Second year technical report on-board processing for future satellite communications systems

Advanced baseband and microwave switching techniques for large domestic communications satellites operating in the 30/20 GHz frequency bands are discussed. The nominal baseband processor throughput is one million packets per second (1.6 Gb/s) from one thousand T1 carrier rate customer premises terminals. A frequency reuse factor of sixteen is assumed by using 16 spot antenna beams with the same 100 MHz bandwidth per beam and a modulation with a one b/s per Hz bandwidth efficiency. Eight of the beams are fixed on major metropolitan areas and eight are scanning beams which periodically cover the remainder of the U.S. under dynamic control. User signals are regenerated (demodulated/remodulated) and message packages are reformatted on board. Frequency division multiple access and time division multiplex are employed on the uplinks and downlinks, respectively, for terminals within the coverage area and dwell interval of a scanning beam. Link establishment and packet routing protocols are defined. Also described is a detailed design of a separate 100 x 100 microwave switch capable of handling nonregenerated signals occupying the remaining 2.4 GHz bandwidth with 60 dB of isolation, at an estimated weight and power consumption of approximately 400 kg and 100 W, respectively

Англійська мова для студентів електромеханічних спеціальностей

Навчальний посібник розрахований на студентів напряму підготовки 6.050702 Електромеханіка. Містить уроки, що структуровані за тематичними розділами, граматичний коментар, короткі англо-український і українсько- англійський словники та додатки, які спрямовані на закріплення загальних навичок володіння англійською мовою. Акцентований на ɨсобливості термінології, що застосовується у науково-технічній галузі, зокрема, в електромеханіці та виконання запропонованих завдань, що буде сприяти формуванню навичок перекладу з англійської та української мов, сприйняттю письмової та усної англійської мови, вмінню письмового викладення англійською мовою науково-технічних та інших текстів під час професійної діяльності, спілкуванню з професійних та загальних питань тощо

A mixed-integer convex approximation for optimal load redistribution in bipolar DC networks with multiple constant power terminals

This paper proposes a mixed-integer convex model for optimal load-balancing in bipolar DC networks while considering multiple constant power terminals. The proposed convex model combines the Branch and Cut method with interior point optimization to solve the problem of optimal load balancing in bipolar DC networks. Additionally, the proposed convex model guarantees that global optimum of the problem is found, which ensures minimal power losses in the bipolar DC distribution grid branches, as the total monopolar load consumption has been balanced at the substation's terminals. In addition, an optimal load balancing improves the voltage profiles due to current redistribution between the positive and negative poles. Numerical results in the 21- and 85-bus test feeders and a comparison with three metaheuristic techniques show the effectiveness of the proposed convex model in reducing the total grid imbalance while minimizing the power losses and improving the voltage profiles

Measurements, Models, Systems and Design

531 s.

Application of advanced on-board processing concepts to future satellite communications systems

An initial definition of on-board processing requirements for an advanced satellite communications system to service domestic markets in the 1990's is presented. An exemplar system architecture with both RF on-board switching and demodulation/remodulation baseband processing was used to identify important issues related to system implementation, cost, and technology development

Management and Protection of High-Voltage Direct Current Systems Based on Modular Multilevel Converters

The electrical grid is undergoing large changes due to the massive integration of renewable energy systems and the electrification of transport and heating sectors. These new resources are typically non-dispatchable and dependent on external factors (e.g., weather, user patterns). These two aspects make the generation and demand less predictable, facilitating a larger power variability. As a consequence, rejecting disturbances and respecting power quality constraints gets more challenging, as small power imbalances can create large frequency deviations with faster transients. In order to deal with these challenges, the energy system needs an upgraded infrastructure and improved control system. In this regard, high-voltage direct current (HVdc) systems can increase the controllability of the power system, facilitating the integration of large renewable energy systems. This thesis contributes to the advancement of the state of the art in HVdc systems, addressing the modeling, control and protection of HVdc systems, adopting modular multilevel converter (MMC) technology, with focus in providing services to ac systems. HVdc system control and protection studies need for an accurate HVdc terminal modeling in largely different time frames. Thus, as a first step, this thesis presents a guideline for the necessary level of deepness of the power electronics modeling with respect to the power system problem under study. Starting from a proper modeling for power system studies, this thesis proposes an HVdc frequency regulation approach, which adapts the power consumption of voltage-dependent loads by means of controlled reactive power injections, that control the voltage in the grid. This solution enables a fast and accurate load power control, able to minimize the frequency swing in asynchronous or embedded HVdc applications. One key challenge of HVdc systems is a proper protection system and particularly dc circuit breaker (CB) design, which necessitates fault current analysis for a large number of grid scenarios and parameters. This thesis applies the knowledge developed in the modeling and control of HVdc systems, to develop a fast and accurate fault current estimation method for MMC-based HVdc system. This method, including the HVdc control, achieved to accurately estimate the fault current peak value and slope with very small computational effort compared to the conventional approach using EMT-simulations. This work is concluded introducing a new protection methodology, that involves the fault blocking capability of MMCs with mixed submodule (SM) structure, without the need for an additional CB. The main focus is the adaption of the MMC topology with reduced number of bipolar SM to achieve similar fault clearing performance as with dc CB and tolerable SM over-voltage

