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The increasing integration of inverter-based renewable generation into the network as Grid-Following inverters (GFL), combined with the reduction in traditional Synchronous Generation (SG) leads to a reduction in inertia and to instabilities. To alleviate this, researchers have proposed using a mix of GFL and Grid-Forming controllers (GFM). However, there is a lack of simple system-wide analytical models. This paper proposes a swing equation to describe the transient frequency response of GFL that has droop regulation of real and reactive power. The swing equation for GFL with droop has an inertia and a damping term as do SG and GFM swing equations. Simulations show that the use of swing equations for GFM and GFL is accurate to study the transient frequency stability following a loss of infeed. GFM and GFL damping are equivalent, and their sum allows prediction of frequency deviation. However, although SG and GFM inertia terms limit the initial Rate of Change of Frequency (RoCoF), the GFL inertia term is found not to contribute towards limitation of the initial RoCoF. Instead, the GFL RoCoF is seen to follow adjacent GFM RoCoF and worsens slightly when the GFL Phase Locked Loop (PLL) bandwidth is reduced.

In future power systems, reduced overall inertia caused by an increased dominance of asynchronous generation and interconnections would make frequency control particularly challenging. As the number and power rating of voltage source converter (VSC) HVDC systems increases, network service provision would be expected from such systems and to do so would require overload capacity to be included in the converter specifications. This paper studies the provision of frequency services from modular multilevel converter (MMC)-based VSC HVDC interconnections using temperature-constrained overload capability. Overload of the MMC-based HVDC system is achieved through controlled circulating currents, at the expense of higher losses, and subject to a control scheme that dynamically limits the overload available in order to keep the semiconductor junction temperatures within operational limits. Two frequency control schemes that use the obtained overload capacity to provide frequency response during emergency conditions are investigated. The controllers' performance is demonstrated in the context of the future Great Britain transmission grid through a reduced equivalent test system. Simulation results show that even modest temperature margins which allow overload of MMC-based HVDC systems for a few seconds are effective as a primary frequency reserve and also reduce the loss of infeed requirements of such interconnections.

Voltage dependent loads can collectively provide a certain amount of power reserve (by virtue of the ability to change their power consumption within the stipulated voltage tolerance) which could be exploited for grid frequency regulation through voltage control at the substation/feeder or at the point of load. The amount of such power reserve would vary with time of the day depending on the incidence of different types of voltage dependent loads and also the voltage profile across the feeders. It is important for the grid operators to know the aggregate power reserve from the voltage dependent loads during different times of the day in order to schedule other forms of reserves accordingly. This paper presents a methodology to estimate such power reserve from the measured power and voltage at the bulk supply points without knowing the actual distribution network topology and/or load profile of individual customers. The proposed method is applied to estimate the time variation of the aggregate reserve offered by the voltage dependent loads within the domestic sector in Great Britain (GB). Studies on a standard IEEE distribution network are presented to validate the estimated reserve margins under typical voltage profiles across the distribution feeders.

IEEE Three-phase electric spring (3-ph ES) has recently been proposed as a fast demand response technology for applications in unbalanced power systems fed with a mixture of conventional and renewable power generation. Using the Instantaneous Power Theory as the theoretical framework, this paper presents the criteria and conditions for minimizing the average and oscillating power of the 3-ph ES for the first time. A detailed analysis of the use of 3-ph ES is included for providing multiple control objectives of voltage regulation and power balancing of the 3-ph power system, and minimization of the average and oscillating ac power of the ES. A corresponding control scheme implementable in a single controller is included and explained. The control scheme has been practically verified with experiments.

Human laugh is able to convey various kinds of meanings in human communications. There exists various kinds of human laugh signal, for example: vocalized laugh and non vocalized laugh. Following the theories of psychology, among all the vocalized laugh type, rhythmic staccato-vocalization significantly evokes the positive responses in the interactions. In this paper we attempt to exploit this observation to detect human laugh occurrences, i.e., the laughter, in multiparty conversations from the AMI meeting corpus. First, we separate the high energy frames from speech, leaving out the low energy frames through power spectral density estimation. We borrow the algorithm of rhythm detection from the area of music analysis to use that on the high energy frames. Finally, we detect rhythmic laugh frames, analyzing the candidate rhythmic frames using statistics. This novel approach for detection of `positive' rhythmic human laughter performs better than the standard laughter classification baseline., Comment: 5 pages, 1 figure, conference paper

Document Image Analysis, like any Digital Image Analysis requires identification and extraction of proper features, which are generally extracted from uncompressed images, though in reality images are made available in compressed form for the reasons such as transmission and storage efficiency. However, this implies that the compressed image should be decompressed, which indents additional computing resources. This limitation induces the motivation to research in extracting features directly from the compressed image. In this research, we propose to extract essential features such as projection profile, run-histogram and entropy for text document analysis directly from run-length compressed text-documents. The experimentation illustrates that features are extracted directly from the compressed image without going through the stage of decompression, because of which the computing time is reduced. The feature values so extracted are exactly identical to those extracted from uncompressed images., Comment: Published by IEEE in Proceedings of ACPR-2013. arXiv admin note: text overlap with arXiv:1403.7783

Extracting a block of interest referred to as segmenting a specified block in an image and studying its characteristics is of general research interest, and could be a challenging if such a segmentation task has to be carried out directly in a compressed image. This is the objective of the present research work. The proposal is to evolve a method which would segment and extract a specified block, and carry out its characterization without decompressing a compressed image, for two major reasons that most of the image archives contain images in compressed format and decompressing an image indents additional computing time and space. Specifically in this research work, the proposal is to work on run-length compressed document images., Comment: 7 Pages and Published with International Journal of Computer Applications (IJCA)

We report our observation of a correlation between the extrinsic electroresistance (EER) and magnetoresistance (EMR) via grain size in fine-grained La0.7Ca0.3MnO3. The nature of dependence of EER and EMR on grain size (~0.2-1.0 micron) indicates that for finer grains with low-resistive boundaries both of them follow similar trend whereas they differ for coarser grains with high-resistive boundaries. This could be due to a crossover in the mechanism of charge transport across the grain boundaries - from spin-depedent scattering process to spin-polarized tunneling one - as a function of grain size., Comment: 19 pages including 4 figures; pdf only

A human malignant Schwannoma was serially transplanted through three generations in nude mice. The tumours grew readily and the take-up rate was 100 per cent. No metastasis was observed in nude mice. Morphological features of the original tumour were strictly maintained through all the transplant generations. The tumour cells of the original and of the transplants showed features of primitive Schwann cells of embryonic nerve trunks.

Based on the results of field-dependent dielectric and magnetic measurements, we observe several interesting behaviors and phase transitions in this geometrically frustrated spinel system CdCr2S4. (1) A glassy dipolar state occurs near T-C similar to 85 K, which is induced by the onset of ferromagnetic ordering. (2) A ferroelectric ordering occurs near T-p similar to 56 K, which is enhanced by externally applying electric field. (3) Both the magnitude and step-up temperature of dielectric constant (epsilon(')) near T-C are suppressed by an electric field yet are increased by the magnetic field. (4) Both electric and magnetic fields colossally enhance the magnitude of dielectric constant (epsilon(')) near T-p. (5) A clear dip of magnetization under various electric fields is observed near T-p indicating the different spin-dipole interactions near T-C and T-p. Attempts are made to analyze these field-dependent properties by considering the strong spin-lattice coupling and exchange striction effect in this novel multiferroic material.