Probabilistic Assessment of the Frequency of Islanded Microgrids in the Presence of Renewable Sources via Unscented Transformation
Electric Microgrids. Islanded Operation. Uncertainty Modeling. Unscented Transformation. Renewable Generation.
In the islanded operation of alternating current microgrids, the steady-state frequency may deviate from the nominal value. This is attributed to the operational characteristics of dispatchable generators (such as microturbines) which function on a frequency droop characteristic, and renewable generators (wind and solar) that inject power based on their capacities. Given the variability in load and the power injected by renewable generators, the frequency fluctuates to maintain power balance. This aspect should be considered during the planning stage of the microgrid to ensure that frequency limits are adhered to, aiming to maintain the quality of energy supplied to consumers. When load values and renewable generation are known, steady-state analysis (frequency calculation) can be conducted using deterministic power flow. However, in the face of uncertainties, such powers are modeled based on a statistical distribution, and a probabilistic power flow (PPF) must be executed. Monte Carlo Simulation (MCS) is the most commonly used method for this purpose, despite its high computational effort. In this context, this work presents a PPF for islanded microgrids aimed at calculating the statistical values associated with the steady-state frequency using the Unscented Transformation (UT). UT is distinguished by its use of a significantly lower number of samples, thereby reducing computational effort. Results for a 33-bus microgrid indicate a 99% reduction in computational time, while maintaining the accuracy of the results.