A ZCS/ZVS DC–DC Partial Power Converter with Reconfigurable H-Bridge and Variable Turns Ratio for an Integrated On-Board Charger

Series-connected partial power converters (S-PPCs) present the advantage of reduced losses due to part of the load power be delivered without any processing,
i.e.
, losslessly. The remaining amount of processed power is required to offer load voltage or current regulation and it is subject of switching and conduction losses. Hence, the efficiency of a S-PPC is quite dependent on keeping its voltage regulation range (
$ \Delta {v}$
) as narrow as possible. For electric vehicles (EVs) battery chargers,
$ \Delta {v}$
must cover from discharged to full charged traction battery pack voltage values, which often cover a wide voltage range and, thus, may minimize the benefits in employing S-PPC. To maintain the S-PPC advantages for such a wider voltage regulation range, this paper proposes a step-up/down S-PPC with a reconfigurable H-bridge and variable turns ratio for the dc–dc stage of an integrated on-board charger (OBC). This way,
$ \Delta {v}$
is split into multiple regions, covering from narrow to wider portions that allows the design of the S-PPC to be optimized for the narrow
$ \Delta {v}$
during most of the constant current (CC) charging mode. This feature provides a significant efficiency improvement and it is achieved by using a tapped primary winding that allows the PWM switching pattern to be exchanged among the three primary-side H-bridge legs yielding in a set of three distinct transformer turns ratios specially designed to cover each region of
$ \Delta {v}$
and reducing the current through the S-PPC. Additionally, zero-current switching (ZCS) is achieved for the primary switches and zero-voltage switching (ZVS) for the secondary switches, which are ensured via two fixed-frequency modulation strategies,
i.e.
, without any additional circuit component to suppress the high voltage spikes across the primary switches. To validate the analyzes, a scale-down prototype was built for an OBC application example (2.2 kW), reaching a peak efficiency of 98.7% during charging.