Research On The Algorithm Of Reactive And Harmonic Currents Compensation By Active Power Filter

Along with the widely use of power electronic equipment,the electrical quality is made for much more use of.However,with more and more nonlinear,impactive loads put to use,the harmonic pollution in public supply network becomes more and more severely,so the studies and exploitations in active power fileter have very important significance,and has been widely used and developed in the recent years.Comparied with passive filters,APF have many advantages,good dynamic response performance and are not easily affected by system impedance.An accurate and real-time detecting approach is critical for APF to accurately compensate harmonic currents.This paper mainly deal with harmonic current detecting approaches.In the widely used detecting approach of harmonic currents for APF,ip-iq approach based on theory of instantaneous reactive power is used most widely.The method has simple structure and perfect real time detecting effect However,the current detecting methods of active power filter have some limitations.Through theoretic analyzing,the strongpoint and disadvantage of several kinds of APF is compared,and makes detail study on the two critical technologies:harmonic and reactive power current detecting approaches and PWM control strategies;based on this,to solve the disadvantages focus on that big distortion caused by compensation circuits when load current varies promptly in a large scope and distinct error occurred when ip-iq detecting approach is used in the case of unbalanced 3-phase voltage, a developed detecting approach is proposed. Double close-loop control for DC link voltage are added in the method to achieve good tracing behavior of compensating current. A phase A fundamental positive sequence voltage selected unit based on LPF substitutes for the original ip-iq PLL to ensure exact voltage of A phase is selected even in case of imbalance three phase voltage.To testify the validity of this new method,the detailed dynamic simulation on MATLAB6.5 have been done,and the results of the dynamic simulation verified that the method is valid and feasible.