The brushless DC motor is a kind of synchronous motor, that is to say, the speed of the rotor of the motor is affected by the speed of the rotating magnetic field of the motor stator and the number of poles of the rotor (p):
n=120.f / p. In the case of a fixed number of rotor poles, changing the frequency of the rotating magnetic field of the stator can change the rotational speed of the rotor. The DC brushless motor is a method in which the synchronous motor is electronically controlled (driver), the frequency of the rotating magnetic field of the stator is controlled, and the rotational speed of the motor rotor is fed back to the control center for repeated correction, in order to achieve a near-DC motor characteristic. That is to say, the brushless DC motor can control the rotor of the motor to maintain a certain speed when the load changes within the rated load range.
The DC brushless driver includes a power supply unit and a control unit, and a power supply unit that supplies three-phase power to the motor, and the control unit converts the input power frequency according to requirements.
The power supply unit can directly input DC (usually 24v) or AC input (110v/220 v). If the input is AC, it must be converted to DC by converter. Whether the DC input or the AC input is to be transferred to the motor coil, the DC voltage must be converted from an inverter to a 3-phase voltage to drive the motor. The inverter is generally divided into six upper power transistors (q1, q3, q5)/lower arms (q2, q4, q6) by six power transistors (q1 to q6) to connect the motor as a switch for controlling the flow through the motor coil.
The control unit provides pwm (pulse width modulation) to determine the switching frequency of the power transistor and the timing of commutation of the inverter. DC brushless motors generally use speed control that can stabilize the set value without changing too much when the load changes, so the Hall is equipped with a Hall-sensor capable of inducing a magnetic field. Closed loop control is also used as the basis for phase sequence control. But this is only used as speed control and can not be used as positioning control.
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