Primary frequency control with refrigerators under startup dynamics and lockout constraints

There is a growing interest in utilizing demand-side flexibility to provide ancillary services. Various methods have been proposed for frequency control with thermostatically controlled loads, yet few consider practical load constraints. In this paper, we develop a fully decentralized method to provide primary frequency control (PFC) with domestic refrigerators taking into account startup compressor dynamics and lockout constraints. The proposed method relies on probabilistic switching to avoid synchronization among loads and large deviations from loads' baseline consumption, and on dynamic resetting of temperature deadbands to provide accurate PFC reserves. We demonstrate the method's performance via simulations with an extract of real frequency data, and via dynamic simulations with a one-area power system model. The results show that the method performs very well in both cases, and allows refrigerator aggregations to mimic conventional generators' droop characteristic and substitute them in PFC. To illustrate the importance of considering startup dynamics and lockout constraints in control design, we show that our approach achieves better results compared to an existing approach that neglects such constraints.