Research On MMMC-based PHEV Power Comprehensive Conversion System

In recent years,new energy vehicles represented by plug-in hybrid and pure electric vehicles have been widely used and their output and market demand have grown rapidly.In 2018,China's new energy vehicle sales reached about 260,000,of which plug-in hybrid vehicles accounted for about 19%.By 2019,the sales increased to about 830,000,with plug-in hybrid vehicles accounting for 28%.In 2019,the Ministry of Finance,the Ministry of Industry and Information Technology,the Ministry of Science and Technology and the Development and Reform Commission jointly issued the "Notice on Further Improving the Financial Subsidy Policy for the Promotion and Application of New Energy Vehicles",which vigorously promoted the development of core technology reserves and high-scale effect enterprises in the entire industrial chain.It is estimated that the sales volume of new energy vehicles will reach about 25%by 2025.Under this top-level design,new energy vehicles with electric,intelligent,networked and shared advantages will play an important role.In contrast,plug-in hybrid vehicles,which have a slightly lower technical threshold and more flexible energy distribution,have become a hot topic in this field at home and abroad as an intermediate transition product.This paper firstly introduces the research status of core technologies such as car chargers and battery management systems for new energy vehicles at home and abroad.It can be known from the literatures that in order to meet the requirements of large capacity,high power,two-way flow,etc.,the car charger mainly uses a two-level inverter topology.The topology and control are complicated.The external charging circuit of the battery pack is generally separated from the battery management system.Therefore,the power density has no advantage.With the development of new modular multilevel converters,traditional multilevel topologies have the advantages of lower harmonic content,easy modular isolation and high reliability,making them feasible in electric vehicle applications.At present,modular multilevel converters are mainly used in micro-grid applications and there are still many key problems to be solved for large-scale applications in electric vehicles.In order to apply the traditional multilevel topology to the electric vehicle power conversion system and to pursue the important issues of the lightweight design,vehicle integration and system integration design of the new generation of electric vehicles,this paper proposes a modular multilevel matrix transformation Plug-in hybrid electric vehicle comprehensive conversion system.The topological structure of the device has very strong practical significance.This paper focuses on the basic topology and working principle of a comprehensive conversion system based on a modular multilevel matrix converter.Firstly,according to the topology of the modular multilevel matrix converter,a comparative analysis is performed in the aspects of voltage and current level,system complexity,reliability,etc.and the feasibility of the proposed topology is obtained.Secondly,the problem of DC-side capacitor voltage imbalance in the modularmultilevel matrix converter is analyzed.Aiming at this problem,this paper deduces the power transfer equation of the converter based on a mathematical model,and proposes a layered battery charge state equalization charge control strategy based on direct control of bridge arm current.While charging the battery pack,taking into account the control of the battery management system,the purpose of balanced and fast charging are achieved.Finally,the motor drive control strategies for various driving modes of hybrid vehicles are studied.In this paper,a small-signal model and a switch state equation are used to propose a balanced discharge control strategy for a power integrated conversion system combined with a motor drive control strategy,which achieves good motor drive and battery balanced discharge control.In order to verify the feasibility of the topology and control strategy,this paper presents the software simulation results for the balanced multi-level matrix vehicle-mounted converter equalization charge,discharge and motor drive control.Based on the Rtlab real-time simulator,the comprehensive change system was verified by hardware-in-the-loop experiments.The results confirm the feasibility and effectiveness of the modular multilevel matrix vehicle integrated power conversion system proposed in this paper,which has excellent dynamic and static characteristics.