Browsing by Author "Akin, Bilal"
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Item A Fast Phase Variable abc Model of Brushless PM Motors under Demagnetization Faults(Institute of Electrical and Electronics Engineers Inc.) Mazaheri-Tehrani, E.; Faiz, J.; Zafarani, Mohsen; Akin, Bilal; 0000-0002-3714-5081 (Zafarani, M); 0000-0001-6912-7219 (Akin, B); Zafarani, Mohsen; Akin, BilalThis paper addresses a simple and computationally efficient dynamic model for brushless permanent magnet (PM) motors under PM demagnetization faults. The impact of stator slots and spatial disposition of the windings are taken into account to improve the accuracy of a lumped-parameter abc model. This model is suitable for tracking the dynamic behavior of fault components as it can be accompanied by any control scheme and/or be used for model-based fault detection schemes. In addition, parameters of this model can be automatically tuned by an optimization process in the off-line phase of the healthy machine. Finite element simulations are carried out for proving the effectiveness of the proposed model. Verifica-tion is done in both time and frequency domains for four PM motors with different rotor and stator configurations. The simulation results are experimentally verified.Item A First Principles Approach to Closing the “10-100 eV GAP” for Electron Thermalization in Wurtzite GaN(May 2023) Nielsen, Dallin O 1993-; Fischetti, Massimo V.; Akin, Bilal; Vandenberghe, William; Cho, Kyeongjae; Gelb, Lev D.Since the 1960s, when radiation-induced disruption of electronic devices in space was first observed, the study of the effects of ionizing radiation on electronics has grown into an extensive field of its own. The present work is concerned with accurately modelling the energy-loss processes that control the thermalization of hot carriers (electrons and/or electron-hole pairs) that are generated by high-energy radiation in wurtzite GaN, using an ab initio approach. Current physical models of the nuclear/particle physics community cover the high-energy range (kinetic energies exceeding ~100 eV), and the electronic-device community has done extensive work in the lower-energy range (below ~10 eV). However, the processes that control the energy losses and thermalization of electrons and holes in the intermediate energy range of about 10-100 eV are poorly known (the “10-100 eV gap”). The aim of this research is to close this gap. To this end, Density Functional Theory (DFT) is utilized to obtain the band structure of GaN for bands reaching energies above 100 eV. Furthermore, charge-carrier scattering rates for the major charge-carrier interactions (phonon scattering, impact ionization, and plasmon emission) are calculated, using the DFT results and first-order perturbation theory (Fermi’s Golden Rule). With this information, the thermalization of electrons starting at 100 eV is simulated in a Monte Carlo code, allowing the electrons to interact stochastically according to the calculated interaction rates and generate electron-hole pairs as they go, which are also tracked in the simulation. Full thermalization of electrons is complete within 1 ps, and that of holes is complete in approximately half the time. Electrons lose 90% of their energy (90 eV) during the first few ~0.1 fs, due to rapid plasmon emission and impact ionization at high energies. The remainder is lost more slowly as phonon emission dominates at lower energies (below ~10 eV). During the thermalization, hot electrons generate electron-hole pairs with an average energy of ~8.9 eV/pair (11-12 pairs per hot electron). Additionally, upon full thermalization, the average electron displacement from its original position is found to be on the order of 100 nm.Item A New LMS Algorithm Based Dead-Time Compensation Method for PMSM FOC Drives(Institute of Electrical and Electronics Engineers Inc.) Tang, Zhuangyao; Akin, Bilal; 0000-0002-8704-3884 (Tang, Z); 0000-0001-6912-7219 (Akin, B); Tang, Zhuangyao; Akin, BilalThis paper presents a new least-mean-square (LMS) algorithm based dead-time compensation method to suppress the current distortion in permanent-magnet synchronous motor (PMSM) field-oriented control (FOC) drives. Compared to conventional average value compensations, the proposed method is robust to switching device parameter variations thanks to the online adaptation capability of the LMS algorithm. Similarly, the disturbance observer compensators are also immune to switching device parameter variations; however, varying motor parameters degrades their compensation performance. Without prior knowledge of switching device or motor parameters, the proposed method can directly reduce the dead-time current harmonics by generating compensation voltage references. In addition, the proposed method is easy to implement since it doesn't require voltage errors estimation or current harmonics extraction which are necessary for disturbance observer and adaptive filter based methods. The proposed method is tested on a 2.5 kW voltage-source inverter (VSI) PMSM drive controlled by FOC algorithm. Its effectiveness is validated by both experimental results and spectrum analysis.Item A Robust Method for Induction Motor Magnetizing Curve Identification at Standstill(Institute of Electrical and Electronics Engineers Inc., 2019) Erturk, Feyzullah; Akin, Bilal; 0000-0001-6912-7219 (Akin, B); 0000-0002-5775-0019 (Erturk, F); Erturk, Feyzullah; Akin, BilalModern electric drives use a self-commissioning procedure to precisely identify motor parameters for achieving high-performance control. Typically, the induction motor magnetizing curve is identified using no-load rotational test. However, some applications necessitate the electric drive to identify the magnetizing curve at standstill conditions. As one of the well-known standstill approaches, the traditional flux integration exhibits several practical problems. Any imperfection in measured current, estimated stator resistance, and dead-time compensation directly affects the accuracy of the estimated magnetizing curve because of error accumulation in open-loop integration. This paper proposes a robust yet simple solution against those practical concerns. It can identify the magnetizing curve without using any dead-time compensation and stator resistance. Only industry-standard dc-link voltage and phase current measurements are used. Its superior features are experimentally verified on a number of motors and the results are confirmed by no-load rotational test results. Its robustness against current offset and extra longer integration duration is also proved.Item Analysis of Vₜₕ Variations in IGBTs Under Thermal Stress for Improved Condition Monitoring in Automotive Power Conversion Systems(Institute of Electrical and Electronics Engineers Inc, 2018-11-12) Ali, Syed Huzaif; Ugur, Enes; Akin, Bilal; 0000-0001-6912-7219 (Akin, B); Ali, Syed Huzaif; Ugur, Enes; Akin, BilalToday, power conversion in automotive industry depends heavily on the reliable operation of insulated-gate bipolar transistors (IGBTs). Condition monitoring of IGBTs and reporting imminent faults to driver dashboard are critical for avoiding any fatal accidents. In this study, first, a comprehensive comparison is carried out between on-state collector-emitter drop (V_{ce,on}) with gate threshold voltage (Vₜₕ), as two reliable aging precursors. In order to enrich current understanding of IGBT aging prognosis, accelerated aging methods are applied under a wide variety of thermal stresses. Aging mechanisms and physical phenomena responsible for variation in both V_{ce,on} and Vₜₕ have been methodically investigated. These explanations are also supported by detailed failure analysis. Based on the extensive result sets for tested samples from different manufacturers with different structural types, it is found that V_{ce,on} show different trends at different stress levels, whereas under the same test conditions Vₜₕ provides more consistent and robust state-of-health information. Finally, an example experiment has been performed in which continuous V_{ce,on} measurements coupled with Vₜₕ information has been used to provide more insight about the device aging as well as faults in an automobile's sub-systems.Item Common-mode Current and EMI Analysis for Wide Bandgap Device Based Power Converters(August 2022) Kumar, Saurabh; Akin, Bilal; Ouyang, Jessica; Ma, Dongsheng Brian; Gardner, Matthew; Balsara, Poras T.Wide bandgap devices such as Silicon Carbide (SiC) and Gallium Nitride (GaN) are facilitating higher switching frequencies for power electronic converters. Their faster switching speed combined with low on-state resistance helps in increasing the efficiency and power density of the converters. However, high voltage and current slew rates (dv/dt and di/dt) associated with wide bandgap devices also increase Electromagnetic Interference (EMI) which may cause malfunctioning or failure of the converter itself or other sensitive circuits onboard. EMI issues are further worsened when high switching speed and high frequency operation is used for high power applications. Apart from hard switched wide bandgap power converters, dv/dt rates can also be high in wide bandgap converters which offer Zero Voltage Switching (ZVS) resulting into high Common-Mode (CM) currents through parasitic capacitances. High CM current leads to EMI. Dual Active Bridge (DAB) converter is a DC-DC converter offering ZVS along with bi-directional power transfer, isolation, and voltage matching. It finds applications in Electric Vehicles (EVs), battery charging stations, Solid State Transformers (SSTs) etc. High dv/dt, high switching frequency combined with multiple parasitic elements present in an isolated converter like DAB, make EMI mitigation difficult. This dissertation presents CM current and EMI analysis for single phase DAB converter. Conventional and Neutral Point Clamp (NPC) based architectures are studied with regard to their suitability to reduce CM current. Design and control variables in Active NPC (ANPC) - DAB converter are used