Mechanical-state estimator for doubly-fed induction generators — Application to encoder-fault tolerance and sensorless control

In this paper a new model reference adaptive system observer for estimating the mechanical quantities of a doubly-fed induction generator, namely position, speed and electromagnetic torque and power, is presented. It is based on the computation the air gap power vector, considering saturation by using a variable magnetizing inductance. This algorithm can be used as a back-up in case of encoder fault thanks to an associated fault detection and isolation technique, combining a cumulative-sum function and a state-space adaptive model. Experimental tests on a 3 kW 4-pole doubly-fed induction generator show that a varying magnetizing inductance is recommended if the reactive power flow at stator terminals has to be varied in a large range. The encoder-fault detection time does not vary significantly with speed, torque or stator reactive power flow.