Impact of Time-Shiftable Traffic Demands on Coupled Transportation and Power Distribution Systems

Abstract

With the increasing penetration of electric vehicles in modern cities, the tie between urban transportation system and power distribution system is becoming more evident. Spatial and temporal distributions of load demands in fast charging stations alter power flow patterns, raising the risk of over-low bus voltage and congestions, and thus threaten distribution system security. Similar to the flexible demand in smart grid, traffic demand in the transportation system, which is defined as the volume of vehicles travelling from one place to another in unit time, is also shiftable over time, as motorists would like to avoid rush hours and save travel time. This paper proposed a multi-period traffic assignment model with time-shiftable traffic demands. In order to capture the deliberate postponed or advanced travels, the dynamic traffic demand between each origin-destination pair nodes over time is formulated as a matrix variable. The traffic assignment model consists of several Wardrop user equilibrium problems in consecutive periods coupled by demand conservation constraints, and gives rise to a convex program with polyhedral constraints. The charging station loads are assumed to be proportional to the traffic flow in the service area. The power distribution system is operated in accordance with optimal power flow. Case studies demonstrate the benefit brought by the temporal flexibility of traffic demand.