This thesis aims to identify methods for detection of damper winding faults in synchronous machines (SMs) powered by variable frequency drives (VFDs). The problem of failing damper windings has received attention after reports of serious damage which have been discovered during maintenance checks. Since SMs often are used for critical applications, failures can be devastating if they cause total breakdowns. Also, VFDs are believed to cause additional stress in the damper windings of SMs and since the utilisation of VFDs is increasing, the problem is expected to become more common in the future. Currently, there is no method for detection of failures during normal operation of SMs, thus research in the area is required. Simulations based on the finite element method as well as laboratory experiments have been performed in order to examine the impact of VFDs and to find a way of detecting damper winding failures. The results confirm that utilization of VFDs produce higher currents in the damper winding compared to direct-online operation. The results also show that in case of a damper bar failure, the current distribution among the damper winding segments is affected. However, monitoring of all damper winding segments is unrealistic due to the number of sensors required. Another approach, which has been investigated, involves monitoring of the current through the pole interconnectors of one of the endrings. Potential fault indicators have been found by analysing the currents in the frequency domain. However, further studies are required in order to evaluate the method. Also the temperature of the damper winding was investigated as an indicator.

Thesis. 1978. M.S.--Massachusetts Institute of Technology. Dept. of Electrical Engineering and Computer Science. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Includes bibliographical references. / M.S.

nÃo hà / Este trabalho apresenta um novo mÃtodo de fluxo de potÃncia linear o fluxo de potÃncia linear V-teta tambÃm apresenta uma nova modelagem do gerador sÃncrono para estudos de fluxo de potÃncia trifÃsico em redes de distribuiÃÃo desequilibradas radiais e uma modelagem do gerador eÃlico sÃncrono em componentes de fase para estudos de curto-circuito em sistemas de distribuiÃÃo radiais Os resultados revelam que 1) Para o fluxo de potÃncia linear V-teta à possÃvel o cÃlculo de forma desacoplada e linear dos fluxos de potÃncia ativa e reativa no sistema Assim os erros obtidos com o fluxo de potÃncia linear V-teta sÃo em geral menores que os erros obtidos no mÃtodo clÃssico de fluxo de potÃncia CC e espera-se que o mesmo seja usado em muitas aplicaÃÃes onde o mÃtodo clÃssico de fluxo de potÃncia CC à atualmente utilizado 2) Uma nova modelagem à proposta considerando o gerador sÃncrono diretamente conectado a rede elÃtrica Uma outra modelagem jà existente na literatura considerando a conexÃo do gerador atravÃs de retificador e inversor tambÃm à usada As duas modelagens sÃo utilizadas para a realizaÃÃo de estudos de impacto dos sistemas de excitaÃÃo dos geradores sÃncronos em sistemas de distribuiÃÃo com modelagem trifÃsica Os resultados sÃo obtidos utilizando-se o sistema IEEE-13 barras A modelagem do gerador sÃncrono em componentes de fase sob condiÃÃes desequilibradas permite: a) calcular as injeÃÃes ou consumo de potÃncias ativa/reativa de cada fase na mÃquina, b) simular o gerador sÃncrono como barra do tipo PQ e como barra do tipo PV Juntamente com esses estudos uma anÃlise inÃdita e detalhada de desequilÃbrio de tensÃo inclusive com uma demonstraÃÃo matemÃtica à apresentada 3) A representaÃÃo em componentes de fase do gerador eÃlico sÃncrono nos cÃlculos de faltas de sistemas de distribuiÃÃo radiais obtÃm resultados mais precisos do que o mÃtodo tradicional das componentes simÃtricas uma vez que valores de impedÃncias mÃtuas de diferentes valores podem ser considerados na anÃlise do sistema / This thesis presents a new method of linear power flow linear power flow V-theta it also presents a new model of synchronous generator for power flow studies in three phase unbalanced radial distribution networks and modeling of wind synchronous generator in phase components for studies of short-circuit in radial distribution systems The results reveal that 1) For the linear power flow V-theta is possible to calculate like a linear and uncoupled form the active and reactive power flows in the system Thus the errors obtained with the linear power flow V-theta are usually smaller than the errors obtained in classical method of DC power flow and it is expected that the linear power flow V-theta can be used in many applications where the classical method of DC power flow is currently used 2) A new model is proposed, considering the synchronous generator directly connected to the power grid Another existing literature modeling considering the connection from the generator through rectifier and inverter is also used The two modeling are used to perform impact studies of synchronous generators excitation systems for distribution systems with three-phase modeling The results are obtained using the IEEE 13 bus - test system The modeling of synchronous generator in phase components under unbalanced conditions allow: a) calculate the active / reactive power injections in each phase of the machine b) simulate the synchronous generator as PQ bus-type and as PV bustype Along with these studies an unprecedented and detailed analysis of voltage unbalance including a mathematical proof is presented 3) the representation of synchronous windmill generators in phase components calculations in short-circuits of radial distribution systems get more accurate results than the traditional method of symmetrical components since values of mutual impedances of different values can be considered in the analysis of the system

