I. Introduction
Fault-tolerant optimal tip-speed-ratio (OTSR) tracking control of wind turbines subject to actuation failures has been proven to be a promising technique to increase the efficiency of power conversion in wind turbines. Most existing maximum power point tracking (MPPT) control methods can be categorized into three types: the hill climb searching (HCS) method, the power signal feedback (PSF) method, and the OTSR method. The HCS method directs the system to the maximum power point (MPP) by perturbing the generator speed [1], [2]. However, its application is limited to small-scale wind turbine systems due to the drawbacks of deteriorated power quality as power ripple always exists, and the tracking speed is normally slow. The PSF method can achieve fast tracking speed with low-power-ripple features [3]– [5]. However, it is only effective within restrictive operational ranges. This work is focused on the OTSR method. By designing a proper control scheme, the rotor speed of a wind turbine can track the desired speed, which allows for the variable-speed wind turbine (VSWT) to operate near the OTSR, producing near-maximum power. Hence, this method converts the MPPT problem into a speed tracking control problem.