M. Ghaffarian Niasar
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1
Increasing wind farm capacity via overplanting enhances energy production but risks accelerating cable aging if transmission capacity is poorly managed. Consequently, resilient Dynamic Cable Rating (DCR) prediction-defined as the ability to maintain stability under data quality degradation and operational shifts-is crucial for reliable operation. However, achieving this is challenged by limited datasets, missing data, and complex spatio-temporal correlations. To address these issues, a resilient DCR prediction and thermal estimation framework is developed. First, a Conditional Generative Adversarial Network (CGAN) is applied to synthetically augment limited datasets, effectively resolving the load data imbalance. Second, a Spatio-Temporal Graph Attention Residual Shrinkage Network (STGARSN) is proposed. This model integrates an extended Long Short-Term Memory (LSTM) network with Temporal Convolutional Networks (TCN) and a graph attention mechanism to capture complex correlations. Crucially, it incorporates a residual shrinkage module to filter noise and outliers, thereby ensuring model resilience. Finally, to optimize economic performance while minimizing cable aging, a comparative analysis of various overplanting strategies is conducted. Experiments on real cable temperature measurements demonstrate the superior resilience of the proposed model, maintaining high accuracy not only across different forecasting horizons but also under conditions of missing data and sensor noise. The proposed framework accurately predicts DCR and supports long-term offshore wind farm operations through improved economic and technical decision-making.
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Increasing wind farm capacity via overplanting enhances energy production but risks accelerating cable aging if transmission capacity is poorly managed. Consequently, resilient Dynamic Cable Rating (DCR) prediction-defined as the ability to maintain stability under data quality degradation and operational shifts-is crucial for reliable operation. However, achieving this is challenged by limited datasets, missing data, and complex spatio-temporal correlations. To address these issues, a resilient DCR prediction and thermal estimation framework is developed. First, a Conditional Generative Adversarial Network (CGAN) is applied to synthetically augment limited datasets, effectively resolving the load data imbalance. Second, a Spatio-Temporal Graph Attention Residual Shrinkage Network (STGARSN) is proposed. This model integrates an extended Long Short-Term Memory (LSTM) network with Temporal Convolutional Networks (TCN) and a graph attention mechanism to capture complex correlations. Crucially, it incorporates a residual shrinkage module to filter noise and outliers, thereby ensuring model resilience. Finally, to optimize economic performance while minimizing cable aging, a comparative analysis of various overplanting strategies is conducted. Experiments on real cable temperature measurements demonstrate the superior resilience of the proposed model, maintaining high accuracy not only across different forecasting horizons but also under conditions of missing data and sensor noise. The proposed framework accurately predicts DCR and supports long-term offshore wind farm operations through improved economic and technical decision-making.
Journal article
(2026)
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S. Ghafoor, R. Mirzadarani, H. Dialani, P.T.M. Vaessen, M. Ghaffarian Niasar
This article presents a scalable transformer-coupled open-loop gate-driving technique that enables voltage balancing across series-connected GaN devices. High-voltage pulse generation with short rise times at kilovolt levels is a significant challenge. Conventional solid-state devices such as insulated-gate bipolar transistors and SiC metal–oxide–semiconductor field-effect transistors, though capable of high blocking voltages, are limited in switching speed and cannot reach the nanosecond regime. Gallium nitride (GaN) high-electron-mobility transistors (HEMTs) due to their lateral structure offer low gate charge and ability to switch faster than 50 V/ns, are an attractive potential candidate. However, due to their lateral architecture, GaN HEMTs also have limited voltage-blocking capability, with most commercially available GaN power devices rated up to approximately 650 V, limiting their direct use in fast high voltage waveform generation at kilo-volts level. Series-connecting GaN devices can overcome this limitation but introduces severe voltage-balancing challenges, as even minor gate-signal mismatch at nanosecond timescale can cause destructive imbalance. Conventional closed-loop balancing methods, are difficult to implement at GaN switching speeds due to feedback latency. This article presents a simple open loop technique for driving GaN devices in series with a transformer-coupled gate driver. The proposed gate drive ensures simultaneous turn-on/off with identical gate signals across all devices. An ultrafast full-bridge GaN based inverter excites wideband gate-drive transformers designed to preserve the ultrafast transition speeds of individual devices, while providing high-voltage isolation and near-equal voltage sharing establishing a scalable solution. Experimental results with two series-connected GaN HEMTs confirm nearly balanced voltage sharing at 1 kV across varying loads and currents
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This article presents a scalable transformer-coupled open-loop gate-driving technique that enables voltage balancing across series-connected GaN devices. High-voltage pulse generation with short rise times at kilovolt levels is a significant challenge. Conventional solid-state devices such as insulated-gate bipolar transistors and SiC metal–oxide–semiconductor field-effect transistors, though capable of high blocking voltages, are limited in switching speed and cannot reach the nanosecond regime. Gallium nitride (GaN) high-electron-mobility transistors (HEMTs) due to their lateral structure offer low gate charge and ability to switch faster than 50 V/ns, are an attractive potential candidate. However, due to their lateral architecture, GaN HEMTs also have limited voltage-blocking capability, with most commercially available GaN power devices rated up to approximately 650 V, limiting their direct use in fast high voltage waveform generation at kilo-volts level. Series-connecting GaN devices can overcome this limitation but introduces severe voltage-balancing challenges, as even minor gate-signal mismatch at nanosecond timescale can cause destructive imbalance. Conventional closed-loop balancing methods, are difficult to implement at GaN switching speeds due to feedback latency. This article presents a simple open loop technique for driving GaN devices in series with a transformer-coupled gate driver. The proposed gate drive ensures simultaneous turn-on/off with identical gate signals across all devices. An ultrafast full-bridge GaN based inverter excites wideband gate-drive transformers designed to preserve the ultrafast transition speeds of individual devices, while providing high-voltage isolation and near-equal voltage sharing establishing a scalable solution. Experimental results with two series-connected GaN HEMTs confirm nearly balanced voltage sharing at 1 kV across varying loads and currents
The increasing penetration of renewable energy sources and frequent lightning and switching events have intensified transient phenomena in modern power systems, exposing power transformers to resonance at critical frequencies. These conditions may cause internal overvoltages, and insulation failure. While many studies focus on wide-band transformer modeling and resonance identification, their primary objective is accurate frequency-domain representation rather than revealing the physical origin of resonance inside the transformer. This paper does not aim to introduce a new transformer modeling method. Instead, it presents a visualization-based approach to identify transformer components responsible for resonance. By analyzing the branch current matrix of a transformer disk model and visualizing current distribution using a color map, dominant resonance-driving elements are identified. This visualization enables protection and future design enhancement.
