Constant Power Method Research Articles

Design and Implementation of the Linear LED Driver

This brief presents a new LED control scheme to maintain a constant LED power. In LED control schemes, the conventional approach is to maintain a constant LED current. However, this traditional approach will bring high power at high input voltage and then generate high heat. The higher heat will shorten the life time of the product and reduce the reliability. The proposed scheme can solve this problem. The LED driver with the proposed scheme has been successfully fabricated by Macronix and the feasibility of the method has been verified. From the experimental results, the higher the input voltage, the lower the LED current. This constant power method can effectively avoid overheating at high input voltage. The control scheme, the theoretical analysis and the circuit implementation are presented in this brief.

Design and Implementation MPPT-CPG for Constant Power Battery Charger

The power produced by photovoltaic is very dependent on irradiation conditions and temperature so that the power can be low or high. The load cannot work if the power is low, but it harms the load if the power is too high. Two modes are used for this system, they are MPPT and CPG mode. When PV power is less than limit power (Plimit), then it works on MPPT mode. The MPPT finds maximum power, then if PV power reaches Plimit or more, it works on CPG mode. During CPG mode, SEPIC converter output power is maintained constant at Plimit so the battery can be charged using the Constant Power Method. The Algorithm used for each mode is the variable Step Size Climbing. The Variable Step Size Hill-Climbing on MPPT performs maximum power according to irradiation conditions. Variables Step Size Hill-Climbing on CPG stabilizes the output power value of SEPIC being constant to charge the battery using the power constant method by keeping the power as constant as its limit power, voltage and current electricity bring into line with charge conditions. The results of the hardware integrated test for MPPT-CPG, the Variable Step Size Hill Climbing algorithm can search for the maximum power point (MPP) generated by PV and can produce an output power of 27.97 W in average.

Research on small flow detection method based on constant power method

In the field of three phase flow testing, real-time and online wellhead production detection has become an indispensable trend for evaluating well production and well condition. At present, the production of most conventional oil fields in China is low, and there are many Wells with less than 10 m3 d−1. It is difficult to detect the flow of low-flow Wells with conventional metering methods. Therefore, this paper proposes to use thermal flowmeter temperature difference method to measure the flow value. First, COMSOL Multiphysics software was used to build the model of the thermal flow meter and set the size of the temperature probe, heating probe and velocity probe. Secondly, relevant parameters are set to simulate two steady state forms with different water content and different flow rate. Finally, the temperature changes of the velocity probe are simulated under the two conditions. The simulation results show that when the water content is the same and the flow velocity is between 0.0059 m s−1 and 0.059 m s−1, the temperature of the probe decreases with the flow velocity increasing, and the temperature of the probe increases with the flow velocity decreasing. At the same flow rate and water content between 0% and 100%, the higher the water content, the lower the temperature of the speed-measuring probe, and the smaller the water content, the higher the temperature of the speed-measuring probe. The simulation results show that thermal flowmeter can be competent for flow detection of low production fluid and low flow well, which provides the basis for the detection method of low production fluid in the future and lays the foundation for the design of thermal flowmeter.

Bis(trifluoromethanesulfonyl)imide Metallic Salts Based Electrolytes for Electrochemical Capacitor Application: Theoretical vs Experimental Performance

In this work we have studied the effect of 1 M bis(trifluoromethanesulfonyl)imide metallic salts in acetonitrile (1 M MeTFSI, where Me = Li, Na, K, Cs or Mg) as an electrolyte for electrochemical capacitors (ECs), using computational quantum mechanical modelling, Raman analysis, cyclic voltammetry, electrochemical impedance spectroscopy and constant power methods. Also, the ionic conductivities of 1 M MeTFSI in AN have been measured and discussed. The ECs based on the 1 M KTFSI in AN electrolyte deliver the higher power density and energy density compared to other MeTFSI based electrolytes and showing excellent characteristics applicable in high energy and power EC devices.

