The Research Of Three-phase Four-wire Active Power Filter Based On DSP

The pollution of harmonics and reactive power in power grid becomes serious and endangers the power system and customers while power electronic devices and other nonlinear loads are applied widely. The study on shunt active power filter, which is a novel device compensating harmonics and reactive power current simultaneously, is the focus in the field of power quality control. In recent years, the issues of harmonics and loads unbalance in three-phase four-wire power grid are more and more serious, so a compensation of harmonics, reactive power and nonbalanced current simultaneously in three-phase four-wire power grid is studied in this paper.And an analog-digital controlled shunt active power filter based on DSP is designed in this paper.The harmonic current detection is the key element for the shunt active power filter to keep a well dynamic performance. The detecting method of harmonics and reactive currents in single-phase is applied in three-phase four-wire system ,so harmonic current detection and compensation of each phase can be performed separately but without affected by nonbalanced system . To control output of the PWM inverter, an improved hysteresis control strategy to control APF inverter is given. In order to guarantee the stability of capacity voltage on the DC side of inverter, a control strategy of the stability of capacity voltage on the DC side is given.In addition, this paper separately designs hardware realization method which is composed of the microprocessor units of control system, synchronization sampling signal generating,phase-locked Loop generating units,current detection circuit,DAC conversion unit and its hardware realization method, and driven and protection current ;According to the hardware scheme of control system,the software realization scheme is given ,which includes the design flow chart of harmonic separating algorithm, the main program and its interrupt service routine.Simulation and Experimental results verify the feasibility and validity of the proposed control circuit and control algorithm. And these experimental results give a good reference for true application.