Compared with DC motor and asynchronous motor, the key technical characteristics of Brushless DC motor are:

1.The operating characteristics of DC motor are obtained by electronic control. It has better controllability and wide speed range.

2.Rotor position feedback information and electronic multiphase inverter driver are needed.

3.Essentially, AC motor can work at high speed without spark and abrasion of brush and commutator. It has high reliability, long working life and no need of maintenance.

4.Brushless DC motor has high power factor, no loss of rotor and heat, and high efficiency: compared with data, the efficiency of 7.5 kW asynchronous motor is 86.4%, and the efficiency of the same capacity brushless DC motor can reach 92.4%.

5.There must be electronic control parts, the total cost is higher than the DC motor.

There are mainly two kinds of motors used in AC system: induction motor and permanent magnet synchronous motor. Permanent magnet synchronous motor can be divided into sinusoidal back EMF permanent magnet synchronous motor (PMSM) and square wave back EMF brushless DC motor (BLDCM) according to different working principle. So that their driving current and control mode are different.

The back EMF of sinusoidal permanent magnet synchronous motor is sinusoidal. For the motor to produce smooth torque, the current flowing through the motor winding must be sinusoidal. Therefore, the continuous rotor position signal must be known, and the inverter can provide sinusoidal voltage or current to the motor. Therefore, PMSM needs to adopt high voltage or current. The resolution of the position encoder or resolver is also very complicated.

BLDCM does not need high-resolution position sensor, the feedback device is simple, and the control algorithm is relatively simple. In addition, the air gap magnetic field of BLDCM trapezoidal wave is more efficient than that of PMSM sinusoidal wave, and the power density of BLDCM is higher than that of PMSM. Therefore, the application and research of permanent magnet brushless DC motor has received more and more attention.