Analysis of an Active Power Factor Correction Circuit with Indirect Input Current Control

Abstract: A simple and practical active power factor correction circuit with indirect input current control is analyzed, and simulation and experimental results are given.

Keywords: active power factor correction; total harmonic distortion; power factor; simulation

Active Power Factor Corrector with Indirect Control Method

Xu Yun-zhong,Xiao Rui

Abstract:A simple and effective active power factor corrector with the indirect control method is analyzed.The simulation and experiment results is given.

Keywords:Active power factor correction;Total harmonic distortion;Power factor;Simulation

1 Introduction

There are three commonly used active power factor correction (APFC) methods, namely, current peak control method, current hysteresis control method and average current control method [1]. All three control methods require the detection of the output voltage of the rectifier bridge and are active power factor correction methods that directly control the input current. They can correct the input power factor of the circuit to above 0.99, but the control principle is relatively complex, the amount of detection required is large, the detection circuit is relatively complex, and the control circuit cost is relatively high.

This article analyzes an active power factor correction circuit with indirect input current control. It only needs to detect the inductor current. The control principle and control circuit are relatively simple and practical, and the cost of the control circuit is very low.

2 Principle Analysis of Active Power Factor Correction Method with Direct Input Current Control

FIG1 shows a commonly used Boost active power factor correction schematic.

Figure 1 Schematic diagram of commonly used APFC

After comparing the output voltage Uo of the main circuit with the reference voltage Ur, it is input to the voltage error amplifier VA. The output voltage Udcc of the rectifier bridge and the output voltage signal of VA are added to the input end of the multiplier M. The output of the multiplier M is used as the reference signal for current feedback control. After comparing it with the switching current is, it is added to the PWM control part through the current error amplifier CA to control the on and off of the switch tube S, so that the waveform of the input current (i.e., the inductor current) iL is consistent with the waveform of the rectifier bridge output voltage Udc, thereby greatly reducing the current harmonics and improving the input power factor of the circuit.

3 Principle Analysis of Active Power Factor Correction Method with Indirect Input Current Control

The active power factor correction method with indirect input current control can detect any of the following three quantities: inductor current, switch tube current,

Figure 2 is a control principle diagram for detecting inductor current.

Figure 2 Schematic diagram of input current indirect control APFC

The output voltage Udc of the rectifier bridge is the input voltage of the subsequent Boost circuit. The on-duty ratio of the switch tube S is set to Don, then

Uo=Udc/(1－Don) （1）

So there is

Udc/iL=(1－Don)Uo/iL (2)

Assuming the circuit input power factor is 1, we have

Udc/iL=Rin (3)

From equations (2) and (3), we can derive

Don=1－(Rin/Uo)iL （4）

Assume Rin/Uo=k (k is a constant), then

Don=1－kiL （5）

From the above derivation, it can be seen that by controlling the on-duty cycle Don of the switch tube according to equation (5), the circuit input power factor can theoretically be made 1.

4 Simulation and Experimental Results

According to the schematic diagram in Figure 2, set the following experimental parameters:

Ui=311sin(100πt)V (i.e. AC input), L=1mH, Co=940μF (two 470μFs in parallel), Cin=0.1μF, R=200Ω, switching frequency fs=40kHz, switch tube S uses IRFP460, diode D uses DSEI30-10A, control chip uses TL494, inductor current uses Hall detection (the ratio of current to voltage is 1:0.3), and the bandwidth of the low-pass filter formed by the inertia link is set to 1kHz.

In the MatlabSimulink environment, the above actual system is modeled and simulated, and the simulation results are shown in Figure 3.

Figure 3 Input voltage and input current simulation results

The total harmonic distortion rate THD of the input current in the above simulation is 13.41%, and the input power factor PF is 0.994.

The measured input voltage and input current waveforms of the circuit are shown in Figure 4.

Figure 4 Experimental measured input voltage and input current waveforms (voltage 100 V/grid, current 5 A/grid)

The total harmonic distortion rate of input voltage THD=10.87%, the total harmonic distortion rate of input current THD=14.13%, and the circuit input power factor PF=0.992.

It is worth pointing out that the cost of the control circuit composed of TL494 and its peripheral circuits is much lower than the cost of the commonly used control circuit composed of UC3854 and its peripheral circuits.

5 Conclusion

Both simulation and experimental results show that the active power factor correction method with indirect input current control can make the input power factor of the circuit reach above 0.99, and the control principle is simple and practical, and the control circuit cost is very low.