Control of Unit Power Factor PWM Rectifier

doi:10.4236/epe.2013.54B023

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Energy and Power Engineering, 2013, 5, 121-124

doi:10.4236/epe.2013.54B023 Published Online July 2013 (http://www.scirp.org/journal/epe)

Control of Unit Power Factor PWM Rectifier*

Meifang Xue, Mingzhi He

School of Electrical Engineering, Beijing Jiaotong University, Beijing, China

Email: [email protected]

Received March, 2013

ABSTRACT

To solve the problem of harmonic pollution to the power grid that caused by traditional diode rectifier and phase con-

trolled rectifier, the unit power factor PWM rectifier is designed. The topology structure of the rectifier circuit is intro-

duced and the double closed-loop control strategy in three-phase stationary coordinate system is analyzed. For the defi-

ciency of control strategy, the control strategy in two-phase synchronous rotating coordinate system is proposed. This

makes the independent control of active current and reactive current to be realized. The simulation model of the PWM

rectifier is built and the effectiveness of the control method proposed in this paper is verified by simulation.

Keywords: Control; PWM Rectifier; Unit Power Factor; d, q Coordinates

1. Introduction

Unity power factor PWM rectifier has the advantages of

high power factor, low harmonic content of grid side

current, energy bidirectional transmission etc, is widely

used in AC drive, reactive power compensation, active

power filter, unified power flow control, as well as unin-

terruptible power supply, etc[1]. This paper introduces

the topology of three-phase PWM rectifier, and describes

the control method of the rectifier in three-phase static

coordinate system. On the basis of the analysis of the

advantages and disadvantages of this control method, the

control method in two-phase synchronous rotating coor-

dinate system is put forward. Then the mathematical

model of three-phase PWM rectifier in d, q coordinates is

established and the single control of active current and

relative current is realized.

2. The Control Method of Three-phase

Voltage Source PWM Rectifier in

Three-phase Static Coordinate System

Figure 1 shows the topology of three-phase voltage source

PWM rectifier, abc

is three-phase voltage source, C is

the dc side filtering capacity and

eee

R is the load.

In order to realize the control of input current and

output voltage, the traditional method is controlling the

three-phase input current directly. The control of the in-

put current is also the control of the flow of energy, thus

the control of the output voltage can be realized. The

control method of PWM rectifier in the three-phase sta-

tionary coordinate system is shown in Figure 2.

In this control method, the outer loop controls the DC

voltage. The difference value of the command signal and

actual signal of DC side voltage is imported to PI regu-

lator. The output value of PI regulator is DC current sig-

nal m

, m

is proportional to the amplitude of AC input

current. So the command signal of three-phase AC cur-

rent a*

、*

can be obtained by separately

multiplying m

by sinusoidal signal whose phase is the

same as three-phase voltage. The difference value of

command current and actual current is imported to PI

regulator, and the sinusoidal modulation wave can be

deserved. By comparing the sinusoidal modulation wave

with carrier wave, the PWM wave which can control the

switch can be deserved.

Figure 1. The topology of three-phase voltage source PWM

rectifier.

sin t



sin( )







sin( )







Figure 2. The control method of PWM rectifier in three-

phase stationary coordinate system.

*Project Supported by National Natural Science Foundation of China

(51207008)

M. F. XUE, M. Z. HE

122

This control method is simple, but the command cur-

rent in control system is a varying sine time-varying sig-

nal which has a certain frequency, amplitude and phase

angle. The effect of steady-state performance is not de-

sirable, and the independent control of the active current

and the reactive current can’t be achieved[3].

3. The Control Method of Three-phase

Voltage Source PWM Rectifier in

Two-phase Synchronous Rotating

Coordinate System

In order to realize the non-static error control of three-

phase current and independent control of active current

and reactive current, the control method of unit power

factor PWM Rectifier in two-phase synchronous rotating

coordinate system will be introduced.

Figure 3 shows the control method of unity power

factor PWM rectifier in dq rotating coordinate system.

