考虑系统稳定性的级联H桥有源滤波器控制策略研究

Study on Control Strategy of Cascade H-bridge Active Power Filter Considering System Stability

系统内的无功补偿电容器会改变电网的阻抗特性,从而和有源滤波器的阻抗在某些频率下相匹配,引发谐振,导致系统失稳。论文针对这一问题,以基于级联H桥拓扑的有源滤波器为应用对象,提出了兼顾滤波和无功补偿的协同控制策略,在滤波的同时取代并联电容器进行无功补偿,以确保系统的稳定运行。该控制策略为了补偿谐波电流,在旋转坐标系解耦控制中的电流内环引入准比例谐振控制器;为补偿无功,采用PI控制器产生q轴基波电流,叠加在q轴谐波电流上来实现。最后,基于考虑并联电容器的电网阻抗和滤波器阻抗进行了系统稳定性分析,根据阻抗稳定性理论论证了为确保系统稳定,让有源滤波器取代并联电容器进行无功补偿的必要性。基于PSCAD/EMTDC的仿真结果表明了所提控制策略的有效性和可行性。

The reactive compensation capacitor in the system can change the impedance characteristics of the power grid,thereby match with the impedance of active power filters at certain frequencies,causing resonance and leading to system instability. Aiming at this problem in this paper and with the active power filter based on cascade H-bridge topology as the application object,the synergy control strategy considering both filtering and reactive power compensation is proposed which,at the time of filtering,replace the shunt capacitor for reactive power compensation so to assure stable operation of the system. In order to compensate the harmonic current by the control strategy,a quasi-proportional resonance controller is introduced into the current inner loop in the decoupling control of the rotating coordinate system. For reactive power compensation,the PI controller is adopted to generate the q-axis fundamental current,which is achieved by superimposing on the q-axis harmonic current. Finally,the system stability analysis is performed on the basis of considering the network impedance of shunt capacitors and filter impedance,and the necessity of replacing shunt capacitors with active power filters for reactive power compensation is demonstrated in accordance with the impedance stability theory so to ensure system stability. The effectiveness and feasibility of the proposed control strategy are indicated by the simulation results based on PSCAD/EMTDC.