Real-time temperature estimation for power MOSFETs considering thermal ageing effects

This paper presents a novel real-time power-device temperature estimation method that monitors the power MOSFET's junction temperature shift arising from thermal aging effects and incorporates the updated electrothermal models of power modules into digital controllers. Currently, the real-time estimator is emerging as an important tool for active control of device junction temperature as well as online health monitoring for power electronic systems, but its thermal model fails to address the device's ongoing degradation. Because of a mismatch of coefficients of thermal expansion between layers of power devices, repetitive thermal cycling will cause cracks, voids, and even delamination within the device components, particularly in the solder and thermal grease layers. Consequently, the thermal resistance of power devices will increase, making it possible to use thermal resistance (and junction temperature) as key indicators for condition monitoring and control purposes. In this paper, the predicted device temperature via threshold voltage measurements is compared with the real-time estimated ones, and the difference is attributed to the aging of the device. The thermal models in digital controllers are frequently updated to correct the shift caused by thermal aging effects. Experimental results on three power MOSFETs confirm that the proposed methodologies are effective to incorporate the thermal aging effects in the power-device temperature estimator with good accuracy. The developed adaptive technologies can be applied to other power devices such as IGBTs and SiC MOSFETs, and have significant economic implications.

Vaihtosuuntaajan reaaliaikainen lämpömalli

Vaihtosuuntaajan IGBT-moduulin liitosten lämpötiloja ei voida suoraan mitata, joten niiden arviointiin tarvitaan reaaliaikainen lämpömalli. Tässä työssä on tavoitteena kehittää tähän tarkoitukseen C-kielellä implementoitu ratkaisu, joka on riittävän tarkka ja samalla mahdollisimman laskennallisesti tehokas. Ohjelmallisen toteutuksen täytyy myös sopia erilaisille moduulityypeille ja sen on tarvittaessa otettava huomioon saman moduulin muiden sirujen lämmittävä vaikutus toisiinsa. Kirjallisuuskatsauksen perusteella valitaan olemassa olevista lämpömalleista käytännön toteutuksen pohjaksi lämpöimpedanssimatriisiin perustuva malli. Lämpöimpedanssimatriisista tehdään Simulink-ohjelmalla s-tason simulointimalli, jota käytetään referenssinä muun muassa implementoinnin tarkkuuden verifiointiin. Lämpömalli tarvitsee tiedon vaihtosuuntaajan häviöistä, joten työssä on selvitetty eri vaihtoehtoja häviölaskentaan. Lämpömallin kehittäminen s-tason mallista valmiiksi C-kieliseksi koodiksi on kuvattu tarkasti. Ensin s-tason malli diskretoidaan z-tasoon. Z-tason siirtofunktiot muutetaan puolestaan ensimmäisen kertaluvun differenssiyhtälöiksi. Työssä kehitetty monen aikatason lämpömalli saadaan jakamalla ensimmäisen kertaluvun differenssiyhtälöt eri aikatasoille suoritettavaksi sen mukaan, mikä niiden kuvaileman termin vaatima päivitysnopeus on. Tällainen toteutus voi parhaimmillaan kuluttaa alle viidesosan kellojaksoja verrattuna suoraviivaiseen yhden aikatason toteutukseen. Implementoinnin tarkkuus on hyvä. Implementoinnin vaatimia suoritusaikoja testattiin Texas Instrumentsin TMS320C6727- prosessorilla (300 MHz). Esimerkkimallin laskemisen määritettiin kuluttavan vaihtosuuntaajan toimiessa 5 kHz kytkentätaajuudella vain 0,4 % prosessorin kellojaksoista. Toteutuksen tarkkuus ja laskentakapasiteetin vähäinen vaatimus mahdollistavat lämpömallin käyttämisen lämpösuojaukseen ja lisäämisen osaksi muuta jo prosessorilla olemassa olevaa systeemiä.

