Skip to main content

Closed loop diagram; P, PI, PD, PID

Short answer

Closed-loop system: reference r compared with sensor feedback y to produce error e; controller computes u; actuator drives plant; sensor measures output. P controller (u=Kp·e) gives fast response but steady-state offset. PI adds integral to eliminate offset. PD adds derivative for damping and reduced overshoot. PID combines all three for zero error, good damping, and fast response but requires tuning three gains.

Draw a clear block diagram of a closed-loop control system and explain its various parts. Differentiate between P, PI, PD, and PID controllers.

Closed-loop control system

 r -->(+)-e->[Controller]-u->[Actuator]->[Plant]--+--> y
       ^ -                          d --^           |
       |                                            |
       +----------------[Sensor]<-------------------+
  • Reference input (r): desired value (set-point).
  • Summing junction: computes the error e = r - y.
  • Controller: converts the error into a control signal u.
  • Actuator: converts u into a physical action (motor, valve, throttle).
  • Plant (process): the system being controlled.
  • Sensor: measures the output and feeds it back (with ADC/conditioning).
  • Disturbance (d): unwanted external input, e.g. a slope or load change.

P, PI, PD and PID controllers

ControllerControl lawEffectDrawback
Pu = Kp·eFaster response, simpleSteady-state offset
PIu = Kp·e + Ki·∫e dtRemoves steady-state errorSlower, more overshoot
PDu = Kp·e + Kd·de/dtDamping, less overshoot, fasterOffset remains; noise sensitive
PIDu = Kp·e + Ki·∫e dt + Kd·de/dtZero error, good dampingThree gains to tune

✓ Answer checked by Claude Opus 5.5 (high effort)

Related questions

All Embedded System chapter 7 questions →