Experimental modeling and aggregation strategy for thermoelectric refrigeration units as flexible loads

In the last years, the interest regarding thermoelectric refrigerators has increased thanks to their properties such as the absence of moving parts and toxic or fire-sensitive refrigerants, robustness, and low weight. These devices are also quite flexible and may represent a suitable solution to offer grid services to proper demand response programs. In this article, an aggregation strategy is proposed to fulfil system operator requests on power de- viations with limited information exchange between the aggregator and each refrigerator. Downward and up- ward flexibility in energy consumption can be offered, allowing an aggregated set of loads to provide balancing services such as frequency containment reserve, frequency restoration reserve or replacement reserve to the electrical grid. First, a dynamic model of a thermoelectric refrigerator is built and validated using experimental data collected from a real device under controlled and replicable experimental conditions. A modified tem- perature controller is proposed and an aggregation strategy with reduced communication requirements is for- mulated. Then, the aggregation of thermoelectric refrigerators is represented with a linear model to determine that this aggregation can behave as flexible load for reserve provision and demand response applications. It is shown through extensive simulations that a set of refrigerators can operate as in a flexible way by modifying their internal temperature set points, responding in less than 30 s to any power deviation command and sus- taining the modified consumption for up to 15 min in the frequency containment and restoration reserves services, and up to 1 h in the replacement reserve service, without overshoots, rebounds, or synchronization problems.