Photovoltaic Electric Vehicle Charging System with the Function of

Active Power Filter

Quan Liua, Xiang-ning Xiao, Zheng Chen

North China Electric Power University, Beijing, China

aleon-liuq@hotmail.com

Keywords: electric vehicle; grid-connected photovoltaic generation; active power filter; power

quality

Abstract. According to power capacity shortage and harmonic pollution caused by the development

of electric vehicles (EV), a photovoltaic (PV) charging system with the function of active power

filter (APF) is designed. The system could provide charging power and harmonic compensation for

electric vehicle charging machines at the same time. When sunlight is insufficient the PV charging

system could continue to work in APF mode. In this paper, detailed analyses of system structure

and control algorithms are given. Finally, the proposed system is simulated in PSCAD/EMTDC,

and the simulation results validate the correctness and feasibility.

Introduction

As a new generation of transport devices, electric vehicles have incomparable advantages in

energy saving and environment protection. However, the huge demand for charging power cannot

be ignored while electric vehicles develop into a certain large scale. Power generation capacity need

to increase to meet the charging requirements. Also, as non-linear devices EV charging machines

will produce harmonic current and that would reduce the power quality of power system [1].

Grid-connected photovoltaic power generation technology is maturing. Construction period of

photovoltaic power generation system is short, and the system can be flexibly designed according to

the electric load capacity requirement. There has been lots of demonstration project about electric

vehicle charging stations integrated with photovoltaic power generation system around the world

[2]. APF can suppress the harmonic current produced by EV charging machines. However, APF

development is facing the obstacles of high-cost and single function.

If unified control strategy could be applied to integrate PV charging system with APF, charging

power supply and harmonics suppression could be realized at the same time and full advantages of

the two devices could be taken to reduce construction costs and improve equipment utilization.

According to the demand of charging power capacity and the harmonic pollution of charging

machine, a grid-connected photovoltaic power system with the function of active power filter is

designed. The system can provide charging power and harmonic current compensation for electric

vehicle chargers. The system can continue to work as an APF when sunlight is insufficient. In this

paper, a detailed analysis of the structure of the system and control algorithms was given. The

system is simulated in PSCAD/EMTDC at last and the results validate the correctness and

feasibility.

Structure of proposed system

Proposed system mainly consists of three parts: power grid, PV generation system, and EV

charging machine. The simplified topology of proposed system is shown in figure 1:

Advanced Materials Research Vols. 724-725 (2013) pp 1459-1464Online available since 2013/Aug/16 at www.scientific.net© (2013) Trans Tech Publications, Switzerlanddoi:10.4028/www.scientific.net/AMR.724-725.1459

All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP,www.ttp.net. (ID: 130.207.50.37, Georgia Tech Library, Atlanta, USA-13/11/14,15:48:58)

EV Charging Machine. General structure of EV charging machine is consist of two parts: diode

rectifier and high-frequency DC-DC converter. In this paper, a nonlinear resistor RC is used as an

approximate equivalent input impedance of high-frequency DC-DC converter. The RC equation

could be expressed as:

2 2 2

0 0 0

B B B BC

U U U UR

I P P U I

η η= = = == = = == = = == = = =

.

(1)

η is EV machine charging efficiency, P0 is charging power, and UB is the DC side voltage of EV

charging machine. The formula (1) shows that the nonlinear resistor RC changes with charging

power P0. And empirical formula of lead-acid battery’s charging power is taken in this paper [3]:

0.048

0max

0 0.0205( /60 150)

0max

0.79 ( / 60) 0s<t 9000s( )

9000 <t 16200st

P tP t

P e s− −

≤=

≤ .

(2)

Harmonic Current Analysis of EV Charging Machine. Harmonic currents produced by EV

charging machines mainly come from the diode rectifier. Diode rectifier mainly produces harmonic

current with order of 6k±1(k=1, 2, 3, …). Especially the content of 5th, 7th harmonics is the

highest and harmonic current’s content and amplitude decrease with the harmonic order increase.

