Study and Analysis of Asymmetrical Charging as A New Electrical Vehicle (EV) Smart Charging Method

Sammanfattning: Currently, the proliferation of electrified vehicles (EV) has increased rapidly. Considering EV users’ point of view, the duration of charging, and the place to charge their car are essential factors. Increase of EV penetration gives also impact on the electrical network such as overloading, and power quality issues. IEC 61851 and ISO 15118 are the two primary standards to provide requirements for electric vehicle supply equipment (EVSE) to ensure the process of charging can be adequately conducted without disrupting the electric system in general. Following standards and considering the user’s preference in charging place, a new charging method that can draw higher energy than existing technique should be developed. A three-phase grid connected home system is modeled in this study to see the impact of unbalance household load to a three-phase charging. The load modeling covers the variation level of load in summer, spring/fall, and winter. Specific usages of electricity are distributed in a three-phase home system which consists of phase 1: cold appliance, cooking, standby appliances, and other loads; phase 2: heat pumps, audiovisual (Television and sound system) and computer size; and phase 3: Lightning and washing. Two methods of charging are defined in this model, which are symmetrical (existing standard) and asymmetrical (proposed). In symmetrical technique, the On-board Charger (OBC) will draw equal phase current independent of home loads connected in each phase of three phase system. The three phase system will not balanced completely in this method. Meanwhile, in asymmetrical method, the OBC will draw the leftover of current in each phase according to its real-time availability by balancing all three phase in the home. The asymmetrical method is expected to achieve faster charging duration than symmetrical charging due to higher energy availability. There three main cases defined in this study: theoretical case (the EV is charged from hour 00:00), 0-100% SOC case, and the user case (the distance targeted determines Car Demand). The result of simulation reveals that Asymmetrical charging method can provide higher energy available than asymmetrical technique. Fuse-rating level influences a lot on this result. If the higher fuse rating applied in the same load profile, the gap of energy availability between symmetrical and asymmetrical will be reduced. But still the symmetrical method never perform better energy availability than the asymmetrical method, either with 16 A fuse and 20 A fuse. This result of energy availability becomes an indication for 3 the theoretical case, in which asymmetrical method can provide more charging cycles than the symmetrical method, especially for 16 A fuse system. For all cases that have been simulated, the asymmetrical method shows benefits in terms of reduction in time and cost reduction. In a year, the saving of hours of charging duration which could be achieved by new charging method in a 16 A fuse system is as high as 8 hours and 4 hours for 0-100% SOC cases and partial charging user cases respectively (less than 50% approx.). In a three-year cost comparison, the money that could be saved by the asymmetrical method in a 16 A fuse system are as high as 35 Euro for 0-100% case and 23,405 Euro in the user case. After simulations result obtained, asymmetrical method demonstrates a promising performance of the new charging technique in terms of duration and saving. There is a need to push a new standard to realize the implementation of this charging activity. A communication scheme between energy meter, EVSE, and OBC should be established to exchange real-time current availability information. New AC information sequences could be adapted from the DC charging communication standard, IEC 61851-24.