Constant Resistive Load Research Articles

Decomposition of Power Electronic and Conventional Loads of Modern Power Systems by Discrete Wavelet Transform

Load composition data is used in different static and dynamic studies of present power systems. Increasing the number and capacity of power electronic loads in the modern power systems, especially microgrids, makes it necessary to perform various harmonic studies, beside considering this new load type in the conventional studies. For this purpose, new methods are required to decompose power electronic loads from conventional loads of power systems. This paper introduces a novel non-intrusive decomposition method, based on digital wavelet transform. The contribution of the proposed method is its ability to decompose most common power electronic loads, including uncontrolled/semi-controlled rectifiers with both constant power and resistive DC loads, in steady state and especially in transient and asymmetric conditions. Moreover, this method is significantly easier and more accurate than available machine learning-based decomposition methods. Another advantage of this paper is employing excellent denoising ability of digital wavelet transform, compared to conventional digital filters, for noise elimination of actual measured waveforms. The validity of proposed decomposition method is evaluated by simulation of dominating rectifiers in combination with induction motor and inductive load, as conventional load, in MATLAB/Simulink. Laboratory-implementation of the test system is also employed for further validation of the proposed method.Keywords: Denoising, Discrete Wavelet Transform, Line-Commutated Rectifiers, Load Decomposition, Microgrids, Transient Conditions

PEM fuel cell short stack performances of silica doped nanocomposite membranes

In this study, an air-cooled Proton Exchange Membrane Fuel Cell (PEMFC) short stack with Nafion/Silica nanocomposite membrane was designed and fabricated for net 100 W net power output to improve the stack performance at low relative humidity conditions. Composite membrane was prepared by solution casting method. Gas Diffusion Electrodes (GDE's) were produced by ultrasonic spray coating technique. Short stack design was based on electrochemical data obtained at 0.60 V was 0.45 A/cm2 from performance tests of a single cell having the same membrane electrode assemblies (MEA) that had an active area of 100 cm2. The short stack was tested in the constant resistance load regime, in dead-end mode, with controlling temperature by air on-off control system. A maximum power of 117 W was obtained from the short stack.

Simulation of temperature rise in Li-ion cells at very high currents

The Dualfoil model is used to simulate the electrochemical behavior and temperature rise for MCMB/LiCoO2 Li-ion cells under a small constant-resistance load, approaching a short-circuit condition. Radial mass transport of lithium from the center of the pore to the pore wall has been added to the model to describe better current limitations at very high discharge currents. Electrolyte and solid-surface-concentration profiles of lithium ions across the cell at various times are developed and analyzed to explain the lithium-ion transport limitations. Sensitivity tests are conducted by changing solution and solid-state diffusion coefficients, and the heat-transfer coefficient. Because diffusion coefficients increase at high temperature, calculated discharge curves can show currents dropping initially but then rising to a second peak, with most of the available capacity being consumed in the second peak. Conditions which lead to such a second peak are explored.

Simulation of Li-ion Cells by Dualfoil Model under Constant-Resistance Load

The Dualfoil model is used to simulate the electrochemical behavior and temperature rise for MCMB/LiCoO2 Li-ion cells under constant-resistance load operation, approaching a short-circuit condition. Electrolyte and solid surface concentration profiles of lithium-ion across the cell at various time scales are developed and analyzed to explain the lithium-ion transport limitations. Sensitivity simulative tests are conducted using selected values of the heat-transfer coefficient, lithium-ion diffusion coefficient in the solution and solid phases, electrode kinetic rate constants, and film resistance. Radial mass transport of lithium from the center of the pore to the pore wall (in the CoO2) has been added to the model to describe better current limitations at very high discharge currents. The results show that excessive overheating in batteries can result under conditions approaching short circuit.

