Sensorless Control Methods for BLDC Motor Drives: A Review

Permanent magnet motors, such as Brushless DC (BLDC) motors, are widely adopted in today’s industry for their high power density, torque-to-weight ratio, and uncomplicated design. Furthermore, electrical motor drive systems are increasingly adopting (position) sensorless control methods. Sensorless techniques have several advantages over sensor-based methods, including enhanced reliability, prolonged motor lifespans, simplified inverter-motor connections, and lower costs. Several sensorless techniques have been proposed over the past few decades, such as methods based on terminal voltage measurement, third harmonic back electromotive force (back-EMF) signals, and estimation methods. Research in recent years has focused on improving conventional sensorless methods and developing new ones, including those based on flux linkage functions and neural networks. These advancements address challenges associated with high-speed BLDC drives where the phase lag of the LPF is significant, tackle issues in very low-speed applications where back-EMF signal amplitudes are low, improve position estimation speed to enable one-cycle estimation, enhance control system accuracy for BLDC motors with nonideal back-EMFs, and consider asymmetric back-EMF signals. This paper examines the benefits, limitations, and challenges of sensorless drives for BLDC motors, alongside innovative solutions for nonideal and asymmetric back-EMF issues, with an eye toward future developments.