Research On STATCOM/BESS Control Strategy For Wind Turbine With Squirrel-cage Induction Generator

With the development of wind power generation, the installed capacity proportion to the power system rises year by year, so that it has become one of the key technologies to improve the power quality of wind turbines in this field. The STATCOM/BESS system is introduced to work together with the squirrel-cage asynchronous wind turbines and its corresponding control strategy is investigated in this thesis to improve the power quality of squirrel-cage asynchronous wind turbines and make the BESS work in the reasonable condition so as to avoid the battery overcharge and over discharge, extend the lifetime of battery and reduce the cost of wind power system operation.Firstly, the background, purpose and significance of the subject is introduced in this thesis, the domestic and oversea development situation of reactive power compensation and energy storage system in wind power in recent years is surveyed, and the research content of this thesis is pointed out.Secondly, the overall structure and working principle of STATCOM/BESS system in squirrel-cage wind turbine are introduced, and the working principle and modulation mode of STACOME are discussed. Based on the introduction to the mathematical model of BESS system, the structure and parameters of BESS system are designed. Furthermore, the parameters of the filter inductor, the filter capacitor and dc-link capacitor in STATCOM/BESS main circuit are designed.Thirdly, based on the introduction to the conventional vector control strategy of STATCOM, the active and reactive power decoupling control strategy of STATCOM/BESS is proposed. This control strategy can not only suppress output power fluctuation of wind turbine efficiently and achieve gird- connected unit power factor control so as to improve the power quality of wind turbine output significantly, but also timely adjust the additional feed power into the power grid according to the state of the BESS as so to make BESS work in a reasonable condition all the time and avoid over-charging or over-discharging of BESS so that its lifetime and reliability are improved.Finally, the whole system simulation model, which includes squirrel-cage wind turbine, STATCOM/BESS system and its controller, is established in PSCAD. The simulation results indicate that under constant and disturbance wind speed, step and disturbance wind speed, gradient and disturbance wind speed, the control strategy of STATCOM/BESS proposed in this thesis is able to not only smooth the fluctuation of active power conveyed to grid accurately, quickly and effectively, achieve unity power factor control and upgrade the power quality of wind turbines significantly, but also make BESS work in safety area all the time by adopting active power-regulating algorithm so as to improve the lifetime and reliability of the BESS system.