# What is the control law of pid

### PID control is what control?

1, PID is proportional, integral and differential three-part role of the superposition of the composite control.

Features: on the basis of the proportional role can improve the stability of the system, coupled with the integral role can eliminate the residual difference, but also δ, TI, TD three parameters can be adjusted, and therefore can make the system to obtain a high quality of control.

2, PD is the nature of differential control.

Features: make the stability of the system increase, maximum deviation and residual difference decrease, speed up the control process, improve the quality of control.

3, PI is mainly used in the nature of integral control.

### What is pid control_pid control principle

PID that is: Proportional (Proportional), Integral (Integral), Differential (Differential) abbreviation, PID control algorithm is a combination of proportional, integral and differential three links in one control algorithm.

It is one of the most mature and widely used control algorithms in continuous systems, which appeared in the 1930s and 1940s, and is suitable for occasions where the model of the controlled object is not clearly understood. The experience of actual operation and theoretical analysis have shown that the use of this control law to control many industrial processes, can be more satisfactory results. the essence of the PID control is based on the input deviation value, according to the proportional, integral, differential function of the relationship between the operation, the results of the operation is used to control the output.

In industrial applications PID and its derivative algorithms are one of the most widely used algorithms, is deservedly universal algorithms, if you can master the design and implementation of PID algorithms, for the general research and development personnel, should be enough to deal with general research and development issues, and the valuable thing is that in many control algorithms, PID control algorithms and the most simple, most representative of the feedback idea of control algorithms, can be used to control the output of the PID control algorithm. Feedback idea of the control algorithm, can be called the classic in the classic. Classic may not be complex, classic things are often simple, and the simplest.

### What is PID control

Today’s closed-loop automatic control techniques are based on the concept of feedback to reduce uncertainty. The elements of feedback theory consist of three parts:measurement, comparison, and implementation. Measurement is concerned with the actual value of the controlled variable, comparing it with the desired value, and using this deviation to correct the system’s response and perform regulatory control. In engineering practice, the most widely used regulator control laws for proportional, integral and differential control, referred to as PID control, also known as PID regulation.

The PID controller (Proportional-Integral-Differential Controller) is a feedback loop component common in industrial control applications, consisting of a proportional unit P, an integral unit I, and a differential unit D. The PID controller is a feedback loop component that is used to control the response of the system.

The key to this theory and application is how best to correct the system after making the correct measurements and comparisons.

PID (proportional (proportion), integral (integration), differential (differentiation)) controller as the earliest practical controller for nearly a hundred years, and now is still the most widely used industrial controllers. PID controllers are simple and easy to understand, the use of the system does not require accurate modeling and other prerequisites, thus becoming the most widely used controller. PID controllers are easy to understand and do not require preconditions such as an accurate system model for use, making them the most widely used controllers.

The PID controller consists of a proportional unit (P), an integral unit (I) and a differential unit (D). The relationship between its input e(t) and output u(t) is

u(t)=kp[e(t)+1/TI∫e(t)dt+TD*de(t)/dt] where the upper and lower limits of the integral are 0 and t, respectively

Therefore, it has the transfer function:G(s)=U(s)/E(s)=kp[1+1/(TI*s)+TD*s]

Where kp is the proportionality coefficient; TI is the integral time constant; TD is the differential time constant

PID (Proportional-Integral-Derivative) controllers as the earliest practical controller has more than 50 years of history, and now is still the most widely used industrial controllers. PID controllers are simple and easy to understand, and the use of the system does not require accurate modeling and other prerequisites, and therefore become the most widely used controller. PID controllers are the most widely used controllers.

The PID controller consists of a proportional unit (P), an integral unit (I) and a differential unit (D). Its input e (t) and output u (t) of the relationship between

Therefore, its transfer function is:

It is because of the wide range of uses, the use of flexible, there is a series of products, the use of only need to set three parameters (Kp, Ki and Kd) can be. In many cases, it is not necessary to need all three units, you can take one or two of them, but the proportional control unit is essential.

First, PID has a wide range of applications. Although many industrial processes are nonlinear or time-varying, but by simplifying them can be turned into a basically linear and dynamic characteristics do not change over time system, so that PID can be controlled.

Secondly, PID parameters are easier to adjust. That is, the PID parameters Kp, Ki and Kd can be adjusted in time according to the dynamic characteristics of the process. If the dynamic characteristics of the process change, for example, may be caused by the change of load changes in the dynamic characteristics of the system, the PID parameters can be re-adjusted.

Thirdly, PID controllers have been improved in practice, and the following are two examples of such improvements.

In factories, many circuits are always seen in manual mode because it is difficult to get the process to work smoothly in “automatic” mode. Because of these shortcomings, industrial control systems using PIDs have been plagued by problems with product quality, safety, throughput, and energy waste, and PID parameter self-tuning was created to deal with this problem of PID parameter tuning. Now, auto-tuning or self-tuning PID controllers are a standard for commercial single-loop controllers and decentralized control systems.

PID controllers designed for specific systems control well in some cases, but they still have some problems to solve:

If self-tuning is to be model-based, it is difficult to find and maintain a good model of the process online in order to re-tune the PID parameters. Closed loop operation requires a test signal to be inserted into the process. This method causes perturbations, so model-based self-tuning of PID parameters is not too good for industrial applications.

If self-tuning is based on control laws, it is often difficult to separate the effects caused by load disturbances from those caused by changes in the dynamic characteristics of the process, so the controller affected by the disturbances overshoots and produces an unwanted adaptive transition. In addition, because there is no mature stability analysis method for control law-based systems, there are many questions about the reliability of parameter tuning.

As a result, many PID controllers that self-tune their parameters often operate in auto-tune mode rather than continuous self-tune mode. Auto-tuning usually means automatically calculating PID parameters based on a simple process model determined from the open-loop state.

PIDs don’t work well when controlling complex processes that are nonlinear, time-varying, coupled, and have uncertain parameters and structure. Most importantly, if the PID controller cannot control the complex process, no matter how the parameters are tuned, it is useless.

### What is pID

p is proportional, i is integral, d is differential. pid is a control system that uses these three things for closed-loop control of a system of analog control (e.g., pressure, flow, temperature, etc.). It can be a small program, or a solid-state module, or directly according to the conditions of use of the use of the scope made into a direct use of the product.