Moein Borghei

The growing energy demand and the global warming crisis require increasing the share of sustainable energy sources. Fusion energy has the potential to provide a zero-carbon, low-waste energy source that revolutionizes the energy industry. A gram of hydrogen isotope as fusion fuel can give equal energy to burning 16 m 3 of coal. In a novel approach to producing fusion energy, the Orbitron concept has been introduced in which ions are electrostatically confined around a high voltage (H.V.)… Show more

The growing energy demand and the global warming crisis require increasing the share of sustainable energy sources. Fusion energy has the potential to provide a zero-carbon, low-waste energy source that revolutionizes the energy industry. A gram of hydrogen isotope as fusion fuel can give equal energy to burning 16 m 3 of coal. In a novel approach to producing fusion energy, the Orbitron concept has been introduced in which ions are electrostatically confined around a high voltage (H.V.) cathode. In this method, the cathode voltage should be as high as hundreds of kVs. One of the major engineering challenges lies in the transmission of such voltage levels from the atmospheric pressure to a high vacuum environment (p< 10 −8 Torr). One should be concerned not only about the breakdown of the vacuum or dielectric but also about the surface flashover across the insulator’s surface. This study proposes an innovative design for a compact, 300-kV bushing to achieve the aforementioned goal. Show less

Insulation system health is crucial for reliable, lifelong operation of almost any electrical apparatus. While many studies have focused on the testing, modeling, and analysis of insulation aging mechanisms, research is needed to overcome new challenges in electric power systems. Fortunately, the progress in data analytics methods has opened up new opportunities to extract information from datasets. This study aims to make use of deep learning algorithms to lay the foundation for an online… Show more

Insulation system health is crucial for reliable, lifelong operation of almost any electrical apparatus. While many studies have focused on the testing, modeling, and analysis of insulation aging mechanisms, research is needed to overcome new challenges in electric power systems. Fortunately, the progress in data analytics methods has opened up new opportunities to extract information from datasets. This study aims to make use of deep learning algorithms to lay the foundation for an online condition monitoring system that is capable of discriminating single- and multi-source corona discharges. In this article, we report the results of experimental testing and conversion of the data into phase-resolved partial discharge images, which we fed into deep neural networks. We begin by reviewing some of the most successful image recognition models including AlexNet, Inception-V3, residual network (ResNet), and DenseNet. Thereafter, we develop and optimize a ResNet model to achieve the highest accuracy model with the lowest computational cost. Show less

Many sectors, such as transportation systems, are undergoing rapid electrification due to the need for the mitigation of CO2 emissions. To ensure safe and reliable operation, the electrical equipment must be able to work under various environmental conditions. At high altitudes, the low pressure can adversely affect the health of insulating materials of electrical systems in electric aircraft. A well-known, primary aging mechanism in dielectrics is partial discharge (PD). This study targets… Show more

Many sectors, such as transportation systems, are undergoing rapid electrification due to the need for the mitigation of CO2 emissions. To ensure safe and reliable operation, the electrical equipment must be able to work under various environmental conditions. At high altitudes, the low pressure can adversely affect the health of insulating materials of electrical systems in electric aircraft. A well-known, primary aging mechanism in dielectrics is partial discharge (PD). This study targets internal PD evaluation in an insulated-gate bipolar transistor (IGBT) module under low-pressure conditions. The estimation of electric field distribution is conducted through 3D finite element analysis (FEA) using COMSOL Multiphysics®. The procedure of PD detection and transient modeling is performed in MATLAB for two pressure levels (atmospheric and half-atmospheric). The case study is the IGBT module with a void or two voids in the proximity of triple joints. The single-void case demonstrates that at half-atmospheric pressure, the intensity of discharges per voltage cycle increases by more than 40% compared to atmospheric pressure. The double-void case further shows that a void that is harmless at sea level can turn into an additional source of aging and couple with the other voids to escalate PD intensity by a factor of two or more. Show less

