Implementation of noval sensorless control based on back EMF difference estimation method

Recently, the Brushless DC (BLDC) motor is becoming popular in various applications because of its high efficiency, high power factor, high torque, simple control, and lower maintenance. BLDC motor had a substantial impact in some industry markets, primarily plastics and fibres and mining company etc. The BLDC motor is designed to utilize the trapezoidal back-EMF with square wave currents to generate constant torque. Conventional BLDC motor drive is generally implemented via six-switch three-phase inverter and three Hall Effect position sensors that provide six commutation points per electrical cycle. For some applications it is important to reduce the manufacturing cost of the drive. The general solution to the problem is the open-loop start-up method named `align and go´. The procedure is to excite two phases of the three-phase windings for a preset time. The permanent magnet rotor will then rotate to align to a specific position. With a known initial rotor position and a given commutation logic, an open-loop control scheme is then applied to accelerate the motor from a standstill.