This research addresses some of the difficulties faced when operating voltage controlled inverters with synchronous generators in microgrids. First, an overview of microgrid value propositions is provided, and the problems faced when attempting to use microgrids to provide improved power quality are discussed. Design considerations for different types of microgrids are provided to enable microgrids to deliver the desired functionality without adding unnecessary cost. The main body of this research investigates the poor transient load sharing encountered between voltage controlled inverters and synchronous generators in islanded operation. Poor transient load sharing results in high peak inverter rating requirements and high cost. The tradeoff between power quality and power sharing is highlighted, and methods to improve transient load sharing are proposed. The use of current limiting to protect inverters during faults and overloads is also investigated. Stability problems are identified when using simple inverter current limiting methods when operating in parallel with synchronous generators. Virtual impedance current limiting is proposed to improve transient stability during current limiting. The methods proposed in this thesis for mitigating inverter overloads and faults will allow for more reliable and cost effective application of inverter based distributed energy resources with synchronous generators in microgrids.

This research work focuses on the reactive power compensation of the permanent magnet synchronous generator (PSG) in wind power plants. PSG feeds a fixed voltage dc grid through a rectifier bridge. In variable speed operation, the PSG will be able to build torque only in small speed range. This is due to the fixed magnet of the PSG. External reactive power compensation provides an attractive solution to overcome this problem. Different reactive power compensation configurations were examined. Statics synchronous series compensation and a shunt passive filter were chosen as a compensation method. Simulation and implementation of small wind power plant were performed. The wind power plant consists of the synchronous generator, inverter, rectifier, coupling transformers and shunt passive filter. The experimental results agree to the proposed theory and simulation results. / Der Schwerpunkt meiner Promotion ist die Blindleistungskompensation bei einem permanenterregten Synchrongenerator. Der Synchrongenerator speist das Gleichsspannungsnetz über ein Gleichrichter. In der Drehzahlvariablen Betriebsverhalten können Nachteile auftreten. Die Folge ist, dass bei konstanter Gleichspannung und fester Erregung durch die Permanenterregung nur ein sehr kleiner Drehzahlbereich mit vernünftiger Drehmomentausbeute bedienbar ist. Ein möglicher Ausweg wäre eine variable Kompensationsspannung. Verschiedene Kompensationsverfahren wurden untersucht. Ein Series Active Filter und ein Shunt Passive-Filter wurden als Blindleistungskompensation gewählt. Im Rahmen meiner Dissertation beschäftige ich mich mit dem Aufbau und der Simulation einer Windkraftanlage. Diese besteht aus einem permanenterregten Synchrongenerator, einem Wechselrichrter, einem Gleichrichter, drei Transformatoren und einem passiven Filter. Das Versuchsergebnis zeigt, dass die Theorie mit der Simulation übereinstimmt.

