AN ABSTRACT OF A DISSERTATION
submitted in partial fulfillment of the
requirements for the degree
DOCTOR OF PHILOSOPHY
Mike Wiegers
Department of Electrical & Computer Engineering
Carl R. Ice College of Engineering
KANSAS STATE UNIVERSITY
Manhattan, Kansas
2021
Abstract
This dissertation focuses on improving the dynamic behavior of microgrids during the abnormal
conditions. For this purpose, novel approaches are presented to turn the conventional
inverters implemented in distributed generation (DG) units into smart inverters capable of
dealing with disturbances. In the context of microgrids, the smartness of an inverter is tied
to its ability to cope with abnormalities such as sudden load changes, loss of generation, and
transitions between different modes of operation. Founded on these principles, this dissertation
advances the state-of-the-art in enhancing the dynamic response of microgrids. To
this end, firstly, a new approach of forming smart loads in a fleet of nanogrids, which is
also referred as a grid of nanogrids (GNG), is presented in this dissertation. The proposed
smart load configuration is obtained via series connection of electric dampers (EDs) with
critical loads to cope with disturbances at the point of critical loads. A systematic approach
is presented for modeling of the proposed smart loads considering the switching states of
EDs. The stability of the smart loads is then studied using the developed state-space model.
Secondly, the conventional controllers of battery energy storage system (BESS) and photovoltaic
(PV) units are modified in this dissertation in order to enable them to participate
in dynamic-response enhancement of islanded mixed-inertia microgrids. For this purpose,
two piecewise linear-elliptic (PLE) droops are proposed and employed in BESS to improve
the voltage and frequency profiles during abnormalities. Besides, the controllers of PV units
are equipped with an adaptive piecewise droop (APD) to cope with disturbances. Lastly,
an approach is presented in this dissertation for seamless interconnection of three singlephase
feeders at distribution level for residential communities that are suffering from power
imbalance within the phases during islanded mode. To attain this, a seamless transition
algorithm is presented which monitors the system condition in real time and sends appropriate
commands to the static transfer switches (STSs) and modified controllers of single-phase
inverters. Using the proposed method for interconnecting the isolated single-phase feeders
results in forming a unified single-phase residential microgrid and maintaining the power
balance and voltage level within all three phases. Moreover, the proposed approach enables
the residential community to seamlessly reconnect to the main grid after resolving the abnormal
condition on the grid side. In this dissertation, numerous case studies are carried
out in PSCAD/EMTDC environment to validate the viability of proposed approaches in
improving the dynamic behavior of microgrids.
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