Research On Voltage And Current Balance Control Of The Cascaded Matrix-Type Power Electronic Transformer

The power electronic transformer(PET),consisting of power electronic converters and a high-frequency transformer,works at a higher frequency than the traditional line-frequency transformer,which saves the amount of transformer metal used and is environmentally friendly.Power electronic converters achieve power conversion,and PET,which is multifunctional,has been applied to many fields,including renewable energy access,traction power supply system,and electric vehicle quick charging.Under the condition of medium-high voltage and high power,the cascaded modular topology with input-serial and output-parallel structure is usually adopted,due to the limited voltage withstand capability of the power semiconductors,reducing voltage stresses and achieving power expansion.However,the inevitable parameter differences between modules can unbalance the voltage,current,power,and heat between modules,which affects the normal operation and even leads to system breakdown.To ensure the stable and safe operation of the system,this paper studies the voltage and current balance control of the cascaded matrix-type PET.First of all,the topology of the cascaded matrix-type PET is proposed,and the operating principles and characteristics of the component modules are analyzed,which lays a foundation for the subsequent power imbalance analysis and control strategy.Secondly,considering the parameter mismatch of each module caused by the parameter differences of power components and the loss difference of the system,the theoretical analysis of the system power imbalance is carried out.The influence of each factor on the system power imbalance is analyzed quantitatively.According to the power imbalance analysis,a decentralized balance control strategy based on prestage voltage compensation is proposed by analyzing the relationship between the input voltage balance and the output current balance.In this control strategy,current compensation,calculated by the pre-stage voltage balance controller,modifies the reference current in the outputstage power balance control strategy,achieving the goal of system power balance.Finally,the correctness of the proposed control method is verified by simulation.And an experimental prototype of the cascaded matrix-type PET is built for experimental verification.Experimental results show that the presented control strategy achieves power balance among modules and keeps the system functioning normally and reliably.72 figures,20 tables,73 references.