Merged multi-stage power conversion : a hybrid switched-capacitor/magnetics approach

Abstract

Emerging applications of power electronics introduce challenging design requirements. Increasing the system complexity in appropriate ways can bring many advantages, yielding reduced system volume and/or improved system performance. This thesis explores new circuit design techniques that can leverage the advantages of merged multi-stage power conversion through a hybrid switched-capacitor/magnetics approach. Multiple circuits and system aspects of this approach are investigated in this thesis. A 70 W grid-interfaced solar micro-inverter with a multilevel energy buffer and voltage modulator (MEB) is developed to demonstrate the advantages of a merged multi-stage system in dc-ac applications. By synthesizing a multilevel voltage in pace with the ac grid voltage using the energy buffer, the wide operation range of the inverter stage is compressed, leading to a significantly improved overall system performance. A high-power-density wide-input-voltage-range isolated dc-dc converter with a Multi- Track power conversion architecture is also investigated. The MultiTrack architecture delivers power in multiple voltage domains and current tracks. It incorporates multiple distributed circuit cells, and benefits from the way they are merged together. By changing the use of multiple cells according to the system operating condition, the overall device utilization of the system is enhanced, leading to significantly improved power density as compared to conventional designs while maintaining high efficiency. The prototype 18 V-80 V input, 5 V output, 75 W isolated dc-dc converter achieves 453.7 W/inch³ power density, which is 3x higher than the best commercial product presently available. It maintains high efficiency across a wide (>4:1) input voltage range, and has a peak efficiency of 91.3%. Advanced magnetics structures are an enabling technique on the path to improved power conversion. This thesis developed a systematic approach to modeling impedances and current distribution in planar magnetics. It captures electromagnetic coupling relationships using an analytical lumped circuit model, and enables rapid evaluation of planar magnetics designs. The effectiveness of the model is verified by numerical methods and experimental measurements. A software package - M2Spice - that can rapidly convert design information into SPICE netlists has been developed and is being utilized in many real designs.