Shunt compensation devices have been a powerful candidate for expanding the limits of transmission facilities, allowing more active power transport and supporting voltage and overall stability of the network. An example of such devices is the Static Synchronous Compensator (STATCOM) which is based on Voltage Source Converter (VSC) which synthesizes output voltage and current for mainly reactive power compensation. STATCOMs might be accompanied with a Thyristor Switched Capacitor (TSC) or Reactor (TSR) which are controllable shunt devices for extra VARs required, along with passive filters for absorbing the switching harmonics generated by the VSC. Such STATCOM topology is referred as the Hybrid STATCOM.However, such configuration typically results in parallel resonances with the maingrid’s passive elements at different harmonic frequencies. This leads to amplification of background harmonics, if any exist, at the Point of Common Coupling (PCC) where the Hybrid STATCOM is connected. This thesis deals with the VSC control in the STATCOM to mitigate the harmonic amplification behavior by active filtering,which is based on emulating an impedance by the control. Also, the overall system passivity is essentially studied, which ensures a passive system with respect to harmonics. / Shunt-kompensationsanordningar har varit en kraftfull kandidat för att öka gränserna för överföringsanläggningar, vilket möjliggör högre aktiv effekt och understöderspännings-stabilitet och övergripande stabilitet i kraftnätet. Ett exempel på sådana enheter är Static Synchronous Compensator (STATCOM) som är baserat på Voltage Source Converter (VSC) som syntetiserar utspänning och ström för huvudsakligen reaktiv effektkompensation. STATCOMs kan åtföljas av en Thyristor Switched kapacitor (TSC) eller Reaktor (TSR) som är kontrollerbara shunt-apparater som ökar kapaciteten för reaktiv effekt (VARs), tillsammans med passiva filter för att absorbera övertoner som genereras av VSC. Sådan STATCOM-topologi kallas HybridSTATCOM. Emellertid, en sådan konfiguration resulterar i parallella resonanser med huvudnätets passiva element vid olika övertoner. Detta leder till förstärkning av bakgrundsövertoner, om någon existerar, vid Point of Common Coupling (PCC) där Hybrid STATCOM är ansluten. Denna avhandling behandlar hur VSC kontrolleras i STATCOM för att mildra förstärkningen av nivåer för övertoner genom aktivfiltrering, vilket är baserat på att VSC kontrollen emulerar en impedans. Dessutom studeras övergripande systempassivitet, vilket säkerställer ett passivt system med avseende på övertoner.

To mitigate the carbon footprint and the need to fulfil the energy goals in terms of sustainability, it is required to deploy a large integration of green energies. Therefore, in the previous and the coming years, there will be a high research and technological interest in the high penetration of converter-based generation. With the replacement and integration of power converters into the bulk power grid, new challenges and issues must be faced to maintain the system´s stability and reliability in terms of procedures for the transmission system operators. The main objective of this thesis project is to analyze and to implement the current- limiting techniques implemented in voltage source converters, which are equipped with grid-forming functionalities so that these electronic devices are safeguarded during a severe transient event as three-phase short-circuit and remain connected to the grid during the fault scenario. The model of the voltage source converter with grid-forming strategies is described as well as the grid-forming strategies (droop control, virtual synchronous machine (VSM) and dispatchable virtual oscillator control (dVOC)) utilized in the outer loop. The low-inertia and zero-inertia system in the IEEE 9-Bus test system were exhibited to be resilient towards 3-phase fault events, and their behavior shows neither significant oscillations during and after the incident of the fault nor noticeable difference in their performance regarding the location. In this test system model, the current-limiting techniques were validated and analyzed results display good effectiveness for the current and frequency. The Hydro-Québec network model was employed to have a more practical approach in the behavior of the current limitation strategies in the power converters in a real power system. The fault location and the percentage of participation of the voltage source converters in the energy generation were the two main scenarios, in which the proposed control strategies for restricting the current work but simultaneously, it is required an appropriate control to keep the system´s stability. / För att minska koldioxidutsläppet och uppnå energimålen med avseende på hållbarhet krävs integrering av hållbara energikällor. Därmed, under de föregående och kommande  åren kommer stort fokus riktas mot forskning kring ökad penetration av kraftelektronikomriktare i kraftsystemet. När kraftelektronikomriktare ersätter traditionella generationsenheter uppkommer nya utmaningar och problem som behöver lösas för att upprätthålla systemets stabilitet och pålitlighet med avseende på tillvägagångssätt för systemansvariga för överföringssystemet.  