Research Of Harmonic Current Detection And Control Strategy In Active Power Filters

Electric energy is the indispensable to modem society. However, a large number of power electronic devices connected to power system in recent years greatly endanger the safe operation of power systems and other power consumers due to mass of harmonic current it generate now. Active power filter (APF) is the most effective equipment for harmonic suppression. Although researchers and institutes have been researched for some years, the performance of conventional design and control methods for active power filters is far from perfect.This paper presents analysis of conventional harmonic detection and control methods, and proposes a novel harmonic current detection and zero-steady-state-error control strategy. The new control strategy is based on synchronous reference frame (SRF) rotating at harmonic frequency. The n-th harmonic current is transformed to dc value in SRF rotating at harmonic frequency. This dc value can be regulated by PI controllers with no steady state error output. Other frequency of harmonic current is regulated in the same way. The sum of output of all harmonic current controllers is the last output of APF current controller. In this way, all harmonic current selected is suppressed in load current. Loads no longer inject selected harmonic current to power grids. The theoretical analysis has proved that the novel control strategy is effective for APF. Simulation results of Simulink show that harmonic distortion of selected harmonic current decreases to below0.3%and transient response time is less than10ms with the compensation of APF applying the novel control strategy.This paper also designed an APF prototype base on TMS320F28335DSP and EP2C8Q208FPGA, in order to test the performances of the novel harmonic current detection and control strategy. The conventional control method and the novel control strategy is applied to the APF prototype, respectively. The experiment results show that the novel control strategy is effective for APF:harmonic distortion of selected harmonic current decreases to below0.3%and transient response time is less than10ms with the compensation of APF applying novel control strategy. The steady state accuracy of novel strategy is much better than conventional method.The novel harmonic current detection and control strategy response accurate in steady state and fast in transient state. The hardware consumption of calculation and memory units is acceptable for most DSP. The novel control strategy has good prospects for engineering applications.