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X-WR-CALDESC:Events for EE
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TZID:Asia/Kolkata
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DTSTART:20240101T000000
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BEGIN:VEVENT
DTSTART;TZID=Asia/Kolkata:20240307T100000
DTEND;TZID=Asia/Kolkata:20240307T120000
DTSTAMP:20260527T101521
CREATED:20240305T092013Z
LAST-MODIFIED:20240305T092532Z
UID:241397-1709805600-1709812800@ee.iisc.ac.in
SUMMARY:Phd Thesis Defense
DESCRIPTION:Title: Pulse Width Modulation Techniques of Two-level Inverter Fed Asymmetrical Six-phase Machine Drive in Linear and Overmodulation Regions \nName of the Student: Sayan Paul \nName of the Advisor: Dr. Kaushik Basu \nDegree Registered: Ph.D. \nDate and Time: 07th March\, 2024\, 10:00 AM  \nTeams Meeting Link \nALL ARE CORDIALLY INVITED. \nAbstract: \nMulti-phase machines (MPMs) have more than three windings in their stator\, rotor\, or both. With the broader adoption of power-electronic converters for efficient driving of the machines\, MPMs are gaining attention in different applications due to their certain advantages over three-phase machines. One such advantage is higher fault tolerance due to having higher phase redundancy\, which makes it suitable for safety-critical applications like electric vehicles (EVs)\, ship propulsions\, electric aircraft\, etc. Another advantage is that MPMs allow power splitting across multiple phases. Hence\, the power rating per phase drive unit becomes low\, making it suitable for high-power applications like railway traction\, pumps\, compressors\, etc. Recent literature also proposes using the same multi-phase converter fed MPM\, otherwise used for propulsion\, as an onboard battery charger; it substantially reduces space\, weight\, and cost. During charging mode\, the leakage inductance of the machine provides the required inductance for the grid connection\, and MPM’s higher degrees of freedom are used to lock the rotor electronically. An asymmetrical six-phase machine (ASPM) is one of such MPMs and is very common in EVs. This thesis aims to devise the pulse-width modulation (PWM) techniques of a two-level six-phase inverter fed ASPM to improve the overall drive efficiency.  \nASPM has two sets of balanced three-phase windings\, which are spatially shifted by 30 degrees (electrical angle). In one of the popular configurations\, the two three-phase winding sets are connected in star fashion with two isolated neutral points. This machine is conventionally analyzed in two two-dimensional (2D) orthogonal subspaces. One of these subspaces is associated with electromagnetic energy transfer and torque production. The other subspace doesn’t transfer energy through the air gap and the equivalent circuit in this plane\, consisting of winding resistance and leakage inductance\, provides a low impedance. Therefore\, excitation of this non-energy-transferring subspace causes a large current and associated copper loss. Any PWM technique of ASPM aims to synthesize the desired voltages in the energy-transferring plane and minimize the applied voltage in the non-energy-transferring subspace.  \nLinear modulation techniques (LMTs) of ASPM apply zero average voltage in the non-energy-transferring subspace and synthesize the desired voltages in the energy-transferring plane on an average over a switching cycle. It is desired that these LMTs should avoid more than two switching transitions of an inverter leg within a carrier period to limit the instantaneous switching loss. Through an innovative approach\, our work finds a way to account for all possible infinitely many LMTs that follow the rule of at most two transitions per leg. But each of them results in a different current ripple performance. Ripple current is inevitable in PWM converters and should be minimized through modulation to reduce the associated copper loss. The total ripple current RMS of ASPM is contributed by both energy-transferring and non-transferring planes. One machine parameter also impacts this performance\, which is the ratio of high-frequency inductances in these two subspaces. For all reference voltage vectors and the whole feasible range of the machine parameter\, our work finds the techniques with minimum current ripple RMS among the above infinite possible LMTs through numerical optimization. A hybrid PWM strategy is proposed with these optimal techniques\, which outperforms all existing techniques in terms of current ripple performance. \nOvermodulation (OVM) techniques of ASPM attain higher voltage gain in energy-transferring subspace than LMTs by applying non-zero average voltage in the non-energy transferring subspace. This operation doesn’t cause any torque ripple\, but the applied voltage in non-energy transferring subspace should be minimized to reduce unwanted current and associated loss. The existing OVM technique in the literature minimizes this average voltage from the space-vector perspective with a pre-defined set of four active vectors. To find the best technique\, one needs to perform the above minimization problem with all possible sets of active vectors\, which can give higher voltage gain. So\, this requires the evaluation of a large number of cases. In this thesis\, we have formulated the above minimization problem in terms of average voltage vectors of two three-phase inverters\, where active vectors need not be specified beforehand. Thus\, the analysis is more general. Following the above analysis\, eight switching sequences in one part and two in another part of OVM are derived\, which attain the minimum average voltage injection in the non-energy