A Novel Stator Current Observer for Fault Tolerant Control of Stator Current Sensor in DFIG

In order to diagnose the failure of the stator current sensor in variable speed constant frequency (VSCF) wind power generation system with doubly fed induction generator (DFIG) and realize the fault tolerant control after sensor failure, a novel adaptive observer for the estimation of the actual stator current based on model reference adaptive method is proposed. By using matrix transformation, the coefficient matrix of state variables in the reference model is decomposed into a constant matrix and a time-varying matrix with rotor speed variables. To avoid the complicated pole-assignment problem in the state observation of time-varying system and ensure the performance of the adaptive observer in the full speed range of the generator, the constant matrix and the time-varying matrix are used as the coefficient matrix of state variables and input variables in the adaptive model, respectively. Traditionally, the differential term of the stator current in the adaptive law is ignored when the generator is in an ideal steady state. By formula derivation, it is proposed and proved that the differential term of the stator current can be replaced by the differential term of the rotor current in the adaptive model. Then, the accuracy and anti-interference ability of the adaptive observer are improved when the adaptive law based on Lyapunov stability theory is optimized. As a result, the fault can be diagnosed by the error between the estimated values (obtained by observer) and the measured values (obtained by sensor) when the stator current sensor fails. Meanwhile, the fault tolerant control of sensor can be realized by using the estimated stator current as the controlled object. Finally, the correctness and feasibility of the proposed ideas are proved by the results of simulation.