АНАЛИЗ ТЕПЛОВЫХ СВОЙСТВ ЛИНЕЕК СВЕТОДИОДОВ МЕТОДОМ ПЕРЕХОДНЫХ ЭЛЕКТРИЧЕСКИХ ПРОЦЕССОВ

Increasing the solid lighting facilities operational energy-efficiency in the national economy of the Republic of Belarus is of current concern. The modern problems of energy-saving lighting are multifaceted and broad-ranging. It is particularly burning amidst the energy crisis and the world commercial slump. Thus, the lighting demands 10–13 % of the total electric energy consumption in Belarus. That is to say, there is a significant potential of energy saving in transition to energy-efficient lighting. The paper considers the issues of reliability and service period of the solid-state lighting devices created on the basis of lines of light-emitting-diodes (LED) produced by Paragon Semiconductor Lighting Technology Co., Ltd. The optoelectronic apparatuses reliability assessment is based on investigation of the development principles and deterioration mechanisms leading to failures of one kind or another. The deterioration causes ascertainment is indispensable for acting upon them later on and thus reducing the degradation speed and extent. One of the LED-devices deterioration main sources is the temperature overheat of the LED-chip active area. Therefore, techniques for evaluating the heat characteristics of solid lighting devices become the issue of the day. The article investigates thermal properties of high-capacity blue LED-lines by method of electrical transient processes. The authors calculate temperatures in the LED-lines active areas at various heat-dissipation conditions and injection currents values. They realize computer generated simulation of the heated lines thermal fields applying the ANSYS packet. The study concludes that out of the degree of temperature-distribution heterogeneity along the line impossibility of the line chip structural units thermal characteristics extraction arises based on all LEDs homogenized over the line temperature-time dependences. The paper indicates that one can with reasonable accuracy obtain the LED-lines thermal parameters employing the line representation with two equivalent RC-strings corresponding the thermal ways ‘LED active area – aluminium base’ and ‘aluminium base – environment’. For these areas thermal time constants, thermal resistances and thermal capacities are determined. Повышение энергоэффективности работы твердотельных осветительных устройств в народном хозяйстве Республики Беларусь является актуальной задачей. Современные проблемы энергоэффективного освещения многогранны и имеют широкий спектр. Особенно это актуально в условиях энергетического и мирового экономического кризиса. Так, на освещение в Беларуси расходуется 10–13 % от общего потребления электроэнергии. Таким образом, имеется значительный потенциал энергосбережения за счет перехода к энергоэффективному освещению. Рассмотрены вопросы надежности и долговечности работы твердотельных осветительных устройств, созданных на основе светодиодных линеек фирмы Paragon Semiconductor Lighting Technology Co., Ltd. Оценка надежности оптоэлектронных приборов базируется на исследовании закономерностей развития механизмов деградации, приводящих к отказам того или иного типа. Выяснение причин деградации необходимо, чтобы затем, целенаправленно воздействуя на них, уменьшить скорость и величину деградации. Одной из основных причин деградации светодиодных устройств является температурный перегрев активной области светодиодного чипа. Поэтому актуальными становятся методы оценки тепловых характеристик твердотельных осветительных устройств. В статье исследованы тепловые свойства мощных синих светодиодных линеек методом переходных электрических процессов. Рассчитаны температуры активной области светодиодов в линейках при различных условиях теплоотвода и значениях токов инжекции. Проведено компьютерное моделирование тепловых полей линеек при нагреве с использованием пакета ANSYS. Установлено, что из степени неоднородности распределения температуры вдоль линейки следует невозможность выделения тепловых свойств элементов структуры чипов линейки на основе усредненных по всем светодиодам временных зависимостей температуры. Показано, что тепловые параметры линеек светодиодов с достаточной точностью можно получить, используя представление линейки только двумя эквивалентными RC-цепочками, соответствующими тепловым путям «активная область светоизлучающего светодиода – алюминиевая подложка» и «алюминиевая подложка – окружающая среда». Для данных областей определены тепловые постоянные времени, тепловые сопротивления и теплоемкости.

