Abstract - Applications of electric vehicles need to build a large number of charging stations. In order to reduce the grid load, it is necessary to develop smart electric vehicle charging stations. The Electric vehicle charging stations communicate with the gird. The Electric vehicle charge at night to reduce the cost and the grid load, simultaneously fill the valley. When grid load increase, electric vehicles battery discharge to the grid to improve grid stability. As distributed storage units, electric vehicles are important components of smart grid. New technology of high power factor PWM rectifier-inverter is one of the key technologies for the smart electric vehicle charging system. In this paper, three-phase PWM rectifier used for smart charging and discharging system of electric vehicle is analyzed and designed. The paper includes the principle of PWM Rectifier-Inverter and direct current control strategy. Also, the SVPWM and system design of three-phase PWM rectifier are analyzed. A 10kW prototype is developed. Simulation and experiment results show that the three-phase PWM rectifier can improve power factor. From the experimental results, PWM rectifier implements the grid current sinusoidal and achieves the unit power factor.

I. INTRODUCTION Electric vehicle charging systems are infrastructures and

equipment which provide power supply to power battery of electric vehicle, mainly including battery exchange station and charging pole and charging station. V2G mode refers that electric vehicle communicate with energy management system, and under its control to exchange energy with the grid. Under V2G mode, electric vehicles can be used as energy storage units and transfer power to grid.

The traditional electric vehicle charging system use diode rectifier bridges topology cascade with DC-DC. Diode Rectifier Bridges have the following disadvantages: the input current harmonic content is high and absorbs reactive power from the grid. Hence the input power factor is very low, and can only transfer power from grid to load.

To solve the above problems, this paper presents three-phase PWM rectifier topology for electric charging station. Three-phase PWM rectifier has the following advantages: sinusoidal grid current, low THD, and unit power factor. In rectifier mode, three-phase PWM rectifier charges the battery. Also in inverter mode, three-phase PWM rectifier transfers the power to the grid. Therefore three-phase PWM rectifier achieves electric vehicle V2G mode.

II. PRINCIPLE OF PWM RECTIFIER-INVERTER The following Fig. 1 is main circuit of a two-level voltage

This Paper was supported by the National Science Foundation of China, Project no (51077122)

three-phase PWM rectifier, which is composed of three phase inductance, three-phase IGBT bridge, the capacitor, and the battery load.

Fig. 1. Three-phase PWM rectifier

When the input three-phase voltage is balanced, three phase PWM rectifier is equivalent to single phase circuit. In this Fig. 2, Ea is the grid potential, L is power inductor, and the equivalent resistor R is resistance of source plus with the resistance of inductor. Va is the equivalent inverted DC voltage.

Fig. 2. Single-phase equivalent circuit

The following Fig. 3 and Fig. 4 are the operation modes of three-phase PWM rectifier, in which the three-phase PWM rectifier can operate in four quadrants. E is the grid potential vector, VL is the inductance voltage vector, and V is the voltage vector. Ignoring the equivalent resistance R, three-phase PWM rectifier can operate in four special modes.

Fig. 3. Pure inductor unity power factor rectifier

When it operates on A point, the PWM rectifier only absorbs inductive reactive power from power grid. When operates on B point, we can achieve unity power factor rectifier control.

Fig. 4. Pure capacitor unity power factor inverter

A Novel High Power Factor PWM Rectifier Inverter for Electric Vehicle Charging Station

Lei Shi, Haiping Xu, Dongxu Li, Zengquan Yuan Institute of Electrical Engineering, Chinese Academy of Sciences, China

E-mail: shilei@mail.iee.ac.cn

When it operates on C point, the PWM rectifier absorbs capacitive reactive power from power grid. When it operates on D point, we can achieve unity power factor active inverter control.

When the voltage vector V runs in the circular arcs AB, the three-phase PWM rectifier operates in rectifier mode and absorbs active power and inductive reactive power from grid. When the voltage vector V runs in the circular arcs BC, the three-phase PWM rectifier operates in rectifier mode and absorbs active power and capacitive reactive power from grid. When the voltage vector V runs in the circular arcs CD, the three-phase PWM rectifier operates in active inverter mode. Hence the gird absorbs power from DC load. When the voltage vector V runs in the circular arcs DA, the three-phase PWM rectifier operates in active inverter mode. Hence the gird absorbs active power and inductive reactive power from DC load.

