Position Error Compensation for PMSM in Sensorless Control Based on Maximum Output Power per Unit Current

In order to resolve the problem of rotor position estimation accuracy, which is affected by parameter variations during operation of permanent magnet synchronous motor (PMSM), a position error compensation method based on the maximum power output per unit current is proposed. First, a simple and efficient sensorless control scheme based on the back electromotive force (EMF) observer is presented, and the effect of motor parameters error, especially inductance error, on the accuracy of position estimation is analyzed. The increase of inductance error leads to larger estimation error, less power per unit current, and the decline of the motor efficiency. To eliminate the position error, a variable step tracking strategy is proposed to track maximum output power per unit current through injecting compensation inductance to back-EMF observer in real time. Position error caused by inductance variation is finally eliminated as the compensating inductance quickly converges to completely compensated inductance errors. The proposed method does not require extra signal injection or complex calculations, which can effectively simplify the implementation and variable step size search strategy guarantee both good dynamic and steady state performance. The effectiveness and merit of the proposed method have been validated by adequate simulations.