The Study Of Control Strategy And Simulation Method Of Active Power Filter Based On Switched System Theory

With wide application of nonlinear loads, such as power electronic devices, etc, in power system, the harmonic pollution in power grid become more and more serious. It is contradictory to the demands for high quality electricity of modern industry. The harmonic pollution has become a serious problem to be solved. Active Power Filter (APF) can effectively suppress harmonic and improve power quality. It has become an important tendency to improve power quality and manage the harmonic pollution in the power system using Active Power Filter. So it is very important and necessary to improve its compensation performance by means of analyzing the model of Active Power Filter, proposing a new current detection algorithm and finding a novel current tracking control strategy. The works done in this paper are shown as follows.(1) The switched dynamic model of shut three-phase three wire APF system is established by analyzing the main circuit of APF based on switched system theory. Considering the non-linear characteristics of APF, the model is established by introducing the concept of switching function. It makes every switch mode of the main circuit of APF, corresponding to different differential equations has a unified mathematical expression. And the error switched affine linear system model is established based on the control objective of APF.(2) The mechanisms of p-q and ip-iq current detection algorithms based on the instantaneous reactive power theory are analyzed in this paper. The effect of the parameter selection of low pass filter (LPF) on the result of harmonic detection is analyzed based on the simulation results. And the results also verify that the p-q current detection algorithm is inaccurate when the power grid voltage is distortion. Then the mechanism of synchronous coordinate transformation harmonic current detection algorithm is analyzed. And simulation results verify its effectiveness. This paper also discussed the relationship between this algorithm and ip-iq current detection algorithm.(3) A novel current tracking control strategy for three-phase three-wire Active Power Filter is proposed based on switched system theory. The quadratic stability of the system is proven based on the stability theory of switched affine system and the voltage space vector method. A switching sequence is put forward for APF via common Lyapunov function method. In order to realize the control procedure digitally, the discrete switched affine system model of APF is presented. Making use of the predicted state values and the hybrid characteristics of APF, an optimized switching rule is proposed to guarantee the optimal performance during each sampling period. Simulation results show that the proposed method can realize the accurate tracking of the reference current, decrease the switching frequency and improve the dynamic performance effectively.(4) The algebraic loop is widely existed in the SimPowerSystem-based simulation of APF, which is extremely time-consuming and needs many memory resources. An efficient simulation method of APF is proposed in this paper based on analyzing the dynamic behavior of the switched subsystems of parallel three-phase three-line APF. The simulation model of each subsystem is built via Simulink. A unified simulation model of the main circuit of APF is then obtained by integrating all the subsystems. Because APF can be regarded as discrete event dynamic system, based on the unified simulation model and Finite State Machine theory, the dynamic simulation of APF is completed using the StateFlow module. Simulation results show that the simulation method can effectively present the dynamic performances of APF and avoid the algebraic loop problem. So the simulation efficiency can be improved significantly. The proposed method provides a new approach to the performance analysis and controller verification of APF.