A Laser Joining System for Titanium and Polyethylene Terephthalate Plastic Controlled by Multiple Signal Sources

Laser direct joining of metal and plastic plays a significant role in manufacturing of multiple material structures. To improve the strength of the joint, a controllable laser joining system was developed for polyethylene terephthalate plastic and titanium based on the detected multiple signal sources. The main contribution of this paper lies in sensing 1) the intensity of thermal radiation to control process heat by adjusting the laser power; and 2) the reflection of the helium–neon laser to control the movement of the specimens. The response speeds of thermal radiation intensity when increasing or decreasing the laser powers were measured to guide the adjustment of laser power. The intensities of reflective light before and after the joining process were measured to guide the movement control. Then, the integrated control process was set up. Width, tensile shear strength, and fracture position of the joint produced by the controllable joining system were compared with those produced by the conventional constant power method, which validated the advantage of this newly developed system.

Electric Drive Simulation for Drilling Machine Spinner

The present work discloses the scheme of the automated control system that allows automated leaving the vibration mode by the drilling machine with the indirect vibration measuring method. In addition, the system allows entering the constant power method by the engine. This paper presents a system simulation and reveals that the machine spinner electric drive engine facilitates operating the working branch of mechanical characteristics in the mode of maintaining the set speed to the maximum torque (power specified), followed by moving into the constant power mode that facilitates moving the machine off the vibration zone by means of a small decrease of the drilling string rotation frequency. The article proves that the most radical automation approach suggests using the asynchronous engine drive vector control system in a manner that provides the best regulation accuracy possible.

Increasing the stability of very high potential electrical double layer capacitors by operando passivation

Electrochemical behaviour of titanium carbide-derived carbon (TiC-CDC) electrodes in 1 M (C2H5)3CH3NBF4 + acetonitrile electrolyte has been studied using cyclic voltammetry, constant current charge-discharge, impedance and constant power methods. After step by step cell potential widening and repetitive cell potential cyclization up to 3.4 V, surface passivation, i.e. decrease of faradic reaction currents at potentials higher than 3.4 V, has been detected. Based on Raman spectroscopy data, the passivation effect has been explained by repetitive oxidation-reduction of more active carbon sites from the surface of TiC-CDC and exposition of the more stable graphitic regions. After very careful electrode surface passivation/modification, the region of ideal polarizability can be widened up to 3.7 V and nearly ideal capacitive behaviour with phase angle more negative than −88° and stable series capacitance (∼120 F g−1) have been obtained. Very high experimental energy densities (30 Wh kg−1) at power densities 40 kW kg−1 (ΔE ≥ 3.4 V) have been measured, comparable even with the sol-gel TiC-CDC/(acetonitrile + (C2H5)3CH3NBF4) two-electrode electrical double layer capacitor system. Much higher energy and power values have been achieved at ΔE = 3.7 V, being the maximal cell potential limit, where nearly ideal polarizability for few hundred cycles was achieved.

Short-Circuit Fault Simulations in an HTS Wind Generator With Different Mechanical Conditions

The high-temperature superconducting (HTS) generators are proposed as a promising method to reduce the weight and size of the large-scale off-shore wind generators. However, the lower reactance of an HTS generator makes short-circuit faults heavier. The short-circuit fault problems of an HTS generator are complicated. A simulation is an effective way to study the generator's performances under fault conditions. However, different mechanical conditions affect the simulation results. In this paper, the performance of a 2.5 MW HTS wind generator under short-circuit fault conditions is studied by coupling the finite element method model and the equivalent circuit model. The mechanical conditions are set by three different methods that are the constant rotation speed method, the constant torque method, and the constant power method. The results in these three methods show similar peak values in transient processes, but different developing processes and different final states. The peak values of the electromagnetic torque, armature current, and field winding current appearing in the transient process should be considered when designing the HTS wind generators. This study provides a criterion to set mechanical conditions in the short-circuit fault model of an HTS wind generator, and also provides data for future work about the quench protection of the HTS field windings.