Through coordinate transformation, three-phase station-

ary coordinate system (a, b, c), can be converted to syn-

chronous rotating (d, q) coordinate system that synchro-

nous rotate with the grid fundamental wave[2]. The

transformation matrix is:



sin120 sin120

sin

2/3 cos cos120 cos120





















(1)

The inverse transformation matrix is:





sin cos

2 / 3sin120cos120

sin120 cos120









 



















(2)

The most prominent advantage of this transformation

is the fundamental sinusoidal quantitative in (a, b, c) co-

ordinate system can be converted into a DC variable in (d,

Figure 3. The control method of PWM rectifier in dq rotat-

ing coordinate system.

q) Coordinate system. In this transformation, the d-axis

in two-phase synchronous rotating coordinate system rep-

resents the active component, and the q-axis represents

the reactive component. If we take the position of input

voltage vector as the positive direction of d-axis, and the

three-phase input voltage can be written as:





cos

cos 120

eU wt



















(3)

Through coordinate transformation the power supply

voltage in dq coordinate system can be written as:











 (4)

According to the instantaneous power theory, the in-

stantaneous active power p and reactive power q of the

system is:



dd qq

dq qd

peiei

qeiei













(5)

Because 0



, the equation (5) can be simplified as

pei

qei













(6)

If we don’t consider the fluctuations in grid voltage,

d is a fixed value. So the instantaneous active power p

and instantaneous reactive power q of PWM rectifier is

proportional to d and q. So that by controlling d

and q, the active and reactive power of PWM rectifier

can be controlled[4].

i ii

In three-phase PWM rectifier, the input instantaneous

value of active power in the DC side is dcdc , if the

loss of PWM rectifier is not considered, from equation

pui

(6), we can know that 3

dc dc

ui p . When the grid

voltage is a fixed value and the loss of rectifier is ignored,

the DC side voltage dc is proportional to d, so that

DC side voltage of PWM rectifier can be controlled by

the control of .

u i

The control method shown in Figure 3 also consists of

voltage outer loop and current inner loop. Introducing

DC feedback and the non-static error control of DC

voltage can be realized. Due to the DC voltage can be

controlled by the control of d, the output value of volt-

age outer loop of PI regulator is the reference value of

current inner loop, so that the active power of PWM

rectifier can be adjusted. The reference value of reactive

M. F. XUE, M. Z. HE 123

current is based on the reference value of reactive power,

so when , PWM rectifier operates on unit power

factor state.

i

In this control method, the PI regulator can realize non-

static error control. Compared with the control method in

three-phase static coordinate system, the steady state

performance is better. At the same time, the independent

control of active current and reactive current can be real-

ized[5].

4. The Simulink Results

MATLAB/SIMULINK is used to establish the simula-

tion model of PWM rectifier. Simulation parameters are

as follows: the voltage of power grid is 380 V/50Hz. the

inductance in AC side is 0.8 mH. The given value of DC

side capacitor voltage is 700 V. The resistance load is

3.72 Ω. Figure 4 shows the three-phase input current

wave and its FFT analysis of unit power factor PWM

rectifier under the control of three-phase static coordinate

system. Figure 5 shows the three-phase input current

0.30.320.34 0.36 0.380.4

-400

-300

-200

-100

100

200

300

400 ia ib ic

(a) Three-phase input current wave under the control of three-phase

static coordinate system

0200 400 6008001000

0.2

0.4

0.6

Harmonic order

Fundamental (50Hz) = 284.2 , THD= 1.41%

Mag (% of Fundamental)

(b) FFT analysis of input current under the control of three-phase static

coordinate system

Figure 4. Three-phase input current wave and its FFT

analysis of unit power factor PWM rectifier under the con-

trol of three-phase static coordinate system.

0.30.32 0.340.36 0.380.4

-400

-300

-200

-100

100

200

300

400 ib icia

(a) Three-phase input current wave under the control of two-phase

synchronous rotating coordinate system

0200400 6008001000

0.2

0.4

0.6

Harm onic order

Fundamental (50Hz) = 284.5 , THD= 1.08%

Mag (% of Fundamental)

(b) FFT analysis of input current under the control of two-phase syn-

chronous rotating coordinate system

Figure 5. Three-phase input current wave and its FFT

analysis of unit power factor PWM rectifier under the con-

trol of two-phase synchronous rotating coordinate system.

0.20.250.30.350.4

690

695

700

705

710

Figure 6. DC side capacitor voltage in two-phase synchro-

nous rotating coordinate system.

wave and its FFT analysis of unit power factor PWM

rectifier under the control of two-phase synchronous ro-

tating coordinate system. Figure 6 shows the control

effect of DC side capacitor voltage in two-phase syn-

chronous rotating coordinate system. It can be seen from

the FFT analysis of current waveform that control in two-

phase synchronous rotating coordinate system has a bet-

ter steady state response than control in three-phase static

M. F. XUE, M. Z. HE

124

coordinate system.

5. Conclusions

This paper respectively introduced the control strategy of

unit power factor PWM rectifier in three-phase static

coordinate system and two-phase rotating coordinate

system, and the two control method are compared. The-

oretical analysis and simulation results show that the

control in synchronous rotating coordinate system has

better steady state performance.

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