Both these terms: controller(forexample PID controller) and compensator(Lead compensator) are often encountered in control systems,but what is difference between these two?

Brain douglas in this following video tells that both these terms controller and compensaator are used interchangeably


But in the below link ee SE question with almost same content/query ,controller and compensator are mentioned as different entities

Difference between a controller (e.g PD) and a compensator(e.g Lead)?

I have also attached snapshot of pg5 of qnet vtol workbook where i have highlighted "compensator" term used with PID instead of "controller" term?enter image description here


3 Answers 3


Both these terms: controller(for example PID controller) and compensator(Lead compensator) are often encountered in control systems, but what is the difference between these two?

A controller is a closed-loop to have the difference between the output signal and the reference signal minimum. A compensator is also a closed-loop but it changes the shape of the controller's response to meet some requirements (e.g. transient response, rapid load changes, etc.).

Think of them as teachers: One (controller) is the teacher in your school yet the other (compensator) is a private teacher. Your expectation from your school teacher is nearly constant, so you may not give enough attention to him/her. As for the private teacher, you pay him/her to improve your scores and studies.


Both controllers and compensators basically perform the same function which is to tailor the open loop response with the knock on effect of tailoring the closed loop system response. The idea of adding either a controller or compensator to a closed loop system is to force the plant to behave as we want it to rather than how it would naturally.

When adding a compensator (lag, lead or lag-lead) we are tailoring the phase and gain of the open loop response and therefore changing stability margins which has the effect of determining both rise time and overshoot of the closed loop system.

When we add and tune a controller (such as a PID controller), by setting Kp, Ki and Kd, we are also setting both rise time and overshoot of the closed loop system but with a PID controller we have more control of the position of the closed loop poles on the 's' plane and because of this we can adjust rise time and overshoot independently, for example we can have a fast response to a change in the set point (fast rise time) with a small overshoot. Also the integral term in a PID controller will remove steady state error.

So, although a compensator and controller basically do the same thing (tailor the closed loop system response), you could say that a compensator is a more basic form of a controller as it has more limited control over the closed loop system behaviour.

  • \$\begingroup\$ By your last para,do you mean,controller is an advanced form of compensator? \$\endgroup\$
    – DSP_CS
    Commented Dec 17, 2022 at 16:31

In a switching converter, the controller represents the integrated circuit which hosts all the logic gates, clock and driver to operate/control the power supply. This silicon chip features a feedback input which receives the signal from the compensator to drive the control variable (duty ratio, frequency etc.).

The compensator is the active (or passive) circuit which lets you place poles, zeroes, gains (or attenuation) to shape the open-loop response: choose the compensation strategy to force a crossover frequency and various margins (phase and gain) for specific transient response or rejection capabilities.

In analog electronics, a compensator is an active filter built around an op-amp, a transconductance amplifier (OTA), a shunt regulator (TL431) etc. In a digital world, the compensator can be coded or hard-wired to form a PID structure (for example) effectively placing poles and zeroes adequately.


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