Sistemas Elétricos de Potência (SEPs) muitas vezes não são capazes de retomarem a uma nova condição de equilíbrio após grandes perdas de geração ou mesmo pela retirada de importantes linhas de transmissão. O déficit de potência causado por alguns desses distúrbios pode acarretar no declínio gradual da freqüência do sistema. Caso a reserva girante ou o próprio sistema de transmissão não sejam capazes de recompor o SEP, medidas corretivas devem ser tomadas para evitar o colapso do mesmo. Nesta condição de emergência, um montante de carga deve ser desconectado de forma a restaurar uma nova condição de equilíbrio através de um esquema emergencial conhecido como plano de corte de carga por subfrequência. Muitos trabalhos vem sendo desenvolvidos ao longo dos anos, nos quais são propostas diferentes técnicas para a determinação de planos de corte de carga. Na maioria delas utiliza-se uma modelagem equivalente e linearizada do sistema. Tais simplificações trazem grandes facilidades para a representação do sistema. Porém, para que a integridade do mesmo seja garantida, muitas vezes os planos de corte de carga envolvem montantes de carga maiores que o necessário. A metodologia apresentada neste trabalho utiliza uma representação não linear para o SEP, o que permite um estudo do comportamento dinâmico de suas unidades geradoras para que os limites de frequência sejam determinados. Assim, os planos podem ser determinados com eficiência, reduzindo o número de consumidores desprovidos de energia elétrica durante o processo de alívio de carga. Entretanto, a escolha de um modelo mais completo para a representação do sistema pode acarretar num grande esforço na análise e determinação dos esquemas de alívio de carga, quando aplicados em sistemas de grande porte. Sendo assim, é proposta neste trabalho uma metodologia capaz de auxiliar tais estudos, o que diminui os esforços tanto da parte computacional quanto da parte empregada pelo projetista. Uma abordagem energética é aplicada ao problema e, dessa forma, dada uma perda de geração é possível determinar o valor mínimo de frequência atingido pelo sistema sem que haja a necessidade de se conhecer a trajetória do ponto de operação do sistema. Portanto, é proposta uma metodologia baseada em funções energia para a determinação de planos de corte de carga e, posteriormente, são realizadas simulações em uma representação simplificada de um sistema elétrico de potência para a validação da mesma. Também é mostrado o comportamento da frequência do sistema durante uma condição de subfrequência sobre duas perspectivas. Uma delas utiliza-se de uma modelagem não linear para a representação do sistema e a outra utiliza-se do modelo linearizado para a representação deste mesmo sistema. Este trabalho tem por finalidade o estudo e modelagem matemática do problema emergencial de alívio de carga de uma forma introdutória, para que posteriormente, possa ser desenvolvida de uma ferramenta capaz de auxiliar tais estudos. O método proposto demonstrou-se muito promissor, apesar das simplificações utilizadas para a construção do modelo. / Electric power systems (EPS) are not always capable of achieving a new stable equilibrium point after a severe generation loss or even after the loss of important transmission lines. The lack of active power generation caused by some of these disturbances can lead to a gradual decay of the system frequency. If the spinning reserve or even the bulk transmission system are not capable of restoring the system, then, corrective actions should be taken to avoid a system collapse. Under this emergency condition, a portion of the load should be disconnected, as a way to restore a new stable equilibrium condition, through an emergency scheme known as under frequency load shedding (UFLS). Several works have been developed in this field throughout the years, in which different techniques are proposed to determine the load shedding schemes. The majority of these works use an equivalent linearized model of the system, which facilitates the system representation. However, in order to keep the integrity of the system, it is common to overestimate the shedding of loads. The validation of load shedding schemes that use a linear methodology is generally performed through simulations based on nonlinear models of the whole system. The methodology presented in this work uses a nonlinear representation for the EPS for developing an UFLS scheme, which permits a study of the dynamic behavior of its generators in order to find the frequency limits. ln this way, the schemes can be efficiently determined, aiming a reduction on the number of consumers affected by the load shedding scheme, and avoiding additional simulations to validate the designed scheme. An energetic approach is applied to the problem and, in this way, given a generation loss it is possible to determine the minimum frequency value achieved by the system without the need for the knowledge of the trajectory of the system\'s operating point. Voltage regulators and speed governors are neglected, and the loads and network equipments are represented through a constant impedance model, whereas the generators are modeled through its classical model.

No description available.

The Morse/Long Range (MLR) potential has become one of the most reliable and highly used potential energy functions for diatomic molecules. It includes the theoretical long range behaviour that diatomic molecules are known to exhibit as they approach the dissociation limit. Heavy alkali metals with adjacent electronic states often exhibit strong coupling between the spin and orbital angular momentum. The ground state X¹Σg⁺ and the lowest lying triplet state aᶟΣᵤ⁺ of Cs₂ exhibit such coupling effects and as a result, modeling the highest vibrational states of these states is a non-trivial problem. Utilizing scattering length values obtained from published analysis of 60 Feshbach resonances, the correct form of the potential energy function was determined. Moreover, the scattering length values were used to determine the correct leading dispersion coefficient that describes the true form of the long-range potential energy functions. All previous attempts to determine global potential energy functions for these states have considered only the optical spectroscopic data. This is the first ever effort attempting to use scattering lengths determined from cold atom collision experiments in a combined analysis with conventional spectroscopic data.