Thermodynamic, Energy Efficiency, and Power Density Analysis of Reverse Electrodialysis Power Generation with Natural Salinity Gradients

Reverse electrodialysis (RED) can harness the Gibbs free energy of mixing when fresh river water flows into the sea for sustainable power generation. In this study, we carry out a thermodynamic and energy efficiency analysis of RED power generation, and assess the membrane power density. First, we present a reversible thermodynamic model for RED and verify that the theoretical maximum extractable work in a reversible RED process is identical to the Gibbs free energy of mixing. Work extraction in an irreversible process with maximized power density using a constant-resistance load is then examined to assess the energy conversion efficiency and power density. With equal volumes of seawater and river water, energy conversion efficiency of ∼ 33-44% can be obtained in RED, while the rest is lost through dissipation in the internal resistance of the ion-exchange membrane stack. We show that imperfections in the selectivity of typical ion exchange membranes (namely, co-ion transport, osmosis, and electro-osmosis) can detrimentally lower efficiency by up to 26%, with co-ion leakage being the dominant effect. Further inspection of the power density profile during RED revealed inherent ineffectiveness toward the end of the process. By judicious early discontinuation of the controlled mixing process, the overall power density performance can be considerably enhanced by up to 7-fold, without significant compromise to the energy efficiency. Additionally, membrane resistance was found to be an important factor in determining the power densities attainable. Lastly, the performance of an RED stack was examined for different membrane conductivities and intermembrane distances simulating high performance membranes and stack design. By thoughtful selection of the operating parameters, an efficiency of ∼ 37% and an overall gross power density of 3.5 W/m(2) represent the maximum performance that can potentially be achieved in a seawater-river water RED system with low-resistance ion exchange membranes (0.5 Ω cm(2)) at very small spacing intervals (50 μm).

Power Flow Calculation in Distribution System Considering Different Load Model

In traditional power flow calculation used constant power load model, it was completely unreasonable to assume that all load nodes in power system can be classified as PQ nodes.In that the result of constant power load model does not accurately reflect the distribution characteristics of network power flow. To put forward power flow calculation considering load models ,such as constant power load ,constant current load and constant resistance load, derives error equations of the node power, calculates element of Jacobian matrix. So, by using MATLAB simulation software ,the program for power flow are presented, which based on the method of different load models, taking 21-node system for example and makes comparative calculations. The research shows that power flow calculation considering different load models can get more reasonable solution.

Thermal and electrical experimental characterisation of a 1 kW PEM fuel cell stack

The present work describes the experimental characterisation of a self-humidified 1 kW PEM fuel stack with 24 cells. A test bench was prepared and used to operate a PEMFC stack, and several parameters, such as the temperature, pressure, stoichiometry, current and voltage of each cell, were monitored with a LabView platform to obtain a complete thermal and electrical characterisation. The stack was operated in the constant resistance load regime, in dead-end mode (with periodic releases of hydrogen), with 30% relative humidity air and with temperature control from a cooling water circuit. The need to operate the stack for significant periods of time to achieve repeatable performance behaviour was observed, as was the advantage of using some recuperation techniques to improve electrical energy production. At low temperatures, the individual cell voltage measurements show lower values for the cells nearer to the cooling channels. The performance of the fuel cell stack decreases at operating temperatures above 40 °C. The stack showed the best performance and stability at 30 °C, with 300 mbar of hydrogen and 500 mbar of air pressure. The optimised hydrogen purge interval was 15 s, and the most favourable air stoichiometry was 2. Between 15 A and 32 A, the maximum electrical efficiency was 40%, and the thermal energy recovery in the cooling system was 40.8%; these values are based on the HHV. Electrical efficiencies above 40% were obtained between 10 and 55 A. The variation in the electrical efficiency is explained by the variation in the following independently measured factors: the fuel utilisation coefficient and the faradic and voltage efficiencies. The deviation between the product of the factors and the measured electrical efficiency is below 0.5%. Measurements were taken to identify all the losses from the fuel cell stack; namely, the energy balance to the cooling water, which is the main portion. The other quantified losses by order of importance are the purged hydrogen and the latent and sensible heat losses from the cathode exhaust. The heat losses to the environment were also estimated based on the measured stack surface temperature. The sum of all the losses and the electrical output has a closure error below 2% except at the highest and lowest loads.

