Control strategy for a distributed DC power system with renewable energy

This paper deals with a DC-micro-grid with renewable energy. The proposed method is composed of a gearless wind power generation system, a battery, and DC loads in a DC distribution system. The battery helps to avoid the DC over-voltages by absorbing the power of the permanent magnet synchronous generator (PMSG) during line-fault. In addition, the control schemes presented in this paper including the maximum power point tracking (MPPT) control and a pitch angle control for the gearless wind turbine generator. By means of the proposed method, high-reliable power can be supplied to the DC distribution system during the line-fault and stable power supply from the PMSG can be achieved after line-fault clearing. The effectiveness of the proposed method is examined in a MATLAB/Simulink^® environment.     

Flame flickering frequency on a rotating Bunsen burner

The empirical correlation (St^*2/Ri=0.00028Re^*2/3: St^* is the reduced Strouhal number, Ri the Richardson number, Re^* the reduced Reynolds number) proposed by Kostiuk and Cheng [1995. The coupling of conical wrinkled laminar flames with gravity. Combustion and Flame 103, 27-40] for predicting buoyancy-induced flame flickering frequency, has been experimentally investigated under the swirling flow conditions produced by a rotating Bunsen burner, focusing on how the flame flickering frequency changes with increasing swirl number S. Under low swirling conditions up to S≈0.1, the flame flickering frequency f_t did not change and monotonically increased with increasing the bulk flow velocity from the burner tube U. The trend of the data is similar to those obtained by Durox et al. [1995. Some effects of gravity on the behavior of premixed flames. Combustion and Flame 82, 66-74] and Kostiuk and Cheng (1995) and could be fitted well with the empirical correlation Kostiuk and Cheng (1995). However, under high swirling  conditions (S>1), f_t significantly decreased up to ≈80% of that with non-swirling condition, and became insensitive to U. As a result, the data under S>1 could not be correlated by the empirical equation. From results obtained by laser doppler velocimetry (LDV), this inconsistency is due to flow divergence shown by the change in the velocity distribution between the burner exit and the flame tip with burner rotation. A minimum value of the centerline velocity u_j,min between the burner exit and the flame tip fulfills an important role in controlling the flame flickering frequency. The use of this parameter allows the empirical correlation to be extended to the high swirling case by means of a modified empirical correlation St^*2/Ri=0.00028(Re^*exp(-0.64S^1.78))^2/3.     

Electrokinetic microslit experiments to analyse the charge formation at solid/liquid interfaces

Electrokinetic effects play an important role in microfluidics and nanofluidics. Although the related phenomena are often utilized to control fluid flow and sample transport in lab-on-a-chip devices, their dependency on the surface charges on the channel walls often remain enigmatic. This is mainly due to the lack of adequate experimental methods to analyse the electrical charging of solid/liquid interfaces of interest. To address this need, an experimental set-up—designated as microslit electrokinetic set-up (MES)—has been recently developed and applied for the investigation of charge formation processes at planar solid/liquid interfaces. The device permits to perform streaming potential and streaming current measurements across a rectangular streaming channel formed by two parallel sample carriers (20×10×3 mm³) at variable distance allowing for the determination of the surface conductivity. Utilizing the MES, charge characteristics can be determined for a wide variety of materials prepared as thin films on top of planar glass substrates. Streaming potential and streaming current data permit to investigate the mechanisms of charge formation while surface conductivity data provide information about mobile charge carriers located in different zones at the interface. The applicability of this advanced experimental approach is demonstrated with examples obtained for surfaces with different levels of complexity:

1. Preferential ion adsorption onto unpolar fluoropolymer (Teflon^® AF) films was characterized in simple electrolyte solutions; the results were quantitatively evaluated with respect to interfacial ion concentrations.
2. Interrelation of charge density and conformation of grafted poly(L-glutamic acid layers) were unravelled from the determination of pH-depended variations of surface conductivity and layer thickness.
3. The impact of spatial confinements of surface functional groups on their acid–base behaviour was studied with self-assembled monomolecular films of alkanethiols chemisorbed on gold.
4. Charging of and ion mobility within poly(acrylic acid) (PAA) brushes prepared by a Langmuir–Blodgett technique were analysed at varied pH and ionic strength.
5. Interfacial modes of adsorbed proteins were distinguished at two polymer surfaces with varied hydrophobicity/charge density.

     

Analysis of lightning surge propagation in wind farm

Wind power generation is expected to become more important in future distribution systems. Although several prospective reports such as IEC 61400‐24 and NREL SR‐500‐31115 indicate an insulation scheme and grounding design for lighting protection, there still seems to be too few investigations on the problems. This paper therefore discusses lightning surge analysis using a wind farm model with 2 or 10 ideal wind turbines. Changing parameters such as grounding resistance and lightning strike points, several cases were studied. As a result of the analysis using digital simulator ARENE, it is clear that the surge tends to propagate toward the end of a distribution line in a wind farm and there is the possibility of insulation accidents at the other wind turbines when lightning attacks a wind turbine. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 162(2): 30– 38, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20364     