to reduce CM conducted as well as radiated EMI. While doing so, it is insured that all possible modulation schemes used in DAB converters remain unaffected. To further reduce CM current than what is possible by design and/or control, an Input Parallel Output Parallel (IPOP) ANPC-DAB architecture is proposed for high power DAB converters. This architecture uses power sharing and dv/dt cancellation to reduce CM current injection. Factors causing nonideal dv/dt cancellations are discussed with their possible solutions. Finally in a contrasting work, EMI is investigated as a noninvasive system monitoring tool. A low cost radiated EMI sensing circuit is developed to detect dynamic current unbalancing in parallel connected wide bandgap devices. Apart from its hardware validation for paralleled SiC MOSFETs, possibilities to use it for EMI precompliance testing and online junction temperature monitoring are also discussed.Item Condition Monitoring for Discrete Packaged Insulated Gate Bipolar Transistors in Power Converters(2018-08) Ali, Syed Huzaif; 0000-0002-2425-1475 (Ali, SH); Akin, BilalExtensive utilization of insulated gate bipolar transistor (IGBTs) in the power converters has significantly increased concerns over its reliability. Failure of such critical component eventually cause unexpected shut downs and even lead to catastrophic faults resulting in huge economic loss. So, tools for incipient fault diagnosis and aging prognosis have to be utilized for reducing the risk of faults and accidents. Yet, established tools are not mature enough and there exist a major reliability gap exist in condition monitoring of IGBTs. In order to improve current prognostic and diagnostic tools, this dissertation investigates ongoing aging induced degradation and corresponding shifts in electrical parameters for IGBTs. Such useful electrical parameters are referred as aging precursors which are obtained after extensive thermal aging tests. Based on the aging test results, aging precursors are identified and an in-situ condition monitoring circuit has been proposed as well. Due to low component count, the proposed circuit is cost effective and can be easily integrated to conventional gate driver circuits. Based on the data measurements, further remaining useful lifetime estimation for IGBTs have been carried out as well. It is conceived that such tools lay foundations for smart-energy conversion systems which are self-capable in evaluating the degradation information using aging precursors to prevent imminent failures in the system. Briefly, this dissertation discusses: o identification and characterization of aging precursors, o development of innovate and easy-to-integrate condition monitoring circuit o development of remaining useful lifetime estimation tool based on the monitored data for advancing smart power conversion systems.Item Condition Monitoring Techniques for Permanent Magnet Synchronous Motors(2018-08) Zafarani, Mohsen; Akin, BilalDue to the variety of electric motor applications in critical service systems, they need precise control and accurate health monitoring in order to operate reliably and safely. Fault diagnosis, as the earliest step of system health management, identifies impending faults through pre-specified indexes. This is a critical process as it provides early warnings for catastrophic failures well beforehand and enables preventive maintenance schedule updates. The most important advance in this field is the implementation of fault diagnosis system embedded to drive system. In this technology, the health monitoring system is programmed in the main CPU used for controlling purposes. Also, there is no need to install any additional sensor since the same measurement used for control is sent for monitoring. This technology is growing up and still is not mature enough to be used in industries widely. In this study, rotor related faults such as magnet defect and eccentricity faults and their corresponding reflections on permanent magnet (PM) motor stator variables are investigated. An analytical approach based on a partitioned magnetic equivalent circuit is developed to determine the influence of rotor related faults on PM motor variables. Stator winding configuration, winding connection type and location of damaged rotor magnets are some of the physical properties affecting the fault signature characteristics. Several cases with different numbers of pole and slot are investigated through the proposed method. In addition, different winding connections (including star and delta connection), different winding configurations (including single and double layer, fractional and full coil pitch), and different magnet defect numbers and locations are scrutinized. The proposed tool significantly reduces the computational burden and provides sufficient accuracy which significantly eases to simulate several magnet fault scenarios and examine detailed topology dependencies in shorter times. At the last part of this research, a motor specific fault severity assessment method