Software system “DIORES” for the operation diagnosis of a steam power plant unit

Despite the long operating experience with steam power units in the Electric Power System of Serbia (out of which some are at the end of or had even passed their planned working lives), unfortunately, there is a lack of data for their operating regimes, process parameters and performance deviations, the economy and operating states for the previous period. These data would not only be useful for optimal process control, but also for the planning of maintenance, retrofits and repowering of power plants. For these and other equally important reasons, the software system for the diagnosis of operating conditions, control of economy and operating states of different components has been developed for the referential steam power unit. A better control of the process and operating state, thanks to the use of the results obtained with this software system, will bring a lasting benefit to the efficiency and economy increase. Furthermore, it will enable an increase of reliability and availability of steam turbine units and make their working life longer. The basic characteristics of this software system and some of the results obtained by its testing using the available data base for referential unit operation are presented in this paper.     

A lightweight low‐speed permanent magnet electrical generator for direct‐drive wind turbines

The evolution, design and test results of a novel permanent magnet generator for use in direct‐drive wind turbines are presented. This generator topology is based on steel C‐core modules (which make up the rotor) and an air‐cored stator winding. This topology allows a reduction in structural mass for large diameter generators, which can lead to lightweight generators. Copyright © 2009 John Wiley & Sons, Ltd.     

Development and on-orbit operation of lithium-ion pouch battery for small scientific satellite “REIMEI”

A lithium-ion battery was developed using off-the-shelf pouch cells and launched with a small scientific satellite “REIMEI.” The cells were potted with polyurethane or epoxy resin to protect the battery from vacuum in space. Preliminary experimental test results of pouch cells potted in a soft aluminum cap suggested that the cells tended to swell in vacuum, although they had been reinforced with the resins. Bread board models (BBMs), in which pouch cells were potted with resins in a hard aluminum case, were fabricated for cycle life performance tests in the laboratory. The test results indicated that the performance of epoxy-potted BBM was superior to that of the polyurethane-potted BBM. The measured cell resistance implied that the electrolyte solution leaked through the polyurethane resin, resulting in premature deterioration. The epoxy resin was used for the flight battery. The end-of-discharge-voltage (EoDV) trend of the flight battery on orbit was compared with the laboratory test results corrected based on a post-launch cycle test using a fresh cell. The corrected EoDV trend in the laboratory was in good agreement with the on-orbit trend for the early cycle period, indicating that the on-orbit battery was not inadvertently affected by conditions in space.     

The operation of permanent magnet DC motors powered by a commonsource of solar cells

In a photovoltaic water-pumping system, the solar cell array is usually designed to power a single motor-load pump. Several water-pumping systems of the same or different types that are in close proximity to each other can be powered by separate solar cell arrays (sources) for each one, or, alternatively, by a common solar cell source for all the water pumping systems. The authors introduce a procedure for comparing the performances of these two setups. One system includes a permanent magnet DC motor and a volumetric pump, and the other a permanent magnet DC motor and a centrifugal pump. The comparison was also done for the same systems when a maximum-power point tracker (MPPT) was included for both the separate and the common solar cell source. It is shown, for example, that in systems not including MPPTs the total performance of the two motor-pumps in the common source system is improved as compared to the performance of the two motor-pumps when they are powered separately by individual sources     

The use of an axial flux permanent magnet in-wheel direct drive in an electric bicycle

The research described in this paper concentrates on the development of an electronic converter. Successful completion of this converter provides the final component for the larger electric bicycle project. The controller developed for the bicycle is rated at 400 W and is hard-switched. It uses MOSFETs as power switching devices. There are three Hall effect sensors placed 120 electrical degrees apart from each other in the motor for velocity and position sensing. The torque generated by the machine is controlled by hysteresis band current control. In order for the motor/controller to be commercially viable, particular attention was paid to the costs of the controller. The result, an efficient yet cheap controller. Measurement of efficiency is difficult in high performance power electronic controllers [Patterson DJA very high efficiency controller for an axial flux permanent magnet wheel drive in a solar powered vehicle. 2nd IEEE International Conference on Power Electronics Drives and Energy Systems for Industrial Growth, IEEE PEDES ’98, Perth, 30th November–3rd December, 1998.]. The paper includes discussion of a calorimetric method for measurement.     

