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Aiming problems arising from the wind turbine with the frequency converter, this paper proposes a design for wind turbine based on differential speed regulation. The dynamic characteristics and parameter determination method of the structural components including differential gear train and speed regulating motor (SRM) were studied and the dynamic characteristic expression were obtained. The critical conditions about input power or output power for ring gear driven by SRM were researched. The way to determine the optimal structure parameters of SRM was put forward. The minimum peak power of SRM was regarded as the objective function while the transmission ratios of three gear sets which were placed in the different positions of overall structure scheme was optimized. A SIMULINK model of 1.5 MW wind turbine based on differential speed regulation was built and ran. The rotational speed, torque and power of the wind rotor, the SRM and the synchronous generator were obtained respectively. The simulation results can verify effectiveness of the theoretical analysis and parameter configuration.

The variable speed and constant frequency wind turbine with differential speed regulation consist of wind rotor, speed regulating motor, differential gear train, and synchronous generator. The differential gear train has characteristics of double input and single output. The wind rotor with variable speed work as one input; the output speed of differential gear train is regulated to be stable by speed regulating motor as another input. The constant frequency current is generated by a synchronous generator. The system is simplified into three shafts rigid model for dynamic analysis, and the numerical simulation is made in SIMULINK. The frequency conversion motor is used in the test rig as variable speed input of differential gearbox. Servo motor is adopted to regulate speed. The speed of shaft under different speed input is studied. Modal analysis is carried out to get the resonance frequencies of differential gearbox, and moment inertia of test rig is calculated by software to ensure parameters are consistent with simulation. The principle feasibility of variable speed and constant frequency wind turbine with differential speed regulation is verified by the numerical simulation and experiment.

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The differential gear train and speed regulating motor constitute the variable ratio transmission for grid-connected wind turbine with differential speed regulation. The synchronous generator in the system can accessing the power grid without frequency converter. The transmission can realize the mode of variable speed constant frequency that the wind rotor speed is varying and the generator rotor speed is constant. The power control method is studied under the different wind speed which is lower or higher than rated wind speed with using the relational expression of utilization rate of wind energy Cp, pitch angle β and the tip speed ratio λ. The SIMULINK software is used to build the 1500 kW wind turbine model with differential speed regulation. Some different wind speed is made as input. The feasibility of power control method for grid-connected wind turbine with differential speed regulation is verified by the comparison between the simulation results and the theoretical value of the key parameters.

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