A non-isolated bidirectional multi-input DC-DC converter for a battery/ultra-capacitor hybrid energy storage system in electric vehicles

Growing environmental and economic concerns make electric vehicles greatly attractive. Among these vehicles, battery electric vehicle is the most popular one due to advantages that batteries present, such as, high energy density, reliability. However, the number of commercial battery electric vehicles has not been yet significant since batteries also present some drawbacks, such as low cycle life, high cost, and low power density. In order to suppress these drawbacks, researchers have suggested hybrid energy storage system concept in electric vehicles. The utmost control of power in hybrid energy storage systems is only achievable through utilizing power converters; in these systems, despite of numerous power converter topologies presented, utilizing multi-input power converters have drawn wide attention thanks to their advantages of reduced part count, low cost, control simplicity, etc. This thesis proposes a novel bidirectional non-isolated multi-input converter topology that constructs a battery/ultra-capacitor hybrid energy storage system to be used in electric vehicles. The proposed converter has the abilities of controlling the power bidirectionally and allowing active power sharing between sources whose voltage levels can be higher or lower than the output voltage. The inductors of the converter are connected to a single switch; therefore, the converter requires only one extra active switch for each input unlike its counterparts, hence results in reduced element count. In this thesis, the proposed multi-input converter topology is compared with its counterparts concerning various parameters. It is analyzed in detail, and then this analysis is validated by simulation and experiment. Through the developed converter prototypes with two different power levels, developed control strategies are evaluated on an experimental setup and a concept electric vehicle.