A linearly tunable low-voltage CMOS transconductor with improved common-mode stability and its application to (gm)-C filters

A linearly tunable low-voltage CMOS transconductor featuring a new adaptative-bias mechanism that considerably improves the stability of the processed-signal common,mode voltage over the tuning range, critical for very-low voltage applications, is introduced. It embeds a feedback loop that holds input devices on triode region while boosting the output resistance. Analysis of the integrator frequency response gives an insight into the location of secondary poles and zeros as function of design parameters. A third-order low-pass Cauer filter employing the proposed transconductor was designed and integrated on a 0.8-mum n-well CMOS standard process. For a 1.8-V supply, filter characterization revealed f(p) = 0.93 MHz, f(s) = 1.82 MHz, A(min) = 44.08, dB, and A(max) = 0.64 dB at nominal tuning. Mined by a de voltage V-TUNE, the filter bandwidth was linearly adjusted at a rate of 11.48 kHz/mV over nearly one frequency decade. A maximum 13-mV deviation on the common-mode voltage at the filter output was measured over the interval 25 mV less than or equal to V-TUNE less than or equal to 200 mV. For V-out = 300 mV(pp) and V-TUNE = 100 mV, THD was -55.4 dB. Noise spectral density was 0.84 muV/Hz(1/2) @1 kHz and S/N = 41 dB @ V-out = 300 mV(pp) and 1-MHz bandwidth. Idle power consumption was 1.73 mW @V-TUNE = 100 mV. A tradeoff between dynamic range, bandwidth, power consumption, and chip area has then been achieved.

Direct power control with common mode voltage elimination for open-winding brushless doubly-fed wind power generators

In this paper, a new open-winding control strategy is proposed for a brushless doubly-fed reluctance generator (BDFRG) applicable for wind turbines. The BDFRG control winding is fed via a dual two-level three-phase converter using a single dc bus. Direct power control based on maximum power point tracking with common mode voltage elimination is designed, which not only the active and reactive power is decoupled, but the reliability and redundancy are all improved greatly by increasing the switching modes of operation, while DC-link voltage and rating of power devices decreased by 50% comparing to the traditional three-level converter systems. Consequently its effectiveness is evaluated by simulation tests based on a 42-kW prototype generator.

Stability Condition Based Sliding Mode Modulators for Multilevel Power Converters

Sliding mode controllers for power converters usually employ hysteresis comparators to directly generate the power semiconductors switching states. This paper presents a new sliding mode modulator based on the direct implementation of the sliding mode stability condition, which for multilevel power converters shows advantages, as branch equalized switching frequencies and less distortion on the ac currents when operating near the rated converter power. The new sliding mode multilevel modulator is used to control a three-phase multilevel converter, operated as a reactive power compensator (STATCOM), implementing the stability condition in a digital signal processing system. The performance of this new sliding mode modulator is compared with a multilevel modulator based on hysteresis comparators. Simulation and experimental results are presented in order to highlight the system operation and control robustness.

On designing linearly-tunable ultra-low voltage CMOS gm-C filters

A linearly-tunable ULV transconductor featuring excellent stability of the processed signal common-mode voltage upon tuning, critical for very-low voltage applications, is presented. Its employment to the synthesis of CMOS gm-C high-frequency and voiceband filters is discussed. SPICE data describe the filter characteristics. For a 1.3 V-supply, their nominal passband frequencies are 1.0 MHz and 3.78 KHz, respectively, with tuning rates of 12.52 KHz/mV and 0.16 KHz/m V, input-referred noise spectral density of 1.3 μV/Hz1/2 and 5.0μV/Hz1/2 and standby consumption of 0.87 mW and 11.8 μW. Large-signal distortion given by THD = 1% corresponds to a differential output-swing of 360 mVpp and 480 mVpp, respectively. Common-mode voltage deviation is less than 4 mV over tuning interval.