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The increasing penetration of renewable energy sources and frequent lightning and switching events have intensified transient phenomena in modern power systems, exposing power transformers to resonance at critical frequencies. These conditions may cause internal overvoltages, and insulation failure. While many studies focus on wide-band transformer modeling and resonance identification, their primary objective is accurate frequency-domain representation rather than revealing the physical origin of resonance inside the transformer. This paper does not aim to introduce a new transformer modeling method. Instead, it presents a visualization-based approach to identify transformer components responsible for resonance. By analyzing the branch current matrix of a transformer disk model and visualizing current distribution using a color map, dominant resonance-driving elements are identified. This visualization enables protection and future design enhancement.
Transient Overvoltages in Onshore HVDC Cable Joints
Surge Reflections and the Influence of Grounding Configurations
This study examines transient overvoltage phenomena in 525 kV high-voltage direct current (HVDC) onshore cable systems, with particular emphasis on the influence of grounding configurations in two joint types: straight-through and screen-separated. Transient overvoltages arising from wave propagation and reflections are analysed, highlighting the impact of joint types, bonding cable configurations (coaxial vs. noncoaxial) and bonding cable length on the resulting overvoltage magnitudes. The necessity of modelling screen-to-earth representations of sectionalised cables at grounded joint locations in the vicinity of faults is emphasised, whereas simplified representations of ungrounded and grounded straight-through joints are identified as sufficient for system-level simulations. To address the computational challenges of detailed electromagnetic transient simulations, a stand-alone simplified circuit is proposed to analyse grounded joint transients and to mitigate errors caused by insufficient time-step resolution. The results provide practical insights for insulation coordination, supporting the reliable integration of HVDC technology into long-distance cable-based transmission networks while enhancing system resilience.
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This study examines transient overvoltage phenomena in 525 kV high-voltage direct current (HVDC) onshore cable systems, with particular emphasis on the influence of grounding configurations in two joint types: straight-through and screen-separated. Transient overvoltages arising from wave propagation and reflections are analysed, highlighting the impact of joint types, bonding cable configurations (coaxial vs. noncoaxial) and bonding cable length on the resulting overvoltage magnitudes. The necessity of modelling screen-to-earth representations of sectionalised cables at grounded joint locations in the vicinity of faults is emphasised, whereas simplified representations of ungrounded and grounded straight-through joints are identified as sufficient for system-level simulations. To address the computational challenges of detailed electromagnetic transient simulations, a stand-alone simplified circuit is proposed to analyse grounded joint transients and to mitigate errors caused by insufficient time-step resolution. The results provide practical insights for insulation coordination, supporting the reliable integration of HVDC technology into long-distance cable-based transmission networks while enhancing system resilience.
Perfluoroalkoxy alkane (PFA) is a promising candidate for onbaord high-voltage cable insulation due to its superior dielectric properties, chemical resistance, and high thermal stability. Understanding the thermal aging behavior of PFA is essential for ensuring the long-term reliability of insulation materials in hybrid-electric aircraft, where high thermal fluctuations are common. This study investigates the chemical, structural, mechanical, and dielectric properties of PFA aged at 280 °C for up to 1000 h, simulating real-world aerospace operational environments. Results show that PFA undergoes chain scission and chemicrystallization in the early aging stages (0-480 h), leading to an increase in crystallinity. However, at longer aging times e.g. (>480 h), oxidative degradation becomes dominant, resulting in chemical and structural changes correlated with microstructural damage, including crack formation, tie-chain loss, and lamellar disruption. Dynamic mechanical analysis and tensile results show a significant decrease in molecular rigidity with a reduction in glass transition temperature (Tg), indicating a loss of material stiffness and a reduction in tensile strength (42.16%) and elongation (30.2%) after long term exposure (1000 h). Dielectric characterization demonstrates monotonic increase in dielectric constant (from 1.90 to 2.15), dissipation factor, and AC conductivity, attributed to the formation of polar oxidation products and defect-assisted interfacial polarization. The dielectric strength also decreases from 95.2 kV/mm to 87.1 kV/mm after 1000 h of aging. Molecular dynamics simulations (MDS) are also performed to study the temperature effect on PFA, revealing that at high temperatures, the PFA molecular structure is increasingly destroyed by thermal chain scission. These findings provide valuable insight into the degradation mechanisms governing PFA performance and contribute to evaluating its reliability as an insulation material for high-voltage cable systems in hybrid-electric aircraft.