is proposed to calculate the amplitude of magnet defect fault signatures in the stator current and back-emf through machine and controller parameters of PMSM drive. A detailed mathematical analysis is developed based on the linear model of PMSM to predict the behavior of fault signatures in motor variables at various operating points. In order to understand and decouple the effects of motor controllers and operating points, the derivations are further extended to clarify the effects of current loop gains. Under the light of findings, the fault severity impact on the current and back-emf fault signatures is investigated exhaustively.Item Degradation Assessment and Precursor Identification for SiC MOSFETs under High Temp Cycling(Institute of Electrical and Electronics Engineers Inc., 2019-01-07) Ugur, Enes; Yang, Fei; Pu, Shi; Zhao, S.; Akin, Bilal; 0000-0001-6912-7219 (Akin, B); Ugur, Enes; Yang, Fei; Pu, Shi; Akin, BilalSilicon carbide (SiC) power mosfets are promising alternatives to Si devices in high-voltage, high-frequency, and high-temperature applications. The rapid and widespread deployment of SiC devices raises long-term reliability concerns, particularly for mission and safety critical systems due to limited field data and potential uncertainties. Therefore, it is essential to investigate progressive degradations and parameter shifts in SiC devices to develop system integrated degradation monitoring tools for self-monitoring converters, which can recognize failure precursors at the earliest stage and prevent catastrophic failures. This paper presents a comprehensive long-term reliability analysis of commercially available SiC mosfets under high temperature operation and high temperature swing, degradation related key precursors, and possible causes behind them. For this purpose, discrete SiC devices are power cycled and all datasheet parameters are recorded at certain intervals with the aid of the curve tracer. Variation of electrical parameters throughout the tests is presented in order to assess their correlation with the aging/degradation state of the switch. Among them, gate oxide charge trapping related threshold voltage drift and corresponding on state resistance variation has been observed for all samples. For some samples, bond wire heel cracking is found to be the root cause of sudden on state resistance and body diode voltage increases. The discussions regarding aging precursors are supported by failure analysis obtained through the decapsulation of failed devices. Finally, the findings are evaluated in order to define the suitability of electrical parameters as an aging precursor parameter under the light of practical implementation related issues. ©1972-2012 IEEE.Item Design and Analysis of Integrated Planar Transformer for LLC Converter(2018-05) Gurusamy, Vigneshwaran; 0000-0002-9366-1777 (Gurusamy, V); Akin, BilalPlanar Magnetics is replacing conventional magnetic structures in many applications. Especially Planar transformers are good choice for applications requiring integrated magnetics. LLC converter takes advantage of the features of planar magnetics resulting in power density improvement of the converter system. This thesis deals with design of one such integrated planar transformer for LLC converter. Design flow of integrated planar magnetics is discussed in detail. The major issue of high frequency eddy current loss and achieving required leakage inductance are highlighted. The reason behind the high frequency eddy current losses due to proximity effect and skin effect are discussed and solution to address the high frequency loss are provide. It is shown that the solutions to reduce eddy current losses reduces leakage inductance which is good for converter systems where only magnetizing inductance of transformer plays vital role and the leakage inductance, a parasitic parameter causes undesired effects. For integrated transformer where we need significant leakage inductance, modifying design to include a leakage layer is shown to improve leakage without compromising losses.Item Design of a High-Performance DC Power Cycling Test Setup for SiC MOSFETs(Institute of Electrical and Electronics Engineers Inc., 2019-03-17) Yang, Fei; Ugur, Enes; Pu, Shi; Akin, Bilal; 0000-0001-6912-7219 (Akin, B); Yang, Fei; Ugur, Enes; Pu, Shi; Akin, BilalIn this paper, a high-performance DC power cycling setup dedicated for SiC power MOSFETs is presented. Different from the previous DC power cycling setup designs focusing on circuit topology and operation principle, this paper discusses the detailed design considerations to ensure the measurement accuracy and control the voltage spikes within the safe voltage range of the data acquisition (DAQ) equipment. Specifically, the transient behavior of the circuit is analyzed, and a simulation model is built in LTspice to facilitate the design. From the simulation result, it is observed that the gate timing control is critical to limit the measurement spikes. In addition, adding decoupling capacitors helps to attenuate