Presently power systems are being operated under high stress level conditions unforeseen at the moment they were designed. These operating conditions have negatively impacted reliability, controllability and security margins. FACTS devices and HVDC transmissions have emerged as solutions to help power systems to increase the stability margins. VSC-HVDC transmissions are of particular interest since the principal characteristic of this type of transmission is its ability to independently control active power and reactive power. This thesis presents various control strategies to improve damping of electromechanical oscillations, and also enhance transient and voltage stability by using VSC-HVDC transmissions. These control strategies are based of different theory frames, namely, modal analysis, nonlinear control (Lyapunov theory) and model predictive control. In the derivation of the control strategies two models of VSC-HVDC transmissions were also derived. They are Injection Model and Simple Model. Simulations done in the HVDC Light Open Model showed the validity of the derived models of VSC-HVDC transmissions and the effectiveness of the control strategies. Furthermore the thesis presents an analysis of local and remote information used as inputs signals in the control strategies. It also describes an approach to relate modal analysis and the SIME method. This approach allowed the application of SIME method with a reduced number of generators, which were selected based on modal analysis. As a general conclusion it was shown that VSC-HVDC transmissions with an appropriate input signal and control strategy was an effective means to improve the system stability. / QC 20110412

The infrared, Raman and ultraviolet spectra of pyridine-d0 and pyridine-d5 were recorded and assigned with a focus on the low-frequency vibrational modes in the S1(n,pi*) electronic excited state. An energy map for the low-frequency modes was constructed and the data for the v18 mode allowed a highly anharmonic one-dimensional potential energy function to be determined for the S1 excited state. In this S1(n,pi*) state, pyridine is quasi-planar and very floppy with a barrier to planarity of 3 cm^-1. The infrared, Raman and ultraviolet spectra of 2-fluoropyridine (2FPy) and 3-fluoropyridine (3FPy) have been collected and assigned. For 2FPy about 150 bands were observed for the transitions to the vibronic levels of the S(pi, pi*) state at 38,030.4 cm^-1. For 3FPy more than a hundred absorption bands associated with the S(n,pi*) state at 35,051.7 cm^-1 and about forty broad bands associated with the S(pi, pi*) state at 37,339 cm^-1 were observed. The experimental work was complemented by ab initio calculations and these also provided calculated structures for 2FPy, 3FPy, and pyridine. They showed that the fluorine atom on the ring participates in the pi bonding. The gas-phase Raman spectra of 1,3-butadiene and its 2,3-d2, 1,1,4,4-d4, and d6 isotopomers have been recorded with high sensitivity in the region below 350 cm-1, in order to investigate the internal rotation (torsional) vibration. The data for all the isotopomers were then fit using a one-dimensional potential energy function of the form V = (1/2)Sigma(Vn(1-cos (phi))). The energy difference between trans and gauche forms was determined to be about 1030 cm^-1 (2.94 kcal/mol), and the barrier between the two equivalent gauche forms to be about 180 cm^-1 (0.51 kcal/mol), which agrees well with high-level ab initio calculations. The results from an alternative set of assignments also fits the data quite well are also presented. Combination and hot band series involving the v13 torsional vibration of the trans rotamer were observed for each of the butadiene isotopomers. In addition, the high signal to noise of the Raman spectra made it possible to detect several dozen bands of the gauche rotor which makes up only about 2% of the molecules at ambient temperature.

The Morse/Long Range (MLR) potential has become one of the most reliable and highly used potential energy functions for diatomic molecules. It includes the theoretical long range behaviour that diatomic molecules are known to exhibit as they approach the dissociation limit. Heavy alkali metals with adjacent electronic states often exhibit strong coupling between the spin and orbital angular momentum. The ground state X¹Σg⁺ and the lowest lying triplet state aᶟΣᵤ⁺ of Cs₂ exhibit such coupling effects and as a result, modeling the highest vibrational states of these states is a non-trivial problem. Utilizing scattering length values obtained from published analysis of 60 Feshbach resonances, the correct form of the potential energy function was determined. Moreover, the scattering length values were used to determine the correct leading dispersion coefficient that describes the true form of the long-range potential energy functions. All previous attempts to determine global potential energy functions for these states have considered only the optical spectroscopic data. This is the first ever effort attempting to use scattering lengths determined from cold atom collision experiments in a combined analysis with conventional spectroscopic data.