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Perfluoroalkoxy alkane (PFA) is a promising candidate for onbaord high-voltage cable insulation due to its superior dielectric properties, chemical resistance, and high thermal stability. Understanding the thermal aging behavior of PFA is essential for ensuring the long-term reliability of insulation materials in hybrid-electric aircraft, where high thermal fluctuations are common. This study investigates the chemical, structural, mechanical, and dielectric properties of PFA aged at 280 °C for up to 1000 h, simulating real-world aerospace operational environments. Results show that PFA undergoes chain scission and chemicrystallization in the early aging stages (0-480 h), leading to an increase in crystallinity. However, at longer aging times e.g. (>480 h), oxidative degradation becomes dominant, resulting in chemical and structural changes correlated with microstructural damage, including crack formation, tie-chain loss, and lamellar disruption. Dynamic mechanical analysis and tensile results show a significant decrease in molecular rigidity with a reduction in glass transition temperature (Tg), indicating a loss of material stiffness and a reduction in tensile strength (42.16%) and elongation (30.2%) after long term exposure (1000 h). Dielectric characterization demonstrates monotonic increase in dielectric constant (from 1.90 to 2.15), dissipation factor, and AC conductivity, attributed to the formation of polar oxidation products and defect-assisted interfacial polarization. The dielectric strength also decreases from 95.2 kV/mm to 87.1 kV/mm after 1000 h of aging. Molecular dynamics simulations (MDS) are also performed to study the temperature effect on PFA, revealing that at high temperatures, the PFA molecular structure is increasingly destroyed by thermal chain scission. These findings provide valuable insight into the degradation mechanisms governing PFA performance and contribute to evaluating its reliability as an insulation material for high-voltage cable systems in hybrid-electric aircraft.
Review
(2026)
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Zhengzhao Li, Reza Mirzadarani, Jarno van der Weg, Werner Heyns, Robin van der Sande, Mohamad Ghaffarian Niasar, Aditya Shekhar, Pavol Bauer, Zian Qin
This paper introduces a novel control strategy for Modular Multilevel Resonant converters (MMR) in Solid-State Transformer (SST) applications, with a focus on medium-voltage conversion for hydrogen electrolyzers. The article first reviews voltage control methods in MMR, analyzing their operational principles and regulation capabilities. A continuous modulation index control method with double-step staircase waveform modulation is then proposed, simplifying the control scheme to a single control variable while maintaining robust controllability. Meanwhile, the proposed approach maintains comparable power loss and harmonic performance to existing methods under the investigated operating conditions. Simulations and experiments are conducted to verify the feasibility and practical implementation of the proposed approach.
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This paper introduces a novel control strategy for Modular Multilevel Resonant converters (MMR) in Solid-State Transformer (SST) applications, with a focus on medium-voltage conversion for hydrogen electrolyzers. The article first reviews voltage control methods in MMR, analyzing their operational principles and regulation capabilities. A continuous modulation index control method with double-step staircase waveform modulation is then proposed, simplifying the control scheme to a single control variable while maintaining robust controllability. Meanwhile, the proposed approach maintains comparable power loss and harmonic performance to existing methods under the investigated operating conditions. Simulations and experiments are conducted to verify the feasibility and practical implementation of the proposed approach.
Journal article
(2026)
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Reza Mirzadarani, Zhengzhao Li, Zian Qin, Peter Vaessen, Pavol Bauer, Mohamad Ghaffarian Niasar
This study presents a current balancing technique for high-current windings in medium-frequency transformers (MFTs), particularly relevant to solid-state transformer (SST) applications. Handling high currents on the low-voltage high-current winding of MFTs is challenging due to skin and proximity effects. Conventional techniques, such as continuously transposed conductors (CTCs) and parallel winding paths, are applicable but have limitations in medium-and high-frequency applications such as SSTs due to skin and proximity effects. To address these issues, a modular and tunable compensation method is proposed, based on adding small, series-connected inductive elements (compensation toroids) to each parallel winding path. Experimental results from a prototype validate the proposed compensation technique, highlighting its effectiveness in mitigating unbalanced current distribution. Finite element analysis (FEA) and experimental validation across a wide frequency range (1–10 kHz) confirm the effectiveness of the method. The results demonstrate a significant reduction in current imbalance with minimal added losses or system impact.