Partial discharge (PD) is a major aging factor in insulation systems. The first step toward ensuring the health of insulation systems is the identification of PD sources. This would enable the system operator to take proper actions before the occurrence of the final breakdown. This fundamental study targets building and training a deep residual neural network (ResNet) model to detect and discriminate single and multiple sources of corona discharge that are acting simultaneously. The input of… Show more

Partial discharge (PD) is a major aging factor in insulation systems. The first step toward ensuring the health of insulation systems is the identification of PD sources. This would enable the system operator to take proper actions before the occurrence of the final breakdown. This fundamental study targets building and training a deep residual neural network (ResNet) model to detect and discriminate single and multiple sources of corona discharge that are acting simultaneously. The input of the ResNet model is the actual PD measurements under atmospheric pressure for seven electrode configurations: four single-source and three double-source configurations which expands from weakly nonuniform to extremely nonuniform electric field distribution. In this study, the measurement data are converted into standardized phase-resolved PD (PRPD) images that would be further used as input to the optimized ResNet model. The validation of the 62-layer deep neural network is evaluated through 30% randomly chosen images from the original dataset. Show less

A well-known symptom of the aging phenomenon in electrical insulations is partial discharge (PD) which can occur in all media. Internal PDs in solid dielectrics occur in air-filled voids which are difficult to eliminate thoroughly and may appear simply during the manufacturing process. Although much research on PD measurement for solid dielectrics has been conducted, the modeling of PD based on a priori experiment is not investigated sufficiently. In this paper, a finite element analysis (FEA)… Show more

A well-known symptom of the aging phenomenon in electrical insulations is partial discharge (PD) which can occur in all media. Internal PDs in solid dielectrics occur in air-filled voids which are difficult to eliminate thoroughly and may appear simply during the manufacturing process. Although much research on PD measurement for solid dielectrics has been conducted, the modeling of PD based on a priori experiment is not investigated sufficiently. In this paper, a finite element analysis (FEA) model for internal PD in an air-filled cylindrical void inside a solid dielectric (case 1) under 60 Hz sinusoidal voltage is developed. The experiments are conducted to provide a basis for the estimation of parameters in the FEA model. The findings, then, would be used to investigate the prediction of PD behavior in another case study (case 2). In each case, a cylindrical void was artificially made within a 3D-printed polylactic acid (PLA) block. Then, phase-resolved partial discharge (PRPD) patterns were measured for the mentioned samples. Using deterministic PD measurement data for case 1, an FEA model was developed. This model will help us understand and explain internal PD behavior for case 2 with another size of void and a different insulation size. The results show acceptable agreement between the predicted and the measured PD activities. An accurate prediction of PD behavior only through simulation is a cost-effective and time-efficient approach to assess the reliability of insulation systems. Show less

The global warming crisis has started a movement toward the reduction of emissions and fossil-fuel dependency. A major potential resides in the transportation sector which has led to the proliferation of electric vehicles. Similarly, significant progress has been made toward electrification in the aviation industry. Unlike electric cars, electrification in the commercial aircraft industry still looks far. One of the major bottlenecks in this path is the reliability of electrical equipment in… Show more

The global warming crisis has started a movement toward the reduction of emissions and fossil-fuel dependency. A major potential resides in the transportation sector which has led to the proliferation of electric vehicles. Similarly, significant progress has been made toward electrification in the aviation industry. Unlike electric cars, electrification in the commercial aircraft industry still looks far. One of the major bottlenecks in this path is the reliability of electrical equipment in aeronautical applications. The harsh environmental conditions along with the higher electric tension imposed by the high-power density equipment (which are necessary for the aviation industry) can accelerate the aging of insulation systems. The insulation system is regarded as the heart of the electrical equipment and its failure results in the breakdown of the system. A major deterioration mechanism in the insulation system is partial discharge (PD). In this study, we develop a framework for the condition monitoring of insulation systems at high altitudes based on deep learning. Different cases of corona discharge are tested based on standard IEC 60270 as potential sources of threat to the electrical systems. The measured signals are the input of the Dielectric Online Condition Monitoring System (DOCMS) that preprocesses the data, converts them into phase-resolved PD (PRPD) images, and classifies them based on their source type using EfficientNet. Then, DOCMS updates the system engineer about the status of electrical equipment in case of unsafe operation. The results demonstrate the high accuracy and fastness of the proposed approach to identify potential threats to the health of the insulation systems. Show less

