DC motor control principle

hit count: Updated: 2018-10-11 16:52:10 [ close ] share:

    The control principle of the DC motor. To make the motor rotate, the control unit first determines the order of turning on (or off) the power transistors in the inverter according to the stator winding based on the position of the motor rotor. , AH, BH, CH (these are called upper-arm power transistors) and AL, BL, CL (these are called lower-arm power transistors) in the inverter, so that current flows through the motor coils in sequence to generate a forward (or reverse) rotating magnetic field And interact with the magnet of the rotor, so that the motor can rotate clockwise / counterclockwise. When the rotor of the motor rotates to the position where the hall-sensor senses another set of signals, the control unit turns on the next group of power transistors, so that the cycle motor can continue to rotate in the same direction until the control unit decides that the motor rotor is stopped and the power is turned off. Transistor (or only the lower arm power transistor); if the motor rotor is reversed, the power transistor turn on sequence is reversed.

    Basically, the method of opening the power transistor can be exemplified as follows: AH, BL group → AH, CL group → BH, CL group → BH, AL group → CH, AL group → CH, BL group, but must not Open into AH, AL or BH, BL or CH, CL. In addition, because electronic parts always have the response time of the switch, the staggered time of the power transistor in the off and on time must take into account the response time of the part, otherwise when the upper arm (or lower arm) has not been closed, the lower arm (or upper arm) is already turned on. As a result, the upper and lower arms are shorted and the power transistor is burned.

    When the motor rotates, the control unit will compare (or calculate by software) the command (Command) composed of the speed set by the driver and the acceleration / deceleration rate and the change speed of the hall-sensor signal to determine the next group ( AH, BL or AH, CL or BH, CL or ...) the switch is turned on, and the length of the turn on time. If the speed is not enough, it will open long, and if the speed is too high, it will be shortened. This part of the work is completed by PWM. PWM is a way to determine whether the motor speed is fast or slow. How to generate such PWM is the core of speed control.

    High-speed speed control considers whether the resolution of the system's CLOCK is sufficient to grasp the time required to process software instructions. In addition, data access methods for changes in hall-sensor signals also affect processor performance and correctness and real-time determination. As for the low-speed speed control, especially the low-speed start, because the return hall-sensor signal changes more slowly, how to capture the signal method, processing timing, and appropriately configure the control parameter value according to the characteristics of the motor becomes very important. Or the change of speed return is based on the change of the encoder, so that the signal resolution is increased in order to get better control. The motor can run smoothly and respond well, and the appropriateness of PID control cannot be ignored. As mentioned earlier, the DC brushless motor is closed-loop control, so the feedback signal is equivalent to telling the control unit how much the motor speed is far from the target speed. This is the error. If you know the error, you will naturally have to compensate for it. There are traditional engineering controls such as PID control. However, the state and environment of the control are actually complex and changeable. If the control is sturdy and durable, the factors to be considered may not be mastered by traditional engineering control, so fuzzy control, expert systems and neural networks will also be incorporated into intelligent PIDs. An important theory of control.

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