Design of a Smart Grid Compatible, Bidirectional Modular Battery Charger for Plug-In Electric Vehicles

Abstract

Wide electrification of the vehicles puts the electric vehicle and grid interaction to a crucial point in terms of research and development for both academics and industry. Moreover, electric vehicles can act as distributed energy sources for the smart grid when necessary. This flexibility makes the electric vehicles an important player among its internal combustion engine counterparts. However, since electric vehicles store and use significant amount of power, their impacts on the utility grid should be well researched and studied to make a smoother transition from classical fuel burning vehicles to electric vehicles. Any efficiency improvement that will be gained in the charging or discharging of electric vehicles’ batteries will have profound impact in the long term. This thesis proposes a bidirectional modular battery charger design that will utilize an optimization control algorithm to determine the operating points of the individual modules in the system to achieve efficiency increase especially at light to middle loads. As power electronic basis for the modules, an isolated single-stage bidirectional topology is selected, analyzed and simulated in the computer medium. An isolated topology is more advantageous in terms of safety that is of the utmost importance for a vehicle. Modular design and optimization algorithm are also verified through computer simulations. Then, two hardware prototype modules are designed and built for 220 V grid voltage; however, tests are conducted at 120 V grid voltage so as not to put the limited number of modules at risk. Experimental study for the modular operation of the two modules is conducted and efficiency improvement compared to conventional modular design is shown in both G2V and V2G modes.