Analysis and development of a low-cost permanent magnet brushless DC motor drive for PV-array fed water pumping system

This paper deals with the analysis and development of a permanent magnet brushless DC (PMBLDC) motor drive coupled to a pump load powered by solar photovoltaic (PV) array for water pumping system. A simple low-cost prototype controller has been designed and developed without current and position sensors which reduces drastically the overall cost of the drive system. This controller is used to test the dynamic behavior of the PMBLDC motor drive system. The mathematical model of the system is developed with a view to carry out a comparison between experimental and simulated response of the drive system. A simple filter circuit incorporated in between PV-array and an inverter to reduce ripples and to improve the performance of the PV-array. The necessary computer algorithm is developed to analyze the performance under different conditions of varying solar insolation for a pump load.     

Meeting modern grid codes with large direct‐drive permanent magnet generator‐based wind turbines—low‐voltage ride‐through

Ambitious offshore wind energy targets continue to drive technological innovation, with the latest direct‐drive permanent magnet generator‐based wind turbines promising higher efficiency and availability. However, these machines have fixed rotor flux, provided by the magnets, which means that their voltage rises with speed. Further, high machine stator reactance leads to significant magnetic energy storage in the stator windings. Both these aspects provide new challenges for the power converter when designing to meet modern low‐voltage ride‐through requirements. This paper therefore proposes a novel control strategy, using a minimally rated chopper and dynamic brake resistor (DBR) integrated with the wind turbine's power converter, to help these systems to meet the demands of modern grid codes. This control method may allow the chopper and DBR to be rated at only 40% of a fully rated version. Despite only partially rating the DBR system, the control method minimizes the torsional oscillations in the drive train, thereby protecting the mechanical system. Copyright © 2011 John Wiley & Sons, Ltd.     

Analysis of a concentrated winding induction machine for adjustablespeed drive applications. I. Motor analysis

The performance of multiphase machines designed for operation with static power converters is investigated. The winding distributions are intentionally rectangular to better accommodate the rectangular waveforms of solid-state inverters. Equations which define the transient as well as steady-state behavior, including the computation of all machine inductances, are derived. In deriving these equations the space harmonics are specifically included. Equations for calculation of terminal voltages and electromagnetic torque are modified to account for nonsinusoidal air-gap-flux distributions. A conventional three-phase induction motor including the effect of space harmonics is simulated     

Two-phase Flow Patterns in a Square Mini-channel

This paper presents a new set of experimental data of air-water flow patterns in a channel with a cross-section of 1×1 mm2. The ranges of the gas and liquid superficial velocities are 0.1-10 m/s and 0.2~7 m/s, respectively. Bubble, bubble-slug, slug, and frothy flows are observed. The present data are compared with other data in mini-channels reported in literature, and also compared with those in normal channel at microgravity, in which the Bond number has the same order of magnitude. The slug-frothy boundary is in consistent with each other, but for the bubble-slug transition, a much smaller value for the transition quality in the drift-flux model is obtained in the present study than those predicted by the empirical relations for the case of microgravity. It's shown that the mini-scale modeling may not be an effective way to anticipate the bubble-slug transition of two-phase flow at microgravity.     

Interplay between morphology and electrochemical performance of “core–shell” electrocatalysts for oxygen reduction reaction based on a PtNix carbon nitride “shell” and a pyrolyzed polyketone nanoball “core”

The interplay between morphology and electrochemical performance of a new class of “core–shell” electrocatalysts for the oxygen reduction reaction (ORR) is studied. The electrocatalysts, labelled PtNi–CN_lT_f/ST_p, consist of a “core” of pyrolyzed polyketone nanoballs (indicated as ST_p “core” support) covered by a carbon nitride (CN) “shell” matrix embedding PtNi_x alloy NPs (indicated as PtNi_x-CN). The electrocatalysts are characterized by means of: (a) high-resolution transmission electron microscopy (HR-TEM); and (b) cyclic voltammetry with the thin-film rotating ring-disk electrode (CV-TF-RRDE) method. The structure of the ST_p “core” supports and the details of the preparation procedure, such as pyrolysis temperature, T_f, and treatment with H₂O₂, play a crucial role on modulating: (a) the morphology; and (b) the ORR performance of the electrocatalysts. In particular, the best results are achieved for PtNi–CN_lT_f/ST_p systems: (a) including a ST_p “core” support with a high porosity; and (b) obtained at T_f = 600 °C. It is demonstrated that in general, the treatment with H₂O₂ of electrocatalysts is detrimental for the ORR performance. Nevertheless, in particular conditions, the treatment in H₂O₂ improves the ORR performance of PtNi-CN_lT_f/ST_p. The results presented in this work allow to elucidate the complex correlation existing between: (a) the composition; (b) the interactions in PtNi_x-CN; (c) the morphology of ST_p and PtNi–CN_lT_f/ST_p; and (d) the ORR performance of the electrocatalysts.     

