New Constant Electrical Power Soft-Stalling Control for Small-Scale VAWTs

This paper presents a constant power soft-stall control scheme for a vertical-axis wind turbine (VAWT) fitted with a permanent magnet generator. Small-scale VAWTs are attractive due to their ability to capture wind from different directions without using yaw; this simplifies the design and gives the turbine tolerance to turbulence in urban areas. One difficulty with VAWTs is to prevent overspeeding and component overloading at excessive wind velocities. This paper suggests that necessary control can be achieved by controlling the electric power in order to operate the turbine in the stall region. This control strategy attenuates the stress in the system, while smoothing the power generated. It is shown that the controller can stabilize the nonlinear system using an adaptive current feedback loop. The controller does not need wind velocity or turbine speed, but is based on the current and voltage measured on the dc side of the rectifier connected to the permanent magnet synchronous generator. Maximum power point tracking (MPPT) control is provided in normal operation. Simulation and experimental results are presented.