A PID controller computes a correction signal u(t) from the error between setpoint and output:
u(t) = Kp·e + Ki·∫e dt + Kd·ė
- Kp — ProportionalReacts to present error. Higher Kp → faster response but more overshoot and potential instability.
- Ki — IntegralEliminates steady-state error by accumulating past error. Too high → integral windup & oscillation.
- Kd — DerivativeAnticipates future error via rate of change. Adds damping; sensitive to noise.
Ziegler–Nichols Rule
Increase Kp until sustained oscillations appear (Ku, period Tu). Then set Kp = 0.6Ku, Ti = Tu/2, Td = Tu/8.
Closed-Loop TF
C(s)G(s) / (1 + C(s)G(s)) where C(s) = Kp + Ki/s + Kd·s
Key Metrics
- Rise Time — time to first reach 90% of setpoint.
- Overshoot — peak output above setpoint (%).
- Settling Time — time to stay within ±2% band.
- SSE — steady-state error as t→∞.