AbstractâIn this paper, a simple and low cost AC/AC/DC converter is proposed to charge EV( Electric Vehicle) batteries. An exclusive Z-Source (LC) network, ...
2012 IEEE 7th International Power Electronics and Motion Control Conference - ECCE Asia June 2-5, 2012, Harbin, China
EV battery charger that Uses Z-source AC/AC converter Xinyu Fang, Da Xie, Zhiwen Yu, Junqi Feng, Qian Ai Dept. of Electrical Engineering Shanghai Jiaotong University Shanghai, China
situation and has a larger range of output voltages, reducing inrush, and harmonic suppression. However, there are few people applying Z-source AC/AC converters to EV battery charger, where a wide range of output voltages is needed when charging battery series in different scales.
Abstract—In this paper, a simple and low cost AC/AC/DC converter is proposed to charge EV( Electric Vehicle) batteries. An exclusive Z-Source (LC) network, which acts as a static transformer, is connected in front of the PI filter and uncontrolled full-bridge rectifier. By controlling the shootthrough duty ratio, the output voltage of the converter can be regulated in a large range rapidly, which can meet the charging demands of EV battery series in different scales. Compared to the conventional charger, the bulk is small. In this topology, fewer switches are needed. It’s safer, doesn’t need to take account of the dead zone and the control strategy is simpler. More over, inheriting the advantages of Z-source, the novel charger reduces in-rush and harmonic current, which makes it more flexible to the grid. The qualitative and quantitative analysis of the proposed topology and the control method are presented. Simulations of charging polymer Li-ion battery series are given, and the results prove the validity of the analysis, and verify the good application of the novel EV battery charger.
In this paper, a novel topology of EV battery charger, as Figure 2 shows, which uses Z-source AC/AC converter is proposed. It consists of three parts: a Z-source AC/AC converter, a PI filter and an uncontrolled full bridge rectifier. This topology inherits the merits of Z-source. The novel charger has other advantages: a simple structure, low costs and simple control strategy. The analysis of the circuit is presented. Simulations for charging the polymer Li-ion battery series are given, and the results show that the topology has a good performance for EV battery charging
Keywords- Charger; Z-Source; Ac/Ac converter; Li-ion battery
I.
INTRODUCTION
Nowadays, electric vehicles (EVs), are becoming an attractive alternative to gasoline driven cars, due to the deepening crises of the climate change and resource depletion. The energy conservation is very impressive because EVs offer about 60% greater mileage from the same amount of primary energy [1].
Figure 1. Conventional two-stage PWM battery charger.
The continued increase in the number of EVs calls for the technological progress on EV battery charger. Studies have been performed over the last decade on various topologies [2][9]. Figure 1 shows the typical two-stage topology consists of a PWM AC/DC converter and a DC/DC converter. The DC-DC converter is cascaded to obtain a DC output voltage, which is much smaller than the input. However, there are some limitations for using, such as non-shoot-through allowed in a bridge leg, which leads to lower EMI reliability. Furthermore, the cascaded system may be lower efficiency and more complicated [10].
Figure 2. EV battery charger using Z-source AC/AC converter.
II.
Z-source has been verified as an alternative ways to overcome the above disadvantages in convention [11]-[22]. Recently, research on Z-source converters has focused mainly on DC/AC inverters and AC/AC converters. In applications where only voltage regulation is needed, the family of singlephase Z-source AC/AC converters presented in [11]–[17] have a number of merits, for example, it can work in boost or buck
THE TOPOLOGY OF THE PROPOSED EV BATTERY CHARGER
As Figure 2 shows, the Z-source AC/AC converter utilizes two switches S1 and S2, which is constituted by two active devices Q1 and Q2 with D1 and D2 as the body diodes. The two active devices are connected to constitute four-quadrant switch, for bidirectional voltage blocking and bidirectional
Project supported by the National High Technology Research and Development Program of China (863 Program) (2011AA05A108). 2673
978-1-4577-2088-8/11/$26.00 ©2012 IEEE
current paths. The symmetrical Z-Source network combined with two same inductors and two same capacitors is the energy storage and filtering element [14]. S1 and S2 are turned on and off in complement. By controlling shoot-through duty ratio, defined as D, of S1, the output voltage of the AC/AC converter can be regulated as need. The PI filter is combined with two capacitors, Cf1 and Cf2, and an inductor Lf . The values of the capacitors and inductance are both small. The small inductor L0 is to prevent Cf1 from voltage leaping. In analysis, it is neglectful. In the end, there is the uncontrolled full-bridge rectifier, which consists of four diodes. The capacitor C3 followed has is used to stabilize voltage of the charger. III.
