A DC-to-Three-Phase-AC High-Frequency Link Converter With Compensation for Nonlinear Distortion

This paper focuses on a new high-frequency (HF) link dc-to-three-phase-ac power converter. The least number of switching devices among other HF link dc-to-three-phase-ac converters, improved power density due to the absence of devices of bidirectional voltage-blocking capability, simple commutation requirements, and isolation between input and output are the integral features of this topology. The commutation process of the converter requires zero portions in the link voltage. This causes a nonlinear distortion in the output three-phase voltages. The mathematical analysis is carried out to investigate the problem, and suitable compensation in modulating signal is proposed for different types of carrier. Along with the modified modulator structure, a synchronously rotating reference-frame-based control scheme is adopted for the three-phase ac side in order to achieve high dynamic performance. The effectiveness of the proposed scheme has been investigated and verified through computer simulations and experimental results with 1-kVA prototype.

Principle of a Dual Current Source Converter for AC Motor Drives

The principle of operation of a dual current source converter is briefly explained. The combination of two single current source converters (SCSC) to form a ``dual (duplex) current source converter'' (DCSC) is proposed. The DCSC is shown to have the following merits: 1) it retains all the advantages of the SCSC; 2) it reduces the harmonic content of the current waveform considerably; and 3) since the load current is shared equally between two current source converters, ratings of the individual components employed in the circuit are considerably lowered. A DCSC can be an attractive choice for sophisticated large horsepower drives where a good performance of the drive rather than cost is a prime factor. An open-loop control scheme employing the DCSC for an ac motor drive has been successfully implemented in the laboratory. Oscillograms of the improved load current waveforms are shown.

A Resonant Integrator Based PLL and AC Current Controller for Single Phase Grid Connected PWM-VSI

Grid connected PWM-VSIs are being increasingly used for applications such as Distributed Generation (DG), power quality, UPS etc. Appropriate control strategies for grid synchronisation and line current regulation are required to establish such a grid interconnection and power transfer. Control of three phase VSIs is widely reported in iterature. Conventionally, dq control in Synchronous Reference Frame(SRF) is employed for both PLL and line current control where PI-controllers are used to track the DC references. Single phase systems do not have defined direct (d) and quadrature (q) axis components that are required for SRF transformation. Thus, references are AC in nature and hence usage of PI controllers cannot yield zero steady state errors. Resonant controllers have the ability to track AC references accurately. In this work, a resonant controller based single phase PLL and current control technique are being employed for tracking grid frequency and the AC current reference respectively. A single phase full bridge converter is being operated as a STATCOM for performance evaluation of the control scheme.

Artificial commutation for inversion into a weak AC system in a multiterminal HVDC system

This paper deals with the application of artificial commutation for a normally rated inverter connecting a weak AC system in a multiterminal HVDC (MTDC) system. Artificial commutation is achieved using series capacitors. A modular digital simulation technique is developed to study the dynamic performance of the system. It is shown that by a proper selection of the value of the capacitor it is possible to limit the valve stresses and the DC harmonics to acceptable levels and achieve an improved performance during severe transient conditions. The determination of the value of the series capacitor is based on a parametric study.

AC impedance spectroscopic characterization of 10 mol% MgO doped ZnO varistors

The performance parameters e.g. non-linear coefficient (α) and breakdown electric field (Eb1mA/cm2) of ZnO based ceramic varistors were found to improve after the addition of 10 mol% MgO. The improvement in the varistor properties is examined by ac impedance spectroscopy technique in the frequency range (1 Hz–10 MHz) between temperature 25–250°C and understood in terms of differing contributions from the equivalent electrical circuit elements.

A structure-preserving energy function for stability analysis of AC/DC systems

Direct stability analysis ofAC/DC power systems using a structure-preserving energy function (SPEF) is proposed in this paper. The system model considered retains the load buses thereby enabling the representation of nonlinear voltage dependent loads. TheHVDC system is represented with the same degree of detail as is normally done in transient stability simulation. The converter controllers can be represented by simplified or detailed models. Two or multi-terminalDC systems can be considered. The stability analysis is illustrated with a 3-machine system example and encouraging results have been obtained.

