Temperature and time dependent threshold voltage characterization of AlGaN/GaN high electron mobility transistors

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Current Mode with RMS Voltage and Offset Control Loops for a Single-Phase Aircraft Inverter Suitable for Parallel and 3-Phase Operation Modes

Rms voltage regulation may be an attractive possibility for controlling power inverters. Combined with a Hall Effect sensor for current control, it keeps its parallel operation capability while increasing its noise immunity, which may lead to a reduction of the Total Harmonic Distortion (THD). Besides, as voltage regulation is designed in DC, a simple PI regulator can provide accurate voltage tracking. Nevertheless, this approach does not lack drawbacks. Its narrow voltage bandwidth makes transients last longer and it increases the voltage THD when feeding non-linear loads, such as rectifying stages. On the other hand, the implementation can fall into offset voltage error. Furthermore, the information of the output voltage phase is hidden for the control as well, making the synchronization of a 3-phase setup not trivial. This paper explains the concept, design and implementation of the whole control scheme, in an on board inverter able to run in parallel and within a 3-phase setup. Special attention is paid to solve the problems foreseen at implementation level: a third analog loop accounts for the offset level is added and a digital algorithm guarantees 3-phase voltage synchronization.

Signal analysis and feature generation for pattern identification of partial discharges in high-voltage equipment

This paper proposes a method for the identification of different partial discharges (PDs) sources through the analysis of a collection of PD signals acquired with a PD measurement system. This method, robust and sensitive enough to cope with noisy data and external interferences, combines the characterization of each signal from the collection, with a clustering procedure, the CLARA algorithm. Several features are proposed for the characterization of the signals, being the wavelet variances, the frequency estimated with the Prony method, and the energy, the most relevant for the performance of the clustering procedure. The result of the unsupervised classification is a set of clusters each containing those signals which are more similar to each other than to those in other clusters. The analysis of the classification results permits both the identification of different PD sources and the discrimination between original PD signals, reflections, noise and external interferences. The methods and graphical tools detailed in this paper have been coded and published as a contributed package of the R environment under a GNU/GPL license.

Voltage recovery in intermediate band solar cells

The intermediate band solar cell (IBSC) is based on a novel photovoltaic concept and has a limiting efficiency of 63.2%, which compares favorably with the 40.7% efficiency of a conventional, single junction solar cell. It is characterized by a material hosting a collection of energy levels within its bandgap, allowing the cell to exploit photons with sub-bandgap energies in a two-step absorption process, thus improving the utilization of the solar spectrum. However, these intermediate levels are often regarded as an inherent source of supplementary recombination, although this harmful effect can in theory be counteracted by the use of concentrated light. We present here a novel, low-temperature characterization technique using concentrated light that reveals how the initially enhanced recombination in the IBSC is reduced so that its open-circuit voltage is completely recovered and reaches that of a conventional solar cell.

High-efficiency voltage regulator and stabilizer for outdoor lighting installations

This paper presents a high performance system of regulation and stabilization of luminous flux for public street lighting installations. Its purpose is to reduce the luminous flux of the luminaries efficiently by reducing their voltage supply, resulting in the improvement of energy efficiency in the installation. The system is basically composed of electromagnetic components which provide robustness and high-performance to the device, as well as minimum maintenance requirements. However, the voltage regulation is based on the application of voltage steps. Aging studies of the luminaries have been carried out to analyze the impact of this discrete voltage regulation. A specific prototype of this voltage and stabilizer regulator have been in operation in a real outdoor lighting installation for more than one year.

Sensorless explicit model predictive control for multi-phase buck converters with variable output voltage

The purpose of this paper is to use the predictive control to take advantage of the future information in order to improve the reference tracking. The control attempts to increase the bandwidth of the conventional regulators by using the future information of the reference, which is supposed to be known in advance. A method for designing a controller is also proposed. A comparison in simulation with a conventional regulator is made controlling a four-phase Buck converter. Advantages and disadvantages are analyzed based on simulation results.

Comparison of V2IC control with voltage mode and current mode controls for high frequency (MHz) and very fast response applications

High switching frequencies (several MHz) allow the integration of low power DC/DC converters. Although, in theory, a high switching frequency would make possible to implement a conventional Voltage Mode control (VMC) or Peak Current Mode control (PCMC) with very high bandwidth, in practice, parasitic effects and robustness limits the applicability of these control techniques. This paper compares VMC and CMC techniques with the V2IC control. This control is based on two loops. The fast internal loop has information of the output capacitor current and the error voltage, providing fast dynamic response under load and voltage reference steps, while the slow external voltage loop provides accurate steady state regulation. This paper shows the fast dynamic response of the V2IC control under load and output voltage reference steps and its robustness operating with additional output capacitors added by the customer.

Current-voltage response of a spherical plasma contactor

A theoretical model for a contactor, collecting electrons from an ambient, unmagnetized plasma and emitting a current Iiis discussed. The relation between Ii and the potential bias of the contactor is found to be crucial for the formation of a quasineutral core around the anode and, consequently, for the current colleted. Approximate analytical laws and charts for the current-voltage response are provided.

Low Voltage Ride-through in DFIG Wind Generators by Controlling the Rotor Current without Crowbars

Among all the different types of electric wind generators, those that are based on doubly fed induction generators, or DFIG technology, are the most vulnerable to grid faults such as voltage sags. This paper proposes a new control strategy for this type of wind generator, that allows these devices to withstand the effects of a voltage sag while following the new requirements imposed by grid operators. This new control strategy makes the use of complementary devices such as crowbars unnecessary, as it greatly reduces the value of currents originated by the fault. This ensures less costly designs for the rotor systems as well as a more economic sizing of the necessary power electronics. The strategy described here uses an electric generator model based on space-phasor theory that provides a direct control over the position of the rotor magnetic flux. Controlling the rotor magnetic flux has a direct influence on the rest of the electrical variables enabling the machine to evolve to a desired work point during the transient imposed by the grid disturbance. Simulation studies have been carried out, as well as test bench trials, in order to prove the viability and functionality of the proposed control strategy.

