| Active power filter(APF)is an important device to improve the quality of power grid,which is widely used in industrial and agricultural production.Taking shunt three-phase four-bridge active power filter as the research object,the whole system of shunt three-phase four-bridge active power filter under unbalanced grid and load is analyzed in detail.Firstly,the working principle of SAPF is introduced,the structure and mathematical model of three-phase four-bridge APF designed in this paper are given,and the parameters of LCL filter are designed.Several current detection methods based on instantaneous reactive power theory are analyzed.Finally,the d-q detection method is used as the harmonic current detection method in this paper.Secondly,by analyzing the principles of PI controller,quasi-PR controller and repetitive controller,it is determined that the DC voltage closed-loop control uses PI controller,and the harmonic current closed-loop uses quasi-PR and repetitive controller.After the controller and harmonic current detection method have been determined,the control strategy for unbalanced load and grid voltage is given.On this basis,the main components of a three-phase four-bridge APF with a capacity of 2640 Var are calculated.The simulation model of three-phase four-bridge APF under unbalanced load and power grid is built by using MATLAB software.The correctness of the system is verified by comparing the current waveform and total harmonic distortion around simulation.Finally,the core control chip of the system is TMS320F28335,and the hardware circuit of the control cabinet with capacity of 2640 Var is designed.According to the system flow chart of the software program,the software flow chart of three-phase four-bridge APF is given.According to the parameters calculated by simulation andsoftware,the experimental waveforms before and after compensation are observed to verify the correctness of the three-phase four-bridge active power filter designed in this paper. |
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