(c)
THE ANALYSIS OF THE PROPOSED TOPOLOGY
Since different types of batteries have different characteristics, we replace the battery by a resistance RL for analysis. The bidirectional switches S1 and S2, which are turned on and off in complement, have two operation states, on and off. The uncontrolled full bridge rectifier also has two states, shoot-through and shutoff. As a result, four states lead to four operation states of the proposed charger. As Figure 3 shows, they are:
(d) Figure 3. Four states of the proposed topology: (a) state 1; (b) state 2; (c) state 3; (d) state 4.
Since the inductors and capacitors in Z-network have the same inductances and capacitances, it is symmetrical. So we have
1.
State 1, the rectifier is shutoff, S1 turns off, and S2 turns on.
2.
State 2, the rectifier is shutoff, S1 turns on, and S2 turns off.
3.
State 3, the rectifier is shoot-through, S1 turns off, and S2 turns on.
4.
⎧ iL1 = iL2 = iL ⎨ ⎩U C1 = U C 2 = U C .
(1)
For analysis convenience, we just consider L1 and C2.
State 4, the rectifier is shoot-through, S1 turns on, and S2 turns off.
In state 1 and state 2, the voltage of Cf2 is smaller than that of C3, and the rectifier is shutoff. The output voltage of the first two parts which consists of Z-source AC/AC converter and PI filter is sinusoidal. Capacitor C3 and resistance RL constitute a closed loop and C3 discharges through RL. Suppose the switch period is T, while in the time t~t+DT, we have (2), as shown in the next page. While in the time t+DT~t+T, we have (3). Then, we get the average equation (4) from (2) and (3). In steady state, we have (5). Since the inductances in the Z-source and the PI filter are very small, we can ignore the voltage drop across the inductor. Thus, we have
(a)
D ⎧ U C 2 (t ) = U i (t ) ⎪ 1 − 2D ⎪⎪ D (ω 2 L f C f − 2)iL f (t ) ⎨ iL1 (t ) = 2D −1 ⎪ ⎪U C = U C = U C 2 (t ) = D U i (t ). f1 ⎪⎩ f 2 1 − 2D
(b)
(6)
Thus, we can regulate the voltage of CF1 by controlling the shoot-through duty ratio D.