Avhandlingens huvudmål är att analysera och implementera strömbegränsande metoder för kraftelektronikomriktare av typen voltage source converters med en nätformande (”grid- forming”) funktionalitet. Strömbegränsaren ska säkerställa att kraftelektronikomriktaren skyddas under allvarliga transienta händelser och att kraftelektronikomriktaren förblir ansluten till nätet under händelsen. Modellen av kraftelektronikomriktaren med nätformande egenskaper är beskrivna tillsammans med nätformande kontrollstrategier, virtuella synkronmaskniner (VSM) och användande av avsändande virtuell oscillerande kontroll i den yttre slingan.  Den låga trögheten och noll-tröghetssystemet i IEEE 9-Bus test-system visade sig vara motståndskraftig mot trefasfel eftersom testsystemets beteende visade varken signifikanta oscillationer under och efter felet eller märkbar förändring i dess prestanda beroende på var felet inträffade. I denna testsystemsmodell var strömbegränsande tekniker validerade och de analyserande resultaten visade på god effektivitet för strömmen och för frekvensen.  Hydro-Québec nätverks-modellen användes för att få en mer praktisk inriktning med hänsyn till beteendet hos strömbegränsarna där olika strategier har använts. Felpositionen och andelen av kraftelektronikomriktare i energigenereringen var två huvudsakliga scenarion, där de föreslagna kontrollstrategierna för att begränsa strömmen fungerade men kräver samtidigt att en lämplig kontroll för att behålla systemets stabilitet.

In order to meet the increasing demand ofenergy in today’s society while at the same time minimizing theenvironmental impact, renewable energy sources will be requiredto be integrated into the existing energy mix. Technologicaladvances in high voltage direct current (HVDC) grids playa crucial role in making this possible. Therefore the purposeof this project has been to validate the properties of basiccontrol strategies in terms of how they respond to four differentsimulation cases. All simulations have been conducted on asimplified version of the CIGR ́E B4 test grid, consisting offour monopolar HVDC converters. After analyzing the resultsobtained from each control strategy it became evident thatprovided if the benefits of the redundancy introduced by amulti-terminal grid are to be fully utilized, a distributed voltagecontrol should be used. Moreover, after substituting one ofthe four internal controllers with an external one, it becameclear that simply deciding the droop constants based on resultsfrom the simulation model wouldn’t be sufficient for real worldapplications. / För att möta det ökande energibehovet i dagens samhälle, samtidigt som energiproduktionens miljöpåverkan ska minimeras, krävs det att förnyelsebara energikällor integreras i den existerande energimixen. Tekniska framsteg inom högspända likströmsnät (HVDC) spelar en avgörande roll i att göra detta möjligt. Därför har syftet med detta projekt varit att validera egenskaperna hos grundläggande kontrollstrategier efter hur dem reagerar på fyra olika simuleringsfall. Alla simuleringar har genomförts på en förenklad version av CIGRE´ B4 testsystem, bestående av fyra monopolära HVDC omriktare. Efter att analyserat de erhållna resultaten från varje kontrollstrategi blev det uppenbart att om fördelarna med multiterminala elnät skulle uppnås, bör en distribuerad spänningskontroll användas. Dessutom, efter att ha bytt ut en av dem fyra interna kontrollerna med en extern, visade det sig att endast bestämma droppkonstanterna baserat på resultat från simuleringsmodellen inte är tillräckligt för verkliga applikationer. / Kandidatexjobb i elektroteknik 2020, KTH, Stockholm

