Doctoral Dissertations

Date of Award

12-2024

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Electrical Engineering

Major Professor

Leon M. Tolbert

Committee Members

Leon M. Tolbert, Hua (Kevin) Bai, Fangxing Fran Li, Yunting Liu

Abstract

The penetration of photovoltaic (PV) generations has rapidly increased in today’s power systems. The high integration of PV systems into power grids has brought challenges in terms of grid resiliency and reliability.

One solution to enable the high integration of PV systems in power grids is the use of energy storage systems (ESSs). The ESSs act as energy buffers of PV systems by storing excess energy and later using it to maintain power balance in the power systems. Supercapacitors (SCs) are one promising energy storage technology for grid applications. SCs can be employed with PV systems to smooth power fluctuations generated by PV systems, thereby, reducing voltage fluctuations on power grids.

Studying SC dynamics in power systems can be challenging due to the difficulty in maintaining the consistency of physical SCs during tests. Therefore, this dissertation investigates SC dynamics in PV systems by developing a grid-connected PV with SC system (PVSS) emulator, which serves power system studies on a hardware testbed (HTB) platform. The PVSS emulator’s accuracy is verified by comparing it to MATLAB/Simulink simulation results.

The PVSS emulator incorporates grid support functions, including voltage support, frequency support and inertia emulation, and fault ride-through operations (FRT). During FRT operation, when the PVSS stability is most vulnerable, a state of charge (SOC) reservation concept is proposed to ensure the SC's availability to provide FRT operations that comply with grid code requirements. Additionally, a SOC management control strategy is proposed to quickly restore the SC’s SOC to its working region after FRT operations while ensuring the safe operations of both grid and PVSS. The performances of the proposed control strategies are validated on the HTB.

Finally, this dissertation investigates reactive power support from PV systems to improve voltage in power grids based on a transactive energy (TE) approach. The concept of considering the location of PV systems as reactive power suppliers is proposed for the TE approach to reduce losses in the power system caused by supplying reactive power over long distances. The proposed modified reactive power supply curve is validated to demonstrate its efficiency using an IEEE standard test feeder.

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