Key factors affecting voltage oscillations of distribution networks with distributed generation and induction motor loads

The existence of critical voltage modes in distribution systems and the key factors responsible for them are presented in this paper. The analysis is carried out over a distribution test system for different types of induction motors. Eigenvalues and participation factors are used to investigate the modal interaction within the system. This study shows that load voltage dynamics significantly influence damping of the voltage modes. These modes have frequencies of oscillations between the electromechanical and subsynchronous oscillations of power systems. Significant parameters of the system which affect the damping and frequencies of the oscillations are identified to provide a clear understanding of the problem. A bifurcation study is performed to determine the dynamic loadability limit of the system. Time-domain simulations are carried out to verify the validity of the modal analysis and provide a physical feel for the types of oscillations that occur in distribution systems. The impact of various distribution network configurations on these modes is also demonstrated through nonlinear simulations.