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This paper studies the effect of stator winding configuration on the performance of five-phase induction machines under healthy as well as faulty conditions. The study compares two connections, namely, star and pentagon connection...
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This paper studies the effect of stator winding configuration on the performance of five-phase induction machines under healthy as well as faulty conditions. The study compares two connections, namely, star and pentagon connections. The comparison is conducted using both simulation and experimental results. The steady-state model based on symmetrical components theory is introduced for both connections with one-line open due to a converter fault, and the corresponding machine characteristic curves are estimated. During faults, two alternatives for machine operation are possible, namely, open-loop control and optimal current control. While the first alternative corresponds to higher torque ripple and unbalanced winding currents, the second option necessitates unbalanced phase voltages and typically an increased dc-link voltage to source the required optimal currents. Consequently, an increase in the employed semiconductor device rating is required, which is a critical design factor particularly in medium-voltage applications. A new V/f control technique is proposed to ensure disturbance-free operation with one-line open for both winding connections. Based on the unbalanced machine model and experimental verification, the derating factors that ensure safe machine operation for both winding connection alternatives are calculated. The comparison between the two connections shows the superiority of the pentagon connection under fault conditions in terms of efficiency, average torque, torque ripples, and derating factor.
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Five-phase induction machines are generally modeled using multiple dq planes or using a phase variable model. This paper considers modeling five-phase induction machines using a voltage-behind-reactance (VBR) configuration. This c...
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Five-phase induction machines are generally modeled using multiple dq planes or using a phase variable model. This paper considers modeling five-phase induction machines using a voltage-behind-reactance (VBR) configuration. This configuration lends itself suitable for time-domain circuit-based simulators as the MATLAB/Simulink SimPowerSystems (SPS) toolbox. The stator electrical dynamics are represented in five-phase coordinates, while the rotor electrical circuit is modeled using rotor flux linkage as the state variable and expressed in the dq stator reference frame. The VBR model is equivalent to a conventional dq model; however, it facilitates the connection of an external inductance without affecting numerical accuracy and calculation efficiency. It also facilitates the simulation of different winding connections, series-connected multimotors, and open phase(s) conditions. The model is, first, derived for a magnetically linear system and then it is extended to include the effect of magnetic saturation. The flux correction method is used to represent the effect of magnetic saturation with a simple modification to represent the effect of cross coupling between fundamental and third sequence planes due to saturation effect. The dynamic cross saturation is considered by adding compensating terms that depend on magnetizing inductance variation. The proposed model is experimentally verified using a prototype 1.5-hp five-phase induction machine under different operating conditions.
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DNA sequencing is the basic workhorse of modern day biology and medicine. Shotgun sequencing is the dominant technique used: many randomly located short fragments called reads are extracted from the DNA sequence, and these reads a...
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DNA sequencing is the basic workhorse of modern day biology and medicine. Shotgun sequencing is the dominant technique used: many randomly located short fragments called reads are extracted from the DNA sequence, and these reads are assembled to reconstruct the original sequence. A basic question is: given a sequencing technology and the statistics of the DNA sequence, what is the minimum number of reads required for reliable reconstruction? This number provides a fundamental limit to the performance of any assembly algorithm. For a simple statistical model of the DNA sequence and the read process, we show that the answer admits a critical phenomenon in the asymptotic limit of long DNA sequences: if the read length is below a threshold, reconstruction is impossible no matter how many reads are observed, and if the read length is above the threshold, having enough reads to cover the DNA sequence is sufficient to reconstruct. The threshold is computed in terms of the Renyi entropy rate of the DNA sequence. We also study the impact of noise in the read process on the performance.
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In a pinched-beam ion diode, an intense electron beam focuses on-axis at the center of the anode and passes through the thin anode foil into a beam dump region behind the anode foil. The beam dump usually consists of an evacuated ...
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In a pinched-beam ion diode, an intense electron beam focuses on-axis at the center of the anode and passes through the thin anode foil into a beam dump region behind the anode foil. The beam dump usually consists of an evacuated cylindrical anode-can. Because of energy deposition from the intense electron beam, the interior surfaces of the anode-can are expected to be space-charge-limited emitters. Therefore, the electron space charge from the beam in the anode-can will draw ions off these surfaces. There is evidence from nuclear activation which suggests that ions exist in the anode-can with energies that significantly exceed those associated with the diode voltage. Analysis and particle-in-cell simulations show that a virtual cathode can form in the anode-can that accelerates ions up to the energy associated with the diode voltage. Additionally, a subset of these ions can form current bursts that are driven to the outer wall of the anode-can with ion energies as high as a few times the energy associated with the diode voltage.
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This paper presents an in-depth stability analysis of injection-locked multimode oscillators. The various types of bifurcations, or qualitative stability changes, occurring in these systems when varying the input power are studied...
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This paper presents an in-depth stability analysis of injection-locked multimode oscillators. The various types of bifurcations, or qualitative stability changes, occurring in these systems when varying the input power are studied in detail. It is shown that, for low injection power, each stable injection-locked oscillation coexists with as many two-fundamental quasi-periodic solutions as the number of stable periodic oscillations in the original free-running circuit. The mechanisms leading to the successive extinctions of these undesired stable quasi-periodic solutions are investigated in-depth, as well as the possible stabilization of periodic oscillation modes that were originally unstable in free-running conditions. The overall study enables a thorough understanding and anticipation of the complex nonlinear dynamics of these multimode systems. It is demonstrated that, by changing the injection frequency, together with control of the bias voltage, it is possible to switch between the various injection-locked oscillations, obtaining a reconfigurable system. The study is illustrated through application to a demonstrator, consisting of a ring oscillator in which six stable oscillation modes were measured at different operation points and frequencies comprised between 9.4 and 15.4 GHz.
