Transformer Volume Reduction: A New Analysis and Design of an SSSA Control Based 20kW High Power Density Wide Range Resonant Converter

Isolated DC/DC converters play a pivotal role
in the realm of power electronics, particularly in the context
of electric vehicle (EV) fast charging. These converters are
responsible for delivering high-voltage direct current to
EVs, sourced from a 3-phase power factor correction (PFC)
converter, and exhibit compatibility with both low-voltage
and high-voltage vehicle batteries. However, in many
instances, the demand for constant power charging in
various applications results in a significant portion of the
transformer volume, thereby leading to a decrease in
converter power density. This paper presents a new
analysis and design for a converter based on secondary
side semi-active (SSSA) control. This analysis provides
theoretical support for transformer volume reduction and
power density increase. It employs SSSA control to
transfer stored energy from the transformer to the resonant
network during boost operation, even when fs > fr, with the
excitation inductance participating in resonance. Based on
this analysis, the design of a 20kW 650-850V input to
300-900V with 66.7A max output prototype is discussed.
The objective is to achieve the highest feasible converter
power density. The designed results confirm that the
2*PQ6535 (or 1*PQ6549) core can effectively serve the
20kW transformer, resulting in an ultra-high power density
of 14.36 kW/L (235 W/in3).