Double-Layered Droop Control-Based Frequency Restoration and Seamless Reconnection of Isolated Neighboring Microgrids for Power Sharing

Abstract

This article describes a seamless reconnection topology for power sharing between distant rural community microgrids (CMGs), which is based on a double-layered droop-controlled (DLDC) frequency restoration scheme. Increased load demand, along with the intermittent nature of renewable energy sources, may result in a power deficit in isolated CMGs. In order to overcome this restriction, the connection of autonomous neighboring CMGs may be a viable alternative to intelligent load shedding. When dealing with active power fluctuation and setting a frequency set point becomes difficult in the absence of a grid frequency reference, this DLDC-based approach can resolve the issue. The DLDC adds a self-synchronized feature by parallel shifting of the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$f - P$ </tex-math></inline-formula> slope to restore the operating frequency to its nominal value. The difference in frequency enables to shift the voltage axis accordingly through the change in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$V_{d}$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$V_{q}$ </tex-math></inline-formula> reference of the terminal voltage for appropriate power sharing. The stability of the proposed controller has been analyzed by using a mathematical model considering communication delay in the distributed secondary controller. Finally, the efficacy of the proposed controller is shown via the use of unique processor-in-the-loop (PIL) experimental findings, in which OPAL-RT and PLECS RT boxes are used to build both the CMGs and a TI-based F28069M microprocessor is utilized as a controller.