Gallium nitride high electron mobility transistors in chip scale packaging: evaluation of performance in radio frequency power amplifiers and thermomechanical reliability characterization

2017 Summer.Includes bibliographical references.Wide bandgap semiconductors such as Gallium Nitride (GaN) have many advantages over their Si counterparts, such as a higher energy bandgap, critical electric field, and saturated electron drift velocity. These parameters translate into devices which operate at higher frequency, voltage, and efficiency than comparable Si devices, and have been utilized in varying degrees for power amplification purposes at >1 MHz for years. Previously, these devices required costly substrates such as sapphire (Al2O3), limiting applications to little more than aerospace and military. Furthermore, the typical breakdown voltage ratings of these parts have historically been below ~200 V, with many targeted as replacements for 50 V Si LDMOS as used in cellular infrastructure and industrial, scientific, and medical (ISM) applications between 1 MHz and 1 GHz. Fortunately within the past five years, devices have become commercially available with attractive key specifications: GaN on Si subtrates, with breakdown voltages of over 600 V, realized in cost effective chip scale packages, and with inherently low parasitic capacitances and inductances. In this work, two types of inexpensive commercially available AlGaN/GaN high electron mobility transistors (HEMTs) in chip scale packages are evaluated in a set of three interconnected experiments. The first explores the feasibility of creating a radio frequency power amplifier for use in the ISM bands of 2 MHz and 13.56 MHz, at power levels of up to 1 kW, using a Class E topology. Experiments confirm that a DC to RF efficiency of 94% is easily achievable using these devices. The second group of experiments considers both the steady state and transient thermal characterization of the HEMTs when installed in a typical industrial application. It is shown that both types of devices have acceptable steady state thermal resistance performance; approximately 5.27 °C/W and 0.93 °C/W are achievable for the source pad (bottom) cooled and top thermal pad cooled device types, respectively. Transient thermal behavior was found to exceed industry recommended maximum dT/dt by over 80x for the bottom cooled devices; a factor of 20x was noted with the top cooled devices. Extrapolations using the lumped capacitance method for transient conduction support even higher initial channel dT/dt rates. Although this rate of change decays to recommended levels within one second, it was hypothesized that the accumulated mechanical strain on the HEMTs would cause early life failures if left uncontrolled. The third set of experiments uses the thermal data to design a set of experiments with the goal of quantifying the cycles to failure under power cycling. It is confirmed that to achieve a high number of thermal cycles to failure as required in high reliability industrial systems, the devices under test require significant thermal parameter derating to levels on the order of 50%

Prognostics of Power Electronic Converters in renewable energy systems: an approach based on acoustic emission measurement and thermal modelling

Renewable energy conversion systems play an important role in delivering energy from natural resources. Power Electronic Converters (PECs) are vital for efficiently conditioning the generated energy to align with the requirements of the source. One of the obstacles in the wide adaptation of renewable energies is the lack of efficiency and reliability in these systems. In wind turbines, Electrical circuits, including the PEC, contribute to 24% of total failures experienced by the system. One of the key components in a PEC is the Insulated Gate Bipolar Transistor (IGBT) which is used as a switching device in PECs. They occur due to different factors such as operating conditions, environmental factors (temperature and humidity) and the internal structure of the IGBTs which are formed of layers of different material with different properties. This research focuses on exploring the relationship between the changes in temperature of the IGBT chip with acoustic emissions signals. The aim of this research project is the development of a more cost-effective method for condition monitoring and prognostics of PECs. In this thesis, a thorough literature review of current condition monitoring schemes is provided and the gap in research is identified. A great number of scholars and experts have experimented with the AE in PECs however the link between the increase in temperature of this chip and the fluctuations in AE signals is not yet established. Under certain loading conditions, the temperature of IGBT chip changed from the ambient temperature (20℃) to 55℃. The acoustic emissions were measured in 5℃ intervals and it was discovered that after the temperature surpasses the 40℃ mark, the AE signal amplitude drops to 0.1 percent of its value at 20℃. Moreover, the rising temperature creates new peaks in the frequency domain at frequencies between 400-600 kHz

