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Discrete approximations of some continuous controllers

Table H.1: Tustin equivalents for common continuous-time controllers.
Phase Lag/Lead PI PID
Continuous \(k\dfrac{s+Z}{s+p}\) \(K_{P}+\dfrac{K_{I}}{s}\) \(K_{P}+\dfrac{K_{I}}{s}+K_{D}s\)
Discrete \(k\dfrac{b_{0}+b_{1}z^{-1}}{a_{0}+a_{1}z^{-1}}\) \(\dfrac{b_{0}+b_{1}z^{-1}}{a_{0}+a_{1}z^{-1}}\) \(\dfrac{b_{0}+b_{1}z^{-1}+b_{2}z^{-2}}{a_{0}+a_{1}z^{-1}+a_{2}z^{-2}}\)
Differential equation \(\dfrac{dy}{dt}+py=k\left(\dfrac{dx}{dt}+Zx\right)\) \(y=K_{P}x+K_{I}\displaystyle\int_{0}^{t}x\,dt\) \(y=K_{P}x+K_{I}\displaystyle\int_{0}^{t}x\,dt+K_{D}\dfrac{dx}{dt}\)
Difference equation \(\begin{aligned}y(n)&=-\dfrac{a_{1}}{a_{0}}y(n-1)\\&+\dfrac{b_{0}}{a_{0}}x(n)\\&+\dfrac{b_{1}}{a_{0}}x(n-1)\end{aligned}\) \(\begin{aligned}y(n)&=-\dfrac{a_{1}}{a_{0}}y(n-1)\\&+\dfrac{b_{0}}{a_{0}}x(n)\\&+\dfrac{b_{1}}{a_{0}}x(n-1)\end{aligned}\) \(\begin{aligned}y(n)&=-\dfrac{a_{1}}{a_{0}}y(n-1)\\&-\dfrac{a_{2}}{a_{0}}y(n-2)\\&+\dfrac{b_{0}}{a_{0}}x(n)\\&+\dfrac{b_{1}}{a_{0}}x(n-1)\\&+\dfrac{b_{2}}{a_{0}}x(n-2)\end{aligned}\)
\(a_0\) \(1\) \(1\) \(1\)
\(a_1\) \((pT-2)/(pT+2)\) \(-1\) \(0\)
\(a_2\) \(-1\)
\(b_0\) \(k(ZT+2)/(pT+2)\) \(K_P+K_I T/2\) \(K_P+K_I T/2+2K_D/T\)
\(b_1\) \(k(ZT-2)/(pT+2)\) \(-K_P+K_I T/2\) \(K_I T-4K_D/T\)
\(b_2\) \(-K_P+K_I T/2+2K_D/T\)