A low-voltage programmable-gain CMOS amplifier with very-low temperature-drift

A new topology for a LVLP variable-gain CMOS amplifier is presented. Input- and load-stage are built around triode-transconductors so that voltage-gain is fully defined by a linear relationship involving only device-geometries and biases. Excellent gain-accuracy, temperature-insensitivity; and wide range of programmability, are thus achieved. Moreover, adaptative biasing improves the common-mode voltage stability upon gain-adjusting. As an example, a 0-40dB programmablegain audio-amplifier is designed. Its performance is supported by a range of simulations. For VDD=1.8V and 20dB-nominal gain, one has Av=19.97dB, f3db=770KHz and quiescent dissipation of 378μW. Over temperatures from -25°C to 125°C, the 0. ldB-bandwidth is 52KHz. Dynamic-range is optimized to 57.2dB and 42.6dB for gains of 20dB and 40dB, respectively. THD figures correspond to -60.6dB@Vout= 1Vpp and -79.7dB@Vout= 0.5 Vpp. A nearly constant bandwidth for different gains is also attained.

High performance liquid level monitoring system based on polymer fiber Bragg gratings embedded in silicone rubber diaphragm

Liquid-level sensing technologies have attracted great prominence, because such measurements are essential to industrial applications, such as fuel storage, flood warning and in the biochemical industry. Traditional liquid level sensors are based on electromechanical techniques; however they suffer from intrinsic safety concerns in explosive environments. In recent years, given that optical fiber sensors have lots of well-established advantages such as high accuracy, costeffectiveness, compact size, and ease of multiplexing, several optical fiber liquid level sensors have been investigated which are based on different operating principles such as side-polishing the cladding and a portion of core, using a spiral side-emitting optical fiber or using silica fiber gratings. The present work proposes a novel and highly sensitive liquid level sensor making use of polymer optical fiber Bragg gratings (POFBGs). The key elements of the system are a set of POFBGs embedded in silicone rubber diaphragms. This is a new development building on the idea of determining liquid level by measuring the pressure at the bottom of a liquid container, however it has a number of critical advantages. The system features several FBG-based pressure sensors as described above placed at different depths. Any sensor above the surface of the liquid will read the same ambient pressure. Sensors below the surface of the liquid will read pressures that increase linearly with depth. The position of the liquid surface can therefore be approximately identified as lying between the first sensor to read an above-ambient pressure and the next higher sensor. This level of precision would not in general be sufficient for most liquid level monitoring applications; however a much more precise determination of liquid level can be made by linear regression to the pressure readings from the sub-surface sensors. There are numerous advantages to this multi-sensor approach. First, the use of linear regression using multiple sensors is inherently more accurate than using a single pressure reading to estimate depth. Second, common mode temperature induced wavelength shifts in the individual sensors are automatically compensated. Thirdly, temperature induced changes in the sensor pressure sensitivity are also compensated. Fourthly, the approach provides the possibility to detect and compensate for malfunctioning sensors. Finally, the system is immune to changes in the density of the monitored fluid and even to changes in the effective force of gravity, as might be obtained in an aerospace application. The performance of an individual sensor was characterized and displays a sensitivity (54 pm/cm), enhanced by more than a factor of 2 when compared to a sensor head configuration based on a silica FBG published in the literature, resulting from the much lower elastic modulus of POF. Furthermore, the temperature/humidity behavior and measurement resolution were also studied in detail. The proposed configuration also displays a highly linear response, high resolution and good repeatability. The results suggest the new configuration can be a useful tool in many different applications, such as aircraft fuel monitoring, and biochemical and environmental sensing, where accuracy and stability are fundamental. © (2015) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

Design of switched-capacitor filters using low gain amplifiers

Dissertação para obtenção do Grau de Mestre em Engenharia Electrotécnica e de Computadores

Lausannevirus Seroprevalence among Asymptomatic Young Adults.

