Control Structure Of DC Motor

The control structure of the brushless DC motor, 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 rotor poles (P), N=120. f/P. When the number of rotor poles is fixed, changing the frequency of the stator rotating magnetic field can change the rotor speed. The brushless DC motor is a synchronous motor with electronic control (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 method close to the characteristics of a DC motor. That is to say, the DC brushless motor can still control the motor rotor to maintain a certain speed when the load changes within the rated load range.

The brushless DC driver includes a power supply part and a control part: the power supply part provides three-phase power to the motor, and the control part converts the input power frequency according to the demand. The power supply can be directly input with DC power (usually 24V) or input with AC power (110V/220 V). If the input is AC power, it must be converted into DC first through a converter. Whether it is DC input or AC input, the DC voltage must be converted from an inverter to a 3-phase voltage to drive the motor before it is transferred to the motor coil. The inverter is generally divided into upper arm (Q1, Q3, Q5)/lower arm (Q2, Q4, Q6) by 6 power transistors (Q1-Q6), which are connected to the motor as a switch that controls the flow through the motor coil. The control unit provides PWM (Pulse Width Modulation) to determine the switching frequency of the power transistors and the timing of commutation of the inverter. The brushless DC motor generally hopes to use the speed control in which the speed can be stabilized at the set value without changing too much when the load changes, so the motor is equipped with a hall sensor (hall-sensor) that can sense the magnetic field, as a function of the speed. Closed-loop control is also used as the basis for phase sequence control. But this is only used for speed control and cannot be used for positioning control.