Control principle of DC brushless motor
In order to make the motor rotate, firstly, the control unit must determine the current position of the rotor of the motor according to the HALL-SENSOR, and then determine the order of turning on (or off) the power transistors in the inverter (INVERTER) according to the stator winding, as shown below. b) AH, BH, CH (these are called upper arm power transistors) and AL, BL, CL (these are called lower arm power transistors) in INVERTER, so that the current flows sequentially through the motor coil to produce a forward (or reverse) rotation. The magnetic field interacts with the magnet of the rotor, which allows the motor to rotate clockwise/reverse. 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 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.
Basically, the power transistor can be opened as follows:
AH, BL group → AH, CL group → BH, CL group → BH, AL group → CH, AL group → CH, BL group, but never open AH, AL or BH, BL or CH , CL. 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 (COMMAND) with the speed of the HALL-SENSOR signal change (or by software operation) to determine the next group ( 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 take into account whether the system's CLOCK resolution is sufficient to master the time to process software instructions. In addition, the data access mode for HALL-SENSOR signal changes also affects processor performance and determination accuracy and real-time. As for the low speed speed control, especially the low speed start, the return of the HALL-SENSOR signal becomes slower. It is very important to learn the signal mode, the processing timing and the proper configuration of the control parameter value according to the motor characteristics. Or the speed return change is referenced to the ENCODER change, which increases the signal resolution for better control. The motor can run smoothly and respond well, and the proper control of P.I.D. 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 (ERROR). Knowing the error naturally requires compensation, and the method has traditional engineering control such as P.I.D. control. However, the state and environment of control are complex and changeable. If the control is to be sturdy 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.
48V brushless motor electric vehicle wiring principle
Eight lines, three thick lines are yellow, blue and green, different cars, five Hall lines, red, black, blue, green and yellow. The red and black inside the five Hall lines must not be connected to the wrong color, and the other three thin lines are connected by color. The three thick lines are connected by color. After the connection, the motor may tremble. If it does not turn or reverse, you can connect the three thick lines at random. The thin lines can not be confused except red and black. The other three can also be connected at will.
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