A systematic procedure is proposed in this thesis to study the effect of temperature change to the power system load demand by using the typical load patterns of customer classes. The billing data of all service customers are retrieved to derive the daily load profile of the selected Taipower district. To verify the accuracy of the estimated load composition, the simulation results are compared to the actual load profile collected by the SCADA system. The sensitivity analysis of load demand with respect to the temperature change for each customer class is performed by statistic regression according to the actual customer power consumption and temperature data. With temperature rise, the load contribution by each customer class is updated by the corresponding temperature sensitivity and integrated together to form the new load profile of the service district. To investigate the effect of customer load characteristics to system stability, the equivalent circuit of Taipower 345 KV network is created. With the integration of the load composition by load survey study and temperature sensitivity of customer load, the load demand of each load bus is derived. For fault contingency of system buses, the transient stability analysis has performed to determine the critical clearing time under different temperature conditions.

To increase the allowable capacity of wind generation and system reliability of distribution system for islanding operation, an actual Taipower feeder has been selected for computer simulation. The voltage enhancement of distribution feeders with fixed speed wind generator has been obtained by using the static synchronous compensator(STATCOM). The model of Doubly-Fed induction generator(DFIG) in Matlab/Simulink has also been applied in the feasibility study of islanding operation for Taipower feeder. The critical clearing time of fault contingency is solved by considering the low voltage ride through (LVRT) capability of wind generators (WG) and the CBEMA curve of sensitive loads. In this way, feeder circuit breaker(CB) can be tripped in time to achieve islanding operation of distribution feeders without causing the tripping of WG due to voltage disturbance for the system fault contingency. To restore the stable operation of distribution feeders after being isolated from the rest of the power system, an adaptive load shedding scheme has been presented to disconnect the proper amount of system loading to achieve the balance of wind power generation and load demand according to the variations of feeder load profile and wind speed. It is found that system voltage sag problem due to severe fault contingency can be mitigated effectively by using the STATCOM for the support of low voltage ride through capability of WG. With the proper design of protection relay settings for feeder CB tripping and load shedding scheme, the WG and critical loads can be prevented from tripping during transient disturbance to ensure the successful islanding operation of distribution system.

ABSTRACT In this thesis, relationship between two most important transient stability indices, critical clearing time and generator rotor angle is examined for one machine-infinite bus system and then extended to the multimachine case and is observed to be linear. By using the linear relationship between critical clearing time and generator rotor angle and utilizing the daily load curve, a new preventive method is proposed. The aim of this method is to make all critical clearing times longer than the relay and circuit breaker combination operation time. In the proposed method, desired critical clearing times are obtained by using on line system data and daily load curves. Then desired values are adjusted by generators output rescheduling and terminals voltage control Visual computer language is used for graphical and numerical solutions. Comprehension of one machine infinite bus system and multimachine system transient stability become easier.

Alternative renewable energy sources such as solar, wind, and bio energy have brought uncertainties into the power flow of electric power systems. Purely deterministic tools and models are suitable to guarantee the safe operation of these systems. A necessity arises to develop and use methods that deal with uncertainties in the analysis. Several methodologies have been proposed to assess the transient stability of power systems considering uncertainties. However, most of these techniques are based on the execution of successive simulations, requiring a high computational effort. Hence, they are limited to off-line applications in small systems. In view of the foregoing, this work proposes the development of two methodologies to assess – in real time – the transient stability of power systems with parametric and operational uncertainties. The first one is an extension of PEBS, which is a direct method for stability assessment. This method, called robust PEBS, employs an interval energy function of the power system to determine a robust estimate critical clearing time. The second one is the use of optimization methods to find a robust estimate critical clearing time. Notably, we employ the Simulated Annealing and Differential Evolution algorithms. Besides developing methods to estimate the critical clearing time, this work also contributes to the analysis of power systems with uncertainties by introducing a technique to reduce the analysis effort. To be specific, a methodology is proposed to identify the most influential parameters for the transient analysis assessment based on a sensitivity analysis of the generator angles with respect to the system parameters. / A utilização crescente de fontes alternativas intermitentes de energia como eólica e solar tem trazido incertezas em relação ao nível de geração e ao fluxo de potência em Sistemas Elétricos de Potência (SEP). Assim, a utilização de modelagem e ferramentas puramente determinísticas na análise de estabilidade não são mais suficientes para garantir a operação segura destes sistemas. Torna-se necessário, então, o desenvolvimento e utilização de métodos que incluam essas incertezas nas análises. Diversas metodologias foram propostas para avaliar a estabilidade transitória de Sistemas Elétricos de Potência considerando incertezas. Porém, grande parte destas técnicas é baseada em execuções de inúmeras simulações e, portanto, exige grande esforços computacionais e são limitadas a aplicações off-line e em sistemas elétricos de pequeno porte. Face ao exposto, propõe-se o desenvolvimento de uma metodologia rápida para a avaliação de estabilidade transitória de SEPs em tempo real considerando incertezas paramétricas. Esta metodologia deverá ser capaz de fornecer rapidamente um resultado robusto sobre a estabilidade. Para tal pretende-se estender a aplicação do método direto PEBS para a análise de estabilidade de sistemas elétricos com incertezas. Além disso, neste trabalho, aplicam-se métodos de otimização para se encontrar o tempo crítico de abertura sem o uso de uma simulação de Monte Carlo e determinam-se os parâmetros que mais influenciam para o estudo de estabilidade transitória utilizando uma análise de sensibilidade dos ângulos dos geradores em relação aos parâmetros do sistema elétrico de potência.

