Research On Active Power Filter System Based On DPC

With more and more nonlinear power electronic devices used in real life,the power of pollution has become increasingly serious.In order to improve the power quality,Active power filter is getting more and more attention at home and abroad.In this paper,the control strategy of shunt active power filter is taken as the main research focus.In this paper,the mathematical model of three-phase three wire system and the four bridge arm is established in the abc coordinate system and dq coordinate system,and the cause of the influence of DC side capacitor voltage fluctuation is analyzed.In the harmonic detection part,aiming at the unbalanced grid voltage p?q detection method and i_p?i_q ?detection method error,an improved i_p?i_q ? detection method is proposed.The method increases the extraction of fundamental positive sequence voltage component,eliminates the error caused by the phase locked loop when the voltage is asymmetric.The width of the power hysteresis comparator is constant and the switching frequency is high and the range is large for the direct power control strategy,the direct power control strategy of fuzzy self-tuning bandwidth is proposed.According to the deviation of power and the power of coupling,the hysteresis bandwidth of hysteresis comparator is obtained,and the bandwidth of hysteresis comparator is set up;The simulation results show that the control strategy has a smaller maximum switching frequency and a smaller frequency range,which reduces the switching frequency and its fluctuation range,and the switching frequency is basically unchanged and has better robustness when load mutation.In order to optimize the overshoot and dynamic performance of DC side voltage of the active power filter,a direct power control strategy based on double fuzzy adaptive PI is proposed.When DC side voltage fluctuation is large,the fuzzy rule 1 is used for rough adjustment to speed up the dynamic response of the system,on the contrary,the fuzzy rule 2 is used for fine adjustment to guarantee the steady precision of the system;The simulation results show that the proposed method improves the stability of the DC side voltage,effectively inhibits the overshoot,and improves the dynamic performance of the system,at the same time,the precision of harmonic compensation is greatly improved.A control strategy based on the new double switch vector table is proposed for the existence of reactive power fluctuation in the traditional switch vector table.The control strategy adopts two switching vector table to judge the reactive power deviation,different switching vector table is chosed according to the size changes,to achieve the purpose of fast adjustment of reactive power and better harmonic compensation performance is obtained.Acompound selective control has been adapted in four-leg active power filter,which is a combination of direct power control and hysteresis control.It includes the characteristics of two control,on the one hand,there is no need to detect the harmonic current and improve the real-time performance.On the other hand,the control is more simple and can selectively compensate the harmonic current and the neutral current under different current unbalance degree,and realize the balance of the three phase currents.