The Study About Compensation And Self-stabilising Voltage Of H-bridge Cascaded Active Power Filter

With the development of new energy industries,the cascaded H-bridge multilevel topology has become a hot research topic in the field of high voltage and high power,and its application in active power filter(APF)can control the harmonic pollution in the high voltage power grid.The research of cascaded H-bridge APF is launched under the laboratory environment in this paper.The paper introduces several kinds of multilevel level topology,and analyzes operation mode of single H bridge,and introduces carrier phase shifted(CPS-SPWM)modulation technique,and analyzes the AC side output voltage of the cascaded H-bridge converter to verify the superiority of the modulation algorithm.While calculating the modulation wave,the paper also introduces extraction of the fundamental positive and negative sequence and harmonic current based on the double synchronous rotating coordinate system to ensure that the cascaded APF accurately compensates harmonic current.In current tracking strategy,the repetitive control is used to solve the steady-state accuracy of compensation current.The paper analyzs how to select the power switch tube,griding reactor and DC side capacitor in main circuit of cascaded H-bridge APF.The paper explains unbalance reasons of DC side voltage of H-bridge,and establishes power exchange model between APF and power grid.Based on the nonlinear characteristics of the compensation current,it is concluded that each DC side voltage is stabilized by three-level control to ensure the stable operation of the system.At last,the paper introduces three-phase and single-phase PLL to get the phase of grid voltage vector precisely。The simulation using Matlab/Simulink and experimental platform for symmetrical and asymmetric load in three-phase three-wire system under low voltage environment is built.DC side voltage stabilization and harmonic compensation attain expectantw efficacy,so it verifies the feasibility of the cascaded H-bridge APF control strategy in this paper and provides the basis for application of the APF to a higher voltage level.