Research On Key Technology Of Integrated PHEV Battery Management And Power Conversion Based On BMMC Topology

With the continuous development of the economy,China's car ownership,especially fuel cars,has increased significantly.However,this has.not only increased the country's dependence on oil imports,but also brought national environmental pollution problems such as smog.For this reason,China and other countries and regions have adopted the development of new energy vehicles,especially electric vehicles as a national development strategy,and have successively put forward clear timetables for the ban on the sale of fuel vehicles.In addition,with the construction and development of smart grid and energy Internet,electric vehicles as a distributed energy storage device will become an important part of the energy Internet through V2G(Vehicle to Grid)technology.The multiple functions of peak shaving,optimizing the operation of the power system,also provides an opportunity for consumers to participate in power market transactions.In new energy vehicles,plug-in hybrid electric vehicles(PHEV)can work in a purely electric state to meet the needs of low-carbon and green environmental protection,and because they have a complete fuel-powered system,they can reduce the "mileage anxiety" brought by traditional pure electric vehicles.At the current stage where domestic charging facilities are not yet perfect,it can be a good transition product for pure electric vehicles to replace fuel vehicles.However,most PHEVs include multiple independent converters such as AC/DC,DC/AC,and DC/DC,as well as a battery management system(BMS)with higher cost and independent operation.Such a structure is not conducive to integrated and lightweight design of the entire vehicle.This dissertation introduces the currently applied and researched integrated topologies and control strategies for electric vehicle driving and charging,compares various BMS battery state of charge(SOC)equalization methods,then proposes a hybrid PHEV based on Back-to-Back Modular Multilevel Converter(BMMC)integrated topology(hereinafter referred to as BMMC-PHEV),it integrates multiple charging functions and drive modes,and without additional circuits,it achieves the SOC balance control of the power battery under various working conditions.The integrated topology proposed in this dissertation is conducive to the integrated design of vehicles,and has important theoretical significance and application value for the development of new-generation electric vehicle power conversion technology.This dissertation focuses on the topology and working principle of the BMMC-PHEV.First,the dissertation analyzes the power flow when the integrated topology is used for motor drive and external single-phase AC power charging.Because the submodule uses a half-bridge structure,the arm voltage in the topology has unipolar characteristics.When the power battery integrated in the sub-module is charged by an external single-phase AC power supply,the AC current flowing through the arm and the arm voltage will generate a negative power situation within half a power frequency cycle,that is,the process of the power battery's energy feedback to the single-phase AC power source.This process not only increases the battery loss,but also increases the reactive load of the power supply to some extent.In order to solve this problem,this dissertation proposes a half-wave-arm-current charging method that is suitable for working with BMMC-PHEV under single-phase AC charging,and an improved modulation method is proposed based on the traditional carrier phase shift modulation method.Secondly,the dissertation uses the structure and characteristics of the BMMC-PHEV to design a hierarchical battery SOC equalization control strategy,and combines it with single-phase AC charging control and motor control of a separate motor operation to form a multi-loop control system to achieve integration.This dissertation implements the integration of multiple controls such as topology external charging,motor drive,and battery SOC equalization in BMS.In order to verify the theoretical feasibility of the integrated topology and the effectiveness of the corresponding control strategies,this dissertation uses Simulink simulation environment and RT-LAB platform to build a model.Among them,two RT-LABs are used as the main circuit and controller respectively.Using I/O port connection to simulate hardware-in-the-loop experiments.The results confirm the feasibility of the integrated topology and the effectiveness of the control strategy.