How did the USSR miss stealth technology? Part 1 P.Yu. Ufimtsev and the edge wave method-Como a URSS perdeu a tecnologia furtiva? Parte 1 P.Yu. Ufimtsev e o método da onda de borda

The discovery that actually enabled the development of the Lockheed F-117, the first truly stealthy aircraft, was achieved by the Russian physicist Pyotr Ufimtsev, who in 1962 published a paper on a new method (not the first) for estimating edge diffraction, which became known as the Physical Theory of Diffraction. Ufimtsev postulated that Maxwell's equations would make it possible to calculate the behavior of radar waves relayed from a reflective object. The radar return would depend in part on the shape of the object.

Probably one of the main achievements of the Soviet era is the enormous development of technical and basic sciences. It is worth saying that during the period 1950–1970, 7 people became Nobel Prize laureates in physics, 1 in chemistry (from 1980 to 2019, only 3, and that’s a stretch). The number of scientific workers in the USSR in 1975 was a quarter (a quarter, Karl) of the scientific workers of the whole world. 

The era of 1950-1970 was marked by brilliant achievements in astronautics, nuclear energy and the aviation industry. It’s the last one I’d like to talk about. Ufimtsev and the edge wave method All this enormous scientific potential often transformed from quantity to quality. So, in 1962, a young scientist, 

P.Ya. Ufimtsev published a monograph “The method of edge waves in the physical theory of diffraction.”

Being familiar with it from a course in electrodynamics, I can say that the reading is quite difficult, but entertaining, and non-specialists in the field of antennas and microwave devices will understand little in it. This book consists of solving diffraction problems on simple bodies and mainly consists of deriving formulas. Here are some, for example:

Example of output of one of the formulas 

 With the help of such calculations, solutions to a number of diffraction problems for a wedge and disk were obtained, and non-uniform parts of the current were found for these bodies. The theory of physical optics existing at that time did not take into account the uneven part of the current, which was concentrated near the kink. To put it more roughly, it turned out to be possible to more accurately describe the further behavior of electromagnetic waves when falling on surfaces with kinks and sharp edges. More accurately predict the structure of scattered waves. It would seem, what does aviation have to do with it?

Stealth aircraft concept Since the mid-20th century, almost all countries have used radar stations to monitor air or water space.

Let's focus only on air. The detection range of an object: an airplane, a helicopter, a seagull or a crow is largely determined by the characteristics of the radar, but there is one characteristic that is inherent to the object - the effective scattering area (ESR). EPR is a quantitative measure of the scattering of an electromagnetic wave. The higher the EPR value, the further away the object can be detected. The EPR is determined by the physical and geometric properties of the object.

The problems solved by Ufimtsev allowed us to formulate the concept of inconspicuous objects. Using such an ideology in the construction of aircraft and knowing the characteristics of enemy radars, it was possible to significantly reduce the detection range. This technology, which will later become evident in Yugoslavia (this will be discussed in Part 2), can provide a huge advantage. Let me remind you that the time of writing the monograph was 1962, the time of the Cuban Missile Crisis and the Cold War. The world was on the brink of war and destruction. The arms race continued and the use of stealth technology could make it possible to take the lead in this race.

However, the Soviet Union did not take the idea seriously. And there are many reasons for this. At that time, the Soviet Union focused on the speed and maneuverability of aircraft (MiG-15, MiG-17). The new concept implied a complete abandonment of these parameters. To build an airplane using stealth technology, it was necessary to reinvent the airplane, just as Steve Jobs later reinvented the telephone. Unfortunately, the USSR is not a country in which any discussion on this matter was possible. The exact reason why the Soviet Union abandoned the development of a low-observability aircraft is unknown. The monograph sold a large circulation of 6,500 copies and it is doubtful that none of the management thought about using this theory. 

