Our group has recently developed and studied "finger"-type divertors that are a simplified version of the helium-cooled modular divertor with multiple jets (HEMJ) using coupled computational fluid ...dynamics and thermal stress simulations. Such a simplified geometry could reduce complexity and cost given the large number of fingers required to cover the total divertor target area. Previous experimental studies for this simplified flat design reported lower heat transfer coefficients and higher pressure drops than the HEMJ, contrary to numerical predictions. Subsequent measurements determined that the original test section had significant dimensional variations in the jet exit holes. A new test section was therefore manufactured and tested in the Georgia Tech (GT) helium loop. The experimental results presented here for this test section at maximum heat flux of 7.1 MW/m
2
are in good agreement with numerical predictions. Correlations developed from these experimental data are extrapolated to predict the maximum heat flux that can be accommodated by the flat design and the coolant pumping power requirements under prototypical conditions. Finally, numerical simulations are used to estimate the sensitivity of the flat design to geometric variations typical of manufacturing tolerances and variations in the gap width.
Some of the most demanding tests of interface methods for two-phase flows with surface tension which use fixed Eulerian grids occur at the two extremes of highly dynamic flows or static equilibrium ...conditions. It has been difficult to design an interface method to operate accurately across this spectrum especially for 3D fluid flow calculations which, on the one hand, do not often have the required grid resolution to capture all of the fine scale structures that typically appear in highly stretched interfaces nor, on the other hand, the required accuracy in calculating surface tension forces. We present improvements to the interface reconstruction procedure in the level contour reconstruction method (LCRM) J. Comput. Phys. 180 (2002) 427, which now allow the reconstruction to proceed using a locally instead of a globally calculated contour value. These improvements allow more precise control of the interface reconstruction in highly dynamic flows with coalescence and rupture and also avoid the problem of local mass redistribution in poorly resolved calculations. In addition, a new hybrid technique for surface tension calculation in the context of the front tracking method is demonstrated and shown to result in a marked improvement in suppressing parasitic currents by generally two orders of magnitude. We compare and validate these new procedures in various test cases.
This paper presents an indirect vector control scheme with an improved flux pattern using third harmonic injection. The control objective is to independently control both flux and torque and to ...generate a nearly rectangular air-gap flux, resulting in improved machine power density. If there is a proportional relation between the third harmonic and fundamental plane currents, variable misalignment between fundamental and third air-gap flux components occurs with varying mechanical loading. Due to this misalignment, saturation may take place. Accordingly, the total flux is saturated and iron loss increases. Hence, coupling results between different sequence planes. Instead of a proportional relation between the current components, direct and quadrature current components of the injected third harmonic current reference are a function of the fundamental direct and quadrature reference current components, respectively. These functions ensure that the air-gap flux is near rectangular with a maximum value of 1 p.u. from no load to full load. Moreover, this controller guarantees complete decoupling between the sequence planes. An eleven-phase induction machine is used to validate the proposed controller experimentally, while supporting simulation results and theoretical analysis use both MATLAB and finite element platforms.
The falling particle receiver is a technology that can increase the operating temperature of concentrating solar power (CSP) systems, improving efficiency and lowering the costs of energy storage. ...Unlike conventional receivers that employ fluid flowing through tubular receivers, falling particle receivers use solid particles that are heated directly as they fall through a beam of concentrated sunlight for direct heat absorption and storage. Because the solar energy is directly absorbed by the particles, the flux limitations associated with tubular central receivers are mitigated. Once heated, the particles may be stored in an insulated tank and/or used to heat a secondary working fluid (e.g., steam, CO2, air) for the power cycle. Thermal energy storage costs can be significantly reduced by directly storing heat at higher temperatures in a relatively inexpensive, stable medium. This paper presents an overview of recent advancements being pursued in key areas of falling particle receiver technology, including
(1) advances in receiver design with consideration of particle recirculation, air recirculation, and interconnected porous structures; (2) advances in particle materials to increase the solar absorptance and durability; and (3) advances in the balance of plant for falling particle receiver systems including thermal storage, heat exchange, and particle conveyance.
A Four-Switch Three-Phase SEPIC-Based Inverter Diab, Mohamed S.; Elserougi, Ahmed; Massoud, Ahmed M. ...
IEEE transactions on power electronics,
09/2015, Letnik:
30, Številka:
9
Journal Article
Recenzirano
The four-switch three-phase (FSTP) inverter has been proposed as an innovative inverter design to reduce the cost, complexity, size, and switching losses of the dc-ac conversion system. Traditional ...FSTP inverter usually operates at half the dc input voltage; hence, the output line voltage cannot exceed this value. This paper proposes a novel design for the FSTP inverter based on the topology of the single-ended primary-inductance converter (SEPIC). The proposed topology provides pure sinusoidal output voltages with no need for output filter. Compared to traditional FSTP inverter, the proposed FSTP SEPIC inverter improves the voltage utilization factor of the input dc supply, where the proposed topology provides higher output line voltage which can be extended up to the full value of the dc input voltage. The integral sliding-mode control is used with the proposed topology to optimize its dynamics and to ensure robustness of the system during different operating conditions. Derivation of the equations describing the parameters design, components ratings, and the operation of the proposed SEPIC inverter is presented in this paper. Simulation model and experimental setup are used to validate the proposed concept. Simulations and experimental results show the effectiveness of the proposed inverter.
