Development Of Control System Of Three-phase Active Power Filters

With the application of large sums of power electronic devices, the power systemharmonic pollution is becoming more and more serious. Active Power Filter (APF) isconsidered to be the most effective method to solve the grid harmonics and improve thepower quality. However, the application of APF in the domestic is far from the mature stage,expanding in-depth study on the APF is of great significance.The thesis analyzes the commonly used APF harmonic current detection methods. In thecase of grid voltage asymmetry and distortion, the result of traditional dq method hasdetection error in detect the positive sequence reactive current. In view of this, the thesis putsforward a new synchronous detection method to detect the harmonic current, which is basedon the supply voltage and without Phase Locked Loop (PLL). Build a simulation model onthe condition of the grid voltage asymmetry and distortion, the results proved the accuracy ofsynchronous detection method which is based on the supply voltage and without PLL.The thesis analyzes the control methods of the APF. In order to control the DC voltage,using the active power conservation method to avoid the traditional Proportion Integration (PI)method whose control parameters design is complex and difficult to achieve an optimalcontrol. Analyzed the main control methods of the converter, based on the analysis above,choosing timer hysteresis control method which is simple and facilitate to implement withsoftware and hardware.An APF control system is designed in this thesis, including hardware circuit andsoftware of the control system. The control system hardware circuit design mainly includesthe input module which can detect the current and voltage of the object, processor modulewhich can calculate the instruction current and generate control pulses, and fault protectionmodule. The input module is designed to avoid the PLL hardware circuit, so as to improve theresponse speed of the system. The processor module is independent of the other modules,which make the system software’s upgrade become easy. The fault protection module isdesigned to protect the whole system and warning. The design of the software of controlsystem includes sampling, filtering, instruction current calculation, as well as the generationof control pulses.The simulation model and experimental platform of the entire system are built, throughcomparison the study between simulation and experiments, the feasibility and effectiveness ofthe control system’s hardware circuit and software design are verified.