Magnetic saturation of permanent magnet motor coil as key effect for initial rotor position detection

Permanent magnet (PM) motors, due to it's simplicity, reliability and overall efficiency are currently taking "most wanted" epithet in the number of consumer appliances. In recent two decades a lot of scientific papers were published regarding sensor-less control of permanent magnet DC motors. One of the most critical challenges is start from the stand still, with or without load, due to absence of back electromotive force in the motor coils. Core magnetic effect which enables detection of position, when motor is still, is based on magnetic saturation. Aim of this paper is to give magnetic explanation of this phenomena, which is generally neglected in most of motor control related textbooks and papers as well, also most of the motor models are based on linear magnetic approximation of the coils, hiding this key effect which provides information about initial position.