Study Of Two Stage Power Conversion System Used For Battery Energy Storage

In twenty-first century, the change of world’s energy structure and the aggravation of environmental pollution, that more widely promote the research and utilization of new energy power technologies in wind energy, solar energy and so on. Battery energy storage system has the advantage of high economic benefit, less service conditions, convenient installation and maintenance and so on, so widely used in new energy power generation and the electric vehicle. Power Conversion System(PCS), that’s an important part of the Battery Energy Storage System(BESS), and also the bridge between the power grid and BESS, can play a unique role in BESS. Because of the unique role of bidirectional converter in energy storage system, there is more and more extensive research on bidirectional converter, and the studies focus on the circuit topology with flexible modular and efficient charge discharge and control strategy.In this paper, the control strategy and the design of the main circuit parameters are the main research content of high power converter. And they are verified in the simulation and experiment.First, Several popular PCS topologies are compared and analyzed in this thesis. Combined with the design requirements of PCS, two-stage non-isolated PCS has been chosen as the basic power conversion unit. And the main circuit parameters design have been carried out on the two-stage PCS, including the DC bus capacitor, the filters.Secondly, this paper analyzes the principle and the mathematics model of PCS. And detailed model have been carried out on the three major components of two-stage PCS:LCL filter, three-phase two level DC-AC converter and the bi-directional DC-DC converter using subsystem-integration approach. Simplified models are also developed for controller design.Thirdly, research on the control strategies of PCS in detail. According to the control principle of DC-AC converter and DC-DC converter, the method of coordination control are analyzed and the stage of charging and dis-charging control model within the unified control strategy are studied also. In order to improve the system performance, DC bus outer loop fuzzy PI controller of DC-AC inverter is designed. System simulation model that is built by using MATLAB software are simulated.Finally, small power experiments of PCS that with three bi-directional DC-DC converters and one bi-directional DC-AC converter are carried out. The experimental results show that the proposed design meets the design requirements, verify the correctness and feasibility of the proposed control strategy.