted 25 October 2017 0038-092X/ © 2017 Elsevier Ltd. All rights reserved.
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Nomenclature
C1 C2
Cpv Cdc D1 & D2 Dchar Ddisc
Dpv fs G Ibat Iload
Ipv Ipv − mpp Llk1
Llk2 Lm
n = N2/ N1 turns ratio of the transformer of the converter connected to the PV module. PV module output power (W). Ppv Pchar charging power of the Li-ion battery (W). Pdischar discharging power of the Li-ion battery (W). Pload total electric power supplied to the three-phase inverter and traction motor (W). Ppv − mpp PV module output power at maximum power point (W). Rbat − esr equivalent series resistance (ESR) of the Li-ion battery (Ω). R esr ESR of the DC-link capacitor (Ω). input resistance of the converter connected to the PV Rin module (Ω). RL equivalent load resistance observed from the output terminal of the converter connected to the PV module (Ω). R Lbat resistance of the inductance Lbat of the bidirectional boostbuck converter connected to the Li-ion battery (Ω). N-MOSFET switch used in the converter connected to the Spv PV module. T PV module temperature (°C). switching period of the converter connected to the PV Ts module (sec). Tb switching period of the control signal supplied to the converter connected to the Li-ion battery (sec). Vbat Li-ion battery output voltage (V). Vdc DC-link voltage (V). PV module output voltage (V). Vpv Vpv − mpp PV module output voltage at maximum power point (V).
parasitic capacitance of the N-MOSFET switch of the converter connected to the PV module (F). secondary-side capacitor of the converter connected to the PV module (F). input capacitor of the converter connected to the PV module (F). DC-link capacitor (F). diodes of the converter connected to the PV module. duty cycle of the control signal supplied to the converter connected to the Li-ion battery in charging mode. duty cycle of the control signal supplied to the converter connected to the Li-ion battery in discharging mode. duty cycle of the converter connected to the PV module. constant switching frequency of the converter connected to the PV module (Hz). solar irradiance on the PV module surface (Wm−2 ). Li-ion battery output current (A). load current supplied to the three-phase inverter and traction motor (A). PV module output current (A). PV module output current at maximum power point (A). primary-side leakage inductor of the transformer of the converter connected to the PV module (H). secondary-side leakage inductor of the transformer of the converter connected to the PV module (H). equivalent magnetizing inductor of the transformer of the converter connected to the PV module (H).
as follows. The proposed battery/PV hybrid power source is designed and implemented in Section 2. Details about the constructed hybrid power source and experimental verifications are given in Section 3, and the paper is concluded in Section 4.
applications because of its limitations in design and implementation. For instance, a solar car should be lightweight, and this enforces the manufacturers to use polymer composites in manufacturing process that makes a solar car unsafe in practical applications such as daily trips, traveling abroad, etc (Gören, 2017). A few research works addressing solar energy harvesting in EVs and HEVs are also available that all are simulation based works (models) Ezzat and Dincer, 2016. Modeling and simulation of utilizing a PV power source in a fuel cell hybrid electric vehicle (FCHEV) with a small-scale 3 kW electric motor was performed in Matlab/Simulink environment (Mokrani et al., 2014). Similarly, a mathematical model implemented in Matlab/Simulink environment theoretically showed that a PV based power generation system can be used in small-scale HEVs (Chowdhury et al., 2016). The main drawback of a PHEV is that it uses an internal combustion engine to extend its cruising range, and to produce the electric power needed to be supplied to its electric motor when the charge level of the vehicle’s battery becomes low and gets to a predetermined SOC. It is clear that utilizing a gasoline-powered internal combustion engine in a PHEV cannot be considered as an optimal solution because of environmental issues. A detailed overview in the literature demonstrates that there is not any research work giving a solution. This study addresses this problem by presenting a novel battery/PV hybrid power source to be utilized in PHEVs. In the proposed hybrid power source, the internal combustion engine has been replaced with a small-size PV module located on the roof of the PHEV, and solar energy has been utilized as a clean and renewable energy to extend the cruising range of the PHEV. A prototype of the battery/PV hybrid power source has been built, and experimental verifications are given that explicitly substantiate utilizing the PV module adds 13.4 km to the cruising range of a PHEV with the weight of 1880 kg during a sunny day, and provides higher power efficiency (91.1%) and speed (121 km/h). Highly accurate DC-link voltage regulation and producing an appropriate threephase stator current for the traction motor by using PWM technique are the other contributions of this work. The rest of this paper is organized