The harmonic current would affect the power quality of electric customers connect into the same

point of common coupling. The normal operation of the charging station equipment would be

affected, and even more it may cause burnout fault or protection misoperation of transformers,

cables, compensation capacitors, electronic measurement and control devices, et al [4]. Therefore,

harmonic current suppression devices should be installed in EV charging stations.

Unified Control of PV Generation and APF

Feasibility Analysis. To satisfy both the requirements for EV charging power and harmonic

current suppression, a PV-APF grid-connected generation system is designed.

DC voltage control is one of the key technologies of APF, the stability of DC voltage is the

critical requirement of reactive and harmonic current compensation. While DC voltage is lower than

set value, APF would absorb active power from power grid to pump DC voltage; While DC voltage

1460 Applied Energy Technology

is higher than set value, APF would inject active power into power grid to reduce DC voltage. It

means that APF could inject active power into power grid through properly control strategy. This is

the theoretical basis of unified control of PV generation and APF [5].

Control Algorithm of Proposed System. Connect PV array into the DC side of APF, control

DC side voltage at the maximum power point of PV array through MPPT technology which could

form the active fundamental current command. And then synthetize the active fundamental current

with the harmonic and reactive compensation current extracted from AC charging current to acquire

output current command of PV system. Finally, control PV system according to the output current

command with appropriate strategy. The harmonic current compensation and grid connected PV

generation would realize synchronously.

1) Extraction of Harmonics

The ability to quickly and accurately detect the harmonic current decision system functions.

Harmonic current detection generally do not need to decomposition of each harmonic component,

and only need to detect the total harmonic distortion of current in addition to the fundamental active

current or positive sequence component of fundamental active current). There are many existing

harmonic current detection method. Small change by the power frequency harmonic detection

method based on instantaneous reactive power theory, a simple circuit, short delay, real-time

application wide harmonic detection method [6]. Based on instantaneous reactive power theory of

harmonic current detection circuit shown in Figure 2

Figure1. Algorithm of Harmonic Current Extraction

In figure 2, PLL (Phase Locked Loop) module is used in real-time tracking of grid voltage to

obtain the same phase signal with the grid voltage and ensure the current detection accuracy; C32 is

the coordinate transformation matrix of abc coordinate system to αβ coordinate system; Cpq is the

coordinate transformation matrix of αβ coordinate system to dq rotating coordinate system;

C32-1

and Cpq-1

are the inverse transformation matrixes respectively corresponding to C32 and Cpq. The

expressions of C32 and Cpq are shown as follows:

32

1 11

2 2 2

3 3 30

2 2

C

− − =

− ，

sin cos

cos sinpq

t tC

t t

ω ωω ω

− = − −

(3)

pqC

1

pqC− 1

32C−

iβ−

−

−

+

+

+

PLL

0

LPF

cos tωsin tω

*iαiα pi*

piai

bi

ci*iβ

1ai

1bi

1ci*

qi

ahi

bhi

chi

au

Advanced Materials Research Vols. 724-725 1461

2) Reference Current

Algorithm of 3-phase fundamental active reference current is shown in figure 3.

Figure2. Algorithm of Fundamental Current

In figure 3, udc_ref is the maximum power point of PV array calculated by MPPT module, udc is

the real-time voltage of the DC side in PV-APF system.

Add harmonic compensation current with grid-connected active current, the reference current of

PV-APF system is shown as follows:

ia_out=iah+iapv; ib_out=ibh+ibpv; ic_out=ich+icpv

（4） In formula (4), iah/ ibh/ ich are harmonic current extracted from charging machine, and iapv/ ibpv /

icpv is PV generation reference current.

Simulation Results

The proposed system is simulated in PSCAD/EMTDC. Simulation results reveal that: 1) EV

charging power is all or part from PV generation; 2) Harmonic current produced by EV charging

machine is well suppressed by PV-APF system.

The major simulation parameters are shown as follows:

1) Maximum power of PV generation is 60kW, and the capacitance of DC side is 6000uF;

2) Phase to phase voltage of three-phase grid is 380V;

3) The filter inductor of PV converter AC side is 6mH, and filter capacitor 10uF;

4) The maximum charging power of electric vehicle is 15kW.

