Modeling Inverter Losses for Circuit Simulation

Transformer-like inverter models can represent a very good alternative to common switch-diode models for simulation, reducing convergence problems and/or calculation time. They may also provide easier insight into the converter operation and power loss effects, at least from the point of view of the applicants, aiding for design and teaching purposes. The paper shows how conduction and switching losses can be incorporated in the transformer-like inverter model in a simple and intuitive way, which requires very few parameters and allows for separate modeling of lossless behavior, conduction losses and the switching losses. Loss models are proposed in some versions differing for the accuracy and simulation easiness. In any case, the resulting inverter lossy model is very compact and can be implemented by just a pair of nonlinear controlled sources as basic building blocks, available in any circuit simulation program, as the free of charge and widely used PSpice student version

Can thermal storage assist with the electrification of heat through peak shaving?

The majority of heat in the UK comes from the combustion of natural gas, and heat is responsible for 37% of the nation’s carbon emissions. Thus the decarbonisation of heat is a major challenge. Electrification is one possible approach to decarbonisation; however, huge increases in the electrical grid’s generation and transmission capacity would be needed to meet the peaks in space heat demand during cold winter weather. Thermal energy storage (TES) may have a role to play in alleviating this problem, by shifting heat demand by hours or longer periods, enabling peaks to be shaved.This work considers the utility of two varieties of thermal energy storage for this application. Adsorption thermal storage (ATS) is a technology offering long term storage at a high energy density, but is a costly and relatively immature option. By contrast, storage of sensible heat in hot water tanks is already widespread, although it has relatively short storage duration and lower density.Here, we simulate the deployment of these technologies in a small residential neighbourhood, in tandem with demand-side management (DSM), to attempt the reduction of peaks in demand. With no storage or DSM, electrification causes peaks to increase by a factor of 2.36. Results so far suggest that both TES technologies have potential to reduce peaks, with a 14% decrease achievable by either 5 m3 of hot water storage, or 0.25 m^3 of ATS, in each dwelling. However, it is thought unlikely that adsorption storage is attractive for a purely peak shaving application, given its cost and complexity

The Funding Debate: Optimizing Pension Risk within a Corporate Risk Budget

Defined Benefit (DB) pension risk management has traditionally focused on achieving a balance between the risks associated with the liabilities and the expected returns on investments. This approach does not capture the fact that a DB pension plan is part of running an overall business and must compete for capital against alternative investments the corporation can make. Pension funding strategies should be assessed against other corporate cash uses and strategies, such as investment in productive capacity, research and development initiatives, share or debt buybacks, or potential acquisitions. Considering pension funding relative to potential corporate actions within the same net present value (NPV), internal rate of return (IRR) or similar analytical framework, a company can optimise the use of available cash resources and balance alternative strategies against each other

Cost-effective Line Termination Net for IGBT PWM VSI AC Motor drives

The full performance of a series line termination net (LTN) has already been achieved by means of parallel ferrite-core inductors and not inductive power resistors, affecting integration and cost-effectiveness in medium-power PWM AC motor drives. A novel LTN design concept is here presented, namely IRONET, based on the exploitation of the inductor core loss as part of the wanted high-frequency LTN response. Iron cores are adopted instead of larger ferrite-core thanks to proper eddy-current density, set by design of lamination thickness and winding turns. The effective high-frequency behaviour of lossy power inductors is analysed and discussed, defining small-size R-C simple compensation. An IRONET prototype has been realised and tested for a 55 kW-rated IGBT induction motor, showing IRONET effectiveness very close to full performance even by common 0.35 mm laminations

Energy density and storage capacity cost comparison of conceptual solid and liquid sorption seasonal heat storage systems for low-temperature space heating

Sorption heat storage can potentially store thermal energy for long time periods with a higher energy density compared to conventional storage technologies. A performance comparison in terms of energy density and storage capacity costs of different sorption system concepts used for seasonal heat storage is carried out. The reference scenario for the analysis consisted of satisfying the yearly heating demand of a passive house. Three salt hydrates (MgCl2, Na2S, and SrBr2), one adsorbent (zeolite 13X) and one ideal composite based on CaCl2, are used as active materials in solid sorption systems. One liquid sorption system based on NaOH is also considered in this analysis. The focus is on open solid sorption systems, which are compared with closed sorption systems and with the liquid sorption system. The main results show that, for the assumed reactor layouts, the closed solid sorption systems are generally more expensive compared to open systems. The use of the ideal composite represented a good compromise between energy density and storage capacity costs, assuming a sufficient hydrothermal stability. The ideal liquid system resulted more affordable in terms of reactor and active material costs but less compact compared to the systems based on the pure adsorbent and certain salt hydrates. Among the main conclusions, this analysis shows that the costs for the investigated ideal systems based on sorption reactions, even considering only the active material and the reactor material costs, are relatively high compared to the acceptable storage capacity costs defined for different users. However, acceptable storage capacity costs reflect the present market condition, and they can sensibly increase or decrease in a relatively short period due to for e.g. the variation of fossil fuels prices. Therefore, in the upcoming future, systems like the ones investigated in this work can become more competitive in the energy sector.This project receives the support of the European Union, the European Regional Development Fund ERDF, Flanders Innovation & Entrepreneurship and the Province of Limburg. TU/e has received funding from European Union’s Horizon 2020 research and innovation programme under grant agreement Nº 657466 (INPATH-TES). The results of this study can contribute to the development of educational material within INPATH-TES