The electrification trend in the aviation industry is expected to accelerate. The incentives to this trend include but are not limited to the lower operating cost, lower CO2 emission, and higher fault tolerability of more and all electric aircraft than conventional aircraft. However, the wide bandgap (WBG)-based power conversion systems – despite their superior characteristics such as higher switching frequency/slew rate, higher efficiency, and smaller form factor – are susceptible to partial… Show more

The electrification trend in the aviation industry is expected to accelerate. The incentives to this trend include but are not limited to the lower operating cost, lower CO2 emission, and higher fault tolerability of more and all electric aircraft than conventional aircraft. However, the wide bandgap (WBG)-based power conversion systems – despite their superior characteristics such as higher switching frequency/slew rate, higher efficiency, and smaller form factor – are susceptible to partial discharges (PDs). The vulnerability of the insulation system in these devices even exacerbates at higher altitudes due to the lower PD inception voltage, meaning that the discharge ignites sooner than expected. This paper puts forth the modeling of the internal PDs in the insulation systems of the WBG power module using Finite Element Analysis (FEA). The modeling is carried out in COMSOL Multiphysics® and tested on a high power-density IGBT module for two cases where the module operates at (1) sea level (a normal condition) and (2) altitude of 18000 ft. (a low-pressure condition). The results of these cases are thoroughly compared and discussed. Show less

The reliability of electrical equipment is closely tied with the health of their insulation system. A well-known symptom of the aging phenomenon in dielectrics is partial discharge (PD) which can occur in all media. Internal PDs in solid dielectrics occur in air-filled voids which are difficult to eliminate thoroughly and may appear simply during the manufacturing process. Although much research on PD measurement for solid dielectrics has been conducted, this is not the case for PD modeling… Show more

The reliability of electrical equipment is closely tied with the health of their insulation system. A well-known symptom of the aging phenomenon in dielectrics is partial discharge (PD) which can occur in all media. Internal PDs in solid dielectrics occur in air-filled voids which are difficult to eliminate thoroughly and may appear simply during the manufacturing process. Although much research on PD measurement for solid dielectrics has been conducted, this is not the case for PD modeling. Besides, the simulation of a case study and its comparison with experimental results can provide further insights into the possibility of other PD sources. In this paper, a finite element analysis (FEA) model for internal PD in an air-filled cylindrical void inside a solid dielectric under 60 Hz sinusoidal voltage is developed. For the estimation of the parameters of the model, experimental data is needed. To this end, a cylindrical void was artificially made within a 3D-printed polylactic acid (PLA) block. Then, phase-resolved partial discharge (PRPD) patterns were measured for the mentioned samples. Using deterministic PD measurement data, an FEA model was developed. This model will help us understand and explain internal PD behavior for the case of a cylindrical void and study the influence of void size on PD behavior. Show less

In recent decades, extensive research has been conducted on the electrification of commercial aircraft to reduce the dependency on mechanical, hydraulic, and pneumatic systems and replace them with electrical systems. A primary goal of this path is to make the power density of the more/all-electric aircraft (MEA/AEA) closer to that of conventional aircraft. While current commercial aircraft operate at voltages below 1 kV, it is widely accepted that higher operating voltage is necessary for… Show more

In recent decades, extensive research has been conducted on the electrification of commercial aircraft to reduce the dependency on mechanical, hydraulic, and pneumatic systems and replace them with electrical systems. A primary goal of this path is to make the power density of the more/all-electric aircraft (MEA/AEA) closer to that of conventional aircraft. While current commercial aircraft operate at voltages below 1 kV, it is widely accepted that higher operating voltage is necessary for MEA/AEA. NASA has envisaged a voltage level of at least 6 kV for more electric aircraft. In the language of electrical insulation technology, higher voltage levels translate into higher electric tension on the insulation system. A serious challenge stems from the fact that at high altitudes, high voltage insulation design strategies are not necessarily as efficient as at sea level due to differences in environmental conditions, including lower pressure, higher moisture level, micro-gravity, and plasma radiation. In this paper, challenges associated with the electrical insulation design of future aircraft are reviewed. These challenges extend to almost any part of the electric power system in an aircraft, such as electric machines, power converters, cables, and printed circuit boards (PCBs). An overview of the aging factors, such as internal discharges, arc tracking, and thermal degradation, is accompanied by a discussion of the potential of novel insulating material and the ways to reinforce the current commercial dielectric materials. Finally, considerations for testing at simulated high-altitude conditions as well as the existing standards and their deficits are investigated. Show less

