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Peter Hippe
A Systematic Solution to the Problems caused by Input Saturation
Keywords: input saturation, windup prevention, MIMO control, directionality problem, rate saturation
In control applications where the linear controller assures a desired behaviour, input saturation can cause large overshoots or even an unstable behaviour. These windup effects are attributable to two different factors, namely the dynamics of the controller (controller windup) and the dynamics of the controlled plant (plant windup). Controller windup can be prevented systematically by the so-called observer technique, because after its application the possibly remaining undesired effects of input saturation are independent of the controller dynamics. A prevention of the (oscillatory) plant windup is possible by introducing additional dynamic elements in the controller. Controller and (oscillatory) plant windup are the only undesired effects of input saturation in single input systems. An additional plant windup effect occurs in multivariable systems, namely that of directionality. By a nonlinear reference shaping filter, the problem of directionality can also be prevented systematically. In some applications, not only the amplitude, but also the rate of change of the input signal is restricted. Using a special ersatz model of an amplitude and rate restricted actuator containing only one saturation element, nearly all known windup prevention measures are readily applicable also to this problem. Three examples demonstrate the application of the presented methods.
at – Automatisierungstechnik, Oldenbourg Wissenschaftsverlag
Print ISSN: 0178-2312
Volume: 55, 08/2007
Pages: 377 - 393