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In this paper we consider state estimation of a discrete time linear system using multiple sensors, where the sensors quantize their individual innovations, which are then combined at the fusion center to form a global state estim...
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In this paper we consider state estimation of a discrete time linear system using multiple sensors, where the sensors quantize their individual innovations, which are then combined at the fusion center to form a global state estimate. We prove the stability of the estimation scheme under sufficiently high bit rates. We obtain asymptotic approximations for the error covariance matrix that relates the system parameters and quantization levels used by the different sensors. Numerical results show close agreement with the true error covariance for quantization at high rates. An optimal rate allocation problem amongst the different sensors is also considered.
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We propose a novel method of positioning using a high-frequency radio-frequency identification (HF RFID) system for navigating autonomous vehicles when a sparse grid of floor tags is employed. For this, we propose a novel triangul...
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We propose a novel method of positioning using a high-frequency radio-frequency identification (HF RFID) system for navigating autonomous vehicles when a sparse grid of floor tags is employed. For this, we propose a novel triangular multiloop-bridge reader antenna which generates an error signal in the form of bridge potential that is a function of the tags' location. The proposed positioning algorithm combines the information from the reader database with the error signals generated by the bridge loop and couples them with any available data from the wheel encoders of an autonomously moving object to deduce its position and orientation. The accuracy and efficacy of the proposed algorithm are evaluated using both simulations and experiments using an autonomous wheelchair. The results indicate that the proposed method offers a significant improvement over existing HF-RFID-based positioning methods for larger floor-tag-grid separation.
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We demonstrate the ability of linear mode single carrier multiplication (SCM) avalanche photodiode (APD)-based optical receivers to discriminate single-photon-initiated avalanche events from dark-current-initiated events. Because ...
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We demonstrate the ability of linear mode single carrier multiplication (SCM) avalanche photodiode (APD)-based optical receivers to discriminate single-photon-initiated avalanche events from dark-current-initiated events. Because of their random spatial origin in discrete regions of the depletion region, in the SCM APD the dark-generated carriers multiply differently than the photon-generated carriers. This causes different count distributions and necessitates different statistical descriptions of the signal contributions from photon- and dark-originating impulse responses. To include dark carriers in the performance models of the SCM APD, we considered the influence of the spatial origin of the ionization chains on a receiver's noise performance over the times the optical pulse is integrated by the receiver's decision circuits. We compare instantaneous (time-resolved) numeric and pseudo-DC analytical models to measured SCM APD data. It is shown that it is necessary to consider both the distribution of spatial origin and the instantaneous properties of the ionization chains to describe statistically an SCM APD receiver. The ability of SCM APD receivers to discriminate single photon events from single dark events is demonstrated, and the effective gain and excess noise contributions of the light- and dark-initiated avalanche events and their influence on receiver sensitivity and signal-to-noise characteristics are shown.
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Conventional industrial microgrids (IMGs) consist of factories with distributed energy resources (DERs) and electric loads that rely on combined heat and power (CHP) systems while the developing IMGs are expected to also include r...
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Conventional industrial microgrids (IMGs) consist of factories with distributed energy resources (DERs) and electric loads that rely on combined heat and power (CHP) systems while the developing IMGs are expected to also include renewable DERs and plug-in electric vehicles (PEVs) with different vehicle ratings and charging characteristics. This paper presents an electricity and heat generation scheduling method coordinated with PEV charging in an IMG considering photovoltaic (PV) generation systems coupled with PV storages. The proposed method is based on dynamic optimal power flow (DOPF) over a 24-hour period and includes security-constrained optimal power flow (SCOPF), IMG's factories constraints, PV storage constraints and PEVs dynamic charging constraints. It will utilize the generators waste heat to fulfill thermal requirements while considering the status of renewable DERs to decrease the overall cost of IMGs. To demonstrate the effectiveness of the proposed method, detailed simulation results are presented and analyzed for an 18-bus IMG consisting of 12 factories and 6 types of PEVs without/with PV generation systems operating in grid-connected and stand-alone modes. The main contribution is including PEVs with dynamic constraints that have changed the nature of scheduling formulation from a simple hourly OPF to a dynamic OPF.
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Direct-drive permanent magnet (PM) generators have become a strong contender in medium and large rating wind energy conversion systems as they not only provide higher efficiency and annual energy production, but also reduce the op...
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Direct-drive permanent magnet (PM) generators have become a strong contender in medium and large rating wind energy conversion systems as they not only provide higher efficiency and annual energy production, but also reduce the operational and maintenance cost. PM generators with nonoverlap single-layer windings provide a cost-effective design variation that eases manufacturing, reduces torque ripples, enhances voltage quality, and provides fault tolerant capability. The performance of such machines depends mainly on the proper selection of the pole and slot numbers, which results in negligible coupling between phases. The preferred slots per phase per pole (SPP) ratios eliminate the effect of low order harmonics in the stator magnetomotive force (MMF), and thereby the vibration and stray loss are reduced. This paper proposes a new three-phase winding configuration based on the 20 slots/18 poles five-phase PM machine. The proposed design is compared with the well-known 24 slots/20 poles three-phase PM machine. The comparison shows that the proposed generator offers reduced torque ripples, improved output voltage quality, and less core loss for the same machine volume.
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