As severe weather events disrupt the power system more frequently and more harshly, the concern is growing around the ability of future grids to recover from such natural disasters. Recently, a major research focus has been on microgrids (MGs) as a potential source of resiliency. While most of the works done so far center on how to benefit from existing MGs through operation schemes, this study focuses on the planning of MGs to strengthen the network against severe faults. In this regard, three… Show more

As severe weather events disrupt the power system more frequently and more harshly, the concern is growing around the ability of future grids to recover from such natural disasters. Recently, a major research focus has been on microgrids (MGs) as a potential source of resiliency. While most of the works done so far center on how to benefit from existing MGs through operation schemes, this study focuses on the planning of MGs to strengthen the network against severe faults. In this regard, three solution approaches are proposed aiming to determine the optimal nodes for the connection of MGs as well as the capacity of the dispatchable generation units deployed within MGs. These algorithms satisfy the power balance of MGs and the main grid as well as the operational and topological constraints. A computationally-efficient heuristic method is developed in two stationary (S-HM) and time-dependent (T-HM) versions. The concept of the heuristic approach, which was first introduced by the authors and is matured in this study, is based on a multi-stage search algorithm that efficiently reduces the undesirable restoration strategies and utilizes the original power flow equations. The other approach is a multi-objective mixed-integer linear programming (MO-MILP) that strives to find the globally-optimal solution in a time-dependent scheme. The validity of the outputs of these methods is assessed using an exhaustive search algorithm (ESA), capable of finding the globally-optimal solution. The MG model constitutes renewable and dispatchable generation units, energy storage systems, and local loads. The uncertainty of intermittent energy resources is tackled through robust optimization formulation based on the worst-case scenario. The performance of the proposed methods are evaluated by the IEEE 37- and IEEE 123-bus test systems under several severe fault scenarios. Show less

Natural disasters and cascading events have historically caused severe disruptions of the electric power system. For instance, in 2012, hurricane Sandy left over 8 million people in darkness and caused total damage costing $65 billion. Under emergency conditions, microgrids can help the electric power system recover critical loads, such as hospitals, data centers, and water pumping stations. While the literature has mostly focused on the utilization of existing microgrids, the idea of planning… Show more

Natural disasters and cascading events have historically caused severe disruptions of the electric power system. For instance, in 2012, hurricane Sandy left over 8 million people in darkness and caused total damage costing $65 billion. Under emergency conditions, microgrids can help the electric power system recover critical loads, such as hospitals, data centers, and water pumping stations. While the literature has mostly focused on the utilization of existing microgrids, the idea of planning for future microgrids in combination with switching operations to make the grid more resilient against devastating events is investigated in this study. This work aims to simultaneously maximize the resiliency of distribution networks - in terms of service to the critical loads - and minimize the dispatchable generation capacity of microgrids. The considered microgrid model entails dispatchable power generators, renewable energy resources, and electrical energy storage systems (ESS) to serve consumers. Considering the topological and operational limitations, the robust optimization scheme optimizes the objectives by the effective selection of the node for microgrid connection and the minimum change in its generation capacity. While the problem is modeled as a multi-objective, mixed-integer linear programming (MO-MILP) problem, the results show more than 99% accuracy compared to the exact results of an exhaustive search algorithm. Numerical tests are performed on the IEEE 37-node test feeder and the IEEE 123-node test feeder to assess the proposed method's performance. Given the accuracy, computation time efficacy, and the generic formulation of the problem, the optimization scheme can be easily applied to any real network. Show less

