Nonlinear Heat Exchanger Control through the Use of Partially Linearized Control Variables

The use of partial linearization by nonlinear state variable feedback has been proposed as a means of reducing the detrimental effects of severe system nonlinearities upon the performance of linear control schemes used with severely nonlinear systems. In this paper a set of generalized transformed variables are derived for a single pass shell and tube heat exchanger using this technique. The implementation of these generalized transformed variables, which reduce the apparent nonlinear behavior of single pass heat exchangers, eliminates the need to rederive a nonlinear transformation for each heat exchanger control design. The open loop behavior of the system is examined in the time domain to evaluate the ability of the transformed variables to reduce the asymmetry of system response to changes to system inputs. The closed loop performance of the chosen system is evaluated for both servo and regulator control. Finally, the effect of model error upon the robustness of the closed loop controller performance is examined.