40 research outputs found
A high-throughput approach developing lithium-niobium-tantalum oxides as electrolyte/cathode interlayers for high-voltage all-solid-state lithium batteries
No full textThe ever-increasing interest in sustainable mobility is driving the development of innovative batteries with increased energy densities relative to currently commercialized lithium-ion batteries. All-solid-state batteries using 5 V-class positive electrodes are one of those batteries due to their larger volumetric energy density and their superior durability. However, their power density tends to be limited by the large charge transfer resistance at their electrolyte/5 V-electrode interfaces; one explanation for this is the development of significant Li+ deficient layers at the interface. Here we propose a new interlayer material that would effectively resolve the Li+ deficient layers. The partially-crystallized Li56Nb22Ta22 oxide was identified using the molecular beam epitaxy (MBE) based high-throughput physical vapor deposition (HT-PVD) approach. Its higher ionic conductivity of 4.2 ?S cm?1 and higher permittivity of 165 when measured at 254 kHz, relative to those of conventional LiNbO3 interlayer (1.8 ?S cm?1 and 95, respectively) will be effective for fast charge transfer reactions at the electrolyte /cathode interfaces in 5 V-class all-solid-state batteries
A Park transform-based method for condition monitoring of three-phase electromechanical systems
No full textThis paper presents a Park transform-based method for preprocessing stator current data from a motor and transforming it into a form that is useful for fault detection and diagnostics. The proposed method generates power signatures that are invariant to the initial electrical angle of the voltage when the motor is connected to the utility, and can also adapt to variations in the electrical angle of the supply voltage over time. A modified nonlinear least squares algorithm identifies and tracks the parameters of the supply voltage over time, ensuring that the supply voltage and the argument of the Park transformation remain synchronized. Experimental results are presented that illustrate the method's effectiveness for identifying changes in the mechanical load on a 3/4 HP refrigeration compressor
A two-step method for estimating the parameters of induction machine models
No full textThis paper describes and demonstrates a mathematical algorithm that can monitor the physical parameters of the motor solely by observing the stator electrical currents. This method uses measurements of transient stator currents to identify the parameters of an electromechanical model of the induction motor. These parameters are obtained from a relatively poor initial guess, which is constrained only to be within an order of magnitude of the physical parameters, by using a two-step strategy based upon nonlinear least-squares regression techniques. This makes the approach in this paper useful for diagnostic monitoring and energy scorekeeping. Experimental results are presented which demonstrate the effectiveness of this method on identifying the parameters of a 1 HP induction motor connected to a squirrel cage fan in an air-handling unit.Grainger FoundationAmes Research CenterNational Science Foundation (U.S.)NEMOmetrics (Firm)United States. Office of Naval Research (ESRDC program
Extremum Seeking Control for Energy Optimization of Vapor Compression Systems
No full textIn this paper, an energy optimizing extremum seeking controller is developed for vapor compression systems (VCS) that automatically discovers sets of inputs that minimizes the energy consumption while the machine is in operation. This controller optimizes an input-output map (from VCS inputs to electrical energy consumed) in realtime, and without relying on a model of the dynamics of a vapor compression system. A detailed algorithm and rules for tuning the controller gains will be described. Experiments are performed on an inverter-driven room air conditioner that demonstrate convergence of inputs to their optimal values, resulting in an improvement in COP of 10-20% for some operating points
Comparisons of predicted bore evolutions by the Benjamin-Davis-Ono and Navier-Stokes equations for idealized mesopause thermal ducts
No full textNumerical simulation of bore generation and morphology in thermal and Doppler ducts
No full textWe perform a series of numerical simulations employing a model describing
nonlinear incompressible dynamics to explore bore generation and morphology
for several ducting geometries. These include idealized thermal ducts in
close proximity to, and more remote from, reflecting boundaries, an
idealized Doppler duct remote from boundaries, and a combination of thermal
and Doppler ducts at nearby altitudes. Based on observed bore environments,
we assume initial long-wave perturbations having sinusoidal form and large
amplitudes. Results indicate that close proximity of a duct to reflecting
boundaries enhances bore development, that both thermal and Doppler ducts
support bore development for long-wave perturbations of sufficiently large
amplitudes, and that bore structures and evolutions exhibit both features
anticipated by idealized bore theory and departures that remain to be
explored in detail
Non-Intrusive Fault Detection in Reciprocating Compressors
No full textThis research presents techniques developed for non-intrusive sensing and fault detection in reciprocating compressors driven by induction motors. These procedures are “non-intrusive” because they rely only on voltage and current signals measured on the compressor power cable. The electrical sensor based method allows for easy and non-intrusive determination of many fault sensitive signals that usually require complicated, expensive, and time consuming operations to measure. The electric signals are processed and used with the inverted dynamic motor model equations and motor parameters (which are also determined non-intrusively) to recover the instantaneous angular speed of the compressor shaft, as well as the torque of electromagnetic origin provided by the motor. These two intermediate signals and compressor parameters such as crank shaft inertia are then used to solve for the compressor load torque. This load torque signal has high fault diagnostic value because it is composed of pressure and friction torques, and these signals are close to mechanical phenomena of diagnostic interest in the compressor. All these signals are recovered at a fine resolution giving high level of detail on a sub-shaft revolution basis. The use of the load torque signal in determining faults and additional diagnostic information is also given. A procedure for determining the cylinder suction and discharge pressure from the load torque signal and knowable cylinder parameters such as cylinder volume, crank arm length, and gas coefficients is discussed. The load torque signal is also useful directly: for the two piston machine used in the research, symmetry of the twice per rotation peak of the load torque is a valuable diagnostic measure. Reed valve leakage faults were investigated by drilling small holes of varying sizes in one cylinder’s suction reed. The asymmetry in each cylinder’s pressure torque peak increases with increasing leak size, providing both an indication and measure of leakage severity
Evaluating Fault Detection and Diagnostics Protocols Applied to Air-Cooled Vapor Compression Air-Conditioners
No full textFault detection and diagnostics (FDD) tools are being increasingly applied in air-conditioning systems. There are many different protocols used in these FDD tools, so an important question to ask is: how well do the protocols work? This paper describes the ongoing development of the first standardized method of evaluation for FDD protocols applied to air-cooled vapor compression air-conditioning systems. The general approach is to feed a library of data – including temperatures, pressures, and humidity – to a candidate FDD protocol, and observe the responses of the protocol. The library includes data from units operating with no fault or with single faults. The faults include undercharge or overcharge of refrigerant; impaired heat transfer in the condenser or evaporator; liquid line flow restriction; presence of non-condensable gas in the refrigerant; and compressor valve leakage. The outputs from the test are categorized, and statistics and figures are generated. A preliminary evaluation of RCA, a public domain FDD protocol, has been conducted using laboratory measurement data from 13 air conditioning systems. The rates of (a) no response, (b) correct, (c) false alarm, (d) missed detection, and (e) misdiagnosis show that the protocol performed poorly. This underscores the need for standardized FDD evaluation methods
Tsunami‐driven gravity waves in the presence of vertically varying background and tidal wind structures
No full text