Control design for mechanical hardware‐in‐the‐loop operation of dynamometers for testing full‐scale drive trains

Advanced testing methods are becoming more and more prevalent to increase the reliability of wind turbines. In this field, dynamometers that allow for system level tests of full‐scale nacelles will play an important role. Operating these test benches in a hardware‐in‐the‐loop (HiL) set‐up that emulates realistic drive train modes is challenging because of the relatively low stiffness of the load machines' drive trains. This paper proposes a control method for enabling the said operation mode. It is based on the idea that the HiL‐controller overrides the present unrealistic dynamics and directly imposes desired realistic dynamics on the test bench. A solution for the control problem is given and applied in a design study with a generic wind turbine and a test bench model obtained from construction data of a real test bench. In the design study, the HiL‐controller robustly imposes desired drive train dynamics on the test bench model. Despite measurement noise, unmodelled parametric uncertainty, and unmodelled delays, the first drive train mode is correctly reproduced. This is confirmed by a comparison with simulation results from a full servo‐aero‐elastic code. Furthermore, an implementation of the test bench model on a programmable logic controller showed the real‐time feasibility of the proposed method. Copyright © 2016 John Wiley & Sons, Ltd.     

垂直向上气液两相流中T形柱体两相斯托拉赫数的研究

试验研究了两种规格的Ｔ形柱体在垂直上升气液两相流中发生气液两相涡街时,气液两相斯托拉赫数的变化规律。在测得大量数据的基础上,得出了此时气液两相斯托拉赫数的通用关系式。研究表明,气液两相斯托拉赫数在两相工况下为一变数,与来流截面含气率、涡街发生体形状和特征尺寸、来流方向等因素有关。根据测得的两相涡街频率应用此关系式,可将涡街发生体作为测量两相流流量与组合的测量元件。     

Palladium nanoparticles “breathe” hydrogen; a surgical view with X-ray diffraction

High resolution in situ XRD was used to study the hydriding behavior of palladium electrocatalysts, prepared from two precursors, (NH₄)₂PdCl₆ (4.3 nm), and palladium acetylacetonate [Pd(acac)₂] (6.2 nm), and supported on porous carbon XC-72R. X-ray line profile analysis revealed a defective fcc lattice with internal strains and a high stacking fault probability of 12%. Importantly, no change, neither of the size, nor the state of defects was observed during the phase transition (α ↔ β). Based on this finding, a two-phase model adopted from bulk palladium hydride was proposed to describe the transition trough the miscibility gap (MG). Apparently, Pd nanoparticles can “breathe” hydrogen, without modifying their intrinsic crystal structure: A 3-parameter algorithm perfectly reproduces the anomalous line profiles observed inside the MG by a simple rescaling of the intensity profiles measured outside the MG. The algorithm delivers accurate values for the phase boundaries α-max, β-min. They depend sensitively on the particles size and surface state, but also surprisingly on the branch of the hysteresis loop. Time dependent studies verify a hindered kinetics of hydride formation in the presence of surface oxide species.     

Two-phase pressure drop of air–water in minichannels

Results of experimental investigations of pressure drop in two-phase adiabatic flow in tubular minichannels are presented. Air–water mixture was used as a working fluid. Eight tubular minichannels with internal diameter d_w = 1.05 ÷ 2.30 mm and the test section length of 300 mm made from stainless steel were used. The investigations were conducted within the range: mass flow rate of water 0.65 ÷ 59 kg/h, mass flow rate of air 0.011 ÷ 0.72 kg/h, mass fraction of air in the two-phase mixture x = 0.0003 ÷ 0.22, total mass flux (wρ) = 139 ÷ 8582 kg/(m² s). It was found, on the basis of the experimental investigations, that the application of commonly used methods to evaluation of pressure drop in two-phase flow, provided poor results. It is therefore necessary to make some corrections and modifications for the two-phase flow in minichannels correlations.     

