Autonomous Bidirectional Converter for Electric Vehicles in DC Microgrid

Abstract

This paper proposes a bidirectional resonant DC-DC converter with high efficiency and highpower density while keeping the cost minimized over a wide range of battery voltages. In the forward mode, the resonant boost functionality is achieved by PWM based forward converter action i-e simultaneous power flow towards secondary side. Whereas in the backward mode, the power flow is achieved by neutral point clamped (NPC) action. Unlike conventional full bridge primary side, the introduction of actively clamped primary side removes the two switches along with their bulky heat sinks, thereby reducing the switch count and improving the power density. Backwards power flow is achieved by modulating the primary side switches and the middle switches of NPC structure on secondary side with a fixed duty cycle and the half bridge NPC switches are modulated variably. This enables, low switch count and improved power density. The soft switching is achieved due to series resonant tank and deadband interval. Although, the primary and secondary structures are different, symmetric operation is achieved by modulation. A hardware prototype of 1000W having a variable low voltage side of 50V to 70V and high voltage side of 380V was implemented to validate this topology.