Agradecimentos A Deus, por sempre iluminar o meu caminho. A meu pai, Marcos Sohn e a minha mãe, Terezinha de Jesus Prodóssimo Sohn, pelo amor incondicional. Ao Professor Luís Fernando Costa Alberto, pelos ensinamentos, orientação e ser uma referência aos seus alunos. Aos Professores Romeu Reginatto, José Carlos de Melo Vieira Júnior e Maurício Barbosa de Camargo Salles, pelos conhecimentos compartilhados, pela disposição em colaborar quando necessário, pelas avaliações desta dissertação e valiosas contribuições. Ao Professor Rodrigo Andrade Ramos por me auxiliar quando necessário e disponibilizar o programa computacional PSS/E, fundamental para a realização desta dissertação.

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The authors report on a step towards the development of direct methods for transient stability assessment of power systems with integrated wind turbine generators subject to low voltage ride‐through constraints. In this study, they propose an approach to assess transient stability of a single wind turbine generator against an infinite bus using an energy function along with an extension of the potential energy boundary surface method. The proposed approach exploits the theory of constrained dynamical systems and the concept of constrained stability region to efficiently estimate critical clearing times taking into account not only the issue of stability due to rotor acceleration but also the issue of operational limit violations, such as low‐voltage ride‐through curve violations. Very often, wind turbine generators are disconnected due to violation of operational limits, such as under‐voltage limits, instead of rotor acceleration. The proposed approach correctly estimates the critical clearing times to avoid operational limit violations, such as the low‐voltage ride‐through constraint violation, while traditional direct methods would fail to appropriately estimate such clearing times. They illustrate the effectiveness of the proposed approach by means of case studies considering two types of wind turbine generators, the fixed‐ and limited‐variable‐speed wind turbine generators.