Sensorless field oriented control of induction motors considering main flux saturation effects on test signal injection

The field oriented control of induction motor drives without a speed sensor requires the calculation of the flux vector and the speed by a model from stator voltages and currents. In the case of faulty estimation of the flux vector, e.g., due to incorrect model parameters, the stability of the system is at risk. Calculating an orientation error between the estimated model flux vector and the real flux vector supplies information to stabilize the sensorless control loop. At higher stator frequencies this orientation error can be calculated directly from the stator voltage equation, while at lower stator frequencies a test signal is applied. The orientation error is estimated subsequently from the system´s response to the test signal. A new method is proposed, which considers main flux saturation while calculating the flux vector even down to zero hertz stator frequency, thus ensuring stable operation in the entire torque-speed-plane.