research highlights
A New Approach to Calculate Votage Stability Margin RPI has recently been studying a new method for computing steady-state voltage stability margins that will address singularities in power flow calculations that are common at maximum loading. Using a power flow method with a new bus type, the group will be able to ensure that current operating conditions are voltage stable. The new bus type, called an AQ bus, specifies both the angle (A) and the reactive power (Q), and will be used to replace a conventional PQ-type load bus. The major advantage of this unique approach is that the singularity at the maximum loading condition is eliminated, and the voltage stability margin can be calculated reliably and quickly. In addition, the AQ-bus approach has readily applicable conventional power flow algorithms such as generator reactive power limits and tap-changing transformers. This is because the only difference between the AQ approach and a regular power flow is the bus type. In the lab, the method has been developed for a simple two-bus system and applied to the Klein-RogersKundur 2-area system with a generator variable limit. Multiple loads and generators were then added to the method, and it was tested on the Northeast Power Coordinating Council’s (NPCC) 48 machine system for analysis. The research group at RPI envisions that the AQ-bus method has strong potential for both real-time and offline voltage stability analysis.
Fig. 1 NPCC 48-machine system with multiple loads, generators, and line outage contingencies
Game Theory Being Used for Distributed Control of the Grid The quality of power delivered to customers is a measure of the reliability of a power grid. Complex interactions exist between the various power system components, where the overall objective is to ensure that power is delivered within acceptable voltage and frequency levels. Tuskegee University is working towards a novel concept based on a Game-Theoretical approach for distributed control of the power system. Researchers have developed an algorithm that analyzes complex interactions between system control elements such as generators, tap-changing transformers and compensators for optimization of system parameters. This ensures a controlled reactive power flow and a uniform voltage profile across all buses. The research group successfully implemented localized control using an IEEE 6-bus system, and is now working with the IEEE New England 39-bus system that has been divided into four independent areas to implement distributed control. The future work includes the integration of renewable energy sources to serve as compensators to address voltage and frequency perturbations in the system. Reactive power requirements from the Game Theory algorithm will set reference levels for reactive power production from the wind turbine and the PV generations being integrated into the system to assist in the regulation of the power system to obtain the acceptable frequency and voltage level requirements.
newsletter August 2013 3