A modular interleaved converter for output current ripple minimization in dc fast chargers for electric vehicles

In this work, a DC off-board fast battery charger topology is presented, designed, and tested. It is expected to be able to fight the range anxiety by significantly diminish the EVs' charging times up to 15-20 minutes, meanwhile keeping low manufacturing, Operation and Maintenance (O&M) costs. The charger is made out of two main power stages the AC/DC and DC/DC converters. In order to keep the costs lower as possible, both parts are designed using interleaved topologies organized by using the same two-level three-phase modules coupled through reactors. This architecture allows to use the already well-known industrial three-phase modules taking advantage of the benefits guaranteed by mass production and at the same time permitting an effortless expansion thanks to its modularity. Thanks to the interleaved connections, it is possible to reach a high efficiency by distributing current and power evenly among the legs. Furthermore, this topology can handle bidirectional power flows, and it might be used for operating in both Grid to Vehicle (G2V) and Vehicle to Grid (V2G) modalities. In order to reduce the dimensions, and the costs of the filters, a control strategy able to keep a zero current ripple at any operative condition is developed. The proposed charger architecture uses an AC input BUS followed by an active rectifier stage. A ripple-free strategy acts on the variable DC BUS voltage according to the chopper duty cycle keeping the current ripple null. Meanwhile, DC/DC provides the requested output current. This strategy involves the AC/DC with the tasks to regulate the DC BUS voltage level and correcting the input power factor. A model-based control system ensures that every leg’s current follows an average current reference signal. Legs’ currents are actively rebalanced throughout a current rebalancing network. Finally, the simulation results are carried out trough MATLAB Simulink and validated with laboratory measurements on an adequately scaled prototype.