P $^{3}$ DCT - Partial-Power Pre-Regulated DC Transformer

In this paper a new approach to regulate the output voltage of a resonant, constant voltage transfer ratio 380 V/48 V isolated DC/DC converter is presented. Rather than applying variable frequency control to the resonant converter which would result in reactive power processing and a more complicated EMC filter design, the converter remains in its optimal operating point all time and an additional partial-power (PP) processing auxiliary converter is used to tightly regulate the output voltage. The PP converter, supplied through a tertiary winding of the resonant converter's transformer, regulates the output by adding or subtracting voltage from the DC input and has only a marginal impact on the overall efficiency of the DC/DC converter. The principal of operation is explained in detail including Sankey diagrams to illustrate the power processing of the converter. A hardware demonstrator rated at 1.5kW is implemented to cope with input voltage variations between 340 V - 420 V and experimental results are provided showing that the the output voltage can be kept within -1% of the nominal 48 V even under harsh input voltage and load transients. The realized DC/DC converter with PP pre-regulation features an overall efficiency of 97:7% at rated power and a power density of 8:6kW/dm $^{3}$ (141W/in $^{3}$ ). This paper is accompanied with supplementary video material demonstrating the principle of operation of the implemented prototype.