research on the model of electric vehicle charging device based on pscad

7/21/2019 Research on the Model of Electric Vehicle Charging Device Based on PSCAD

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Energy and Power Engineering, 2013, 5, 1372-1376doi:10.4236/epe.2013.54B260 Published Online July 2013 (http://www.scirp.org/journal/epe)

Research on the Model of Electric Vehicle Charging Device

Based on PSCAD

Run-rong Fan, Tian-yuan Tan, Yun-peng Gao, Hui ChangSchool of Electrical Engineering, Wuhan University, Wuhan, China

Email: [email protected], [email protected], [email protected], [email protected]

Received May, 2013

ABSTRACT

As the energy and environment issues are becoming increasingly prominent, electric vehicles have become the mainnew energy vehicles of future development because of their advantage of environmental protection, clean and energyconservation. Electric vehicle charging station is a very important part of electric vehicle facilities, the development and

popularization of electric vehicles can't do with the construction of the charging station. The chargers in charging sta-tions are nonlinear equipment, and they will produce harmonic pollution, so it's of practical significance to do a researchon the chargers and their harmonic problems. By using power system simulation software PSCAD as the simulation andanalysis tool, this thesis focuses on electric vehicle charging device modeling and harmonic problem research.

Keywords: Electric Vehicles; Modeling; Harmonic Analysis; PSCAD Simulation

1. Introduction

The car makes a great contribution to the advance of

human civilization [1]. It makes human life more con-

venient and comfortable, but at the same it also brings to

the society inevitable consequences such as the waste of

resources and serious environmental pollution [2, 3]. In

order to reduce its dependence on traditional energy

sources and to protect the natural environment for human

survival, doing researches on new energy has become a

worldwide subject [4, 5]. As a representative of the new

energy vehicles, electric vehicles have obvious advantage

of environmentally-friendly, energy-saving and so on

compared to traditional gasoline cars [6].

The electric vehicle charging system is the basic sup-

porting systems of electric vehicles. [7]The charging

device’s research is of great significance to the promo-

tion and application of the electric car, and to its turningto industrial production.

This paper is based on the program of electric vehicle

charging device. Six pulse wave uncontrolled rectifica-

tion charger circuit was built in PSCAD so that it can

charge a storage battery. And it also calculated the

Nth-degree harmonics current and the distortion rate of

total current harmonic. It also analyzed the harmonics of

the car charging model. And compared it with the theo-

retical value, which proved correctness of the analysis. In

the end, it gives the prospects of the researches that need

to be done in this field.

2. The Design of Electric Vehicles’ ChargingDevice

The charging device system of electric vehicles is actu-

ally a DC power supply. To design such a power supply,

the charging models, the methods of charging and many

other factors should to be considered.

2.1. The Charging Model and Charging Methodof the Electric Vehicle

As for the electric vehicle charging programs, there are

three choices: models of conventional charging, fast

charging and mechanical charging [8]. The three charg-

ing modes have their own characteristics and scope of

application. Ac-cording to the characteristics and control

of the operational characteristics of the conventional pure

electric vehicles and the use of conventional battery

management strategy, usually conventional charging and

supplementary charging are taken. The supplementarycharging is still in the form of the conventional charging,

but the charging time is the hospitality gap. It can be re-

placed by the battery charging if necessary.

There are mainly three conventional charging methods

of the electric cars: constant current charging method,

constant voltage charging method and stage charging

method [9]. Of the three methods,, stage charging meth-

od can avoid large charging current at the beginning

phase of the constant voltage charging, it can also avoid

the phenomenon of overcharge at the later phase of the

constant current charging. Stage charging method is used

Copyright © 2013 SciRes. EPE



R.-R. FAN ET AL. 1373

on the power battery of the charger’s charging methods

and charging control strategy. So this paper takes stage

charging method to charge electric vehicles.

2.2. The Overall Design of the Electric Vehicle’s

Charging Device

The charging device system of electric vehicles is actu-

ally a DC power supply. And the design of the charging

system is in fact the design of a power supply. But the

power supply must be controlled by a certain algorithm

so that the output voltage and current are in line with the

curve of battery charging. The charging power supplies

that commonly used in industrial applications are the

following three types: linear power, SCR power supply

and switching power supply [10]. According to the

working principle and method of the switching power

supply, the block diagram of the charger designed in this

paper is shown in Figure 1.

3. The Modeling of the Charger and its Sim-ulation Analysis

According to the requirements of the electric vehicle

battery charging and the design requirements of the

charging device, in this paper we build a charging device

circuit in PSCAD, set the parameters of each device in

the circuit and then run the circuit, we obtained a portion

of the output voltage and current waveforms of the power

supply.

