Variable Structure Control In Shunt Active Power Filter

With the development of modern industrial and power electronic equipment's extensive using, non-linear loads in electric power system largely increased. The grid system has being polluted, and power quality has become worse and worse. Using the APF to suppress the harmonic and compensate the reactive power is an effective way to resolving the harmonic contaminator in grid system. By comparison to conventional passive LC-filter, APF has the advantage of quick response, good output wave shape and dynamic performance.The focus of this paper is about the influence of SAPF's DC link voltage to system performance. A Sliding-mode Variable Structure Controller for DC link voltage is presented.First of all, the basic principle, assortment, and structure of APF are introduced. This paper put emphasis upon the structure and principle of shunt active power filter.At present, there are many measurements to pick-up the harmonic current and reactive power; Lots of them based on the instant reactive power theory. This paper discusses the p-q, I_p-I_q and d-q method for the detecting current.The Ip-Iq method is used for the simulation. In order to make the injecting current sinus, we have to use some control method to make the compensation current trace the command current. There are three ways to tracing the command current. One is linear control of triangular wave carrier; the other is hysteresis current control; the third is the periodic sampling control. This section emphases the energy exchange between the DC link and AC side, and the influence of DC link voltage to system's compensating effectiveness. The advantage and disadvantage of the conventional control method is discussed. A new VSC controller which has strong robustness was presented.The foundation of the variable structure control was introduced. This paper discusses the design process and means in detail, and analyses the whipping problem in depth. The way to weaken or eliminate the whip is also presented.