the ringing noise in the voltage measurement. A prototype is built, and the experimental results indicate that a precise measurement can be realized with the proposed DC power cycling setup under various conditions. © 2019 IEEE.Item Diagnosis of Inter Turn Short Circuit Fault in Permanent Magnet Synchronous Machines(2018-11-13) Qi, Yuan; Akin, BilalInter turn short circuit (ITSC) fault is one of the most common faults in permanent magnet synchronous machines (PMSM). ITSC fault has limited impact on system performance in early stages, but it can turn into several failures without proper treatment. Therefore, it is important to characterize ITSC fault of PMSM and develop reliable fault diagnosis algorithms. In the past few years, many studies proposed different kinds of ITSC fault detection algorithms, such as motor current signature analysis, parameter identifications, real-time estimators and searching coils. Recently, the study about ITSC fault mitigation algorithms has drawn more attentions due to its potential of extending the fault machine lifetime. Instead of immediate replacement, the fault machine can operate with proper control techniques, which can prevent the deterioration of existing ITSC fault and reduce the risk of system total failure. This technique is essential to mission and cost critical systems, which are unable to replace the fault machine immediately. By applying fault mitigation algorithms, the fault machine can still operate until the next available maintenance for replacement. However, the precise and reliable mitigation algorithm requires a good understanding of ITSC fault condition, particularly the number of shorted turns and short circuit current. The number of shorted turns is the key parameter used in modeling the ITSC fault machine. The short circuit current is the main reason that causes damage on insulation material. A reliable mitigation method should be able to limit the short circuit current in a safety range. However, it is impossible to measure the short circuit current in real application. Therefore, it requires short circuit current estimation method in order to provide a feedback for evaluating the performance of ITSC fault mitigation algorithms. In this study, the characterization of ITSC fault is analyzed in detail at first. Following that, a parameter identification method is provided to estimate the number of shorted turns at standstill condition. At last, a short circuit current estimation algorithm is developed based on back electromotive force (back-EMF) estimation.Item Efficiency Optimization of Double-sided LCC Matching Network for Electric Vehicle Inductive Power Transfer System(2022-05-01T05:00:00.000Z) Nguyen, Van Thuan; Fahimi, Babak; Liu, Cong; Balsara, Poras T.; Akin, Bilal; Lee, HoiThis thesis presents an efficiency optimization of double-sided inductor-capacitor-capacitor (LCC) matching network for inductive power transfer (IPT) systems. Compensation factors of the primary and secondary LCC circuit are defined and optimized, both analytically and numerically. Through this investigation, the secondary compensation factor, krx, highly influences the copper loss of the wireless coupler, while the primary compensation factor, ktx, affects the switching loss and conduction loss of the input inverter. With a proper selection of these compensation factors, it is possible to achieve a high and sustained efficiency over a wide range of load and misalignment. For the analysis-based optimization, the matching networks are assumed to be lossless in order to simplify the process of the analytical derivation. The established formulae presented in this thesis is compact and convenient to use. In order to take into account the conduction loss of the input inverter and rectifier, and the losses on components of matching networks, a Genetic Algorithm (GA) - based optimization is implemented. The primary and secondary compensation factor are the variables needed to be solved by the GA optimization. The fitness function is the total loss of the circuit, and the GA optimization will search for a pair of variables, ktx and krx, to minimize the fitness function, while satisfies a constraint, which is the output power. It will be shown later that the results of the GA optimization agree excellently with the ones from the analysis-based optimization. Therefore, both methods presented can be utilized in practice, providing a convenient tool for designers who deals with the LCC-LCC matching network in IPT applications. In addition, a sensitivity analysis study is presented in this thesis in order to investigate the impact of components’ tolerance on the winding-to-winding efficiency and input power factor. In order to demonstrate the feasibility and validity of the proposed method, a scaled-down prototype of an IPT system has been implemented with the operating frequency of 85kHz, transfer gap of 170mm and misalignment of up to 100mm. Experimental results show a good agreement with the theoretical analysis. The peak efficiency of the