Research On Current Control Strategy Of Threephase Active Power Filter

With the vigorous development of China’s power industry, the total installed capacity of various power devices continue to increase. There are more and more attention paying to the control work of power quality pollution. The product market to improve power quality and save energy is expanding rapidly. Active power filter is as one of power quality improving device, the main function of which is to filter harmonics, are now widely attention and study.In this paper, the two key parts that affect the compensate performance of the current control strategy are presented, which are the selection of command current and the tracking control of the command current. Choosing different command currents will directly affect the dynamic response speed of the active power filter. When using the load-side current detection to extract reference current, it is necessary to separate the harmonic current as a command, the process of which uses the low pass filter. It will cause the dynamic response delay, impacting response compensation. This paper presents a method to directly detect the side current of power grid as the instruction current. The method does not need to separate harmonic, which can shorten the time of dynamic response of current compensation, and reduce the amount of detection and computation, and reduce the complexity of the program design. It is also given control strategy and parameter design which extracts command current from the grid side to compensate.The feasibility of the method is proved theoretically and the advantages are verified through the simulation.Another key factor affecting the compensation performance of active power filter is the instruction current tracking control. The advantages and disadvantages of the traditional PI control, PR control and repetitive control are analyzed in this paper. A kind of vector resonant controller is improved according to the traditional PR controller,. The controller has the advantages of stronger anti-interference ability and greater gain at the resonance point, and it can improve the accuracy of harmonic compensation in the current compensation control. This article also designs the controller in the form of digital control system in detail. Finally, when the current compensation control of active power filter use the grid side current as the current instruction and apply the vector resonant controller, the simulation waveform and harmonic analysis are given. It is proved that the control strategy can further reduce the harmonic content and improve the compensation precision.Finally the main circuit and the control circuit of APF are designed. A prototype platform is built. The analog signal debug, PWM modulation wave, the load current and load increase experimental waveform are given when compensation. It illustrates the correctness of this design APF works and research of current control strategies.