PID controller
proportional control
Kpe(t)=Kp[u(t)−y(t)]
Example: Given the closed-loop transfer function is T(s)=1+Gp(s)Gp(s)=s+21
adding proportional
closed-loop transfer function is:
T(s)=1+KpGpKpGp
integral control
Closed loop here yields
T(s)=s2+s+KIKI
steady state error is 0, while steady-state output is 1
PI control
proportional-integral
Closed-loop transfer function
T(s)=s2+(1+Kp)s+KIKI+sKp
- PC: impact on speed of response
- IC: force steady-state error to 0
derivative control
T(s)=(1+KD)s+1KDs
- introduces an open-loop zero
- KD increases system might not be stable
T(s)=s2+2(ζ+2KDPωn)ωns+ωn2sKDPωn2
damping effect ζ′=ζ+2KDPωn
PID control
GC(s)=Kp+sKI+KDs
in time domain:
u(t)=KPe(t)+KI∫0te(η)dη+KDdtd(e(t))
Component | Discrete-Time Equation |
---|
Proportional | u(k)=KPe(k) |
Integral | u(k)=KIT∑i=1ke(i) |
Derivative | u(k)=TKD[e(k)−e(k−1)] |
approximate of PID controller: u(k)=KPe(k)+KIT∑i=1ne(i)+TKD[e(k)−e(k−1)]