The uncertainty and variability of renewable generation pose significant challenges to reliable power-grid operations. This paper designs robust online strategies for jointly operating energy storage units and fossil-fuel generators to achieve provably reliable grid operations at all times under high renewable uncertainty, without the need of renewable curtailment. In particular, we jointly consider two power system operations, namely day-ahead reliability assessment commitment (RAC) and real-time dispatch. We first extend the concept of “safe-dispatch sets” to our setting. While finding such safe-dispatch sets and checking their non-emptiness provide crucial answers to both RAC and real-time dispatch, their computation incurs high complexity in general. To develop computationally-efficient solutions, we first study a single-bus case with one generator-storage pair, where we derive necessary conditions and sufficient conditions for the safe-dispatch sets. Our results reveal fundamental trade-offs between storage capacity and generator ramp-up/-down limits to ensure grid reliability. Then, for the more general multi-bus scenario, we split the net-demand among virtual generator-storage pairs (VGSPs) and apply our single-bus decision strategy to each VGSP. Simulation results on an IEEE 30-bus system show that, compared with state-of-art solutions, our scheme requires significantly less storage to ensure reliable grid operation without any renewable curtailment.

In this paper, we are interested in online multistage decisions to ensure robust power grid operations under high renewable uncertainty. We jointly consider both the reliability assessment commitment (RAC) and the real-time dispatch problems. We first focus on the real-time dispatch problem and define “maximally robust algorithms,” which can provably ensure grid safety whenever there exists any other algorithm that can ensure grid safety under the same level of future uncertainty. We characterize a class of maximally robust algorithms using the concept of “safe dispatch set,” which also provides conditions for verifying grid safety for RAC. However, in general such safe dispatch sets may be difficult to compute. We then develop efficient computational algorithms for characterizing the safe dispatch sets. Specifically, for a simpler single-bus two-generator case, we show that the safe dispatch sets can be exactly characterized by a polynomial number of convex constraints. Then, based on this two-generator characterization, we develop a new solution for the multi-bus multi-generator case using the idea of virtual demand splitting (VDS), which can effectively compute a suitable subset of the safe-dispatch set. Our numerical results demonstrate that a VDS-based economic dispatch algorithm outperforms the standard economic dispatch algorithm in terms of robustness, without sacrificing economy.