Electrical Microgrids Research Articles

Performance Optimization of Luminescent Solar Concentrators under Several Shading Conditions

The need of clean energy is constantly increasing, and Building Integrated PhotoVoltaic (BIPV) technologies represent valuable assets to expand even further the photovoltaic market. Thanks to BIPVs. a new concept of local electric microgrid will probably emerge as this kind of technology can turn buildings from energy wells to energy sources. Luminescent Solar Concentrator (LSC) panels are perfect to achieve this goal, indeed, contrary to standard flat PhotoVoltaic (PV) modules, they can be exploited in transparent or semi-transparent building façades. Thus, the purpose of this work was the optimization of the performance of LSC panels for BIPV applications. Being an application-oriented study, we paid particular attention to the scalability of the assembling process and the use of LSC slabs functionalized only with widely available organic commercial dyes and high-performance commercial silicon solar cells. The electrical and optical performance of the LSC panels were firstly simulated and then, once the most promising configurations were identified, the respective prototypes were assembled to compare the simulation results with the experimental measurements. These analyses were performed both under uniform illumination and in some relevant shading configurations typical for BIPV devices in operating conditions. The obtained results show that LSC panels that employ PV cells coupled with reflective films can yield a higher efficiency than a traditional system with cells placed along four sides.

Energy Management Electronic Device for Islanded Microgrids Based on Renewable Energy Sources and Battery-based Energy Storage

Energy management systems are one of the most important components in the operation of an electric microgrid. They are responsible for ensuring the supervision of the electrical system, as well as the coordination and reliability of all loads and distributed energy resources in order for the microgrid to be operated as a unified entity. Because of that, an energy management system should be fast enough at processing data and defining control action to guarantee the correct performance of the microgrid. This paper explores the design and implementation of an energy management system deployed over a dedicated electronic device. The proposed energy management device coordinates the distributed energy resources and loads in a residential-scale islanded microgrid, in accordance with a rule-based energy management strategy that ensures reliable and safe operation of the battery-based energy storage system. A hardware-int-he-loop test was performed with a real-time simulation platform to show the operation of the electronic device

Data-Driven LPV Controller Design for Islanded Microgrids

Abstract This paper presents a data-driven multivariable Linear Parameter Varying (LPV) controller design method. The synthesis process is based on frequency-domain data corresponding to different operating points of the plant. The H∞ performance and also stability constraints for frozen scheduling parameter are convexified around an initial stabilizing controller and solved using a convex optimization solver. This method has been applied to the combined primary and secondary controller design problem of electrical microgrids. The performance of the proposed method has been validated through simulating a microgrid including a synchronous generator, a battery storage and a photo-voltaic unit. The results show that using this method, high performance is achieved in different operating points.

Analysis of the Technico-Economic Viability of an Electric Micro-Grid with Renewable Electricity Production Sources in Elokato-Bingerville, Cote d’Ivoire

In this study, the technico-economic viability is studied, on the basis of different scenarios of electric micro-grids with renewable energy production sources, autonomous and supplied by the interconnected grid. HOMER Pro 3.13.3 Pro simulation and optimization software, Xlstat and Energy sentinel software are used for the evaluation of different technical and economic scenarios of system components, in order to obtain the most cost-effective configuration. To do this, the case study of the village of ELOKATO identifies the optimal options for the use of renewable energies for rural electrification in order to increase the electricity coverage rate. In our case study, after the various simulations, HOMER identified 13 scenarios and configurations deemed to be the most profitable, from the parameters and configurations without photovoltaic components have high COEs and very high initial investment costs in the order of several million US $. Renewable energy power generators require high initial investments and relatively low operating costs. The most important costs are generated by the battery park and then come the photovoltaic panels. The hybrid PV/wind/diesel/hydropower system is profitable if the distance from the village to the transformer station is greater than 1.90 km. The results show great potential for using these hybridized production sources with or without a generator to meet the electricity needs of a village.

