Research On Modeling And Simulation Of Variable Speed Wind Turbine

With the growing interconnection among regional power grids, the scale of the modern power systems becomes larger and larger. Therefore, it’s necessary to construct appropriate wind turbine model for studying large scale wind farm connecting power grid. Some researchers have carried out extensive study on detailed wind turbine model. Meanwhile, the electromagnetic transient model has been established on software like MATLAB and PSCAD. The detailed electromagnetic transient model, however, is so complex that causes a slow speed of calculation and a bad numerical convergence. It is not suitable for analyzing the performance of the large-scale grid-connected wind power system, whereas such analysis is indispensable on the research of security and stability of power grid with renewable energy. Thus it is necessary to establish an appropriate model of the wind turbine on popular software for power system electromechanical transient analysis. The dissertation studies modelling and control strategy of direct-driven permanent magnet synchronous generator wind turbine system (PMSG).First, the mathematical model of D-PMSG is revealed. The control system including maximum power point tracking (MPPT) control, pitch control, low voltage ride through control and converter control is investigated.Second, an adaptive control strategy for realizing the maximum power point tracking (MPPT) applicable to the wind energy generation system with D-PMSG is proposed. In some cases, the input saturation of converter, which caused by situations like greatly changed wind speed, influences the system stability. The disturbance caused by the loss torque and parameter uncertainty also influences the system performance. Aiming at obtaining an optimal electromagnetic torque to overcome the problems above, an adaptive control law is designed based on Lyapunov stability. Simulations are carried out to demonstrate the effectiveness of the proposed control strategy. The results show that the adaptive control strategy ensures the system stability and solves the contradiction between overshoot and quick response, even though the converter input saturation occurs. Finally it improves the ability for MPPT.Third, a method for an electromechanical transient model of D-PMSG and establishes models using PSASP user define (UD) is proposed, which is for analyzing the impact on stability and security of grid power system. Both the generator with its converter control system and the grid side converter with control system are greatly simplified. The model also consists of braking resister and considers the dynamic process of DC voltage. Then the whole D-PMSG model is established using PSASP UD. Simulations in a single machine infinite bus system are carried out considering both variable wind speed and short circuit fault. Results demonstrate that the proposed model can describe the electromechanical transient characteristics of the wind power system.Last, static and transient security for wind farm connected S power grid is analyzed based on the wind turbine UD model. Also, the impacts of the capacity of the planned wind farm on the system bus voltage level are analyzed. In addition, the transient stability of wind farm connected power grid after three-phase permanent short circuit is analyzed. Finally, the impacts that whether the wind farm has the potential of low voltage ride through has on system stability are analyzed.