THE ASSESSMENT OF DYNAMIC RESILIENCE: THE EFFECT OF NON-MINIMUM PHASE ELEMENTS (DEADTIMES, ZEROS, TIME DELAYS)

The quality of control achievable on a given system, the dynamic resilience, represents a new and important concept in process control. It is a quality independent of controllers and their tuning as it depends only on the nature of the system itself. Systems with non-minimum phase elements, deadtimes and right-half-plane transmission zeros, are systems where the achievable dynamic performance can be severely limited. Because of their importance in chemical engineering systems, this work examines how non-minimum phase elements restrict the dynamic resilience and the design of controllers for systems which contain them.;For multivariable systems with deadtimes, simple procedures are developed to determine bounds on the achievable dynamic performance. This work demonstrates when dynamic decoupling should be pursued and it indicates how, and when, modifying the design by increasing deadtimes can improve the performance. Closely related to the analysis is the design of controllers. The issues involved are resolved and techniques to design multivariable time delay compensators presented and demonstrated.;For systems which contain right-half-plane transmission zeros, the location of the zero is related to the effect on the dynamic resilience for both single and multivariable systems. For multivariable systems techniques to shift the impact of the zeros to different combinations of outputs, including isolating the effect on a single output, are developed.;This work suggests techniques to analyze systems which contain both types of non-minimum phase elements simultaneously. It also demonstrates how the robustness, the closed loop stability in the face of modelling uncertainty, is influenced by the presence of these elements.;The framework developed here provides a convenient means of measuring the dynamic resilience. It allows different designs to be compared, existing designs to be modified, or provides a standard to judge existing controllers, all on a dynamic basis.