transferring subspace. \nAlthough the above OVM sequences apply the same average voltages in the two subspaces\, they have different high-frequency ripple currents due to having different switching strategies. The current ripple study of the OVM techniques of ASPM is missing in the literature. Hence\, one of our works in the thesis studies the current ripple performances of the above PWM sequences in the OVM region\, which apply minimum average voltage in the non-energy-transferring subspace. The article finds the sequence with the best ripple performance for a given reference vector in the OVM region and the machine parameter. After that\, a PWM technique is proposed\, which substantially improves the high-frequency current ripple RMS compared to two existing OVM techniques for a feasible machine parameter. \nFinally\, simple carrier-comparison-based implementation methods of the proposed LMTs and OVM sequences will be discussed. The six-phase inverter is split into two three-phase inverters\, and the proposed strategy implements the PWM sequences per three-phase inverter basis. In carrier-based implementations\, the duty signal of the top switch of an inverter leg is compared with a triangular carrier. The bottom switch’s gating pulse complements the top switch’s pulse with a fixed dead time. The duty signal of the top switch of any leg has two components- a modulation signal and a common-mode signal. And two 180-degree phase-shifted carrier signals are required to implement the proposed sequences. The energy-transferring plane of ASPM is divided into twenty-four equivalent sectors; the carrier signals and the expressions of modulation and common-mode signals differ from one sector to another. Henceforth\, a sector-independent algorithm is proposed in this thesis to derive these signals with a lower computational burden and smaller size of program memory. \nThe above theoretical analyses are validated through MATLAB Simulink simulation and experiments on a hardware prototype at a power level of 4 kW. \n 
URL:https://ee.iisc.ac.in/event/phd/
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DTSTART;TZID=Asia/Kolkata:20240325T080000
DTEND;TZID=Asia/Kolkata:20240325T110000
DTSTAMP:20260527T101521
CREATED:20240313T091258Z
LAST-MODIFIED:20240313T104335Z
UID:241415-1711353600-1711364400@ee.iisc.ac.in
SUMMARY:PhD Oral Exam
DESCRIPTION:Title: Reduced Electrolytic Capacitor-Based Single-Phase Converters: Topologies\, Control\, and StabilityName of the Student: Anwesha MukhopadhyayName of the Advisor: Prof. Vinod JohnDegree Registered: Ph.D.Date and Time:  25th March\, 2024\, 08:00 AMTeams Meeting Link:Abstract: Single-phase power converters find wide applications as inverters. Applications ranging from a few hundred Watts for household solar micro-inverters\, to multi-Megawatt levels for electric traction power train\, single-phase converters are adopted worldwide.In single-phase power conversion\, there is always a mismatch between the instantaneous input and output power\, producing a second-harmonic ripple in the dc link current. Electrolytic capacitors are conventionally deployed for filtering the second-harmonic ripple due to their low cost and excellent energy density. However\, their frequent premature failures often compromise the lifespan of the converters. In recent technologies demanding high power density\, active filters have minimised the electrolytic capacitors in the circuit. However\, the cost\, efficiency\, and power density trade-offs need scrutiny before adopting an active filter topology.Among the reported active filters (AF) for second-harmonic ripple mitigation\, series capacitor stacked buffer (SSB) topology has emerged as a popular choice owing to its high efficiency and compactness. The use of low VA-rated switching devices enables achieving the high efficiency equivalent to passive filters. Despite its prospective utility in a range of applications\, the model of the SSB\, essential for implementing functional engineering control strategies under a wide range of operating conditions\, is not discussed in existing literature.In the first part of the work\, the plant model for controlling the buffer converter in voltage control mode as well as current control mode is developed. Using the proposed model\, a closed-loop control scheme is developed\, which ensures a fixed-frequency switching of the buffer converter. A step-by-step controller design procedure is elaborated\, and the controller gain limit is identified to ensure closed-loop stability.Based on the developed SSB model\, an average current mode control is implemented in the second part of the work. Unlike the existing methods of current mode control\, in the proposed scheme\, the current reference is estimated without using the dc-link current sensor\, which is verified experimentally.The SSB-based existing topologies\, though promising for many applications\, are not realised with minimum switch counts. As opposed to four switch H-bridge-based buffer converter\, two switch-based series capacitor stacked buffer converter topologies are synthesised in this part of the work. The generalised topology synthesis procedure and control challenges are identified. One of the proposed two-switch-based topologies named Series Capacitor Boost Hybrid Filter (SC-BOHF) is implemented and verified experimentally.Apart from the active solutions\, an alternative dc bus filter structure\, consisting of a combination of an inductor (L) and capacitor (C)\, tuned at the second harmonic (2ω) frequency\, reduces the capacitance requirement\, enhancing the likelihood of deployment of film capacitors. The proposed solid-state tuning restorer (SSTR) offers