US Patent 7176650 Operation of an electrical machine

An electrical machine is controlled without using a physical rotor position detector. Rotor position is estimated by an algorithm which receives feedback from a parameter which represents the behavior of a phase of the machine. Before the algorithm estimates position, it checks the value of the parameter to ensure that the phase is healthy. In the event of the parameter indicating that the phase is faulty, the algorithm does not attempt to estimate position from that phase, thereby avoiding the generation of faulty position data. Operation of the machine may be continued using only the healthy phases.