Grid-Connected Operation Control For Energy Storage Based Direct-drive Permanent Magnet Wind Power System

Wind power is one of most effective ways to solve the world's environmental pollution and energy crisis in renewable energy generation. It is a power generation mode with the most large-scale development conditions and commercial prospects, which has been drawn more attention to many countries. The intermittent and random fluctuation of wind speed result that wind power grid-connected power fluctuates largely, which has a negative influence to stability and economy of power grid operation. Currently, the new power grid rules require that wind turbines have low voltage ride through (LVRT) capacity. When the short-circuit fault occurs, wind turbine not only can grid-connected operation, but also can provide a certain reactive power. With the construction of GW class wind farms, the scale of wind power is growing and grid penetration of wind power is rising, so the adverse effects of output power fluctuations must be resolved. Taking the Power Electronics Science and Education Development Program of Delta Environmental & Educational Foundation and State Key Lab. of Power System project "Energy storage based direct-drive permanent magnet wind power grid-connected operation control system" as the background of the subject, the main study contents in this paper are that using battery energy storage to improve LVRT capability and smooth output power based on direct-drive permanent magnet wind turbine, in order to effectively improve power quality and stability of the large-scale grid-connected wind farms.Firstly, according to direct-drive permanent magnet wind turbine working principle, this paper proposes dual PWM converter control strategy and designs SPLL. The simulation results show that the correctness and affectivity of the MPPT control of wind, SPLL, SVPWM control algorithm and dual PWM converter control strategy.Secondly, this paper analyzes the characteristics of VRB. According to VRB working principle, its equivalent circuit mode is built. The simulation results show its good charge and discharge characteristics. The two ways to improve wind turbines LVRT capacity by adding unloading resistance and VRB ESS at DC-Side are analyzed and modeled, and the simulation results show the correctness of two control strategies. The simulation model is built which VRB ESS are equipped at the outlet of wind farm to smooth output power. The simulation results show that the proposed control strategy of AC/DC PWM converter is correct and effective for VRB ESS. Finally, the hardware and software of ESS are designed. The small power hardware test platform of smoothing wind power output power with battery energy storage is built. The experimental results verify that the energy storage battery can fast throughput output power fluctuation and effectively smooth wind power output power and the proposed control strategies are correct and effective.The work of this paper provides theoretical basis and reference for improving the LVRT capacity of direct-drive permanent magnet synchronous wind turbine and power quality and stability of grid-connected wind farm, and also provides the foundation for the engineering application.