Objectives: The giant Lausannevirus was recently identified as a parasite of amoeba that replicates rapidly in these professional phagocytes. This study aimed at assessing Lausannevirus seroprevalence among asymptomatic young men in Switzerland and hopefully identifying possible sources of contact with this giant virus. Methods: The presence of anti-Lausannevirus antibodies was assessed in sera from 517 asymptomatic volunteers who filled a detailed questionnaire. The coreactivity between Lausannevirus and amoeba-resisting bacteria was assessed. Results: Lausannevirus prevalence ranged from 1.74 to 2.51%. Sporadic condom use or multiple sexual partners, although frequent (53.97 and 60.35%, respectively), were not associated with anti-Lausannevirus antibodies. On the contrary, frequent outdoor sport practice as well as milk consumption were significantly associated with positive Lausannevirus serologies (p = 0.0066 and 0.028, respectively). Coreactivity analyses revealed an association between Criblamydia sequanensis (an amoeba-resisting bacterium present in water environments) and Lausannevirus seropositivity (p = 0.001). Conclusions: Lausannevirus seroprevalence is low in asymptomatic Swiss men. However, the association between virus seropositivity and frequent sport practice suggests that this member of the Megavirales may be transmitted by aerosols and/or exposure to specific outdoor environments. Milk intake was also associated with seropositivity. Whether the coreactivity observed for C. sequanensis and Lausannevirus reflects a common mode of acquisition or some unexpected cross-reactivity remains to be determined. © 2013 S. Karger AG, Basel.

Epidemiology of Chagas disease in non endemic countries: the role of international migration

Human infection with the protozoa Trypanosoma cruzi extends through North, Central, and South America, affecting 21 countries. Most human infections in the Western Hemisphere occur through contact with infected bloodsucking insects of the triatomine species. As T. cruzi can be detected in the blood of untreated infected individuals, decades after infection took place; the infection can be also transmitted through blood transfusion and organ transplant, which is considered the second most common mode of transmission for T. cruzi. The third mode of transmission is congenital infection. Economic hardship, political problems, or both, have spurred migration from Chagas endemic countries to developed countries. The main destination of this immigration is Australia, Canada, Spain, and the United States. In fact, human infection through blood or organ transplantation, as well as confirmed or potential cases of congenital infections has been described in Spain and in the United States. Estimates reported here indicates that in Australia in 2005-2006, 1067 of the 65,255 Latin American immigrants (16 per 1000) may be infected with T. cruzi, and in Canada, in 2001, 1218 of the 131,135 immigrants (9 per 1000) whose country of origin was identified may have been also infected. In Spain, a magnet for Latin American immigrants since the 2000, 5125 of 241,866 legal immigrants in 2003 (25 per 1000), could be infected. In the United States, 56,028 to 357,205 of the 7,20 million, legal immigrants (8 to 50 per 1000), depending on the scenario, from the period 1981-2005 may be infected with T. cruzi. On the other hand, 33,193 to 336,097 of the estimated 5,6 million undocumented immigrants in 2000 (6 to 59 per 1000) could be infected. Non endemic countries receiving immigrants from the endemic ones should develop policies to protect organ recipients from T. cruzi infection, prevent tainting the blood supply with T. cruzi, and implement secondary prevention of congenital Chagas disease.

La fibrose rétropéritonéale, une maladie inflammatoire méconnue. Observations cliniques et revue de la littérature [Retroperitoneal fibrosis, an unrecognized inflammatory disease. Clinical observations and review of the literature]

Retroperitoneal fibrosis (RF) is a rare disease, typically with an insidious clinical course. The peak incidence is seen in patients 40 to 60 years of age and mostly in man. The characteristic finding in this disease is a periaortic fibrous mass that often surrounds the ureters. Although usually regarded as an obstructive uropathy, there has been growing recognition of the condition as a generalized disease. It may have a wide variety of manifestations including mediastinitis, thyroiditis and sclerosing cholangitis. The most common mode of presentation remains abdominal or flank pain with uremia, anemia and a high sedimentation rate. Although ultrasound and renal scintigraphy may contribute to the general evaluation of patients with RF, CT-scanner is the preferred imaging method. The multiplanar imaging capability of magnetic resonance may facilitate assessment of disease extent. The pathogenesis of the disease remains unknown. Steroids and, more recently tamoxifen, appear to be effective in the treatment of the RF. In most instances, RF does not lead to long-term morbidity or affect survival. The three cases of RF reported herein illustrate the varied mode of presentation and the response to the treatment.