Effect of Resistive Load on the Inspiratory Work and Power of Breathing during Exertion

The resistive work of breathing against an external load during inspiration (WRI) was measured at the mouth, during sub-maximal exercise in healthy participants. This measure (which excludes the elastic work component) allows the relationship between resistive work and power, ventilation and exercise modality to be explored. A total of 45 adult participants with healthy lung function took part in a series of exercise protocols, in which the relationship between WRI, power of breathing, PRI and minute ventilation, were assessed during rest, while treadmill walking or ergometer cycling, over a range of exercise intensities (up to 150 Watts) and ventilation rates (up to 48 L min−1) with applied constant resistive loads of 0.75 and 1.5 kPa.L.sec−1. Resting WRI was 0.12 JL−1 and PRI was 0.9 W. At each resistive load, independent of the breathing pattern or exercise mode, the WRI increased in a linear fashion at 20 mJ per litre of , while PRI increased exponentially. With increasing resistive load the work and power at any given increased exponentially. Calculation of the power to work ratio during loaded breathing suggests that loads above 1.5 kPa.L.sec−1 make the work of resistive breathing become inhibitive at even a moderate (>30 L sec−1). The relationship between work done and power generated while breathing against resistive loads is independent of the exercise mode (cycling or walking) and that ventilation is limited by the work required to breathe, rather than an inability to maintain or generate power.

Acid-base balance at lactate threshold in resistance exercise

To evaluate acid-base status during constant-load resistance exercise at the lactate threshold (LT) intensity. Seven healthy men underwent two protocols on a leg press machine. One maximal incremental test to determine LT intensity and a constant-load resistance protocol executed at this intensity. The participants performed 15 sets of 20 repetitions lasting 1 min with 1 min rest intervals during the constant-load exercise. Capillary blood samples were collected during the tests in order to evaluate blood lactate concentration, pH, bicarbonate, base excess, peripheral blood gas levels and oxygen saturation. Blood lactate concentration increased significantly ( P ≤ 0.017; significant level with Bonferroni correction) between rest (0.65 ± 0.21 mmol.L −1 ) and set 15 (4.58 ± 1.96 mmol.L −1 ). Blood lactate concentration remained stable during the constant-load resistance exercise ( P > 0.017). Bicarbonate, base excess and partial pressure of carbon dioxide had a significant decrease (26.4 ± 2.1 mmol.L −1 , 2.7 ± 2.4 and 36.0 ± 2.7 mmHg at rest, respectively, to 19.6 ± 4.3 mmol.L −1 , −5.0 ± 3.4, 30.2 ± 4.0 mmHg at set 15, respectively; P ≤ 0.017). Oxygen saturation and pH also remained constant during the exercise (97.2 ± 1.8% and 7.47 ± 0.03 at rest to 97.0 ± 1.4 and 7.41 ± 0.05 at set 15, respectively; P > 0.017). During a constant-load resistance exercise at LT intensity pH remained constant and this intensity seems to correspond to a metabolic steady state. Évaluer la réaction de l’acido-basique au cours de l’exercice de musculation à charge constante, au seuil de l’intensité de lactate (ET). Sept hommes en bonne santé ont été soumis à deux protocoles dans une machine « Leg Press ». Un test incremental afin de déterminer l’intensité des ET et un protocole de résistance à charge constante ont été exécutés à cette intensité. Les participants ont réalisé 15 séries de 20 répétitions en une minute avec des intervalles de une minute de repos au cours de l’exercice à charge constante. Des échantillons de sang capillaire ont été recueillis au cours des essais en vue d’évaluer la concentration sanguine de lactate, le pH, le bicarbonate, excès de base, périphériquesdes gaz du sang et de la saturation en oxygène. La concentration de lactate sanguin a augmenté de manière significative ( p ≤ 0,017 ; niveau significatif avec correction de Bonferroni) entre le repos (0,65 ± 0,21 mmol.L −1 ) et après 15 séries (4,58 ± 1,96 mmol.L −1 ). La concentration de lactate sanguin est resté stable au cours des exercices de résistanceà charge constante ( p > 0,017). Le bicarbonate et la pression, de l’excès et partielle basique du dioxyde de carbone avait une diminution (respectivement 26,4 ± 2,1 mmol.L −1 , 2,7 ± 2,4 et 36,0 ± 2,7 mmHg au repos, 19,6 ± 4,3 mmol.L −1 , −5,0 ± 3,4, 30,2 ± 4,0 mmHg après 15 séries, p ≤ 0,017). La saturation d’oxygène et le pH sont également restés constants au cours de l’exercice (respectivement 97,2 ± 1,8 % et 7,47 ± 0,03 au repos, 97,0 ± 1,4 et 7,41 ± 0,05 après 15 séries, p > 0,017). Au cours d’un exercice de résistance à charge constante d’intensité des ET le pH est resté constant et cette intensité semble correspondre à un état métabolique stable.