consistent filtering performance of the LC filter under frequency and parameter variations. As per the tuning requirement of the LC filter\, SSTR acts as an electronic inductor or capacitor. It also ensures a graceful degradation in the filter characteristics during SSTR converter failure modes. The evolution of the SSTR configuration\, analysis of its VA rating\, and control requirements are studied in this work.The realisation that SSTR requires to behave as an electronic inductor and capacitor as per the sense of LC filter detuning motivated this part of the work\, where a unified active capacitor and inductor (UACI) is proposed and implemented without using any dc capacitor. Based on the current reference\, the proposed configuration emulates inductive or capacitive characteristics and smoothly transits from one characteristic to another. The operation of the proposed UACI is studied\, and a closed-loop control scheme is developed.All the proposed methods are validated on hardware prototypes that have been developed as a part of the research.             ——————           ALL ARE WELCOME               —————
URL:https://ee.iisc.ac.in/event/phd-oral-exam/
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BEGIN:VEVENT
DTSTART;TZID=Asia/Kolkata:20240326T090000
DTEND;TZID=Asia/Kolkata:20240326T110000
DTSTAMP:20260527T101521
CREATED:20240325T061036Z
LAST-MODIFIED:20240325T061324Z
UID:241418-1711443600-1711450800@ee.iisc.ac.in
SUMMARY:PhD Thesis defence on Imaging Inverse Problems
DESCRIPTION:Title : Improved Derivative-based Regularizations for Imaging Inverse   problems\n\nStudent : Manu Ghulyani\n\nAdvisor : Prof. Muthuvel Arigovindan\n\nThesis Examiner:  Prof.  Ajit Rajwade\nDepartment of Computer Science and Engineering\,\nIIT Bombay.\n\nDate and Time:   26.03.2024 (Tuesday)\,  :.9:00  am\n\nVenue :  MMCR\, Department of Electrical Engineering\n\nAlso online in Teams\n\n\n\nAbstract:\n\n\nImages undergo degradation during the capturing process due to physical limitations inherent to the capturing devices. Addressing this degradation and recovering high-quality images constitute the image recovery problem\, a crucial concern with diverse applications across various fields such as biology\, astronomy\, and medicine. The enhancement of captured image resolution significantly influences these disciplines. Examples of this problem include tasks like reconstructing computed tomography images\, magnetic resonance imaging\, image deconvolution\, and microscopic image reconstruction.\n\nImage recovery is frequently approached using regularization techniques\, with derivative-based regularizations being popular due to their ability to exploit image smoothness\, yielding interpretable results devoid of introduced artifacts. Total Variation regularization (TV)\, proposed by Rudin\, Osher\, and Fatemi\, is a seminal approach for image recovery. TV involves the norm of the image’s gradient\, aggregated over all pixel locations. As TV encourages minimal values in the derivative norm\, it leads to piece-wise constant solutions\, resulting in what is known as the “staircase effect.” To mitigate this effect\, the Hessian Schatten norm regularization (HSN) employs second-order derivatives\, represented by the pth norm of eigenvalues in the image hessian vector\, summed across all pixels. HSN demonstrates superior structure-preserving properties compared to TV. However\, HSN solutions tend to be overly smoothed. To address this\, we introduce a non-convex shrinkage penalty applied to the Hessian’s eigenvalues\, deviating from the convex lp norm. While the analytical form of this penalty was unknown\, we derived the algorithm using proximal operations. We established that the proposed regularization adhered to restricted proximal regularity\, ensuring the algorithm’s convergence. The images recovered by this regularization were sharper than the convex counterparts.\n\nIn the subsequent work\, we extend the concept of the Hessian-Schatten norm. By encompassing Schatten norms of the Hessian and introducing a smoothness constraint\, we broaden the scope of Hessian Schatten norm. The resulting regularization can be derived as a Lagrange dual of the Hessian Schatten norm\, akin to the total generalized variation. Furthermore\, we present an efficient variable splitting scheme for solving image restoration challenges.\n\nTotal Generalized Variation (TGV) represents an important generalization of Total Variation. TGV involves multiple orders of derivatives\, with higher-order TGV leading to improved recovered image quality. This enhancement has been validated through numerical experiments in image denoising. Consequently\, a demand arises for an algorithm capable of solving TGV for any order. While various methods address TGV regularization\, many are confined to second-order TGV\, and only a few explore orders greater than three for image recovery with TGV regularization. To our knowledge\, no algorithm resolves image recovery challenges employing TGV regularization for orders exceeding three under a general forward model. This challenge arises from the intricate nature of TGV representation. We surmount this obstacle by presenting two simple matrix based representations of TGV: the direct and compact forms. We prove the equivalence of both forms with the original TGV definition. Leveraging the compact representation\, we propose a generalized ADMM-based algorithm to solve TGV regularization for any order.\n\nALL ARE WECOME.
URL:https://ee.iisc.ac.in/event/phd-thesis-defence-on-imaging-inverse-problems/
LOCATION:Multi-Media Class Room (MMCR)\, EE Department (Hybrid mode)
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