Mitigating Tap Changer Limit Cycles in Modern Electricity Networks Embedded With Local Generation Units

Cascaded on-load tap changers (OLTCs) are widely used for coarse control of voltages in largely interconnected electric power systems. There could be interactions between load dynamics and OLTC control under certain system operating conditions which may lead to the OLTC limit cycle phenomena, thereby resulting into long-term voltage oscillations in the system. In recent years, renewable and nonrenewable local generation (LG) units have been getting interconnected in modern power systems. The existence of OLTC limit cycles in the presence of LG has not been addressed in the literature in greater details. In this paper, the OLTC limit cycle phenomenon, which can occur due to interactions among load dynamics, OLTC controls, and LG operation in electricity networks, has been investigated. Also, a novel strategy is explored for mitigating the power system oscillations introduced by OLTC limit cycles, especially for a network embedded with LG. The proposed mitigation strategy including detailed investigations and analyses has been verified for a two-bus test system and successfully tested on a multibus system using MATLAB.