Two-phase Load Research Articles

Two-phase load balancing of In-Memory Key-Value Storages using Network Functions Virtualization (NFV)

Social networks and other clouding applications should require fast responses from datacenter's infrastructure. One of the techniques that have been widely used for achieving such requirement is the employment of In-Memory Key-Value Storage (IMKVS) as caching mechanisms in order to improve overall user experience. Memcached and Redis are applications that use IMKVS approach. Commonly IMKVS systems use Consistent Hashing to decide where to store an object, which may cause network load imbalance due to its simplistic approach. Furthermore, these systems work only at the application layer, so network conditions are not considered to distribute user's accesses. This paper proposes a new cache architecture based on a two-phase load balancing to improve IMKVS performance, which has adopted a Network Function Virtualization (NFV) architecture to manage the load balancing mechanism. The proposal was evaluated in the Mininet and shows an improvement of 23% on the load of the caching servers and 5% on the load of the network compared to Consistent Hashing, which results in better resource usage and better user experience.

An Experimental Model Study of Steam Generator Tube Loading During a Sudden Depressurization

This paper presents the results of an experimental model study of the transient loading of steam generator tubes during a postulated main steam line break (MSLB) accident in a nuclear power plant. The problem involves complex transient two-phase flow dynamics and fluid-structural loading processes. A better understanding of this phenomenon will permit the development of improved design tools to ensure steam generator tube integrity. The pressure and temperature were measured upstream and downstream of a sectional model of a tube bundle in cross-flow, and the transient tube loads were directly measured using dynamic piezoelectric load cells. High-speed videos were taken to observe and better understand the flow phenomena causing the tube loading. The working fluid was R-134a and the tube bundle was a normal triangular array with a pitch ratio of 1.36. The flow through the bundle was choked for the majority of the transient. The transient tube loading is explained in terms of the associated fluid mechanics. An empirical model is developed that enables the prediction of the maximum tube loads once the pressure drop is known.

Discontinuous SVPWM Techniques of Three-Leg VSI-Fed Balanced Two-Phase Loads for Reduced Switching Losses and Current Ripple

In this paper, various types of discontinuous space vector pulse-width modulation techniques for a three-leg voltage source inverter supplying balanced two-phase loads are proposed. The main objectives of the paper are to analyze switching loss characteristics associated with semiconductor devices and to reduce output current ripple by dealing with various types of zero space vector time in each switching sequence. Capabilities of reductions in switching losses and current ripple for both balanced and unbalanced output phase voltages at high modulation index and load power factor angle of 30° lagging are focused. The validity of the proposed techniques is verified by simulation and experimental results in terms of voltage spectrum, current waveforms, reductions in switching losses, and output current ripple at high modulation index when compared to a continuous space vector pulse-width modulation technique.

Loading estimate methods to support integrated watershed-lake modelling: Duffins Creek, Lake Ontario

Integrated watershed-lake modelling requires high quality data for calibration and validation. The two-phase loading estimate approach presented here provides a more confident estimate of nutrient loads for these models. Phase 1 establishes the initial range of the loading estimates using averaging algorithms, ratio estimators, event mean concentration (EMC) and regression-based methods. For Duffins Creek outlet, the 2007, 2008 and 2009 ranges are 6.2–30, 22.3–78 and 19.5–242 tonnes of total phosphorus (TP), respectively. After combining the Beale ratio estimator and the regression-based methods in Phase 2, the 2007, 2008 and 2009 ranges are reduced to 13–17, 57–73 and 69–92 tonnes TP, respectively. The reduction represents the 0 and 28.07% upper bound bias of the regression-based method. Applying this information to the regression-based methods, daily and monthly ranges with a lower bound with no adjustment and with upper bound as 1.2807 times the regression-based TP load estimates are established. These loads are then used in integrated watershed-lake model calibration and validation to improve the model predictions.

A Carrier-Based Unbalanced PWM Method for Four-Leg Voltage Source Inverter Fed Unsymmetrical Two-Phase Induction Motor

This paper presents a carrier-based unbalanced pulsewidth-modulated method for a two-phase four-leg voltage source inverter (VSI) and its realization for an unsymmetrical two-phase induction motor. A modulation strategy is developed to synthesize unbalanced two-phase output voltage waveforms based on the unipolar modulation technique with open-loop <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> / <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</i> control. The proposed control scheme allows independent magnitude controllability and quadrature phase angle for unbalanced two-phase output voltages. Thus, the modulation algorithm makes the four-leg VSI inequitable with unbalanced two-phase loads. Simulation and experimental results confirm the feasibility of the control method for the inverter.

