Storage in IX: a High Performance Storage Layer for a Dataplane Operating System

As storage hardware evolves, the systems and components which interact with them must adapt as well. Outdated assumptions at the operating system level necessitate a dramatic rethinking of the storage path as emerging storage technology offer performance speeds several orders of magnitude faster than traditional hard disks. This thesis investigates the design space of contemporary storage systems, in particular for non-volatile memory (NVM) technology, and presents a survey of the techniques currently being employed to build systems for NVM. We identify and examine relevant systems to determine features applicable to building a storage extension for IX, a data- plane operating system. We present the design and implementation of such a system and detail the assumptions and principles we strove to incorporate.

Human Exposure to Close-Range Resonant Wireless Power Transfer Systems as a Function of Design Parameters

Nicolas Chavannes, Juan Ramon Mosig

In this study, human exposure to close-range wireless power transfer (WPT) systems operating in the frequency range 0.1-10 MHz with coil diameters up to 150 mm are investigated. Approximation formulae, which include scaling factors derived from numerical simulations that take variations of complex human anatomies into consideration, are proposed to conservatively estimate human exposure with respect to the most authoritative exposure guidelines. The approximation has been verified for two precommercial prototype WPT systems, the first of which, a 5-W system operating at 100 kHz, has been evaluated in this study; the second system been verified was reported in a separate study and operates at 6.78 MHz with a nominal current of 5.4 A rms. Based on the results obtained, the optimal operational frequency range for WPT with respect to compliance with exposure safety guidelines is revealed to be ca. 1-2.5 MHz. In summary, this study provides novel and insightful information for the design of an exposure-compliant close-range magnetic resonant WPT system.

Institute of Electrical and Electronics Engineers2014

Synthèse multimodèle d'un régulateur polynomial robuste

Yves Henri Philippe Piguet

Two new approaches are proposed for the multimodel synthesis of a two-degrees-of-freedom polynomial controller : the multimodel pole placement and the multiobjective optimisation. Using several models enables taking into account the parametric variations of the controlled system without introducing conservativeness, be they due to modelling mismatch or changes in the operating conditions. The resulting controller is robust with respect to stability and performances. Multimodel pole placement consists in specifying the closed-loop pole position corresponding to the whole set of models. It is shown that only an approximate pole placement is possible. The distances between the desired and the actual poles are weighted to penalize more the error on the poles which have the most effect on the stability and the performances, and minimized with the least-squares method. An iterative approach is proposed for improving the performances, and an interactive computer-aided design program is developed that enables the user ﬁnding easily which compromises are possible between performances and robustness. In multiobjective optimisation, one considers a set of performance criteria which should be made as close as possible to goal values, also for several models. This results in a minimax problem. Taking into account the H∞ norm of the sensitivity guarantees robust stability. Many different objectives can be included, such as limits on the time- and frequency-domain responses. The result is a compromise between all the speciﬁcations, which is often the purpose of the design. Depending on the optimisation method used, local minima may prevent from reaching the global optimum ; however, this method can signiﬁcantly improve an existing solution. Both approaches are applied to the design of a controller for a ßexible arm. This system exhibits poorly damped modes and large parametric variations. The speciﬁcations concern robust stability and performances. Multimodel pole placement is used to obtain a controller which satisﬁes all of them. Then multiobjective optimisation enables improving the whole set of performance criteria, or more speciﬁcally reducing the amplitude of the control signal.

EPFL1997

What is the design objective for portable power generation: Efficiency or energy density?

Benoît Chachuat

Recently, various alternatives to batteries, such as microfabricated fuel cell systems, have been proposed for portable power generation. In large-scale power production plants emphasis is placed on energy conversion efficiency. On the other hand, the intrinsic design objective for portable power generation devices is the energy density, i.e., the electrical energy generated from a given mass or volume of device and fuel cartridge. It is plausible to stipulate that an increase in the energy conversion efficiency of a system leads to an increase in energy density, but we demonstrate through theoretical analysis and case studies that the two metrics are not equivalent. In some cases, such as systems with a combination of fuels, maximizing efficiency leads to drastically different design, operation and performance than maximizing energy density. Another interesting observation is that, due to interaction between components, maximal component efficiency does not always imply maximal system efficiency.

2007

Synthèse multimodèle d'un régulateur polynomial robuste

Yves Henri Philippe Piguet

EPFL1997