Isolated Triple Active Bridge AC//DC//DC Converter for Electric Vehicle Chargers With Local Storage

Abstract

In order to reduce the impact of fast Electric Vehicle (EV) chargers on the grid, incorporating local energy storage will become a must. Thus, an improved EV charger is proposed that can be seen as a multiple-port system, where one port is the electrical grid, a second port is the EV battery and another one consists of a local energy storage system, such as buffer batteries integrated in the charger. This forms a 3-port system in which one port is AC and the others are DC type. For such a complex system, a multiple-port converter with bidirectional switches, as the one analyzed in this work, suits perfectly due to its intrinsic galvanic isolation and its reduced size, in comparison with a multi-converter solution, one per connected device. This paper proposes a Triple Active Bridge (TAB) converter in which one port is modified to accept AC signals by means of bidirectional switches. The paper details how to control the TAB converter to achieve different control objectives in each port, such as constant current/constant voltage charge for the EV battery and the reduction of power peaks in the grid side port. The proposed control is validated through simulations and by means of a scaled-down 1 kW prototype. It shows that the suggested solution is 5% more efficient and more compact than the corresponding multi-converter solution.