Sensorless commutation method for low-voltage BLDC motors based on unfiltered line voltage

Abstract

This study presents a filterless and sensorless commutation method for low-voltage brushless DC motors. The proposed method utilizes controlled DC-link inverter instead of the Pulse-Width Modulation (PWM) scheme. Therefore, motor voltages and currents become free from the high-frequency noise of PWM switching, thereby decreasing motor losses. Consequently, the method does not require any Low-Pass Filter (LPF) and it does not involve speed-dependent phase delay caused by the LPF. However, current commutation deteriorates waveform of line voltages. Thus, specific functions are defined to compensate for the current commutation spikes and remove false zero-crossing points of line voltages. Furthermore, the use of unfiltered line voltages eliminates the requirement of any phase shifter. Hence, the main superiority of the proposed method over preceding sensorless commutation methods is the simultaneous elimination of the phase shifter and LPF, which makes the method simple and cost-effective. The simulation and experimental results show the effectiveness and validity of the method.