Utilization of power electronics based controllable systems (or devices) in transmission systems has opened new opportunities for the power industry to optimize utilization of the existing transmission systems, and at the same time to keep high system reliability and security. As a member of these controllable systems, Voltage Source Converters-based High Voltage direct current (VSC-HVdc) systems have the ability to rapidly control the transmitted active power, and also to independently exchange reactive power with transmissions systems. Therefore, VSC-HVdcs with a suitable control scheme can offer an alternative means to enhance transient stability, to improve power oscillations damping, and to provide voltage support. An interesting application of this system is the analysis of a power system when a VSC-HVdc is connected in parallel with ac transmission lines. This thesis presents the derivation of control strategies to damp power oscillations, to enhance the transient stability and to provide voltage support for a VSC-HVdc. The thesis also formulates a multichoice control strategy and its application when the VSC-HVdc is connected in a synchronous system. The control strategy for enhancing transient stability is based on the theory of Control Lyapunov Function. The control strategy for increasing the damping is based on Linear Analysis. A very effective well known way to increase damping in the system is modulating the active power through the HVdc. However, besides the control of active power, the thesis explores an alternative way to mitigate power oscillations by controlling the reactive power. This condition might be very useful when the dc link in the VSC-HVdc system is out of service, but the converter stations are in operating conditions. A simple model of VSC-HVdc is considered in order to test the control strategy. The model represents the VSC-HVdc as an element in the power system that provides adequate interaction with other systems elements. The model is intended for analysis of power flows and electromechanical transients. It is then sufficient to consider the power frequency components of voltages and currents represented by phasors that vary with time during transients. The model is valid for symmetrical conditions, i.e. positive sequence phasors are used for the representation of the electrical state. / QC 20101117

Då tillverkningsindustrin går mot en högre grad av kundanpassning och implementering av Lean, samtidigt som föråldrade traditionella kalkyleringsmetoder fortfarande används i moderna industriföretag, är det intressant att utreda relationerna mellan produktionsflöden av kundanpassad karaktär, Lean samt olika kalkyleringsmetoder. Syftet är att öka kostnadsprecisionen i förkalkylen för ett produktionsflöde av kundanpassad och Lean karaktär och beskriva en generaliserbar arbetsprocess för detta. Syftet är även att ta fram generella rekommendationer för val av kalkyleringsmetod genom att utifrån denna produktions karaktär genomföra en jämförande analys av kalkyleringsmetoder (traditionella kalkylmetoder, ABC och kalkylering enligt Lean). Genom en litteraturstudie samt en fallstudie av ett produktionsflöde med många varianter och inslag av Lean har båda syftena uppfyllts. Fallstudien har utförts genom intervjuer och observationer. Problem och positiva faktorer som enligt litteratur karaktäriserar produktion av kundanpassade produkter har även återfunnits på fallföretaget. Det sambandet har kunnat användas för att stödja analysen av relationerna. Relationerna mellan kalkyleringsmetoder, Lean samt produktionsflöden av kundanpassad karaktär har analyserats genom att jämföra litteratur och resultat från fallstudien. Det framkom att Value Stream Costing (VSC) är den mest lämpliga kalkyleringsmetoden för produktionsflöden med kundanpassade produkter som uppnått en hög mognadsgrad av Lean. Förkalkyleringen på fallföretaget är beroende av tillförlitliga operationstider, vilket tagits fram på fallföretaget samtidigt som en generell arbetsprocess utarbetats. Operationstiderna togs i detta fall fram genom videoupptagning av produktionsmomenten samt efterföljande analys i mjukvaran AviX. Genom att följa den generella arbetsprocessen som utarbetats erhålls både ett bra underlag till förkalkylering samt ständiga förbättringar i produktionsflödet. Eftersom forskning visar att Lean bör implementeras i hela organisationen om full fördel med Lean ska uppnås, kan VSC vara en utmärkt kalkyleringsmetod för att komma ifrån föråldrade, traditionella kalkyleringsmetoder samtidigt som denna kalkyleringsmetod förenklar kalkylering i produktion av kundanpassad karaktär. / Since the manufacturing industry is heading for a higher level of customization and implementation of Lean, at the same time as outmoded traditional costing methods is still used in modern industrial organizations, it is interesting to explore the relations between production flows of customized character, Lean and different costing methods. The purpose of this thesis is to increase the cost precision in the preliminary calculation for a product flow of customer adapted and Lean character, and to describe a generalizable work process for this. The purpose is also to develop general recommendations regarding the choice of costing methods by, on a basis of the character of this production, a comparative analysis of costing methods (traditional costing methods, ABC and Lean accounting/VSC). Through a literature study and a case study