Acute Cardiorespiratory and Metabolic Responses During Resistance Exercise In The Lactate Threshold Intensity

The aims were both to determine lactate and ventilatory threshold during incremental resistance training and to analyze the acute cardiorespiratory and metabolic responses during constant-load resistance exercise at lactate threshold (LT) intensity. Ten healthy men performed 2 protocols on leg press machine. The incremental test was performed to determine the lactate and ventilatory thresholds through an algorithmic adjustment method. After 48 h, a constant-load exercise at LT intensity was executed. The intensity of LT and ventilatory threshold was 27.1±3.7 and 30.3±7.9% of 1RM, respectively (P=0.142). During the constant-load resistance exercise, no significant variation was observed between set 9 and set 15 for blood lactate concentration (3.3±0.9 and 4.1±1.4 mmol x L(-1), respectively. P=0.166) and BORG scale (11.5±2.9 and 13.0±3.5, respectively, P=0.783). No significant variation was observed between set 6 and set 15 for minute ventilation (19.4±4.9 and 22.4±5.5 L x min(-1), respectively, P=0.091) and between S3 and S15 for VO2 (0.77±0.18 and 0.83±0.16 L x min(-1), respectively, P=1.0). Constant-load resistance exercise at LT intensity corresponds to a steady state of ventilatory, cardio-metabolic parameters and ratings of perceived exertion.

Performance Evaluation of Small-Scaled Wind Power Generator with Outer Permanent Magnet Rotor considering Electromagnetic Losses (1) - Magnetic Field Analysis and Electrical Parameters Derivation using Electromagnetic Transfer Relations Theorem -

This paper deals with analytical techniques for performance evaluation of small scaled wind power generator with outer permanent magnet rotor. In part (1), using transfer relations theorem, magnetic field distribution characteristics by PM and armature reaction field are derived. Moreover, electrical parameters such as back-EMF, inductance and resistance are calculated from the obtained field characteristic equations. The proposed analytical techniques are validated by nonlinear finite element method using commercial software 'Maxwell' and performance experiments of the manufactured generator. In part (2), generating characteristics analysis such as constant speed characteristics and constant resistive load characteristics, and performance evaluation according to variation of wind speed will be accomplished using the derived electrical parameters.

Large-signal stability analysis of solar array power system

A large-signal stability analysis of the solar array regulator system is performed to facilitate the design and analysis of a low-earth-orbit (LEO) satellite power system. The effective load characteristics of various control methods in the solar array regulator system, such as the constant power load, variable power load, constant voltage load, constant current load, and constant resistive load, are classified to analyze the large-signal stability. Then, using the state plane analysis technique, the large-signal behavior of the solar array system is portrayed and the stability of various equilibrium points is analyzed. Thus, this approach can be contributed to organize the optimal controller structure of the system by representing the relationship between the control method of the solar array regulator and the large-signal stability. For the verification of the proposed large-signal analysis, a solar array regulator system that consists of two 100 W parallel module buck converters has been built and tested using a real 200 W solar array.

