A Two-Level Hierarchical Controller to Enhance Stability and Dynamic Performance of Islanded Inverter-Based Microgrids With Static and Dynamic Loads

This paper proposes phasor measurement unit (PMU) supported two-level hierarchical controller to enhance stability and dynamic performance of islanded inverter-based microgrids with static and dynamic loads. The proposed hierarchical controller consists of a local decentralized controller for each inverter-interfaced distributed generation (IIDG) unit at the primary level helped by a multi-input multioutput centralized controller at the secondary level. The primary-level decentralized controller incorporates the addition of auxiliary control terms to the conventional droop controller. The auxiliary control terms are based on the total real and reactive power generation information acquired from wide area measurement system through PMUs and the desired power sharing of each IIDG unit. The secondary-level centralized controller, on the other hand, enhances the performance of each local decentralized controller by compensating the voltage and frequency deviations caused by the load disturbances. The performance of the proposed hierarchical controller has been demonstrated through eigenvalue analysis and time-domain simulation results carried out in MATLAB/SIMULINK environment. Further, in order to have a fair comparison, the performance of the proposed hierarchical controller, based on modal-based extended linear quadratic Gaussian (LQG) approach, has been compared with that of hierarchical controller based on state-based extended LQG approach. Simulation results revealed the capability of the proposed hierarchical controller to mitigate the unstable oscillations as well as to settle quickly at different operating points under the application of small-signal disturbances.