Design and Testing of a Bidirectional Smart Charger Prototype

Abstract

Rising greenhouse gas emissions, increased fuel costs, and recent technological advances are causing a paradigm shift in the auto-industry away from traditional internal combustion engine vehicles to Electric Vehicles (EVs). Although good for the environment, mass deployment of electric and hybrid electric vehicles has the possibility to cause negative effects to the power grid, such as phase imbalances, voltage deviations, and distribution transformer overloading, since some EVs can potentially draw as high as 19.2 kW in a household from a single-phase outlet. However, if charging is properly controlled and coordinated, EVs have the potential to support the power grid, possibly acting as distributed generation or a storage unit. This thesis aims to address the aforementioned issues by developing a fully-functional “smart” bidirectional EV charger prototype. The term smart refers to the charger’s ability to control the charging and discharging of the battery pack based on the preferences of the car owner, the electricity price at the time of use, battery’s operational constraints, and the distribution system’s requirements at the command of the utility or Local Distribution Company (LDC). Bidirectional refers to power flow, i.e., the charger will employ a design that allows the power to flow from the grid to the battery and vise-versa. The thesis first reviews existing bidirectional charger topologies and smart grid communication technologies. Then, relevant standards, battery technologies, and controller options are discussed; this finally is followed by the charger design process and simulation results to validate the design. Finally, the smart bidirectional charger prototype is presented and tested, to validate and demonstrate its effectiveness in addressing power grid issues.