DC brushless motor control structure
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 poles of the rotor, 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 rotor of the motor is fed back to the control center for repeated correction, in order to achieve a close to the characteristics of the DC motor. 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 as shown in Fig. (1): the power supply unit supplies three-phase power to the motor, and the control unit converts the input power frequency according to requirements.
The power supply unit can be directly connected to the DC input (usually 24V) or AC input (110V/220V). If the input is AC, it must be converted to DC by the converter (CONVERTER). Whether the DC input or the AC input is to be transferred to the motor coil, the DC voltage must be converted from the inverter (INVERTER) to the 3-phase voltage to drive the motor. The inverter (INVERTER) is generally divided into six upper power transistors (Q1, Q3, Q5)/lower arm (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 the commutation of the inverter (INVERTER). DC brushless motors generally use a speed sensor that can stabilize the set value without changing too much when the load changes, so the Hall is equipped with a Hall sensor (HALL-SENSOR) that can sense the magnetic field. The 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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