Suggested Response - Q5

** What are the three components of a PID controller? How do they work and what are their limitations?

 

Response:

The three main components of a PID controller are proportional, integral, and derivative control.

Proportional control

Proportional control adjusts the output to a controller, based on the error.

It does this with a factor, which is proportional gain. It also has a bias output, which is the output when the error is zero.

CO(t) = Kc ε(t) + B

A limiting factor of proportional control is that it will always have an offset.

Integral control

Integral control integrates the error over time and uses this term to eliminate the offset. It has a factor called the integral time constant. The lower this value is, the greater the impact of the integral term:

C O subscript I equals K subscript C over T subscript I integral subscript 0 superscript t epsilon d t

Integral control can lead to oscillations if the integral time constant is too low. It is also prone to integral windup.

Derivative control

Derivative control takes into account the rate of change in the error and uses this to predict what the error will be in the future. It uses a factor called derivative time. The higher the derivative time, the greater the resultant impact of the derivative control term:

C O subscript D equals T subscript D fraction numerator d epsilon over denominator d t end fraction

Derivative control can lead to oscillations and does not respond well to noisy signals or noisy controls. It is not suited to fast acting systems.

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