Position Sensorless Control of PMBLDC Motor by Using the Zero Crossings of Line Voltage Differences with Six and Four Switch Inverter-A Comparison

This paper presents a back EMF sensing scheme, indirect back EMF detection, for sensorless control of Brushless DC (BLDC) motor drive from the terminal voltages. Using this scheme, the motor neutral voltage is not needed to measure the back EMF. Instead the method utilizes difference of line voltages measured at the terminals of the motor. The difference of the line voltages shows an inverted and amplified version of the back EMF. Since the motor neutral is not needed, the developed back EMF sensing method is immune to switching noise and common mode voltage. In this paper, a simple position sensorless control strategy for six switch and four-switch three-phase BLDC motor drives is proposed. Four-switch inverter can reduce cost of drivers by replacing power devices with capacitors. The performance of six switch inverter is compared with the four switch inverter. The position sensorless BLDC drive proposed is based on detection of zero crossing from the line voltage differences. The effectiveness of the proposed drive system is clarified from simulation results.