Analyzing the Control Principle of Brushless Motors.
In order to rotate the motor, the control unit must first determine the current position of the motor rotor detected by the Hall sensor, and then turn on (or off) the power transistors in the converter (inverter) according to the order of the stator winding. As shown in the figure below, the AH, BH, CH (referred to as upper arm power transistors) and AL, BL, CL (referred to as lower arm power transistors) in the inverter generate a forward (or reverse) rotating magnetic field by flowing current through the motor coil and interacting with the rotor magnet, causing the motor to rotate clockwise/counterclockwise. When the motor rotor rotates to the position where the Hall sensor detects another set of signals, the control unit opens the next set of power transistors, causing the circulating motor to continue rotating in the same direction until the control unit decides to stop the motor rotor or turn off the power transistor (or only turn off the lower arm power transistor) and reverse the motor rotor. The power transistors are turned on in reverse order.
Basically, the opening of power transistors can be explained as follows:
AH, BL group AH, CL group BH, CL group BH, AL group CH, AL group CH, BL group, but cannot be classified as AH, AL or BH, BL or CH, CL. In addition, since electronic components always have switch response time, power transistors should consider the response time of components in the interleaving time between switches. Otherwise, when the upper arm (or lower arm) is not fully closed, the lower arm (or upper arm) has already opened, causing a short circuit between the upper and lower arms and burning out the power transistor.
When the motor rotates, the control unit compares the speed of the Hall sensor signal with a command consisting of the speed and acceleration/deceleration rate set by the driver (or software), and then determines the next group (AH). (BL or AH, CL or BH, CL or...) opening and opening time. If the speed is not enough, the speed will be shortened, which is done by PWM. PWM is a method of determining whether the motor speed is fast or slow. How to generate such PWM is the core of achieving more precise speed control. High speed speed control must consider whether the clock resolution of the system is sufficient to grasp the time required to process software instructions. In addition, changing the data access method used for HALL-SENSOR signals can also affect the performance of the processor, as well as the accuracy and real-time performance of the judgment. For speed control at low speeds, especially at low starting speeds, the Hall sensor signal changes slowly. It is important to retrieve signal patterns based on the characteristics of the motor, processing time, and correct configuration of control parameters. Alternatively, the velocity echo can serve as a reference for encoder changes, resulting in an increase in signal resolution for better control. The motor runs smoothly and responds well. Suitable for PID control and cannot be ignored. As mentioned earlier, brushless DC motors are closed-loop controlled, so the feedback signal is equal to telling the control unit how much the current motor speed differs from the target speed. This is an error. Compensating for errors is natural, including traditional engineering controls such as P.I.D. control. However, the state and environment of control are complex and ever-changing. If control is strong and persistent, these factors should be taken into account. Therefore, fuzzy control, expert systems, and neural networks will be incorporated into the important theoretical control of intelligent motion.