III. DIRECT CURRENT CONTROL STRATEGY Phase and amplitude control which generates voltage

modulation signal based on the steady-state voltage vector is the first proposed control strategy of PWM rectifier-inverter. Since the control of current loop is not involved, the control strategy is based on relationship of system in steady-state. Thus, the system does not have a good current regulation and a rapid dynamic response and the control of system rely on the parameters of system.

PWM rectifier-inverter with direct current control[1] [3] [4] can get a good current regulation and a good current tracking speed because of the introduction of the current loop control.

Fig. 5. DQ coordinate system

The Fig. 5 is the Rotating coordinate system. Direction of d axes coincides with composite vector of three-phase voltage and rotating coordinate system rotates synchronously with composite vector of three-phase voltage in angular speed . q-axes leads d-axes in 90 degreed. Three-phase voltage and three-phase current can transform into variables of rotating coordinate system according to the PARK transformation and CLARK transformation. Expression of PARK transformation is shown below.

ID Id cos Iq sin IQ Id sin Iq cos (1) is the angle difference of rotating coordinate and static

coordinate. Variables of d-axes and q-axes are direct current components when the input three-phase voltage is balanced. D-axes is the active power axes of rotating coordinate system. Differential equation of current in d axes and q axes is given below according to the d-q coordinate transform module.

L e Ri V LiL e Ri V Li

(2)

Hence control of system current closed loop is designed, and the control module is shown below.

V K K S i i e LiV K K S i i e Li

(3)

Coupling current in d-axes and q-axes can be eliminated by the method of coordinate transform and feed forward decoupling control. Thus, the direct control can achieve decoupling control of active and positive power of grid voltage.

Frame of control strategy is shown in Fig. 6. The outer is voltage loop control which is to control the output of DC voltage. The outer voltage loop output is the Q axis current reference, and the positive Q axis current reference means the power flow is from the grid to load, meanwhile the negative Q axis current reference means the power flow is from the load to grid. The inner current loop regulates the DQ current by PI controller to achieve the unit power factor.

LL

Fig. 6. Direct current control

IV. SVPWM OF PWM RECTIFIER-INVERTER The fundamental line-to-line output voltage generated by

SVPWM is 1.15 times higher than SPWM. Space vector of voltage generated by SVPWM track the reference space vector generated by current regulator in rotating d-q coordinate system. Three phase space vector contains six nonzero vectors and two zero vectors. The objective of space vector PWM technique is to approximate the reference voltage vector by a combination of the eight switching patterns. The Fig. 7 is the explanation of SVPWM.

Six vectors divide the complex plane to six sectors and any voltage vector reference in the sector can be approximated by the two fundamental vectors in the sector.

Fig. 7. SVPWM

Symmetric space vector PWM waveforms are shown in Fig. 8. Sap Sbp Scp are the waveforms of upper switches of PWM rectifier. To reduce switch loss, the zero vectors should

be chosen appropriately.

Fig. 8. SVPWM wave form

V. SYSTEM DESIGN & CALCULATION The main circuit of the 10kW prototype of PWM rectifier

consists of three-phase inductances, IGBT Rectifier Bridge, DC capacitor, and resistance load. The IGBT Rectifier Bridge used here is 1200V/100A IPM module from MITSUBISHI, which can protect over current, over voltage and over heat. The current LEM sample the currents in phase A and B, and the voltage LEM sample the input line voltage Uab and the bus bar voltage Udc. The sampling frequency and the switching frequency are 10 kHz. The PWM wave is generated according to the SVPWM.

The value of the inductance in the alternate current circuit is relative to the static operation point, the current responses, and the amplitude of the harmonic currents. The rapid current response requires a relatively high value of di/dt, but a lower value is needed in order to limit the amplitude of the harmonic currents. The minimum value of the inductance to limit the harmonic currents meets the requirement below:

L 2Vdc3EmEmTs2VdcImax (4) Vdc stands for direct current voltage, and Em is the

voltage peak value in the power grid. Imax is the maxim value for the current pulse, 10% of the currents peak value. Ts is switching frequency.

The maxim value of the inductance for rapid tracking the current zero point meets the requirement as follows:

L VI (5) Within this formula, is the angular frequency of the

power grid. Im is 1.5 times as high as the peak value of the current in the grid side when the output power is normal rated.