Innovative appraisement of smart grid operation considering large-scale integration of electric vehicles enabling V2G and G2V systems

Upgrading the internal combustion engine (ICE) driven cars to the electric vehicles (EVs) offers the opportunity to reduce the fossil fuel consumption, emission rates and total driving costs. However, the large scale utilization of the EVs introduces a stochastic load demand to the power grid. The effect of EVs charging demand on the distribution network operation should be investigated properly. This paper proposed a novel model to study the effects of power exchange between the grid and EVs on the power system demand profile, the operation stability index, and the reliability indices. To this end, the operation instability indices are introduced by the range and standard deviation of the load factor of the network components to evaluate the system stability. Further, the CAIFI,11Customer Average Interruption Frequency Index. SAIDI,22System Average Interruption Duration Index. SAIFI,33System Average Interruption Frequency Index. and ASAI44Average Service Availability Index. reliability indices are calculated for various vehicle-to-grid (V2G) and grid-to-vehicle (G2V) power level to estimate the impact of different level of power exchange on system reliability. We introduced an EV charging scheduling approach which considers the specification of Li-Ion battery and the limitations for increasing battery life. The power exchange profile for V2G is also calculated using the constant power method to discharge the energy at different levels for times which cars are parked at the workplace. Due to the stochastic nature of EVs, the minimal path method is used to compute the stability and reliability parameters and the backward–forward algorithm is used to load flow analysis. The proposed model is evaluated via modified IEEE 33-bus test system.

Ionic liquid-1,2-dimethoxyethane mixture as electrolyte for high power density supercapacitors

In this work we have studied the effect of 1,2-dimethoxyethane (1,2-DME) addition (from 0 to 90 vol%) on the electrochemical behaviour of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulphonyl)imide (EMImTFSI) as an electrolyte for supercapacitors, using cyclic voltammetry, electrochemical impedance spectroscopy and constant power methods. Also, the ionic conductivity and viscosity of EMImTFSI and 1,2-DME have been measured and discussed. The conductivity of the EMImTFSI could be increased from 5.67mS/cm up to 24.21mS/cm by mixing EMImTFSI with 1,2-DME. The stored power values for supercapacitors increased from 13kW/kg to 20.5kW/kg (correspond to 2s application line), when the concentration of 1,2-DME increased up to 40 vol%. The supercapacitors based on the 40 vol% of 1,2-DME deliver the higher power density at the constant energy density, showing an excellent characteristics applicable in high rate supercapacitor devices. Nearly ideal capacitive behaviour has been established at potential scan rates v≤10mV/s and cell potential ΔE≤2.7V.

Supercapacitors Based on Propylene Carbonate with Addition of Sulfur Containing Organic Solvents

The electrochemical characteristics of electrical double layer capacitors consisting of the mainly microporous titanium carbide derived carbon (TiC-CDC) electrodes in 1 M (C2H5)3CH3NBF4 solutions in propylene carbonate (PC) and mixtures of PC with diethyl sulfite (DES) or 1,3-propylene sulfite, (PS) at different volume ratios have been studied using cyclic voltammetry, electrochemical impedance spectroscopy, constant current charge/discharge and constant power methods. The specific capacitance, phase angle and other values dependent on the solvent system used and temperature applied (from -45 ºC to 60 ºC) have been established. The region of ideal polarizability DE ≥ 2.7 V has been demonstrated for TiC-CDC electrodes in all mixed non-aqueous electrolytes and at temperatures investigated. Specific conductivity values have been obtained and correlated with the electrochemistry data. The limiting capacitance, the characteristic time constant and complex power and energy values calculated depend noticeably on the solvent mixture used, i.e., on the specific conductivity of electrolyte solution.

