Lorenzo Reyes-Chamorro

Smart Microgrids as a Solution for Rural Electrification: Ensuring Long-Term Sustainability Through Cadastre and Business Models

The provision of energy at the local level by using renewable and local resources is increasingly acknowledged as a techno-economic solution for rural electrification. This work describes an approach for implementing microgrid projects at the institutional level by means of a specific entity that uses methods that engage the community in microgrid operation and maintenance (O&M), which ensures long-run benefits. The first step, related to macro-level barriers, is addressed by building a complete cadastre of isolated communities, while the second, at the micro level, focuses on business models for covering investment and O&M costs. A cadastre uncovers the key characteristics of each location (energy resources, availability, socio-economic conditions, environment, etc.). A cadastre also helps identify local needs, develop monitoring strategies, and determine benchmarks among microgrids. Its information also assists with proposing new projects, securing funding, and monitoring actual microgrids. At the micro level, local stakeholders, economic capabilities, social capital, and organizational structures are identified, which contribute to the selection of a tailored business model that can enable fundraising and O&M activities. The approach is presented in a four-stage framework: 1) background data collection; 2) community profile building; 3) system design; and 4) detailed engineering. Each community is evaluated by a prioritization index that considers the electrical conditions of each residence.

Dispatching Stochastic Heterogeneous Resources Accounting for Grid and Battery Losses

We compute an optimal day-ahead dispatch plan for distribution networks with stochastic resources and batteries, while accounting for grid and battery losses. We formulate and solve a scenario-based AC Optimal Power Flow (OPF), which is by construction non-convex. We explain why the existing relaxation methods do not apply and we propose a novel iterative scheme, corrected DistFlow (CoDistFlow), to solve the scenario-based AC OPF problem in radial networks. It uses a modified branch flow model for radial networks with angle relaxation that accounts for line shunt capacitances. At each step, it solves a convex problem based on a modified DistFlow OPF with correction terms for line losses and node voltages. Then, it updates the correction terms using the results of a full load flow. We prove that under a mild condition, a fixed point of CoDistFlow provides an exact solution to the full AC power flow equations. We propose treating battery losses similarly to grid losses by using a single-port electrical equivalent instead of battery efficiencies. We evaluate the performance of the proposed scheme in a simple and real electrical networks. We conclude that grid and battery losses affect the feasibility of the day-ahead dispatch plan and show how CoDistFlow can handle them correctly.

Experimental Validation of an Explicit Power-Flow Primary Control in Microgrids

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; and 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.

Real-time power-reference tracking method for PV converters

Due to the increasing presence of renewable inertia-less energy sources, power electronics interfaces are required to exploit their flexibility in order to support the overall grid quality of service. One way to achieve this, is that power converters are capable of actively track active and reactive power-setpoints, that are computed by suitable centralized or decentralized control schemes. In this paper, we propose a novel algorithm which enables the control of a boost converter to achieve arbitrary active-power reference tracking for photovoltaic plants, not operating in maximum power point tracking (MPPT) mode.

Handling large power steps in real-time microgrid control via explicit power setpoints

We consider a microgrid with real-time control using explicit power-setpoints. Sudden power-steps, such as load disconnections or load in-rushes, directly affect the decisions of the microgrid controller that aims at avoiding voltage or line-ampacity violations. When trying to completely avoid these violations, the grid operation may be too restricted, which may lead to large suboptimality. However, temporary violations of the steady-state bounds are allowed by grid standards and could enable the exploitation of the flexibility of other resources to better control the systems state. In this paper, we propose a method by which such temporary violations are controlled so that they remain within the limits imposed by grid standards and safe operation. The method is experimentally tested and validated on a real microgrid.

Aggregation of power capabilities of heterogeneous resources for real-time control of power grids

Aggregation of electric resources is a fundamental function for the operation of power grids at different time scales. In the context of a recently proposed framework for the real-time control of microgrids with explicit power setpoints, we define and formally specify an aggregation method that explicitly accounts for delays and message asynchronism. The method allows to abstract the details of resources using high-level concepts that are device and grid-independent. We demonstrate the application of the method to a Cigre benchmark with heterogenous and low-inertia resources.

Real-time control of microgrids with explicit power setpoints: Unintentional islanding

We propose a method to perform a safe unintentional islanding maneuver of microgrids. The method is derived in the context of a framework for the real-time control of microgrids, called Commelec, recently proposed by the Authors. The framework uses a hierarchy of software agents that communicate with each other using a common, device independent protocol in order to define explicit power setpoints without the need of droop controllers. We show that the features of the framework allow to design a generic control method for treating unintentional islanding with the following properties. First, the method is able to choose the best candidate slack resource, based on the information obtained from the agents. Second, as the agent responsible for the grid has a global view of the networks status and its resources, it is possible to optimize the performance of the network during and after the islanding transition. Third, after the islanding maneuver it allows for the online switching of the slack resource to that with the best capabilities to face the networks needs. Finally, the method is suitable for inertia-less systems as the control is performed using explicit power setpoints and it does not rely on the frequency signal. We illustrate the benefits of the proposed method via simulation on the LV microgrid benchmark defined by the CIGRÉ Task Force C6.04.02, by comparing its performance to that of the standard droop-based method called load drop anticipator.

T-RECS: A Virtual Commissioning Tool for Software-Based Control of Electric Grids: Design, Validation, and Operation

In real-time control of electric grids using multiple software agents, the control performance depends on (1) the proper functioning of the software agents, i.e., absence of software faults, and (2) the behavior of software agents in the presence of non-ideal communication networks such as message losses and delays. To evaluate the control performance of such systems, we propose T-RECS, a virtual commissioning tool. T-RECS enables testing the performance of software-based control in-silico (before the actual deployment of software agents in the grid), saving both time and money. Developers can run the binaries of their software agents in T-RECS where these binaries exchange real messages by using an emulated network and simulated models of the electric grid and resources. Consequently, the control of an entire microgrid can be tested on a standard computer. In this paper, we first describe the design and the open-source implementation of T-RECS. Second, we measure its CPU and memory usage and show that our implementation can accommodate eight software agents on a standard laptop computer. Third, we validate the simulated grid used in T-RECS by replaying data collected from experiments performed in a real low-voltage microgrid. We find that the average error is 0.037% and the 99th percentile of the error is less than 0.1%. Finally, we present some typical use-cases of T-RECS such as performance evaluation (1) under extreme grid conditions and (2) with non-ideal communication networks. The former, i.e., performance evaluation under extreme grid conditions, is difficult to test in the field due to safety concerns.

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.