Sliding Mode Observer SMO
The sensor less FOC is highly demand solution to because cheap and rugged.
The sliding mode observer implements a motor model with fixed and dynamic digital filters.
The vector mathematic function is applied on motor voltage and currents to minimize estimated bEMF vector error.
The SMO is probably the only usable option when operates at very high speed. The SMO was succesfully tested up 500 KRPM one pair pole motor.
As because the rotor position IP can be switched on the fly, the SMO is also useful when used with other sensor for redundancy or to reduce ripple current when operates at cruise speed.