Vapor compression refrigeration cycle for electronics cooling - Part II: gain-scheduling control for critical heat flux avoidance

This paper addresses the feedback control of a vapor compression cycle for electronics cooling at different operating conditions including near the critical heat flux (CHF) condition. The control objective is to maintain the temperature of the heated wall below a safe threshold during large transient heat loads. The lumped-parameter model developed for this system is used to design the control strategy. Our experimental testbed is used for evaluation and validation. Linear controller design is applied based on the linearization about specific operating points. The controllers are tuned to achieve good robustness margins to guard against nonlinearity and other modeling errors. When the system traverses through multiple operating points, a gain-scheduling approach is used to switch between the controllers. For heat load changes which would lead to CHF, a dual-input gain-scheduling controller, using both expansion valve and compressor speed, is designed using the evaporator wall temperature as the feedback variable as well as the scheduling variable. Comparison between open-loop and closed-loop experiments for the same operating conditions shows that a 80 °C rise in the wall temperature is avoided with the gain-scheduling controller.