Análise de estabilidade baseada em impedância de um inversor formador de rede para microrredes CA

Author(s)

Igor Alves Maronni

• Document type: Master's Dissertation
• Press: Campinas, SP.
• Institution: Universidade Estadual de Campinas (UNICAMP). Faculdade de Engenharia Elétrica e de Computação
• Defense date: 2023-01-26

Examining board members

José Antenor Pomilio; Simone Buso; Tárcio André dos Santos Barros

• Advisor: José Antenor Pomilio; Joel Filipe Guerreiro

Abstract

The electrical system has been through major changes towards a more decentralized organization, in which the concept of microgrids has gained importance. However, stability issues related to the increased penetration of power converters may arise due to the interaction among the converters themselves and the network. This problem has motivated the development of methods and criteria for the assessment of the overall system’s stability, among which the impedance-based stability criteria have attracted attention. These criteria, though, require the impedances of the network to be known, which, in turn, can be identified by the power converters themselves. In this sense, this dissertation aims at the stability examination in an isolated-microgrid scenario, focusing on three main aspects—the impedance identification, the controller of a grid-forming inverter, and the stability assessment of an interconnected-converter system. For the identification, the cross-correlation method, based on the injection of pseudorandom binary sequences, is used. For all tested cases, the method presented a satisfactory accuracy for frequencies ranging from twice the fundamental component up to at least one tenth of the binary sequence generation frequency, which was adequate for both for controller and stability analyses. Concerning the second topic, the deadbeat predictive controller is thoroughly analyzed and tested. Impedance models for the grid-forming inverter are derived, and the identification method is used to experimentally measure its impedance. By comparing the measured impedance with the analytical model, the controller could be diagnosed and improved, reaching significant voltage distortion reductions on distorted current scenarios. Finally, concerning the third topic, the identification method is employed for the stability assessment of an interconnected system composed by the grid-forming inverter and an active rectifier, pointing out the practical challenges regarding the stability evaluation. It was shown that the discussed methods could correctly assess the overall stability; yet, safe margins must be considered in real applications due to identification accuracy limitations within certain frequency ranges. Besides, it was shown that the presence of passive impedances in the system—as line inductance—complicates the stability evaluation (AU)

• FAPESP's process: 20/09598-0 - Stability Identification and controllers self-tuning procedures applied to electronic power converter in microgrid
• Grantee: Igor Alves Maronni
• Support Opportunities: Scholarships in Brazil - Master