Supervisor:
Josep M. Guerrero

Co-Supervisor:
Juan C. Vasquez

Assessment Committee:
Associate Professor Yanbo Wang (Chair)
Associate Professor Mattia Ricco, University of Bologna, Italy
Associate Professor Nursyarizal Mohd Nor, Universiti Teknologi PETRONAS, Malaysia

Moderator:
Associate Professor Sanjay Chaudhary

Abstract:

With the increasing penetration of renewable energy (RE) sources, grid-connected microgrids have been extensively developed, where the currents and voltages can be easily distorted by harmonics of nonlinear loads and nonideal grids. Although some research has been done for harmonic suppression, the reduction of the inverter output impedance in most harmonic control methods will result in an increase of the inverter inrush fault current under grid faults, which impairs the fault ride-through (FRT) capability of the system. To address this issue, this PhD thesis focuses on the harmonic and fault current mitigation approaches development as well as impedance-based modeling and stability analysis for grid-connected RE-based microgrids. The PhD project is conducted under joint cooperation with the WindFlag project, a collaborative project between Denmark and Turkey for large-scale offshore wind power plant integration.

With regard to harmonic control, several active harmonic control strategies are put forth for grid-interfaced RE-based microgrids with and without nonlinear loads to improve harmonic suppression effect and system robustness, including a stability-oriented optimal active filter parameter tuning method to balance harmonic mitigation and system stability margin; a decomposed harmonic compensation method to reduce system sensitivity to parameters variation in inverter output impedance, shunt capacitance, and grid impedance; and a hierarchical harmonic control architecture for multibus wind power plants. For fault management, a virtual-impedance-based fault current limitation method is proposed upon grid voltage sag to improve the dynamic current damping and transient fault current limitation performance. Subsequently, a harmonic current and fault current coordinated mitigation method is proposed in the thesis for the RE-based microgrids with nonlinear loads under nonideal grid conditions to improve the grid current power quality and system FRT capability, considering both symmetrical and asymmetrical grid faults.