Research And Design On Energy Storage System Based On Cascaded Half-Bridge Topology

In order to deal with the trouble of energy and environmental in the future,the academia circles and industry circles have got a common view to the cascade utilization of returned batteries of electric vehicles.However,with so many different types,structures and capacity fading of batteries,it has been a key and urgent problem in the development of the domain how to regroup,operate and manage batteries for reducing costs.Research about batteries regrouping,life prediction,discretization and integration management are the emphases of the study in our countries and overseas.One of them,the flexible battery group technology aims to group batteries indirectly with power electronic devices,and it has the function of batteries status monitoring and independent power control.The technology has the beneficial effects of improving energy utilization efficiency,decreasing the consistency requirements,and cutting down the costs.It is also suitable for new batteries,so it has a wonderful development prospect.The keystone of the dissertation is the energy storage system based on cascaded half-bridge topology,including the modular distributed control.the stability and operating performance analysis of the system.And the related results will be applied to the engineering flexible energy storage converter.This paper makes study on the following aspects.(1)The working principle of cascaded half-bridge topological energy storage system is analyzed.With independent control core,the battery power module is constituted by battery and half-bridge topology circuit.The energy storage series is constituted by several module outputs in series,and several series constitute the energy storage system in parallel connection.The topology is suitable for dc bus of medium or low voltage,and medium power applications,with distributed control for high cost requirement situation.Based on the basic working principle and parameter design of the module,the multiplexing modulation method is presented,and the system parameters are designed.The influence of pulse dead zone to control is analyzed,and the carrier phase shifting method of multi-module is verified by simulation and experiment.(2)The distributed control method is presented for the cascaded half-bridge topological energy storage system.The parallel droop control of converters widely used in microgrid is introduced into the modular series system according to the duality principle,and series droop control is presented.A small signal linear model of the energy storage series is established,and the paper reports the closed loop power control and module independent power control method.The system has the redundancy capability of some modules,and dc bus voltage is allowed appropriately adjust to adapt the state changing of batteries.The secondary regulation of the series will compensate the static error for droop control.The validity of the distributed control is verified by simulation.(3)The energy storage system is connected to ac grid by the bidirectional DC/AC converter which controls the dc bus voltage,and the energy storage series controls the energy storage power.The closed loop impedance model of the energy storage system is derived based on small signal linear model,and the stability of system is analyzed by using impedance ratio criterion.The power static error of the energy storage series based on droop control is analyzed,and the droop coefficient range and the number of redundant modules is derived.Based on the steady-state model and small signal linear model,the influence of the power adjustment,dc bus voltage instruction,the influence of module cut-in and cut-out is also analyzed.The paper reports the method to improve the dynamic performance,and the stable operation of the energy storage system is achieved.(4)An engineering flexible energy storage converter is developed to verify the modular distributed control and the analysis of operating performance,and it is applied to actual protect.The flexible battery group method,the multiple module modulation,the modular distributed control,the stability and operating performance analysis are verified.The device has good static and dynamic performance with satisfying the actual application requirements,and the project also provides a reference for related engineering project.