Transformerless PV inverters - recent test results and a discussion of DC current injection and safety issues

With the variety of PV inverter types and the number of transformerless PV inverters on the Australian market increasing, we revisit some of the issues associated with these topologies. A recent electric shock incident in Queensland (luckily without serious outcome) associated with a transformerless PV system, highlights the need for earthing PV array structures and PV module frames to prevent capacitive leakage currents causing electric shock. The presented test results of the relevant voltages associated with leakage currents of five transformerless PV inverters stress this requirement, which is currently being addressed by both the Clean Energy Council and Standards Australia. DC current injection tests were performed on the same five inverters and were used to develop preliminary recommendations for a more meaningful DC current test procedure for AS4777 Part 2. The test circuit, methodology and results are presented and discussed. A notable temperature dependency of DC current injections with three of the five inverters suggests that DC current injection should be tested at high and low internal inverter temperatures whereas the power dependency noted only for one inverter does not seem to justify recommendations for a (rather involved) standard test procedure at different power levels.

Common Ground Method of Current Injection in Electrical Impedance Tomography

Surface electrodes are essentially required to be switched for boundary data collection in electrical impedance tomography (Ell). Parallel digital data bits are required to operate the multiplexers used, generally, for electrode switching in ELT. More the electrodes in an EIT system more the digital data bits are needed. For a sixteen electrode system. 16 parallel digital data bits are required to operate the multiplexers in opposite or neighbouring current injection method. In this paper a common ground current injection is proposed for EIT and the resistivity imaging is studied. Common ground method needs only two analog multiplexers each of which need only 4 digital data bits and hence only 8 digital bits are required to switch the 16 surface electrodes. Results show that the USB based data acquisition system sequentially generate digital data required for multiplexers operating in common ground current injection method. The profile of the boundary data collected from practical phantom show that the multiplexers are operating in the required sequence in common ground current injection protocol. The voltage peaks obtained for all the inhomogeneity configurations are found at the accurate positions in the boundary data matrix which proved the sequential operation of multiplexers. Resistivity images reconstructed from the boundary data collected from the practical phantom with different configurations also show that the entire digital data generation module is functioning properly. Reconstructed images and their image parameters proved that the boundary data are successfully acquired by the DAQ system which in turn indicates a sequential and proper operation of multiplexers.

Harmonic Current Injection based Powerline Communication Method for Grid Connected Single Phase Inverters in Domestic Microgrids

The following paper presents a Powerline Communication (PLC) Method for Single Phase interfaced inverters in domestic microgrids. The PLC method is based on the injection of a repeating sequence of a specific harmonic, which is then modulated on the fundamental component of the grid current supplied by the inverters to the microgrid. The power flow and information exchange are simultaneously accomplished by the grid interacting inverters based on current programmed vector control, hence there is no need for dedicated hardware. Simulation results have been shown for inter-inverter communication under different operating conditions to propose the viability. These simulations have been experimentally validated and the corresponding results have also been presented in the paper.

High-power AlGaInP laser diodes with current-injection-free region near the laser facet

A high-power AlGaInP laser diode with current-injection-free region near the facet is successfully fabricated by metaorganic chemical vapor deposition (MOCVD) using the (100) direction n-GaAs substrates with a misorientation of 15 deg toward the (011) direction. The maximum continuous wave output power is about 90 mW for the traditional structure. In comparison, the maximum output power is enhanced by about 67%, and achieves 150 mW for LDs with current-infection-free regions. The fundamental transverse-mode operation is obtained up to 70 mW. Output characteristics at high temperatures are also improved greatly for an LD with a current-injection-free region, and the highest operation temperature is 70 C at 50 mW without kink. The threshold current is about 33 mA, the operation current and the slope efficiency at 100 mW are 120 mA and 0.9 mW/mA, respectively. The lasing wavelength is 658.4 nm at room-temperature 50 mW. (c) 2006 Society of Photo-Optical Instrumentation Engineers.

Current patch test results with the European baseline series and extensions to it from the 'European Surveillance System on Contact Allergy' network, 2007-2008

The pattern of contact sensitization to the supposedly most important allergens assembled in the baseline series differs between countries, presumably at least partly because of exposure differences. Objectives. To describe the prevalence of contact sensitization to allergens tested in consecutive patients in the years 2007 and 2008, and to discuss possible differences.

Chain-link based HVDC voltage source converter using current injection

VSC converters are becoming more prevalent for HVDC applications. Two circuits are commercially available at present, a traditional six-switch, PWM inverter, implemented using series connected IGBTs - ABBs HVDC Light®, and the other a modular multi-level converter (MMC) - Siemens HVDC-PLUS. This paper presents an alternative MMC topology, which utilises a novel current injection technique, and exhibits several desirable characteristics.

A high-power-factor, three-phase isolated AC-DC converter using high-frequency current injection

A single-stage, three-phase AC-to-DC converter topology is proposed for high-frequency power supply applications. The principal features of the circuit include continuous current operation of the three AC input inductors, inherent shaping of the input currents, resulting in high power factor, a transformer isolated output, and only two active devices are required, both soft-switched. Resonant conversion techniques are used, and a high power factor is achieved by injecting high-frequency currents into the three-phase rectifier, producing a high frequency modulation of the rectifier input voltages. The current injection principle is explained and the system operation is confirmed by a combination of simulation and experimental results.

