Research On Selective Harmonic Compensation Technology For Three-phase Four-switch APF

With the wide use of power electronic devices in power grid,increasingly serious harm has been revealed due to the resulting harmonic and reactive power. Compared with the traditional LC passive filter, the parallel active power filter(APF), which possesses many advantages including fast response speed, flexible compensation strategy, and reactive power compensation, has been proven effective in addressing the harmonic problem in the power grid. To achieve the harmonic compensation, a command signal would be obtained through detecting the harmonic current in the nonlinear load of the power grid, subsequently, the APF system would send a complementary current to the load access point, so that the nonlinear load only draws the fundamental current from the grid.Aiming at the development of three-phase four-switch inverse parallel APF, the mathematical model of switching function is studied, and analyzed the tracking control strategy for main circuit of parallel APF, like hysteresis loop tracking and triangular wave comparison. Furthermore, given the importance of harmonic detection in harmonic compensation, we had also studied several widely used harmonic detection methods in both advantages and disadvantages. Then proposed a selected harmonic compensation technology to balance the effect of APF harmonic compensation and the compensation capacity. This strategy will obtain the selected current of selected harmonic by switching the nonlinear load current through dqo coordinate transformation, and then realize the compensation of the specified sub harmonic of the three-phase four switch inverter.By using Simulink toolbox in MATLAB, we had built the simulation model of the three-phase four-switch parallel APF, developed the APF hardware platform based upon the DSP2812 chip.And we had also designed a phase lock program used for grid voltage zero crossing and another program to extract the harmonic current and calculate the space vector PVM driving signal.Our system simulation and experimental results successfully verify the feasibility of the proposed three-phase four-switch inverter for parallel APF. The resulted waveforms of harmonic compensation at different times provided further evidence for the validity of the proposed harmonic compensation technique.