Nonlinear behavior in high-frequency aggregate control of thermostatically controlled loads

Coordinated control of electric loads can provide valuable grid services, such as frequency regulation. However, due to the nonlinear characteristics of such load ensembles, it is important to systematically analyze their behavior and establish a thorough understanding of undesirable phenomena that can potentially arise. In this paper, we analyze the frequency response of an aggregate control scheme, with the goal of exploring controller performance limits. We show that rapid switching commands can induce oscillations in the power output due to the inherent lockout mechanism of the underlying devices. We demonstrate that highly detailed aggregate models are required to capture such phenomena. Such models enable deeper understanding of the control boundaries and therefore play an important role in avoiding the introduction of undesirable effects on the grid. •Frequency response analysis of a thermostatically controlled load aggregation.•Rapid switching commands can induce low-frequency power oscillations.•Oscillations are linked to the lockout mechanism protecting the compressor.•Highly detailed aggregate models are needed to capture the oscillations.•Case studies demonstrate the oscillation phenomenon and model performance.