Preliminary assessment of a microgrid integrated with a biomass gasification CHP system for a production facility in Central Italy

The aim to reduce carbon dioxide emissions and to improve buildings energy efficiency has led to develop smart grids to manage electricity and heat. The work deals with the thermal and electric microgrid analysis of the Loccioni Company: the production facility consists of high-energy performance industrial and office buildings, partially powered by produced on-site renewable energy (solar PV, hydropower plants, water ground heat pumps). The challenge of continuous improvement in the use of energy led the company to develop a thermal microgrid for optimal management of the heat produced by a small-scale CHP system (50 kWel/110 kWth). The cogeneration system is based on biomass (pellet) chemical degradation process of gasification. The work discusses preliminary results relating to the first months of the system operation, to highlight the energy benefits and the critical issues. Data are collected by the Company monitoring system and a laboratory feedstock physico-chemical characterization is carried out. The main goal of this paper is to lay the foundations for the development of an energy management system that regulates energy flows between buildings. The development of the thermal microgrid will guarantee not only tangible benefits in terms of energy savings but also an increase in the resilience of the entire building/plant system.

Energy Bill Reduction by Optimizing Both Active and Reactive Power in an Electrical Microgrid

The aim of this paper is to develop tools for the Optimal Power Flow Management Control (OPFMC) in a microgrid (MG). It consists of a photovoltaic system, an energy storage system, a gas turbine, and a main grid (energy exchange). Unlike the conventional approaches, which are limited to the distribution of the active power, this paper relies on an electrical modeling system in order to coordinate and to optimize both the active and the reactive power flow using discrete controls. The proposed optimal power management strategy has two objectives: (i) it aims at forecasting, over a time horizon of 24-hours, the optimal distribution of the active and the reactive power required for each power source connected to the microgrid. The proposed management incorporates the consumption forecasts, the weather, and the tariffs; (ii) it aims at reducing the solicitation of the main grid while taking into consideration the requested reactive power. This is done by using dynamic programming based on Bellman algorithm. Such management has been tested by simulation in a Matlab/Simulink environment and its performance has been compared to the conventional management strategy.

Fast moving horizon estimation using multi-level iterations for microgrid control

Abstract Accurate state-estimation is a vital prerequisite for fast feedback control methods such as Nonlinear Model Predictive Control (NMPC). For efficient process control, it is of great importance that the estimation process is carried out as fast as possible to provide the feedback mechanism with fresh information and enable fast reactions in case of any disturbances. We discuss how Multi-Level Iterations (MLI), known from NMPC, can be applied to the Moving Horizon Estimation (MHE) method for estimating the states and parameters of a system described by a Differential Algebraic Equation model. A challenging field of application for the proposed MLI-MHE method are electric microgrids. These push current control approaches to their limits due to the rising penetration of volatile renewable energy sources and the fast electrical system dynamics. We investigate the closed-loop control performance of the proposed MLI-MHE algorithm in combination with an NMPC controller for a realistic sized microgrid as a numerical example.

Control Predictivo Econ´omico para la gesti´on de energ´ıa en una microrred

En este articulo se propone una estrategia de dise~no para sistemas de control de flujos de energ´ıa en microrredes el´ectricas con generaci´on renovables, aplicando el Control Predictivo Econ´omico basado en Modelo (EMPC).El modelo de microrred utilizado se compone por un sistema de almacenamiento, una fuente de generaci´on renovable, un perfil de consumo tipo residencial y se considera la posibilidad de intercambiar energ´ıa con la red principal, permiti´endole as´ı a la microrred, la posibilidad de actuar y participar dentro del mercado el´ectrico.El funcional propuesto para el controlador, considera los costos de uso para los sistemas de la microrred, como tambi´en el beneficio por la venta de energ´ıa hacia la red el´ectrica principal. Se comprueba el funcionamiento del sistema, simul´andolo en distintos escenarios.