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Nowadays, power systems are dealing with some new challenges raisedby the major changes that have been taken place since 80’s, e.g., deregu-lation in electricity markets, significant increase of electricity demands andmore recently large-scale integration of renewable energy resources such aswind power. Therefore, system operators must make some adjustments toaccommodate these changes into the future of power systems.One of the main challenges is maintaining the system stability since theextra stress caused by the above changes reduces the stability margin, andmay lead to rise of many undesirable phenomena. The other important chal-lenge is to cope with uncertainty and variability of renewable energy sourceswhich make power systems to become more stochastic in nature, and lesscontrollable.Flexible AC Transmission Systems (FACTS) have emerged as a solutionto help power systems with these new challenges. This thesis aims to ap-propriately utilize such devices in order to increase the transmission capacityand flexibility, improve the dynamic behavior of power systems and integratemore renewable energy into the system. To this end, the most appropriatelocations and settings of these controllable devices need to be determined.This thesis mainly looks at (i) rotor angle stability, i.e., small signal andtransient stability (ii) system operation under wind uncertainty. In the firstpart of this thesis, trajectory sensitivity analysis is used to determine themost suitable placement of FACTS devices for improving rotor angle sta-bility, while in the second part, optimal settings of such devices are foundto maximize the level of wind power integration. As a general conclusion,it was demonstrated that FACTS devices, installed in proper locations andtuned appropriately, are effective means to enhance the system stability andto handle wind uncertainty.The last objective of this thesis work is to propose an efficient solutionapproach based on Benders’ decomposition to solve a network-constrained acunit commitment problem in a wind-integrated power system. The numericalresults show validity, accuracy and efficiency of the proposed approach. / <p>The Doctoral Degrees issued upon completion of the programme are issued by Comillas Pontifical University, Delft University of Technology and KTH Royal Institute of Technology. The invested degrees are official in Spain, the Netherlands and Sweden, respectively.QC 20141028</p>

The research is motivated by the need to address two major challenges in wind power integration: how to mitigate wind power fluctuation and how to ensure stability of the farm and host grid. It is envisaged that wind farm power output fluctuation can be reduced by using a specific type of buffer, such as an energy storage system (ESS), to absorb its negative impact. The proposed solution, therefore, employs ESS to solve the problems. The key research findings include a new technique for calculating the desired power output profile, an ESS charge-discharge scheme, a novel direct-calculation (optimization-based) method for determining ESS optimal rating, and an ESS operation scheme for improving wind farm transient stability. Analysis with 14 wind farms and a compressed-air energy storage system (CAES) shows that the charge-discharge scheme and the desired output calculation technique are appropriate for ESS operation. The optimal ESSs for the 14 wind farms perform four or less switching operations daily (73.2%-85.5% of the 365 days) while regulating the farms output variation. On average, the ESSs carry out 2.5 to 3.1 switching operations per day. By using the direct-calculation method, an optimal ESS rating can be found for any wind farm with a high degree of accuracy. The method has a considerable advantage over traditional differential-based methods because it does not require knowledge of the analytical form of the objective function. For ESSs optimal rating, the improvement in wind energy integration is between 1.7% and 8%. In addition, a net increase in grid steady-state voltage stability of 8.3%-18.3% is achieved by 13 of the 14 evaluated ESSs. For improving wind farm transient stability, the proposed ESS operation scheme is effective. It exploits the use of a synchronous-machine-based ESS as a synchronous condenser to dynamically supply a wind farm with reactive power during faults. Analysis with an ESS and a 60-MW wind farm consisting of stall-regulated wind turbines shows that the ESS increases the farm critical clearing time (CCT) by 1 cycle for worst-case bolted three-phase-to-ground faults. For bolted single-phase-to-ground faults, the CCT is improved by 23.1%-52.2%. / text