SVM Based Hysteresis Predictive Current Controller For A Shunt Active Power Filter

The harmonic pollution of power system is becoming more and more serious with the wide use of power electronic equipment in power system. As one of the most effective solutions to suppress harmonics, Active Power Filter (APF) that can trace and compensate harmonics whose frequencies and amplitudes vary and its compensation characteristics is immune to the impedance variation of the utility, attracts more attention from people. Therefore, research on APF has momentous theoretical significance and great practical value.The widely used shunt-APF has studied intensively in this thesis. Shunt-APF is composed of power circuit,capacitor,coupling transformer,control algorithm and so on, and harmonic current detecting and compensative current controlling are the key links of its control algorithm. As for harmonic current detecting, the widely used algorithm i_p-i_q based on the instantaneous reactive power theory is adopted in this paper. In view of APF based on conventional DSP controller has a unit delay of sample time and causes the problem that compensative current doesn't tally with harmonic current, an algorithm using previous harmonic current values to predict the compensative current of next beat is proposed in this thesis, in order to realize the deadbeat control of APF. This algorithm combined with perceptron cell to complete exact current prediction of next beat, is simple and can be applied to DSP controller. As for compensative current controlling, advanced Space Vector Modulation (SVM) based on hysteresis current controller, which has fast transient response and high precision, is adopted. A timer comparator instead of hysteresis current controller is used to limit its maximum switching frequencies and decrease its average switching frequency at the same time.Blocks of APF and its parameters designing are presented in the paper. Through the simulation software MATLAB, simulation results indicate that shunt-APF using this predictive current control method achieves excellent compensation effect on harmonic current caused by nonlinear load.