Metodologia de simulação numérica do comportamento térmico em equipamentos eletroeletrônicos

Pós-graduação em Engenharia Elétrica - FEIS

In situ diagnostics and prognostics of solder fatigue in IGBT modules for electric vehicle drives

This paper proposes an in situ diagnostic and prognostic (D&P) technology to monitor the health condition of insulated gate bipolar transistors (IGBTs) used in EVs with a focus on the IGBTs' solder layer fatigue. IGBTs' thermal impedance and the junction temperature can be used as health indicators for through-life condition monitoring (CM) where the terminal characteristics are measured and the devices' internal temperature-sensitive parameters are employed as temperature sensors to estimate the junction temperature. An auxiliary power supply unit, which can be converted from the battery's 12-V dc supply, provides power to the in situ test circuits and CM data can be stored in the on-board data-logger for further offline analysis. The proposed method is experimentally validated on the developed test circuitry and also compared with finite-element thermoelectrical simulation. The test results from thermal cycling are also compared with acoustic microscope and thermal images. The developed circuitry is proved to be effective to detect solder fatigue while each IGBT in the converter can be examined sequentially during red-light stopping or services. The D&P circuitry can utilize existing on-board hardware and be embedded in the IGBT's gate drive unit.

COMPREHENSIVE ELECTRICAL/OPTICAL/THERMAL CHARACTERIZATIONS OF HIGH POWER LIGHT EMITTING DIODES AND LASER DIODES

Thermal characterizations of high power light emitting diodes (LEDs) and laser diodes (LDs) are one of the most critical issues to achieve optimal performance such as center wavelength, spectrum, power efficiency, and reliability. Unique electrical/optical/thermal characterizations are proposed to analyze the complex thermal issues of high power LEDs and LDs. First, an advanced inverse approach, based on the transient junction temperature behavior, is proposed and implemented to quantify the resistance of the die-attach thermal interface (DTI) in high power LEDs. A hybrid analytical/numerical model is utilized to determine an approximate transient junction temperature behavior, which is governed predominantly by the resistance of the DTI. Then, an accurate value of the resistance of the DTI is determined inversely from the experimental data over the predetermined transient time domain using numerical modeling. Secondly, the effect of junction temperature on heat dissipation of high power LEDs is investigated. The theoretical aspect of junction temperature dependency of two major parameters – the forward voltage and the radiant flux – on heat dissipation is reviewed. Actual measurements of the heat dissipation over a wide range of junction temperatures are followed to quantify the effect of the parameters using commercially available LEDs. An empirical model of heat dissipation is proposed for applications in practice. Finally, a hybrid experimental/numerical method is proposed to predict the junction temperature distribution of a high power LD bar. A commercial water-cooled LD bar is used to present the proposed method. A unique experimental setup is developed and implemented to measure the average junction temperatures of the LD bar. After measuring the heat dissipation of the LD bar, the effective heat transfer coefficient of the cooling system is determined inversely. The characterized properties are used to predict the junction temperature distribution over the LD bar under high operating currents. The results are presented in conjunction with the wall-plug efficiency and the center wavelength shift.

Long-term reliability of power GaN HEMTS

The world is quickly changing, and the field of power electronics assumes a pivotal role in addressing the challenges posed by climate change, global warming, and energy management. The introduction of wide-bandgap semiconductors, particularly gallium nitride (GaN), in contrast to the traditional silicon technology, is leading to lightweight, compact and evermore efficient circuitry. However, GaN technology is not mature yet and still presents reliability issues which constrain its widespread adoption. Therefore, GaN reliability is a hotspot for the research community. Extensive efforts have been directed toward understanding the physical mechanisms underlying the performance and reliability of GaN power devices. The goal of this thesis is to propose a novel in-circuit degradation analysis in order to evaluate the long-term reliability of GaN-based power devices accurately. The in-circuit setup is based on measure-stress-measure methodology where a high-speed synchronous buck converter ensures the stress while the measure is performed by means of full I-V characterizations. The switch from stress mode to characterization mode and vice versa is automatic thanks to electromechanical and solid-state relays controlled by external unit control. Because these relays are located in critical paths of the converter layout, the design has required a comprehensive study of electrical and thermal problems originated by the use of GaN technology. In addition, during the validation phase of the converter, electromagnetic-lumped-element circuit simulations are carried out to monitor the signal integrity and junction temperature of the devices under test. However, the core of this work is the in-circuit reliability analysis conducted with 80 V GaN HEMTs under several operating conditions of the converter in order to figure out the main stressors which contribute to the device's degradation.

Lifetime Modeling of SiC Power Modules in Automotive Traction Inverters

This thesis presents a model-based software implementation for the estimation of the damage of a power module inside and automotive traction inverter with few hardware test setup performed to support the simulation with real-life data.

