Design of a Unified Power Controller for Variable-Speed Fixed-Pitch Wind Energy Conversion System

A unified power controller for variable-speed fixed-pitch wind energy conversion system (WECS) is designed covering the whole range of wind speed in this paper. The proposed controller is composed of a modified maximum power point tracking (MPPT) controller in low wind speed and a new constant speed and constant power controller in high wind speed. For the former, a combination of modified hill climb searching (HCS) and power signal feedback (PSF) MPPT algorithms is used. The modified HCS method is activated to search for the maximum power point (MPP) first, which is followed by the PSF method once one MPP is found. By using this controller, not only the a priori knowledge of the aerodynamic characteristics of turbine blades is avoided, but also low torque/power ripple is achieved; for the latter, a new auxiliary passive stall control method is proposed. It temporarily increases the output power to force the turbine to operate in deep stall regime, thus to decrease the captured power of the turbine. The proposed controller is implemented on a digital signal processor. The validity of the proposed method is verified by experimental results done on a 10-kW WECS.