Test Bed Emulation of Secondary Loop Refrigeration Units Using Peltier Elements: An Impedance Control Approach

Abstract

Advanced control methods help to increase the efficiency of refrigerated applications, easing their economic and ecological burden. However, approaches from literature have rarely been validated experimentally. One significant reason is the high expenses when conducting control experiments on full-sized plants. Low-maintenance, low-cost testing facilities constitute a possible remedy. Therefore, this work proposes a test bed refrigeration unit based on Peltier elements, for which impedance control compensates the behavioral differences to an actual secondary loop refrigeration unit. The two-degree-of-freedom control architecture comprises a static feedforward and a PID path that is robustified by choosing a linear design model based on the nu-gap metric. Experimental validation using a 260 min cycle shows that the achieved system trajectory lies within sensor accuracy to the desired one for more than 99% of the time, proving adequate emulation. Thus, the proposed concept is suitable to experimentally investigate highlevel temperature control algorithms for refrigerated applications.