A novel soft-stall power control for a small wind turbine

In this paper, the problem of Soft-stall power control design for a small wind turbine is considered. Passive stalling and furling methods are widely used to limit the output power of small wind turbines at above-rated wind speed conditions. However, these methods have substantial limitations, for instance, related to tracking the maximum power at some wind speed levels, limited variable speed operation and introducing unbalanced forces on wind turbine blades. Soft-stall power control is a promising technique to overcome above limitations and improve the performance of small wind turbines. Small wind turbines have a comparatively low moment of inertia value, and it is possible to make fast speed changes by generator torque control which is essential to the successful implementation of proposed control method. A sliding-mode controller is developed as the wind turbine speed controller. Furthermore, two sliding-mode current controllers are utilized in the field oriented control system of the generator. A simulation study is illustrated to validate the proposed soft-stall power control technique and results are compared with two other speed control strategies which confirm the applicability of the proposed control technique for small wind turbines.