Hence L=7mH. The value of the DC capacitor is relative to the maximum

voltage increase from rectifier mode to inverter mode, the DC voltage responses, and the amplitude of the voltage harmonic. If the PWM rectifier changes from rectifier mode to inverter mode, the DC capacitor increases rapidly. In the time t, the DC capacitor voltage changes from the diode rectifier voltage to reference voltage. Hence the maxim DC capacitor is derived.

C RDC

VI RDCVI RDC

(6)

In the formula, V=1.25Uab Uab is line voltage RMS

value. The minimum value of the DC capacitor is relative to

the voltage fluctuation When the PWM rectifier switch rectifier mode to inverter mode. The energy in the DC capacitor is W and the maximum voltage fluctuation is V. C WV V (7)

V 10%V P=10kW I 0.9I V 600V If the PWM rectifier changes from rectifier mode to

inverter mode, the rectifier output rated power during 20 sample periods.

Hence 555uF C 1244 C=1200uF. TMS320 F2812 DSP is chosen as the control core of VSR

and MAX502 is chosen as DA chip. The control program is designed in C language and control flow-process diagram is shown in Fig9. A main program and an interrupt program are contained in the control program.

After the system is initialized, the cycle program is run for waiting for the timer1 interrupt. System run the timer1 interrupt program every 100us and the interrupt program flow-process diagram is shown in Fig. 9. Interrupt program contains AD sample, system safe model, detect of zero crossing of grid voltage, detect of line voltage synchronous angle, d-q transformation, voltage and current regulation, and calculation of switching time of SVPWM. After calculating the switching time of the switches, the program exit the interrupt program, and return to the cycle program.

Fig. 9. Timer interrupt program

VI. SIMULATION RESULTS Three-phase voltage-source PWM rectifier is simulated in

the Saber environment. Simulation parameter settings are the followings: inductor 7mH, resistor 0.1ohm, grid voltage 220V 50Hz, output capacitor 600uF. Power devices are ideal switches.

In the Open-loop mode, Simulation parameter settings are the followings: grid voltage 28V, the 82V battery. The Fig. 10 is three-phase voltage waveforms and current waveforms in

the open-loop rectifier mode. The modulation wave lags in phase of the corresponding grid 30 degrees. SPWM modulation is 1.From top to bottom; the figure10 is the phase A phase B phase C voltage waveforms and current waveforms. Simulation results show that in rectifier mode the power factor is 1.

Fig. 10. Three-phase grid voltage and current in rectifier mode

The Fig. 11 is three-phase voltage and current waveforms in the open-loop inverter mode. The grid lags in phase of the corresponding modulation wave 30 degrees. SPWM modulation is 1. From top to bottom, the figure11 is the phase A phases B phase C voltage waveforms and current waveforms. Simulation results show that in inverter mode the power factor is 1.

Fig. 11. Three-phase grid voltage and current in inverter mode

In the Closed-loop mode, Simulation parameter settings are the followings: grid voltage 220V 50Hz and the 700V battery. In the current loop DQ coordinate transformation is used to control Id and Iq. In the voltage loop, SPWM modulation is calculated. From top to bottom, the Fig. 12 is the phase A phase B phase C voltage waveforms and current waveforms in the close-loop mode. Simulation results show that in rectifier mode the power factor is 1.

Fig. 12. Three-phase grid voltage and current in rectifier mode

From top to bottom, the Fig. 13 is the phase A phase B phase C voltage waveforms and current waveforms in the close-loop mode. Simulation results show that in inverter mode the power factor is 1.

Fig. 13. Three-phase grid voltage and current in inverter mode

VII. EXPERIMENT RESULTS The Fig. 14 is three-phase SVPWM waveform and CH1

CH2 CH3 is phase A phase B phase C SVPWM respectively. Experimental waveforms show that the three-phase SVPWM are correct.

Fig. 14. Three-phase SVPWM

The Fig. 15 is line voltage Uab zero crossing detection waveform.CH3 is the line voltage Uab (100V/div), CH1 is the line voltage Uab sample, and CH2 is zero crossing detection. Experimental waveforms show that zero crossing detection synchronize line voltage.

Fig. 15. Line voltage zero crossing detection

The Fig. 16 is line voltage Uab synchronization waveform. CH1 is the line voltage Uab (25V/div), and CH3 is the phase voltage UA phase angle. Experimental waveforms show that the line voltage Uab lead phase voltage UA phase angle 30 degrees.

