Research On Cascade Multilevel Inverter And Control Strategy

ABSTRACT:In recent years, the cascade multilevel inverter has become one of hotspots in the field of power electronic technology. This kind of inverter was widely used in the new energy grid-connected system, battery energy storage system, high voltage inverter, etc. The cascade multilevel inverter has the characteristics of small harmonic content, high voltage and power levels. In this paper, the cascade multilevel inverter has carried on the detailed research. This dissertation takes H-bridge cascaded inverter and hybrid cascaded multilevel inverter as the research object. Type of H-bridge cascaded inverter and hybrid cascaded multilevel inverter has carried on the detailed theoretical analysis, simulation analysis and experimental verification.First of all, in this paper, the basic working principle and modulation method of the H-bridge cascaded inverter are introduced. For a series of problems existing in the traditional battery energy storage system, H-bridge cascaded inverter and low voltage battery module formed with the combination of the battery module H-bridge cascaded type energy storage system. This dissertation detailed researched the control strategy of the H-bridge cascaded energy storage system. The control strategy mainly includes three aspects of the control:Through the study of the proportional distribution of each phase total modulation ratio to realize independent control of each battery module charge and discharge current; To realize grid power decoupling control; Through the study of the voltage compensation of three-phase symmetrical voltage modulation method to realize the balance control of the grid side power, ensure the balance of three-phase grid current at the same time.Then, the topology and work principle of the hybrid cascaded inverter are analyzed in detail, and according to the advantages of the topology to optimize control strategy research, finally from two aspects of reduce output voltage jump and dead zone compensation to carry on the optimized control. By the choice of the redundant work mode switch to reduce the jump of the output voltage, and reduce the switching loss, the efficiency of the inverter has been improved. Through the dead band time loss modulation voltage equivalent calculation and compensation, to improve the current distortion when the electric current passing zero, and decrease the harmonic content, improve the performance of interconnection.In the simulation phase, I set up simulation model of two inverters respectively, and the control strategies of two kinds of inverters have been detailed simulation analysis, and have verified the effectiveness of the control strategy described in this article.Finally, through the design of hardware and software, build the two inverter structure of experiment platform. In the H-bridge cascaded inverter experiment, achieve the grid current closed-loop control, analyzes the H-bridge cascaded inverter’s output characteristics, and verified the independence of the dc side current control strategy.In the hybrid cascaded inverter experiment,the output characteristic of the hybrid cascaded inverter and two optimization control strategy which were proposed were verified, and obtained the good experimental effect.