Iron Loss Calculation of AC Filter Inductor for Three‐Phase PWM Inverters

In recent years, remarkable advancement of new power semiconductor devices, such as SiC and GaN, enables the increase of switching frequency of power converters, and hence the volume of passive components, such as ac filters and transformers, can be reduced. However, temperature rise caused by the inductor loss is increasing, and hence iron loss evaluation of the inductor is one of the most important issues to realize high power density converters. Conventionally, an improved generalized Steinmetz equation (iGSE) has proposed in order to calculate the iron loss under a pulse voltage magnetizing condition. However, accurate iron loss calculation of the ac filter inductor used in a PWM inverter cannot be realized. The authors have proposed two methods of iron loss evaluation of ac filter inductors. The first one is a loss map method which can calculate the iron loss without using a real PWM inverter. Another one is an ILA (Inductor Loss Analyzer) which can measure the iron loss in every switching period in a real PWM inverter. In this paper, comparisons of the iron loss between the ILA and the loss map method on both the single‐phase and three‐phase inverters are studied. It is found that iron loss of the ac filter inductor in the three‐phase PWM inverter which is calculated by the loss map method cause a large error on a specific condition. In order to prevent the calculation error, the authors proposed a revised loss map method and proved the effectiveness of the method.     

Multicomponent diffusion in phase-separating polymer blends with different frictional interactions: a mean-friction model

We present a compact formula for describing the mean frictional forces acting on a molecule in multicomponent systems. The friction-based diffusion theory of Zielinski and Hanley was extended to newly include the friction-average molar velocity as a reference frame. The results showed that the previous diffusion theories are unified by the friction-average concept by properly choosing the average velocity. The present model based on the diffusivity-related molar average velocity provides better predictions for the diffusive flux in a ternary miscible liquid compared to the other existing theories. The application of the model in phase-separating ternary systems revealed that the introduction of a highly diffusive third component into demixing polymer blends promotes a particular enhancement of the spinodal decomposition due to the difference in the frictional interactions between polymers.     

Electrostatic switching of biopolymer layers. Insights from combined electrokinetics and reflectometric interference

Structural integrity and functional characteristics of biomacromolecules are largely defined by electrostatic forces between ionized moieties, which are often altered at interfaces. Unraveling these changes requires access to charge state and structure of surface-confined biopolymers in aqueous environments. We therefore combined electrokinetic measurements of interfacial electrical potentials with the simultaneous determination of the optical layer thickness by reflectometric interference spectroscopy. Two examples are summarized to demonstrate the resulting options: The pH-switching of grafted poly(l-glutamic acid) layers caused by dissociation-dependent helix-coil transitions was studied; potential distribution and ion mobility within the grafted polyelectrolyte were unraveled using an new theoretical model for the charging of polyelectrolyte layers. The charge-driven modulation of biopolymers at interfaces was furthermore analyzed in the adsorption of fibronectin onto polymer substrates with varied charge density; the results permit us to reach a conclusion about the relevance of electrostatic matching for orientation and anchorage of the protein. Altogether, the introduced methodology was found suitable to follow the electrosurface characteristics of biomacromolecules in situ.     

Mice with focal pulmonary fibrosis caused by monocrotaline are insensitive to urethane induction of lung tumorigenesis

To establish the characteristics of an optimized pulmonary fibrosis model, male ICR mice were given 4 weekly sc injections of 150 or 0 mg/kg monocrotaline (MCT) and maintained without further treatment for 33 wk (Experiment 1). The final mortality in the MCT group was 64%. Epithelial cells with large bizarre nuclei and an increased incidence of alveolar/bronchiolar hyperplasias were typically observed. In areas of pulmonary fibrosis, the PCNA labeling index (LI) in the alveolar/airway epithelium was significantly elevated. DNA content analysis demonstrated a larger range (4-8C) for the ploidy pattern of alveolar epithelium with large bizarre nuclei than in the normal epithelium (2C). In Experiment 2, the relationship between pulmonary fibrosis development and lung tumorigenesis was investigated. Mice were given 4 weekly sc injections of 150 and 0 mg/kg MCT, followed by a single i.p. injection of 1,000 or 500 mg/kg urethane (UR) on week 7, then maintained without further treatment for an additional 15 wk. UR following MCT-induced inflammatory changes, fibrosis, and epithelia with large bizarre nuclei but no tumorous lesions, in spite of the fact that treatment with UR alone caused a high incidence of pulmonary tumors. Hyperplasias were seen in all groups, but the multiplicity in the combined groups tended to be decreased by the MCT pretreatment. The present study demonstrated that this new protocol is more suitable than previous one for the experimental production of pulmonary fibrosis. Furthermore, the induction of lung tumors by UR was completely depressed in mice with MCT-induced pulmonary fibrosis, suggesting that alveolar epithelial cells are resistant to this lung carcinogen under these conditions.     

基于用户体验质量和系统能耗的异构网络联合接入选择和功率分配策略

为了解决无线网络能耗和用户体验质量的问题,提出了一种应用于异构无线网络环境的基于多目标优化的联合接入选择和功率分配策略。该策略以最小化系统整体能耗和最大化用户平均体验质量为目标,建立了多目标优化联合分配模型,通过差分进化算法得到联合分配模型的最优解集,并结合 TOPSIS 的方法从最优解集中得到折中的联合分配方案。仿真结果表明,本文所提的策略能够有效地降低系统能耗,并提升用户整体的服务体验。