A SuperCapacitor Agent for Providing Real-Time Power Services to the Grid

Supercapacitors-based storage systems are expected to play a key role in microgrids in view of their capability to compensate high-power imbalances. We define an agent for the control of supercapacitor arrays within the context of the novel control framework Commelec, proposed by the Authors as a composable method for real-time control of active distribution networks with explicit power setpoints. An important function of such an agent is to advertise the real-time power capabilities and operational preferences of the supercapacitor array based on local information. Given the small energy capacity of such a device, its internal state can largely vary from one setpoint implementation to the next one. For this reason, the use of an accurate model is crucial in the agent definition. We show that it is possible to infer the real-time power capabilities of the device by using simple measurements on the supercapacitor array suitably coupled with an accurate representation of the cells composing the array. Results show that the agent is able to speak for the resource, thus allowing its use from an external controller

Real-Time Control Framework for Active Distribution Networks Theoretical Definition and Experimental Validation

Lorenzo Enrique Reyes Chamorro

The great challenge of massively integrating the volatile distributed power-generation into the power system is strongly related to the evolution of their operation and control. The literature of the last decade has suggested two models for such an evolution: (i) the supergrid model, based on enhanced continental/intercontinental network interconnections (mainly DC) for bulk transmission, (ii) the microgrid mode, where small medium/low voltage networks interfacing heterogeneous resources, such as local generation, energy storage and active customers, are intelligently managed so that they are operated as independent cells capable of providing different services from each other and operate in islanded mode. Irrespective of the model that will eventually emerge, the control of heterogeneous distributed resources represents a fundamental challenge for both supergrid and microgrid models. This requires the definition of scalable and composable control methods that guarantee the optimal and feasible operation of distribution grids in order to satisfy local objectives (e.g., distribution grid power balance), as well as the provision of ancillary services to the external bulk transmission (e.g., primary and secondary frequency supports). Several control methodologies have been proposed to achieve these goals, and the majority of them have been inspired by the classic time-layered approach traditionally adopted in power systems that are associated with different time-scales and extension of the controlling area, i.e. primary, secondary and tertiary controls, ranging from sub-seconds to hours, respectively. In the context of microgrids, these three levels of control can be associated with a decision process that can be centralized (i.e., a dedicated central controller decides on the operation of the system resources) and/or decentralized (each element decides based on its own rules). In the current literature, the former is used for long-term, whereas the latter for short-term decisions. In particular, primary controls are typically deployed through fully decentralized schemes mainly relying on the use of droop control. With this in mind, in this thesis we propose, and experimentally validate, a novel control framework called COMMELEC â A Composable Framework for Real-Time Control of Active Distribution Networks, Using Explicit Power Set-Points. It controls a power grid in real-time based on a multi-agent structure, using a simple and low-bandwidth communication protocol. Such a framework enables a controller to easily steer an entire network as an equivalent energy resource, thus making an entire system able to provide grid support by exploiting the flexibility of its components in real-time. The main features of the framework are (i) that it is able to indirectly control the reserve of the storage systems, thus maximizing the autonomy of the islanding operation, (ii) that it keeps the system in feasible operation conditions and better explores, compared to traditional techniques, the various degrees of freedom that characterize the system, and (iii) that it maintains the system power-equilibrium without using the frequency as a global variable, even being able to do so in inertia-less systems. Our framework has been extensively validated, first by simulations but, more importantly, in a real-scale microgrid laboratory specially designed and setup for this goal. This is the first real-scale experiment that proves the applicability of a droop-less explicit power-flow control mechanism in microgrids.

EPFL2016

A composable method for real-time control of active distribution networks with explicit power set points. Part II: Implementation and validation

Andrey Bernstein, Jean-Yves Le Boudec, Mario Paolone, Lorenzo Enrique Reyes Chamorro

In this second part, we evaluate the performances of our control framework by applying it to a casestudy that contains a minimum set of elements allowing to show its applicability and potentials. Weshow how the computation of the PQt profiles, belief functions, and virtual costs can be synthesized forgeneric resources (i.e., dispatchable and stochastic generation systems, storage units, loads). The metricsof interest are: quality-of-service of the network represented by voltages magnitudes and lines currentmagnitudes in comparison with their operational boundaries; state-of-charge of electric and thermalstorage devices; proportion of curtailed renewables; and propensity of microgrid collapse in the case ofrenewables overproduction. We compare our method to two classic ones relying on droop control: thefirst one with only primary control on both frequency and voltage and the second one with an additionalsecondary frequency control operated by the slack device. We find that our method is able to indirectlycontrol the reserve of the storage systems connected to the microgrid, thus maximizing the autonomy inthe islanded operation and, at the same time, reducing renewables curtailment. Moreover, the proposedcontrol framework keeps the system in feasible operation conditions, better explores the various degreesof freedom of the whole system and connected devices, and prevents its collapse in case of extremeoperation of stochastic resources. All of these properties are obtained with a simple and generic controlframework that supports aggregation and composability.

Elsevier2015

Compilation of real-time control strategies for heterogeneous resources at MV and LV

Plouton Grammatikos, Rahul Kumar Gupta, Mario Paolone, Antonio Zecchino

Description of deliverable and goal 1.1. Executive summary The core of this activity is to provide distribution system operators with tools for the operation of utility-scale distributed battery energy storage systems (BESSs) in order to optimize the integration of stochastic distributed generation. The main goal of this deliverable is to assess two possible strategies for the real-time control of a utility-scale BESS to follow a day-ahead computed dispatch plan. In particular, one solution is based on a grid-aware optimal power flow (OPF)-based control accounting for both grid and BESS operational constraints (thoroughly described in D1.4.4c) [1], whereas the second one is based on the COMMELEC (thoroughly described in D1.2.3c) [2], [3]. The goal of the first method is to achieve the real-time dispatch plan tracking using a grid-aware model predictive control (MPC) to determine the active and reactive power set-points of the BESS so that the aggregated power of all the resources connected to a medium voltage power grid contribution track the dispatch plan while obeying to BESS’s operational constraints as well as the grid’s ones. The grid constraints are modelled using the Augmented Relaxed OPF [4]. COMMELEC is a framework proposed in the literature ([2], [3]) for the real-time control of power grids. It uses a hierarchy of agents to compute explicit active and reactive power setpoints for the resources connected to the grid. Each resource is equipped with a resource agent (RA) whose job is to translate the internal state of the resource into a device-independent format (advertisement). The advertisements are collected by the grid agent (GA), which computes the optimal power setpoints that optimize a global objective. The global objective is the weighted sum of various objectives, including tracking a predetermined dispatch plan at the slack bus, minimizing grid’s nodal voltage deviations from the nominal value, limiting the line currents below the respective ampacities and achieving target internal states for the resources. The proposed control frameworks are validated by dispatching the operation of a 12kV/20MVA MV distribution network in Aigle, Switzerland (i.e. the REeL demonstrator) using a 1.5 MW/2.5 MWh BESS, which is controlled in real-time given the online grid state estimation enabled by the deployed distributed PMU-based sensing infrastructure.

SCCER-FURIES2021