of a production flow with a high level of variety and influence from Lean, both of the purposes has been fulfilled. The case study has been accomplished through interviews and observations. Problems and positive elements that according to literature characterize the production of customized products have also been found in the case company. That connection has been used to support the analysis of the relations. The relations between costing methods, Lean and production flows of customized character has been analyzed through a comparison between findings in literature and results from the case study. It has been found that Value Stream Costing (VSC) is the most appropriate costing method for production flows of customized products that has reached a high maturity level of Lean. The preliminary costing is dependent on reliable operation times which have been produced on the case study company, while a general work process has been developed. The operation times were in this case identified through video recordings of the production moments and a following analysis in the software AviX. By following the general work process that has been developed, useful material for preliminary costing and continuous improvements in the production flow will be obtained. Since research is showing that Lean should be implemented in the whole organization if full advantages of Lean shall be obtained, VSC is found to be an ideal costing method to replace outmoded, traditional costing methods at the same time as this costing method simplifies costing in production flows of customized character.

This thesis describes the flexible voltage control of a multi-level-voltage-reinjection voltage source converter. The main purposes are to achieve reactive power generation flexibility when applied for HVdc transmission systems, reduce dynamic voltage balancing for direct series connected switches and an improvement of high power converter efficiency and reliability. Waveform shapes and the impact on ac harmonics caused by the modulation process are studied in detail. A configuration is proposed embracing concepts of multi level, soft-switching and harmonic cancellation. For the configuration, the firing sequence, waveform analysis, steady-state and dynamic performances and close-loop control strategies are presented. In order not to severely compromise the original advantages of the converter, the modulated waveforms are proposed based on the restrictions imposed mathematically by the harmonic cancellation concept and practically by the synthesis circuit complexity and high switching losses. The harmonic impact on the ac power system prompted by the modulation process is studied from idealistic and practical aspects. The circuit topology being proposed in this thesis is developed from a 12-pulse bridge and a converter used classically for inverting power from separated dc sources. Switching functions are deduced and current paths through the converter are analysed. Safe and steady-state operating regions of the converter are studied in phasor diagrams to facilitate the design of simple controllers for active power transfer and reactive power generations. An investigation into the application of this topology to the back-to-back VSC HVdc interconnection is preformed via EMTDC simulations.

Gotland har länge präglats av mycket speciella lösningar och legat i framkant vad gäller ny teknik. Under ca 20 år har Gotland haft en VSC-HVDC-station som har stabiliserat spänningen i det gotländska nätet. HVDC Light har löst en del av de tekniska begränsningarna som hindrat utvecklingen av vindkraftverk. Anläggningen börjar lida mot slutet av sin tekniska livslängd och examensarbetet är ett första steg i utredningen för en eventuell ersättning. Med hjälp av elkvalitetsmätare kartlagdes prestanda och eventuella förbättringsområden. Den svenska stamnätsoperatören Svenska kraftnät har sedan 2016 haft en VSC-HVDC-station som använts för att utväxla energi till asynkrona systemet i Östeuropa. Svenska kraftnät har på senare tid velat utnyttja spänningsregleringsmöjligheterna och utreda mättekniska metoder. Elkvalitetsmätare placerades ut på lämpliga mätpunkter för att utreda anläggningens beteenden. ELSPEC G4500 elkvalitetsmätare installerades på Nordbalt och Gotlands HVDC Light för att mäta under sensommar till hösten 2017. Skillnader mellan CVT och IVT samt Rogowskispole och CT mättes. Valet av ELSPEC lämpade sig bra eftersom att inga triggningsvillkor behövdes som tillåter att man kan upptäcka små men viktiga avvikelser. Gotlands HVDC Light stabiliserar nätet främst mot spänningsdippar efter kortslutningar i 10 kV-elnätet och flimmer ifrån vindkraftsparkerna i ände 2. Märkeffekten för en uppdaterad anläggning kommer baseras på den kortslutningseffekt i 10 kV-nätet som