⎡ L1 ⎢ ⎢ ⎢ ⎢ ⎢ ⎢ ⎣
Lf C2 Cf1
0 ⎤ ⎡ iL1 ( t ) ⎤ ⎡0 −1 ⎥ ⎢ ⎥ ⎢i 0 0 ⎥ d ⎢ L f ( t ) ⎥ ⎢0 ⎥ ⎢ uC2 ( t ) ⎥ = ⎢1 − ω 2 L f C f − 2 0 ⎥ ⎢ ⎥ dt ⎢ 2 0 ⎥ ⎢uC f 1 ( t ) ⎥ ⎢0 ω L f C f + 1 ⎢ ⎥ C f 2 ⎥⎦ ⎣uC f 2 ( t ) ⎦ ⎢⎣0 1 0
2674
0 0 ⎤ ⎡ iL1 ( t ) ⎤ ⎡ui (t )⎤ ⎢ ⎥ 1 − 1⎥⎥ ⎢ iL f (t ) ⎥ ⎢⎢ 0 ⎥⎥ 0 0 ⎥ ⎢ u C2 ( t ) ⎥ + ⎢ 0 ⎥ ⎥ ⎢ ⎥⎢ ⎥ 0 0 ⎥ ⎢ uC f 1 ( t ) ⎥ ⎢ 0 ⎥ 0 0 ⎥⎦ ⎢⎣uC f 2 ( t ) ⎥⎦ ⎢⎣ 0 ⎥⎦
(2)
⎡ L1 ⎢ ⎢ ⎢ ⎢ ⎢ ⎢ ⎣ ⎡ L1 ⎢ ⎢ ⎢ ⎢ ⎢ ⎢ ⎣
Lf C2 Cf1
Lf C2 C f1
⎤ ⎡ iL1 (t ) ⎤ ⎡0 0 ⎥ ⎢ ⎥ ⎢i 0 ⎥ d ⎢ L f ( t ) ⎥ ⎢0 ⎢ ⎥ ⎥ uC2 ( t ) = ⎢1 0 ⎥ ⎢ ⎥ dt ⎢ 2 u ⎥ ⎢ C f 1 ( t ) ⎥ ⎢0 ω L f C f + 1 C f 2 ⎥⎦ ⎢⎣uC f 2 ( t ) ⎥⎦ ⎢⎣0 1
1 0 0 ⎤ ⎡ iL1 ( t ) ⎤ ⎢ ⎥ 0 1 − 1⎥⎥ ⎢ iL f ( t ) ⎥ 0 0 0 ⎥ ⎢ uC 2 ( t ) ⎥ ⎥ ⎥⎢ 0 0 0 ⎥ ⎢ uC f 1 ( t ) ⎥ 0 0 0 ⎥⎦ ⎢⎣uC f 2 ( t ) ⎥⎦
0 1 − 2D ⎤ ⎡ i L1 ( t ) ⎤ ⎡ 0 ⎥ ⎢ ⎥ ⎢i 0 0 ⎥ d ⎢ L f (t ) ⎥ ⎢ 0 ⎥ ⎢ u C2 ( t ) ⎥ = ⎢ 2 D − 1 − D(ω 2 L f C f + 2) 0 ⎥ ⎢ ⎥ dt ⎢ 2 u 0 ω Lf C f +1 ⎥ ⎢ C f 1 (t ) ⎥ ⎢ 0 C f 2 ⎥⎦ ⎢⎣u C f 2 (t ) ⎥⎦ ⎢⎣ 0 1 0
⎡ L1 ⎢ ⎢ ⎢ ⎢ ⎢ ⎢ ⎣
Lf C2 C f1
⎤ ⎥ ⎥ d ⎥ ⎥ dt ⎥ C f 2 ⎥⎦
In state 3 and state 4, the voltage of Cf2 is larger than C3, the full bridge rectifier is shoot-through. When the switching frequency is high enough, the input of the proposed circuit can be regarded as a constant. Analysis of the proposed circuit in state 3 and state 4 is shown in Figure 4. In the time from t~ t+DT, the circuit is in state 3. S1 is closed and S2 is open. AC source and capacitors in the Z-network are the source of the circuit. As Figure 4 shows, Uc1 drops. Inductors in the Znetwork are charged and iL1 rises. The PI filter is also charged and UCf2 rises with a delay mainly caused by Lf. C3 is charged by the front part and discharging through RL, and the capacitance is large, so UC3 is relatively stable. In the time from t+DT~ t+T, the circuit is in state 4. S1 is open and S2 is closed. Z-network separates from the filter. Inductors in the Znetwork charge the capacitors. So, UC1 rises and IL1 drops. The filter and C3 discharge though RL together. Thus, UCf2 drops with a little delay. UC3 is stable.
