Integration of Utility-Scale Variable Generation into Resistive Networks
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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. The resistivity of sub-transmission networks creates a strong coupling between power flows and voltage magnitudes that is atypical in high-voltage transmission systems. This, in the presence of generation variability can lead to extreme voltages, unusual (active and reactive) power flow patterns throughout the network, line congestions and increased losses. This can also cause excessive switching of electromechanical devices in the system, in particular On-Load Tap Changers (OLTCs).
These issues can be substantially mitigated with flexible methods of network operation and control and more capable tools for optimizing and planning variable generation capacity. I have developed an optimal voltage control scheme to better coordinate the voltage regulation of wind farms 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 switching operations. I have also applied the concept of semi-definite relaxation of optimal power flow for wind capacity allocation problems in meshed resistive networks.