proposed system is 91.6% under the perfect alignment or at the coupling coefficient of 0.172. The efficiency still remains at 86.37% even under 100mm misalignment with the coupling coefficient of 0.123. The optimization method presented in this thesis is for the double-sided LCC topology, however, the author believes the optimization methodology can be applied for other topologies of matching networks in IPT systems.Item Electromagnetic Optimization of Switched Reluctance Motor for Torque Ripple and Vibration Mitigation(2022-12-01T06:00:00.000Z) Movahed Mohammadi, Seyed Ehsan; Fahimi, Babak; Prasad, Shalini; Nourani, Mehrdad; Balsara, Poras T.; Akin, BilalSwitched reluctance motor (SRM) generates torque based on the principle of reluctance torque using a discontinuous rotating magnetic field. Double saliency of SRM causes magnetic reluctance to change with respect to rotor position. SRM is singly excited on the stator and it does not need magnetic excitation on its rotor. This feature makes SRM to be a simple, low cost, and robust configuration that makes it desirable for high speed and harsh applications. However, SRM exhibits high levels of torque ripple contributing to its acoustic response. The main contributing factor to this behavior is the non-uniform distribution of the flux and force density in SRM. To elaborate, SRM experiences a sudden rise in the flux density, in the airgap when rotor and stator poles start to overlap. This causes a sudden rise in the force density in both tangential and radial components of force at points close to the stator slot and that leads to the vibration and torque ripple. To address this problem, a novel rotor geometry with optimally designed flux barriers has been proposed in this dissertation to be used along with a conventional SRM stator. An optimization algorithm comprised of Genetic Algorithm (GA) and Finite Element Analysis (FEA) has been used to identify the best rotor geometry for maintaining average torque while minimizing torque ripple and tangential vibration of the stator. The performance of the optimized motor is then compared with a conventional SRM of the same size through experiments. The results show significant improvement in torque ripple as well as vibration for the new topology with no tangible drop in efficiency at high speeds.Item Energy Trading in Local Electricity Markets With Distributed Energy Resources(2022-12-01T06:00:00.000Z) He, Li; Nguyen, Tien; Zhang, Jie; Akin, Bilal; Al-dhahir, Naofal; Li, YaoyuThe energy system has been under dramatic transformation in recent years because of the advent of smart grid technologies and the increasing penetration of distributed energy resources (DERs), such as distributed photovoltaic (PV), wind turbines, energy storage systems, electric vehicles (EV), smart appliances, and others. While the increasing penetration of DERs helps the grid decarbonization, it imposes challenges on power system operation and economics. Some regions such as California that possesses the largest PV installation in the U.S., will have to deal with the fast solar capacity expansion. When the sun shines, the systems must make frequent regulations to offset the imbalance between demand and renewable energy production. After sunset, utility companies must rapidly increase other forms of generators to compensate for the loss of solar power. Besides, DERs have also disturbed the traditional electricity market by introducing a larger proportion of flexibility to the demand side. Therefore, it calls for a reconsideration of the economic model for future electricity markets. The concept of local electricity market (LEM) has emerged as a promising trading framework for future smart grids. Different from the wholesale electricity market, LEM enables participants to share their resources such as excess renewable generation, unused energy storage capacity, extra rooftop space, flexible appliances, etc., to other entities who are in shortage. LEM can be leveraged not only to efficiently manage the local supply and demand, but also to decrease the local community’s reliance on the main grid. This dissertation proposes to mitigate the over-generation issues with ever-increasing DERs in foreseeable future by designing and evaluating different LEM architectures considering the characteristics of distributed solar, residential load, multiple market entities/stakeholders, and their interactions. More specifically, in this dissertation LEMs are categorized into two main groups: peer-to-peer (P2P) models and subscription models, to investigate the interactions between different participating entities with various supply/demand and optimization goals. Besides, different pricing strategies are explored, to incentivize local customers to actively manage their energy resources. For P2P markets, we explore potential cooperative and non-cooperative energy sharing and trading strategies among prosumers and consumers. For subscription markets, unique and discriminated dynamic pricing strategies that take in account