Molecular structure of Lantadene-B&C, triterpenoids ofantana camara, red variety: Lantadene-B, 22β-angeloyloxy-3-oxoolean-12-en-28-oic acid; Lantadene-C, 22 β-(S)-2′-methyl butanoyloxy-3-oxoolean-12-en-28-oic acid

(I)Lantadene-B: C35H52O5,M r =552.80, MonoclinicC2,a=25.65(1),b=6.819(9),c=18.75(1) Å,beta=100.61(9),V=3223(5) Å3,Z=4,D x =1.14 g cm–3 CuKagr (lambda=1.5418A),mgr=5.5 cm–1,F(000)=1208,R=0.118,wR=0.132 for 1527 observed reflections withF o ge2sgr(F o ). (II)Lantadene-C: C35H54O5·CH3OH,Mr=586.85, Monoclinic,P21,a=9.822(3),b=10.909(3),c=16.120(8)Å,beta=99.82(4),V=1702(1)Å3,Z=2,D x =1.145 g cm–3, MoKagr (lambda=0.7107Å), mgr=0.708 cm–1 F(000)=644,R=0.098, wR=0.094 for 1073 observed reflections. The rings A, B, C, D, and E aretrans, trans, trans, cis fused and are in chair, chair, sofa, half-chair, chair conformations, respectively, in both the structures. In the unit cell the molecules are stabilized by O-HctdotO hydrogen bonds in both the structures, however an additional C-HctdotO interaction is observed in the case of Lantadene-C.

Study of voltage collapse at converter bus in asynchronous MTDC-AC systems

This paper presents the analysis and study of voltage collapse at any converter bus in an AC system interconnected by multiterminal DC (MTDC) links. The analysis is based on the use of the voltage sensitivity factor (VSF) as a voltage collapse proximity indicator (VCPI). In this paper the VSF is defined as a matrix which is applicable to MTDC systems. The VSF matrix is derived from the basic steady state equations of the converter, control, DC and AC networks. The structure of the matrix enables the derivation of some of the basic properties which are generally applicable. A detailed case study of a four-terminal MTDC system is presented to illustrate the effects of control strategies at the voltage setting terminal (VST) and other terminals. The controls considered are either constant angle, DC voltage, AC voltage, reactive current and reactive power at the VST and constant power or current at the other terminals. The effect of the strength of the AC system (measured by short circuit ratio) on the VSF is investigated. Several interesting and new results are presented. An analytical expression for the self VSF at VST is also derived for some specific cases which help to explain the number of transitions in VSF around the critical values of SCR.

Synthesis, characterization and photoluminescence properties of CaSiO3: Eu3+ red phosphor

CaSiO3:Eu3+ (1-5 mol%) red emitting phosphors have been synthesized by a low-temperature solution combustion method. The phosphors have been well characterized by powder X-ray diffraction (PXRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and optical spectroscopy. PXRD patterns reveal monoclinic CaSiO3 phase can be obtained at 900 degrees C. The SEM micrographs show the crystallites with irregular shape, mostly angular. Upon 254 nm excitation, the phosphor show characteristic fluorescence D-5(0) -> F-7(J) (J = 0, 1, 2, 3, 4) of the Eu3+ ions. The electronic transition located at 614 nm corresponding to D-5(0) -> F-7(2) of Eu3+ ions, which is stronger than the magnetic dipole transition located at 593 nm corresponding to D-5(0) -> F-7(1) of Eu3+ ions. Different pathways involved in emission process have been studied. Concentration quenching has been observed for Eu3+ concentration >4 mol%. UV-visible absorption shows an intense band at 240 nm in undoped and 270 nm in Eu3+ doped CaSiO3 which is attributed to oxygen to silicon (O-Si) ligand-to-metal charge-transfer (LMCT) band in the SiO32- group. The optical energy band gap is widened with increase of Eu3+ ion dopant. (C) 2010 Elsevier B.V. All rights reserved.

