Study On Digital Power Factor Correction Based On Predictive Current Control

Power factor correction is an effective way to suppress current harmonics and reactive power. With more and more attention in recent years, it is mostly used in AC-DC switching power supply which becomes more intelligent and digital with high-speed, low-cost controller chips appear. In this background, APFC under the control of TMS320F2812 is researched in this issue. Compared with analog implementations, the bottleneck of digital control for power factor correction implementations is mainly due to this problem between calculating speed of DSP and limited switching frequency. The research motivation of this thesis is to explore new digital control strategies for power factor correction in order to achieve higher switching frequency with lower cost, lower calculation requirement and better performance than the convention PFC control methods.Firstly, this thesis describes the development, basic concepts and significance of power factor correction and introduces the basic topology, control method and parameters selection.Then the model of single-phase PFC based on average current control is built and PI controller is designed to keep the system in good performance. Predictive current control strategy, by which duty in the current cycle is generated in last cycle, is proposed to solve the problem between the switch frequency and DSP processing speed. The characteristics of two strategies are compared and analyzed by simulation in Matlab.Finally, APFC system implementation based on the control of TMS320F2812 is described in detail, which contains the sampling circuit, driver circuit, and assistant power supply. Block diagram of main program and interrupt program are given.A non-fixed point sampling method is designed to avoid switching noise interference produced when the switch is on or off.This paper design an APFC system based on improved predictive control, with a switching frequency at 100 kHz. From the experimental results, output voltage is stability, and input current waveform which is nearly sinusoidal is in phase with input voltage. The proposed predictive PFC control strategy can achieve unity power factor even if the input voltage is distorted.