Decentralised frequency-based control of a population of heterogeneous ACs without power oscillations
In power system, the control performance deteriorates due to the penetration of the fluctuating renewable generation if no advanced control strategy is implemented. In this study, the authors investigate a class of thermostatically controlled loads – air conditioners (ACs) – to provide fast frequency regulation service in system contingencies by switching ON/OFF state based on the system frequency deviation in a decentralised way. First, an estimation of the steady-state aggregate power of a population of heterogeneous ACs is derived corresponding to the ambient temperature, and the power overshoot caused by a safe protocol (SP) is discussed analytically, both of which are verified by simulations. Then, a decentralised frequency-based control strategy is designed and a multi-stage frequency responsive model is implemented implicitly. An SP with the timer is introduced in the strategy in order to eliminate the power oscillations during the load pick-up period. Finally, the proposed strategy is incorporated into the primary control of the power system to provide fast frequency regulation service in power contingencies. Comparing with other decentralised strategies, the proposed method can obtain a lower-frequency deviation and the smoothest demand trajectory without long-term power oscillations when a power contingency occurs. Meanwhile, the comfort of the consumers is guaranteed during the demand response.