Impact of increased photovoltaic generation on inter-area oscillations in the Western North American power system

The primary goal of this project was to assess the impact of an increase in the penetration of photovoltaic (PV) solar generation on small-signal stability in the western North American power system. Small-signal stability is concerned with the response of the system to small disturbances where a linearized model sufficiently describes the system behavior. Two different approaches were applied to assess small-signal stability. The first approach was to excite the modes of oscillation in simulation and use Prony´s method to perform ringdown analysis. General Electric´s Positive Sequence Load Flow (PSLF) software was used to simulate dynamic brake insertions, and MATLAB was used to extract the modal content from the measured ringdowns. The second approach was to use the analytical linearization techniques provided by the Small Signal Analysis Tool (SSAT) from Powertech Labs. To study the effect of variation in system loading, two different Western Electric Coordinating Council (WECC) base cases were analyzed. Each base case was augmented by increasing the percentage of wind and photovoltaic generation. Potential concerns identified by this study were an increase in observability and decrease in damping exhibited by an East-West mode of oscillation under light loading conditions. The main finding is that mode frequency tends to increase as a function of renewable energy penetration, while damping is relatively unaffected.