Stability Analysis of DC Distribution System Considering Stochastic State of Electric Vehicle Charging Stations

A DC distribution system integrated with electric vehicle charging stations (EVCSs) is typically constructed to satisfy the large power exchange demand of electric vehicles (EVs). However, the stochastic operating state of the EVCSs results in difficulties in the stability analysis of the DC distribution system. In this study, a linearized model of the DC distribution system connected with multiple EVCSs is established, which considers the charging and the discharging states of the EVCSs. Based on the similarity transformation, this study theoretically verifies the generalized conclusion that a DC distribution system has a higher possibility of instability if the EVCSs are in the charging rather than the discharging state, and that the system stability is the worst if all the EVCSs operate at the maximum charging state. Moreover, a method to quickly evaluate the stability region of the DC distribution system is proposed. It can provide a numerical instability risk estimation of a complex DC distribution system considering all the possible states of the EVCSs. Lastly, the conclusions are validated by two SIMULINK cases, and the application of the numerical instability risk estimation to the DC distribution system is demonstrated.