Research On Drive Train Modeling And Torque Control Strategy Of Front-end Variable Speed Wind Turbine

ABSTRACT:With the increasing of wind turbines capacity in the grid, the wind turbines grid-code requirements have been improving increasingly. The doubly fed wind turbine as the main wind turbine in the current wind power generation market cannot meet the strict grid-code requirements, which include low voltage ride-through ability, active power adjustment ability and reactive power support ability etc. The situation seriously affects the further development and utilization of wind power generation. However, if the doubly fed induction generator in the wind turbines can be replaced by the conventional synchronous generator, then the wind turbines grid-code requirements can be met.The paper investigates the front-end variable speed wind turbine embedded with variable ratio gearbox(VRG), which is proposed by the advantages of the synchronous generator. The wind turbine is able to adjust its transmission ratio between the rotor and the synchronous generator and maintain the generator to operate at synchronous generator constant speed. Therefore, the conventional synchronous generator can be used to build the new type wind turbine and meet the wind turbine grid-code requirements.Firstly, the fundamental structure and operational mechanism of the front-end variable speed wind turbine are introduced in the paper. To further reveal the salient features of the new type wind turbine, a three-mass drive train model is proposed with considering the torsional flexibility of the wind turbine drive train shaft between the rotor and the synchronous generator. Then the wind turbine drive train model is established by using the second Lagrange equation. On the basic of the established model, the drive train model after the wind turbine access to the grid is derived.Then, the paper focuses on the motor torque control strategies for research and analysis under the condition of wind turbine maximum power tracking. The motor torque control strategy is designed by applying the robust PI control idea. And the corresponding control parameters are designed from the perspective of realize the optimal control. Finally, the control effect of the robust PI control strategy is verified by the Matlab/Simulink simulation software. Matlab/Simulink simulation results show that the control strategy not only can achieve the motor desired speed tracking, but also can obtain the maximum power. Furthermore, for further research the motor control strategy of the new type wind turbine, the adaptive motor torque control method is proposed, which doesn’t depend on the front-end variable speed wind unknown parameters. The control strategy is verified by the Lyapunov equation and Matlab/Simulink simulation. Theoretical analysis and simulation results show that the adaptive control method is able to achieve the motor desired speed tracking and maximum power tracking under the condition of wind turbine system parameters are unknown.This work was supported by the National Key Basic Research Program of China (Grant No.2012CB215202), the National High Technology Research and Development Program of China (Grant No.2012AA052302) and the National Natural Science Foundation of China (Grant No.51207007).