Technical and Economical Analysis of Bidirectional Charging Consid-ering Wear-Costs and Variable Efficiency Factors

Abstract:
Bidirectional charging of battery electric vehicles plays a crucial role in the energy and mobility transition. To evaluate the usefulness for the customer, it is important to compare different kinds of system configurations. This allows an eval-uation of the economic benefits of bidirectional charging of battery electric vehicles including different factors such as variable efficiencies, wear costs and different energy tariffs. To analyze this, first, this paper presents the results of two experimental measurements. One measurement evaluates a single-phase GaN full bridge with a voltage range of 380 V to 420 V and a SiC-based three-phase B6 bridge rectifier with a voltage range from 750 V to 900 V within a rapid prototype environment in different operating points and switching frequencies. A second measurement performs an eval-uation of the overall charging performance of a battery electric vehicle charging system. When comparing these meas-urements, it becomes apparent that the battery electric vehicle's charging system maximum efficiency of 90.6 % performs worse than the power electronics subsystem with an efficiency of up to 98 %. This is caused by the electric vehicle's internal peripheries. These results are transferred into an optimization model. Then different scenarios of bidirectional charging are analyzed. A unidirectional battery electric vehicle with an 8 kWh stationary battery storage system has the lowest energy costs. Compared to that a bidirectional battery electric vehicle without a storage system causes higher costs of up to 420 €. By adding a small battery storage to this system, the differences can be reduced to 10 €. Another optimi-zation potential relies on a better overall efficiency of the bidirectional battery electric vehicle charging system. This reduces the cost difference to 140 € compared to the 420 €. This shows the importance of the efficiency and operating time optimization of the charging system in the future to ramp up the use of bidirectional charging of a battery electric vehicle.