Wind turbine control strategy for shaft stress reduction

The issue of fatigue loading on wind turbine drive trains due to the fluctuating nature of wind is a major cause of premature gearbox failures. A new control scheme is proposed and investigated which aims to maintain speed control of the wind turbine, as well as being able to compensate for torque pulsations as a result of wind speed variations. These torque pulsations are the main cause of shaft overstressing and result in the premature failure of gearboxes, rotors and drive trains. The control strategy implemented makes use of well-known Proportional (P) and Proportional Derivative (PD) controllers, and therefore does not need sophisticated models of the wind turbine system requiring knowledge of parameters specific to the machine. The controller implemented consists of two control loops, the one being a speed control and the other a torque controller. The controller is implemented on a 2kW three-phase permanent magnet wind turbine. System simulations showed that the control strategy was able to operate successfully, however, in practice it was found that the speed control loop operated but the torque control was unsuccessful. This was due to high levels of noise as a result of the differential action on the torque feedback loop.