0 1 0 0 0
0 ⎤ ⎡ i L1 ( t ) ⎤ ⎡ Du i (t )⎤ ⎢ ⎥ − 1⎥⎥ ⎢ i L f (t ) ⎥ ⎢⎢ 0 ⎥⎥ 0 ⎥ ⎢ u C2 ( t ) ⎥ + ⎢ 0 ⎥ ⎥ ⎢ ⎥⎢ ⎥ 0 ⎥ ⎢u C f 1 (t ) ⎥ ⎢ 0 ⎥ 0 ⎥⎦ ⎢⎣u C f 2 (t ) ⎥⎦ ⎢⎣ 0 ⎥⎦
⎡ i L1 (t ) ⎤ ⎢i ⎥ ⎢ L f (t ) ⎥ ⎢ u C 2 (t ) ⎥ = 0 ⎢ ⎥ ⎢ u C f 1 (t ) ⎥ ⎢u C ( t ) ⎥ ⎣ f2 ⎦
(3)
(4)
(5)
Voltage(V)
L1=L2=0.35mH, C1=C2=0.47mF, Cf1=Cf2=10μF, Lf=10μH, C3=2mF, R=50 ohms. Table 1 shows the simulation results at D ranges from 0.05 to 0.95. It gives the peak value and trough value of the voltage of C3. Theoretical value means peak voltage of Cf2 calculated from (6). Error rate means rate of the difference between peak value and theoretical value and theoretical value. Due to the load RL and difference calculation and simulation, error rate exists. However, when D ranges from 0.40 to 0.60, error rate is too large. So the interval is the instable zoon. As shown in Table 1, the voltage can be regulated from 15.8V to 704.1V, and the range meets the charging requirements of EV batteries.
Figure 5. The static simulation results of the proposed circuit.
To get the speed of the voltage regulation, the simulation is also carried out. Figure 6 shows the simulation results, where D=0.20, 0.25, 0.30. So, in the boost progress, there is almost no delay. Figure 7 shows the simulation results, where D=0.35, 0.25, 0.30. In the buck progress, the speed of the voltage regulation depends on the discharging speed of closed circuit constituted by C3 and RL. In the simulation, the buck delay is about 8ms, which is too short for battery charging. Thus, the speed of the voltage regulation also meets the charging requirements of EV batteries.
Figure 4. Analysis of the proposed circuit in state 3 and state 4.
Figure 5 shows the static simulation results of the proposed circuit where Vi=311V, frequency of Vi is 50Hz, a constant D and the switching frequency is 20kHz. The parameters were
2675
TABLE I.
SIMULATION RESULTS WITH D RANGING FROM 0.05 TO 0.95
Duty Ratio
Peaks (V)
Troughs (V)
Theoretical Value (V)
Error Rate
0.05
15.8
14.7
17.1
7.6
0.10
37.6
34.9
38.9
2.8
0.15
65.5
60.9
66.6
1.7
0.20
102.5
95.3
103.6
1.1
0.25
153.9
143.0
155.5
1.0
0.30
228.7
213.3
233.3
2.0
0.35
341.4
319.0
362.8
5.9
0.40
440.5
410.0
622.0
×
0.45
275.5
256.5
1399.5
×
0.50
instability
instability
Inf
×
0.55
372.8
347.5
1710.5
×
0.60
721.4
675.1
933.0
×
0.65
704.1
658.9
673.8
4.5
0.70
571.1
535.3
544.3
4.9
0.75
483.4
452.5
466.5
3.6
0.80
427.0
399.1
414.7
3.0
0.85
384.8
360.9
377.6
1.9
0.90
355.4
331.2
349.9
1.6
0.95
333.6
310.6
328.3
ion battery, shown in Figure 8. Figure 9 shows the open-circuit voltage curve of new 850-mAh TCL PL-383562 polymer Liion battery when charging. In our simulation, we used the proposed charger to charge 50 batteries in series. We didn’t take an account of the differences between the batteries. The parameters of the charger were: Vi=311V, fVi=50Hz, fswitch = 20kHz, L1=L2=0.35mH, C1=C2=0.47mF, Cf1=Cf2=10μF, Lf =10μH, C3=2mF.
Figure 8. Electrical battery model. 4 . 5
4
3 . 5
3
0
5 0 0
10 00
15 00
20 00
25 00
30 00
35 00
40 00
45 00
50 00
Time(s)
1.6
Figure 9. Open-circuit voltage of the charging Li-ion battery in test.
