While a compensator may still act as a controller, the role of comensators is to change (shape) input-output characteristics of the original plant. Compensators are often used in conjunction with additional controllers. In this case, compensators are designed to impart some desirable characteristics to the original plant and the controller regulates the new 'modified' plant to the desired output.

Hi Manoj,

A controller is an element whose role is to maintain a physical quantity in a desired level. For exemple we have a Temperature controller, pH controller, speed control, PID controller. In other words, aim of controller design is to reduce the error between the reference and the output signal which is feedback to the controller with input (reference) signal.

A compensator : modification of system dynamics, to improve characteristics of the open-loop plant so that it can safely be used with feedback control. For exemple to improve stability, uncouple a system, to a 'lead/lag compensator, phase compensator. In case of Lead and Lag compensator which are often designed to satisfy phase and gain margins, these bode plot of the system itself changes after the insertion of compensator, bode plot indirectly represents system dynamics.

Good understanding

To me this s just a matter of wording. A simple controller designed using classical control design techniques, such as lag, lead, lag-lead, PI, etc, is often referred to as a "compensator"; while the term controller is general and is used for any type of system/algorithm that controls the plant behavior.

Recall the definition of a controller : It is a math structure which can change the (open or closed loop) dynamics of a given plant. Naturally, such structure can be (electronically or numerically)  implemented. Depending of a specific task of the controller, you can particularize the name but basically, it is a way to change the dynamics of a plant in a desired one.

Dearest,

Hope this slide could help

arinal

In my oppinion, compensators are designed to suit plant characteristics such as gain and phase margins. PID controllers are frequently designed considering this atributes. In other side, controllers may perform various other tasks depending on the type and structure. For example, adaptive controllers may be used to suit the variations of the plant and maintaining the performance index. Still, optimal control can be designed to maximize a performance index or minimize the energy consumed to drive a process. Several other approaches of controllers as preditive, fuzzy, neural, sliding mode, IA based, and more, drive the system considering different ways to obtain the control signal and can result in better performance, improved robustness, less energy,.... 

The PID family of controllers were used in the area of Process Control even prior to 1950.  We have the famous Ziglous Nichol tuning algorithm (1948) for finding the controller parameters. Of course, now a days there are so many design algorithms to find the controller parameters.

However, compensator was developed much later by the control engineers for the problems of their area. The compensator parameters are calculated based on the system requirements and by following some design steps. 

Therefore,  given some system's requirements, we can design either a controller from the PID family or a compensator from that family to meet the requirements. As such there is no difference. 

Since compensator was designed by control group, they wanted a separate name. 

     If we talk only about PID controllers, the compensator can be almost the same thing. However, PID is one of the simplest controller and several other control approaches can perform better than PID. So, if you ask for a better performance, robustness, energy saving, you should search for deadbeat, optimal control, sliding mode and a lot more approaches. 

A compensator is a form of controller designed to alter certain characteristics (such as gain/phase) of the open-loop system. In my opinion, a controller with fixed configuration is basically a compensator.

The difference between them is as follows: the compensator change the behavior of the open loop system while controller change the behavior of the close loop system.

same one.

A compensator is a component in the control system and it is used to regulate another system. Most of the time, it is done by conditioning the input or the output to that system.

Adjusting a control system in order to improve its performance might lead to unexpected behavior (e.g. poor stability or even instability by increasing the gain value). In order to make the system behave as desired, it is necessary to redesign the system and add a compensator, a device which compensates for the deficient performance of the original system. [Wikipedia]

Hope this helps!

A controller is the general broad name given to any piece of hardware (or sowftware) that aims to control some processes.

A compensator is a specific control-box-tool to correct (or compensate) some lacking aspect of a system property under concern, such as phase, lag, magnitude

Best regards

Check of these links:

https://en.wikibooks.org/wiki/Control_Systems/Controllers_and_Compensators

Difference between Compensators and Controllers:

https://www.youtube.com/watch?v=xbcbzzlI56Q

Best regards

dear all, please guide how can i take differential form of following lead lag controller

Controllers generate control signals to achieve desired control objectives such as tracking, stability, and disturbance rejection. A Proportional-Integral (PI) controller combines proportional and integral actions to eliminate steady-state error and handle disturbances.

Compensators modify the system’s dynamic response to meet performance requirements. A lag compensator, for example, introduces a phase lag to improve transient and steady-state responses by boosting low-frequency gain.

Key differences between controllers and compensators include their purpose, components, design goals, and application. Controllers focus on generating control actions, while compensators manipulate frequency response.

In summary, controllers shape control signals for control objectives, while compensators modify system dynamics to enhance performance characteristics.