Switched-Capacitor Voltage Doubler Design Using 0.5 μm Technology

While integrated circuit (IC) power management has been an eternal topic for chip designers, inductor based DC-DC converters have been dominant in the field for years. However, because of the natures of inductors: large electro-magnetic interference, high coupling noise, and difficult silicon fabrication process, they are not favorable to on-chip solutions. Switched-capacitor (SC) DC-DC converters, which adopt capacitors for their energy storage components, have become increasingly popular among both the academia and the industry, because, apparently, they avoid the drawbacks of the inductor counterparts, and can be directly implemented on-chip without additional fabrication process. In this paper, we will investigate one of the most famous SC voltage doubler topologies, which is known as Favrat Cell . By designing a chip, which converts 1.5 V voltage input to 2.5 V voltage output at 1 mA current load, we will walk through the details of a SC DC-DC converter design, including the switch cell, timing system, regulation loop and efficiency analysis. The design uses two 200 pF pumping capacitors and a 400 pF output capacitor in On-Semi half-micron technology. Four-way interleaved phase structure is adopted to reduce the output voltage ripple. The gate-drive strategy of the switches has been improved to further reduce the reverse current injections during transitions. A new high-ratio voltage booster topology based on the cross-coupled topology has been introduced and will be discussed in comparison with the Dickson charge pump topology

New protection algorithms for HVDC grids

233 p.Los sistemas HVDC representan una alternativa prometedora para futuras expansiones del sistema eléctrico gracias a las ventajas que presentan en comparación con el transporte convencional en corriente alterna. Además, el interés por desarrollar redes HVDC multiterminales ha crecido en los últimos años, sin embargo, su implementación se ha visto ralentizada debido a la complejidad que presenta la protección ante faltas en estos sistemas. El objetivo principal de esta tesis es proponer un nuevo algoritmo de protección contra faltas, apropiado para dichas redes y capaz de superar las limitaciones presentes en algoritmos existentes. El algoritmo propuesto es un algoritmo de tensión de inductancia basado en el cálculo del ratio entre las medidas de tensión tomadas a ambos lados de la inductancia limitadora y la derivada de dicho ratio. Es capaz de detectar faltas rápidamente y de discriminar de manera selectiva entre faltas dentro y fuera de la zona de protección. También se propone una metodología para la selección del valor umbral necesario para la operación de algoritmos locales. A continuación, sedesarrolla un esquema de protección completo que se compone de protecciones de línea primaria y de respaldo, protección de barra y protección ante fallo del interruptor. Esta última protección es, así mismo, un nuevo algoritmo propuesto en la tesis, que presenta una operación más rápida que algoritmos convencionales de detección de fallo en el interruptor. Finalmente, la operación del esquema de protección propuesto es validada y analizada a través de simulaciones en un modelo de red de cuatro terminales con diferentes escenarios de falta, comparándolo con algoritmos existentes

Trapping and Reliability Investigations in GaN-based HEMTs

GaN-based high electron mobility transistors (HEMTs) are promising candidates for future microwave equipment, such as new solid state power amplifiers (SSPAs), thanks to their excellent performance. A first demonstration of GaN-MMIC transmitter has been developed and put on board the PROBA-V mission. But this technology still suffers from the trapping phenomena, principally due to lattice defects. Thus, the aim of this research is to investigate the trapping effects and the reliability aspects of the GH50 power transistors for C-band applications. A new trap investigation protocol to obtain a complete overview of trap behavior from DC to radio-frequency operation modes, based on combined pulsed I/V measurements, DC and RF drain current measurements, and low-frequency dispersion measurements, is proposed. Furthermore, a nonlinear electro-thermal AlGaN/GaN model with a new additive thermal-trap model including the dynamic behavior of these trap states and their associated temperature variations is presented, in order to correctly predict the RF performance during real RF operating conditions. Finally, an advanced time-domain methodology is presented in order to investigate the device’s reliability and to determine its safe operating area. This methodology is based on the continual monitoring of the RF waveforms and DC parameters under overdrive conditions in order to assess the degradation of the transistor characteristics in the RF power amplifier

