A Low Inductance Busbar Design Of Modular Multilevel Converter In UPFC

Unified Power Flow Controller(UPFC)is composed of a series and a shunt voltage source inverter,which make a hybrid structure.The system voltage,current and power factor angle can be controlled with corresponding control strategy,which is benefical for optimization of the system operation state,improvement of system transient stability and suppression of system oscillation significantly.With Modular Multilevel Converter(MMC),UPFC can be applied in high voltage transmission system to improve the security level of power system operation.Sub-Module(SM)is the basic and fundamental unit of MMC.It is the precondition,which MMC can be applied successfully in high voltage and large capacity condition,that SM must be operated reliably and stably in high electromagnetic interference environments.In this paper,the research work was carried on for the optimal design of SM’s structure,especially for the low inductance dc bus.Firstly,according to analyzing the mechanism of the SM overvoltage generation,it was considered that the low inductance dc bus can reduce stray inductance and suppress SM’s overvoltage very effectively.And calculation method of the stray inductance also was presented.Then,according to the requirements of the UPFC parameters and design limits,the main parameters of UPFC main circuit and SM components were calculated,and the structure of SM was designed.The structure module of SM was establish in AnsoftQ3D,stray inductance and surface charge density of copper busbar and low inductance busbar were analyzed,and the suppressing effect of stray inductance by low inductance busbar was verified.Finally,less stray inductance and more uniform charge distribution was realized by the optional structure design of low stray inductance busbar.According to the modeling analysis in AnsoftQ3D,It can be considered that the structure optimized SM has less stray inductance value,and surface density of charge was distributed more uniformly,which had meet the requirements of practical engineering application.