Battery testing by calculated discharge-curve method—Constant resistive load algorithm

Battery testing by calculated discharge-curve method (CDCM) includes battery, battery average cell and each of battery's cell 3D discharge curves. These discharge curves were generated by calculated discharge-curve algorithm (CDCA), using either high- or low-frequency monitored discharge data and are lying in battery/cell rectangular parallelepiped: open-circuit voltage–initial discharge current–time. CDCA defines the ordered six-tuple: time–current–voltage–capacity–energy on load–internal energy losses by which battery and battery's cells dynamic characteristics may be analyzed. Any of the six-tuple variables may be divided into the set of i = 1, …, n steps by constant step across the overall discharge interval and used as the domain of CDC algorithm procedure. CDCM, respectively, introduced average current and average voltage as the ratio of capacity to time and energy to capacity. Battery/cell rectangular parallelepiped: time–average current–average voltage is defined at any step of discharging. In this paper, the linear dependencies of average characteristics on the both power of battery/cell internal resistance and load intensity were presented and algebrically proofed. Battery's cells may be compared to battery average cell and may be classified by any characteristics. Discharge curves of alkaline-manganese MALLORY batteries, 9K62 (50 and 100 Ω), PX24 (100 and 166 Ω), PX21 (150 and 250 Ω) and 7K62 (100, 200 and 500 Ω) [T.R. Crompton, Small Batteries 2 (1982) 52] were used to demonstrate battery and battery average cell standard and CDC method characteristics. The mathematical calculations were conducting on IBM PC using Microsoft Excel software.

Femoral artery inflow in relation to external and total work rate at different knee extensor contraction rates.

Whether limb blood flow is directly regulated to match the work rate, independent of the rate of contraction, remains elusive. This study therefore investigated the relationship between femoral arterial blood flow (FABF; Doppler ultrasound) and "external" (applied load) as well as "total" [external + "internal" (potential and kinetic energy changes of the moving lower leg)] work rate, during steady-state one-legged, dynamic, knee extensor exercise (1L-KEE) in the sitting position at different contraction rates. Ten subjects performed 1L-KEE at 30, 60, and 90 contractions/min (cpm) 1) at constant resistive loads of 0.2 and 0.5 kg inducing incremental external work rates (study I) and 2) at different relative resistive loads inducing constant external work rates of 9 and 18 W (study II). Moreover, 3) six subjects performed 1L-KEE at 60 and 100 cpm at incremental total work rates of 40, 50, 60, and 70 W (study III). In study I, FABF increased (P < 0.001) with increasing contraction frequency and external work rate, for each resistive load. In study II, FABF increased (P < 0.001) with increasing contraction frequency for each constant external work rate. Of major importance in study III, however, was that FABF, although increasing linearly with the total work rate, was not different (P = not significant) between contraction rates, at the total work rates of 40, 50, 60, and 70 W, respectively. Furthermore, FABF correlated linearly and positively with both the external and total work rate for each contraction frequency. In conclusion, the findings support the concept that leg blood flow during 1L-KEE in a normal knee extensor ergometer is matched directly in relation to the total work rate and metabolic activity, irrespective of the contraction frequency. The rate of contraction seems erroneously to influence the results only when it is related to the external work rate without taking into account the internal work component.

Further results related to power supply design and analysis in the undergraduate curriculum

The power supply analysis and design results of Sherman and Hamacher are extended to include approximate solutions to the nonlinear equations that define the rectifier turn-on angles. Additionally, peak rectifier current solely as a function of ripple factor as well as the inverse relationship, i.e., ripple factor as a function of peak rectifier current, are also provided. Simplified exact equations and also new approximations are given for RMS transformer current. These new approximations allow the ripple factor to be determined as a function of RMS transformer current. These results are for both constant current and resistive load supplies.

