SMALL SIGNAL STABILITY OF A MICROGRID

Abstract

The distributed energy sources can be combined with the electricity delivery network through microgrids. The distributed generation units are worked upon in either islanded mode where they are separated from the main grid or in grid connected mode, where they are operated coupled to the main grid. Due to dynamical interactions between the system components and various loads, system stability issues arise. In this dissertation, small signal model for the autonomous operation of inverter-based microgrid has been developed. Here current and voltage controllers of the inverter are PI-regulator based. Each sub-module such as inverters, network and load is modeled in d-q reference frame in state space form and combined together on common reference frame. This complete model is linearised about an operating point and the resultant system matrix is used for eigenvalue analysis and has been used to determine the small signal stability of the system. The relationship between the small signal stability of microgrid and affecting factors such as controller parameters have been studied. Later, we have focused on improvement of small signal stability of the system and to get better transient performance. For this purpose, the conventional PI-based current and voltage control loops are replaced by the internal model-based current and voltage controllers. Both the control loops are designed based on IMC approach. Small signal model of the islanded inverter-based microgrid with IMC-based controllers is derived using the same method. It’s eigen value analysis is performed to evaluate its small signal stability. Simulations are performed to compare the results with those of same microgrid but with conventional PI-based regulators. Results show that the proposed IMC-based control approach has superior eigenvalue patterns and improved stability. The transient performance of the system is also improved.