PNNL

Abstract

Microgrids have proven to be an effective option for increasing the resiliency of critical end-use loads during extreme events. Building on past operational experiences, some microgrid operators are examining the potential to network microgrids to further improve resiliency. However, the frequency deviations experienced on isolated microgrids during transient events are significantly larger than those typically seen on bulk transmission systems. The larger frequency deviations can cause a loss of inverter-connected assets, resulting in a loss of power to critical end-use loads. This paper presents a method of mitigating the impact of transient events by engaging end-use loads using Grid-Friendly Appliance\texttrademark\ (GFA) controllers while minimizing the interruptions to end-use loads. An online, i.e., real-time, device-level algorithm is presented, which adjusts individual GFA controller frequency setpoints based on the operational characteristics of each end-use load, and on the changing grid dynamic characteristics to engage the right amount of loads for mitigating the switching transients. The presented method improves the dynamic stability of the networked microgrid operations. Dynamic simulations validate the presented work using a modified version of the IEEE 123-node test system with three microgrids, using the GridLAB-D\texttrademark\ simulation environment.