Effects of Sampling on Stability and Performance of Electronically Controlled Pressure-Reducing Valves
Tomasz Janus, Bogumił Ulanicki
Abstract
This paper explains and demonstrates how increasing a sampling period in pressure control may worsen a system’s performance and lead to instability. The notion of stability of continuous-time and discrete-time systems is briefly introduced and applied to a simple closed-loop inertial system. It is then demonstrated how the stability of dynamic systems depends on a sampling period as well as on gain. Subsequently, the analysis is applied to a model of an electronically controlled pressure-reducing valve (PRV) coupled with a transient model of a water distribution network (WDN). The occurrence of instabilities at overly long sampling periods is demonstrated. Practical recommendations on the appropriate choice of sampling times are put forth based on simulation results and control engineering rules of thumb given the closed-loop system’s dynamics. Performance of a theoretical pressure control scheme is then simulated under time-varying demands and with controllers designed to work at different sampling frequencies.