Abstract
Renewable portfolio standards are targeting high levels of variable solar photovoltaics (PV) in electric distribution systems, which makes reliability more challenging to maintain for distribution system operators (DSOs). Distributed energy resources (DERs), including smart, connected appliances and PV inverters, represent responsive grid resources that can provide flexibility to support the DSO in actively managing their networks to facilitate reliability under extreme levels of solar PV. This flexibility can also be used to optimize system operations with respect to economic signals from wholesale energy and ancillary service markets. Here, we present a novel hierarchical scheme that actively controls behind-the-meter DERs to reliably manage each unbalanced distribution feeder and exploits the available flexibility to ensure reliable operation and economically optimizes the entire distribution network. Each layer of the scheme employs advanced optimization methods at different timescales to ensure that the system operates within both grid and device limits. The hierarchy is validated in a large-scale realistic simulation based on data from the industry. Simulation results show that coordination of flexibility improves both system reliability and economics, and enables greater penetration of solar PV. Discussion is also provided on the practical viability of the required communications and controls to implement the presented scheme within a large DSO.
Highlights
The objective of the feeder operational layer (FOL) is to coordinate the flexibility of the responsive virtual battery (VB) and PV inverters with the legacy control devices, such as capacitor banks (CBs) and on-load tap changers (OLTCs), to reshape net power exchanges at the feeders’ head-nodes in response to economically optimized power set-points provided by the grid market layer (GML), which updates every five minutes and represents the top level of the hierarchy
The presented GML-FOL-service transformer layer (STL)-Distributed energy resources (DERs) hierarchical scheme represents a novel, scalable, and practically implementable approach to the Market distribution system operators (DSOs)’s task of coordinating DERs while accounting for individual device and AC grid constraints; The scheme employs optimization-based methods within each layer to ensure that DERs are utilized optimally and in a “grid-aware” manner, and integrates the layers with feedback-based control schemes to be robust against model-mismatch and forecast errors
While the previous section highlighted the practical viability of real-time feedback control and communications between the different layers, this section focuses on large-scale simulation and validation of the coupled GML-FOL-STL-DER energy resource hierarchy
Summary
Distribution system operators (DSOs) have managed a system wherein power flowed from large, central thermal generators in high voltage (HV) transmission networks to medium. Distribution feeders with the expected MWs of solar PV and flexible demand represent a grid that interacts with thousands of controllable inverters and kW-scale loads, such as thermostatically controlled loads (e.g., electric water heaters, residential air-conditioners), deferrable loads (e.g., electric vehicle chargers, smart appliances), and distributed batteries. These “future” systems are already being enabled by cheap “printable” embedded hardware platforms, such as the Internet of Things (IoT), and people’s desire for comfort and convenience that are opening up a new frontier for energy digitization [5]. There is a need to reconsider the role of the distribution system operators (DSOs) as solar PV and smart inverters are increasingly deployed and demand becomes flexible
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