Publication:

Novel two-stage three-level converter with inherently-balanced dc voltage for EV fast-charging applications

The design of EV fast chargers faces a new challenge due to the boost in the battery voltage of electric cars and heavyduty electric vehicles. Two-stage converters, that consist of an isolated dc-dc stage and an extra regulated dc-dc converter, are attracting an increasing attention thanks to their outstanding performance. The potential benefits of multilevel converters, such as lower power losses and more compact filters, can be incorporated to two-stage architectures at the expense of simplicity due to the need of a voltage balancing method. In this article, a novel dc-dc two-stage three-level (2S3L) architecture is presented, which guarantees that the multilevel input dc voltages are balanced without any specific balancing technique or extra components. Moreover, it accomplishes lossless switching in the isolated dc-dc stage, enabling a high efficiency. A 15 kW test bench is built in order to experimentally verify the inherentlybalanced voltages. The experimental tests demonstrate that the dc-link voltages are inherently-balanced (no control needed) in both transient and steady states, and that it is robust against tolerances and faulty operation. The test bench is able to provide a wide output voltage, from 200 to 900 V, and reaches a high peak efficiency of 98.2% at rated power.