3.1. The Design of the Charging Device Circuit

The main circuit diagram of electric vehicle charging

device build in PSCAD is shown in Figure 2. This paper

mainly analyzes the charger’s output voltage and current.

For more convenient analysis, a simple resistive load is

given.

In order to simulate the charging system as real as

possible, we set the sys-tem input 10kv, and transformed

to 380V after △/Y transformer to supply power for the

charging system. The charging system rectifier links use

three-phase controlled rectifier diode, the three-phase

380V AC voltage becomes 514V DC voltage through athree-phase rectifier bridge rectifier and capacitor fil-

ter ,and turn to high-frequency pulse voltage after H-

bridge inverter, then we get the required adjustable DC

voltage and adjustable DC current after high-frequency

rectifier and filter.

Figure 1. Block diagram of the charger.

A

B

C

RLC

RLC

RLC

T T T

T T T

2

0

0

0

. 0

[ u

F

]

A

B

C

A

B

C380 [V]

#2#1

10.0 [kV]

1.0 [MVA]V

A

U1

T T

G1

T T

G2

T T

G2

T T

G1

#2

#3

#1

T

T

0.001 [H]

Uo

Io2

0

0

0

. 0

[ u

F

]

1

. 0

[ o

h

m

]

1 [mH]

Figure 2 The main circuit of the electric vehicle charging

device.

G1

G2

G1

G2

U1 U1

Ua Ua

Ia Ia

Uo Uo

Io Io

Figure 3. Drive control circuit and waveform analysis cir-

cuit.

The drive control circuit and the waveform analysis

circuit shown in Figure 3.

3.2. Simulation Analysis of the Charging Device

The waveforms of the output voltage and current can be

obtained through the simulation of the entire charging

device circuit, waveform diagram shown in Figure 4 (a)

and the unit is V. waveform diagram shown in Figure 4

(b) and the unit is A.

As can be seen from the output voltage and current

waveform, the charger model designed in this paper can

get a better DC power supply.

4. The Harmonic Analysis of Electric VehicleCharging Device Connected to the Grid

High power charger in charging stations is a kind of

highly non-linear electrical equipment. Sinusoidal volt-

age puts pressure on non-linear loads, the fundamental

current will be distorted and harmonic will be generated.

Especially in large charging stations, a large number of

charger works at the same time, harmonic currents gen-

erated will have great impact on power grid and other

electrical equipments. Therefore, in the construction of

charging stations, we need to consider the harmonic

problems.




R.-R. FAN ET AL.1374

4.1. The Design of the Equivalent Model of theCharger’s Harmonic Analysis

The working principle of the charging machine is the

input three-phase AC current rectified by rectifying cir-

cuit, after the filter circuit, providing the DC input forhigh frequency DC-DC power conversion circuit, the

output of the power conversion circuit after the output

filter circuit to charge rechargeable battery of vehicles,

charger block diagram shown in Figure 5.

At present, as for the charging method and chargingcontrol strategy of the charging machine’s battery, we

usually adopt a typical two-stage method. The first half isthe constant current but with limited pressure, the latterhalf is the constant pressure but with limited current.

Usually the conventional charging time of charging

machine is 4-6 hours. In this process, the output voltage

and current is changeable, but in the charging time of a

micro-element, we think the output current and the output voltage of the charging machine is constant, i.e.in a

(a)

(b)

Figure 4 (a) U o waveform graph; (b) I 0 waveform graph.

0I

0U

Figure 5. Block diagram of the charger.

micro element we can use a non-resistor R to approxi-

mate the input impedance of the high frequency power

conversion circuits, therefore we can use a nonlinear re-

sistance R in the entire process of charging to the equiv-

alent in place of the high-frequency power transform

circuit, the value of R calculated as:

2 2

1 1 1 1

1 1 o o

U U U U R

2

o I P P U

I (1)

In the formula,

1—the input voltage of the high frequency power

conversion circuit;

U

1 I —the input current of the high-frequency power

conversion circuit;

o—the output voltage of the high-frequency power

conversion circuit;

U

o I —the output current of the high-frequency power

conversion circuit;o—the output power of the high-frequency power

conversion circuit;

P

—The efficiency of power conversion modules.

The power conversion efficiency of the module is

generally more than 95%. In order to analysis the har-

monic, will be set as 95% directly. We use nonlinear

resistor R Instead of the charger power conversion unit

we can get the approximate equivalent model. According

to recorded data of the battery’s charging process, using

the curve fitting method, we can get the output power of

the charging machine:

0.048

omaxo 0.021 (t-150)

omax

0.79 t ,0 t 150te ,150 t 270

PPP

（） (2)

For example, the power of charger is 9kw, parameters

of the charger machine as follows, omax = 75V, omaxU I

= 120A, omax omax omaxP U I = 9kW, the charging time

t = 270 min.