Frequency domain temperature model :a new method in on-line temperature estimation for power modules in drives applications

D. Eng.The operating temperature of the components within an electronic device has a significant impact on the reliability of a product. In a variable speed drive the power semiconductors in the inverter stage are often operated close to their maximum temperature when the inverter is operating at a low output frequency or during an overload. The temperature of these components must be continuously monitored to prevent them from overheating, but direct measurement of the temperature is only possible if a special test configuration can be used. This is not practicable in a commercial drive and to protect the inverter the temperature of the power semiconductors must be estimated by an on-line thermal model. The work presented in this thesis describes the development of a novel thermal model that can be implemented using the existing computational resources available in a commercial variable speed drive. The thermal model is based on the transient thermal impedance measured between each device and the internal thermistor in a power module. These form a thermal impedance matrix which can be used to calculate the instantaneous temperature of every device in the inverter. However, with the existing computational resources it is not possible to implement the complete matrix without aliasing. To reduce the risk of aliasing the number of calculations performed during each sample period must be reduced. This is achieved by using a frequency domain model that has been developed to calculate the peak temperature of the hottest devices. To validate the thermal model it has been implemented in a commercial drive. The drive has been modified to allow the temperature of the power semiconductors in the inverter to be measured using a high speed thermal camera. This allows the temperature estimated by the on-line thermal model to be compared directly with the temperatures measured when the inverter is operating under typical load conditions. Comparisons of the measured and estimated temperatures in several operating conditions are presented. These conditions were chosen to highlight the advantages and disadvantages of the frequency domain model

THERMAL MODELING AND CHARACTERIZATION OF HIGH POWER DEVICES

Ph.DDOCTOR OF PHILOSOPH

Thermal characterisation and reliability analysis of power electronic devices in wind and solar energy systems

Power electronic converters (PECs) are used for conditioning the flow of energy between renewable energy applications and grid or stand-alone connected loads. Insulated gate bipolar transistors (IGBTs) are critical components used as switching devices in PECs. IGBTs are multi-layered devices made of different coefficient of thermal expansion (CTE) based materials. In wind and solar energy applications, IGBT’s reliability is highly influenced by the operating conditions such as variable wind speed and solar irradiance. Power losses occur in switching transient of high current/voltage which causes temperature fluctuations among the layers of the IGBTs. This is the main stress mechanism which accelerates deterioration and eventual failures among IGBT layers due to the dissimilar CTEs. Therefore, proper thermal monitoring is essential for accurate estimation of PECs reliability and end lifetime. Several thermal models have been proposed in literature, which are not capable of representing accurate temperature profiles among multichip IGBTs. These models are mostly derived from offline modelling approaches which cannot take operating conditions and control mechanisms of PECs into account and unable to represent actual heat path among each chip. This research offers an accurate and powerful electro thermal and reliability monitoring tool for such devices. Three-dimensional finite element (FE) IGBT models are implemented using COMSOL, by considering complex heat interactions among each layer. Based on the obtained thermal characteristics, electro thermal and thermo mechanical models were developed in SIMULINK to determine the thermal behaviour of each layer and provide total lifetime consumption analysis. The developed models were verified by real-time (RT) experiments using dSPACE environment. New materials, such as silicon carbide (SiC) devices, were found to exhibit approximately 20°C less thermal profile compared to conventional silicon IGBTs. For PECs used within wind energy systems, PECs driving algorithms were derived within the proposed models and by adjusting switching frequency PECs cycling temperatures were reduced by 12°C which led to a significant reduction in thermal stress; approximately 27 MPa. Total life consumption for the proposed method was calculated as 3.26x10-5 which is approximately 1x10-5 less compared to the other both methods. Effects of maximum power tracking algorithms, used in photovoltaic solar systems, on thermal stress were also explored. The converter’s thermal cycling was found approximately 3 °C higher with the IC algorithm. The steady state temperature was 52.7°C for the IC while it was 42.6 °C for P&O. In conclusion, IC algorithm offers more accurate tracking accuracy; however, this is on the expense of harsher thermal stress which has led to approximately 1.4 times of life consumption compared to P&O under specific operating conditions