Space vector PWM for a two-phase VSI

This paper proposes space vector pulse width modulation (SVPWM) technique to control a two-phase full bridge voltage source inverter (VSI) having reduced number of static switches with higher phase voltage output. SVPWM gives higher fundamental component amplitude, provides more efficient use of DC supply voltage and generates less harmonic distortion in the output voltages and currents than other pulse width modulation (PWM) techniques. Between asymmetric and symmetric SVPWM only symmetric one is considered so that the harmonic contents are minimized and two different timing sequences and corresponding switching states are proposed. For the implementation three level switching patterns are determined by using software. For real time application these theoretically determined switching signals for the six power transistors are generated by a digital signal processor (DSP) kit and finally the two-phase output voltages are applied to load. The experimental results are found good and in agreement with the theoretical results. Mathematical analysis along with theoretical and experimental performance of the proposed inverter are presented. Total harmonic distortion (THD) and distortion factor (DF) show that the output voltage quality is good enough to apply in any type of practical two-phase load.

Structures and modulation algorithms of direct ac/ac converters with two legs and three legs for two‐phase systems

AbstractTwo‐phase ac/ac matrix converter configurations are presented based on direct power conversion processes from three‐phase input ac supplies to two‐phase output ac loads. Two types of two‐phase matrix converter topologies, utilizing the standard matrix converter configuration, are introduced with two‐leg and three‐leg based structures. Pulse width modulation (PWM) strategies with high‐frequency composition for the two‐leg and the three‐leg based two‐phase matrix converters are developed to synthesize sinusoidal output waveforms of two‐phase loads from time‐varying input ac voltages. Grounded on the developed modulation algorithms, the presented matrix converters directly generate controllable two‐phase output voltages from sinusoidal input voltages with no intermediate dc conversion and concomittant dc‐link elements. The proposed matrix converters can provide sinusoidal output current/voltage waveforms with independently controlled magnitude and 90° phase angle to two‐phase loads. Thus, the converters are effective for both balanced and unbalanced two‐phase loads. The presented two‐phase operations with the standard matrix converter structures add the versatility for the matrix converter systems to function in multi‐phase loads as a universal converter. Simulation and experimental results are presented to verify the developed modulation techniques and the converter configurations for the two‐phase matrix converters. Copyright © 2009 John Wiley &amp; Sons, Ltd.

Direct AC to AC Matrix Converter and Control Method for Two-phase Loads

This article presents a two-phase matrix converter, a modulation strategy, and its realization for two-phase loads. The converter directly links three-phase input AC lines to two-phase output AC loads through switching devices. A modulation technique is developed to synthesize two sinusoidal output waveforms with variable voltage and variable frequency from input AC voltages. The proposed control scheme allows independent magnitude controllability and quadrature phase angle for two output phases. Thus, the modulation algorithm makes the two-phase matrix converter commensurate with both balanced and unbalanced two-phase loads. Simulation and experimental results confirm the feasibility of the control method for the converter.

Development of Modulation Strategy for Two-Phase AC–AC Matrix Converters

A two-phase ac-ac matrix converter configuration is presented based on direct power conversion without any intermediate dc stage. The modulation strategy is developed to provide sinusoidal output waveforms with two-phase loads. The proposed strategy can generate the two-phase output voltages/currents where the magnitudes are independently controlled, and the phase difference is fixed at 90/spl deg/.

Lateral load pattern in pushover analysis

The seismic capacity curves of three types of buildings including frame, frame-shear wall and shear wall obtained by pushover analysis under different lateral load patterns are compared with those from nonlinear time history analysis. Based on the numerical results obtained a two-phase load pattern; an inverted triangle (first mode) load pattern until the base shear force reachesβ times its maximum value, Vmax, followed by a (x/H)α form, hereβ and α being some coefficients depending on the type of the structures considered, is proposed in the paper, which can provide excellent approximation of the seismic capacity curve for low-to-mid-rise shear type buildings. Furthermore, it is shown both the two-phase load pattern proposed and the invariant uniform pattern can be used for low-to-mid-rise shear-bending type and low-rise bending type of buildings. No suitable load patterns have been found for high-rise buildings.