 Development in the USA

 Let's move to the USA. At that time, American aircraft could not boast of their power. The first development of a stealth aircraft in the United States began in 1958. However, the attempts were unsuccessful. The planes were much inferior to the Soviet ones, as demonstrated by the Vietnam War. Their basic science lagged behind. They had not heard about the edge wave method until they accidentally (or maybe not) translated Ufimtsev’s monograph in 1971. Having got their hands on the theory, the missing link, they began development. The project received funding of several billion dollars. Lockheed and Northrop, using Ufimtsev’s theory and computer modeling (this was already possible in the USA in 1975), were able to develop in 1983 the first aircraft completely made using Stealth technology (Stealth - cunning) - the F-117 Night Hawk. one of the F-117 developers stated

“Ufimtsev’s contribution to the construction of this aircraft is about 30-40%, that is, a controlling stake.”

Many journalists began to write about the "invisible plane." But this is absolutely incorrect. Firstly, it is visible in the optical range, and secondly, it is inconspicuous in a certain sector of angles for certain radars.

 I will share my calculation, carried out while still at the institute. If you look at the scattering diagram of the F-117, you can see how much lower its frontal RCS is. Thanks to this shape, the aircraft re-radiates most of the energy of electromagnetic waves into the upper hemisphere. In the direction of the radar, the radiation is extremely small. The ESR of the F-117 aircraft when irradiated from frontal and tail angles is reduced to 0.1-0.01 m2, which is approximately 100-200 times less than that of a conventional aircraft of similar sizes.

Pyotr Yakovlevich Ufimtsev, who at that time was working at a research institute in Moscow, did not know anything about the fact that an airplane had been developed in the USA based on his monograph. Imagine his surprise when, in 1990, he went to a conference in the USA by invitation, after finishing his report, the audience gave him a standing ovation, but he could not understand how he had gained such fame. In the USSR he was known to few people. But his monograph became a reference book for Lokcheed Martin engineers. After so many years, he got what he deserved. True, not in my home country. In the 90s, no one in Russia needed scientific personnel, the economic crisis and meager salaries. Ufimtsev goes to work at the University of California at Los Angeles as a visiting professor and participates in the creation of the B2 strategic bomber. Now Ufimtsev is 88 years old and lives in America.

P.Ya. Ufimtsev published a monograph “The method of edge waves in the physical theory of diffraction.” «Метод краевых волн в физической теории дифракции».

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Design and characterization of a three-phase current source inverter using 1.7kV SiC power devices for photovoltaic applications Luis Gabriel Alves Rodrigues THÈSE Pour obtenir le grade de DOCTEUR DE LA COMMUNAUTE UNIVERSITE GRENOBLE ALPES Spécialité : Génie Electrique

 

Design and characterization of a three-phase current source inverter using 1.7kV SiC power devices for photovoltaic applications 

Luis Gabriel Alves Rodrigues 

 THÈSE Pour obtenir le grade de DOCTEUR DE LA COMMUNAUTE UNIVERSITE GRENOBLE ALPES Spécialité : Génie Electrique 

 Abstract

 Classically, the energy conversion architecture found in photovoltaic (PV) power plants includes solar arrays delivering a maximum voltage of 1kV followed by a step-up chopper connected to a three-phase Voltage Source Inverter. This multistage conversion system (DC/DC + DC/AC) is then connected to the medium-voltage grid through a low-voltage/medium-voltage transformer. In order to simplify the PV systems, this research work focuses on the study and implementation of a DC/AC topology employing a single power processing stage: the three-phase Current Source Inverter (CSI). To deal with the inconvenient of high conduction losses when implementing this topology, wide-bandgap Silicon Carbide (SiC) semiconductors are used, allowing to efficiently convert energy while keeping a relatively high switching frequency. Nonetheless, since the available power semiconductor modules on the market are not compatible with the CSI, a novel 1.7kV SiC-based voltage bidirectional module is developed in the context of this thesis. Hence, the dynamic characterization of the new SiC device is carried out and serves as the basis for the design of a 60kW CSI prototype. Finally, the inverter efficiency is evaluated at nominal operating conditions, employing both a calorimetric and electrical methods. The obtained results confirm the CSI ability to operate efficiently at high switching frequencies (η>98.5% @60kHz). The originality of this work lies mainly in the design, characterization and implementation of the new 1.7kV full-SiC power module adapted to the CSI topology.

