Graduation Year


Document Type




Degree Granting Department

Electrical Engineering

Major Professor

Alex Domijan, Ph.D.

Co-Major Professor

Sanjukta Bhanja, Ph.D.

Committee Member

Lingling Fan, Ph.D.

Committee Member

Jim Mihelcic, Ph.D.

Committee Member

Tom Crisman, Ph.D.


Renewable Energy, Smart Grid, Bifurcation, Decentralization, Voltage Sag


Photovoltaic (PV) DGs can be optimized to provide reactive power support to the grid,

although this feature is currently rarely utilized as most DG systems are designed to

operate with unity power factor and supply real power only to the grid. In this work, the

voltage stability of a power system embedded with PV DG is examined in the context of

the high reactive power requirement after a voltage sag or fault. A real-time dynamic

multi-function power controller that enables renewable source PV DGs to provide the

reactive power support necessary to maintain the voltage stability of the microgrid, and

consequently, the wider power system is proposed.

The loadability limit necessary to maintain the voltage stability of an interconnected

microgrid is determined by using bifurcation analysis to test for the singularity of the

network Jacobian and load differential equations with and without the contribution of

the DG. The maximum and minimum real and reactive power support permissible from

the DG is obtained from the loadability limit and used as the limiting factors in

controlling the real and reactive power contribution from the PV source. The designed

controller regulates the voltage output based on instantaneous power theory at the

point-of-common coupling (PCC) while the reactive power supply is controlled by means

of the power factor and reactive current droop method. The control method is

implemented in a modified IEEE 13-bus test feeder system using PSCAD® power system

analysis software and is applied to the model of a Tampa Electric® PV installation at

Lowry Park Zoo in Tampa, FL.

This dissertation accomplishes the systematic analysis of the voltage impact of a PV DGembedded

power distribution system. The method employed in this work bases the

contribution of the PV resource on the voltage stability margins of the microgrid rather

than the commonly used loss-of-load probability (LOLP) and effective load-carrying

capability (ELCC) measures. The results of the proposed method show good

improvement in the before-, during-, and post-start voltage levels at the motor

terminals. The voltage stability margin approach provides the utility a more useful

measure in sizing and locating PV resources to support the overall power system

stability in an emerging smart grid.