Supercapacitors Based on Propylene Carbonate with Addition of Sulfur Containing Organic Solvents

The widely used mixed electrolytes for supercapacitors are composed of tetraalkyl ammonium salts and mixed solvents such as propylene carbonate (PC), ethylene carbonate (EC) and ethyl methyl carbonate. Cyclic PC and EC have a high dielectric constant, good compatibility with carbon electrodes enabling the dissolution of salts to sufficient concentrations. However, it is highly viscous and gives poor conductivity even at ambient temperatures. When PC or EC is mixed with linear alkyl carbonates, such as diethyl carbonate (DEC), dimethyl carbonate (DMC), or EMC, more rapid ion transport is achieved as a result of lower viscosity and subsequently higher ionic conductivity is observed. The resulting binary or ternary mixed solutions are widely used in commercially available lithium ion batteries. The choice of co-solvent is a critical issue that significantly affects not only the conductivity, but also the electrochemical performance, including the physicochemical properties of solid electrolyte interface (SEI) formation. In recent years, sulfites such as dimethyl sulfite, glycol sulfite, butylene sulfite, and diethyl sulfite have been studied as a film forming and high temperature additives for electrolytes in lithium ion batteries. It should be mentioned that diethyl sulfite (DES) is used as a film forming agent and high temperature additive for electrolytes in lithium ion batteries improving decomposition resistance of the carbonate-based electrolyte. Propylene sulfite (PS) is used as high temperature additive for electrolytes in lithium ion batteries and it improves the decomposition resistance of the electrolyte.The main aim of this paper is to establish the electrochemical characteristics of the supercapacitors consisting of the two identical mainly microporous titanium carbide derived carbon (TiC-CDC) electrodes in 1 M (C2H5)3CH3NBF4 solutions in propylene carbonate (PC) and mixtures of PC with diethyl sulphite (DES), and propylene sulfite (PS) at different volume ratios. Electrochemical analysis has been made for PC:DES or PC:PS mixtures based electrolytes using cyclic voltammetry, electrochemical impedance spectroscopy, constant current charge/discharge and constant power methods. The limiting capacitance, characteristic time constants and complex power values calculated depend noticeably on the solvent composition and on temperature applied, i.e., on the viscosity and specific conductivity of electrolyte solution used. Acknowledgements The present study was supported by The Estonian Centers of Excellence in Science: High Technology Materials for Sustainable Development, ETF Project 9184, European Regional Development Fund Project SLOKT10209T and Project IUT20-13. Authors of the paper would like to thank Ph.D. Tavo Romann for depositing Al on the electrodes.

Supercapacitors Based on Propylene Carbonate with Small Addition of Different Sulfur Containing Organic Solvents

The electrochemical characteristics of electrical double layer capacitors consisting of the mainly microporous titanium carbide derived carbon (TiC-CDC) electrodes in 1 M (C2H5)3CH3NBF4 solutions in 4-methyl-1,3-dioxolan-2-one, (propylene carbonate (PC)) and mixtures of PC with diethyl sulfite (DES) or 2-oxo-1,3,2-dioxathiane (i.e., 1,3-propylene sulfite, (PS)) at different volume ratios have been studied using cyclic voltammetry, electrochemical impedance spectroscopy, constant current charge/discharge and constant power methods. The specific capacitance, phase angle and other values dependent on the solvent system used and temperature applied (from −45°C to 60°C) have been established. The region of ideal polarizability ΔE ≥ 2.7 V has been demonstrated for TiC-CDC electrodes in all mixed non-aqueous electrolytes and at temperatures investigated. Specific conductivity values have been obtained and correlated with the electrochemistry data. The limiting capacitance, the characteristic time constant and complex power and energy values calculated depend noticeably on the solvent mixture used, i.e. on the specific conductivity of electrolyte solution.

Replacing Chlorine with Hydrogen Chloride as a Possible Reactant for Synthesis of Titanium Carbide Derived Carbon Powders for High-Technology Devices

Micro- and mesoporous carbide-derived carbons were synthesized from titanium carbide (TiC) powder via gas phase reaction by using different reactants (Cl2 and HCl) within the temperature range from 700 to 1100 °C. Analysis of XRD results show that TiC-derived carbons (TiC-CDC) consist mainly of graphitic crystallites. The first-order Raman spectra showed the graphite-like absorption peaks at ~1577 cm1 and the disorder-induced peaks at ~1338 cm-1. The energy-related properties of supercapacitors based on 1 M (C2H5)3CH3NBF4 in acetonitrile and carbide-derived carbons (TiC-CDC (Cl2) and TiC-CDC (HCl)) as electrode materials were also investigated using cyclic voltammetry, electrochemical impedance spectroscopy, galvanostatic charge/discharge and constant power methods. The Ragone plots for carbide-derived carbons prepared by using different reactants (Cl2, HCl) are quite similar and at high power loads TiC-CDC (Cl2) material synthesized at 900 °C, i.e. materials with optimal porous structure, deliver higher power at constant energy.