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This study presents a current balancing technique for high-current windings in medium-frequency transformers (MFTs), particularly relevant to solid-state transformer (SST) applications. Handling high currents on the low-voltage high-current winding of MFTs is challenging due to skin and proximity effects. Conventional techniques, such as continuously transposed conductors (CTCs) and parallel winding paths, are applicable but have limitations in medium-and high-frequency applications such as SSTs due to skin and proximity effects. To address these issues, a modular and tunable compensation method is proposed, based on adding small, series-connected inductive elements (compensation toroids) to each parallel winding path. Experimental results from a prototype validate the proposed compensation technique, highlighting its effectiveness in mitigating unbalanced current distribution. Finite element analysis (FEA) and experimental validation across a wide frequency range (1–10 kHz) confirm the effectiveness of the method. The results demonstrate a significant reduction in current imbalance with minimal added losses or system impact.
Accurate frequency-dependent inductances and resistances are essential for high-frequency transformer models. Traditional analytical approaches, such as cases where eddy-current losses are neglected, or resistances and inductances are computed independently, and numerical techniques such as finite element methods (FEM) are either computationally intensive or rely on simplifications that reduce accuracy. This letter proposes a novel machine learning (ML)-based approach to efficiently estimate these parameters by learning from detailed analytical results. Using a localized feature selection strategy with conductors near the nearest neighbors $k$, the model considers complex electromagnetic interactions while achieving a significant reduction in computation time. This allows for generalization across different winding designs, reducing the dependence on traditional simplifications. Furthermore, the trained ML model achieves high accuracy, with predictions within an error margin of 5% for a wide frequency range. Comparison with measurements confirms the validity and effectiveness of the proposed approach, making it a promising solution for electromagnetic transient simulations.
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Accurate frequency-dependent inductances and resistances are essential for high-frequency transformer models. Traditional analytical approaches, such as cases where eddy-current losses are neglected, or resistances and inductances are computed independently, and numerical techniques such as finite element methods (FEM) are either computationally intensive or rely on simplifications that reduce accuracy. This letter proposes a novel machine learning (ML)-based approach to efficiently estimate these parameters by learning from detailed analytical results. Using a localized feature selection strategy with conductors near the nearest neighbors $k$, the model considers complex electromagnetic interactions while achieving a significant reduction in computation time. This allows for generalization across different winding designs, reducing the dependence on traditional simplifications. Furthermore, the trained ML model achieves high accuracy, with predictions within an error margin of 5% for a wide frequency range. Comparison with measurements confirms the validity and effectiveness of the proposed approach, making it a promising solution for electromagnetic transient simulations.
Power transformer energization involves a significant electromagnetic energy exchange among system components, with periodic oscillations at the system's natural frequencies. As a result, weakly damped resonance overvoltages may occur, overstressing the system and thereby leading to potential insulation failure. This phenomenon is particularly notable for topologies where a transformer is supplied via cable, as low-damping resonance frequencies are likely to be formed due to mutual interactions between the cable and the transformer. The prestriking phenomenon during circuit breaker closing plays an important role in the excitation of resonance frequencies. Specifically, repeated prestrikes can create highfrequency resonances during switching-on operations. This paper analyzes the mutual interactions between the cable and the transformer, focusing on how the resonances between the cable and the transformer are created. Then, using a suitable modeling approach, the impact of CB prestrikes on the resultant resonance excitation in cable-transformer systems is investigated. Finally, tests are conducted using an experimental test setup to validate the investigations performed. The obtained results demonstrate that resonance frequencies emerging from cable-transformer interactions lead to the excitation of oscillatory overvoltages with extreme magnitudes.
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Power transformer energization involves a significant electromagnetic energy exchange among system components, with periodic oscillations at the system's natural frequencies. As a result, weakly damped resonance overvoltages may occur, overstressing the system and thereby leading to potential insulation failure. This phenomenon is particularly notable for topologies where a transformer is supplied via cable, as low-damping resonance frequencies are likely to be formed due to mutual interactions between the cable and the transformer. The prestriking phenomenon during circuit breaker closing plays an important role in the excitation of resonance frequencies. Specifically, repeated prestrikes can create highfrequency resonances during switching-on operations. This paper analyzes the mutual interactions between the cable and the transformer, focusing on how the resonances between the cable and the transformer are created. Then, using a suitable modeling approach, the impact of CB prestrikes on the resultant resonance excitation in cable-transformer systems is investigated. Finally, tests are conducted using an experimental test setup to validate the investigations performed. The obtained results demonstrate that resonance frequencies emerging from cable-transformer interactions lead to the excitation of oscillatory overvoltages with extreme magnitudes.
Journal article
(2026)
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Reza Mirzadarani, Zhengzhao Li, Zian Qin, Peter Vaessen, Pavol Bauer, Mohamad Ghaffarian Niasar
This paper presents a practical approach to reduce the size of medium-frequency, medium-voltage dry-type transformers through the innovative use of semiconductive screening. The proposed method minimizes the required air gaps, a critical aspect of dry-type transformer design, particularly for medium-frequency applications. Analytical approaches and Finite Element Method (FEM) simulations in COMSOL are used to demonstrate how to achieve a uniform electric field distribution within the transformers. Experimental investigations by means of partial discharge measurement on a prototype epoxy-based stress cone termination with a semiconductive shield are conducted. The results demonstrate the potential for this method to enhance transformer performance and provide a foundation for further advancements in medium-frequency transformer design.
