A novel initial rotor-position estimation method for BLDC motors based on four voltage pulses

This paper presents a new initial rotor position estimation method for brushless dc motors (BLDC). It consists in injection of four short voltage pulses at the motor terminals and then based on the evaluation of the voltage measured at the terminal of the non-energized (floating) stator phase, the position is estimated. The first three pulses are applied for a very short time to evaluate the rotor position while the fourth (last) pulse is used only for detection of magnet polarity. The estimation time of the position with an uncertainty of 180° is independent of the motor electrical time constant, being less than 140µs, while the detection of magnet polarity could last longer (up to few milliseconds) until the iron core is saturated. The proposed method is proved only for salient pole BLDC motors (Ld≠Lq). The advantages of the proposed method are taught to be: quickness, simplicity, accuracy, low computation effort, and the most important: insensitive to the high voltage disturbances specific to the battery voltage in the vehicles. No current sensor is used for the proposed setup. Experimental results are provided to prove the concept and validate the solution.