30. Thermal properties of porcine myocardial tissue at subzero temperatures: Implication for thermal therapy studies

Cryoablation for atrial fibrillation is a clinically approved technique used to control irregular heart rhythms due to abnormal electrical signals conducted from the pulmonary veins to the atria. The ablation catheter rapidly cools the cardiac tissue to freezing temperatures creating a discrete lesion which terminates these abnormal electrical pulses. Benefits of this approach include decreased risk of thrombus formation, well demarcated lesions, and preservation of extracellular matrix and endothelial integrity. However, possible complications include phrenic nerve injury and pulmonary vein stenosis (although these are not unique to the cryoablative approach). Therefore, further understanding of the mechanisms and thresholds of cryoinjury are required. This study begins to address these issues by improving predictive model accuracy through demonstrating the importance of accurate, temperature-dependent tissue properties. The direct relationship between thermal history and treatment outcome, combined with the difficulties of realtime, clinical thermometry, make heat transfer modeling and numerical predictions important aspects of cryoablation studies. The accuracy of the models depends on numerous factors including the kinetics and energy release during phase change phenomena and knowledge of thermal properties as a function of temperature. However, insufficient data for tissue thermal properties in the subzero domain results in a reliance on property estimations, generally based on water–ice data or weight averaged values from known materials. This study focused on expanding the thermal properties database for biological tissue in the subzero regime for use in cryoablation modeling. Results for porcine myocardium as well as ultrasound gel (a substitute phantom used for cryoprobe characterization) are reported. A differential scanning calorimeter was used to measure the specific heat and to observe latent heat effects. The thermal conductivity was measured using self-heating thermistors, employing both transient pulse decay and quasi-steady constant power methods. Specific heats in porcine myocardium were slightly less than those for ice, ranging from 0.93 J/gK at −150 °C to 2.35 J/gK at −21 °C. Specific heat behavior for ultrasound gel could be bracketed into two ranges, in which the values measured were less than those for ice at temperatures below the glass transition temperature (around −110 °C), and progressively higher than those for ice with temperatures above the glass transition. Thermal conductivities of porcine myocardium rose gradually at lower temperatures, ranging from 1.52 W/mK at −10 °C to 2.31 at −148 °C, and were about 50% less than those values for ice. Thermal conductivities of ultrasound gel were similar to those of porcine myocardium, but with an inflection point at the glass transition temperature after which the rise in thermal conductivity was attenuated. The importance of accurate, temperature-dependent thermal properties is demonstrated by comparing the predicted thermal history versus those estimated from constant property values.

Supercapacitors based on carbide-derived carbons synthesised using HCl and Cl2 as reactants