Xenopus peroxisome proliferator activated receptors: genomic organization, response element recognition, heterodimer formation with retinoid X receptor and activation by fatty acids.

Peroxisome proliferator activated receptors are ligand activated transcription factors belonging to the nuclear hormone receptor superfamily. Three cDNAs encoding such receptors have been isolated from Xenopus laevis (xPPAR alpha, beta, and gamma). Furthermore, the gene coding for xPPAR beta has been cloned, thus being the first member of this subfamily whose genomic organization has been solved. Functionally, xPPAR alpha as well as its mouse and rat homologs are thought to play an important role in lipid metabolism due to their ability to activate transcription of a reporter gene through the promoter of the acyl-CoA oxidase (ACO) gene. ACO catalyzes the rate limiting step in the peroxisomal beta-oxidation of fatty acids. Activation is achieved by the binding of xPPAR alpha on a regulatory element (DR1) found in the promoter region of this gene, xPPAR beta and gamma are also able to recognize the same type of element and are, as PPAR alpha, able to form heterodimers with retinoid X receptor. All three xPPARs appear to be activated by synthetic peroxisome proliferators as well as by naturally occurring fatty acids, suggesting that a common mode of action exists for all the members of this subfamily of nuclear hormone receptors.

Yhteismuotosuodatus taajuusmuuttajan lähdössä

Tässädiplomityössä selvitettiin taajuusmuuttajan synnyttämien yhteismuotoisten häiriöiden syntyä, ominaisuuksia, kulkureittejä sekä erilaisia tekniikoita toteuttaa yhteismuotosuodatus taajuusmuuttajan lähdössä. Työssä suunniteltiin ja mitoitettiin yhteismuotosuodatin, josta valmistettiin prototyyppi. Suodatinta testattiin laboratoriossa ja mittauksissa käytettiin erilaisia suodattimen kapasitanssin arvoja ja neutraalin pisteen kytkennän variaatioita. Mittauksilla selvitettiin suodattimen kyky suodattaa myös yhteismuotoisten jännitteiden lisäksi eromuotoista jännitettä, akselijännitettä ja vaihevirtaa. Mittaustulosten perusteella voitiin todeta suunnitellun suodattimen parantavan merkittävästi taajuusmuuttajalta moottorille syötettävän sähkön laatua ja loiventavan ennen kaikkea yhteismuotoisen jännitepulssin nousureunaa.

Effects of modern variable frequency drive on the reliability of an old crane induction motor

The work aims to analyze the possibilities of utilizing old crane driving AC induction motors in modern pulse-width-modulated variable frequency drives. Bearing currents and voltage stresses are the two main problems associated with modern IGBT inverters, and they may cause premature failure of an old induction motor. The origins of these two problems are studied. An analysis of the mechanism of bearing failure is proposed. Certain types of bearing currents are considered in detail. The most effective and economical means are chosen for bearing currents mitigation. Transient phenomena of cables and mechanism of over voltages occurring at motor terminals are studied in the work. The weakest places of the stator winding insulation system are shown and recommendations are given considering the mitigation of voltage stresses. Only the most appropriate and cost effective preventative methods are chosen for old motor drives. Rewinding of old motors is also considered.

