1 Experimental Validation of an Explicit Power-Flow Primary Control in Microgrids Lorenzo Reyes-Chamorro, Member, IEEE, Andrey Bernstein, Member, IEEE, Niek J. Bouman, Enrica Scolari, Student Member, IEEE, Andreas M. Kettner, Member, IEEE, Benoit Cathiard, Jean-Yves Le Boudec, Fellow, IEEE and Mario Paolone, Senior Member, IEEE Abstract—The existing approaches to control electrical grids combine frequency and voltage controls at different time-scales. When applied in microgrids with stochastic distributed generation, grid quality of service problems may occur, such as under- or overvoltages as well as congestion of lines and transformers. The COMMELEC framework proposes to solve this compelling issue by performing explicit control of power flows with two novel strategies: (1) a common abstract model is used by resources to advertise their state in real time to a grid agent; (2) subsystems can be aggregated into virtual devices that hide their internal complexity in order to ensure scalability. While the framework has already been published in the literature, in this paper we present the first experimental validation of a practicable explicit power- flow primary control applied in a real-scale test-bed microgrid. We demonstrate how an explicit power-flow control solves the active and reactive power sharing problem in real time, easily allowing the microgrid to be dispatchable in real time (i.e. it is able to participate in energy markets) and capable of providing frequency support, while always maintaining quality of service. Index Terms—Explicit Power-Flow Control, Real-Time Control, Real-Time Demand-Response, Primary Control, Microgrids. I. I NTRODUCTION T HE grand challenge of massively integrating volatile dis- tributed generation into the power systems is strictly related to the evolution of their operation and control. The literature of the last decade has suggested two models for their future development [1]: (i) the supergrid, based on enhanced continental/intercontinental interconnections (mainly DC) [2]; or (ii) the microgrid, small medium/low voltage networks interfacing heterogeneous resources such as local generation, energy storage, and active customers, intelligently managed so that they are operated as independent cells capable of providing different services and operate as islands [3]. Irrespective of the model that will emerge, the control of heterogeneous distributed resources represents a fundamental challenge for both. 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 quality of supply) as well as the provision of ancillary services to the external bulk transmission (e.g., primary and secondary frequency supports). L. Reyes-Chamorro, E. Scolari, A. M. Kettner and M. Paolone are with the Distributed Electrical Systems Laboratory, EPFL. A. Bernstein, N. J. Bouman and B. Cathiard were with the Laboratory for Communication and Applications, EPFL. J.-Y. Le Boudec is with the Laboratory for Communication and Applications, EPFL. This work is supported by the SNSF-NRP70 ”Energy Turnaround” project. Several control methodologies have been proposed to achieve these goals (e.g. [4]), and the majority have been inspired by the time-layered approach traditionally adopted in power trans- mission systems, i.e. primary, secondary and tertiary controls, ranging from sub-second to hours time-scales 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, and the latter for short-term decisions. In particular, primary controls are deployed through fully decentralized schemes mainly relying on the use of droop control (e.g. [5]). In this paper, we focus on the control problem associated to the time-scales of the primary and secondary controls. More- over, we focus on microgrids, which are the smallest subsystems where such a control framework can be deployed, due to their small (if not null) inertia, and to the presence of heterogeneous and stochastic devices (e.g., distributed generation and stor- age). Specifically, we use the recently proposed COMMELEC control framework [6] (Composable Method for Real-Time Control of Active Distribution Networks with Explicit Power Setpoints), which is an explicit power-flow primary control. This means that it explicitly computes optimal nodal power injections/absorptions in order to achieve a global objective in real-time. This approach is in contrast to the use of local (e.g. proportional) controls (e.g., droop-based control strategies). It allows to steer an entire network as an equivalent energy resource, thus enabling an entire system to support the main grid by exploiting the flexibility of its components in real- time. In this paper, we report the first real-scale implementation of COMMELEC, thus demonstrating the flexibility of explicit power-flow control in microgrids. The contributions of the paper are the following. Firstly, discuss the requirements for a primary power-flows control to be deployed in real microgrids (Section III), i.e., system awareness infrastructure, dedicated hardware for distributed resources and communication infrastructure. Secondly, describe the modifications that are needed to the internal structure of the COMMELEC grid agent solver in order to be applicable to a real system (Section IV). Thirdly, illustrate the application of the COMMELEC framework to control a set of heterogeneous energy resources (Section V). Finally, report on the first real- scale experiment that proves the applicability of an explicit power-flows control mechanism in microgrids (Section VI).