Tutorial presentations will be held on Monday June 25
José A. Cobos
Universidad Politécnica de Madrid
A fundamental limit of power conversion
(click here to download)
Volume and losses of power converters are determined by the “indirect” power, rather than by the “output” power delivered 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 delivered 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. At system-level, 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 make high-level comparisons of power architectures, and determine the impact of the configuration itself, the number and connection of stages, bus voltage levels, capacitors discharge ratio, etc.
“Differential Power” is also useful to synthesize specific power topologies to operate in this fundamental limit of power processing. This is especially important in the case of 3-port and multi-port converters. Power balancing between stacked sources (PV cells), loads (data processing cores) or batteries are particular cases of “differential power”. “Partial power” configurations may also be assessed with the “differential power” approach. The general methodology is described using internal power models for 2-port and 3-port converters, and applied to multiple cases.
One of the most interesting applications of this methodology are energy buffered converters, as those required in single-phase inverters connected to domestic batteries/PV panels or those required in Power Factor Correction applications. 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.