Adaptive robust speed control for continuously variable transmission in wind turbine under grid faults

Abstract

For the grid-connected wind turbine, the frequency converter is used to connect the generator and the grid, which makes the power quality weaker than the conventional synchronous generator. To solve such a problem, a continuously variable transmission (CVT) can be connected at the high speed end of the gearbox to obtain the constant speed output at varying wind speeds for the generator. The frequency converter can then be neglected. However, shafts of the CVT suffer the external disturbances caused by grid faults. The speed tracking accuracy of the CVT can be affected seriously. So, this paper presents the adaptive robust speed control (ARSC) for the CVT, which regulates the speed output through the permanent magnet synchronous motor (PMSM). Model uncertainties of the PMSM, such as the inertia load, friction force, and external disturbances, are considered in the control scheme. The designed controller guarantees high performance and speed tracking accuracy at different wind speeds and simulated grid faults. The experimental results demonstrate the proposed CVT controller at varying wind speeds simulated via the software of FAST and the simulation of grid faults, such as one phase short-circuit and sudden load fluctuation, at a built testbed, which is used to emulate the wind turbine with the CVT. For the comparison, the PID controller for the CVT is then applied in the testbed. The results show that the ARSC method owns better performance and speed tracking accuracy than the PID method. In order to verify the utility scale for the ARSC based CVT, we build a Simulink program for a 1.5 MW wind turbine with the CVT. Simulation results show that the ARSC based CVT still owns high speed tracking accuracy in the large scale wind turbine.