Integration of Utility-Scale Variable Generation into Resistive Networks.

Abstract

Wind and solar power account for half of newly installed electricity generation capacity worldwide. Due to falling technology costs, this trend is expected to continue despite the global economic turmoil and uncertainty over policy incentives for these fledgling sectors. A sizable portion of this capacity is connected to sub-transmission networks that typically have mesh configurations and are characterized by resistive lines (i.e. lines with X=R 4). The resistivity of subtransmission networks creates a strong coupling between power flows and voltage magnitudes that is atypical in high-voltage transmission systems. In the presence of generation variability, this can lead to extreme voltages, unacceptable voltage fluctuations, unusual (active and reactive) power flow patterns throughout the network, line congestions and increased losses. This can also cause excessive tap-changing operation of transformers with On-Load Tap Changers (OLTCs). These issues can be substantially mitigated with flexible methods of network operation and control. This dissertation examines the impact of variable embedded generation on the voltage profile, structural stability and the OLTC operation of the DTE/ITC network serving Eastern Michigan. It introduces a number of tools and methods to analyze the impact of variable generation in meshed resistive networks. It investigates how network resistivity transforms the impact of the reactive compensation, associated with variable generation, on the structural stability of the system. Finally an optimal voltage control scheme is presented to better coordinate the voltage regulation of variable generation with OLTCs, reduce network losses and enhance the structural stability of the system. The scheme is a model predictive control with an equivalent mixed integer formulation which models the hybrid dynamics of OLTC tap operations.