Adriana C. Luna

Flexible System Integration and Advanced Hierarchical Control Architectures in the Microgrid Research Laboratory of Aalborg University

This paper presents the system integration and hierarchical control implementation in an inverter-based Microgrid Research Laboratory (MGRL) at Aalborg University, Denmark. MGRL aims to provide a flexible experimental platform for comprehensive studies of microgrids. The structure of the laboratory, including the facilities, configurations, and communication network, is first introduced. The complete control system is based on a generic hierarchical control scheme including primary, secondary, and tertiary control. Primary control loops are developed and implemented in digital control platform, while system supervision, advanced secondary, and tertiary management are realized in a microgrid central controller. The software and hardware schemes are described. Several example case studies are introduced and performed to achieve power quality regulation, energy management, and flywheel energy storage system control. Experimental results are presented to show the performance of the whole system.

Mixed-Integer-Linear-Programming-Based Energy Management System for Hybrid PV-Wind-Battery Microgrids: Modeling, Design, and Experimental Verification

Microgrids are energy systems that aggregate distributed energy resources, loads, and power electronics devices in a stable and balanced way. They rely on energy management systems to schedule optimally the distributed energy resources. Conventionally, many scheduling problems have been solved by using complex algorithms that, even so, do not consider the operation of the distributed energy resources. This paper presents the modeling and design of a modular energy management system and its integration to a grid-connected battery-based microgrid. The scheduling model is a power generation-side strategy, defined as a general mixed-integer linear programming by taking into account two stages for proper charging of the storage units. This model is considered as a deterministic problem that aims to minimize operating costs and promote self-consumption based on 24-hour ahead forecast data. The operation of the microgrid is complemented with a supervisory control stage that compensates any mismatch between the offline scheduling process and the real time microgrid operation. The proposal has been tested experimentally in a hybrid microgrid at the Microgrid Research Laboratory, Aalborg University.

Economic power dispatch of distributed generators in a grid-connected microgrid

Grid-connected microgrids with storage systems are reliable configurations for critical loads which can not tolerate interruptions of energy supply. In such cases, some of the energy resources should be scheduled in order to coordinate optimally the power generation according to a defined objective function. This paper defines a generationside power scheduling and economic dispatch of a grid-connected microgrid that supplies a fixed load and then, the scheduling is enhanced by including penalties in order to increase the use of the renewable energy sources and guarantee a high state of charge in the storage system for the next day. Linear models are proposed for the scheduling which are implemented in GAMS. The microgrid model is obtained deploying MATLAB/Simulink toolbox and then downloaded into dSPACE 1006 platform based on real-time simulation to test the economic dispatch. A compromise between cost and use of renewable energy is achieved.

Generation-side power scheduling in a grid-connected DC microgrid

In this paper, a constrained mixed-integer programming model for scheduling the active power supplied by the generation units in storage-based DC microgrids is presented. The optimization problem minimizes operating costs taking into account a two-stage mode operation of the energy storage system so that a more accurate model for optimization of the microgrid operation can be obtained. The model is used in a particular grid-connected DC microgrid that includes two renewable energy sources and an energy storage system which supply a critical load. The results of the scheduling process are including in simulation by establishing a MATLAB/Simulink model of the microgrid and setting several initial conditions of the state of charge of the energy storage system. As a result, we obtain reductions in costs and at the same time guarantee safe levels of state of charge to increase the life-time of the energy storage system.

Optimal power scheduling for a grid-connected hybrid PV-wind-battery microgrid system

In this paper, a lineal mathematical model is proposed to schedule optimally the power references of the distributed energy resources in a grid-connected hybrid PV-wind-battery microgrid. The optimization of the short term scheduling problem is addressed through a mixed-integer linear programming mathematical model, wherein the cost of energy purchased from the main grid is minimized and profits for selling energy generated by photovoltaic arrays are maximized by considering both physical constraints and requirements for a feasible deployment in the real system. The optimization model is tested by using a real-time simulation of the model and uploaded it in a digital control platform. The results show the economic benefit of the proposed optimal scheduling approach in two different scenarios.

