The Study And Design Of Grid Converter In Battery Energy Storage System

With the fossil energy crisis and environment deterioration in recent years, the country vigorously develop wind power, solar energy and other new green energy generation system. Feeding the large scale intermittent wind power which have huge power fluctuations into the grid, will bring serious problem to the safe and stable operation of power system. The configuration of large-scale battery energy storage system in wind farm will effectively suppress power fluctuations. It's an effective method of wind power and other intermittent energy connected to the grid stably. Hence, research on battery energy storage system in wind farms has become a hot spot. In this thesis, research and analysis of the most critical part of the battery energy storage system(BESS): the grid connected converter of the BESS is proposed.In this thesis, based on the analysis of the functional requirements of the grid connected converter of the BESS in wind farm, the main circuit topology based on three phase voltage-type PWM rectifier is established at first, and the overall system design scheme is determined. Respectively, the mathematical models of the grid connected converter of BESS is established in three phase static coordinate and two phase rotating coordinate. Aimed at the key technology for grid connection: three phase PLL, a controller parameter design method of three phase software PLL is proposed. The voltage space vector modulation(SVPWM) technology and its implementation in the grid connected converter is analyzed.Secondly, the current feed-forward decoupling control strategy is employed for independent control of active and reactive power in controller design. Aimed at three different operation modes, which are DC constant voltage rectification and DC constant current rectification, a two-loop control system based on PI regulator is designed to meet the charging need of the battery pack. Meanwhile, aimed at the inverter gird connected mode of the converter, a direct current closed-loop PQ control system is designed to meet the management requirement of the active and reactive power of the grid. The MATLAB simulation results verified the feasibility of the controller design of the BESS grid connected converter.Then, a 1kVA prototype is designed, which includes the main power circuit design, hardware design and systematic software design base on DSP, according to the special application of wind farm. The design of prototype focused on LCL grid connected filter with damping. The effects of the parameters of LCL filter on filter performance is analyzed. And the design method and procedures are introduced in detail.At last, the experiments of the prototype demonstrate the rationality of the design of the control scheme and prototype of the BESS grid connected converter.