Research On Control System Of MMC-STATCOM With Fault Tolerance

Static Synchronous Compensator(Static Synchronous Compensator,STATCOM)is a device that can improve power quality,and which can increase the power factor and inhibit harmonics in the power grid.In this paper,STATCOM for high-voltage and high-power occasions is studied.By comparing several different topology inverters,this paper selects STATCOM based on Modular Multilevel Converter(Modular Multilevel Converter,MMC),and analyzes its working principle and the key technologies.The MMC-STATCOM with fault tolerance proposed in this paper lays a theoretical foundation for high-voltage and high-power static synchronous compensators in the future.The work done in this paper is as follows:First of all,this paper analyzes the MMC topology and working principle,and describes the sub-module structure and working conditions;Though contrasting several modulation methods commonly used of MMC,and in order to better achieve redundant fault control function,this paper chooses the modulation method of the carrier cascade.The voltage sort method is used to balance the capacitance voltage of sub-module.The mechanism of circulation is analyzed,the whole bridge module is adopted to inhibit the circulation,and the specific realization process is introduced.Secondly,in this paper,the control strategy of system of MMC-STATCOM is designed.Among them,choosing the appropriate current detection method is the premise to realize reactive power compensation and harmonic control,this paper adopts ip-iq method without phase locked loop,it can overcome the inaccurate problem of traditional method phase-locked;A vector resonance controller(Vector Resonance Controller,VRC)is adopted to track the current,which can eliminate the specific harmonic and has no phase delay in the resonance point,it doesn't affect the stability of the system.In this paper,several cases of the failure of sub-module are analyzed,and some common redundant fault tolerance schemes are introduced,the non-redundant method of modulation wave reconstruction is proposed to improve the fault tolerance capacity of the system.In order to verify the correctness of the above control strategy,the Matlab/simulink simulation model of the system is built.The validity of the system is verified by analyzing the simulation results.Finally,the hardware and software is designed,and the hardware experimental platform is built.Experiment waveforms and simulation waveforms are consistent,and the feasibility of the control system is verified,the MMC-STATCOM in this paper can effectively compensate system reactive power and harmonic.