Permanent magnet (PM) machines equipped with fractional slot concentrated windings (FSCW) offer a compelling solution for electric vehicles (EVs), boasting high torque and power density, high ...efficiency, a wide operational range, and several other advantageous features. However, faults can impair the magnets' performance, leading to significant issues that negatively affect the EVs' performance and worsen motor reliability. Although fault tolerance can be maintained through innovative control schemes to meet specific performance criteria, these solutions often introduce side issues, such as torque ripple. While extensive studies have focused on mitigating these side issues through control techniques, incorporating solutions at the design stage remains underexplored. This paper presents the design and optimization of a 12-slot / 10-pole permanent magnet synchronous motor (PMSM) aimed at achieving high-quality operation in both healthy conditions and post fault operation under an open-phase fault. A finite element-based multi-objective optimization using a genetic algorithm is proposed to optimize the machine by maximizing average torque and minimizing torque ripple during both healthy operation and in the case of an open phase fault. Embarking on an exploration of diverse rotor topologies and their implications, this study engages in comprehensive theoretical and simulation analyses. The research initiative involves the design and simulation of a 15-kW Interior Permanent Magnet (IPM) motor, crafted to emulate the characteristics of a practical light-duty Electric Vehicle (EV). To validate the conceptual framework, empirical testing is conducted using a 2-kW laboratory-scale Surface-Mounted Permanent Magnet (SPM) motor.
The multiphase induction motor is considered to be the promising alternative to the conventional three-phase induction motor, especially in safety-critical applications because of its inherent ...fault-tolerant feature. Therefore, the attention of many researchers has been paid to develop different techniques for detecting various fault types of multiphase induction motors, to securely switch the control mode of the multiphase drive system to its post-fault operation mode. Therefore, several fault detection methods have been researched and adapted; one of these methods is the indices-based fault detection technique. This technique was firstly introduced to detect open-phase fault of multiphase induction motors. The main advantage of this technique is that its mathematical formulation is straightforward and can easily be understood and implemented. In this paper, the study of the indices-based fault detection technique has been extended to test its applicability in detecting some other stator and rotor fault types of multiphase induction motors, namely, open-phase, open-switch, bad connection and broken rotor bar faults. Experimental and simulation validations of this technique are also introduced using a 1 kW prototype symmetrical six-phase induction motor.
Experiments have been conducted to investigate discrepancies in previously published data for the pressure drop in microchannels. Straight channel test sections with integrated pressure sensors were ...developed with channel hydraulic diameters ranging from 25 to 100
μm. Compressible flow results for 6.8
<
Re
<
18,814 and incompressible flow results for 4.9
<
Re
<
2068 have been obtained. The results suggest that friction factors for microchannels can be accurately determined from data for standard large channels. The large inconsistencies in previously published data are probably due to instrumentation errors and/or improper accounting for compressibility effects.
Multi-terminal high voltage DC transmission currently represents a leading technology in long-distance power transmission systems. Among the main technical challenges facing such technology, DC fault ...isolation, permitting different grounding schemes, providing interoperability, and high DC voltage stepping between different HVDC networks, and allowing high-speed power reversal without power interruption especially when connecting the pre-existing voltage source converters (VSC) and line commutated converters (LCC)-based HVDC networks. This paper introduces a new modular multilevel converter (MMC) based front-to-front DC-DC converter to interconnect two different types (LCC/VSC) of HVDC networks. The proposed topology comprises a voltage source MMC (VS-MMC) and a current source MMC (CS-MMC), while both are coupled via an AC link including the isolating transformer. The proposed topology can successfully provide an uninterruptible bi-directional power flow, high DC voltage stepping with a DC fault blocking capability, and low number of semiconductors due to the usage of only half-bridge SMs. The system design is provided with a detailed mathematical analysis. Furthermore, two active power control methodologies are proposed and compared. The first control technique is simpler and entails lower passive elements, while the second technique ensures a zero reactive power over the full range of active power flow. Furthermore, Losses analysis and comparison are provided between the two proposed control techniques. Finally, Control-Hardware-in-the-Loop (CHiL) test validation is employed to confirm the validity of the proposed system under healthy as well as different fault scenarios.
Capillary gas–liquid two-phase flow occurs in increasingly more modern industrial applications. The existing relevant data are limited and are inconsistent with respect to the reported flow patterns ...and their transition boundaries. A systematic experimental investigation of two-phase flow patterns in microchannels was the objective of this study.
Using air and water, experiments were conducted in circular microchannels with 1.1 and 1.45
mm inner diameters, and in microchannels with semi-triangular (triangular with one corner smoothed) cross-sections with hydraulic diameters 1.09 and 1.49
mm. The gas and liquid superficial velocity ranges were 0.02–80 and 0.02–8
m/s, respectively. Overall, flow patterns and flow pattern maps using gas and liquid superficial velocities as coordinates, were similar for all the test sections. The discernible flow patterns were bubbly, churn, slug, slug–annular and annular. The obtained data were compared with existing experimental data. They were also compared with relevant flow regime transition models and correlations, generally with poor agreement.
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