Understanding factors that influence the risk of a cascade of outages due to inverter disconnection

Because of the rapid growth in distributed solar generation, there is growing concern that inverter-connected generators, which are designed to automatically disconnect under abnormal voltage conditions, could disconnect in a manner that would lead to a cascade of outages and ultimately instability or voltage collapse. This paper studies the conditions under which a cascading inverter collapse of this sort could occur. More specifically, we identify engineering design parameters, such as time constants, that influence the speed and nature of these cascades. While this model is preliminary, the results suggest that risk increases with a number of factors including: large transmission or distribution line impedances, a large variance in inverter voltage setpoints, and an inappropriate number of inverter-based resources that can contribute to supplying too much or not enough power.