2. Implementation of the battery/PV hybrid power source proposed for PHEVs The configuration of the battery/PV hybrid power source proposed to be utilized in PHEVs is shown in Fig. 1. It is composed of a Li-ion rechargeable battery used as the main energy storage device, a bidirectional DC/DC boost-buck converter connected to the Li-ion battery, a single-phase bidirectional DC/AC inverter connected between the battery and grid to provide V2G operation, a PV module used as the auxiliary power source, a unidirectional DC/DC boost converter connected to the PV module, a three-phase bidirectional PWM DC/AC inverter connected the traction motor which is practically a three-phase permanent magnet synchronous motor (PMSM), and a combined power control and maximum power point tracking (MPPT) unit. It is reminded that in a PV system, the MPPT unit tracks the maximum power point (MPP) of the PV module connected to the system (Fathabadi, 2016a). The DC-link voltage is continuously regulated to a designated constant value. Fig. 2 shows the electric circuit of the unidirectional DC/DC boost converter connected to the PV module. The average power efficiency of the converter is 98% and its gain is given as (Fathabadi, 2016b):
Vdc n = Vpv 1−Dpv
(1)
so, the PV voltage is given as:
Vpv =
(1−Dpv ) Vdc n
(2)
As mentioned the DC link voltage is a constant value, so in 244
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accordance with Eq. (2), the MPPT unit continuously tunes the duty cycle Dpv to regulate the voltage of the PV module (Vpv ) to the voltage at MPP (Vpv − mpp ). In detail, when Vpv is less than Vpv − mpp , the MPPT unit decreases the duty cycle Dpv , and contrarily, the duty cycle Dpv is increased by the MPPT unit when Vpv is more than Vpv − mpp . The other way to clearly explain the theoretical concept of the MPPT process is the functional association between the output power of the PV module and the duty cycle Dpv that is formulized in detail as:
Ppv = Vpv Ipv =
2 Vpv
Rin
≈
2 Vpv (1 − Dpv )2 n2
RL
(3)
where Rin and RL introduced in Nomenclature section are shown in Figs. 1–2. Eq. (3) explicitly demonstrates that the PV output power can be regulated to its maximum amount, i.e., the PV power at MPP (Ppv − mpp ) by varying the duty cycle Dpv . As shown in Fig. 1, the PV module output current and voltage, and hence, the PV output power is continually measured by the power control unit. In each step, the measured power is compared to the previous amount to find the maximum available power by varying the duty cycle Dpv . The electric circuit of the bidirectional DC/DC boost-buck converter with the average power efficiency of 90% connected to the Li-ion battery is shown in Fig. 3. The discharging power of the Li-ion battery is given as: (4)
Pdischar = Vbat Ibat
The Li-ion battery output voltage and current (Vbat and Ibat ), and hence, the discharging and charging powers of the Li-ion battery are continuously measured by the power control unit as shown in Fig. 1. Noting Fig. 3 demonstrates that in discharging mode, the converter operates as a boost converter, and the discharging power of the Li-ion battery is expressed as:
Pdischar
⎡ ⎛ 1 ⎢⎛ 1 ⎞ Vbat ⎜ = 0.9 ⎢ ⎝ 1−Ddisc ⎠ ⎜ ⎢ ⎝ ⎣ ⎜
(
1 1 − Ddisc
)V
bat −Vdc ⎞ ⎤
⎟
0.001 + R esr
⎟⎥ ⎟⎥ ⎠⎥ ⎦
(5)
where Ddisc is the duty cycle of the control signal supplied to the gate of the insulated gate bipolar transistor (IGBT) Q1 (discharge switch) as shown in Fig. 3. It is deduced from Eq. (5) that the discharging power can be regulated to a required power rate by varying the duty cycle Ddisc . In charging mode, the direction of the battery current becomes reverse, the converter operates as a buck converter, and the charging power is found as:
Dchar Vdc−Vbat ⎞⎟ Pchar = Dchar Vdc ⎛⎜ + Rbat − esr + R Lbat ⎠ 0.001 ⎝
Fig. 1. Configuration of the battery/PV hybrid power source proposed to be utilized in PHEVs.
(6)
where Dchar is the duty cycle of the switching pulse supplied to the gate of the IGBT Q2 (charge switch) as shown in Fig. 3. Thus, in a similar Fig. 2. Unidirectional DC/DC boost converter connected to the PV module.
