Analysis of capacitive power transfer GaN ISOP multi-cell DC/DC converter systems for single-phase telecom power supply modules

The Input Series Output Parallel (ISOP) multi-cell converter approach allows breaking the performance barriers of conventional single-cell telecom rectifier systems by leveraging the advantages of using multiple interleaved low-voltage and/or low-current converter cells. The ISOP interconnection in the DC/DC converter part of the cells, however, requires the employment of some kind of isolation in each cell, which is typically provided by transformers. An analysis of the losses and of the volume of the entire multi-cell system reveals that these transformers contribute a major part to the system losses and are responsible for a significant share of the total volume. However, as the transformers are mainly required for providing galvanic isolation in the ISOP structure and not for voltage conversion, series capacitors represent an alternative to decouple the series connected input terminals of the cells from the parallel connected output terminals. Compared to conventional solutions with transformers, the resulting capacitive power transfer ISOP multi-cell DC/DC converter (CPT-ISOP-MCC) system features lower losses and a smaller volume. In this paper, the benefits as well as the limitations in the design and operation of CPT-ISOP-MCC systems are analyzed in detail. In order to comprehensively evaluate the CPT against the magnetically isolated concept, i.e. inductive power transfer (IPT) converter topology, a multi-objective optimization is performed with respect to the achievable efficiency and power density for both types of converters. Based on the optimization result, a prototype of a CPT GaN DC/DC converter is realized and compared to its IPT GaN DC/DC converter counterpart, along with measurement results. Furthermore, a complete single-phase 3.3kWAC/DC converter system with a high power density of ρ = 3.92kW/dm
³
and an efficiency of η = 97% is presented, incorporating the CPT-DC/DC converter stages in ISOP topology.