Cooperative energy management for a cluster of households prosumers

The increment of electrical and electronic appliances for improving the lifestyle of residential consumers had led to a larger demand of energy. In order to supply their energy requirements, the consumers have changed the paradigm by integrating renewable energy sources to their power grid. Therefore, consumers become prosumers in which they internally generate and consume energy looking for an autonomous operation. This paper proposes an energy management system for coordinating the operation of distributed household prosumers. It was found that better performance is achieved when cooperative operation with other prosumers in a neighborhood environment is achieved. Simulation and experimental results validate the proposed strategy by comparing the performance of islanded prosumers with the operation in cooperative mode1.

Online energy management system for distributed generators in a grid-connected microgrid

A microgrid is an energy subsystem composed of generation units, energy storage, and loads that requires power management in order to supply the load properly according to defined objectives. This paper proposes an online energy management system for a storage based grid-connected microgrid that feeds a critical load. The optimization problem aims to minimize the operating cost while maximizing the power provided by the renewable energy sources. The power references for the distributed energy resources (DER) are scheduled by using CPLEX solver which uses as input current measurements, stored data and adjusted weather forecast data previously scaled in each iteration considering the current status. The proposed structure is tested in a real time simulation platform (dSPACE 1006) for the microgrid model, by using Labview to data acquisition and Matlab to implement the energy management system. The results show the effectiveness of the proposed energy management system for different initial conditions of the storage system.

Online Energy Management Systems for Microgrids: Experimental Validation and Assessment Framework

Microgrids are energy systems that can work independently from the main grid in a stable and self-sustainable way. They rely on energy management systems to schedule optimally the distributed energy resources. Conventionally, the main research in this field is focused on scheduling problems applicable for specific case studies rather than in generic architectures that can deal with the uncertainties of the renewable energy sources. This paper contributes a design and experimental validation of an adaptable energy management system implemented in an online scheme, as well as an evaluation framework to quantitatively assess the enhancement attained by different online energy management strategies. The proposed architecture allows the interaction of measurement, forecasting and optimization modules, in which a generic generation-side mathematical problem is modeled, aiming to minimize operating costs and load disconnections. The whole energy management system has been tested experimentally in a test bench under both grid-connected and islanded mode. Also, its performance has been proved considering severe mismatches in forecast generation and load. Several experimental results have demonstrated the effectiveness of the proposed EMS, assessed by the corresponding average gap with respect to a selected benchmark strategy and ideal boundaries of the best and worst known solutions.

Cooperative management for a cluster of residential prosumers

This paper proposes an energy management system for coordinating distributed prosumers. The prosumers are residential microgrids which internally produce and consume energy for autonomous operation. However, better performance is achieved by cooperative operation with other prosumers neighbors. Experimental results validate the proposed strategy.

Energy Management Systems and tertiary regulation in hierarchical control architectures for islanded microgrids

In this paper, the structure of the highest level of a hierarchical control architecture for microgrids is proposed. Such structure includes two sub-levels: the Energy Management System (EMS) and the tertiary regulation. The first devoted to energy resources allocation in each time slot based on marginal production costs, the latter aiming at finding the match between production and consumption satisfying the constraints set by the EMS level about the energy production in each time slot. Neglecting the efficiency of the different energy generation systems as well as that of the infrastructure for electrical energy distribution, the problem dealt with by the EMS sub-level is linear and can be solved by well known Linear Programming optimization procedures. The tertiary sub-level, below the EMS, optimizes mainly technical objectives and requires the solution of the Optimal Power Flow problem. After a review of the state of the art on the topic, the higher control sub-levels are described and an application is proposed. The application shows the efficiency of Mixed Integer Linear Programming methods for cost minimization of the energy production systems for microgrids.