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Fig. 3. Bidirectional DC/DC boost-buck converter connected to the Li-ion battery.
manner, the charging power is regulated to a required power rate by varying the duty cycle Dchar . As shown in Fig. 1, the power control unit also measures the DC-link voltage (Vdc ) and load current (Iload ), and then computes the total electric power (Pload ) supplied to the three-phase bidirectional PWM DC/AC inverter and the three-phase traction motor connected to the inverter as:
Ddisc as shown in Fig. 1 and Fig. 3 to provide the additional electric power needed. In this case, the power balance in the hybrid power source is expressed as:
0.98Ppv + 0.9Pdischar = Pload
In this case, the amount of the supplementary electric power that should be provided by discharging the Li-ion battery is found from Eq. (11) as:
(7)
Pload = Vdc Iload
The power control in the battery/PV hybrid power source is performed by the power control unit as below:
Pdischar =
Case 1 (charging mode). If 0.98Ppv ⩾ Pload , then the power control unit sets the Li-ion battery in charging mode by activating the duty cycle Dchar as shown in Fig. 1 and Fig. 3. In this case, the power balance in the hybrid power source is expressed as:
1 Pchar 0.9
1
(8)
⎟
(13)
It is deduced from Eq. (13) that in this case (discharging mode), the power control unit measures Ppv and Pload , and then regulates the discharging power of the Li-ion battery to the amount demanded in Eq. (12) by varying Ddisc .
(9)
The electric circuit of the proposed three-phase bidirectional PWM six-switch DC/AC inverter connected the traction motor is shown in Fig. 4. 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. 4, each IGBT itself includes an emitter-to-collector connected diode, the six diodes operate as a three-phase rectifier to convert the three-phase AC voltage resulted from the regenerative power produced
It is derived from comparing Eq. (6) with Eq. (9) that:
Dchar Vdc−Vbat ⎞ Dchar Vdc ⎛⎜ ⎟ = 0.9(0.98Ppv−Pload ) ⎝ 0.001 + Rbat − esr + R Lbat ⎠
(12)
) Vbat −Vdc ⎞ ⎛( ⎛ 1 ⎞ Vbat 1 − Ddisc = Pload−0.98Ppv ⎜ ⎜ 0.001 + R esr ⎟⎟ ⎝ 1−Ddisc ⎠ ⎝ ⎠
So, the electric power consumed to charge the Li-ion battery is obtained as:
Pchar = 0.9(0.98Ppv−Pload )
1 (Pload−0.98Ppv ) 0.9
By replacing Pdischar from Eq. (5) in Eq. (12), it is found that:
⎜
0.98Ppv = Pload +
(11)
(10)
Eq. (10) explicitly demonstrates that in this case (charging mode), the power control unit measures Ppv and Pload , and then regulates the charging power of the Li-ion battery to the required amount specified in Eq. (9) by varying Dchar . Case 2 (discharging mode). If 0.98Ppv < Pload , then the power control unit sets the Li-ion battery in discharging mode by activating the duty cycle
Fig. 4. Three-phase bidirectional PWM six-switch DC/AC inverter.
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Fig. 5. Electric circuit of the constructed battery/PV hybrid power source proposed to be utilized in PHEVs.
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by the traction motor during decelerating and braking into the DC-link voltage to be used to charge the Li-ion battery. Thus, the proposed three-phase PWM six-switch DC/AC inverter is bidirectional type. 3. Construction of the battery/PV hybrid power source and experimental verifications The configuration of the proposed battery/PV hybrid power source was shown in Fig. 1, based on which the power source has been constructed to provide experimental verifications. The electric circuit of the constructed battery/PV hybrid power source is shown in Fig. 5. As shown in Fig. 5, the microcontroller MC68HC11E9 has been used as the power control and MPPT unit. The PV module output current (Ipv ) is measured by an INA 168, and is supplied to the pin AN2 which is an analog pin of the microcontroller. The PV module output voltage (Vpv ) is first scaled by the potentiometer RV2, and then is supplied to the other analog pin (AN3). In similar manner, the load current (Iload ), DC-link voltage (Vdc ), Li-ion battery output current (Ibat ) and voltage (Vbat ) are measured and respectively supplied to the analog pins AN0, AN1, AN4 and AN5. The duty cycle Dpv is varied by the microcontroller to regulate the DC-link voltage to the appointed value (400 V) according to Eq. (1). The periodic switching pulse with the duty cycle Dpv is then supplied to the switch Spv via the two buffers interconnected in series. The powers Pload , Ppv , Pchar (in charging mode) and Pdischar (in discharging mode) are measured by the microcontroller, and the charging or discharging power of the Li-ion battery is regulated to the required amount respectively specified in Eq. (9) or Eq. (12) by varying Dchar or Ddisc in accordance with Eq. (10) or Eq. (13). The detailed specifications of all the components used to construct the battery/PV hybrid power source proposed to be utilized in PHEVs are listed in Table 1. As reported in Table 1, an 80 kW three-phase PMSM used as the traction motor, a 19.2 kWh Li-ion battery and a PV module KC200GT have been utilized. The waveforms of the line voltages (VAB and VBC ) supplied to the PMSM and the DC-link voltage are shown in Fig. 6. The waveforms of the line
Fig. 6. Experimental results: the waveforms of the line voltages (VAB and VBC ) supplied to the PMSM, and the regulated DC-link voltage.