of customers’ different consumption flexibility with centralized ES are developed. In addition, different data availability and privacy concerns in the LEMs are also investigated. Experimental results indicate that the proposed LEM schemes are beneficial and efficient, which are practical and supportive for the future grid decentralization and decarbonization with the capacity expansion of DERs.Item Evaluation of Alternative Source Connection's Impact on the Reliability of SiC MOSFET(2021-05-10) Zhang, Nathan; Akin, BilalConventional, widely adopted common source packaged silicon-carbide Metal Oxide Semiconductor Field Effect Transistor (SiC MOSFET) has raised concern in generating more switching losses. During every switching cycle, the stray inductance induced by the source bond wire generates a voltage that opposes the MOSFET’s driving signal. This opposing voltage slows down the switching and increases the switching loss, which causes efficiency concerns. A Kelvinconnected gate-source was introduced in recent SiC MOSFET, and it eliminates the effect of parasitic components to avoid any disturbance on the driving signal. However, the Kelvin source SiC MOSFET's lifetime and reliability performance remains undiscovered. This thesis studies the effect of the alternative source connection on MOSFET reliability by comparing their performances under different degradation tests. The conventional commercial device characterization system was found extremely time-consuming and labor-cost during the study. The conventional system can solely characterize one power device each time, and it requires switching devices under test (DUTs) manually, which causes troubles in capturing high-resolution characterization data. As a result, an automatic and large-scale power device characterization system is also proposed in this thesis. The goal of the thesis can be summarized as follows: ● Identify the effect of alternative source connection on the lifetime and reliability performance of SiC MOSFET; ● Develop an automatic and large-scale power device characterization systemItem High Efficiency Bi-Directional DC-DC Converter with Matrix Transformer Isolation for Heavy Duty Hybrid Electric Vehicles(2020-08) Mungekar, Shubham; Gohil, Ghanshyamsinh; Babak, Fahimi; Akin, BilalMedium power DC-DC converter is an essential component in Hybrid Electric Vehicle (HEV) to achieve power transfer from High Voltage bus (HV) to Low Voltage bus (LV) and vice-versa. Dual Active Bridge (DAB) is among the most researched topology for medium and higher power converters with advantages such as bidirectional power transfer, high efficiency, high modularity, and high-power density. Multi-Objective Design Optimization with low converter loss and low converter volume as its objectives is used as a basis of parameters and components design. Integrated planar Matrix transformer is employed for galvanic isolation of the two voltage buses providing lower transformer losses compared to the traditional transformers. Peak Current mode control is implemented in DSP control card to ensure DC offset across the transformer is minimum as well as ensuring faster transient response in cascade with closed loop voltage control. The converter design is prototyped as a proof of concept, which can operate within a wide range of input voltages (400V-800V) and serves low-voltage high-current loads.Item Impact of Threshold Voltage Instability on Static and Switching Performance of GaN Devices with p-GaN Gate(Institute of Electrical and Electronics Engineers Inc., 2019-03-17) Yang, Fei; Xu, Chi; Akin, Bilal; 0000-0001-6912-7219 (Akin, B); Yang, Fei; Xu, Chi; Akin, BilalThe p-GaN gate technology has been adopted to realize enhancement-mode GaN devices. However, the blocking voltage can cause the threshold voltage to drift in p-GaN devices In this paper, the impact of the threshold voltage instability on the static and switching performance of the p-GaN device is studied. Specifically, a Vₜₕ measurement circuit is first designed which is able to characterize the threshold voltage after applying a minimum high voltage pulse of 2 μs. From the experimental result, an increase of more than 0.7 V in Vₜₕ is observed within several μs after blocking the high voltage. The static characteristics of the same device are compared before and after blocking the high voltage, and a reduced knee point in the output characteristic is observed at a low gate-to-source voltage. Due to the static characteristic variation, the switching performance of the device is also changed after stressed with the high drain-to-source voltage. Specifically, from the double pulse test result at 400 V/25 A with R₉ =20 Ω, more than 20% increase of turn-on loss is recognized after blocking the high voltage for 30 minutes. The turn on loss difference is minimized when the gate resistance value is reduced to 0 Ω. For the turn-off loss, the impact of Vₜₕ's shift is negligible. Detailed analysis is also provided to explain the experimental result. It is concluded that higher