kan utvecklas under anläggningens livstid. Spänningsregleringen ska baseras på en PI-regulator och ska kunna reglera fullt på 40 ms. Komponentspänningar kan användas för att ge reaktiv effekt på de faser som behöver det. Behovet mot flimmer ska baseras på en mätning i närmaste konsumtionscentrum, två mil från ände 2. Om behovet finns, ska en separat loop för flimmerkontroll som motverkar 1,5 Hz-komponenter implementeras utifrån en punkt ca 1,5 mil ifrån ände 2. Teknikvalet står mellan two-level generation 3 eller MMC, beroende på uppgradering eller ersättning. Många olika framtida scenarion påverkar HVDC Lights roll och oavsett, kommer mycket resurser behövas för Gotlands och HVDC Lights framtid. Det har observerats två beteenden på Nordbalt varav ena är långsam och det andra beteendet är snabbt. Det snabba beteendet uppstår när lågohmiga fel sker som också synkronmaskinerna tar hand om. Nordbalt kan hjälpa till för mindre spänningsvariationer om den varit snabbare likt beteendet vid lågohmiga fel. En stabilitetsbedömning behövs dock eftersom att snabbare beteende ökar risken för instabilitet. Eftersom att data mellan CVT och IVT skiljde sig mycket, upplystes mättekniska problem. Några lösningar diskuteras varav RCVT och PQSensor gås igenom grundligt. Alternativa lösningar som MoW och mobila enheter presenteras också vagt. Samtliga lösningar visade sig ha praktiska hinder, vilket försvårar genomförandet. Det uppmanas därför att man bör testa teknikerna i laborationsmiljö eftersom begränsat med studier gjorts på dessa samt att konkurrerande tillverkare uppger olika uppgifter. / Gotland has long been known for various special solutions and been on the leading edge regarding new technology. For the past 20 years Gotland has had a VSC-HVDC station that has stabilized the voltage in the Gotlandic grid. HVDC Light has solved some of the technical limitations that has hindered the growth of wind turbines. The station has almost reached the end of its technical lifespan and the thesis is a first step in the investigation for an eventual replacement. With power quality analyzers performance and improvements were investigated. The Swedish transmission system operator Svenska kraftnät have since 2016 had a VSCHVDC station that have been used to exchange energy to the asynchronous system in Eastern Europe. Svenska kraftnät has of lately wanted to take advantage of the voltage control capabilities and investigate measurement technologies. Power quality analyzers were installed on suitable connection points to investigate the behavior of the station. ELSPEC G4500 power quality analyzers were installed on Nordbalt’s and Gotland’s HVDC Light to measure during the late summer to fall of 2017. The differences between CVT and IVT, and Rogowski coil and CT were captured. The choice of ELSPEC suited well since no trigger conditions are needed which allows small but important errors to be discovered. Gotland’s HVDC Light stabilizes the grid mostly against voltage sags for faults in the 10 kVgrid and flicker from the wind farms in node 2. The rated power for an upgrade should be based on the 10 kV-grid short-circuit power to be developed during the station’s life span. The voltage control should be based on a PI-controller and should be able to transmit full power in 40 ms. Component voltages can be used to produce reactive power on the phases in need. The need against flicker should be based on measurements in the closest center of consumption, 2 miles from node 2. If it’s needed, a separate loop for flicker-control that prevents 1.5 Hz-components based on a point 1.5 mile from node 2 should be implemented. Depending on an upgrade or replacement, the topology can either be “two-level generation 3” or MMC. Many different future scenarios affect HVDC Light’s role and more resources will be required for Gotland’s and HVDC Light’s future. Two behaviors have been observed on Nordbalt where one is slow and the other behavior is fast. The fast behavior was only observed when low impedance faults occurs, that the synchronous generators also handles. Nordbalt can contribute to small voltage variations if it was faster, like the behavior for low impedance faults. A consideration in stability is needed since a faster behavior can lead to stability problems. Since the data between CVT and IVT differed a lot, metrology problems were discovered. Some solutions were discussed, of which RCVT and PQSensor was thoroughly reviewed. Alternative solutions like MoW and mobile units were also presented vaguely. All solutions showed practical difficulties, which complicates the implementation. It is therefore encouraged to test the technologies in a laboratory environment since few studies have been made on these and competing manufactures state different information.

