What is PID?

PID stands for Proportional-Integral-Derivative, a widely used type of feedback controller that calculates the deviation or error value (i.e., the difference between the desired set point and the actual output) to continuously adjust the control inputs in order to maintain the system output within the desired range.

The operation of a PID controller can be broken down into three separate parameters:

1. Proportional (P) : The proportional term takes into account the current error. It scales the error to produce a control action that is proportional to the current error. If the error is large, the control is relatively large; if the error is small, the control is small. Proportional control can reduce the error quickly, but when used alone it tends to leave a steady state error.

2. Integral (I): The integral term takes into account past error accumulation. It integrates the error and amplifies this integral value. The purpose of integral control is to eliminate the steady state error accumulated over time, and it regulates the system so that its output reaches the set point by responding to the accumulation of historical error.

3. Differential (D) : The differential term considers the rate of change of the error. It amplifies the change in the error to predict the future trend of the error. The purpose of differential control is to reduce overshoot and oscillations in the system and to smooth the control action by responding to the rate of change of the error.

Combining these three control roles, the PID controller is able to smoothly and quickly regulate the system output to the desired set point while minimizing overshoot and steady-state error.PID controllers are very common in industrial applications such as in temperature control, machine position control, speed control, and other situations where precise control is required. Correct tuning of the PID parameters is critical to system performance and often involves fine tuning of the proportional, integral and differential gains.
PID algorithms can be used in temperature control, water level control, flight attitude control, and other areas.
Automatic Control Systems

In the basic drive of a DC brushed motor, if the motor load is constant, we simply set a fixed duty cycle (voltage) and the motor speed will stabilize in the target range.

However, in practical applications, the load may change, and at this time, if we still output a fixed voltage, the speed of the motor will deviate from the target range. In order to solve this problem, we need to introduce the closed-loop control in the automatic control system. Next we begin to learn the content of the automatic control system.

Concept: automatic control devices, automatic control of key parameters, so that it is subject to external interference and deviation from the normal state, can be automatically adjusted back to the target range.

Application scenarios: electric kettle insulation system, greenhouse temperature control system, water level control system, and so on.

Classification: automatic control system is divided into open-loop control system and closed-loop control system.

② closed-loop control system

In the closed-loop control system, the introduction of a feedback loop, the use of output (actual value) and input (target value) of the deviation of the system control, to avoid deviation from the intended target.

The greenhouse temperature control system is a closed-loop control system, we set the target temperature, the temperature sensor will collect the actual temperature in the greenhouse, and then the target temperature and the actual temperature for the calculation of the deviation, the results of the calculation is input to the control circuit, the control circuit to further control the temperature control equipment to warm up and cool down, at this time, the actual temperature in the greenhouse will be controlled in the target range.

When the actual temperature deviates from the target value due to external influences, the temperature sensor (feedback circuit) can provide timely feedback on the deviation, so that the system can automatically adjust the temperature control equipment to make the actual temperature gradually return to the target range.
① Open-loop control system

In an open-loop control system, the output of the system is only controlled by the input, there is no feedback circuit, and the control accuracy and interference suppression characteristics are poor.

The fan wind control system is an open-loop control system. After we set the target wind power, the control circuit outputs the corresponding voltage (assuming voltage control), and the rotational speed of the motor’s fan blades is then controlled in the target range.

Ideally, the fan’s output wind power can indeed be stabilized near the target value, however, in actual use, the motor will gradually aging, the dust on the fan blades will also make the load increase, at this time we set the target wind power and the actual wind power may be deviated.

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