The aviation industry, as one of the major CO2 producers, anticipates a reduction in its carbon emission. While big manufacturers and governmental agencies are betting on the more- (and soon all-) electrified aircraft to reduce the dependency of this industry on fossil fuels, there are major milestones to be reached in the next three decades. Among those, enhancing the specific power of systems, that are expected to substitute the fuel-based engines, is one of the primary targets. An enabling… Show more

The aviation industry, as one of the major CO2 producers, anticipates a reduction in its carbon emission. While big manufacturers and governmental agencies are betting on the more- (and soon all-) electrified aircraft to reduce the dependency of this industry on fossil fuels, there are major milestones to be reached in the next three decades. Among those, enhancing the specific power of systems, that are expected to substitute the fuel-based engines, is one of the primary targets. An enabling technology to achieve this goal is the wide bandgap (WBG)-based power converting, a promising technology toward increasing the efficiency of electrical systems. However, not only the partial discharges (PDs) -induced by the high voltage, high-frequency, fast-rise square voltages generated by these systems- endanger the insulation system, but also the operation at higher altitudes can be another game-changing factor in the design of power converters. This study puts forth the investigation of the pressure impact in tandem with the impact of short rise-times on various PD characteristics including but not limited to PD true charge magnitude and duration. The results show how the incorporation of harsh environmental conditions and short rise times lead to more intense and prolonged discharges. Moreover, it shows that micro-voids that have negligible PD activities at sea level can turn into serious threats at higher altitudes. In this project, COMSOL Multiphysics interfaced with MATLAB is used to simulate the PD identification process based on the experimental data found in the literature. Show less

The development of a revolutionary design for transmission lines was recently introduced by shifting phase configurations and sub-conductors into “unconventional” arrangements that were geometrically optimized to maximize natural power. The objective of this paper is to study the electromagnetic transients that result from the simultaneous and sequential line energization and re-energization of the previously developed unconventional high surge impedance loading (HSIL) lines. Statistical… Show more

The development of a revolutionary design for transmission lines was recently introduced by shifting phase configurations and sub-conductors into “unconventional” arrangements that were geometrically optimized to maximize natural power. The objective of this paper is to study the electromagnetic transients that result from the simultaneous and sequential line energization and re-energization of the previously developed unconventional high surge impedance loading (HSIL) lines. Statistical switching overvoltage (SSOV) studies are performed using a frequency domain method based on the inverse numerical Laplace transform. Compared to a conventional line, all unconventional HSIL line designs studied in this paper lead to very similar surges for long line lengths (400 km) and similar values for short line lengths (100 km), indicating additional advantages of these lines. The use of a frequency domain method for SSOV studies offers enhanced accuracy, simulation flexibility, and substantially lower computational burden compared with traditional time-domain methods. Show less

The objectives of this paper are (i) to create a revolutionary design for transmission lines by shifting phase configurations and subconductors into “unconventional” arrangements that are geometrically optimized to maximize natural power, and (ii) to study electromagnetic transients owing to simultaneous and sequential line energization for unconventional high surge impedance loading (HSIL) lines via an inverse numerical Laplace transform method. Compared to conventional lines, all… Show more

The objectives of this paper are (i) to create a revolutionary design for transmission lines by shifting phase configurations and subconductors into “unconventional” arrangements that are geometrically optimized to maximize natural power, and (ii) to study electromagnetic transients owing to simultaneous and sequential line energization for unconventional high surge impedance loading (HSIL) lines via an inverse numerical Laplace transform method. Compared to conventional lines, all unconventional HSIL line designs proposed in this paper led to less severe surges, indicating another advantage to these lines. Show less

The aviation industry aims to reduce CO 2 emission by reducing energy consumption and benefitting from more electrical systems than those based on fossil fuels. The more electric aircraft (MEA) can take advantage of the drives based on wide bandgap (WBG)-based power modules that are lighter and can bear higher voltages and currents. However, the fast-rise and repetitive voltage pulses generated by WBG-based systems can endanger the insulating property of dielectric materials due to the partial… Show more

