TY - GEN

T1 - Stability of the integral control of stable nonlinear systems

AU - Weiss, George

AU - Natarajan, Vivek

N1 - Publisher Copyright:
© 2016 IEEE.

PY - 2017/1/4

Y1 - 2017/1/4

N2 - PI controllers are the most widespread type of controllers and there is an intuitive understanding that if their gains are sufficiently small and of the correct sign, then they 'always' work. In this paper we try to give some rigorous backing to this claim, under specific assumptions. Let P be a nonlinear system described by = f (x, u), y = g(x), where the state trajectory x takes values in Rn, u and y are scalar and f, g are of class C1. We assume that there is a Lipschitz function Ξ : [umin, umax] → Rn such that for every constant input u 0 [u min, u max], Ξ(u0) is an exponentially stable equilibrium point of P. We also assume that G(u) = gΞ(u)), which is the steady state input-output map of P, is strictly increasing. Denoting ymin = G(umin) and ymax = G(umax), we assume that the reference value r is in (ymin, ymax). Our aim is that y should track r, i.e., y → r as t →∞ while the input of P is only allowed to be in [umin, umax]. For this, we introduce a variation of the integrator, called the saturating integrator, and connect it in feedback with P in the standard way, with gain k > 0. We show that for any small enough k, the closed-loop system is (locally) exponentially stable around an equilibrium point (Ξ(ur ), ur), with a 'large' region of attraction XT ⊂ Rn × [umin, umax]. When the state (x(t),u(t)) of the closed-loop system converges to (Ξ(ur),ur), then the tracking error r - y tends to zero. The compact set Xt can be made larger by choosing a larger parameter T > 0, resulting in smaller k.

AB - PI controllers are the most widespread type of controllers and there is an intuitive understanding that if their gains are sufficiently small and of the correct sign, then they 'always' work. In this paper we try to give some rigorous backing to this claim, under specific assumptions. Let P be a nonlinear system described by = f (x, u), y = g(x), where the state trajectory x takes values in Rn, u and y are scalar and f, g are of class C1. We assume that there is a Lipschitz function Ξ : [umin, umax] → Rn such that for every constant input u 0 [u min, u max], Ξ(u0) is an exponentially stable equilibrium point of P. We also assume that G(u) = gΞ(u)), which is the steady state input-output map of P, is strictly increasing. Denoting ymin = G(umin) and ymax = G(umax), we assume that the reference value r is in (ymin, ymax). Our aim is that y should track r, i.e., y → r as t →∞ while the input of P is only allowed to be in [umin, umax]. For this, we introduce a variation of the integrator, called the saturating integrator, and connect it in feedback with P in the standard way, with gain k > 0. We show that for any small enough k, the closed-loop system is (locally) exponentially stable around an equilibrium point (Ξ(ur ), ur), with a 'large' region of attraction XT ⊂ Rn × [umin, umax]. When the state (x(t),u(t)) of the closed-loop system converges to (Ξ(ur),ur), then the tracking error r - y tends to zero. The compact set Xt can be made larger by choosing a larger parameter T > 0, resulting in smaller k.

UR - http://www.scopus.com/inward/record.url?scp=85014297001&partnerID=8YFLogxK

U2 - 10.1109/ICSEE.2016.7806191

DO - 10.1109/ICSEE.2016.7806191

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AN - SCOPUS:85014297001

T3 - 2016 IEEE International Conference on the Science of Electrical Engineering, ICSEE 2016

BT - 2016 IEEE International Conference on the Science of Electrical Engineering, ICSEE 2016

PB - Institute of Electrical and Electronics Engineers Inc.

T2 - 2016 IEEE International Conference on the Science of Electrical Engineering, ICSEE 2016

Y2 - 16 November 2016 through 18 November 2016

ER -