Research On Active Power Filter Harmonic Detection Algorithm Based On Software Phase-locking

Currently,with the widespread usage of non-linear loads on the grid supply,voltage and current are polluted.Power quality has become a serious problem,affecting industrial production and people's lives.Active power filter(APF)is considered an ideal equipment to control power quality.While active power filter has been applied into practice,the effect of compensation is not ideal with voltage distortion and frequency viberation.The root cause of inaccuracy is hardware phase locked loop.Based on this,this thesis built up the mathematic model of shunt active power filters,studied the detection accuracy of three-phase shunt active power filters and proposed a harmonic detection algorithm based on software phase-locking.This thesis firstly analyzed the working principle of active power filters.Classified common harmonic detection algorithm and investigated the research status of harmonic detection algorithm?In terms of the active power filter,the topological structure and working principle are established and analyzed.The mathematic model of harmonic detection algorithm based on instantaneous reactive power theory are built.It establishes the theoretical foundation to the research of harmonic detection.In traditional APF harmonic detection,it is necessary to obtain the frequency and phase of grid voltage through hardware phase-locked loop.It can achieve a good waveform and ideal harmonic compensation with the stability of grid voltage and frequency.As for the voltage unbalance and waveform distoration circumstances,a software phase-locking algorithm was proposed.To erase the errors caused by unbalanced three-phase voltage imbalance and voltage distortion,an adaptive fundamental algorithm is used to extract the fundamental voltage of the power system.Double synchronous rotating coordinate system is also adopted to decouple the positive sequence component and the negative sequence component of the fundamental wave.The simulation modle is built in Simulink to validate the effectiveness.To validate the designed algorithm,in the environment of MATLAB/Simulink a simulation is carried out.The simulation results show that after compensating the measured grid current distortion rate of 2.98%,proving the designed algorithm can effectively suppress harmonics and compensate reactive power,with a good dynamic characteristic.Finally,this thesis built a hardware platform of APF based on DSP control in the laboratory environment.The capacitance and inductance parameters of the main circuit of APF are designed.The experimental results show that the design of the software phase-locking algorithm can achieve ideal effect of harmonic compensation under unbalanced and distorted voltage.