Submitted by Renata Lopes (renatasil82@gmail.com) on 2017-04-20T13:39:03Z No. of bitstreams: 1 pedromachadodealmeida.pdf: 13436160 bytes, checksum: 84c66613dade0766ae9ea2bdc8be9f91 (MD5) / Approved for entry into archive by Adriana Oliveira (adriana.oliveira@ufjf.edu.br) on 2017-04-20T14:45:37Z (GMT) No. of bitstreams: 1 pedromachadodealmeida.pdf: 13436160 bytes, checksum: 84c66613dade0766ae9ea2bdc8be9f91 (MD5) / Made available in DSpace on 2017-04-20T14:45:37Z (GMT). No. of bitstreams: 1 pedromachadodealmeida.pdf: 13436160 bytes, checksum: 84c66613dade0766ae9ea2bdc8be9f91 (MD5) Previous issue date: 2011-04-29 / Esta dissertação apresenta uma estratégia de controle para sistemas de geração fotovoltaicos, de único estágio, trifásicos, conectados à rede elétrica de distribuição. São desenvolvidos modelos matemáticos para representar as características dinâmicas dos painéis fotovoltaicos, do conversor fonte de tensão (VSC -“Voltage Source Converter”) e da rede de distribuição. A modelagem do sistema de geração disperso (SGD) é feita no sistema de coordenadas síncrono (dq), fornecendo um sistema de equações diferenciais que pode ser usado para descrever o comportamento dinâmico do sistema quando as tensões da rede estão equilibradas ou desequilibradas. O conversor é controlado no modo de corrente, através da estratégia de modulação vetorial (Space Vector Modulation - SVM). São projetadas duas malhas de controle em cascata para controlar o conversor estático. A malha interna controla a corrente injetada na rede enquanto que a externa controla a tensão no barramento CC do conversor. O controle da tensão CC permite rastrear o ponto de máxima potência do painel PV além de controlar a quantidade de potência ativa injetada na rede CA. Um método ativo de detecção de ilhamento baseado na injeção de corrente de sequência negativa é incorporado ao sistema de controle. Resultados de simulações digitais obtidos com o programa ATP (Alternative Transient Program ) são utilizados para validar os modelos matemáticos e as estratégias de controle. Finalmente, um protótipo experimental de pequena escala é montado em laboratório. Todo o sistema de controle do protótipo experimental foi implementado no DSP TMS320F28212. Os resultados obtidos demonstram o funcionamento do sistema e podem ser usados para validar a estratégia de controle utilizada. / This dissertation presents a control strategy for a single-stage, three-phase, photovoltaic systems to be connected to a distribution network. Mathematical models are developed to represent the dynamic characteristics of the photovoltaic panels, the voltage-source converter (VSC) and the distribution network. The modeling of the dispersed generation system (DGS) is done in the synchronous reference frame (dq), providing a system of differential equations that describes the dynamic behavior of the system when the network voltages are balanced or unbalanced. The converter is controlled in current mode through the space vector modulation (SVM) strategy. Two control loops are designed to control the static converter. The inner loop controls the injected current into the network while the external loop controls the converter DC bus voltage. The DC voltage regulator allows to track the PV maximum power point and to control the active power injected into the AC grid. An active islanding detection method based on negative-sequence current injection is incorporated into the control system. Digital simulations results obtained with Alternative Transients Program (ATP) is used to validate the mathematical models and the control strategies. Finally, a small-scale experimental prototype is implemented in the laboratory. The whole control system of the experimental prototype was programmed in DSP TMS320F2812 of Texas Instruments. The results demonstrate that the operation of the system can be used to validate the applied control strategy.

