Princeton University

School of Engineering & Applied Science

“Differential Power” A fundamental limit of power conversion

José A. Cobos
B205 Engineering Quadrangle
Thursday, September 20, 2018 - 4:30pm

The concepts of “Indirect” Power and “Direct” Power are known since 1966 (Moore and Wilson) and 1969 (Wolaver) for 2-port converters. Volume and losses of power converters are determined by the “indirect” power, rather than by the “output” power supplied to the load, because the “indirect” power accounts for the energy stored and delivered by the reactive components in each switching cycle, whereas the power supplied to the load normally includes some amount of “direct” power which does not contribute to losses nor needs to be stored.
The “indirect” power may be calculated at circuit-level for any specific circuit and operating conditions and may be used to compare power topologies or propose new ones. More relevant is the system-level analysis: it is possible to calculate the lower bound of the “indirect” power for any given specification, which is referred to as “Differential” power. This fundamental limit is very useful to perform high-level comparisons of power architectures, and determine the impact of the configuration itself, the number and connection of stages, bus voltage levels, dc-link capacitors discharge ratio, etc.
In this talk, the main novelty is the “VA interpretation” of power conversion, that enables the calculation of novel continuous power models for 2-port and n-port converters. This methodology also enables the synthesis of specific power topologies to operate in this fundamental limit of power processing.
Key applications are stacking of sources (PV cells), loads (data processing cores) or batteries, that require “Power balancing”. “Partial power” configurations may also be assessed with the “differential power” approach. Even more relevant is the case of energy buffered converters, as those required in single-phase inverters connected to domestic batteries/PV panels or those required in AC adaptors and chargers with Power Factor Correction. Three-phase rectifiers and inverters may also be synthesized to operate in the fundamental limit of power conversion. The methodology is illustrated for the “Little Box Challenge” (Google and IEEE-PELS) specification. The differential power is calculated and compared with the “indirect” power processed by the main alternative architectures. Finally, an inverter is synthesized to operate in this fundamental limit that handles half of the indirect power than the rest of alternatives today.

José A. Cobos is a Full Professor at the Universidad Politécnica de Madrid and Chair of the “Industrial Council @ CEI”. He was RCC Fellow at Harvard University and Fulbrighter at UC Berkeley.
His contributions are focused in the field of power supply systems for industrial, aerospace, telecom, automotive, renewable energy and medical applications. His research interests include energy efficiency in digital systems and RF amplifiers, magnetic components, piezoelectric transformers, transcutaneous energy transfer and the generation of EM fields for water supercooling and biomedical applications. He advised over 40 Master Thesis, 14 Doctoral dissertations, published 300+ technical papers (50+ JCR, h>45), and hold patents co-authored with 6 companies. He conducted professional seminars and tutorials in USA, UK, Austria, Germany, Italy, Sweden, Switzerland, Syria, Mexico and Macedonia.
in 2006, he was the founder Director of the “Centro de Electrónica Industrial, CEI-UPM”, a University research center leading a strong industrial program in power electronics and digital systems. Since 2016 he is the founder President of the “Industrial Council @ CEI” to coordinate Education & Research with Industry.