Impact of Gain and Phase Margins on Stability of Networked Micro-grid Frequency Control System

Abstract

In this paper, a study is presented to assess the impact of gain and phase margins on delay-dependent stability of networked micro-grid frequency systems with time-invariant communication delays. In the networked control system framework, it is observed that transfer of incremental frequency variable (an indication of the in-balance between the generation and the demand) through communication links to effect closed-loop control in micro-grid systems introduces time-delays in the feedback path. The feedback delays exert a destabilizing effect on to the overall performance of the closed -loop system. In addition to stabilization, if the designed controllers are also required to meet relative stability specifications like gain margin and phase margin, the stability of the networked micro-grid system will become more vulnerable to even small magnitudes of network delay. In this paper, using the classical transcendental characteristic equation method, the impact of gain and phase margins on the stable delay margin is investigated. Based on the detailed analysis carried out on a standard bench-mark system, few important inferences are arrived.