Control strategy for seamless transition from islanded to interconnected operation mode of microgrids

Abstract

Microgrids can operate either interconnected to the utility grid or disconnected forming an island. The transition between these modes can cause transient overcurrents or power oscillations jeopardizing the equipment safety or the system stability. This paper proposes a local multi agent control method for a seamless transfer between the islanded and interconnected modes of operation with agents implemented into the microgrid central switch (MCS) and into the microsources inverters. The MCS agent supervises the grid status and controls the switch for the transition of the microgrid through the different operation modes, while it communicates locally with the inverter agents of the microsources. The inverter agents undertake the synchronization process in case of reconnecting and change the inverter control mode depending on the grid status. Simulation and experimental results are presented to show the performance and feasibility of the proposed strategy.

A Smooth Synchronization Methodology for the Reconnection of Autonomous Microgrids

“…Comparing the presented results to recent ones found in the literature (Zeng and Shao 2017;Papadimitriou et al 2017;Du et al 2018), it can be seen that the proposed algorithm has the advantage of controlling the transient dynamic through a single parameter λ, allowing the smoothness and speed of the process to be adjusted by the operator in a convenient way. Furthermore, it should be mentioned that the smoothness of the process can now be characterized numerically, providing another scientific criterion for the synchronization analysis.…”

“…However, there was no numerical approach to characterize the smoothness of the process, and the maximum phase mismatch of 180 • was not investigated in the study. Another control strategy was presented by Papadimitriou et al (2017), which utilized two PLLs to detect phase and frequency of both microgrid and main grid. PI controllers were used in order to set the frequency, phase and amplitude deviations to zero by providing compensator signals that adjusted the conventional droop scheme.…”

Improved Seamless Switching Control Strategy for AC/DC Hybrid Microgrid

“…However, in island mode, the frequency, phase and voltage amplitude of AC/DC hybrid microgrid are quite different from those of public grid. Direct connection will produce transient over-current and voltage, which will lead to power mutation and seriously affect the stability and security of power grid system [15]. Therefore, before closing the PCC grid connected switch, pre-synchronization operation is needed to realize the accurate matching of frequency, phase and voltage amplitude between microgrid and public grid, so as to prevent the impact caused by transient.…”

A retroactive approach to microgrid real-time scheduling in quest of perfect dispatch solution

“…Driven by this trend, microgrids have emerged as a promising solution for settling the generation-demand balance locally. In general, a microgrid integrates distributed energy resources (DERs), including non-dispatchable renewables and dispatchable local generators, and flexible operation modes, i.e., grid-connected or stand-alone modes [1][2][3]. To realize the economic operation of microgrids, it is indispensable to optimize energy scheduling, for coordinating the internal DERs of microgrids and an external grid, to minimize the overall operation cost while satisfying the time-varying load demand [4,5].…”