Study On Control Methods Of Compensating Currents For Active Power Filter

While raising productivity and improving people’s living standard, power electronics equipment injects lots of harmonic currents and reactive currents for the non-line character built in it; this brings pollution to power grid, which causes harmfulness to power system and customers. So far, attention has been paid to harmonic problems.This paper begins with the concept of harmonics; and its origin, harmfulness and disincentive are also introduced simply; on account of the incentive disadvantages of normal Passive Power Filters (PPF), development and application of Active Power Filter (APF) both at home and abroad are given, the main contents of the thesis, frequently-used control measures for compensating currents of APF, are described here, and also their application and development trends.The working principle of APF is given in the paper, as well as the different varieties and their relevant structures; based on the system diagram of three-phase three-wire voltage mode shunt APF, the structure of main circuit and major function of each part are introduced, also the total structure figure of its harmonics detection system is given, which lays foundation for the following studies and researches.Center on the control of compensating currents for APF, related research and design of generator circuit of compensating currents based on digital signal processor for APF is paid attention on firstly, which includes the choice of PWM inverters, distribution and time-delay of PWM signals, driving circuit of IGBT and so on.For the aim of compensating currents following the command currents timely and precisely, the principles of hysteresis comparison control mode and other current tracing control techniques are analyzed, and their block diagram are given, on account of the incentive weakness of normal hysteresis current control mode, improvement is done to the intrinsical control algorithm, and a new control mode, whose ring-width is variable, is proposed, which includes ring-width regulation part and hysteresis current comparator with variable ring-width, it can take real-time computation according to output voltage, bus voltage, etc. and outputs PWM signal. Its implement methods are presented in the thesis, which consists of the basic circuit schematic diagrams and the flow diagram of supporting software.Based on the work above, simulation model of the main circuit for three-phase three-wire voltage mode shunt APF is constructed with PSIM, according to the two different hysteresis current tracing control algorithms, the corresponding simulation models are set up, and the simulation experiments of APF are carried out, comparison and analyses are done specified to the simulation results, which proves that it can reduce the switching frequency and improve the compensation effect and the control accuracy, based on which the correctness and feasibility of the method suggested are tested and verified.According to the research contents and wok that have done above, a summary and some existing shortages are given at the end of the thesis, which show the future effort working towards.