 Keywords: Power electronics, DC/AC converters, Current Source Inverter (CSI), Silicon Carbide (SiC), Photovoltaics, Power module.

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6배압 정류기를 이용한 고전압 전원장치에 관한 연구 (A Study of the High Voltage Power Supply using a Sixfold Voltage-Multiplying Rectifier) 안태영*․길용만** (Tae-Young Ahn․Yongl-Man Gil)----Journal of the Korean Institute of IIIuminating and Electrical Installation Engineers (2015) 29(2)：19～26

6배압 정류기를 이용한 고전압 전원장치에 관한 연구 (A Study of the High Voltage Power Supply using a Sixfold Voltage-Multiplying Rectifier) 안태영*․길용만** (Tae-Young Ahn․Yongl-Man Gil)

 Abstract 

This paper presents design, fabrication, and performance evaluation of a high voltage power supply for Carbon Nano Tube-based planar light sources. The proposed power supply employs an LLC resonant half-bridge converter and a sixfold voltage-multiplying rectifier. Steady-state characteristics of the voltage-multiplying rectifier are analyzed and used to derive the input-to-output voltage conversion ratio of the power supply. The input-to-output frequency response characteristics of the LLC tank circuit are analyzed and utilized in designing a proto-type power supply which produces a 15 KV output using a 400 V input source. The high-voltage transformer is fabricated using a sectional bobbin structure with an epoxy impregnation, in order to provide sufficient insulation for high voltage operations. The performance of the proposed power supply is confirmed with stable and reliable operations at the 15 KV output from no load to nominal load conditions. The proposed power supply is well suited as an electric ballast required stable operations of Carbon Nano Tube-based planar light sources.

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Modeling and Design of Medium-Frequency Transformers for Future Medium-Voltage Power Electronics Interfaces A thesis submitted to attain the degree of DOCTOR OF SCIENCES of ETH ZURICH (Dr. sc. ETH Zurich) presented by THOMAS PAUL HENRI GUILLOD

 Modeling and Design of Medium-Frequency Transformers for Future Medium-Voltage Power Electronics Interfaces A thesis submitted to attain the degree of DOCTOR OF SCIENCES of ETH ZURICH (Dr. sc. ETH Zurich) presented by THOMAS PAUL HENRI GUILLOD MSc ETH born on 09.09.1989 citizen of Bas-Vully, Switzerland accepted on the recommendation of Prof. Dr. Johann W. Kolar, examiner Prof. Dr. Dražen Dujić, co-examiner 2018

