Design and Implementation of the New Sensorless Rotor Position Estimation in Homopolar Salient-Pole Brushless DC Motor

This article presents a novel method for indirect sensing of the rotor position in a homopolar salient-pole brushless dc (BLDC) motor and driving the motor smoothly from a standstill using an inductance bridge. Based on the characteristic of the phase inductance variation, the rotor position can be determined by using the inductance bridge to estimate the inductance of unknown phases. The proposed technique uses the motor winding in Hay’s bridge, and it is adjusted to achieve a balanced condition in an unaligned position when the minimum inductance occurs. In a running mode, by rotating the rotor, an idle phase inductance is changed and Hay’s bridge goes into an unbalanced condition. Then, by injecting extra voltage pulses into idle phases, the bridge output state changes. It then continues to sense the rotor position, while the motor is running by applying the same procedure. Moreover, the proposed method does not have problems like those in previous researches such as mutual inductance effects, need of large memory for locking up of the data, and losing of the estimation accuracy by the change in the sampling rate. As the main salient features of the proposed method, load independent, simplicity in implementation, and flexibility in tuning can be pointed out. Finally, experimental tests have been carried out to confirm the feasibility and practicability of the proposed method.