To master the PID algorithm requires a deep understanding of the feedback mechanism and the actuator and understand its own characteristics.

The PID algorithm is simple in principle and in code. Mainly used in motor control, switching power supply, power management chip and other fields.

Generally, the positional algorithm is given on the principle of automatic control, as shown in the figure below.

The reason is that you don't understand enough about the feedback mechanism of this system.

For example, the 716 hollow cup motor is set at 100 rpm, but you use a 50M clock to work with the PID algorithm, assuming the PID is fully parallel (data throughput is also 50M).

At this time, no matter how you adjust the parameters, the motor is not controlled, it is very fast, and it is very slow.

Quietly think about it, it is not difficult to find the problem.

Assuming that the motor's instantaneous speed is 101 rev / sec, the photoelectric switch only feeds back a speed amount every 4.95 milliseconds, during which there is no feedback.

The set speed is 100 rev / sec. With the 50M full parallel incremental PID algorithm, the error of 1 rev / sec is continuously accumulated in 4.95 ms, and the period is 247.5 times by the PID algorithm!

That is to say, because the working frequency of the PID is too high, the rate of accumulating errors is too fast (from another point of view, the feedback mechanism is too slow), so the motor is not controlled. At this time, you lower the working frequency of the PID. It will be found that the motor is gradually being controlled.

Let's take a complete block diagram of the motor control using the PID algorithm in the FPGA.

In summary, the control algorithm, in addition to paying attention to the characteristics of the algorithm itself, also requires a deep understanding of the feedback mechanism and the actuator.

BTW, in general, the motor control can be controlled by PI or PD. If the PID is used, the parameters are not easy to adjust, and the second is easy to self-excite. Of course, it is not excluded that some special occasions need to use PID three. In the link, even the three-loop control (speed loop, phase loop, current loop) is used. In addition, in addition to PID, commonly used control class algorithms are fuzzy control, MPC (model predictive control) algorithm.