Case 1, remove PV-APF system, charging power is supplied by grid only. The A-phase current’s

waveform and Fast Fourier Transform (FFT) analysis are shown in figure 4. Total harmonic

distortion (THD) of A-phase current is 32%, the content of 5th harmonic current is 20.25%, the

content of 7th harmonic current is 5.63%, and reactive power of grid is 3.7kvar.

Figure3. Simulation results without PV-APF System

1

pqC− 1

32C−

−+

dcu

_dc refu *

pviapv

i

bpvi

cpvi

PLL

MPPT PI

0

dcu

dci

cos tωsin tωau

1462 Applied Energy Technology

Case 2, PV-APF system provides charging power and harmonics current compensation

synchronously. For comparative analysis, switch on PV system after 0.6s. The A-phase current’s

waveform and FFT analysis are shown in figure 5. THD of A-phase current is 4.2%, the content of

5th harmonic current is 0.33%, and the content of 7th harmonic current is 0.18%. Also, remaining

active power 45.5kW generated by PV-APF system is injected into the grid, and power factor in

PCC is 0.999. Simulation results show that the system satisfies the designed requirements.

Figure4. Simulation Results with PV-APF System

Case 3, PV array stop generating and PV-APF system works only in APF mode. The A-phase

current’s waveform and FFT analysis are shown in figure 6. THD of A-phase current is 7.5%, the

content of 5th harmonic current is 2.03%, the content of 7th harmonic current is 0.87%, and the

power factor in PCC is 0.999.

Figure5. Simulation Results with PV-APF System Work in APF Mode

Output current of PV system

Grid current with PV system Grid current without PV system

Grid voltage

Compensating current

Grid-connected current

Advanced Materials Research Vols. 724-725 1463

Conclusion

To resolve the energy demand and harmonic current problems of EVs, a grid-connected

photovoltaic electric vehicle charging system with the function of APF is designed and simulated in

PSCAD / EMTDC. The simulation results reveal that the system could provide charging power for

electric vehicles and compensate harmonics current produced in charging process at the same time,

and the remaining active power converted from solar energy can be fed into the power grid. The

application of this system has important practical significance: (1) Using solar energy to charge

EVs, reducing fossil energy consumption and carbon emissions radically; (2) Unified control of PV

generation and APF could reduce the construction cost of EV charging system; (3) System could

keep working in the APF mode while PV array stop generating, this could improve equipment

utilization. In the future, the authors would build physical test platform based on this research.

References

[1] Hu Ze-chun, Song Yong-hua, Xu Zhi-wei, et.al, “Impacts and Utilization of Electric Vehicles

Integration Into Power Systems” [J], Proceedings of the CSEE, 2012, 32(04): 1-10 (in

Chinese).

[2] M. A. Abella，F. Chenlo, "Photovoltaic Charging Station for Electric Vehicles," In Proceedings

on 3rd World Conference on Photovoltaic Energy Conversion, May 11-18, 2003 Osaka, Japan,

pp. 2280-2283.

[3] Zhou Si-li, “Design and Simulation Research on EV Charging Stations with Photovoltaic

Power”[D], An Hui University, 2010.(in Chinese)

[4] J. Carlos Gómez, Medhat M. Morcos. "Impact of EV Battery Chargers on the Power Qualityof

Distribution Systems", Power Engineering Review, IEEE Volume: 22 , Issue: 10

[5] Xie Bin, Dai Ke, Zhang Shu-quan, et.al, “Optimization Control of DC Link Voltage for Shunt

Active Power Filter”[J], Proceedings of the CSEE, 2011,31(9):23-29 (in Chinese).

[6] Dionne M. Soto, Saritha Balathandayuthapani, Chris S. Edrington. "Mitigation of PHEV

Charging Impact on Transformers via a PV-APF Harmonic Compensation Technique:

Application to V2GIntegration", Vehicle Power and Propulsion Conference (VPPC), 2011

IEEE, pp:1-5

1464 Applied Energy Technology

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