Grid-Connected Operation Control Strategy Study Of Diret-Drive Permanent Magnet Synchronous Wind Power System

With the growing worldwide energy crisis, people are gradually turning to new energy generation. Wind energy has attracted widespread attention as a clean、、 environmentally friendly、using convenient and huge storage capacity of renewable energy. Wind power technology has been the rapid development in the countries all over the world. A direct-drive permanent magnet synchronous wind turbine has become the main way of power generation in various VSCF wind power generation systems and it has a simple structure、does not need the liter-speed gearbox、does not exist the brush and slip ring unit、has high operation stability and reliability.In this paper, the significance of research and research status of the wind power generation as well as the structural features of direct-drive permanent magnet synchronous wind turbine have been understood, direct-drive permanent magnet synchronous wind turbine is used as the research object and comparing the advantages and disadvantages of its three kinds grid-connected circuit as well as the dual PWM converter is used as the main grid-connected circuit for it. The nonlinear mathematical model of permanent magnet synchronous generator in dq coordinate system is deduced. A control strategy is proposed to design the variable structure controller of the generator-side converter, which combines the inverse system method, the variable structure control theory and the rotor flux oriented vector control method, using grid voltage oriented vector control method to design the PI controller of the grid side converter. A simulation model is built. The simulation results indicate that using the proposed control strategy, the accurate control of active power output of PMSG, independent adjust of grid-connected active and reactive power, variable speed constant frequency (VSCF) power generation as well as stability control of dual PWM converter DC side voltage can be achieved. Compared with PI control, variable structure control shows quick dynamic performances and good robustness.Considering the fluctuation and intermission of wind farm output power seriously affect the stable operation of a grid. A vanadium redox flow battery (VRB) energy storage system is equipped at the grid bus of wind farm in order to smooth the output power and improve the stability of grid-connected wind farm. A bi-directional AC/DC converter is used as the power regulator of VRB energy storage system. A control strategy is proposed to design the closed-loop controller of energy storage system, which combines the nonlinear control method、the variable structure control theory and the grid voltage oriented vector control method. A simulation model is built. Simulation results show that using the proposed control strategy, the vanadium battery energy storage system can fast charge and discharge to smooth the fluctuation of wind farm output power when the wind speed rapidly changes, variable structure controller shows better dynamic performances when compared it with PI controller; the independent adjusting of the active and reactive power of VRB energy storage system output can be achieved, and the dynamic performance of system is good.