gate drive voltage and lower gate resistance helps to minimize the threshold voltage instability's effect on the device's performance. © 2019 IEEE.Item In Circuit Frequency Response Analysis for Control Design and Monitoring of Power Converters(2018-05) Bhardwaj, Manish; 0000-0001-5925-5436 (Bhardwaj, M); Akin, BilalIn power electronic applications, frequency response analysis (FRA) data is used to analyze the plant, design the control and verify the control design. Traditionally, external equipment is used to measure the frequency response by breaking the feedback path and injecting signals inside the closed loop system. This limits the use of FRA to design time of the converter. Recently in-circuit FRA measurement techniques have been presented. However, most techniques so far have required either special hardware to run, like FPGA, or required host processing power to do the complete computation. The aim of this research is to: • Design an in-circuit frequency response measurement algorithm that can run in a cycle efficient manner without any host computation requirements and is easily embedded into a commercial microcontroller used for controlling the power stage. • Highlight the constraints and assumptions under which in-circuit FRA can work, along with limits of in-circuit FRA such as noise performance and frequency bands. • Develop and demonstrate use of the designed in-circuit FRA on DC-DC, AC-DC and DC-AC converters, proving and highlighting the wide applicability of the developed technique for rapid control design. • Apply the developed in-circuit FRA for monitoring and diagnostic applications, showcasing applicability for extending capabilities with digital control of power converters.Item Induction Generator Based More Electric Architectures for Commercial Transport Aircraft(2016-12) Jia, Yijiang; Rajashekara, Kaushik; Akin, BilalIn the trend toward more electric aircraft, optimizing the performance of the new electrical power system in terms of reliability, fault-tolerance, size, weight, e ffciency and cost is quite a challenging task, in which the type of the generator has great impact on the overall performance of the system. This dissertation explores and evaluates the option of using an induction generator for the distributed electrical power system of commercial transport more electric aircraft. In this dissertation, induction generator based electrical power generation and management system architectures are developed for both the main engine generation system and auxiliary power unit system. The application of induction generator in the proposed systems improves the system power density compared to synchronous generator based systems, and avoids the excessive faulty current issue caused by permanent magnet (PM) generators. In the main engine generation system, an induction generator based AC/DC hybrid electric power generation system under twin-shaft twin-generator concept is proposed. The proposed AC/DC hybrid generation architecture supplies constant voltage variable frequency power directly from the generator winding terminals, and enables load sharing between the two engine shafts. Control schemes are developed to regulate the AC load voltage and coordinate DC power generation between the two generators. The feasibility of operation of the proposed system is demonstrated by both computer simulation and hardware-in-the-loop real-time emulation. An auxiliary power unit (APU) that allows the regenerative power from the actuators to be absorbed by the turbine shaft of the APU is proposed. An open-end winding induction starter/generator is used to provide direct power flow path from the electro-hydrostatic actuators (EHAs) and/or electro-magnetic actuators (EMAs) to the power source, and to create a separate electric actuation bus without significant additional hardware requirement. A closed-loop control scheme for regulating both main DC bus and actuation DC bus voltages in aircraft emergency power mode is developed and verified by simulation in MATLAB/Simulink. A modular back-up power link unit for re-confi gurable fault-tolerant actuation system architecture is also proposed to provide additional power supply path for the flight safety critical actuator loads in the proposed auxiliary power unit based regenerative power management strategy. A closed-loop control scheme for extracting constant and steady power flow from the primary power source through the modular back-up power link unit is developed and verified by simulation in MATLAB/Simulink. The proposed more electric architectures in this dissertation provide solutions for electri fication development of aircraft systems in terms of enhancing the electric power generation capacity of the aircraft, reducing the hardware requirement of the electric power generation and distribution system, managing the high peak and regenerative power flow from the EHA/EMAs, and enhancing the reliability and availability of the flight safety critical actuation system and the regenerative power management system.