Micro- and mesoporous carbide-derived carbons (CDCs) were synthesised from TiC powder via a gas-phase reaction using HCl and Cl2 within the temperature range of 700–1,100 °C. Analysis of X-ray diffraction results show that TiC-CDCs consist mainly of graphitic crystallites. The first-order Raman spectra showed the graphite-like absorption peaks at ~1,577 cm−1 and the disorder-induced peaks at ~1,338 cm−1. The low-temperature N2 sorption experiments were performed, and specific surface areas up to 1,214 and 1,544 m2 g−1 were obtained for TiC-CDC (HCl) synthesised at T = 800 °C and TiC-CDC (Cl2) synthesised at T = 900 °C, respectively. For the TiC-CDC powders synthesised, a bimodal pore size distribution has been established with the first maximum in the region up to 1.5 nm and the second maximum from 2 to 4 nm. The energy-related properties of supercapacitors based on 1 M (C2H5)3CH3NBF4 in acetonitrile and TiC-CDC (Cl2) and TiC-CDC (HCl) as electrode materials were also investigated by cyclic voltammetry, impedance spectroscopy, galvanostatic charge/discharge and constant power methods. The specific energy, calculated at U = 3.0 V, are maximal for TiC-CDC (Cl2 800 °C) and TiC-CDC (HCl 900 °C), which are 43.1 and 31.1 W h kg−1, respectively. The specific power, calculated at cell potential U = 3.0 V, are maximal for TiC-CDC (Cl2 1,000 °C) and TiC-CDC (HCl 1,000 °C), which are 805.2 and 847.5 kW kg−1, respectively. The Ragone plots for CDCs prepared by using Cl2 or HCl are quite similar, and at high power loads, the TiC-CDC material synthesised using Cl2 at 900 °C, i.e. the material with optimal pore structure, delivers the highest power at constant energy.

Electrochemical Behavior of α-Tungsten Carbide-Derived Carbon Based Electric Double-Layer Capacitors

Cyclic voltammetry, constant current charge/discharge, electrochemical impedance spectroscopy and constant power methods have been applied to establish the electrochemical characteristics for electric double–layer capacitor (EDLC) consisting of 1 M (C2H5)3CH3NBF4 electrolyte in acetonitrile and micro/mesoporous carbon electrodes prepared from α–tungsten carbide, noted as WC–CDC. The N2 sorption (total BET specific surface area (SBET ≤ 1580 m2 g−1), micropore area (Smicro ≤ 1550 m2 g−1), total pore volume (Vtot ≤ 0.89 cm3 g−1) and pore size distribution (obtained by non–local density functional theory) have been correlated with the electrochemical characteristics for EDLCs (region of ideal polarizability (ΔE = 3.0 V), characteristic time constant (τR = 0.41 s), specific series capacitance (Cm;s ≤ 132 F g−1)) dependent on the WC–CDC synthesis temperature. High specific energy (41 W h kg−1) and specific power (430 kW kg−1) values, normalized to the total active mass of both WC–CDC electrodes, synthesized at Tsynt = 1000°C, have been calculated at cell potential 3.0 V.

Sap flow measurements from stem heat balances: a comparison of constant with variable power methods

Two methods of sap flow measurement using the stem surface heat balance approach were compared: the variable power (VP) and constant power (CP) methods. Comparisons were carried out on woody stems in a glasshouse in the UK (Ficus benjamina) and in the field during the rainy season in Niger (Guiera senegalensis). Substantial errors occurred if changes in stem temperature were neglected in the CP method. The simple VP method used neglected conductive losses, but was less affected by changes in stem temperature than the CP method. Therefore, at low flows the VP method overestimated sap fluxes, but at high flows it had a better dynamic response than the CP method. Daily totals of sap flow over 9 days in G. senegalensis stems with leaf areas of 1.3–2.3 m2 ranged from 2 to 9 kg day−1, and the two methods agreed well, although there was a consistent 8–12% higher estimate by the CP method.

Probe controlled transient method for simultaneous determination of thermal conductivity and thermal diffusivity

The parallel wire method for determination of thermal diffusivity of a substance has been modified to determine the thermal conductivity of granular substances and liquids. An auxiliary probe is mounted parallel to the principal probe, which modifies the thermo-EMF generated due to the main probe. This modification makes it useful for accurate and quick determination of thermal conductivity. When used with the pulse technique it is capable of determining thermal conductivity and thermal diffusivity simultaneously. By altering the position of the auxiliary probe, the sensitivity of the technique can be controlled in an ingenious way. The thermal conductivity of glycerine, aluminium powder and aluminium oxide at varying temperatures has been determined by the constant power method and the pulse technique. Values so obtained are compared with those predicted by Hadley's model modified for varying temperatures. Good agreement is obtained between the experimental and theoretical values. A design of the probe for in situ measurement of these properties is also given.