Thesis (MEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: The focus of this thesis is position sensorless control of a transverse-laminated reluctance synchronous machine. Rotor position information is required for high-performance closedloop control of the reluctance synchronous machine and is conventionally supplied by unreliable hardware position resolvers. In addition a FPGA-based rapid prototyping system is completed as part of the research term for control of the machine drive system. For the first time the unified active- ux (AF) method is investigated and implemented for position sensorless control of the transverse-laminated reluctance synchronous machine in this study. The method is based on the torque equation of the machine and is basically the same for any AC machine. The estimation scheme is implemented for closed-loop position sensorless control from low- to rated speed in the entire rated load range with simulation and measured results confirming its capabilities. A number of characteristics of the machine (including generator operation) have implications for implementation of the active- ux (AF) method and are therefore investigated. Another position estimation method investigated is the arbitrary injection (AI) scheme which is derived to be completely machine parameter independent. The method simply requires a current progression at each calculation step allowing use of a smaller injection voltage. This method is implemented again on the reluctance synchronous machine and is shown to be capable of position sensorless current and speed control of the drive from standstill to rated speed with simulation and measured results. However, when the machine is operating above low speeds it is shown that this technique is only capable of position sensorless control at low loads. To deliver position sensorless control in the entire rated speed and load range a new hybrid controller scheme is designed and implemented. The hybrid scheme is speed and load dependent with hysteresis regions for stability at specific working points. The active- ux (AF) method is implemented in the low to rated speed range at medium to rated loads while the arbitrary injection (AI) method is implemented elsewhere. Measured results show that the scheme is capable of position sensorless control in the entire rated speed and load range with some limitations on dynamics. Because of the limitations on dynamics of the hybrid scheme an assisted fundamental model position estimation scheme was investigated. Simulation results show that this controller requires further investigation. / AFRIKAANSE OPSOMMING: Die fokus in hierdie tesis is die posisie-sensorlose beheer van 'n transvers-gelamineerde reluktansie sinchroonmasjien. Rotor posisie inligting word benodig vir geslote-lus beheer van die reluktansie sinchroonmasjien met ho e-werkverrigting, en word normaalweg deur onbetroubare hardeware sensors verskaf. As deel van die navorsings-termyn is 'n FPGAgebaseerde beheerstelsel vir die masjien stelsel voltooi. Die \aktiewe-vloed" posisie-afskattings metode is ondersoek en vir die eerste keer ge mplementeer vir posisie-sensorlose beheer van die transvers-gelamineerde reluktansie sinchroonmasjien. Die metode is dieselfde in konsep vir alle WS masjiene en word basseer op die vergelyking vir wringkrag van die masjien. Vollas geslote-lus posisie-sensorlose beheer van die masjien in die lae tot ho e spoedbereik is suksesvol ge mplementeer met simulasie en gemete resultate. Verkskeie inherente eienskappe van die masjien het implikasies vir gebruik van die \aktiewe-vloed" metode (insluitend generator werking) en is dus ondersoek. Die \arbitr^ere injeksie" metode wat afgelei is om onafhanklik van masjien parameters te wees is ook odersoek. Hierdie metode verlang slegs 'n stroom-afgeleide by elke tydstip en benodig dus 'n kleiner injeksie-spanning. Hierdie metode is weer ge mplementeer op die reluktansie sinchroon masjien met suksesvolle posisie-sensorlose beheer in die hele spoed bereik getoon in simulasie en praktiese resultate. Dit word egter getoon dat hierdie metode slegs onder lae-las toestande posisie sensorlose beheer bo lae-spoed kan bewerkstellig. Ten einde posisie-sensorlose beheer in die hele spoed en wringkrag bereik te verkry is 'n nuwe hibriede beheerskema ontwerp en ge mplementeer. Die skema is spoed en las afhanklik met histerese vir stabiliteit by 'n spesi eke werkpunt. Die \aktiewe-vloed" metode word gebruik bo lae spoed teen 'n minimum las terwyl die \arbitr^ere injeksie" andersins ge mplementeer word. Gemete resultate toon dat die skema posisie-sensorlose beheer van die masjien in die hele spoed en las bereik toelaat met sommige beperkings op dinamika. Met inagneming van die beperkings op die hibriede metode is 'n ondersteunde fundamentele model afskattingskema ondersoek. Simulasie resulate toon dat hierdie beheerder verdere ondersoek benodig.

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In a synchronous machine, radial, tangential, and axial forces are generated. In this thesis, three different technologies to control them are proposed. The first one, involves the utilization of the radial forces that arise between the rotor and the stator. This is achieved by segmenting the rotor field winding into groups of poles and controlling their corresponding magnetization individually. This technology is particularly useful to achieve magnetic balance and to create controllable radial forces. The second technology, involves the control of the rotor field in order to influence the tangential forces that produce torque. This is achieved by inverting the rotor field winding polarity with respect to the stator field. With this technique, breaking and accelerating torques can be created. It is particularly useful to start a synchronous machine. Finally, the application of axial forces with a magnetic thrust bearing is discussed. The main benefits of this technology are higher efficiency and increased reliability. The work presented in this thesis was carried out within the Division of Electricity in the Department of Engineering Sciences at Uppsala University. It is based on original research supported by analytical calculations, computational simulations and extensive experimental work.

This thesis proposes control schemes and converter configurations for high power wound field synchronous motor (WFSM) drives. The model for a salient pole WFSM in any general rotating reference frame is developed which can be used to derive models along known rotor (dq) and stator flux (MT) reference frames. Based on these models, the principle of sensor-less stator flux oriented field-oriented control (FOC) for salient pole WFSM is developed. So far in the literature, control of cylindrical rotor machine only has been addressed and the effects of saliency have generally been neglected. The performance of the proposed sensor-less FOC has been demonstrated by experimentally operating a 15.8 HP salient pole WFSM using a three-level IGBT based voltage source inverter (VSI). The principle of FOC has been later extended to the control of current source load commutated inverter (LCI) fed salient pole WFSM drives, where the drawbacks present in conventional self-control method such as rigorous off-line calculation for generation of look up tables, coupling between flux and torque control etc. are eliminated. This thesis also proposes the combination of a VSI with the LCI power circuit to overcome the different disadvantages that are present in the existing LCI topology. Firstly, a novel starting scheme is proposed, where the LCI fed WFSM is started with the aid of a low power auxiliary VSI converter in a smooth manner with sinusoidal motor currents and voltages. This overcomes the difficulties of the present complex dc link current pulsing technique that has drawbacks such as pulsating torque, long starting time etc. In a second mode of operation, it is shown that the VSI can be connected to the existing LCI fed WFSM drive as a harmonic compensator in On-The-Fly mode; this will make the terminal stator current and voltage sinusoidal apart from cancellation of torque pulsations thus improving the drive performance. The above two schemes have potential as retrofit for existing drives. It is possible to combine both the advantages, mentioned above, by permanently connecting the VSI with the LCI power circuit to feed the WFSM. This proposed hybrid LCI/VSI drive can be regarded as a universal solution for high power synchronous motor drives at all power and speed ranges.