Research On Control Strategies Of Modular Multilevel Matrix Converter

With the rapid development of power electronics and control techniques,the high power and high voltage power converters have been gaining applied widely.Due to the features of low voltage stress and harmonic contents,the multilevel converters become one of the most popular and effective solutions to the high voltage problem.This paper is aimed at the modelling and control aspects of modular multilevel matrix converter(M3C),which is one member of the modular multilevel converter family.Benefiting from the feature of modularity,this converter family presents good performance on scalability,flexibility,redundancy and reliability,thus gaining lots of attention for academic and industry field.This paper takes M3C as the research object,and the research work is focused on some key control strategies,such as modelling,capacitor voltage balancing,capacitor ripple analysis,distributed control and so on.First,this paper adopts the double ??0 transformation to realize the M3C AC side decoupling of input,output,circulating current and common mode voltage,which is the basis of following control scheme.In order to control the capacitor balancing,this paper derives the expression of arm power under double ??0 frame and gives physical meaning of these power terms.For the M3C system,the stability of capacitor voltage is the premise of the normal operation.Therefore,this paper analyzes the capacitor ripple in detail and obtains the unstable points of whole system,which are the low output frequency and equal input-output frequency.Besides,the double ??0 transformation realizes the separation of capacitor ripple spectrum.Then,based on the double ??0 transformation,this paper further derives the diagonal transformation,which can also further decouple the circulating currents.At the same time,applying the diagonal transformation of DC side can divide capacitor deviation to four dimensions,which has clear physical meaning.Aimed at this transformation,this paper also gives the corresponding vector model and control method.Finally,considering the limit of scalability and flexibility from current centralized control,this paper proposes three principles of distributed control,designs the control architecture and algorithm,and gives the modeling and parameters of utilized controllers.The simulation model and experimental platform are constructed,whose results verified the effectiveness and feasibility of proposed control methods.