For the 6-pulse uncontrolled rectifier bridge, output on

the DC-side BU = 2.34, 2U = 514.8V. Making use of

the relationship between R and the output power curve of

the charging machine, we can obtain:

2

o

BU R

P

(3)

In formula (3), is the charging machines’ effi-

ciency, BU is DC voltage of the rectifier bridge, o

substituted into the above equation, we can get a formula

about the equivalent impedance of the high frequency

power converter.

tP（）

The calculated R is a continuously changing non-linear

curve. the R-value change small before 150 minutes,

Structures approximate R model in PSCAD shown in

Figure 6, Among A = 1.1988, B = 0.021.

The value of R changing with time is shown in Figure

7.




R.-R. FAN ET AL. 1375

4.2. Harmonic Simulation Analysis

First, we should make three-phase uncontrolled rectifier

bridge; rectifier DC side filters inductor and capacitor in

PSCAD / EMTDC. Meanwhile, in order to analyze the

harmonic, we should also establish a non-controlled rec-tifier bridge consisting of charging machine simulation

topology; the circuit is shown in Figure 8.

The control loop circuit and waveform display loop

circuit is shown in Figure 9.

Simulation analysis of the circuit to obtain voltage of

the high-voltage input terminal and waveform of the

current. The waveform shown in Figure 10(a) and the

unit is Kv. The waveform shown in Figure 10(b) and the

unit is A.

TIME

R

150

AeBxMax

D

E

Figure 6. Model diagram of R.

Figure 7. R change with time when charging process.

A

B

C

RLC

RLC

RLC

T T T

T T T

V

A

2

0

0

0

. 0

[ u

F

]

1 [mH]

R

+

A

B

C

A

B

C380 [V]

#2#1

10.0 [kV]

1.0 [MVA]

Figure 8. Main circuit of charging simulation topology dia-

gram.

RTIME Ae

BxMaxD

E150

Ua Ua

Ia Ia

Figure 9. Control loop circuit and waveform display loopcircuit.

(a)

(b)

Figure 10. (a) U a waveform graphs; (b) I a waveform graphs.

As can be seen from Figure 10, the input terminal

voltage and current generated distortion, In order to get a

further analysis of the nature of the harmonic, we should

analyze its Fourier. The harmonic analysis of the circuit

is shown in Figure 11.

With the analysis of the circuit simulation, we can get

the current total distortion waveform as is shown in Fig-ure 12; the amplitude of the current total distortion is

6.7%.

The percentage of the each output harmonic wave is

shown in Figure 13.

With the simulation waveforms and the ratio chart, we

can get the higher quality harmonic: (k = 1, 2, 3 ...) har-

monic, and as for the higher harmonic content, the higher

the harmonic frequency, the smaller the amplitude. We

can also conduct harmonic suppression with the installa-

tion of filtering devices and reactive power compensation

device.




R.-R. FAN ET AL.


1376

Mag

Ph

dc

(31)

(31)

F F T

F = 50.0 [Hz]

Ia

HarmonicDistortion

Total

Individual

31

31

THDn

THDi

Figure 11. Harmonic analysis circuit.

Figure 12. Current total harmonic distortion waveform

graphs.

Figure 13. Each output harmonic wave proportion.

5. Conclusions

The use of electric vehicles’ charging problems must be

first considered, while the development and populariza-

tion of electric vehicles cannot be separated from theconstruction of charging stations. In the charging stations,

charging device will produce harmonics and inject har-

monics into the grid. Therefore, before the construction

and functioning of the charging stations, we must study

and solve the electric vehicle’s charging and harmonic

problems.

This paper used appropriate procedures and estab-

lished a simulation model to simulate the charging device

and then analyzed the harmonic impact which is proved

ffective. This paper built a battery model, and re-

searched its charging method. According to the different

waveform of the power supply to charge the battery, we

can use the battery charging model to charge the battery

using the DC current source first and then using the DC

voltage source.

This article analyzed the harmonic generation and impact in theory. It substituted the equivalent input imped-

ance of the charging machine of high frequency DC-DC

power conversion circuit with a nonlinear resistor and

built the model of charging device, and then proceeded to

the harmonic simulation analysis. Compared the har-

monic simulation results with the theoretical analysis of

the value, we can see the 5th,7th,11th,13th,17th,19th and

other harmonic (all odd harmonics) content is higher, and

for higher levels of harmonics, the higher the number, the

smaller the harmonic amplitude. So the result is consis-

tent with the theoretical analysis.

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