Detection of rotational periodic torque deviations in variable-speed wind turbine systems using disturbance observer and phase-locked loop

We discuss the detection of rotational periodic torque deviations in variable speed wind turbine systems. These deviations can be caused by faults in the system. The turbine torque is estimated with an observer and an estimate of the ideal aerodynamical torque is calculated. These torques are analysed using a phase-locked loop to detect deviations. The torque observer is based on the model of the turbine drive train. It is modelled as a two-mass-system with a flexible shaft. The design of the observer and the phase-locked loop are shown and their stability is discussed. Simulations show, that the presented concept is capable of detecting the amplitude of the deviations at different periodicities, online and for variable speed.