Since the resistance of the Li-ion battery series changes with the SOC (State of Charge), the voltage of C3 changes with the resistance correspondingly. Applying closed-loop control of the voltage to the circuit, and regulating D with the change of voltage, we can stabilize the voltage of the batteries relatively. The control strategy is simple. Figure 10 shows the charging voltage curve of the Li-ion battery. The voltage of one battery fluctuates between 4.7V and 4.9V. Figure 11 shows the charging current curve of the Li-ion battery. The maximal fluctuation of the current is 2A. Figure 12 shows the SOC curve of the Li-ion battery. The simulation results verify that the proposed charger has a good performance for EV battery charging.
Figure 6. Voltage regulation where D=0.20, 0.25, 0.30.
Figure 7. Voltage regulation where D=0.35, 0.25, 0.30.
IV.
SIMULATION OF CHARGING LITHIUM-ION BATTERIES
In order to verify the validity of the proposed analysis, simulation of charging polymer Li-ion battery series is conducted. [23] presented an accurate electrical model of Lit-
Figure 10. Charging voltage of the Li-ion battery.
2676
[4]
10
8
[5]
6
4
[6]
2
[7]
0
-2 0
100
200
300
400
500
600
700
800
900
1000
Time (s)
[8] Figure 11. Charging current of the Li-ion battery. [9] 1
0.8
[10]
0.6
[11]
0.4
0.2
0
0
100
200
300
400
500
600
700
800
900
[12]
1000
Time (s)
[13]
Figure 12. SOC of the Li-ion battery.
V.
[14]
CONCLUSION
In this paper, an EV (Electric Vehicle) battery charger that consists of Z-source AC/AC converter, π filter and uncontrolled full-bridge rectifier is proposed. Inheriting the advantages of Z-source network, the Z-source charger has merits such as simple structure, easy control strategy, permitting shoot-through in a bridge leg, voltage regulating in a large range, reducing inrush and harmonic current. Qualitative and quantitative analysis on the proposed circuit in four states is presented, and the output equations are deduced and show the charging voltage can be simply regulated by controlling the shoot-through duty ratio of the switches. Simulations verify the range and the speed of voltage regulating. In the simulation of polymer Li-ion batteries charging, curves of charging voltage, current and SOC (state of charge) are given. The results prove the validity of the analysis and verify the good application of the novel EV battery charger.
[15]
[16]
[17]
[18] [19]
[20]
REFERENCES [1]
[2]
[3]
[21]
Gomez, J.C. and Morcos, M.M., “Impact of EV Battery Chargers on the Power Quality of Distribution Systems,” IEEE Trans. Power Delivery, vol. 18, pp. 975–981, July 2003. Bilgin, B., Emadi, A. and Krishnamurthy, M., “Design considerations for a universal input battery charger circuit for PHEV applications,” IEEE Transactions on Industrial Electronics, pp.3407–3412, July 2010. Ying-Chun Chuang and Yu-Lung Ke, “High-Efficiency and Low-Stress ZVT–PWM DC-to-DC Converter for Battery Charger,” IEEE Transactions on Industrial Electronics, vol. 55, pp.3030–3037, Aug. 2008.
