Leveraging Two-Stage Adaptive Robust Optimization for Power Flexibility Aggregation

To effectively harness the significant flexibility from massive distributed energy resources (DERs) for transmission-distribution interaction, power flexibility aggregation is performed for a distribution system to compute the feasible region of the exchanged power at the substation. Based on the adaptive robust optimization (ARO) framework, this paper proposes a novel methodology for aggregating system-level power flexibility, considering heterogeneous DER facilities, network operational constraints, and unbalanced power flow model. In particular, two power flexibility aggregation models with two-stage optimization are developed for application: one focuses on aggregating active power and computes its optimal feasible intervals over multiple periods, while the other solves the optimal elliptical feasible regions for the aggregate active-reactive power. By leveraging ARO technique, the disaggregation feasibility of the obtained feasible regions is guaranteed with optimality. The numerical simulations conducted on a real-world distribution feeder with 126 multi-phase nodes demonstrate the effectiveness of the proposed method.Comment: 8 Page

Identifying Secure Operating Ranges for DER Control using Bilevel Optimization

Active distribution grids are accommodating an increasing number of controllable electric loads and distributed energy resources (DERs). A majority of these DERs are managed by entities other than the distribution utility, such as individual customers or third-party aggregators, who control the loads and DERs without consideration of any distribution grid constraints. This makes it challenging for a distribution system operator (DSO) to allow third-party aggregators and transmission operators to fully exploit the flexibility offered by these resources while also ensuring that distribution grid constraints such as voltage magnitude limits are not violated. In this paper, we develop a bilevel optimization-based framework to determine the aggregate power flexibility that can be obtained from an unbalanced distribution grid while ensuring that there is no disaggregation solution that leads to grid constraint violations. The results are a set of constraints and operating rules that are easy to communicate, and which provide the entities that procure flexibility from DERs (e.g. transmission operators or third-party aggregators) with the ability to freely implement their own disaggregation strategy without intervention from the DSO. The proposed approach is tested on two unbalanced distribution feeders and our simulation results indicate that it is possible to determine a wide range of aggregate power flexibility, as long as a simple set of rules for DER control activation are followed

Joint Optimal Pricing and Electrical Efficiency Enforcement for Rational Agents in Micro Grids

In electrical distribution grids, the constantly increasing number of power generation devices based on renewables demands a transition from a centralized to a distributed generation paradigm. In fact, power injection from Distributed Energy Resources (DERs) can be selectively controlled to achieve other objectives beyond supporting loads, such as the minimization of the power losses along the distribution lines and the subsequent increase of the grid hosting capacity. However, these technical achievements are only possible if alongside electrical optimization schemes, a suitable market model is set up to promote cooperation from the end users. In contrast with the existing literature, where energy trading and electrical optimization of the grid are often treated separately or the trading strategy is tailored to a specific electrical optimization objective, in this work we consider their joint optimization. Specifically, we present a multi-objective optimization problem accounting for energy trading, where: 1) DERs try to maximize their profit, resulting from selling their surplus energy, 2) the loads try to minimize their expense, and 3) the main power supplier aims at maximizing the electrical grid efficiency through a suitable discount policy. This optimization problem is proved to be non convex, and an equivalent convex formulation is derived. Centralized solutions are discussed first, and are subsequently distributed. Numerical results to demonstrate the effectiveness of the so obtained optimal policies are then presented