Sliding Mode Observer SMO
Sensorless FOC is a highly demanded solution because it is cost-effective and robust.
The Sliding Mode Observer (SMO) implements a motor model that uses both fixed and dynamic digital filters.
Vector-mathematics functions are applied to motor voltages and currents to minimize the error on the estimated back-EMF (bEMF) vector.
The SMO is probably the only practical option when operating at very high speed. It has been successfully tested up to 500 krpm on a single-pole-pair motor.
Since the rotor-position IP can be switched on the fly, the SMO is also useful in combination with other sensors, either for redundancy or to reduce current ripple during cruise-speed operation.