Research On Nonlinear Control Strategies For Active Power Filter

With the development of modern industrial, extensive application of power electronic equipment, and swift increasing of non-linear loads, the grid system has being grievously polluted, and power quality has become worse and worse. Using the Active Power Filter (APF) to suppress the harmonic is an effective method to resolve the harmonic contarminator in grid system. Its working principle is that, from detecting the voltage and current of compensation object by instruction current detection circuit, the command signal of reverse compensation current can be obtained, and the signal convert compensation current by current tracking and control circuit, then compensation current offset the harmonic current of load current, thus it achieves the purposes of suppressing harmonics and compensating reactive power. APF has the advantages of quick response, good shape of output wave and dynamic performance. So APF has been widely researched and developed.Power quality problem in the system is recounted firstly in the paper. The development and actuality of APF are introduced afterward. Then, the detection method and the control strategy, which are the important parts affecting the compensation effect of the APF, are discussed and investigated in detail.In the detection part, several kinds of methods are introduced and compared with. Then, some relevant research is done in simulation to testify the validity of d-q method.In the control part, the model of APF is deduced in detail. Considering that APF is a coupling nonlinear system in synchronous rotating d-q coordinate system. Two methods are adopted to design the controller. One is state-feedback decouple control method with PI adjustment, while the other is variable structure control method basing on the technology of state variable feedback exact linearization. From two angles, which are the output power and current as state variables, the decoupling of APF mathematical is studied aim at decoupling part of state variable feedback exact linearization. Through analysis and comparison, the controller is designed by variable structure control, which current as a state variable. The stabilization of capacitance voltage in the direct current side is realized by PI control.After finished designing of the control system of APF, the models of APF are established to make simulations using MATLAB software. It is indicated by the simulation results that the control strategy presented in this thesis can make APF achieve its functions, and achieve a good control result. In this way, a novel idea can be provided in this paper when one designs the control strategies for APF control system.