Transient performance of three-phase self-excited induction generator during balanced and unbalanced faults

A generalised dynamic model of a delta-connected three-phase self-excited induction generator (SEIG) has been developed using d–q variables in a stationary reference frame. This model can handle symmetrical and unsymmetrical load and capacitor configurations, however, the SEIG performance during balanced and unbalanced faults has been studied, which include cases of extreme unbalance operation. SEIG behaviour has been investigated considering the effects of main and cross flux saturation for load perturbation, three-phase and line-to-line short circuit, opening of one capacitor, two capacitors and a single line at the capacitor bank, opening of single-phase load, two-phase load, and a single line at load. Simulated results are compared with experimental results and a close match between them validates the developed model.

Neural-network controller for parallel-resonant ultrasonic motor drive

A newly designed driving circuit for the traveling-wave type ultrasonic motor (USM), which is composed of a push-pull DC-DC power converter using PWM direct duty-cycle control and a current-source two-phase parallel-resonant capacitor-parallel load inverter, is described in this study. Moreover, since the dynamic characteristics of the USM are difficult to obtain and the motor parameters are time varying, an online trained neural-network (NN) controller is proposed to control the rotor speed and position of the USM. Accurate tracking response can be obtained due to the powerful online learning capability of the NN controller. Furthermore, the influence of parameter variations and external disturbances on the USM drive also can be reduced effectively. The effectiveness of the NN controlled USM drive system is demonstrated by experimental results.

Development of a three-phase bus impedance matrix in the complex frequency domain for transient analysis in unbalanced distribution systems

Abstract Untransposed feeders, a combination of single-phase, two-phase and unequal three-phase loads impose imbalance in distribution systems. This paper presents a generalized computer technique to develop the three-phase bus impedance matrix Z bus3 (s) in the complex frequency domain. The method utilizes the phase-frame representation of the network elements. Consequently, the transient response due to line removals or additions, asymmetrical shunt faults, series faults, and capacitor switching can be simulated by modifying Z bus3 (s) . Thus, the proposed method makes it possible to analyze a power system network considering imbalance and the frequency dependence of the feeder parameters, and to obtain the transient response due to fault or capacitor switching conditions in the presence of harmonic distortion.

Two-phase, five-wire distribution: Its engineering and economic elements

In view of the present trend toward three-phase secondary distribution involving, in some cases, a change from a two-phase system, an analysis of the engineering and economic elements of a two-phase system may be of value. The two-phase five-wire secondary system is examined in the light of fundamental requirements, such as service continuity, safety, standard voltages, flexibility, low cost, etc., and compared particularly with the three-phase, four-wire star system. Many of the advantages of the two-phase, five-wire system result from the diametrical connection of the two phases, from the inherent balance thereby obtained, and from the greater power carried per wire. An important advantage of the two-phase, five-wire system lies in the fact that single-phase, two-wire and three-wire loads and two-phase loads can be supplied at standard voltages from combination lighting and power secondaries and that new loads can be flexibly supplied through all stages of load growth. There are marked advantages from a construction and operating point of view in having ordinarily only two transformers in banks which supply two-phase secondaries from either two-phase or three-phase primaries. The two-phase, five-wire system has certain advantages as to metering and a comparison of the first cost and the annual cost of two-phase and three-phase motor installations, with wiring, shows small differences. The inherent cost differential between two- and three-phase secondaries with several types of primary systems is shown to be of such a small magnitude that the cost of change over from one type of system to another may over shadow the theoretical savings. Accordingly, with a relatively small inherent cost differential between the existent system and one having certain, more or less, proved advantages and disadvantages, the central station engineer must produce extremely strong arguments leading out of his local situation in order to justify a change from the existing system.

Two-Phase, Five-Wire Distribution Its Engineering and Economic Elements

In view of the present trend toward three-phase secondary distribution involving, in some cases, a change from a two-phase system, an analysis of the engineering and economic elements of a two-phase system may be of value. The two-phase five-wire secondary system is examined in the light of fundamental requirements, such as service continuity, safety, standard voltages, flexibility, low cost, etc., and compared particularly with the three-phase, four-wire star system. Many of the advantages of the two-phase, five-wire system result from the diametrical connection of the two phases, from the inherent balance thereby obtained, and from the greater power carried per wire. An important advantage of the two-phase, five-wire system lies in the fact that single-phase, two-wire and three-wire loads and two-phase loads can be supplied at standard voltages from combination lighting and power secondaries and that new loads can be flexibly supplied through all stages of load growth. There are marked advantages from a construction and operating point of view in having ordinarily only two transformers in banks which supply two-phase secondaries from either two-phase or three-phase primaries. The two-phase, five-wire system has certain advantages as to metering and a comparison of the first cost and the annual cost of two-phase and three-phase motor installations, with wiring, shows small differences.