Transformer-coupled converter for voltage modulation techniques

In high performance digital systems as well as in RF systems, voltage scaling and modulation techniques have been adopted to achieve a more efficient processing of the energy. The implementation of such techniques relies on a power supply that is capable of rapidly adjusting the system supply voltage. In this paper, a pulsewidth modulation multiphase topology with magnetic coupling is proposed for its use in voltage modulation techniques. Since the magnetic coupling in this topology is done with transformers instead of coupled inductors, the energy storage is reduced and very fast voltage changes are achieved. Advantages and drawbacks of this topology have been previously presented in the literature and in this paper, the design criteria for implementing a power supply for the envelope elimination and restoration technique in an RF system are presented along with an implementation of the power supply.

Real time power plant simulation platform for training on Electrical Protections and Automatic Voltage Regulators

Electrical Protection systems and Automatic Voltage Regulators (AVR) are essential components of actual power plants. Its installation and setting is performed during the commissioning, and it needs extensive experience since any failure in this process or in the setting, may entails some risk not only for the generator of the power plant, but also for the reliability of the power grid. In this paper, a real time power plant simulation platform is presented as a tool for improving the training and learning process on electrical protections and automatic voltage regulators. The activities of the commissioning procedure which can be practiced are described, and the applicability of this tool for improving the comprehension of this important part of the power plants is discussed. A commercial AVR and a multifunction protective relay have been tested with satisfactory results.

Signal analysis and feature generation for pattern identification of partial discharges in high-voltage equipment

This paper proposes a method for the identification of different partial discharges (PDs) sources through the analysis of a collection of PD signals acquired with a PD measurement system. This method, robust and sensitive enough to cope with noisy data and external interferences, combines the characterization of each signal from the collection, with a clustering procedure, the CLARA algorithm. Several features are proposed for the characterization of the signals, being the wavelet variances, the frequency estimated with the Prony method, and the energy, the most relevant for the performance of the clustering procedure. The result of the unsupervised classification is a set of clusters each containing those signals which are more similar to each other than to those in other clusters. The analysis of the classification results permits both the identification of different PD sources and the discrimination between original PD signals, reflections, noise and external interferences. The methods and graphical tools detailed in this paper have been coded and published as a contributed package of the R environment under a GNU/GPL license.

Voltage limitation analysis in strain-balanced InAs/GaAsN quantum dot solar cells applied to the intermediate band concept

Several attempts have been carried out to manufacture intermediate band solar cells (IBSC) by means of quantum dot (QD) superlattices. This novel photovoltaic concept allows the collection of a wider range of the sunlight spectrum in order to provide higher cell photocurrent while maintaining the open-circuit voltage (VOC) of the cell. In this work, we analyze InAs/GaAsN QD-IBSCs. In these cells, the dilute nitrogen in the barrier plays an important role for the strain-balance (SB) of the QD layer region that would otherwise create dislocations under the effect of the accumulated strain. The introduction of GaAsN SB layers allows increasing the light absorption in the QD region by multi-stacking more than 100 QD layers. The photo-generated current density (JL) versus VOC was measured under varied concentrated light intensity and temperature. We found that the VOC of the cell at 20 K is limited by the bandgap of the GaAsN barriers, which has important consequences regarding IBSC bandgap engineering that are also discussed in this work.

SVD Applied to Voltage Sag State Estimation

The method presented in this paper addresses the problem of voltage sag state estimation (VSSE). The problem consists in estimating the voltage sags frequency at non-monitored buses from the number of sags measured at monitored sites. Usually, due to limitations on the number of available voltage sag monitors, this is an underdetermined problem. In this approach, the mathematical formulation presented is based on the fault positions concept and is solved by means of the Singular Value Decomposition (SVD) technique. The proposed estimation method has been validated by using the IEEE 118 test system and the results obtained have been very satisfactory.

Two-photon photocurrent and voltage up-conversion in a quantum dot intermediate band solar cell

It has been proposed that the use of self-assembled quantum dot (QD) arrays can break the Shockley-Queisser efficiency limit by extending the absorption of solar cells into the low-energy photon range while preserving their output voltage. This would be possible if the infrared photons are absorbed in the two sub-bandgap QD transitions simultaneously and the energy of two photons is added up to produce one single electron-hole pair, as described by the intermediate band model. Here, we present an InAs/Al 0.25Ga 0.75As QD solar cell that exhibits such electrical up-conversion of low-energy photons. When the device is monochromatically illuminated with 1.32 eV photons, open-circuit voltages as high as 1.58 V are measured (for a total gap of 1.8 eV). Moreover, the photocurrent produced by illumination with photons exciting the valence band to intermediate band (VB-IB) and the intermediate band to conduction band (IB-CB) transitions can be both spectrally resolved. The first corresponds to the QD inter-band transition and is observable for photons of energy mayor que 1 eV, and the later corresponds to the QD intra-band transition and peaks around 0.5 eV. The voltage up-conversion process reported here for the first time is the key to the use of the low-energy end of the solar spectrum to increase the conversion efficiency, and not only the photocurrent, of single-junction photovoltaic devices. In spite of the low absorption threshold measured in our devices - 0.25 eV - we report open-circuit voltages at room temperature as high as 1.12 V under concentrated broadband illumination.