Evolved features in MVDC railways and HVDC networks by energy storage systems

Per decenni, la corrente alternata (CA) è stata lo standard per la maggior parte dei sistemi elettrici in tutto il mondo; La corrente continua (CC) era limitata in pochi campi di interesse, di solito in sistemi o reti progettate per scopi specifici (ad esempio trazione ferroviaria o linee di trasmissione su lunge distanze). Tale paradigma sta cambiando dall'inizio del Ventunesimo Secolo, quando i progressi tecnologici nell'elettronica di potenza hanno reso la CC in grado di competere contro la CA in molti campi: attualmente, un gran numero di dispositivi in CC viene usato a tutti i livelli della nostra società, nel privato, negli affari, nell'industria e nei servizi. Questa enorme rivoluzione ha toccato solo marginalmente le già citate reti CC preesistenti; molti notevoli miglioramenti sono stati ottenuti in tali aree, ma la struttura o la funzione generale di questi sistemi sono sempre le stesse: nel campo ferroviario, ad esempio, la maggior parte della distribuzione CC è ancora basata sui vecchi raddrizzatori a diodi; la maggior parte delle linee di trasmissione ad alta tensione in corrente continua (HVDC) si basano ancora sulla classica tecnologia LCC (Line Commutated Converters). Negli ultimi anni, sia nelle reti CA che CC, sta emergendo una nuova serie di critità: picchi di carico più elevati stanno creando problemi di stabilità di tensione e qualità dell'energia; l'inerzia della rete si sta riducendo a causa dell'enorme penetrazione di fonti di energia rinnovabili non programmabili. Questo lavoro analizza le reti ferroviarie e i collegamenti HVDC, due dei più importanti sistemi di alimentazione CC di oggi; in entrambi sono state introdotte caratteristiche evolute da sistemi di accumulo di energia (ESS) e convertitori di potenza (PEC): recupero di energia e stabilizzazione della tensione sulla trazione; inerzia sintetica negli HVDC. Grazie alle elevate prestazioni dinamiche e all'alto livello di controllabilità, i convertitori di potenza e gli ESS possono mitigare i problemi sopra citati. I costi di investimento stanno diminuendo ma sono ancora rilevanti, quindi è necessaria una valutazione tecnico-economica; poiché tale analisi è estremamente complessa, sono state introdotte alcune semplificazioni, utilizzando ipotesi cautelative. L'approccio è top-down (dal generale al particolare), considerando l'attrezzatura come parte di un impianto, concentrandosi principalmente sulle funzionalità; diverse configurazioni sono testate e convalidate da simulazioni. Successivamente, vengono analizzate le soluzioni di progettazione, gli algoritmi di controllo vengono spiegati e confrontati, presentando vantaggi e svantaggi.For decades, Alternating Current (AC) has been the standard for most of electric power systems worldwide; Direct Current (DC) was confined in few fields of interest, usually in networks or grids designed for specific purposes (e.g. rail traction or very long distances transmission lines). Such paradigm is changing since the beginning of the 21st Century, when technological progress in power electronics made DC able to compete against AC in many fields: presently, a huge number of DC power devices is used at every level of our society, in private, business, industry and services. This huge revolution only touched marginally the mentioned pre-existing DC networks; many remarkable improvements have been got in such areas, but the general shape or function of those systems are still the same: in railway field, as example, the most of DC distribution is still based on old-style diode rectifies; majority of Direct Current High Voltage (HVDC) transmission lines are still based on classic Line Commutated Converters (LCC) technology. In recent years, both in AC and DC networks, a new set of critical issues is emerging: higher load peaks are creating problems of voltage stability and power quality; grid inertia is lowering by huge penetration of renewable-not-programmable energy sources. This work analyzes railway grids and HVDC links, two of the most relevant DC power systems of today; in both of them, evolved features are introduced by Energy Storage Systems (ESS) and innovative Power Electronics Converters (PEC): energy recovery and voltage stabilization about traction; synthetic inertia about HVDC. Due to fast dynamic performances and high level of controllability, power converters and ESS can mitigate above mentioned issues. Investment costs are lowering but still relevant, thus technical-economical evaluation is needed; because such analysis is extremely complex, some simplifications have been introduced, using precautionary hypothesis. Approach is top-down, considering equipment as part of a plant, mainly focusing on functionalities; several configurations are tested and validated by simulations. Later on, design solutions are analyzed, control algorithms are explained and compared, presenting advantages and disadvantages.DIPARTIMENTO DI ENERGIA29PIEGARI, LUIGID'ANTONA, GABRIEL

Proceedings of the Second International Mobile Satellite Conference (IMSC 1990)

Presented here are the proceedings of the Second International Mobile Satellite Conference (IMSC), held June 17-20, 1990 in Ottawa, Canada. Topics covered include future mobile satellite communications concepts, aeronautical applications, modulation and coding, propagation and experimental systems, mobile terminal equipment, network architecture and control, regulatory and policy considerations, vehicle antennas, and speech compression