Multi-timescale Modeling of Fast Charging Stations for Power Quality Analysis

Abstract

To accurately simulate the harmonic emission of EV DC fast chargers (DCFCs) and the harmonic voltage of the power grid to which the chargers are connected, a small time-step, i.e., typically smaller than 10μs, is required. However, for harmonic assessment, a long timescale, typically a day, is required. A conflict between accuracy and time efficiency exists. To address this issue, a multitimescale modeling framework of fast charging stations (FCSs) is proposed in this paper. In the presented framework, the DCFCs’ input impedance and harmonic current emission in the ideal grid condition, i.e., the grid impedance is zero and there are no background harmonic voltages, is obtained firstly through a converter switch model with a small timescale. Since the DCFC’s input impedance and harmonic current source change in the charging course, the input impedance and harmonic emission at different input power should be obtained. Then, the DCFCs’ input impedance and harmonic emission will be used in the fast-charging station modeling, where the DCFCs are simplified as their Norton equivalent circuits. In the station level modeling, a bigger time step, i.e., 1 minute, is used, since the DCFCs’ operating power can be assumed as a constant in one minute. With this framework, the FCSs’ long-term power quality performance can be assessed efficiently without neglecting the DCFCs’ small timescale dynamics.