The aviation industry aims to reduce CO 2 emission by reducing energy consumption and benefitting from more electrical systems than those based on fossil fuels. The more electric aircraft (MEA) can take advantage of the drives based on wide bandgap (WBG)-based power modules that are lighter and can bear higher voltages and currents. However, the fast-rise and repetitive voltage pulses generated by WBG-based systems can endanger the insulating property of dielectric materials due to the partial discharges. PDs cause the local breakdown of insulation materials in regions with high electric field magnitude. In the case of power electronic modules, silicone gel, which is a predominant type of encapsulation material, is susceptible to these PDs. In this study, it is aimed to investigate the impact of rise time on various PD characteristics including PD true charge magnitude, inception and extinction fields, duration, and so forth. Besides, those systems that are anticipated to operate under harsh environmental conditions - such as naval or aviation industries - may expect additional threat. Therefore, this paper puts forth the combination of low-pressure conditions and fast-rise, high-frequency square wave pulses. The results demonstrate that more intense and more intense ones are going to be imposed at lower pressures. COMSOL Multiphysics interfaced with MATLAB is used to simulate the PD detection process based on the experimental data found in the literature. Show less

Although much work has been done and significant progress has been made on partial discharge (PD) measurement and detection techniques, this is not the case for PD modeling. Four types of internal PD modeling, in sequential order from first to last developed, are three-capacitance (abc), induced charge concept (ICC), finite-element-analysis (FEA), and Multiphysics models. The abc model is too simple to provide an understanding of the physical phenomena affecting PD. In contrast, Multiphysics… Show more

Although much work has been done and significant progress has been made on partial discharge (PD) measurement and detection techniques, this is not the case for PD modeling. Four types of internal PD modeling, in sequential order from first to last developed, are three-capacitance (abc), induced charge concept (ICC), finite-element-analysis (FEA), and Multiphysics models. The abc model is too simple to provide an understanding of the physical phenomena affecting PD. In contrast, Multiphysics models are immature and require a high number of physical parameters that need to be experimentally determined, which is not a trivial task. Moreover, adjusting the physical parameters to achieve a good agreement between simulation results and measurement results for a specific geometry and dimension may not work for other geometries and dimensions. In this paper, 1) an improved ICC and a FEA capable of describing phenomena occurring during PDs are developed, 2) both developed models are coded and implemented either in MATLAB or in COMSOL Multiphysics linked with MATLAB, and their simulation results are compared and analyzed, and 3) the influence of different parameters including void shape, void size, and void air pressure on PD parameters are studied. Show less

The goal of this paper is to discover “unconventional” high surge impedance loading (HSIL) line designs, through determining the best location of sub-conductors, to maximize SIL while satisfying the structural and electrical constraints through a heuristic algorithm. The paper shows the potential of unconventional HSIL line as an innovative technology to realize high-efficiency future transmission lines for grid modernization. Moreover, a new method to obtain the accurate estimation of electric… Show more

The goal of this paper is to discover “unconventional” high surge impedance loading (HSIL) line designs, through determining the best location of sub-conductors, to maximize SIL while satisfying the structural and electrical constraints through a heuristic algorithm. The paper shows the potential of unconventional HSIL line as an innovative technology to realize high-efficiency future transmission lines for grid modernization. Moreover, a new method to obtain the accurate estimation of electric field intensity around the surface of sub-conductors, as one of the main constraints in the mentioned optimization algorithm, is developed. Show less

When a fault or a series of faults occur in a distribution network, it is of considerable significance to feeding loads, most importantly critical loads. Although network reconfiguration by switching operations has been usually considered as a relatively low-cost method for load restoration, it alone may not able to restore critical loads under extreme weather events such as hurricanes where multiple faults can happen within the network. Under such severe circumstances, one of the complementary… Show more