Preliminary temperature Accelerated Life Test (ALT) on III-V commercial concentrator triple-junction solar cells

A quantitative temperature accelerated life test on sixty GaInP/GaInAs/Ge triple-junction commercial concentrator solar cells is being carried out. The final objective of this experiment is to evaluate the reliability, warranty period, and failure mechanism of high concentration solar cells in a moderate period of time. The acceleration of the degradation is realized by subjecting the solar cells at temperatures markedly higher than the nominal working temperature under a concentrator Three experiments at three different temperatures are necessary in order to obtain the acceleration factor which relates the time at the stress level with the time at nominal working conditions. . However, up to now only the test at the highest temperature has finished. Therefore, we can not provide complete reliability information but we have analyzed the life data and the failure mode of the solar cells inside the climatic chamber at the highest temperature. The failures have been all of them catastrophic. In fact, the solar cells have turned into short circuits. We have fitted the failure distribution to a two parameters Weibull function. The failures are wear-out type. We have observed that the busbar and the surrounding fingers are completely deteriorate

Preliminary temperature accelerated life test (ALT) on lattice mismatched triple-junction concentrator solar cells-on-carriers

A temperature accelerated life test on concentrator lattice mismatched Ga0.37In0.63P/Ga0.83In0.17As/Ge triple-junction solar cells-on-carrier is being carried out. The solar cells have been tested at three different temperatures: 125, 145 and 165°C and the nominal photo-current condition (500X) is emulated by injecting current in darkness. The final objective of these tests is to evaluate the reliability, warranty period, and failure mechanism of these solar cells in a moderate period of time. Up to now only the test at 165°C has finished. Therefore, we cannot provide complete reliability information, but we have carried out preliminary data and failure analysis with the current results.

Room-temperature single-electron junction.

The design, realization, and test performances of an electronic junction based on single-electron phenomena that works in the air at room temperature are hereby reported. The element consists of an electrochemically etched sharp tungsten stylus over whose tip a nanometer-size crystal was synthesized. Langmuir-Blodgett films of cadmium arachidate were transferred onto the stylus and exposed to a H2S atmosphere to yield CdS nanocrystals (30-50 angstrom in diameter) imbedded into an organic matrix. The stylus, biased with respect to a flat electrode, was brought to the tunnel distance from the film and a constant gap value was maintained by a piezo-electric actuator driven by a feedback circuit fed by the tunneling current. With this set-up, it is possible to measure the behavior of the current flowing through the quantum dot when a bias voltage is applied. Voltage-current characteristics measured in the system displayed single-electron trends such as a Coulomb blockade and Coulomb staircase and revealed capacitance values as small as 10(-19) F.

In vitro study of the pulp chamber temperature rise during light-activated bleaching

This study evaluated in vitro the pulp chamber temperature rise induced by the light-activated dental bleaching technique using different light sources. The root portions of 78 extracted sound human mandibular incisors were sectioned approximately 2 mm below the cementoenamel junction. The root cavities of the crowns were enlarged to facilitate the correct placing of the sensor into the pulp chamber. Half of specimens (n=39) was assigned to receive a 35% hydrogen peroxide gel on the buccal surface and the other halt (n=39) not to receive the bleaching agent. Three groups (n=13) were formed for each condition (bleach or no bleach) according to the use of 3 light sources recommended for dental bleaching: a light-emitting diode (LED)laser system, a LED unit and a conventional halogen light. The light sources were positioned perpendicular to the buccal surface at a distance of 5 mm and activated during 30 s. The differences between the initial and the highest temperature readings for each specimen were obtained, and, from the temperature changes, the means for each specimen and each group were calculated. The values of temperature rise were compared using Kruskal-Wallis test at 1% significance level. Temperature rise varied significantly depending on the light-curing unit, with statistically significant differences (p<0.01) among the groups. When the bleaching agent was not applied, the halogen light induced the highest temperature rise (2.38±0.66ºC). The LED unit produced the lowest temperature increase (0.29±0.13ºC); but there was no significant difference between LED unit and LED-laser system (0.35±0.15ºC) (p>0.01). When the bleaching agent was applied, there were significant differences among groups (p<0.01): halogen light induced the highest temperature rise (1.41±0.64ºC), and LED-laser system the lowest (0.33±0.12ºC); however, there was no difference between LED-laser system and LED unit (0.44±0.11ºC). LED and LED-laser system did not differ significantly from each other regardless the temperature rise occurred with or without bleaching agent application. It may be concluded that during light-activated tooth bleaching, with or without the bleaching agent, halogen light promoted higher pulp chamber temperature rise than LED unit and LED-laser system. The tested light-curing units provided increases in the pulp chamber temperature that were compatible with pulpal health.

