Doctoral Thesis: Merged Multi-Stage Power Conversion: A Hybrid Switched-Capacitor/-Magnetics Approach


Event Speaker: 

Minjie Chen

Event Location: 


Event Date/Time: 

Friday, May 8, 2015 - 10:30am


Power electronics applications place sophisticated requirements on
system design. Increasing the system complexity in appropriate ways
can improve device utilization, yield reduced system volume and/or
improved system performance. This thesis explores new circuit
architectures that leverage the advantages of merged multi-stage power
conversion through a hybrid switched-capacitor/-magnetics approach.
Circuit blocks are topologically and/or functionally merged together
to achieve improved system performance. Multiple designs and system
aspects of this approach are investigated in this thesis.

A 70W grid-interfaced solar micro-inverter with a multilevel energy
buffer and voltage modulator is developed to demonstrate the
advantages of a merged multi-stage system in ac-dc applications. By
synthesizing a multilevel voltage in pace with the ac grid using the
energy buffer, the wide operation range of the inverter stage is
compressed, leading to a significantly improved overall system

Advanced magnetics structures are an enabling technique on the path to
improved power conversion. A systematic approach to modeling
impedances and current distribution in planar magnetics is developed
that facilitates development of improved magnetic components. It
captures electromagnetic coupling relationships using an analytical
lumped circuit model, and enables rapid evaluation of planar magnetics
designs through SPICE simulations. 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.

A high-power-density wide-input-voltage-range isolated dc-dc converter
with a MultiTrack power conversion architecture in keeping with the
approach proposed in the thesis 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 improved, leading to
significantly improved power density as compared to conventional
designs while maintaining high efficiency. The prototype 18Vin-80Vin,
75W isolated dc-dc converter achieves 453.7W/inch^3 power density. It
maintains high efficiency across a wide (>4:1) input voltage range,
and has a peak efficiency of 91.3%. Its power density is 3x higher
than the best state-of-art commercial products presently available.
Thesis committee:
Prof. David Perreault (supervisor)
Prof. Khurram Afridi (co-supervisor)
Prof. Jeffrey Lang
Prof. Charles Sullivan