Permanent magnet brushless DC motor and permanent magnet synchronous motor

Update:12 Apr 2021

The materials used in the permanent magnet brushless DC […]

The materials used in the permanent magnet brushless DC motor and the permanent magnet synchronous motor are basically the same, mainly due to the difference in design. Generally, when the brushless DC motor is designed, the air gap magnetic field is square wave (trapezoidal wave) and flat top The flatter the better. Therefore, in the selection of the number of pole pairs, integer-slot concentrated windings such as 4 poles and 12 slots are generally selected, and the magnetic steel is generally a concentric sector ring with radial magnetization. Hall sensors are generally installed to detect the position and Speed, the driving mode is generally six-step square wave drive, which is used for occasions where the position requirement is not very high; while the permanent magnet synchronization is a sine wave air gap, the more sine, the better, so choose the fractional slot winding for the number of pole pairs, such as 4 poles 15 slots, 10 poles, 12 slots, etc. The magnets are generally bread-shaped, magnetized in parallel, and the sensors are generally equipped with incremental encoders, resolvers, absolute encoders, etc. The drive i method generally uses sine wave drive, such as FOC algorithm, etc. .Used in servo applications.

You can judge from the internal structure, sensor, driver, and application. This kind of motor can also be used interchangeably, but it will reduce the performance. For most permanent magnet motors with air gap waveforms between the two, it mainly depends on the driving method .

Brushless DC motors usually use watt-shaped magnets for the rotor poles. After the magnetic circuit design, the air gap flux density of the trapezoidal wave can be obtained. Most of the stator windings use concentrated full-pitch windings, so the induced back electromotive force is also trapezoidal wave. The control of the brushless DC motor requires position information feedback, and it must have a position sensor or adopt a position sensorless estimation technology to form a self-controlled speed regulation system. When controlling, the current of each phase is also controlled as a square wave as much as possible, and the inverter output voltage can be controlled in accordance with the PWM method of the brushed DC motor. In essence, the brushless DC motor is also a permanent magnet synchronous motor, and the speed regulation actually belongs to the category of variable voltage and frequency conversion speed regulation.

Generally speaking, a permanent magnet synchronous motor has a stator three-phase distributed winding and a permanent magnet rotor. In the magnetic circuit structure and winding distribution, it is ensured that the induced electromotive force waveform is sine, and the external stator voltage and current should also be sine waves, generally relying on AC voltage transformation. The inverter is provided. Permanent magnet synchronous motor control systems often adopt automatic control, and position feedback information is also required. Advanced control strategies such as vector control (field-oriented control) or direct torque control can be used.