Hydrogenation of Cast-Mono Silicon Solar Cells

Cast-mono silicon is a potential alternative to monocrystalline silicon solar cells as it produces mono-like silicon wafers using the cost effective process used for multicrystalline silicon wafers. This material has shown to have flaws in the ingot growth process which are mainly the propagation of dislocations during the casting of ingots. The crystallographic properties of these dislocations have been studied and their influence on solar cells produced from this material has been observed. In this thesis different regions of cast-mono silicon ingots (from mono-like to heavily dislocated areas) are studied using lifetime test structures and solar cells manufactured from these regions. The fundamental limitations are identified and presented using standard photovoltaic characterization methods. Hydrogenation has been introduced and implemented in this work as a method of overcoming the limiting defects caused by dislocations in cast-mono silicon. The efficacy of various hydrogenation methods is presented. Changes in the limitations identified in the previous section were observed and analyzed. The maximum benefit of hydrogenation in dislocated areas is shown in this work. Cells and lifetime test structures that were not hydrogenated and hydrogenated were light soaked at elevated temperatures to test their stability in regards to the improvement that was obtained in the dislocated regions. It was shown how stable cast-mono solar cells are before and after hydrogenation and if the benefits of hydrogenation remain after a long duration of light soaking. It was concluded that dislocations are a dominant and problematic defect in cast-mono solar cells with severe losses in the silicon bulk. Hydrogenation can be an effective method for mitigating these effects and improving the performance of cast-mono solar cells. Cast-mono solar cells degrade similar to their multicrystalline counterparts grown using the casting ingot growth method. Hydrogenation can be used to both mitigate and slow down degradation but the dislocations degrade regardless and do not recover after degradation

The thermal properties of an SF6 circuit breaker arc during the current zero period

High speed photographic and time and space resolved spectroscopic investigations have been undertaken to quantify the processes governing arc thermal reignition phenomena. A fixed nozzle and electrode geometry was used with SF6 as the host gas. A sonic flow of gas at the nozzle throat was sustained using an upstream vessel pressure of 7.8 psig. A 35.5mF capacitor bank was used to supply electrical energy for reduced and full power arcing tests using different circuit configurations. Sophisticated optical diagnostic instrumentation has enabled photographic and spectroscopic investigations with high time and space resolution to be made during the current zero period of both the full and reduced power arcing cases. The results of above experimental investigations are of value in determining the thermal structure and the processes governing thermal reignition of the circuit breaker arc of the present investigation. In particular, temperature profiles derived from the above investigations have been used to quantify the important terms of the dynamic current zero energy balance. Experimental investigations have thus been performed during the critical current zero period of a full power circuit breaker arc. The significance of these results has been realised in evaluating the current zero temperature profiles and subsequently the energy conservation equation terms for severe circuit breaking condition

Capacitor Commutation Method for MVDC Hybrid Circuit Breakers

The medium voltage DC (MVDC) type system can connect multiple terminals to a common MVDC bus, so it is possible to connect several renewable DC power sources to the common MVDC bus, but a DC circuit breaker is needed to isolate short circuit accidents that may occur in the MVDC bus. For this purpose, the concept of a hybrid DC circuit breaker that takes advantage of a low conduction loss contact type switch and an arcless-breaking semiconductor switch has been proposed. During break the hybrid switch, a dedicated current commutation device is required to temporarily bypass the load current flowing through the main switch into a semiconductor switch branch. Existing current commutation methods include a proactive method and a reverse current injection method by a LC (Inductor-capacitor) resonant circuit. This paper proposes a power circuit of a new MVDC hybrid circuit breaker using a low withstanding voltage capacitor branch for commutation and a sequence controller according to it, and verifies its operation through an experiment