In order to identify the weakest bus in a power system so that the Unified Power Flow Controller could be connected, an investigation of static and dynamic voltage stability is presented. Two stability indices, static and dynamic, have been proposed in the thesis. Multi-Input Multi-Output (MIMO) analysis has been used for the dynamic stability analysis. Results based on the Western System Coordinate Council (WSCC) 3-machine, 9-bus test system and IEEE 14 bus Reliability Test System (RTS) shows that these indices detect with the degree of accuracy the weakest bus, the weakest line and the voltage stability margin in the test system before suffering from voltage collapse. Recently, Flexible Alternating Current Transmission systems (FACTs) have become significant due to the need to strengthen existing power systems. The UPFC has been identified in literature as the most comprehensive and complex FACTs equipment that has emerged for the control and optimization of power flow in AC transmission systems. Significant research has been done on the UPFC. However, the extent of UPFC capability, connected to the weakest bus in maintaining the power flows under fault conditions, not only in the line where it is installed, but also in adjacent parallel lines, remains to be studied. In the literature, it has normally been assumed the UPFC is disconnected during a fault period. In this investigation it has been shown that fault conditions can affect the UPFC significantly, even if it occurred on far buses of the power system. This forms the main contribution presented in this thesis. The impact of UPFC in minimizing the disturbances in voltages, currents and power flows under fault conditions are investigated. The WSCC 3-machine, 9-bus test system is used to investigate the effect of an unsymmetrical fault type and position on the operation of UPFC controller in accordance to the G59 protection, stability and regulation. Results show that it is necessary to disconnect the UPFC controller from the power system during unsymmetrical fault conditions.

Sistemas de transmissão de energia elétrica em corrente contínua e alta tensão baseados em tecnologia de conversores a fonte de tensão (VSC-HVDC), ao contrário de linhas de transmissão em corrente alternada, operam como elementos de controle de variáveis elétricas, podendo ser úteis na estabilidade do sistema de potência. Mas apesar desta vantagem, sistemas VSC-HVDC possuem limitações no desempenho estável, o que enseja o desenvolvimento de uma metodologia para mapeamento de suas zonas de operação estável e possíveis regiões de instabilidade. Inicialmente estudou-se os detalhes da tecnologia VSC-HVDC tais como o funcionamento da eletrônica de potência e estratégias de controle utilizadas. Em seguida, investigou-se os modelos de geradores síncronos para interconexão com o lado CA das estações conversoras do VSC-HVDC. E, finalmente, aplicou-se a tecnologia VSC-HVDC sobre um modelo de sistema de potência com uma estação conversora localizada em um porto offshore e uma outra no continente, próxima à rede de alta tensão em corrente alternada. Simulações e análise deste sistema foram executadas considerando várias condições operacionais. O gráfico de potência gerada e consumida, obtido pela aplicação da metodologia, apresenta grande potencial de uso prático como por exemplo sua implementação na interface homem-máquina da estação de operação do porto offshore, provendo informação em tempo real de alto nível ao operador do sistema elétrico do porto offshore e consequentemente aumentando sua consciência situacional quanto a proximidade dos limites de instabilidade. / High voltage direct current power transmission systems based on voltage source converters (VSC-HVDC), as opposed to alternating current ones, operates as elements of control of electrical variables, being useful for stability of power system. Besides this advantage, VSC-HVDC systems have limitations in stable performance, which instigates the development of a methodology for mapping its operational zones of stability and possible regions of instability. The author initially studied the details of the VSC-HVDC technology such as the power electronic principles and the control strategies used on this research. Subsequently, the author investigated synchronous generator models for interconnection on the AC side of the VSC-HVDC converter stations. Finally, the author applied the VSC-HVDC technology on a model of power system with two converter stations, one located on an offshore port and the other on the shore, next to an alternating current high voltage power grid. Simulations and analysis of this system were carried out considering various operational conditions. The graphic of generated and consumed power on offshore port, obtained by the application of the methodology for mapping operational zones, presents a great potential of being implemented in the man-machine interface of an operation workstation, thus providing high level online information for the operator of the offshore port electrical system and consequently improving its situational awareness of the proximity to instability limits.