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Cognition of Brushless DC Motor

2021-07-30 10:12:07 Volcano Motor Read

At present, there are two definitions of brushless DC motor(BLDC).

One is that only trapezoidal/square wave brushless DC motor can be called brushless DC motor, while sine wave brushless motor is called permanent magnet synchronous motor

Another definition holds that trapezoidal wave/square wave brushless motor and sine wave brushless motor are brushless DC motors.

Composition of complete equipment

A complete set of brushless DC motor products includes motor body and controller. The stator windings of motor body are mostly made into three-phase symmetrical star (or triangle) connection. And permanent magnets which are magnetized are fixed on the rotor. In order to detect the position of the rotor of the brushless DC motor, a position sensor is installed in the motor.

The controller is composed of power electronic devices and integrated circuits, etc. Its functions are: receiving the control signals of starting, stopping and braking from the outside to control the starting, stopping and braking of the motor; Receiving position sensor signals and positive and negative rotation signals, which are used to control the on-off situation of each power tube of the inverter bridge and generate continuous torque; Receive speed instruction and speed feedback signal to control and adjust speed; Provide overcurrent, overvoltage and undervoltage protection and display, etc.

Principle of Brushless DC Motor

The main circuit is a typical voltage-type AC-DC-AC circuit, or DC-AC circuit. The inverter provides a symmetrical alternating rectangular wave motor with equal amplitude and width, and the N-S positions of permanent magnets on the rotor are alternately exchanged. The position sensor generates three square waves with a phase difference of 120, and combines the forward/reverse signals to generate an effective state coding signal, which is processed by logic components to generate the on-off signals of each power switch tube, so that every time the rotor rotates a pair of N-S poles, six power tubes are In each state, only two-phase windings are energized, which changes one state in turn. The magnetic field axis generated by the stator winding rotates 60 electrical angle in space, and the rotor is in a new position, which makes the position sensor generate a new set of codes. The new codes change the conduction combination of the power tube, which makes the magnetic field axis generated by the stator winding advance 60 electrical angle again. In this way, the brushless DC motor generates continuous torque and drives the load to rotate continuously.

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