Analyses have shown that electric vehicle (EV) loads may considerably affect the secondary service voltage quality. One of the ways to mitigate voltage drop concerns is to use a time-of-use (TOU) pricing scheme. A TOU pricing scheme utilizes the off-peak generation for EV charging, thus deferring any immediate grid upgrade and improving the grid sustainability. This paper evaluates various aspects of EV charging under a TOU schedule, with off-peak rates starting at hours ranging from 8 P.M. to 3 A.M. The study is conducted using an actual residential distribution circuit. A best practical time to begin the off-peak rates is determined so that the effects of EV charging on the secondary service voltages are minimized while ensuring that EVs are fully charged by 7 A.M., thus maximizing both grid and customer benefits. The analysis suggests that the best time to begin off-peak rates is between 11 P.M. and 12 A.M. Furthermore, the analysis also suggests that setting up TOU off-peak rates at the latter half of the peak load demand, for example, at 8 P.M., is detrimental to the distribution circuit voltage quality. The result indicates that the existing utility TOU scheme may exacerbate voltage drop problems due to EV load charging. INDEX TERMS Distribution system, electricity market, electric vehicle (EV), time-of-use (TOU) pricing.
This paper evaluates effects of the distribution circuit parameters on the primary and secondary circuit voltages due to EV loads. The distribution circuit parameters considered here are; location of the service transformer with respect to the substation and location of the EV loads within the secondary service. The voltage analysis is carried out using a 13.8 kV distribution feeder dominated by residential loads. The study reveals that EV charging affects the secondary voltage more significantly than the primary voltage. The short-circuit capacity even at the remote end of the primary distribution line is adequately high; hence, preventing EV loads from affecting its primary voltage. When four 240V/16A EV loads in a secondary service nearby and remote from the substation are charging, the additional voltage drops in their respective primary voltages are 0.023% and 0.13%. However, because the short-circuit capacity at the secondary service wire for both locations (remote/nearby) is significantly lower, additional voltage drops of approximately 4.5% occur in the secondary service voltages. The study also reveals that a single EV load installed on a distant load node from a service transformer leads to comparatively higher additional voltage drop (1.7%) than an EV on a nearby load node (0.81%) in the same secondary service.Index Terms--electric vehicle, distribution system analysis, power quality, voltage fluctuation.
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