**3.3. BLDC motor**

The Brushless Direct Current (BLDC) motor is rapidly gaining popularity by its utilization in various industries. As the name implies, the BLDC motor do not use brushes for commutation; instead of this they are commutated electronically.

The BLDC motors have many advantages over brushed DC motors and induction motors. A few of these are: (1) Better speed versus torque characteristics; (2) High dynamic response; (3) High efficiency; (4) Long operating life; (5) Noiseless operation; (6) Higher speed ranges. In addition, the ratio of torque delivered to the size of the motor is higher, making it useful in applications where space and weight are critical factors (Indu, 2008).

The torque of the BLDC motor is mainly influenced by the waveform of back-EMF (the voltage induced into the stator winding due to rotor movement). Ideally, the BLDC motors have trapezoidal back-EMF waveforms and are fed with rectangular stator currents, which give theoretically constant torque. However, in practice, a torque ripple exists, mainly due to EMF waveform imperfections, current ripple, and phase current commutation. The current ripple follows up from PWM or hysteresis control. The EMF waveform imperfections result from variations in the shapes of slot, skew and magnet of BLDC motor, and are subject to design purposes. Hence, an error can occur between actual value and the simulation results. Several simulation models have been proposed for analysis of BLDC motor (Jeon, 2000).