Method to Improve the Linearity of Active Commutating Mixers Using Dynamic Current Injection

A double balanced (DBM) CMOS mixer providing high linearity is presented in this paper. A cross-coupled pair used in the IF stage of the mixer to dynamically inject current into the to mixer provide a high linearity. The proposed DBM was fabricated using a standard 130-nm CMOS process and was tested on-wafer. The double balanced mixer delivers 10 dB conversion gain, 9.5 dBm IIP3, and input P1dB of -2.4 dBm. RF bandwidth of the proposed mixer is 6 GHz, covering 0.5 GHz to 6.5 GHz with IF bandwidth of 300 MHz. RF to IF and LO to IF isolation are also better than 59 dB in the whole frequency band. The circuit uses an area of 0.015 mm2 excluding bonding pads and draw 4.5mW from a 1.2V supply.

Investigation of the hazards of substrate current injection: transient external latchup and substrate noise coupling

Substrate current injection is the origin of external latchup and substrate noise coupling. The trigger current for external latchup depends on the duration of the trigger event. A physics-based model is provided to model the effects of aggressor to victim spacing and orientation on transient triggering of external latchup. The latchup susceptibility of standard cell based designs is also investigated. Guard rings are used to reduce latchup susceptibility and to reduce the substrate noise coupled to sensitive analog circuits. In this work, the effectiveness of different guard ring topologies for the reduction of substrate noise coupling is also investigated.

Enhanced earth grid performance by improved conductor properties

Encroaching built environment with increased fault current levels is demanding a robust design approach and prolonged improved performance of the earth grid. With this in mind, the aim of the project was to perform a sensitivity analysis of the earth grid and an earthing performance evaluation with graphene coated conductors. Subsequent to these, a conceptual design to continuously monitor the performance of the earth grid was developed. In this study, earth grid design standards were compared to evaluate their appropriate use in determining the safety condition. A process to grow a thin film of graphene on the surface of cylindrical copper rods was developed to evaluate earthing performance in terms of conductivity and corrosion susceptibility.

Studying the resistivity imaging of chicken tissue phantoms with different current patterns in Electrical Impedance Tomography (EIT)

A current injection pattern in Electrical Impedance Tomography (EIT) has its own current distribution profile within the domain under test. Hence, different current patterns have different sensitivity, spatial resolution and distinguishability. Image reconstruction studies with practical phantoms are essential to assess the performance of EIT systems for their validation, calibration and comparison purposes. Impedance imaging of real tissue phantoms with different current injection methods is also essential for better assessment of the biomedical EIT systems. Chicken tissue paste phantoms and chicken tissue block phantoms are developed and the resistivity image reconstruction is studied with different current injection methods. A 16-electrode array is placed inside the phantom tank and the tank is filled with chicken muscle tissue paste or chicken tissue blocks as the background mediums. Chicken fat tissue, chicken bone, air hole and nylon cylinders are used as the inhomogeneity to obtained different phantom configurations. A low magnitude low frequency constant sinusoidal current is injected at the phantom boundary with opposite and neighboring current patterns and the boundary potentials are measured. Resistivity images are reconstructed from the boundary data using EIDORS and the reconstructed images are analyzed with the contrast parameters calculated from their elemental resistivity profiles. Results show that the resistivity profiles of all the phantom domains are successfully reconstructed with a proper background resistivity and high inhomogeneity resistivity for both the current injection methods. Reconstructed images show that, for all the chicken tissue phantoms, the inhomogeneities are suitably reconstructed with both the current injection protocols though the chicken tissue block phantom and opposite method are found more suitable. It is observed that the boundary potentials of the chicken tissue block phantoms are higher than the chicken tissue paste phantom. SNR of the chicken tissue block phantoms are found comparatively more and hence the chicken tissue block phantom is found more suitable for its lower noise performance. The background noise is found less in opposite method for all the phantom configurations which yields the better resistivity images with high PCR and COC and proper IRMean and IRMax neighboring method showed higher noise level for both the chicken tissue paste phantoms and chicken tissue block phantoms with all the inhomogeneities. Opposite method is found more suitable for both the chicken tissue phantoms, and also, chicken tissue block phantoms are found more suitable compared to the chicken tissue paste phantom. (C) 2012 Elsevier Ltd. All rights reserved.

Spin injection into a metal from a topological insulator

We study a junction of a topological insulator with a thin two-dimensional nonmagnetic or partially polarized ferromagnetic metallic film deposited on a three-dimensional insulator. We show, by deriving generic boundary conditions applicable to electrons traversing the junction, that there is a finite spin-current injection into the film whose magnitude can be controlled by tuning a voltage V applied across the junction. For ferromagnetic films, the direction of the component of the spin current along the film magnetization can also be tuned by tuning the barrier potential V-0 at the junction. We point out the role of the chiral spin-momentum locking of the Dirac electrons behind this phenomenon and suggest experiments to test our theory.

Theory and Application of the Transient Injection Well Test

Based on the theory of the pumping well test, the transient injection well test was suggested in this paper. The design method and the scope of application are discussed in detail. The mathematical models are developed for the short-time and long-time transient injection test respectively. A double logarithm type curve matching method was introduced for analyzing the field transient injection test data. A set of methods for the transient injection test design, experiment performance and data analysis were established. Some field tests were analyzed, and the results show that the test model and method are suitable for the transient injection test and can be used to deal with the real engineering problems.

Test results of a superconducting fault current limiter using YBCO coated conductor

A single-phase superconducting fault current limiter (SFCL) using a 0.9 m length of YBCO coated conductor (CC) tape was tested in 220 V-60 Hz line for fault current up to 1 kA, operating in 77 K. In this work are presented the IN experimental curves measured under DC and AC currents for the electrical characterization of the CC tape in order to design a low voltage current limiter. The experimental setup is described and the test results are presented for a unit conducting a steady nominal AC current of 50 A and also during the fault time (I to 5 cycles.) the performance of the CC-based SFCL providing the limiting resistance developed in the whole tape length after few milliseconds of the beginning of the fault was analyzed.