Electrical efficiency | EPFL Graph Search

The efficiency of a system in electronics and electrical engineering is defined as useful power output divided by the total electrical power consumed (a fractional expression), typically denoted by the Greek small letter eta (η – ήτα). : \mathrm{Efficiency}=\frac{\mathrm{Useful\ power\ output}}{\mathrm{Total\ power\ input}} If energy output and input are expressed in the same units, efficiency is a dimensionless number. Where it is not customary or convenient to represent input and output energy in the same units, efficiency-like quantities have units associated with them. For example, the heat rate of a fossil fuel power plant may be expressed in BTU per kilowatt-hour. Luminous efficacy of a light source expresses the amount of visible light for a certain amount of power transfer and has the units of lumens per watt. Efficiency of typical electrical devices Efficiency should not be confused with effectiveness: a system that wastes most of its input pow

Etude formelle pour la synthèse de convertisseurs multiniveaux asymétriques

Jean-Sébastien Mariéthoz

The multilevel converters allow generating a voltage waveform whose magnitude and quality are higher than those of conventional converters. They are devoted to medium and high-voltage, high-switching-frequency applications. Among the series connected cell inverters, the symmetrical multilevel inverters are made of identical cells, which topology is generally the H-bridge inverter. This dissertation deals with asymmetrical multilevel converters, which combine high-voltage cells — made of low conduction loss switches — with low-voltage cells — made of low switching loss switches. The different cells play different roles. The goal is to design a converter that has both better energetic efficiency and higher resolution with the same number of cells. This dissertation develops a set of tools that allows synthesizing an asymmetrical multilevel converter. It develops the cell combination rules, which allow defining several cell association classes. The inverter step uniformity condition determines the finesse that can be reached. The optimized modulation condition allows to reduce the highvoltage cell switching frequency without changing the low-voltage cell switching frequency. This property is essential to derive benefit from combining switches of different characteristics. The power balance condition determine how to control the power sharing between the cells. These association classes are different for the single-phase converters and the three-phase converters — without neutral wire. They allow to select a configuration suitable for a given application. Furthermore, several ways that allow improving the inverter resolution are investigated. The modulation is essential to associate a high-quality signal (which will really be delivered to the load by means of the inverter levels) to the reference signal (which should ideally be applied to the load). The modulator evaluation methods are assessed. An approach—based on the modulated signal decomposition in elementary frames—is proposed. The main modulator drawbacks are highlighted. A modulator—which arrange the frames in order—allows to reduce the modulated signal distortion and number of transitions. The specific control methods that allow to minimize the inverter number of switchings are developed. The active power cell supply implies several conversion stages, which decrease the converter energetic efficiency. Some solutions that allow to reduce these losses are proposed. Finally, this dissertation attempts to determine, which are the more interesting solutions, depending on the application.

EPFL2005

Enhanced-performance integrated Resonant Switched-Capacitor and Buck DC-DC converters for application in extreme radiation and magnetic field environments

Giacomo Ripamonti

DC-DC converters based on Application Specific Integrated Circuits (ASICs) have been developed in this doctoral work for the High-Luminosity Large Hadron Collider (HL-LHC) experiments at CERN. They step down the voltage from a 2.5 V line and supply a load current up to 3 A. The main focus has been the miniaturization of the converters while maintaining high efficiency, together with the improvement of the dynamic performance and the minimization of the impact of substrate parasitic devices. These are challenges that industry and research are facing to power modern microprocessors, with the aim of minimizing the system volume, cost and power consumption, while guaranteeing good regulation performance. Miniaturization is a key requirement for application in the HL-LHC experiments, since any added material is detrimental for the physics performance. In addition, the converters must be tolerant to a high magnetic field (up to 4 T) and to ultra-high levels of radiation. Tolerance to the magnetic field is achieved by employing air-core inductors (which are the bulkiest components on the board), while radiation-hard ASICs have been designed in this work in a commercial 130 nm CMOS technology by extensively applying hardening by design techniques. Converters using two different architectures have been designed: a buck converter, which had been identified in a previous work as a good option to achieve high efficiency and low mass, and a Resonant Switched-Capacitor (ReSC) converter, which can further increase the power density while keeping high efficiency. A novel dual-edge pulse width modulator for the buck converter that has improved dynamic performance compared to conventional solutions has been designed and implemented. Its small-signal response has been modeled, and the model has been validated by measurements. In addition, this thesis proposes an integrated system that monitors in real-time the voltage stress experienced by the devices of the buck converter and adjusts its operation accordingly, in order to guarantee the required reliability, while maximizing the efficiency. The main building block of this system has been designed and has proved to be fully functional. A substrate-currents-aware characterization method that allows the evaluation of the impact of substrate parasitic devices on the circuit performance and reliability has been also devised, and it has been applied to select the best floor-plan for the buck converter. A novel control scheme that optimizes the efficiency of the ReSC converter for the whole load current range by adopting different operation modes has been proposed and implemented. This thesis reports the steady-state analysis of each mode and a small-signal model for one of them. The buck converter uses a 100 nH inductor, and the last prototype shows a peak efficiency of 88.4% for the 2.5 V-to-1.2 V conversion. It complies with the radiation specifications, and mass production will soon start. The designed prototype ReSC converter employs a 12 nH inductor, and its area occupancy and thickness are respectively 20% and 55% lower than the buck. Its efficiency is larger than that of the buck converter in a range of conversion ratios and load currents, reaching a peak efficiency of 91.4% for the 2.5 V-to-1.2 V conversion. Radiation tests have highlighted that the converter complies with Total Ionizing Dose specifications. By introducing a few improvements, a future prototype could be close to production readiness.

EPFL2020

Swiss SOFC Integration Activities : Stacks, Systems, and Applications

Raphaël Ihringer

Solid Oxide Fuel Cell (SOFC) application development is very well represented in Switzerland by two companies. Sulzer Hexis AG is one of the world leaders in the commercialization of SOFC systems for single family houses. A smaller company, HTceramix, is active in novel processing routes for cells and in innovative stack designs. This article first presents the benefits of implementing SOFC in selected applications and markets. Then the current state-of-the-art in stacking is described for both Swiss stack designs, looking at power density, and electrical efficiency. It is remarkable that both stacks currently exhibit a unique characteristic in SOFC design: the absence of side sealing, which permits to significantly simplify the stack assembly and thus improve its reliability. Finally, the two generations of SOFC systems produced by Sulzer Hexis are presented. The HXS 1000 Premiere preseries system is evaluated on the basis of the extended demonstration program currently underway where 110 systems are in operation in single family houses and public buildings. The near-series system is then introduced with respect to the identified needs in reduction of investment and operating costs as well as size and weight.

2004