US Patent 7057362 Operation of an electrical machine

An electrical machine is controlled without using a physical rotor position detector. When the demanded torque output is low, a control method causes the machine to operate on fewer than all the phases, thus increasing the phase current and improving the resolution of the position detection algorithm. The method can include sampling the phase current of the machine, determining whether the phase current is above a predetermined threshold, reducing the number of active phases, and then deriving the value of rotor position from the increased phase current in the remaining phases.