This research investigates the microgrid-based solution to future distribution systems with high penetration of distributed energy resources (DERs). A clustered system architecture is envisioned, in which microgrids are formulated as key building blocks of a smart distribution system. Accordingly, the control and operation can be simplified significantly with the system configured as an interconnected of coupling operated microgrids. By leveraging the highly controllable power electronics (PE) interfaces - voltage source inverters (VSIs), and advanced measurement technology - synchrophasor, we propose a novel interface control strategy, through which desirable power sharing behavior among coupled microgrids can be achieved. Angle droop method is adopted for real power sharing instead of the widely used frequency droop control, which eliminates the need for secondary level frequency control. For reactive power sharing, voltage droop control implemented with integrator is adopted, which pro-vides effective support for voltage dynamics and interaction among interconnected microgrids. Better transient performance can be achieved with the proposed interface control strategy compared with conventional power systems interfaced through synchronous generators (SGs). For the proposed system configuration and interface control strategy, small signal and transient stability problems are investigated. Several criteria are derived, based on which the system stability can be evaluated with computationally efficient algorithms and dynamic security assessed and managed in a timely manner. With future distribution grids configured as microgrid interconnections, a three level hierarchical control framework is proposed. At the primary level the model reference control (MRC) is performed for interface parameter online tuning, through which each VSI-interface is controlled to track a designed reference model. At the secondary level, a droop gain management scheme is proposed to adjust the angle and voltage droop gains based on system stability assessment results. At the tertiary level, an AC power flow (ACPF)-based supervisory control strategy is employed to dispatch the nominal setting to each microgrid central controller (MGCC).
- Xie, Le Professor