[22]
[23]
2677
Vescovi, T.F. and Vun, N.C.H., “A switched-mode 200 A 48 V rectifier/ battery charger for telecommunications applications,” Telecommunications Energy Conf, 1990, pp. 112–118, Oct. 1990. Morcos, M.M., Dillman, N.G. and Mersman, C.R., “Battery chargers for electic vehicles,” IEEE Power Engineering Review, vol. 20, pp. 8-11, 18, Nov. 2000. Pellegrino, G., Armando, E. and Guglielmi, P., “An Integral Battery Charger With Power Factor Correction for Electric Scooter,” IEEE Transactions on Power Electronics, vol. 25, pp. 751-759, March 2010. Lacroix, S., Hilairet, M. and Laboure, E., “A high performance RST controllor for on board battery charger,” IECON 2011 - 37th Annual Conference on IEEE Industrial Electronics Society, pp. 4552-4557, Nov. 2011. Solero, L., “Nonconventional On-Board Charger for Electric Vehicle Propulsion Batteries,” IEEE Transactions on Vehicular Technology, vol. 50, pp. 144–149, Jan 2001. Egan, M.G., O'Sullivan, D.L., Hayes, J.G., Willers, M.J. and Henze, C.P., “ Power-Factor-Corrected Single-Stage Inductive Charger for Electric Vehicle Batteries,” IEEE Transactions on Industrial Electronics, vol. 54, pp. 1217–1226, April 2007. Yeyuan Xie, Zhaoming Qian, Xinping Ding and Fangzheng Peng, “A novel buck-boost Z-source rectifier,” IEEE Power Electronics Specialists Conf., 2006 , pp.1–5, June 2006. Minh-Khai Nguyen, Young-Gook Jung and Young-Cheol Lim, “A single-phase Z-source buck-boost matrix converter,” IEEE Transactions on Power Electronics, vol. 25, pp.453–462, February, 2010. Xupeng Fang and Peng, F.Z., “Novel Three-Phase Current-Fed ZSource AC-AC Converter,” IEEE Power Electronics Specialists Conference, 2007, pp. 2993-2996, June 2007. Xu Peng Fang, Zhao Ming Qian and Fang Zheng Peng, “Single-Phase Z-Source PWM AC-AC Converters,” IEEE Power Electronics Letters, vol. 3, pp. 121-124, Dec. 2005. Yu Tang, Chaohua Zhang and Shaojun Xie, “Z-Source AC–AC Converters Solving Commutation Problem,” IEEE Transactions on Power Electronics, vol. 22, pp. 2146-2154, November, 2007. Xu-Peng Fang, “Three-Phase Z-Source AC-AC Converter for Motor Drives,” IEEE Power Electronics and Motion Control Conference, 2006, vol. 1, pp. 1-5, Aug. 2006. Xu-Peng Fang, “Three-Phase Z-Source AC-AC Converter,” IEEE Power Electronics and Motion Control Conference, 2006, pp. 621-624, Aug. 2006. Senthilkumar, R., Bharanikumar, R. and Jerom, J., “ Z-Source Inverter for UPS Application,” International Conference on Intelligent and Advangced Systems, 2007, pp. 1-6, Nov. 2007. Holland, K. and Peng, F.Z., “,” IEEE Vehicle Power and Propulsion Conf., 2005, pp. 639-644, Sept. 2005. Fatemi, A., Azizi, M., Shahparasti, M., Mohamadian, M. and Yazdian, A., “A Generalized Algorithm for Switch Reduction in Multioutput Single-Phase Inverters,” Power Electronics, Drive Systems and Technologies Conference, 2011, pp. 292-298, Feb. 2011. Curi, M.O., van Emmerik, E.L., Franca, B.W., Rolim, L.G.B. and Aredes, M., “A Novel Topology for Fuel Cell Stack Generation with Flywheel Energy Storage System and Z-Source Converter,” International Conference on Electrical Machines and Systems, 2011, pp. 1-6, Aug. 2011. Loh, P.C., Vilathgamuwa, D.M., Gajanayake, C.J., Wong, L.T.and Ang, C.P., “Z-Source Current-Type Inverters: Digital Modulation and Logic Implementation,” Industry Applications Conference, 2005, vol. 2, pp. 940-942, Oct. 2005. Ellabban, O., Mierlo, J.V. and Lataire, P., “Control of a Bidirectional ZSource Inverter for Hybrid Electric Vehicles in Motoring, Regenerative Braking and Grid Interface Operations,” IEEE Electric Power and Energy Conf., 2010, pp. 1-6, Aug. 2010. Min Chen and Rincon-Mora, G.A., “Accurate Electrical Battery Model Capable of Predicting Runtime and I–V Performance,” IEEE Transactions on Energy Convertion, vol. 21, pp. 504-511, June 2006.
