Current Optimization Of Shunt Active Power Filter Based On Fixed Harmonics Detection

The development and application of power electronics accelerateeffectively the process of modern industrialization, while bringing outserious harmonic pollution to power systems. As a power electronicdevice, shunt active power filters (SAPF) have obvious advantages andwill be the main products to improve the power quality in the future.This paper firstly introduces the reason, damage, internationalstandard and governance method of harmonics. After the relative meritsof passive filters and active filters are discussed, it summarizes the historyand current station of active filter about topology structure and controlstrategy.Traditional active filters always adopt the mode of all harmonics,that all harmonics is calculated and tracked through detecting thefundamental part of grid current. In special grid environment, this modemay lead the device over-current and even damage the switchingelements when compensative harmonics exceed the nominal capacity ofdevice. Therefore, this paper proposes the linear limiting algorithm,which is designed to guarantee the device safety and steady by limitingthe RMS and peak values of reference current. Given the necessity offixed harmonics detection, some algorithm based on Fourier analysis, dq0transformation and adaptive theory are discussed on workload, real-timeand computational accuracy. Besides, this paper also supposes the designmeans of three-phase PLL and single-phase PLL.PI controller is generally used in industry for its simple principle. But the wide frequency spectrum of reference current makes thiscontroller have a large deviation in active filter. So, fuzzy PI adaptivecontroller is proposed to eliminate this error through adjusting the PIparameters online. The dead-time effect of switching elements willinevitably generate voltage harmonics and current harmonics, whichcould be restrained by compensating feed-forward the equivalent deadvoltage from dead-zone compensation arithmetic. Considering that thenatural disturbance caused by hard circuit delay reduces thecompensation accuracy, this paper proposes the harmonicsself-compensation algorithm. According to grid current and harmonicscurrent from converter, the equivalent disturbance voltage could beobtained and compensated feed-forward to overcome the influence madeby transfer delay. In addition, double loop soft-start control method isdesigned to solve the problem that dc voltage and grid side current have ahuge shock when device starts.At last, this paper develops380V/150A active power filter lab platescomposed by three single-phase structure and three-phase structure.Based on hard circuit system and soft control system with FPGA andDSPs, the fixed harmonics detection and current tracking optimizationalgorithms proposed in this paper prove to be true by experimentalresults.