Analysis of a “cluster” strategy for introducing hydrogen vehicles in Southern California

The cost and logistics of building early hydrogen refueling infrastructure are key barriers to the commercialization of fuel cell vehicles. In this paper, we explore a “cluster strategy” for introducing hydrogen vehicles and refueling infrastructure in Southern California over the next decade, to satisfy California's Zero Emission Vehicle regulation. Clustering refers to coordinated introduction of hydrogen vehicles and refueling infrastructure in a few focused geographic areas such as smaller cities (e.g. Santa Monica, Irvine) within a larger region (e.g. Los Angeles Basin). We analyze several transition scenarios for introducing hundreds to tens of thousands of vehicles and 8–42 stations, considering:     

Analysis of a concentrated winding induction machine for adjustablespeed drive applications. II. Motor design and performance

For pt.I. see ibid, vol.6, no.4, p.679-83 (1991). The performance of multiphase machines designed for operation with static power converters is described. The winding distributions are intentionally rectangular to better accommodate the rectangular waveforms of solid-state inverters. Fourier analysis is used for investigation of the effects of different air-gap-field spatial distributions and time harmonics in the supply. The approach to analysis of such machines, derived in Part I, is implemented by means of a digital-computer simulation. Compound results indicate that when operating in conjunction with a converter supply, a specially wound five-phase machine is theoretically capable of a 10% improvement in torque per root-mean-square ampere assuming the same peak air-gap-flux density level in the air gap of the machine as in a conventionally designed induction motor of the same rating     

Two-phase phase distribution in a vertical large diameter pipe

In view of the practical importance of the application of two-phase flow in a large diameter pipe to various fields of engineering, the characteristics and phase distribution patterns of two-phase flow in a vertical large diameter pipe have been experimentally and theoretically studied for various flow conditions. The local measurements for the interfacial parameters (void fraction, Sauter mean diameter and pressure loss) in a vertical upward air-water two-phase flow in a pipe with 0.2 m in inner diameter and 24 m in height have been performed by using the optical probes and differential pressure transducers. The two-phase flow characteristics have been analyzed with experimental data, which shows that the phase distribution patterns in the vertical large diameter pipe can be divided into two basic patterns, namely, wall peak and core peak. With the application of the concept of skewness, the two-phase distribution patterns have been quantitatively distinguished by establishing a phase distribution pattern transition criterion. An empirical relation for the phase distribution transition from wall peak to core peak was fitted by using the phase distribution pattern transition criterion and the present experimental data and verified by other researchers’ experimental data. This study also showed that there existed the flow plugging phenomena in the low region of the test section at high superficial gas velocity conditions in the vertical large diameter pipe.     

Two-phase pressure drops in a helically coiled steam generator

An experimental investigation regarding two-phase diabatic pressure drops inside a helically coiled heat exchanger have been carried out at SIET thermo-hydraulics labs in Piacenza (Italy). The experimental campaign is part of a wide program of study of the IRIS innovative reactor steam generator. The test section consists of an AISI 316 stainless steel tube, 32 m length, 12.53 mm inner diameter, curved in helical shape with a bend radius of 0.5 m and a helix pitch of 0.8 m, resulting in a total height of the steam generator tube of 8 m. The explored operating conditions for two-phase flow experiences range from 192 to 824 kg/m² s for the mass flux, from 0 to 1 for the quality, from 1.1 to 6.3 MPa for the pressure, from 50 to 200 kW/m² for the heat fluxes. A frictional two-phase pressure drops correlation, based on an energy balance of the two-phase mixture and including the 940 experimental points, is proposed. Comparison with existing correlations shows the difficulty in predicting two-phase pressure drops in helical coil steam generators.     

Two-phase hydrodynamics in a miniature direct methanol fuel cell

We present controlled experiments on a miniature direct methanol fuel cell (DMFC) to study the effects of methanol flow rate, current density, and void fraction on pressure drop across the DMFC anode. We also present an experimental technique to measure void fraction, liquid slug length, and velocity of the two-phase slug flow exiting the DMFC. For our channel geometry in which the diameter of the largest inscribed sphere (a) is 500 μm, pressure drop scales with the number of gas slugs in the channel, surface tension, and a. This scaling demonstrates the importance of capillary forces in determining the hydrodynamic characteristics of the DMFC anode. This work is aimed at aiding the design of fuel pumps and anode flow channels for miniature DMFC systems.