When a fault or a series of faults occur in a distribution network, it is of considerable significance to feeding loads, most importantly critical loads. Although network reconfiguration by switching operations has been usually considered as a relatively low-cost method for load restoration, it alone may not able to restore critical loads under extreme weather events such as hurricanes where multiple faults can happen within the network. Under such severe circumstances, one of the complementary methods for service restoration is benefiting from existing installed microgrids. In this paper, the idea of planning future microgrids -in terms of optimal location and capacity- in combination with switching operations to restore critical loads, for the first time, is considered. To this planning-operation concept end, a graph-theoretic method is developed to find optimal switching operations coupled with a heuristic optimization method developed to determine future microgrids' location and capacity to maximize the resiliency of the network while keeping the associated cost with distributed generations (DGs) in microgrids as low as possible. Simulations results on the modified IEEE 37-node distribution network show the effectiveness of the proposed idea. Moreover, using appropriate reduction techniques, the computational efficacy of the method has also been greatly improved. Show less

Wide bandgap (WBG) devices made from materials such as SiC, GaN, Ga2O3 and diamond, which can tolerate higher voltages and currents compared to silicon-based devices, are the most promising approach for reducing the size and weight of power management and conversion systems. Silicone gel, which is the existing commercial option for encapsulation of power modules, is susceptible to partial discharges (PDs). PDs often occur in air-filled cavities located in high electric field regions around the… Show more

Wide bandgap (WBG) devices made from materials such as SiC, GaN, Ga2O3 and diamond, which can tolerate higher voltages and currents compared to silicon-based devices, are the most promising approach for reducing the size and weight of power management and conversion systems. Silicone gel, which is the existing commercial option for encapsulation of power modules, is susceptible to partial discharges (PDs). PDs often occur in air-filled cavities located in high electric field regions around the sharp edges of metallization in the gel. This study focuses on the modeling of PD phenomenon in an air filled-cavity in silicone gel for the combination of (1) a fast, high-frequency square wave voltage and (2) low-pressure conditions. The low-pressure condition is common in the aviation industry where pressure can go as low as 4 psi. To integrate the pressure impact into PD model, in the first place, the model parameters are adjusted with the experimental results reported in the literature and in the second place, the dependencies of various PD characteristics such as dielectric constant and inception electric field on pressure are examined. Finally, the reflections of these changes in PD intensity, duration and inception time are investigated. The results imply that the low pressure at high altitudes can considerably affect the PD inception and extinction criterion, also the transient state conditions during PD events. These changes result in the prolongation of PD events and more intense ones. As the PD model is strongly dependent upon the accurate estimation electric field estimation of the system, a finite-element analysis (FEA) model developed in COMSOL Multiphysics linked with MATLAB is employed that numerically calculates the electric field distribution. Show less

The electrification trend in the aviation industry is expected to accelerate. The incentives to this trend include but are not limited to the lower operating cost, lower CO2 emission, and higher fault tolerability of more electric aircraft than conventional aircraft. However, the wide bandgap (WBG)-based power conversion systems-despite their superior characteristics such as high switching frequency/slew rate, higher efficiency, and smaller form factor-are susceptible to partial discharges… Show more

The electrification trend in the aviation industry is expected to accelerate. The incentives to this trend include but are not limited to the lower operating cost, lower CO2 emission, and higher fault tolerability of more electric aircraft than conventional aircraft. However, the wide bandgap (WBG)-based power conversion systems-despite their superior characteristics such as high switching frequency/slew rate, higher efficiency, and smaller form factor-are susceptible to partial discharges (PDs). The vulnerability of the insulation system in these devices even exacerbates at higher altitudes due to the lower PD inception voltage, meaning that the discharge ignites sooner than expected. This paper puts forth the modeling of the internal PDs in the insulation systems of the WBG power module using Finite Element Analysis (FEA). The modeling is carried out in COMSOL Multiphysics® and tested on a high power-density IGBT module for two cases for the cases that the module operates at (1) sea level (normal condition), and (2) altitude of 18000 ft.(low-pressure conditions). The results of these cases are thoroughly compared and discussed. Show less

Wide bandgap (WBG) devices able to tolerate high voltages and currents and operating at higher frequencies are the most promising approach for reducing the size and weight of power management and conversion systems. These systems are envisaged to be widely used in next generation aircraft, ships, and vehicles, which are expected to be more electric or, possibly, all electric as well as in power grids. However, accelerated aging of solid dielectrics used in various apparatuses for… Show more