Resistance Exercise Countermeasures for Space Flight

While resistance exercise should be a logical choice for prevention of strength loss during unloading, the principle of training specificity cannot be overlooked. Our purpose was to explore training specificity in describing the effect of our constant load exercise countermeasure on isokinetic strength performance. Twelve healthy men (mean ± SD: 28.0 ± 5.2 years, 179.4 ± 3.9 cm, 77.5 ± 13.6 kg) were randomly assigned to no exercise or resistance exercise (REX) during 14 days of bed rest. REX performed five sets of leg press exercise to volitional fatigue (6–10 repetitions) every other day. Unilateral isokinetic concentric-eccentric knee extension testing performed before and on day 15 prior to reambulation included torque-velocity and power-velocity relationships at four velocities (0.52, 1.75, 2.97, and 4.19 rad·s−1), torque-position relationship, and contractile work capacity (10 repetitions at 1.05 rad·s−1). Two (group) · 2 (time) ANOVA revealed no group · time interactions; thus, groups were combined. Across velocities, angle-specific torque fell 18% and average power fell 20% (p < 0.05). No velocity · time or mode (concentric/eccentric) · time interactions were noted. Torque · position decreased on average 24% (p < 0.05). Total contractile work dropped 27% (p < 0.05). Results indicate bed rest induces rapid and marked reductions in strength and our constant load resistance training protocol did not prevent isokinetic strength losses. Differences between closed-chain training and open-chain testing may explain the lack of protection.

Resistance Exercise Countermeasures for Space Flight: Implications of Training Specificity

While resistance exercise should be a logical choice for prevention of strength loss during unloading, the principle of training specificity cannot be overlooked. Our purpose was to explore training specificity in describing the effect of our constant load exercise countermeasure on isokinetic strength performance. Twelve healthy men (mean +/- SD: 28.0 +/- 5.2 years, 179.4 +/- 3.9 cm, 77.5 +/- 13.6 kg) were randomly assigned to no exercise or resistance exercise (REX) during 14 days of bed rest. REX performed five sets of leg press exercise to volitional fatigue (6-10 repetitions) every other day. Unilateral isokinetic concentric-eccentric knee extension testing performed before and on day 15 prior to reambulation included torque-velocity and power-velocity relationships at four velocities (0.52, 1.75, 2.97, and 4.19 rad s-1), torque-position relationship, and contractile work capacity (10 repetitions at 1.05 rad s-1). Two (group) x 2 (time) ANOVA revealed no group x time interactions; thus, groups were combined. Across velocities, angle-specific torque fell 18% and average power fell 20% (p < 0.05). No velocity x time or mode (concentric/eccentric) x time interactions were noted. Torque x position decreased on average 24% (p < 0.05). Total contractile work dropped 27% (p < 0.05). Results indicate bed rest induces rapid and marked reductions in strength and our constant load resistance training protocol did not prevent isokinetic strength losses. Differences between closed-chain training and open-chain testing may explain the lack of protection.

Adaptive passivity‐based control of average dc‐to‐dc power converter models

SUMMARY An adaptive feedback regulation scheme is proposed for the stabilization of average models of dc-to-dc power converters exhibiting unknown but constant resistive loads. The scheme is based on a dynamical feedback policy which suitably modifies the total energy of the closed-loop system while inducing appropriate damping injections on the desired stabilization error dynamics. The performance of the proposed adaptative regulators is tested through computer simulations including stochastic perturbation inputs. ( 1998 John Wiley & Sons, Ltd.

Computerized DC (battery) load flow calculations

The key to properly sizing cables, overcurrent devices, and batteries is correctly calculating load current. The load current for constant-power devices increases as voltage decreases. The opposite is true for constant-resistive devices. If the effects of voltage are neglected, the designer can over-design circuits for constant-resistance loads and under-design circuits for constant-power loads. The authors describe how computerized techniques have existed for some time for AC system analysis and how these techniques can easily be adapted for DC analysis. This will allow designers to quickly perform the what-if games required to strike a balance between conservative design and costs.

Solid-state photovoltaic power and battery unit

The feasibility of an integrated battery/solar module system is demonstrated using a rechargeable lithium battery and a commercially available polycrystalline silicon solar module. The solar module was parallel connected to a prismatic 500 mAh battery and a constant resistance load. This arrangement was subsequently tested under conditions which simulated daylight and night conditions. The combined system was cycled 20 times without severe degradation of the battery or solar module performance.