18-Bit binary inductive voltage divider for self balancing ac bridge applications

The constructional details of an 18-bit binary inductive voltage divider (IVD) for a.c. bridge applications is described. Simplified construction with less number of windings, interconnection of winding through SPDT solid state relays instead of DPDT relays, improves reliability of IVD. High accuracy for most precision measurement achieved without D/A converters. The checks for self consistency in voltage division shows that the error is less than 2 counts in 2(18).

Ac conductivity studies of lithium thioborate glasses

The variation in the exponent s in σa.c. agr ωs as a function of temperature is reported for lithium thioborate glasses. The origin of the observed minimum in s is discussed using the diffusion-controlled relaxation (DCR) model. An entirely new model for the a.c. conductivity of highly modified ionic glasses has been proposed and expressions for relaxation identical with those of the DCR model have been obtained, providing a new explanation for the temperature behaviour of s. The origin of two activation barriers generally observed in a.c. conductivity studies is examined in the light of the new model.

Integrated Magnetics-Based Multisource Quality AC Power Supply

This paper proposes a method of sharing power/energy between multiple sources and multiple loads using an integrated magnetic circuit as a junction between sources and sinks. It also presents a particular use of the magnetic circuit as an ac power supply, delivering sinusoidal voltage to load irrespective of the presence of the grid, taking only active power from the grid. The proposed magnetic circuit is a three-energy-port unit, viz.: 1) power/energy from grid; 2) power energy from battery-inverter unit; and 3) power/energy delivery to the load in its particular application as quality ac power supply (QPS). The product provides sinusoidal regulated output voltage, input power-factor correction, electrical isolation between the sources and loads, low battery voltage, and control simplicity. Unlike conventional series-shunt-compensated uninterruptible power supply topologies with low battery voltage, the isolation is provided using a single magnetic circuit that results in a smaller size and lower cost. The circuit operating principles and analysis, as well as simulation and experimental results, are presented for this QPS.

Characterization of the DNA-binding domain of beta protein, a component of phage lambda Red-pathway by UV catalyzed cross-linking

beta protein, a key component of Red-pathway of phage lambda is necessary for its growth and general genetic recombination in recombination-deficient mutants of Escherichia coli. To facilitate studies on structure-function relationships, we overexpressed beta protein and purified it to homogeneity. A chemical cross-linking reagent, glutaraldehyde, was used to stabilize the physical association of beta protein in solution. A 67-kDa band, corresponding to homodimer, was identified after separation by SDS-polyacrylamide gel electrophoresis. Stoichiometric measurements indicated a site-size of 1 monomer of beta protein/5 nucleotide residues. Electrophoretic gel mobility shift assays suggested that beta protein formed stable nucleoprotein complexes with 36-mer, but not with 27- or 17-mer DNA. Interestingly, the interaction of beta protein with DNA and the stability of nucleoprotein complexes was dependent on the presence of MgCl2, and the binding was abolished by 250 mM NaCl. The K-d of beta protein binding to 36-mer DNA was on the order of 1.8 x 10(-6) M. Photochemical cross-linking of native beta protein or its fragments, generated by chymotrypsin, to 36-mer DNA was performed to identify its DNA-binding domain. Characterization of the cross-linked peptide disclosed that amino acids required for DNA-binding specificity resided within a 20-kDa peptide at the N-terminal end. These findings provide a basis for further understanding oi the structure and function of beta protein.

Dynamic analysis of voltage instability in AC-DC systems

This paper presents the analysis and study of voltage collapse at any converter bus in A C-DC systems considering the dynamics of DC system. The problem of voltage instability is acute when HVDC links are connected to weak AC systems, the strength determined by short circuit ratio (SCR) at the converter bus. The converter control strategies are important in determining voltage instability. Small signal analysis is used to identify critical modes and evaluate the effect of AC system strength and control parameters. A sample two-terminal DC system is studied and the results compared with those obtained from static analysis. Also, the results obtained from small signal analysis are validated with nonlinear simulation.