Along with the increasing scale of the power system and stressed operation in the transmission network, the stability margin is reduced considerably. As a traditional solution, the constructions of new transmission lines and generators sometimes are constrained by local environmental and regulatory constraints. Another characteristic of a modern network is the higher number of transmission inter-connections which appear in the large-scale power system. As an economic benefit, inter-connection can reduce the cost of electricity and enhance system reliability [1]. Those inter-connected tie lines are operated normally under heavy flow to maximize the usage benefit. This characteristic contributes to the complexity of operating and controlling the system. In recent years, along with the development of power electronic devices, the Flexible AC Transmission Systems (FACTS) has been used in the system as an alternative solution. It can maximize the usage benefit of the HV transmission line and make the large-scale power system more controllable. By using FACTS devices, the system can survive serious system contingencies with real-time control action, instead of providing a large steady state stability margin. Therefore, the system transfer capacity can be significantly increased. Electromechanical oscillations are observed in today's power system; such oscillations are recognized as a major concern in power system operation. Once begun, the oscillations may continue for a while before being halted by the damping torque from the system, or they may continue to grow (inadequate damping) and eventually cause system instability by losing synchronicity. The traditional and widely applied solution for oscillation damping is the Power System Stabilizer (PSS), which is efficient in damping local mode oscillation and inter-area oscillation in certain conditions. In recent years, research and development of the application of FACTS devices in suppressing system oscillations, especially for inter-area mode oscillation damping, has attracted increasing interest [1]. The primary objective of this thesis is to design robust FACTS controllers for enhancing power system dynamic stability by damping low frequency electromechanical oscillations. Recently, various nonlinear control techniques have been applied in power system control. The performance of nonlinear controllers is influenced by the parameter uncertainty and external disturbance. This thesis will present a novel approach of a robust Variable Structure Control (VSC)-based FACTS controller for damping multi-mode oscillations. Robust performances of the proposed controllers in different power systems are demonstrated by computer simulation.

In the classic Hill model for muscle contraction, the split between the muscle and tendon is arbitrary and the problem lacks a unique solution. Instead of reformulating the problem to a differential-algebraic equation and solving for a set of initial conditions, a constant tendon length is commonly assumed in musculoskeletal simulation tools. This assumption has not been thoroughly tested and introduces errors of unknown magnitude to the simulations. In this thesis, the contractile element of the Hill model is modelled as a friction clutch in parallel to a viscous damper. This provides an evolution law for the muscle length by which the muscle speed is numerically calculated taking into account a non-zero tendon speed. A simple biceps curl is simulated with the friction clutch model and compared to corresponding commercial musculoskeletal simulations. Overall, the results are similar, in particular for the muscle lengths which are almost identical in every simulation (0.00-0.42% difference). The difference in tendon speed is 0.00-3.26%, with upwards tendencies. In general, the error percentage of the tendon speed appears to decrease by the same amount that the contraction speed is reduced. Conclusively, it can be said that the introduced friction clutch model delivers comparative outcomes to a commercial musculoskeletal simulation software, while not assuming a constant tendon length. However, while presenting a relatively simple solution, an increased computation time is to be expected due to the need of a differential equation solver. Further investigation regarding implementation and computing times in more complex simulations may provide an alternative approach to conventional musculoskeletal simulations.

京都大学 / 0048 / 新制・課程博士 / 博士(エネルギー科学) / 甲第21193号 / エネ博第367号 / 新制||エネ||72(附属図書館) / 京都大学大学院エネルギー科学研究科エネルギー基礎科学専攻 / (主査)教授 木下 正弘, 教授 森井 孝, 教授 片平 正人 / 学位規則第4条第1項該当 / Doctor of Energy Science / Kyoto University / DFAM

Online stability assessment is an important problem that has not been solved completely yet. The purpose of this research is to tackle online transient stability assessment. Currently, most utility companies use step-by-step integration in order to set protective equipment so that they effectively work for critical contingencies. However, there are times an unforeseen contingency may occur which may cause the system to transit and the protective equipment to misoperate and does not isolate the disturbed part of the system. This research introduces a method that automatically determines a group of generators that participate in system separation and hence transient instability. The method consists of four phases: modeling and simulation, critical machines identification, online transient stability assessment, and critical clearing time calculation. In the modeling and simulation phase, the power system is built and the generators’ rotor angles and speeds are captured. In the critical machines identification phase, the average instantaneous rotor accelerating powers, coherency measures, the during-fault rotor angles and speeds characteristics, and the pre- and post-fault rotor angles are used to identify the Severely Disturbed Group (SDG) of machines. The results of this phase are used to calculate the kinetic energy of the SDG and potential energy of another (or possibly the same) group of generators. Utilization and success of the proposed method will be documented using results from the IEEE 39-Bus test system. Each step of each phase will be demonstrated as needed. The proposed method is compared to step-by-step integration and two direct methods. The suitability of the proposed method for operation will be shown in cases where the Y-Bus matrix and rotor angles and speeds are given. The proof of concept of the proposed method was used in simulating the test system and encouraging results of the simulation were published in ‎[1] and ‎[2]. The proof of concept is the foundation of the method proposed in this dissertation to determine transient stability of large-scale power systems.