How does the DC brushless motor work?

In order to make the motor rotate, first, the control unit must determine the current position of the rotor of the motor according to the hall-sensor, and then decide to turn on (or turn off) the order of the power transistors in the inverter according to the stator winding. The sequence flows through the motor coil to produce a forward (or reverse) rotating magnetic field that interacts with the magnet of the rotor, thus enabling the motor to rotate clockwise/reversely.

When the rotor of the motor rotates to the position where the hall-sensor induces another set of signals, the control unit turns on the next set of power transistors, so that the cycle motor can continue to rotate in the same direction until the control unit decides to stop the motor rotor. Transistor (or only the lower arm power transistor); to reverse the motor rotor, the power transistors are turned on in reverse order.

In addition, because the electronic components always have the response time of the switch, the power transistor takes into account the response time of the part during the interleaving time of the off and on. Otherwise, when the upper arm (or lower arm) is not completely closed, the lower arm (or upper arm) is already When turned on, the result is a short circuit between the upper and lower arms, causing the power transistor to burn out.

When the motor rotates, the control unit will compare the speed of the drive setting and the acceleration/deceleration rate with the speed of the hall-sensor signal change (or by software operation) to determine the next set ( AH, BL or AH, CL or BH, CL or ...) The switch is turned on and the length of the on time. If the speed is not enough, it will be long, and if the speed is too long, it will be shortened. This part of the work is done by PWM. PWM is the way to determine whether the motor speed is fast or slow. How to generate such PWM is the core to achieve more precise speed control. High-speed speed control must consider whether the CLOCK resolution of the system is sufficient to master the time of processing software instructions. In addition, the data access mode of the hall-sensor signal change also affects the processor performance and the correctness and real-time. As for the low speed speed control, especially the low speed start, since the return hall-sensor signal changes more slowly, it is very important to learn the signal mode, the processing timing, and appropriately configure the control parameter values ​​according to the motor characteristics. Or the speed feedback change is based on the encoder change, so that the signal resolution is increased in order to get better control.

The motor can run smoothly and respond well, and the properness of PID control cannot be ignored. It is mentioned that the DC brushless motor is closed loop control, so the feedback signal is equal to telling the control unit how much the motor speed is now from the target speed. This is the error. Knowing the error naturally requires compensation, in the form of traditional engineering controls such as PID control. However, the state and environment of control are complex and changeable. If the control is tough and durable, the factors to be considered may not be completely mastered by traditional engineering control, so fuzzy control, expert systems and neural networks will also be incorporated into intelligent An important theory of PID control.

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