Electronic Thesis and Dissertation Repository

Degree

Master of Engineering Science

Program

Electrical and Computer Engineering

Supervisor

Dr. Amirnaser Yazdani

Abstract

Grid-connected photovoltaic (PV) solar systems, like other inverter-based distributed generators, can cause temporary over-voltages (TOVs), especially subsequent to faults and unintentional islanding incidents, and can damage equipment and customers within the host distribution network. Thus, this thesis aims to study the phenomenon and propose corrective measures for it. Thus, the thesis first presents detailed models for a conventional single-stage PV system and a modified single-stage PV system. The conventional system uses a Δ/YG isolation transformer, whereas the modified system, proposed in the literature, assumes a Y/YG isolation transformer that is effectively grounded by an additional half-bridge leg energized by the dc-link of the voltage-sourced inverter (VSI) of the PV system. Moreover, the thesis proposes two TOV mitigation schemes that augment the basic controls of the conventional and modified single-stage PV systems, respectively. Further, the thesis models a two-stage PV system that adopts the same TOV mitigation scheme as that proposed for the conventional single-stage system. Then, the TOV caused by the two-stage system is evaluated, with and without the TOV mitigation scheme. It is shown that the proposed TOV mitigation schemes are effective. The thesis also compares the TOVs caused by the three aforementioned PV systems, with and without the TOV mitigation schemes, and concludes that a two-stage PV system without a TOV mitigation scheme produces smaller TOVs than its single-stage counterparts without TOV mitigation schemes. Similarly, a two-stage PV system with its TOV mitigation scheme produces smaller TOVs than its single-stage counterparts with their respective TOV mitigation schemes.

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