Research On MMC-APF Based On Active Power Decoupling And Active Disturbance Rejection Control

With the development of science and technology,more and more power electronic devices have been developed.These power devices not only bring convenience to people’s lives,but also bring serious harmonic pollution to power system.Active Power Filter(APF)can restrain harmonics effectively and improve Power quality because of its excellent performance.However,with the increase of power system voltage and power,the traditional APF loses its competitive advantage.Modular Multilevel Converter(MMC)has many advantages,such as high modularity,easy expandability and convenient voltage level promotion.Therefore,combined with the advantages of MMC topology and APF,the study of harmonic suppression through MMC-APF is of great practical significance.In this paper,based on the principle of MMC-APF,the aim is to improve the ability of harmonic compensation,based on the current tracking control of MMC-APF,the stability control of MMC system and the suppression of capacitor voltage ripple in MMC sub-module,the following research is carried out:(1)In the current tracking control of MMC-APF,the traditional double closedloop controller controlled by PI is difficult to establish accurate mathematical model and the real-time tracking precision is not enough,an improved MMC-APF double closed-loop Control strategy based on Linear Active Disturbance Rejection Control(LADRC)is presented,which improves the harmonic compensation performance,system response speed and Shandong rod performance of MMC-APF.(2)In the stability control of the MMC system,firstly,the cross-reactance coupling between the two phases and the harmonic of the 2-fold harmonic of the loop current are also existed in the conventional loop suppressor,a novel circulation suppression strategy based on LADRC and second-order generalized integral filter is proposed,and the precise suppression of MMC circulation is realized.Secondly,to solve the problem of voltage unbalance on DC side of MMC,a hierarchical voltage control strategy is proposed to realize voltage balance among phases,bridge arms and sub-modules of MMC.(3)Aiming at the problem of low frequency ripple caused by Power fluctuation of the bridge arm during MMC operation,Active Power Decoupling technology(APD)was proposed to suppress voltage ripple.Through the analysis of decoupling topology,the active power decoupling topology based on Buck type is selected,the method of selecting decoupling circuit parameters is pointed out,and a strategy of capacitor ripple suppression of seed module is given.Finally,the simulation results show that the proposed control strategy can effectively improve the output performance of MMCAPF and the power density of the system.