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This paper presents a practical approach to reduce the size of medium-frequency, medium-voltage dry-type transformers through the innovative use of semiconductive screening. The proposed method minimizes the required air gaps, a critical aspect of dry-type transformer design, particularly for medium-frequency applications. Analytical approaches and Finite Element Method (FEM) simulations in COMSOL are used to demonstrate how to achieve a uniform electric field distribution within the transformers. Experimental investigations by means of partial discharge measurement on a prototype epoxy-based stress cone termination with a semiconductive shield are conducted. The results demonstrate the potential for this method to enhance transformer performance and provide a foundation for further advancements in medium-frequency transformer design.
Journal article
(2026)
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L.F.A. Wymenga, J. van Turnhout, M. Ghaffarian Niasar, H.W. van Zeijl, W.D. van Driel, Kouchi Zhang
Seed production is a vital part of the global food supply chain. Seed surfaces are often contaminated with pathogenic fungal spores and bacteria, which cause plant diseases during germination. These pathogens prevent healthy crop growth and reduce yields by up to 40% in major crops. The future use of pesticides will be restricted by increasingly stringent regulations, while the demand for healthy crops continues to rise. Therefore, there is a growing need for eco-friendly technologies to inactivate seed-borne pathogenic microorganisms, without compromising seed quality. Cold atmospheric plasma (CAP) offers a promising alternative. Generated in ambient air, CAP is an ionized gas containing electrons, photons, ions, and reactive oxygen and nitrogen species (RONS). It does not leave toxic residues. Although CAP has demonstrated effective microbial inactivation at laboratory scale, its industrial implementation remains limited due to challenges in scalability, reliability and heat production. In this study, these limitations are addressed by developing and optimizing a wire-plate dielectric barrier discharge (DBD) for CAP seed disinfection, powered by high voltage pulses. The seed disinfection efficacy of the DBD was evaluated for cabbage and carrot seeds contaminated with bacteria (Xanthomonas campestris pv. campestris (Xcc) and Xanthomonas hortorum pv. carotae (Xhc)) and fungal spores (Alternaria brassicicola). Key parameters (such as treatment time, operating voltage and seed positioning) were investigated. The individual contribution of several plasma components (such as accelerated ions, RONS, pulsed electric fields) to seed disinfection was examined. Our results demonstrate that a large-area pulsed wire-plate DBD can achieve effective disinfection, while no reduction in seedling growth was observed. This highlights its potential as a scalable and sustainable alternative to conventional seed disinfection methods.
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Seed production is a vital part of the global food supply chain. Seed surfaces are often contaminated with pathogenic fungal spores and bacteria, which cause plant diseases during germination. These pathogens prevent healthy crop growth and reduce yields by up to 40% in major crops. The future use of pesticides will be restricted by increasingly stringent regulations, while the demand for healthy crops continues to rise. Therefore, there is a growing need for eco-friendly technologies to inactivate seed-borne pathogenic microorganisms, without compromising seed quality. Cold atmospheric plasma (CAP) offers a promising alternative. Generated in ambient air, CAP is an ionized gas containing electrons, photons, ions, and reactive oxygen and nitrogen species (RONS). It does not leave toxic residues. Although CAP has demonstrated effective microbial inactivation at laboratory scale, its industrial implementation remains limited due to challenges in scalability, reliability and heat production. In this study, these limitations are addressed by developing and optimizing a wire-plate dielectric barrier discharge (DBD) for CAP seed disinfection, powered by high voltage pulses. The seed disinfection efficacy of the DBD was evaluated for cabbage and carrot seeds contaminated with bacteria (Xanthomonas campestris pv. campestris (Xcc) and Xanthomonas hortorum pv. carotae (Xhc)) and fungal spores (Alternaria brassicicola). Key parameters (such as treatment time, operating voltage and seed positioning) were investigated. The individual contribution of several plasma components (such as accelerated ions, RONS, pulsed electric fields) to seed disinfection was examined. Our results demonstrate that a large-area pulsed wire-plate DBD can achieve effective disinfection, while no reduction in seedling growth was observed. This highlights its potential as a scalable and sustainable alternative to conventional seed disinfection methods.
Journal article
(2026)
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Tiantian Xu, Jawad Ahmad, Yawen Liang, Gautham Ram Chandra Mouli, Mohamad Ghaffarian Niasar
Electric aircraft represent a promising low-emission alternative to conventional fuel-powered aviation, driving the demand for lightweight and reliable electrical powertrain architectures. This study presents a design process for an electrical power system with an emphasis on the cabling system and battery in all-electric aircraft (AEA). Design considerations for the cabling system in power distribution architectures are discussed, including cable insulation material selection, conductor choice, sizing, and weight reduction methods. The influence of different system voltages and operating temperatures on cable weight is analyzed to identify optimal design tradeoffs. A comparison of polytetrafluoroethylene (PTFE) and perfluoroalkoxy (PFA) insulation materials, as well as aluminum and copper conductors, highlights their impact on weight and reliability, with PFA offering weight advantages under typical aerospace operating conditions. The batteries are sized based on the energy and power demands of a 90-seater AEA as a case study. After designing the components of the aircraft’s electrical power system, the electrical architectures are presented. Furthermore, a framework for evaluating the electrical power system architectures of AEAs is proposed, using two key criteria: reliability and weight. The weight of the electrical power system is then estimated based on aircraft performance requirements. The proposed framework provides practical guidelines for cable selection and architecture optimization in future AEAs.
