Three-Phase Imbalance Compensation Strategy Based On Two-Phase Half-Bridge Three-Level Converter

As more and more random loads connected to distribution network,power quality problems such as three-phase imbalance,reactive and harmonic currents are becoming more and more serious.Therefore,how to comprehensively solve the three-phase imbalance,reactive and harmonic currents and other power quality problems through compensation device has become one of the current research hotspots.In this paper,a two-leg converter and its three-phase compensation control strategy are studied.The main research work is as follows:Firstly,the principle of three-phase compensation of two-leg converter is described,and the power flow path is analyzed.The formula of dc-link capacitor voltage ripple is deduced based on the power flow path,and the influence of DC ripple on the compensation current is further expounded by analyzing the formula.Then,the suppression strategy of ripple effect is proposed.Finally,simulation results verify the correctness of the formula derivation and the effectiveness of the proposed suppression strategy.Secondly,the common control strategy of single-phase rectifier are analyzed.These control strategies are not suitable for three-phase compensation of two-leg converter exactly.Therefore,based on DQ decoupling control,a cross-DQ decoupling control strategy suitable for this compensation system is proposed for fundamental currents compensation.To compensate the harmonics,a single-phase DQ decoupling detection method is proposed to extract the active and reactive power components of specific oder harmonics,and then realize the harmonic compensation through two-phase specific oder harmonics control.Finally,the above theory is verified by simulation.Then,an experimental system is designed for the proposed three-phase compensation system.The power switchs and its driver IC are selected appropriately and the driver circuit is designed.The three-phase compensation control program is designed based on Verilog HDL.Finally,the design correctness of hardware and software is verified by experiments.The experiment of active power imbalance,reactive and harmonics compensation are carried out under various loads.Under the experimental system,the imbalance can be reduced from 92.1%to 0.8%.The power factor is increased from 0.294 to 0.997,and the three phases are all greater than 0.99.Total harmonic distortion of the worst phase is decreased from 20.4% to 1.9%,and three phases are less than 3%.