Fig. 16. Line voltage synchronization

The current loop experiment is done under different line voltage and phase current. The experimental parameters are: Peak line voltage Uab 140V, current IA RMS 6.92A and 10.3A.The experimental results with Peak line voltage Uab 140V and current IA RMS 6.92A are shown in Fig. 17. CH1 is the line voltage Uab (100V/div), and CH2 is the phase A current IA (5A/div), CH3 is the phase angle of phase A voltage by DA, CH4 is the direct-axis current ID. The line voltage Uab lead phase A current 30 degrees, thus the power factor is 1.

Fig. 17. Current loop experiment1

The experimental results with Peak line voltage Uab 140V and current IA RMS 10.3A are shown in Fig. 18. CH1 is the line voltage Uab (100V/div), and CH2 is the phase A current IA (10A/div). The line voltage Uab lead phase A current 30 degrees. Hence the three-phase PWM rectifier operates in rectifier mode and only absorbs active power from grid. Thus the power factor is 1 under different phase current.

Fig. 18. Current loop experiment2

3kW load rectifier mode experimental waveforms are

shown in Fig. 19. CH1 is the line voltage Uab (250V/div), and CH2 is the phase A current IA (20A/div), CH3 is DC current IDC (10A/div), and CH4 is the Phase C IPM Drain Source Voltage Vds (250V/div). Peak line voltage Uab is 260V, current IA RMS is 11.3A. The load current is DC 7.91A and the load voltage is 404V, hence the PWM rectifier transfer 3196W to the load. The line voltage Uab lead phase A current IA 30 degrees, thus the power factor is 1.

Fig. 19. 3kW load rectifier mode

The above experimental waveforms show that PWM rectifier implements the grid current high sinusoidal. Also it can reach unit power factor under different line voltage and phase current. At the same time, the PWM rectifier only transfer active power to the load. By the power analyzer, power factor can reach 1 and the grid current THD is less than 5%.

VIII. CONCLUSION With the development and popularization of Electric

Vehicle, charging station is essential to large-scale commercial and popular use. High Power Factor PWM Rectifier-Inverter technology is the core technology of electric vehicle charging system.

The PWM rectifier-inverter with direct current control can get a good current regulation and tracking speed because of the introduction of the current loop control. The outer voltage loop output is the Q axis current reference to control the output voltage. The inner current loop regulates the DQ current by PI controller to achieve the unit power factor.

The fundamental line-to-line output voltage generated by SVPWM is 1.15 times higher than SPWM. To reduce switching loss, the zero vectors should be chosen appropriately.

The prototype of three-phase PWM rectifier is developed. Simulation and experimental results show that the high power factor PWM rectifier-inverter can achieve unity power factor and bi-directional energy transmission. Grid current is sinusoidal and THD is less than 5%. At the same time, the PWM rectifier only transfer active power to the load. Thus the PWM rectifier-inverter can be widely used in the Electric Vehicle charging station.

REFERENCES [1] Zhang Chun-Wei, Zhang Xing. PWM Rectifier and Control [M]. Beijing

China Machine Press, 2003. [2] Boon-Teck Ooi, Xiao Wang. Voltage angle lock loop control of the

boost type PWM converter for HVDC application [J].IEEE Transactions on Power Delivery,1990,5 (2):229-235.

[3] M.P.Kazmierkowski, Current control techniques for three-phase voltage-source PWM converters: A Survey, IEEE Trans.on Industrial Electronics, Vol.45, No.5, October 1998, pp.691-703.

[4] J.W.Dixon,Characteristics of a controlled-current PWM rectifier-inverter link,IEEETrans.on Industry Applications, 1987, IA-23,pp.1022-1028.

[5] E.Wernekinck,A.Kawamura,and R.Hoft,A high frequency ac/dc converter with unity power factor and minimum harmonic distortion,in Conf.Rec.IEEE-PESC, 1987, pp.264-270.

[6] T.Rashid,D.Holliday,and D.A.Grant,Effect of DC link capacitance on the transient response of a PWM AC-DC converter,IEE Conf.Power Electronics andVariable Speed DrivesNo.429,1996.

[7] D.C.Lee,G.M.Lee,and K.D.Lee,DC-bus voltage control of three-phase AC DC PWM converters using feedback linearization,IEEE Trans.on IndustryApplications,Vol.36,No.3,May/June 200.

[8] D.T.Ngo,"Low frequency characterization of PWM converters,IEEE-PESC, 1983, pp.377-388.

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