Research On Shunt Active Power Filter Based On FPGA

With the extensive use of nonlinear load, a large number of harmonics and reactive current exist in the network, and have deteriorated power quality. The Shunt Active Power Filter(SAPF) is an efficent, stable and flexible advanced mean for improving the quality of power grid. At present, the Shunt Active Power Filter can be divided into full compensation and selective compensation. In this paper, the Shunt Active Power Filter is designed to focus on the techniques of frequency selective compensation.This paper firstly studies the problem of digital delay in the SAPF system. The digital delay is divided into two part that can be easy to analyse, as the selective harmonic detection time delay and the harmonic current tracking loop delay. The selective harmonic detection time delay changes the signal reference, and directly affects the precision of compensation current. The harmonic current tracking loop delay influences the stability of the system. As the same phase margin, the loop delay becomes longer and the bandwidth decreases to indirectly affect the compensation precision. Through the mathematical derivation, the influence of digtal delay is obtained, and uesd to improve the performance of the SAPF. On the other hand, the model of SAPF with time delay is established, to respectively study the ability of harmonic current tracking based on the Proportional-Resonant regulator with a phase angle compensation. Because of problem of anti disturbance and phase lag, the ideal Proportional-Resonant regulator has some disadvantage. At the same time, the parameter of the Proportional-Resonant regulator with a phase angle compensation is designed based on the Bode and Nyquist. By comparing with the Proportional-Integral regulator, this paper proves the advantage of the Proportional-Resonant regulator in tracking high frequency reference.On the base of above studies, the digital control system of the SAPF is designed with the FPGA, including the harmonic current detection, harmonic current tracking, digtal PWM moudel. The delay time of the digtal control system based on FPGA is lower than the DSP system. Therefore, the SAPF based on the FPGA is advanced.At last, built a 20 A experimental prototype. The realization of FPGA digital control system is introduced in detail, and the parameters of power circuit are given. The experiment of PI an PR regulator in tracking the harmonic current is implemented, simultaneously, the compensation performance of different delay is provied. The results demonstrate the correctly and feasibility of the proposed control system.