The Study On Control Strategy Of Active Power Filter Based On Switching System Theory

With the development of power electronic devices and widely used, harmonic pollution has become an important factor in the threat of power quality. Active power filter can effectively suppress harmonics and improve the power quality, so active power filter applications are used more widely in life and industry. On the other hand, the over-exploitation of primary energy made the environment polluted seriously and the requirement of people for the electric power supply reliability is getting higher and higher. Traditional power supply cannot meet the practical needs; Therefore, people pay more and more attention to the micro-grid. The main circuit of micro-grid inverters and active power filter are very similar, in order to save the investment, the micro-grid can share the same inverters with the active power filters. But now with the micro-grid inverters and active power filter are two different sets of equipment, it is a serious waste of resources.To solve the problem, in this paper, the study on control strategy of active power filter based on switching system theory can effectively filter the harmonics in power system and keep the DC side capacitor voltage stabilize at a high value. And it provides a solid basic viable theory for the micro-grid and the active power filter to use a set of inverter device. It also has very important significance to improve power quality, reduce losses and save the investment.This paper introduces the switching system firstly, it consists of a series of subsystems and the description of the link between the composition of their switching rules. The stability of switching system depends on the switching rules that were chosen. Even its subsystem is stable, if the switching rules are improper, it may cause the entire system to become unstable. Conversely, even if its subsystem is unstable, under appropriate switching rules it can enable the stability of the whole system. The design of the switching rule is the key point of the study on stability of the switching system. Based on Lyapunov’s stability theory, this paper proposed the switching control strategy that makes the system asymptotically stable.Build a mathematical error model of single-phase active power filter which corresponds to the basic form of the switching systems, and single-phase active power filter is divided into two subsystems, according to Lyapunov’s stability theory, to analysis the stability of the subsystem and determine the Lyapunov function to make the subsystem asymptotically stable. Then design a single-phase switching sequence that makes active power filter operated stably, use this to control the power switch of the main circuit of the single-phase active power filter and make the system operate at the best compensation status.This paper proposed a three-phase active power filter harmonic current control strategy based on switching system theory, taking the DC side capacitor voltage and two phases harmonic compensation current of the three-phase active power filter as variables to establish the error model of the system. According to Lyapunov’s stability theory, to design the best switching sequence, so the harmonic compensation current, the DC side capacitor voltage and the error between the reference value decreases and make sure the system operate at the best compensation status.Build a single-phase and a three-phase active power filter simulation model to validate the method presented in this paper, and use the switching sequence designed before to control the power switch of the main circuit of the active power filter. The simulation results show that this method is correct and feasible.