Understand PID control from the process of driving a car

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PID control is a general control method suitable for various controls including temperature control. Here, Changhui Instruments uses driving cars in daily life as an example to explain the various elements of PID control.: How P (proportional control), I (integral control) and D (derivative control) are used. We imagine the driving process of a car stopped at a highway toll station, accelerating from 0 to the target speed of 80km/h. First of all, the target difference from 0 to 80km/h (called deviation in control) is very large, so the accelerator is pressed to the bottom (increase output). Such an operation that is proportional to the deviation from the target is equivalent to proportional control (P). When the car accelerates and approaches 80km/h, if you feel that if you continue to refuel, it will exceed 80km/h, release the accelerator. Such operation of speed changes is equivalent to differential control (D). Finally, in order to maintain the driving speed at exactly 80km/h, the throttle is slightly adjusted to eliminate the slight speed difference. This operation of eliminating the difference (deviation) from the target speed is equivalent to integral control (I). PID yunrun.com.cn/tech/681.html http://yunrun.com.cn/upload/202207/16/202207161751584751.png Next, we imagine encountering an uphill situation while driving at a speed of 80km/h. If you maintain the previous throttle control when going uphill, the vehicle speed will gradually slow down. The driver senses the change in speed and increases the accelerator to maintain speed. The operation at this time is also an action to suppress speed changes and is equivalent to differential control (D). Of course, since a difference (deviation) from the target speed occurs, in order to eliminate the speed difference, it is equivalent to performing integral control (I) at the same time. However, in order to restore the vehicle speed faster, differential control (D) plays a greater role than integral control (I). original: yunrun.com.cn/tech/4329.html http://yunrun.com.cn/upload/202207/16/202207161726236772.png Finally, we interpret another function of proportional control - determining the overall ability to control (control gain). Whether we are driving a car with a top speed of 150km/h or a sports car that can reach a speed of 300km/h, we can all drive like the example. This is because we unconsciously judge the changes in vehicle speed caused by changes in the throttle control amount and take appropriate actions. Assuming that the car and sports car have the same amount of throttle control, in this case the sports car reaches a speed faster than the car (in this case the sports car is twice as fast as the car). Considering that the control object is a car, the acceleration capability of a sports car (called process gain in control) is higher than that of a car. When changing the speed of a sports car with a large control gain, the accelerator control amount (output) must be smaller than the accelerator control amount of the car, so that the speeds of the two cars can be the same. In order to change the response of the control object (in this case, the vehicle speed), the control output (throttle control amount) must be provided. The ratio of the two is called the control gain. For a sports car to change in speed as much as a car, the change in the sports car's throttle must be less than the change in the car's throttle. Therefore, the control gain when driving a sports car is lower than that of a sedan. In PID control, the control gain is determined by the set proportional band. The narrower the proportional band, the greater the control gain; the wider the proportional band, the smaller the control gain. Proportional control like this also has the function of determining the overall control gain of the controlled object. Changhui Instruments explained two driving examples, one is "control of target value changes" when driving at a constant speed, and the other is "control of interference suppression" when driving on a slope. Most controls are usually these two types of controls, both using PID control. Even if we don't know PID control, we can still drive the car. The operations performed while driving have the same principle as PID control, and we use PID control unconsciously. PID control is all around us.