Fast Solving Method Based on Linearized Equations of Branch Power Flow for Coordinated Charging of EVs (EVCC)

Abstract

Reported researches on smart charging methods have the disadvantages of low calculation efficiency or have not simultaneously taken the three-phase imbalance, voltage, and power flow constraints into account. It is an important topic to improve the computational speed to meet the online rolling optimization requirement for EVCC problems. In this paper, the branch power flow equations of balanced and unbalanced distribution system are derived. The linearization methods for the nonlinear terms of the branch power flow equations are proposed. Two stages linear programming (LP) is introduced for EVCC to minimize the total charging costs of the holders where three-phase imbalance, charging demand, voltage, and power flow constraints have been taken into account. Via ignoring the nonlinear terms of the branch power flow equations, the first stage LP is formulated to calculate the estimated branch power and node voltages as the initial points for linearizing the nonlinear terms of branch power flow equations. The second stage LP is formulated to calculate the optimal charging power using the linearized branch power flow equations. Four case studies show that the proposed method without the compromise of precision is significantly faster than state-of-the-art works with respect to the computational speed.