Hybrid LC Filter for Power Electronic Drives: Theory and Implementation

Power electronic converter drives use, for the sake of high efficiency, pulse-width modulation that results in sequences of high-voltage high-frequency steep-edged pulses. Such a signal contains a set of high harmonics not required for control purposes. Harmonics cause reflections in the cable between the motor and the inverter leading to faster winding insulation ageing. Bearing failures and problems with electromagnetic compatibility may also result. Electrical du/dt filters provide an effective solution to problems caused by pulse-width modulation, thereby increasing the performance and service life of the electrical machines. It is shown that RLC filters effectively decrease the reflection phenomena in the cable. Improved (simple, but effective) solutions are found for both differential- and common-mode signals; these solutions use a galvanic connection between the RLC filter star point and the converter DC link. Foil chokes and film capacitors are among the most widely used components in high-power applications. In actual applications they can be placed in different parts of the cabinet. This fact complicates the arrangement of the cabinet and decreases the reliability of the system. In addition, the inductances of connection wires may prevent filtration at high frequencies. This thesis introduces a new hybrid LC filter that uses a natural capacitance between the turns of the foil choke based on integration of an auxiliary layer into it. The main idea of the hybrid LC filter results from the fact that both the foil choke and the film capacitors have the same roll structure. Moreover, the capacitance between the turns (“intra capacitance”) of the foil inductors is the reason for the deterioration of their properties at high frequencies. It is shown that the proposed filter has a natural cancellation of the intra capacitance. A hybrid LC filter may contain two or more foil layers isolated from each other and coiled on a core. The core material can be iron or even air as in the filter considered in this work. One of the foils, called the main foil, can be placed between the inverter and the motor cable. Other ones, called auxiliary foils, may be connected in star to create differential-mode noise paths, and then coupled to the DC link midpoint to guarantee a traveling path, especially for the common-mode currents. This way, there is a remarkable capacitance between the main foil and the auxiliary foil. Investigations showed that such a system can be described by a simple equivalent LC filter in a wide range of frequencies. Because of its simple hybrid construction, the proposed LC filter can be a cost-effective and competitive solution for modern power drives. In the thesis, the application field of the proposed filter is considered and determined. The basics of hybrid LC filter design are developed further. High-frequency behaviour of the proposed filter is analysed by simulations. Finally, the thesis presents experimental data proving that the hybrid LC filter can be used for du/dt of PWM pulses and reduction of common-mode currents.

Parallel-Operating Three-Phase Voltage Source Inverters – Circulating CurrentModeling, Analysis and Mitigation

The maximum realizable power throughput of power electronic converters may be limited or constrained by technical or economical considerations. One solution to this problemis to connect several power converter units in parallel. The parallel connection can be used to increase the current carrying capacity of the overall system beyond the ratings of individual power converter units. Thus, it is possible to use several lower-power converter units, produced in large quantities, as building blocks to construct high-power converters in a modular manner. High-power converters realized by using parallel connection are needed for example in multimegawatt wind power generation systems. Parallel connection of power converter units is also required in emerging applications such as photovoltaic and fuel cell power conversion. The parallel operation of power converter units is not, however, problem free. This is because parallel-operating units are subject to overcurrent stresses, which are caused by unequal load current sharing or currents that flow between the units. Commonly, the term ’circulatingcurrent’ is used to describe both the unequal load current sharing and the currents flowing between the units. Circulating currents, again, are caused by component tolerances and asynchronous operation of the parallel units. Parallel-operating units are also subject to stresses caused by unequal thermal stress distribution. Both of these problemscan, nevertheless, be handled with a proper circulating current control. To design an effective circulating current control system, we need information about circulating current dynamics. The dynamics of the circulating currents can be investigated by developing appropriate mathematical models. In this dissertation, circulating current models aredeveloped for two different types of parallel two-level three-phase inverter configurations. Themodels, which are developed for an arbitrary number of parallel units, provide a framework for analyzing circulating current generation mechanisms and developing circulating current control systems. In addition to developing circulating current models, modulation of parallel inverters is considered. It is illustrated that depending on the parallel inverter configuration and the modulation method applied, common-mode circulating currents may be excited as a consequence of the differential-mode circulating current control. To prevent the common-mode circulating currents that are caused by the modulation, a dual modulator method is introduced. The dual modulator basically consists of two independently operating modulators, the outputs of which eventually constitute the switching commands of the inverter. The two independently operating modulators are referred to as primary and secondary modulators. In its intended usage, the same voltage vector is fed to the primary modulators of each parallel unit, and the inputs of the secondary modulators are obtained from the circulating current controllers. To ensure that voltage commands obtained from the circulating current controllers are realizable, it must be guaranteed that the inverter is not driven into saturation by the primary modulator. The inverter saturation can be prevented by limiting the inputs of the primary and secondary modulators. Because of this, also a limitation algorithm is proposed. The operation of both the proposed dual modulator and the limitation algorithm is verified experimentally.