Abstract 

Newly available fast-switching Medium-Voltage (MV) Silicon-Carbide (SiC) semiconductors are setting new limits for the design space of MV converters. Unprecedented blocking voltages (up to 15 kV), higher switching frequencies (up to 200 kHz), higher commutation speeds (up to 100 kVμs), and high temperature operation can be reached. These semiconductors feature reduced switching and conduction losses and, therefore, allow for the realization of extremely efficient and compact MV converters. Moreover, the increased blocking voltage allows the usage of simple single-cell topologies for MV converters instead of complex multi-cell systems. Hence, the MV SiC semiconductors are interesting for many applications such as locomotive traction chains, datacenter power supply chains, collecting grids for renewable energies, high power electric vehicle chargers, and more-electric aircraft. Most of these applications require an isolated DC-DC converter for providing voltage scaling and galvanic isolation. However, the increased voltages and frequencies allowed by MV SiC semiconductors create new challenges for the design of Medium-Frequency (MF) transformers, which start to become the bottleneck of isolated DC-DC converters in terms of power density and efficiency. More specifically, the winding losses (due to skin and proximity effects) and the core losses (due to eddy currents and hysteresis) are rapidly increasing and mitigate the advantages (e.g., the reduced volt-second product applied to the magnetic core) obtained with the increased operating frequencies. Moreover, the MV/MF PWM voltages with fast switching transitions are also particularly critical for the insulation of MF transformers and can lead to additional losses, thermal breakdowns, and partial discharge induced breakdowns. Finally, the MF transformers of DC-DC converters should feature reduced losses (efficiencies above 99:5 %) in order to match the performance offered by the MV SiC semiconductors. The main focus of this thesis is, thus, set on the design of highly efficient MV/MF transformers employed in isolated DC-DC converters. First, a theoretical analysis of MF transformers is conducted in order to extract the fundamental performance limitations of such devices. The nature of the optimal designs is examined with analytical models, scaling laws, and numerical optimizations. Afterwards, several points are identified as critical and are studied in more detail. First, the impact of model uncertainties and parameter tolerances on MF transformers is examined with statistical methods in order to highlight the achievable modeling accuracy. Then, a 2.5D numerical field simulation method is presented for assessing the impact of non-idealities on the losses produced vii Abstract by litz wire windings (e.g., twisting scheme and pitch length). Afterwards, the impact of MV/MF PWM voltages with fast switching transitions on the insulation is examined. The electric field pattern is analyzed inside, at the surface, and outside the insulation and shielding methods are proposed. Finally, the dielectric loss mechanisms of dry-type insulation materials under PWM voltages is examined in detail. Different analytical expressions are proposed for extracting the insulation losses and it is found that the dielectric losses can be significant for MV/MF transformers operated with MV SiC semiconductors. Design guidelines are proposed for the selection of appropriate insulation materials for MV/MF applications and silicone elastomer is identified as an interesting choice. All the presented results are verified with measurements conducted on different MF transformer prototypes. The derived models and results are applied to a MV isolated DC-DC converter, which is part of a MV AC (3:8 kV, phase-to-neutral RMS voltage) to LV DC (400 V) Solid-State Transformer (SST) demonstrator. This SST is aimed to supply future datacenters directly from the MV grid. The considered 25 kW DC-DC converter operates between a 7 kV DC bus and a 400 V DC bus. The usage of 10 kV SiC MOSFETs allows for the realization of the converter with a single-cell DC-DC Series-Resonant Converter (SRC). The DC-DC SRC is operated at 48 kHz as a DC Transformer (DCX) and the modulation scheme, which allows for Zero-Voltage Switching (ZVS) of all semiconductors, is examined in detail. The realized MV/MF transformer prototype features a power density of 7:4 kWl (121 kWin3, 4:0 kWkg, and 1:8 kWlb) and achieves a full-load efficiency of 99:65 %. The complete DC-DC converter achieves an efficiency of 99:0 % between 50 % and 100 % load with a power density of 3:8 kWl (62Win3, 2:9 kWkg, and 1:3 kWlb). The results obtained with the constructed DC-DC converter, which are significantly beyond the stateof- the-art, demonstrate that MV/MF transformers can utilize the possibilities offered by the new MV SiC semiconductors. .

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Thèse de doctorat en Génie électrique Option: Automatique Présentée par: SAFA AHMED-Etude de la contribution de l’électronique de puissance dans les microréseaux-Ecole Nationale Polytechnique Département Automatique Laboratoire de Commande des Processus

Ecole Nationale Polytechnique Département Automatique Laboratoire de Commande des Processus

Thèse de doctorat en Génie électrique

Option: Automatique

Présentée par:

SAFA AHMED

Magistère en Génie électrique Université de Tiaret.

Composition du Jury :

