Compared with DC motors and asynchronous motors, the key technical characteristics of brushless DC motors are:
1. The operating characteristics similar to DC motors are obtained through electronic control, which has better controllability and a wide speed range.
2. Need rotor position feedback information and electronic multi-phase inverter driver.
3. It is essentially an AC motor. Because there are no sparks and wear problems of brushes and commutators, it can work at high speeds, can obtain high reliability, long working life, and does not require frequent maintenance.
4. The brushless DC motor has a high power factor, no loss and heating of the rotor, and high efficiency: according to data comparison, the efficiency of a 7.5kw asynchronous motor is 86.4%, and the efficiency of a brushless DC motor of the same capacity can reach 92.4%.
5. There must be electronic control part, the total cost is higher than DC motor.
There are two types of motors used in AC systems: induction motors and permanent magnet synchronous motors. Permanent magnet synchronous motors can be divided into sine wave back-EMF permanent magnet synchronous motors (PMSM) and square wave motors according to different working principles. Back-EMF brushless DC motors (BLDCM) have different driving currents and control methods due to different working principles.
The back-EMF of a sinusoidal permanent magnet synchronous motor is sinusoidal. To make the motor generate smooth torque, the current flowing in the motor windings must also be sinusoidal. This requires knowing the continuous rotor position signal so that the inverter can This provides a sinusoidal voltage or current to the motor. Therefore, PMSM requires a high-resolution absolute position encoder or resolver, and the control algorithm is more complicated.
The back-EMF of the brushless DC motor is trapezoidal. As long as the square-wave current is input to the motor winding, the torque is straight. Therefore, BLDCM does not require a high-resolution position sensor, the feedback device is simple, and the control algorithm is relatively simple. In addition, the air gap magnetic field of the BLDCM trapezoidal wave is higher than that of the PMSM sine wave. The utilization rate of the iron core is higher; and the power density of the BLDCM is higher than that of the PMSM, and the output torque per unit volume is greater. Therefore, the application and research of permanent magnet brushless DC motors have been paid more attention.