voltages show that they are the three-level AC voltages with correct magnitude and phase produced using PWM technique by the threephase bidirectional DC/AC inverter, and this 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). The waveforms of the currents (IA and IB ) supplied to the stator of the PMSM are shown in Fig. 7. The periodic switching pulse with the switching frequency of 25 kHz and the duty cycle Dpv and the regulated DC-link voltage are also shown in Fig. 8. As mentioned, the periodic switching pulse is produced by the microcontroller, and then, is supplied to the switch Spv of the unidirectional DC/DC boost converter connected to the PV module. Fig. 8 shows that the duty cycle of the switching pulse supplied
Table 1 Technical specification of the components used in the constructed battery/PV hybrid power source proposed to be utilized in PHEVs. Traction motor
DC/DC boost converter connected to PV module
Model
LSRPM 200 L
Cpv (μF )-Aluminum electrolytic capacitor/400 V
470
Made by
Leroy-Somer Co.
25
Type Phase number Nominal line voltage (V) Rated power (kW) Rated torque (Nm) Rated current (A) Speed range (rpm) Efficiency (%)
Permanent magnet synchronous motor (PMSM) 3 400 80 170 157 0–4500 95.7
Converter switching frequency: fs (kHz) DC-link voltage Vdc (V) DC-link capacitor Cdc (μF )-Aluminum electrolytic capacitor/600 V Average ESR of Cdc : R esr (mΩ ) C2 (μF )-Premium metallized polypropylene capacitor/600 V C1 (nF )-Parasitic capacitance of IRFPS40N60K Type of transformer T n = N2/ N1 MOSFET switch Spv
Maximum torque/rated torque Magnet material
1.4 NdFeB
Diodes: D1 - D2 PV module KC200GT
Maximum current/rated current
1.5
7.61
Moment of inertia (kgm2 ) Weight (kg)
0.15
(G = 1000 Wm−2 , T = 25 °C ) Current at MPP Ipv − mpp (A) Voltage at MPP Vpv − mpp (V)
145
Output power at MPP Ppv − mpp (W)
200.1430
Battery bank: Sixteen 12 V/100 Ah Li-ion batteries Type Li-ion Voltage (V) 48 Current capacity (Ah) 400
Short-circuit current Isc (A)
8.21
Open-circuit voltage Voc (V) DC/DC converter connected to the Li-ion battery bank Type
32.9
Capacity (kWh) Series-connected batteries
19.2 4
IGBT switches: SW, Q1-Q2 R Lbat (mΩ )
Bidirectional boost-buck STGY40NC60VD × 40 10.8
Parallel-connected sets
4
Single-phase inverter (V2G connection) (Single-phase grid voltage: ∼110 VAC, 60 Hz) IGBT switches: Q9-Q12 N4/ N3 Lg (μH )
STGY40NC60VD × 8 39/12 68
Cg (μF )
8.2
2.9 Average ESR (Rbat − esr (mΩ )) Three-phase bidirectional PWM six-switch DC/AC inverter IGBT switches: Q3-Q8 STGY40NC60VD × 5
248
400 680 109 22 1.2 Pulse 20/3 IRFPS40N60K 15ETH06S
26.3
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Fig. 7. Experimental results: the waveforms of the currents (IA and IB ) supplied to the stator of the PMSM. Fig. 10. Power extracted from the PV module KC200GT from hour to hour in daylight (5:00–21:00) during a sunny day.
