A Novel Positive and Negative Sequence Control Strategy for Enhancing Transmission Systems' Performance during Unbalanced Operation

  • Nada Al Awadhi

Student thesis: Master's Thesis

Abstract

Due to the rapid developments in renewable energy technologies, its penetration into existing electrical power grids has been continuously increasing. Renewable Energy sources, such as wind and solar, are usually connected to electric grids through an electronic power interface. The United Arab Emirates has very good solar radiation profile, making the potential for harvesting solar energy extremely favorable. Photo-voltaic plants, which are the most common type of solar power plants, are connected to electric grids using DC/AC converters (inverters). These inverters are typically over-sized in order to tolerate the intermittent nature of solar power. However, they are only fully utilized during a fraction of the day when solar radiation is at its peak. As for the rest of the day, they are only partly utilized or not at all. For instance, the inverters are not utilized at all during the night when the PV arrays are not generating active power. The objective of this thesis is to improve the performance of transmission systems during unbalanced operating conditions by utilizing the full capacity of these inverters. Voltage unbalance has become a sensitive topic with recent grid codes imposing strict limits on it, because of its adverse effects on power systems. Reactive power compensation is one of the techniques applied to mitigate this problem. Typically, costly FACTS devices are installed for this purpose. With more and more large-scale PV plants being connected to the grid, bearing this extra cost might be unnecessary. The grid-tied PV inverters can provide reactive power support using the excess capacity, which is not utilized for active power generation. Therefore, a novel centralized positive and negative sequence control strategy was designed for grid-tied PV inverters to mitigate the effect of voltage unbalance by injecting reactive power. The control strategy was evaluated for steady-state operation, as well as transient operation, on the IEEE 12-bus benchmark for FACTS devices using the power simulation tool PSCAD/EMTDC.
Date of AwardMay 2015
Original languageAmerican English
SupervisorMohamed Shawky (Supervisor)

Keywords

  • Transmission Systems
  • Electrical Systems
  • Renewable Energy Sources
  • Electric Power Grids
  • Electronic Power Interface
  • Solar Radiation in the UAE
  • Solar Power Plants
  • Power Generation.

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