Current-phase relation in graphene Josephson junction

In this thesis, we present the results of high-frequency measurements on superconductor-graphene-superconductor junctions. We obtained the relation between the supercurrent through the junction and the superconducting phase. The relation allowed us to extract true critical current and to determine the transport regime of graphene in our SGS-junction samples at the Dirac point and away from it. An experimental temperature dependence of the current-phase relation is presented. We have calculated theoretical supercurrent-phase relation in the case of ballistic and diffusive junction. For the diffusive case, we have considered short and long limits where the coherence length is larger or smaller than the sample length, respectively.

Building integration photovoltaic module with reference to Ghana: using triple junction amorphous silicon

This paper assesses the potential for using building integrated photovoltaic (BIPV) roof shingles made from triple-junction amorphous silicon (3a-Si) for electrification and as a roofing material in tropical countries, such as Accra, Ghana. A model roof was constructed using triple-junction amorphous (3a-Si) PV on one section and conventional roofing tiles on the other. The performance of the PV module and tiles were measured, over a range of ambient temperatures and solar irradiance. PVSyst (a computer design software) was used to determine the most appropriate angle of tilt. It was observed that 3a-Si performs well in conditions such as Accra, because it is insensitive to high temperatures. Building integration gives security benefits, and reduces construction costs and embodied energy, compared to freestanding PV systems. Again, it serves as a means of protection from salt spray from the oceans and works well even when shaded. However, compared to conventional roofing materials, 3a-Si would increase the indoor temperature by 1-2 °C depending on the surface area of the roof covered with the PV modules. The results presented in this research enhance the understanding of varying factors involved in the selection of an appropriate method of PV installation to offset the short falls of the conventional roofing material in Ghana.

Sample stacking in CZE using dynamic thermal junctions I. Analytes with low dpK(a)/dT crossing a single thermally induced pH junction in a BGE with high dpH/dT

The possibility to compress analyte bands at the beginning of CE runs has many advantages. Analytes at low concentration can be analyzed with high signal-to-noise ratios by using the so-called sample stacking methods. Moreover, sample injections with very narrow initial band widths (small initial standard deviations) are sometimes useful, especially if high resolutions among the bands are required in the shortest run time. In the present work, a method of sample stacking is proposed and demonstrated. It is based on BGEs with high thermal sensitive pHs (high dpH/dT) and analytes with low dpK(a)/dT. High thermal sensitivity means that the working pK(a) of the BGE has a high dpK(a)/dT in modulus. For instance, Tris and Ethanolamine have dpH/dT = -0.028/degrees C and -0.029/degrees C, respectively, whereas carboxylic acids have low dpK(a)/dT values, i.e. in the -0.002/degrees C to+0.002/degrees C range. The action of cooling and heating sections along the capillary during the runs affects also the local viscosity, conductivity, and electric field strength. The effect of these variables on electrophoretic velocity and band compression is theoretically calculated using a simple model. Finally, this stacking method was demonstrated for amino acids derivatized with naphthalene-2,3-dicarboxaldehyde and fluorescamine using a temperature difference of 70 degrees C between two neighbor sections and Tris as separation buffer. In this case, the BGE has a high pH thermal coefficient whereas the carboxylic groups of the analytes have low pK(a) thermal coefficients. The application of these dynamic thermal gradients increased peak height by a factor of two (and decreased the standard deviations of peaks by a factor of two) of aspartic acid and glutamic acid derivatized with naphthalene-2,3-dicarboxaldehyde and serine derivatized with fluorescamine. The effect of thermal compression of bands was not observed when runs were accomplished using phosphate buffer at pH 7 (negative control). Phosphate has a low dpH/dT in this pH range, similar to the dK(a)/dT of analytes. It is shown that vertical bar dK(a)/dT-dpH/dT vertical bar >> 0 is one determinant factor to have significant stacking produced by dynamic thermal junctions.