Delay-Dependent Stability Analysis of Single-Area Load Frequency Control System with Aggregated Inverter Air Conditioners

Smart grids incorporate many inverter air conditioners (IACs) that can be used to regulate the frequency under disturbances. However, employing IACs in smart grids requires a communication network to send and receive control and measurement signals. Depending on the network type and load, such open communication networks will introduce time delays that adversely affect the system dynamics and even lead to instability if the delay exceeds an upper bound known as stability delay margin (SDM). This paper aims to identify SDMs of a single-area load frequency control (LFC) system-based IAC. An analytical method based on eliminating exponential terms in the closed loop characteristic equation is used to obtain accurate SDMs. The effect of proportional-integral (PI) controller gains and the number of IACs on SDMs are investigated. The theoretical values of SDMs are verified by using time simulations and quasi-polynomial mapping-based root finder (QPmR) algorithm.