Decentralized Control for Power Systems Subject to Wind Power Variability

Wednesday, November 10, 2010: 9:50 AM
250 B Room (Salt Palace Convention Center)
Juhua Liu, Electrical Engineering, Carnegie Mellon University, Pittsburgh, PA, Bruce Krogh, Electrical and Computer Engineering, Carnegie Mellon University, Pittsburgh, PA and B. Erik Ydstie, Department of Chemical Engineering, Carnegie Mellon University, Pittsburgh, PA

The frequency of a power system should be maintained nearly constant at nominal frequency to ensure safe and reliable operation. Increasing the proportion of wind power to conventional generators can degrade frequency performance because: 1) fluctuations in wind generation due to wind variations lead to frequency deviations, thus increasing the amount of control effort required to maintain system frequency; 2) displacing conventional generators with modern variable-speed wind turbine generators reduces system inertia, making the power system more sensitive to generation-load imbalances; and 3) as the conventional generators responsible for frequency control being displaced by non-dispatchable wind generation, frequency control in power systems becomes more difficult. H-infinity methods are applied to synthesize new governors for conventional plants in order to attenuate frequency deviations caused by continuous wind power fluctuations.1 Decentralized control is preferred in large-scale systems such as power systems due to lack of infrastructure, unwillingness to share information between different parties, and communication delays. In this paper, we illustrates that a na´ve decentralized control design may lead to instabilities. Therefore, a passivity-based decentralized frequency control framework is proposed for power system subject to wind power variability. The kinetic energy of each rotating machine is chosen as inventories and the local frequency at each bus is identified as intensive variables. An entropy function is introduced for each rotating mass and a proper storage function is provided for passivity-based control. The system is shown to be passive with respect to a decentralized supply rate by using Tellegen's theorem. Negative feedback interconnections of passive subsystems result in a passive and stable overall system. A proportional-integral (PI) controller with positive gains is passive, so we apply the robust PI control theory to design governors for conventional plants to achieve both stability and performance. This work also suggests several directions for further research.

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See more of this Session: Optimization and Control of Energy Systems I
See more of this Group/Topical: Computing and Systems Technology Division