The Research Of Three-Phase Four-Wire Shunt Active Power Filter

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 fully-digital-controlled shunt active power filter based on DSP and FPGA for three-phase four-wire systems is studied and designed in this paper.The harmonic current detection is the key element for the shunt active power filter to keep a well dynamic performance. An ip-iq detection based on instantaneous reactive power theory is taken as the control strategy in this paper. It is still available when the source voltage becomes distorted and unbalanced. However, the traditional ip-iq detection is only fit for three-phase three-wire systems, so it is improved in this paper and extended to three-phase four-wire systems by separating zero-sequence current from the load current. A dynamic hysteresis-band current PWM control arithmetic is also designed to control the voltage of the DC bus, which keeps it steady effectively for the voltage of the neutral point of the DC bus.To realize the control arithmetic more accurately, a fully digital control system based on DSP and FPGA is established in this paper. Harmonic current detection and current PWM control are accomplished by DSP and FPGA separately, which exerts the advantage of each other. It can distill the compensation current reference accurately and fleetly, and is more flexible and reliable than the analog-digital control system.The compensation effect will be also influenced by the output filter of the power circuit for the shunt active power filter. Therefore, a LRC filter is designed and the harmonic of switch frequency is eliminated effectively.A simulation for the system is studied through Matlab, and a 1.5 kW three-phase four-wire shunt active power filter principle prototype is developed finally...