Wide bandgap (WBG) devices able to tolerate high voltages and currents and operating at higher frequencies are the most promising approach for reducing the size and weight of power management and conversion systems. These systems are envisaged to be widely used in next generation aircraft, ships, and vehicles, which are expected to be more electric or, possibly, all electric as well as in power grids. However, accelerated aging of solid dielectrics used in various apparatuses for electrification of the applications above under fast (slew rates (dv /dt) ranging from tens to hundreds of kV/us) and repetitive voltage pulses (frequencies ranging from hundreds of kHz to MHz) originated from WBG-based system due to partial discharges (PD) can offset or even be an obstacle for using WBG-based systems. Several factors affect the happening of PD, of which frequency and rise-time can be enumerated as the most important ones. In this paper, a cavity-dielectric model is developed to investigate the PD phenomena. In order to model the case study, and dynamically monitor the changes in the electric field and voltage distribution in both cavity and dielectric, Finite-Element Analysis (FEA) is employed. The model development and analysis is performed in COMSOL Multiphysics. The occurrence of PD and the impact of different parameters on PD ignition, such as cavity shape, cavity diameter, and frequency are evaluated. Show less

Accelerated aging of insulation systems used in different apparatus under fast, repetitive voltage pulses is the most significant barrier to benefit from wide bandgap (WBG) power electronics. Frequency and slew rate which are higher for WGB devices than Si-based ones are two of the most critical factors of a voltage pulse, influencing the level of degradation of the insulation systems that are exposed to such voltage pulses. Finite element analysis (FEA) has been widely used to study partial… Show more

Accelerated aging of insulation systems used in different apparatus under fast, repetitive voltage pulses is the most significant barrier to benefit from wide bandgap (WBG) power electronics. Frequency and slew rate which are higher for WGB devices than Si-based ones are two of the most critical factors of a voltage pulse, influencing the level of degradation of the insulation systems that are exposed to such voltage pulses. Finite element analysis (FEA) has been widely used to study partial discharge (PD) behavior under a power frequency (50/60 Hz) sinusoidal waveform within cavities in a solid dielectric. However, the new technologies urge the need to utilize it under square waveforms. In this paper, a FEA model of PD activity is developed. The model is used to investigate the change in the electric field distribution before and after PD occurrence and the impact of different involved parameters when repetitive voltage pulses are applied to the dielectric. Show less

This paper develops a revolutionary design for transmission lines by shifting phase configurations and sub-conductors into unconventional arrangements that are geometrically optimized, leading to very high surge impedance loading (HSIL) and very low corridor width (CW) (ultra SIL/CW).

Wide bandgap (WBG) power modules able to tolerate high voltages and currents are the most promising solution to reduce the size and weight of the power management and conversion systems. These systems are envisioned to be widely used in the power grid and the next generation of more (and possibly all) electric aircraft, ships, and vehicles. However, accelerated aging of silicone gel when being exposed to high frequency, fast rise-time voltage pulses that can offset or even be an obstacle for… Show more

Wide bandgap (WBG) power modules able to tolerate high voltages and currents are the most promising solution to reduce the size and weight of the power management and conversion systems. These systems are envisioned to be widely used in the power grid and the next generation of more (and possibly all) electric aircraft, ships, and vehicles. However, accelerated aging of silicone gel when being exposed to high frequency, fast rise-time voltage pulses that can offset or even be an obstacle for using WBG-based systems. Silicone gel is used to insulate conductor parts in the module and encapsulate the module. It has less electrical insulation strength than the substrate and is susceptible to partial discharges (PDs). PDs often occur in the cavities located close to high electric field regions around the sharp edges of metallization in the gel. The vulnerability of silicone gel to PDs occurred in the cavities under repetitive pulses with a high slew rate investigated in this paper. The objective mentioned above is achieved by developing a Finite-Element Analysis (FEA) PD model for fast, repetitive voltage pulses. This work has been done for the first time to the best of our knowledge. By using the model, the influence of frequency and slew rate on the magnitude and rate of PD events is studied. Show less