to the converter connected to the PV module is about 0.562, Vdc = 400 V and Vpv = 26.25 V. Considering the parameters of the converter reported in Table 1 (n = 20/3), these values are exactly compatible with Eq. (1). Comparing the operating voltage of the PV module (26.25 V) to the MPP voltage of the PV module (Vpv − mpp = 26.3 V) under nominal condition (irradiance G = 1000 Wm−2 , temperature T = 25 °C) reported in Table 1 explicitly verifies that the MPPT unit high accurately tracks the MPP of the PV module. The electric power supplied to the traction motor (PMSM) and the total of the electric power produced by the PV module and discharging the Li-ion battery were measured point by point, and then, the power efficiency of the proposed battery/PV hybrid power source was obtained point by point as shown in Fig. 9. The following points which are the main contributions of this study are deduced from the experimental results shown in Figs. 6–9:
Fig. 8. Experimental results: the periodic switching pulse supplied to the switch Spv of the
• The power efficiency curve explicitly demonstrates that the pro-
DC/DC converter connected to the PV module, the DC-link voltage and the operating voltage of the PV module.
• •
posed battery/PV hybrid power source provides a power efficiency of about 91% around the rated power of the traction motor. 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.
Fig. 9. Experimental results: the power efficiency of the battery/PV hybrid power proposed to be utilized in PHEVs.
Fig. 11. Experimental results: power flow measured hour by hour.
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Table 2 Comparison between the technical parameters of the hybrid battery/PV power source in different modes. Mode of the power source
Analysis type
Cruising range (km)
Max. speed (km/h)
0–100 km/h acceleration (sec)
Max. efficiency (%)
PHEV weight (kg)
Battery/PV Battery
Experiment Experiment
123.4 110
121 120
13.4 13.4
91.1 90.2
1880 1880
References
To evaluate the impact of the PV module, three other tests were also performed by utilizing the hybrid power source in a PHEV with the weight of 1880 kg. The tests and measurements have been carried out in the geographic position of (37.9667°N, 23.7167°E) where is outside urban areas, and there is no traffic. In the first test, the power extracted from the PV module KC200GT mounted horizontally on the roof of the PHEV was measured from hour to hour in daylight (5:00–21:00) during a sunny day. The measured power curve is shown in Fig. 10 that explicitly demonstrates the PV module KC200GT produces a daily electric energy of about 1.33 kWh during a sunny day. In the second test, the PV module was in operation, so the power source was in battery/PV hybrid mode. The test was performed in a normal operation of the PHEV composed of working and parking during two sunny days. It is reminded that according to the automobile companies’ standard, a car normally travels about 20,000 km per year or about 110 km per two days. The test was started at 5:00 when the SOC of the Li-ion battery was one (SOC = 1), and was ended on the second day at 18:23 when the SOC reached zero (SOC = 0). The power flow measured hour by hour that represents the power portions provided by the battery and PV module is shown in detail in Fig. 11. In the third test, the PV module was isolated from the system, and so the power source was in battery mode. The results of the two last tests are summarized in Table 2, the experimental measurements and results demonstrate that utilizing the PV module adds 13.4 km to the cruising range in a normal operation of the PHEV during two sunny days, and provides higher power efficiency (91.1%) and speed (121 km/h). As reported in Table 2, a PHEV with the weight of 1880 kg equipped with the proposed battery/PV hybrid power source has a maximum speed of 121 km/h and a cruising range of 123.4 km.
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4. Conclusion In this paper, a novel battery/PV hybrid power source was proposed to be utilized in PHEVs. In the hybrid power source, the gasolinepowered internal combustion engine of a PHEV has been replaced with a small-size PV module positioned horizontally on the roof of the PHEV, and solar energy has been utilized as a clean and renewable energy to extend the cruising range of the PHEV. The power source has the capability of V2G, and utilizes a 19.2 kWh Li-ion battery as the main energy storage device and a 200 W PV module as the auxiliary power source. A prototype of the battery/PV hybrid power source has been built, and experimental verifications were presented. It was demonstrated that utilizing the PV module adds 13.4 km to the cruising range of a PHEV with the weight of 1880 kg in a normal operation of it during two sunny days, and provides higher power efficiency (91.1%) and speed (121 km/h). It was also shown that the power source high accurately regulates the DC-link voltage, and produces suitable stator currents for the traction motor by using PWM technique.
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