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Electric aircraft represent a promising low-emission alternative to conventional fuel-powered aviation, driving the demand for lightweight and reliable electrical powertrain architectures. This study presents a design process for an electrical power system with an emphasis on the cabling system and battery in all-electric aircraft (AEA). Design considerations for the cabling system in power distribution architectures are discussed, including cable insulation material selection, conductor choice, sizing, and weight reduction methods. The influence of different system voltages and operating temperatures on cable weight is analyzed to identify optimal design tradeoffs. A comparison of polytetrafluoroethylene (PTFE) and perfluoroalkoxy (PFA) insulation materials, as well as aluminum and copper conductors, highlights their impact on weight and reliability, with PFA offering weight advantages under typical aerospace operating conditions. The batteries are sized based on the energy and power demands of a 90-seater AEA as a case study. After designing the components of the aircraft’s electrical power system, the electrical architectures are presented. Furthermore, a framework for evaluating the electrical power system architectures of AEAs is proposed, using two key criteria: reliability and weight. The weight of the electrical power system is then estimated based on aircraft performance requirements. The proposed framework provides practical guidelines for cable selection and architecture optimization in future AEAs.
Medium-Frequency Transformer for SST Applications
Design and Optimization
Journal article
(2026)
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Reza Mirzadarani, Leonardo Bolzonella, Zhengzhao Li, Zian Qin, Peter Vaessen, Pavol Bauer, Mohamad Ghaffarian Niasar
This work presents a downscaled validation of a medium-voltage, medium-frequency transformer (MFT) concept designed for high-current operation on the secondary side using multiple parallel paths. The design is based on a modular winding approach, which simplifies the construction process and conductor placement on the bobbin. A systematic design and optimization procedure is developed, combining analytical calculations and finite-element simulations to explore the mass-efficiency tradeoff and to select a candidate design that meets specified leakage inductance and loss targets. The developed prototype serves as a proof of concept, demonstrating that the electrical, magnetic, and insulation requirements of the full-scale MFT can be effectively verified at reduced power levels. The fabricated prototype is tested under short-circuit and partial discharge conditions. The impedance measurements confirmed the expected resonance behavior, and the partial discharge test results verified sufficient insulation performance under high-voltage stress. The results provide experimental evidence for the scalability and feasibility of the proposed transformer design and offer guidelines for the use of 3D-printed supports, grain-oriented electrical steel cores, and windings in medium-voltage, MFT systems for hydrogen production applications.
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This work presents a downscaled validation of a medium-voltage, medium-frequency transformer (MFT) concept designed for high-current operation on the secondary side using multiple parallel paths. The design is based on a modular winding approach, which simplifies the construction process and conductor placement on the bobbin. A systematic design and optimization procedure is developed, combining analytical calculations and finite-element simulations to explore the mass-efficiency tradeoff and to select a candidate design that meets specified leakage inductance and loss targets. The developed prototype serves as a proof of concept, demonstrating that the electrical, magnetic, and insulation requirements of the full-scale MFT can be effectively verified at reduced power levels. The fabricated prototype is tested under short-circuit and partial discharge conditions. The impedance measurements confirmed the expected resonance behavior, and the partial discharge test results verified sufficient insulation performance under high-voltage stress. The results provide experimental evidence for the scalability and feasibility of the proposed transformer design and offer guidelines for the use of 3D-printed supports, grain-oriented electrical steel cores, and windings in medium-voltage, MFT systems for hydrogen production applications.
Low-temperature atmospheric plasma (LTP) is widely used in industrial processes, such as disinfection, surface modification and wastewater treatment. The dielectric barrier discharge (DBD) is regarded as one of the most robust and reliable methods for generating LTP in ambient air. Compared to conventional AC excitation, pulsed powering offers several advantages (i.e., lower energy use and heat production). The present trend is to use short and fast pulses (in the nano- and picosecond range). In this review, the key design parameters of a DBD (barrier thickness, relative permittivity and gap distance) are discussed. Material-specific phenomena like surface charging and degradation are analyzed. The complex interactions between the pulse source and DBD are examined. By mapping the interdependencies, this review aims to support the rational design and optimization of pulsed DBD systems, and to facilitate their broader industrial use.
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Low-temperature atmospheric plasma (LTP) is widely used in industrial processes, such as disinfection, surface modification and wastewater treatment. The dielectric barrier discharge (DBD) is regarded as one of the most robust and reliable methods for generating LTP in ambient air. Compared to conventional AC excitation, pulsed powering offers several advantages (i.e., lower energy use and heat production). The present trend is to use short and fast pulses (in the nano- and picosecond range). In this review, the key design parameters of a DBD (barrier thickness, relative permittivity and gap distance) are discussed. Material-specific phenomena like surface charging and degradation are analyzed. The complex interactions between the pulse source and DBD are examined. By mapping the interdependencies, this review aims to support the rational design and optimization of pulsed DBD systems, and to facilitate their broader industrial use.
