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.

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.

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.

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.

DC current rectification using indium-gallium zinc oxide-based selfswitching diodes

Self-switching diodes have been fabricated within a single layer of indium-gallium zinc oxide (IGZO). Current-voltage (I-V) measurements show the nanometer-scale asymmetric device gave a diode-like response. Full current rectification was achieved using very narrow channel widths of 50nm, with a turn-on voltage, Von, of 2.2V. The device did not breakdown within the -10V bias range measured. This single diode produced a current of 0.1μA at 10V and a reverse current of less than 0.1nA at -10V. Also by adjusting the channel width for these devices, Von could be altered; however, the effectiveness of the rectification also changed. © 2013 IEEE.

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.

Studies of high DC current induced degradation in III-V nitride based heterojunctions

We report experiments on high de current stressing in commercial III-V nitride based heterojunction light-emitting diodes. Stressing currents ranging from 100 mA to 200 mA were used. Degradations in the device properties were investigated through detailed studies of the current-voltage (I-V) characteristics, electroluminescence, deep-level transient Fourier spectroscopy and flicker noise. Our experimental data demonstrated significant distortions in the I-V characteristics subsequent to electrical stressing. The room temperature electro-luminescence of the devices exhibited a 25% decrement in the peak emission intensity. Concentration of the deep-levels was examined by deep-level transient Fourier spectroscopy, which indicated an increase in the density of deep-traps from 2.7 x 10(13) cm(-3) to 4.2 x 10(13) cm(-3) at E-1 = E-C - 1.1 eV. The result is consistent with our study of 1/f noise, which exhibited up to three orders of magnitude increase in the voltage noise power spectra. These traps are typically located at energy levels beyond the range that can be characterized by conventional techniques including DLTS. The two experiments, therefore, provide a more complete picture of trap generation due to high dc current stressing.

Spontaneous DC Current Generation in a Resistively Shunted Semiconductor Superlattice Driven by a TeraHertz Field

We study a resistively shunted semiconductor superlattice subject to a high-frequency electric field. Using a balance equation approach that incorporates the influence of the electric circuit, we determine numerically a range of amplitude and frequency of the ac field for which a dc bias and current are generated spontaneously and show that this region is likely accessible to current experiments. Our simulations reveal that the Bloch frequency corresponding to the spontaneous dc bias is approximately an integer multiple of the ac field frequency.

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.

Common mode DC bus filter for Active Front-End converter

Active Front-End (AFE) converter operation produces electrically noisy DC bus on common mode basis. This results in higher ground current as compared to three phase diode bridge rectifier. Filter topologies for DC bus have to deal problems with switching frequency and harmonic currents. The proposed filter approach reduces common mode voltage and circulates third harmonic current within the system, resulting in minimal ground current injection. The filtering technique, its constrains and design to attenuate common mode voltage and eliminate lower order harmonics injection to ground is discussed. The experimental results for operation of the converter with both SPWM and CSVPWM are presented.