A Minimum-Time Optimal Recharging Controller for High Pressure Gas Storage Systems

A minimum-time optimal recharging control strategy for high pressure gas storage tank systems is described in this work. The goal of the nonlinear model-based controller is to refill the tank in minimum time with a two-component gas mixture of specified composition subject to hard constraints on the component flow rates, tank temperature, and tank pressure. The nonlinearity in this system arises from the non-ideal behavior of the gas at high pressure. The singular minimum-time optimal control law can not be reliably implemented in the target application due to a lack of sensors. Minimum-time optimal control is therefore approximated by a nonlinear model-based constraint controller. In order to account for the uncertainty in the unmeasured state of the storage tank, the state sensitivities to the control and process measurements are propagated along with the state to obtain a state variance estimate. When the variance of the state exceeds a maximum threshold, the constraint control algorithm automatically degrades into a fail-safe operation.