Brushless DC motors and permanent magnet synchronous motors

Update:26 Apr 2021
Summary:

Brushless DC motor: The magnet is magnetized for square […]

Brushless DC motor: The magnet is magnetized for square wave, the control voltage PWM is also square wave, and the current is also square wave. There are 6 space vectors in one electrical cycle. The control is simple, the cost is low, and the general MCU can be realized.

Permanent magnet synchronous motor: The magnet is magnetized by a sine wave, the back electromotive force is also a sine wave, and the current is also a sine wave. Vector control technology is generally used. Generally, there are at least 18 vectors in an electrical cycle (of course, the more the better), which can only be realized by a high-performance MCU or DSP.

DC Servo: This range is very wide. DC servo refers to the control of the DC motor and then the control system to act according to the control instructions (speed, position, angle, etc.), and is generally used for actuators.

1. The difference of sensors:

Brushless DC motor (BLDC): position sensor, such as Hall, etc.;

Permanent magnet synchronous motor (PMSM): speed and position sensors, such as resolvers, photoelectric encoders, etc.;

2. The back EMF waveform is different:

BLDC: approximate trapezoidal wave (ideal state);

PMSM: Sine wave (ideal state

3. The three-phase current waveforms are different:

BLDC: approximate square wave or trapezoidal wave (ideal state);

PMSM: Sine wave (ideal state

4. The difference between the control system:

BLDC: usually includes position controller, speed controller and current (torque) controller;

PMSM: Different control strategies will have different control systems;

5. The difference between design principles and methods:

BLDC: widen the width of the back-EMF waveform as much as possible (make it approximate to a ladder wave);

PMSM: Make the back EMF close to the sine wave;

Reflected in the design is mainly the difference in stator winding and rotor structure (such as pole arc coefficient).

https://www.limingmotor.com

4