High-frequency resonances in cable-transformer systems can result in excessive overvoltages, increasing the probability of insulation failure for critical components such as power transformers. These resonances occur due to the interaction between the cable and transformer and are influenced by the cable’s characteristics, including the length and wave propagation velocity. In addition, the terminating impedances of the cable’s core and sheath conductors affect the resonance characteristic of the cable as well. Applying single-point sheath grounding to the high-voltage cable connecting the switchgear to the power transformer is conventional. This paper demonstrates that the cable-transformer resonances and resulting overvoltages can vary significantly depending on the end at which the sheath conductors are grounded. An in-depth investigation of such effects is carried out through rigorous mathematical analysis, followed by experimental validation and simulations in an electromagnetic transient (EMT)-based software using models that properly represent the equipment behaviors in a wide-frequency range. The results indicate that sheath conductor grounding configuration can profoundly affect the system response, influencing the severity of transient overvoltages caused by cable-transformer resonances.
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High-frequency resonances in cable-transformer systems can result in excessive overvoltages, increasing the probability of insulation failure for critical components such as power transformers. These resonances occur due to the interaction between the cable and transformer and are influenced by the cable’s characteristics, including the length and wave propagation velocity. In addition, the terminating impedances of the cable’s core and sheath conductors affect the resonance characteristic of the cable as well. Applying single-point sheath grounding to the high-voltage cable connecting the switchgear to the power transformer is conventional. This paper demonstrates that the cable-transformer resonances and resulting overvoltages can vary significantly depending on the end at which the sheath conductors are grounded. An in-depth investigation of such effects is carried out through rigorous mathematical analysis, followed by experimental validation and simulations in an electromagnetic transient (EMT)-based software using models that properly represent the equipment behaviors in a wide-frequency range. The results indicate that sheath conductor grounding configuration can profoundly affect the system response, influencing the severity of transient overvoltages caused by cable-transformer resonances.
Partial discharge (PD) within cavities in oil-impregnated paper (OIP) is one of the key aging mechanisms that can alter space-charge behavior and eventually contribute to insulation failure in underground cables. This study investigates the evolution of charge-transport characteristics in a three-layer OIP sample containing an artificial cavity under PD aging. Time-resolved pulsed electroacoustic (PEA) measurements show that PD aging changes the measured space-charge profiles, leading to a lower injected charge density, faster charge redistribution during depolarization, and enhanced charge accumulation near the oil–paper interfaces. To interpret these experimentally observed trends, a modified charge transport model incorporating dual-trap energy levels and hopping conduction is developed. Model fitting to the measured PEA profiles suggests that PD aging is associated with a reduction in the effective deep-trap energy level and an increase in shallow-trap density, which facilitates carrier de-trapping and promotes the redistribution of space charge from the bulk region toward the interfaces. The results provide insight into the relationship between PD-induced charge-transport modification and OIP insulation degradation, and may support the condition assessment and maintenance of underground cable insulation systems.
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Partial discharge (PD) within cavities in oil-impregnated paper (OIP) is one of the key aging mechanisms that can alter space-charge behavior and eventually contribute to insulation failure in underground cables. This study investigates the evolution of charge-transport characteristics in a three-layer OIP sample containing an artificial cavity under PD aging. Time-resolved pulsed electroacoustic (PEA) measurements show that PD aging changes the measured space-charge profiles, leading to a lower injected charge density, faster charge redistribution during depolarization, and enhanced charge accumulation near the oil–paper interfaces. To interpret these experimentally observed trends, a modified charge transport model incorporating dual-trap energy levels and hopping conduction is developed. Model fitting to the measured PEA profiles suggests that PD aging is associated with a reduction in the effective deep-trap energy level and an increase in shallow-trap density, which facilitates carrier de-trapping and promotes the redistribution of space charge from the bulk region toward the interfaces. The results provide insight into the relationship between PD-induced charge-transport modification and OIP insulation degradation, and may support the condition assessment and maintenance of underground cable insulation systems.
This paper presents the prototype development and performance evaluation of a three-stage flyback-based Input Series Converter designed as an Auxiliary Power Supply (APS) for a Modular Multilevel Converter (MMC)-based Arbitrary Waveform Generator (AWG). The APS is connected across the submodule capacitors of the MMC and converts the capacitor voltage to 24V, providing power to the gate drivers and control units within each submodule. The proposed converter features integrated active Input Voltage Sharing (IVS), a scalable architecture, and wide-input voltage operation. A multi-winding flyback transformer ensures high-voltage insulation between the submodule capacitor and the APS output while facilitating active IVS for balancing input capacitor voltages. A transformer prototype has been developed and tested in an open-loop converter configuration. The system’s performance has been evaluated at an output power of 30W across an input voltage range of 300V–3600V.
