Position detection of brushless DC motor using inductance bridge system

This paper introduces a rotor position detection scheme for dc brushless permanent magnet motor commutation control. Since phase coil inductance plays a significant role in the steady-state and dynamic characteristics of electromagnetic devices, the rotor position can be determined using an inductance bridge system to measure unknown inductance and resistance values of the motor. An enhanced scheme is developed for detecting the position of rotor based on inductance variation of phase coils. The inactive or unenergized phase coils can be used as a sensor to detect the magnet rotor position by applying known reference signals and measuring the amplitudes of the returned responses. This technique is ideal for motor rotation at very low speeds.