Research And Design Of Bi-directional Power Conversion System In Battery Test And Emulation Equipment

Power battery is the "heart" of electric vehicle,and its impact on driving performance and vehicle safety can’t be ignored.Power battery testing and simulation instrument is the necessary equipment in the process of battery research and development,production,group application and motor test,so it is very important.In power battery test simulator,bi-directional power conversion system directly charges and discharges batteries,which is the core of energy bi-directional flow.Whether the grid side has strict requirements on its grid-connected power quality,or the load side has strict requirements on its output response and power quality.Therefore,the development of high-performance bidirectional power conversion system is the cornerstone and key to ensure the safe and reliable operation of battery test simulator.In this paper,the bi-directional power conversion system of power battery test simulator is studied and designed,and the system prototype is developed to verify the relevant theory and technology.Mainly reflected in the following aspects:Firstly,the topology design of bidirectional power conversion system is described.According to the system performance index,a three-stage power topology scheme is proposed.For grid-connected bidirectional AC/DC converters,a time-domain continuous model based on switching function is constructed,and the current circuits under different switching modes are analyzed.For load-side bidirectional DC/DC converter,the duty cycle model of Buck-boost topology is deduced,and the basic working principle of triple interleaving parallel and bipolar structure design is elaborated in detail.Secondly,the modulation and control strategies of bidirectional power conversion system are studied.Aiming at the bidirectional AC/DC converter on grid-connected side,a phase-locked loop(PLL)scheme with positive and negative sequence components decoupling is proposed,which solves the adverse effect of voltage imbalance on grid-connected side,and then the double closed-loop PI control strategy based on SVPWM modulation is analyzed.At the same time,the time-domain discrete model of bidirectional AC/DC converter is deduced,and a hybrid control strategy based on current inner-loop MPC algorithm is proposed,with good dynamic response characteristics.Aiming at load-side bidirectional DC/DC converter,the mathematical characteristics of ground current under bipolar synchronous carrier modulation are analyzed,and a ground current suppression strategy based on asynchronous carrier modulation is proposed.Thirdly,the hardware and software design of the bidirectional power conversion system is completed.In the aspect of hardware,the hardware circuit of bidirectional AC/DC control system is introduced,and the parameters of power devices such as output inductance and output capacitance of bidirectional DC/DC converter are analyzed in detail.In software aspect,a task hierarchical programming scheme based on CPU and CLA cooperative processing is proposed.Finally,an experimental prototype of 50 kW bidirectional power conversion system based on SiC MOSFET is built.The bi-directional AC/DC converter grid-connected double closed-loop debugging and triple interleaved bipolar DC/DC converter inductance current debugging are completed.The output characteristics of the prototype have been tested and the expected performance requirements have been achieved.