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This paper presents the prototype development and performance evaluation of a three-stage flyback-based Input Series Converter designed as an Auxiliary Power Supply (APS) for a Modular Multilevel Converter (MMC)-based Arbitrary Waveform Generator (AWG). The APS is connected across the submodule capacitors of the MMC and converts the capacitor voltage to 24V, providing power to the gate drivers and control units within each submodule. The proposed converter features integrated active Input Voltage Sharing (IVS), a scalable architecture, and wide-input voltage operation. A multi-winding flyback transformer ensures high-voltage insulation between the submodule capacitor and the APS output while facilitating active IVS for balancing input capacitor voltages. A transformer prototype has been developed and tested in an open-loop converter configuration. The system’s performance has been evaluated at an output power of 30W across an input voltage range of 300V–3600V.
PCB transformers are emerging as a promising alternative to medium-frequency wire-wound transformers due to their numerous advantages. However, research on FR-4, the primary PCB insulation material, remains limited. This study investigates the dielectric performance of PCB electrodes through interlayer breakdown tests at 50 Hz, yielding an aging curve for this condition. Additionally, layer-to-layer breakdown tests were conducted at 50 Hz and 1 kHz, revealing a reduction in time to breakdown with increasing frequency. Notably, interlayer breakdown is significantly more likely, exhibiting a breakdown strength eight times lower than that of layer-to-layer breakdown.
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PCB transformers are emerging as a promising alternative to medium-frequency wire-wound transformers due to their numerous advantages. However, research on FR-4, the primary PCB insulation material, remains limited. This study investigates the dielectric performance of PCB electrodes through interlayer breakdown tests at 50 Hz, yielding an aging curve for this condition. Additionally, layer-to-layer breakdown tests were conducted at 50 Hz and 1 kHz, revealing a reduction in time to breakdown with increasing frequency. Notably, interlayer breakdown is significantly more likely, exhibiting a breakdown strength eight times lower than that of layer-to-layer breakdown.
This paper presents a comprehensive model for power transformers, by considering eddy current losses in both the core and conductors. This is achieved through a meticulous analytical approach that ensures high fidelity in representing the transformer's electromagnetic properties. The consideration of magnetic flux effects on inductance and resistance values significantly enhances the model's accuracy and validity. Traditional analytical methods often resort to simplified approaches due to the complexity of these calculations. The paper addresses these limitations by evaluating the eddy current losses in the core and conductors, and by providing a detailed understanding of each component's impact on transformer behavior. Furthermore, by considering the core and conductor effects on the magnetic field distribution, the model handles a wide range of frequencies, making it suitable for conducting comprehensive transient analysis. To validate the model, comparisons with the finite element method and empirical measurements are conducted. Additionally, a reduced-order transformer model is developed using admittance matrix reduction. This approach focuses on the nodes of interest, effectively eliminating not-observed nodes and reducing computational complexity without compromising accuracy. In this way, voltages at specific points of interest are computed efficiently, maintaining the accuracy of the original model.
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This paper presents a comprehensive model for power transformers, by considering eddy current losses in both the core and conductors. This is achieved through a meticulous analytical approach that ensures high fidelity in representing the transformer's electromagnetic properties. The consideration of magnetic flux effects on inductance and resistance values significantly enhances the model's accuracy and validity. Traditional analytical methods often resort to simplified approaches due to the complexity of these calculations. The paper addresses these limitations by evaluating the eddy current losses in the core and conductors, and by providing a detailed understanding of each component's impact on transformer behavior. Furthermore, by considering the core and conductor effects on the magnetic field distribution, the model handles a wide range of frequencies, making it suitable for conducting comprehensive transient analysis. To validate the model, comparisons with the finite element method and empirical measurements are conducted. Additionally, a reduced-order transformer model is developed using admittance matrix reduction. This approach focuses on the nodes of interest, effectively eliminating not-observed nodes and reducing computational complexity without compromising accuracy. In this way, voltages at specific points of interest are computed efficiently, maintaining the accuracy of the original model.
This paper presents the design and optimization of a Medium Frequency Transformer (MFT) for use in Solid State Transformer (SST) systems supporting green hydrogen production. Operating at 1 kHz and integrated within an LLC resonant converter, the transformer is optimized for minimal weight and high efficiency while ensuring adequate leakage inductance and insulation performance. A core-type configuration with cylindrical windings was selected based on FEM simulations and mass-efficiency trade-offs. The final prototype, using copper conductors, achieves 97.8% efficiency with a mass below 50 kg and meets the required 7 mH leakage inductance. High-voltage testing, including partial discharge and breakdown tests, confirmed the insulation coordination of the design. The results demonstrate a practical and scalable approach for high-performance SST integration in renewable energy applications.
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This paper presents the design and optimization of a Medium Frequency Transformer (MFT) for use in Solid State Transformer (SST) systems supporting green hydrogen production. Operating at 1 kHz and integrated within an LLC resonant converter, the transformer is optimized for minimal weight and high efficiency while ensuring adequate leakage inductance and insulation performance. A core-type configuration with cylindrical windings was selected based on FEM simulations and mass-efficiency trade-offs. The final prototype, using copper conductors, achieves 97.8% efficiency with a mass below 50 kg and meets the required 7 mH leakage inductance. High-voltage testing, including partial discharge and breakdown tests, confirmed the insulation coordination of the design. The results demonstrate a practical and scalable approach for high-performance SST integration in renewable energy applications.