Sorption heat storage for long-term low-temperature applications: A review on the advancements at material and prototype scale

Sorption heat storage has the potential to store large amounts of thermal energy from renewables and other distributed energy sources. This article provides an overview on the recent advancements on long-term sorption heat storage at material- and prototype- scales. The focus is on applications requiring heat within a temperature range of 30–150 °C such as space heating, domestic hot water production, and some industrial processes. At material level, emphasis is put on solid/gas reactions with water as sorbate. In particular, salt hydrates, adsorbents, and recent advancements on composite materials are reviewed. Most of the investigated salt hydrates comply with requirements such as safety and availability at low cost. However, hydrothermal stability issues such as deliquescence and decomposition at certain operating conditions make their utilization in a pure form challenging. Adsorbents are more hydrothermally stable but have lower energy densities and higher prices. Composite materials are investigated to reduce hydrothermal instabilities while achieving acceptable energy densities and material costs. At prototype-scale, the article provides an updated review on system prototypes based on the reviewed materials. Both open and closed system layouts are addressed, together with the main design issues such as heat and mass transfer in the reactors and materials corrosion resistance. Especially for open systems, the focus is on pure adsorbents rather than salt hydrates as active materials due to their better stability. However, high material costs and desorption temperatures, coupled with lower energy densities at typical system operating conditions, decrease their commercial attractiveness. Among the main conclusions, the implementation within the scientific community of common key performance indicators is suggested together with the inclusion of economic aspects already at material-scale investigations.This project receives the support of the European Union, the European Regional Development Fund ERDF, Flanders Innovation & Entrepreneurship and the Province of Limburg. TU/e has received funding from European Union’s Horizon 2020 research and innovation programme under grant agreement No 657466 (INPATH-TES). The results of this study can contribute to the development of educational material within INPATH-TES

Characterising the discharge cycle of CaCl 2 and LiNO 3 hydrated salts within a vermiculite composite scaffold for thermochemical storage

Transpired solar collectors (TSC) are an efficient means of building heating but due to the demand/use mismatch their capabilities are maximised when paired with a suitable storage technology. The Hydration and/dehydration of inorganic salts provides an appropriate energy storage medium which is compatible with the air temperature provided by a conventional TSC (<70 °C). The study reports on technical appraisal of materials which are compatible with building scale energy storage installations. Two salts (CaCl2, and LiNO3) were impregnated into porous vermiculite to form a salt in matrix (SIM). Their performance during the discharge portion of the cycle at high packing density was examined using a laboratory scale reactor. Reactor and exit temperature increases were considerably lower than those predicted from first principles. Peak reactor temperature rises of only 14 °C were observed with a reduction in temperature output from this initial peak over 60 hours. Poor salt utilization resulting from deliquescence near the reactor inlet was identified as being the source of the reduced performance. Changes in reactor size, orientation and cycling between input periods of moist and dry air did not improve reactor performance. The investigation has identified that moist air transit through the packed SIM reactor column is limited to approximately 100 mm from the air inlet. This has implications for reactor design and the operation of any practical building scale installation. Predictions of building scale energy storage capabilities based on simple scaling of laboratory test considerably under estimate the volume and complexity of equipment required

Feeding in golden hamsters, Mesocricetus auratus

Simultaneous cine and electromyographic records of freely feeding, unanesthetized golden hamsters show that their motion and muscular activity during mastication differ from those of albino rats (Weijs, '75). Rats show only propalinal motion while hamsters show lateral translation as well. The masticatory muscles of hamsters and rats are generally similar, but their molar dentitions differ. The interlocking molar cusps of hamsters restrict propalinal protrusion and retrusion when the molars are in occlusion; however, hamsters readily unlock occlusion by a twisting movement in the horizontal plane. Rats may perform propalinal movements even with the teeth in occlusion. In mastication the hamstery's jaw moves laterally as well as vertically and anteroposteriorly. Chewing orbits typically reverse after one to three orbits. Reversal begins at the start of the upstroke and involves a lateral shift in the opposite direction with the mouth closed. Electromyograms show that symmetric and asymmetric activities of closing protrusive and closing retrusive muscles produce a unilateral force couple on both sides. (This couple accompanies a midline closing stroke.) When the mouth is closed, unilateral activity of closing retrusors and closing protrusors also induces lateral translation. A bilateral force couple pits the retrusors of one side against the protrusors on the opposite side. Simultaneous with lateral excursion to the opposite side of midline and the action of these closing muscles, the anterior digastric and lateral pterygoid muscles of one side fire asymmetrically. The mandible moves downward coincidently with bilateral activity of the digastrics and lateral pterygoids. As the jaw opens further, activity differences of the lateral pterygoids accompany a shift of the mandible toward midline. At the end of the downstroke, all masticatory muscles studied are silent. The jaw returns to midline when the adductors fire asymmetrically at the start of closing. Trituration appears to coincide with an initial simple protrusion, which is subsequently accompanied by lateral translation. Different food types are reduced by distint chewing patterns with the differences clearest when the teeth are near occlusion. During gnawing the lateral pterygoids and digastrics fire longer, and the closing muscles fire less strongly. Chewing patterns in golden hamsters appear more generalized than those of rats; the differences may be directly associated with the ability of hamsters to store food in their cheek pouches.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/50269/1/1051540305_ftp.pd