Research On Key Technology Of Three-phase Four-wire Three-level Active Power Filter

In order to deal with the increasingly harsh grid harmonic pollution problem,more and more people pay attention to power quality control device.Because of its excellent performance and low cost,active power filter has become the mainstream of the current harmonic control means which shunt active power filter is the most widely used.In this thesis,three-phase four-wire three-level shunt active power filter was studied and analyzed.The characteristics of several used filters are compared and analyzed in this thesis,and the APF filter network by the parallel notch filter is desig ned.In order to restrain the resonant peak of the LCL filter,the thesis selected parallel notch as the output ripple filter for determining the system parameters.The filtering effect of LCL filter and parallel notch filter is compared by simulation and experiment.In the vicinity of APF output switching frequency,the ripple is compared to the LCL filter ripple filtered by parallel notch filter in the grid current.The three-phase four-wire APF is modeled and according to the model,the thesis designed current controller based on PI and hysteresis.The control effect of PI control and hysteresis control is compared by simulation and experiment.For PI control,the compensated grid current waveform still contains a large amplitude of the harmonic components,because the PI control cannot track the current without trace.The hysteresis loop control is better than the PI control in the tracking accuracy for current tracking.On the basis of the analysis of the two-level three-dimensional space vector DC bus voltage control,the thesis designed APF DC bus voltage control using three-level three-dimensional space vector method.In the case of grid voltage fluctuations,the control strategy can effectively suppress the fluctuation of positive and negative bus voltage.In the emergence of positive and negative bus voltage offset,the control strategy can adjust the back balance position quickly.The thesis designed the shunt APF system and analyzed the harmonic current detection method based on the FFT method.The effect of different window function to suppress the spectrum leakage is compared.The simulation results of APF system show that the active power filter system designed in this thesis have better harmonic compensation effect for three-phase symmetrical load and three-phase asymmetrical load.