There are significant differences between brushless DC motors and permanent magnet synchronous motors in many aspects. The structure, control strategy, back electromotive force waveform, current harmonics, torque ripple, cost performance, switch conduction state and losses are summarized below. For comparison, those who are interested can learn about it:

1) Structure :

Brushless DC motor: The rotor magnetic poles are usually designed with tile-type magnets. After specific magnetic circuit design, the air gap magnetic density of the trapezoidal wave can be obtained. The stator winding mostly uses concentrated full-pitch winding, so the induced back electromotive force is also a trapezoidal wave.

Permanent magnet synchronous motor: It has a stator three-phase distributed winding and a permanent magnet rotor to ensure that the induced electromotive force waveform is sinusoidal. In addition, the shape of its permanent magnets is usually parabolic to produce a magnetic density as sinusoidal as possible in the air gap.

2) Control strategy :

Brushless DC motor: PWM control is usually used to adjust the current and voltage generated by the motor to control the motor's speed, torque and other parameters. Its control is usually based on position feedback and may require position sensors or position sensorless control technology.

Permanent magnet synchronous motor: Usually a vector control strategy is used to achieve precise control of the motor by controlling the relative position of the stator current and the rotor magnetic field. It usually requires real-time acquisition of rotor position information, so the accuracy of the sensor is required to be high.

3) Back electromotive force waveform :

Brushless DC motor: mostly trapezoidal wave.

Permanent magnet synchronous motor: mostly sine wave.

4) Current harmonics :

Brushless DC motor: Using square wave control, it may produce more current harmonics.

Permanent magnet synchronous motor: In order to produce constant electromagnetic torque, a sinusoidal stator current is required, which helps to reduce current harmonics.

5) Torque ripple :

Brushless DC motor: Since the air gap magnetic field is a square wave, the ideal trapezoidal wave current cannot be obtained due to the influence of the stator winding inductance during commutation, resulting in large torque ripple.

Permanent magnet synchronous motor: Torque ripple is relatively small.

6) Cost-effectiveness :

Brushless DC motor: Due to its mature control technology and modular design, the cost is relatively low, so it is widely used in many fields.

Permanent magnet synchronous motor: requires a more complex controller and powerful computing performance, making its price relatively high. But considering its high efficiency and good performance, it may be more cost-effective in some high-end applications.

7) Switch tube conduction state :

Brushless DC motor: usually adopts the control method of three-phase six-state conduction in pairs. Each phase conducts at an electrical angle of 120° and commutates every 60° electrical angle. Only the position of the commutation point is detected.

Permanent magnet synchronous motor: three phases work simultaneously, and the current of each phase differs by 120° electrical angle.

8) Loss :

Brushless DC motor: less efficient at low speeds and load changes, so greater losses may occur.

Permanent magnet synchronous motor: It adopts vector control technology, which makes its efficiency relatively higher when the speed and load change, so the loss is relatively small.

In summary, there are significant differences between brushless DC motors and permanent magnet synchronous motors in many aspects.