Award Date

1-1-2007

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Electrical and Computer Engineering

First Committee Member

Yahia Baghzouz

Number of Pages

104

Abstract

Distributed generation (DG) is increasingly spreading in the form of solar power, wind power, and fuel cell power. These DGs are connected to the power grid in order to benefit the investors for their economical efficiency and reliability. However, the introduction of DGs, especially at a high level of penetration, brings hidden problems to the conventional power distribution system. The conventional power distribution system has only one direction for the power flow, i.e., from the substation to the end user. This situation may not hold with the introduction of DGs because the power flow may reverse direction in some parts of the feeder. This dissertation will focus on two major problems induced by the introduction of DG: the voltage regulation and the islanding phenomenon; The study shows the introduction of A DG may cause an over-voltage problem in some segment along the distribution line. The level of over-voltage depends on the size and location of the DGs. Furthermore, DGs are known to impair the operation of conventional voltage regulation methods, and the study shows that the LTC transformer may be "fooled" by a DG and fails to react to an under-voltage in some cases. The study also shows that switched capacitors can cause an over-voltage if their controls are not modified after introducing DGs into the feeder. The study reveals the necessity to re-coordinate the control of LTC transformer and the switched capacitors with the introduction of DG units; The introduction of DG may also cause the islanding phenomenon when the grid power trips off. The DG may continue to supply power supply power to the local load during a utility outage. This situation is of great concern to the utility crew when restoring power. According to a national electrical standard, every DG must shut down in case of grid power loss. The study builds a detailed dynamic model of a grid-connected inverter in a MATLAB/SIMULINK environment. The model simulates the dynamic change in voltage, current, real and reactive power of the DG's output under various conditions, and simulates the relay action due to over-voltage and under-voltage (OV/UV) and over-frequency and under-frequency (OF/UF). It gives a sound and easy tool to the study of the DG's dynamics. Based on this model, a novel anti-islanding scheme is present and verified. Also presented are some field tests on the behaviors of two grid-tied PV systems that are equipped with anti-islanding schemes in case of grid outage.

Keywords

Distributed Generation; Generation; Islanding; Islanding; Regulation; Study; Voltage; Voltage Regulation

Controlled Subject

Electrical engineering

File Format

pdf

File Size

2160.64 KB

Degree Grantor

University of Nevada, Las Vegas

Language

English

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