Análise da estabilidade de conversores conectados a redes elétricas com baixo SCR

Abstract

This Ph.D. thesis presents an analysis on the influence of the synchronism system on three-phase converters connected to weak grid combining state space approaches and matrix transfer functions. The generation system modeling is performed on dq synchronous axes in continuous time divided into two domains, the grid domain and the converter domain. The complete converter model, which includes the current, DC bus voltage, reactive power and PLL controllers, is non-linear, and therefore its linearization is performed by small signal perturbation. The eigenvalues-based method will be used to propose guidelines for choosing the PLL and other controllers gains of a three-phase converter connected to a weak grid. Moreover, based on the impedance method, the generation system is divided into two elements represented in matrix transfer functions. The first represents the equivalent admittance of the converter, which is obtained by considering it connected to an ideal grid. The second represents the equivalent impedance of the grid taking into account the line transmission π model. The interconnection between the two elements is performed in transfer function matrices and represented in block diagram form. The stability analysis of the system is performed by using the generalized Nyquist criterion on the product of the admittance of the converter with the grid impedance. Thus, it can be inferred on the influence of the synchronism system on the stability of converters connected to the grid and to estimate the stability conditions of the system. Finally, the analysis will be extended to multiple converters in parallel. Results in the time domain in HIL show a good correlation with those of the theoretical analysis performed in the frequency domain.