Président: TADJINE Mohamed Pr ENP

Examinateurs: MAHMOUDI Mohand Oulhadj Pr ENP

BOUCHAFAA Farid Pr USTHB

ALLAOUI Tayeb Pr U. Tiaret

GHEDAMSI Kaci Pr U. Bejaia

Rapporteurs: MESSLEM Youcef Pr U. Tiaret

BERKOUK El Madjid Pr ENP

ENP 2018

Etude de la contribution de l’électronique

de puissance dans les microréseaux

RESUMO 

A configuração clássica das modernas redes elétricas de alta potência oferece um grande número de vantagens em relação às antigas do ponto de vista da flexibilidade. Além disso, grandes unidades de produção tornam-se mais eficientes e operam apenas com um número relativamente pequeno de pessoal. A rede interligada de transmissão de alta tensão permite minimizar a necessidade de reservas de geração, enviá-la a qualquer momento para a instalação de geração de energia mais eficiente e transportá-la a granel por grandes distâncias com perdas elétricas limitadas. A rede de distribuição pode ser projetada para fluxos de energia unidirecionais e dimensionada para suportar apenas cargas do cliente ou bidirecional. No início da década de 2000, a utilização de energias renováveis, especialmente as baseadas na energia solar e eólica, registou um verdadeiro crescimento. Impulsionados pelos objectivos climáticos e pelos benefícios económicos, vários países em todo o mundo aumentaram as suas ambições. Dada a natureza centralizada das redes eléctricas, a integração de fontes de energia distribuídas (Distributed Energy Sources DES) representa um desafio para os operadores de rede. As autoridades de vários países iniciaram a desregulamentação do mercado energético o que resultou na produção descentralizada, é o caso da rede da Califórnia nos EUA, e na Argélia os textos regulatórios foram desenvolvidos, mas a implementação permanece. Diante dessa nova tendência energética, surgiu um novo conceito: a microrrede (Microgrid MG). Um MG é uma agregação de fontes e cargas que aparece para a rede central como uma carga dinâmica. Portanto, uma microrrede é uma rede dentro de uma rede. As motivações que incentivam a MG são: 

 Redução de emissões gasosas (principalmente CO2). 

 Eficiência energética ou uso racional de energia.

  Desregulamentação ou política de concorrência.

 Diversificação das fontes de energia.

 Requisitos de energia nacionais e globais. Outras razões, mas com ênfase adicional em considerações comerciais, tais como:

  Disponibilidade de centrais eléctricas modulares. 

 Facilidade de encontrar locais para pequenos geradores.

  Tempos de construção curtos e custos de investimento reduzidos para pequenas fábricas.

  A geração pode estar localizada mais próxima da carga, o que pode reduzir os custos de transmissão. Para preservar a estabilidade e a qualidade do serviço, as autoridades reguladoras estabeleceram padrões (especificações) para a microrrede para que possam ser conectadas à rede. Estas normas exigem, entre outras coisas, um determinado mínimo para os índices de qualidade da eletricidade (taxa THD, taxa de desequilíbrio, etc.). O objetivo deste trabalho de tese é desenvolver algoritmos de controle para melhorar a qualidade da eletricidade de uma microrrede para que ela cumpra os diferentes códigos regulatórios. E desenvolver um algoritmo que permita a sincronização do inversor que é o órgão central da rede. Esta tese está dividida em cinco capítulos. No primeiro capítulo é apresentado o princípio da geração distribuída, suas vantagens trazidas para a rede de distribuição e suas desvantagens. O conceito de microrrede (Microgrid MG) é então apresentado como a solução para integração ideal e mais controlada de fontes de geração distribuída. Para se conectar à rede, o MG deve estar alinhado ao padrão de conexão, portanto são citados problemas de qualidade de energia. Para melhorar a qualidade da eletricidade de um MG, um conversor estático, muitas vezes um inversor multifuncional (MultiFunctionql Grid Tied Inverter MFGTI), é conectado ao PCC. O estado da arte das técnicas de sincronização de conversores à rede seguido do estado da arte do controle MFGTI concluirá este primeiro capítulo. O segundo capítulo foca no desenvolvimento de uma técnica de sincronização para conversores conectados em rede. Nosso objetivo é desenvolver um algoritmo que seja insensível à qualidade da tensão da rede e leve para implementação em processadores de baixo custo. O terceiro capítulo apresenta a análise e desenvolvimento de um controle MFGTI baseado nos princípios das potências instantâneas. O Estimador de Componente Fundamental Positiva PFCE desenvolvido no Capítulo 2 será usado para extrair diretamente a fundamental da corrente de carga sem mudança de fase ou erro. Um controle de modo deslizante é desenvolvido para controlar a tensão do barramento CC. Consequentemente, o método desenvolvido neste capítulo é denominado PFCE-SMC. O quarto capítulo é dedicado ao desenvolvimento de um controle baseado no método de controle direto do MFGTI. Um controle de modo deslizante é usado para estimar a amplitude da corrente da fonte a partir da configuração da tensão do barramento CC. Para melhorar o controle, uma ação integral é adicionada com um filtro passa-baixa, daí o nome SMC-LPF. ​

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