Paper Title
Analysis And Mitigation Of Low-Frequency Instabilities In Autonomous Medium-Voltage Converter-Based Micro- Grids With Dynamic Loads

The concept of micro-grid is gaining widespread acceptance in near-term future power networks. Mediumvoltage (MV) micro-grids can be subjected to high penetration level of dynamic loads (e.g. induction motor (IM) loads). The highly-nonlinear IM dynamics that couple the active power, reactive power, voltage and supply frequency dynamics challenge the stability of MV droop- contro lled micro-grids. The electrical distances between reactive power sources and the loads that need reactive compensation are not too much in microgrids. Thus, a coordinated compensation of reactive sources should be implemented to avoid a fast voltage collapse and improve the dynamic voltage profile by proposing a MicroGrid Voltage Stabilizer. The micro-grid operation and power management of the system are studied during the grid-connected mode, the autonomous operation and ride-through between the grid-connected and the autonomous modes. However, detailed analysis, and more importantly, stabilization of MV micro-grids with IM loads are not reported in current literature. To fill-out this gap, this paper presents integrated modeling, analysis and stabilization of MV droop-controlled micro-grids with IM load. A detailed small-signal model of a typical MV droop-controlled micro-grid system with both dynamic and static loads is developed. The proposed model accounts for the impact of supply frequency dynamics associated with the droop-control scheme to accurately link the micro-grid f requency dynamics to the motor dynamics. To stabilize the microgrid system in the presence of IM loads, a two-degree-of-freedom active damping controller is proposed to stabilize the newly introduced oscillatory dynamics. The proposed supplementary active damping controller may not interfere with the steady-state performance and yields robust control performance under wide range of droop parameters, and robust damping performance at small- and large-signal disturbances. A theoretical analysis and simulation are presented to show the effectiveness of the proposed contro l scheme.