Modeling of DSTATCOM Devices to Improve Dynamic Voltage Stability in a Microgrid with High Penetration of Motor Loads

A través de este artículo se propone y valida modelos de dispositivos de tecnología FACTS de tipo Compensador Estático Sincrónico para Distribución (DSTATCOM). En primera instancia, se presenta el modelado de un DSTATCOM simplificado realizado a través de una fuente de corriente controlada. Posteriormente, se expone un DSTATCOM modelado a través de estrategias de control considerando un conversor PWM (Pulse-Width Modulation - Modulación por ancho de pulsos). Los modelos propuestos de dispositivos DSTATCOM se validan en un sistema de prueba de Microrred Eléctrica (MRE) de la CIGRÉ. La presencia de cargas de tipo motor de inducción en la MRE requiere una considerable demanda de potencia reactiva, esto ocasiona inconvenientes para mantener la Estabilidad Dinámica de Tensión (EDT). Ésta situación se agrava ante la ocurrencia de fallas que desencadenen una operación aislada de la MRE. Para solucionar estos inconvenientes se hará uso de un dispositivo DSTATCOM. La conexión y ubicación óptima del DSTATCOM en la MRE se realiza a través de un algoritmo de búsqueda exhaustiva, considerando la premisa del mejor rendimiento en términos de EDT realizado a través de simulaciones dinámicas en PowerFactory DIgSILENT. Comparativamente se presentan los resultados obtenidos para los dos modelos realizados, demostrándose la mejora de la EDT en la operación aislada de la MRE con ambos modelos. Dependiendo del detalle y alcance de los estudios en el sistema de MRE, se puede elegir entre los modelos DSTATCOM desarrollados. Todos los detalles de modelos, esquemas de control y datos de los dispositivos DSTATCOM son proporcionados en este documento.

Equivalent Model of a Three Phase System of Photovoltaic Generation to Analyze Voltage Variations in a Radial Distribution System

In this paper, the modelling of a three-phase photovoltaic system, for analyzing voltage variation in a radial distribution system, is presented. The radial distribution system is represented by a benchmark which is widely used in the analysis of distribution systems with distributed generation, and electrical microgrids. The parameters estimation of this model is performed by selecting the aerial distribution of conductors and then calculating the sequence components. Moreover, a model of a three-phase photovoltaic generation system for analyzing voltage variations is proposed. The model represents an array of photovoltaic panels, a dc/dc converter with its control system, and a three-phase inverter. The software MATLAB/Simulink is chosen to simulate both the distribution and the photovoltaic systems. All the components of the three-phase photovoltaic system are parametrized with information of commercial equipment. To facilitate the implementation of the system model in the analysis program, reduced models of its components are selected. Finally, the proposed model of the three-phase photovoltaic system is validated by simulating single-phase faults along the feeder and changes of irradiance over the photovoltaic generators and observing the voltage behavior in one node of the distribution system. The results show that irradiance changes and single-phase faults affect the voltage behavior depending on the photovoltaic penetration level and the generators location.

An Optimized Balance of Plant for a Medium-Size PEM Electrolyzer: Design, Control and Physical Implementation

The progressive increase in hydrogen technologies’ role in transport, mobility, electrical microgrids, and even in residential applications, as well as in other sectors is expected. However, to achieve it, it is necessary to focus efforts on improving features of hydrogen-based systems, such as efficiency, start-up time, lifespan, and operating power range, among others. A key sector in the development of hydrogen technology is its production, renewable if possible, with the objective to obtain increasingly efficient, lightweight, and durable electrolyzers. For this, scientific works are currently being produced on stacks technology improvement (mainly based on two technologies: polymer electrolyte membrane (PEM) and alkaline) and on the balance of plant (BoP) or the industrial plant (its size depends on the power of the electrolyzer) that runs the stack for its best performance. PEM technology offers distinct advantages, apart from the high cost of its components, its durability that is not yet guaranteed and the availability in the MW range. Therefore, there is an open field of research for achievements in this technology. The two elements to improve are the stacks and BoP, also bearing in mind that improving BoP will positively affect the stack operation. This paper develops the design, implementation, and practical experimentation of a BoP for a medium-size PEM electrolyzer. It is based on the realization of the optimal design of the BoP, paying special attention to the subsystems that comprise it: the power supply subsystem, water management subsystem, hydrogen production subsystem, cooling subsystem, and control subsystem. Based on this, a control logic has been developed that guarantees efficient and safe operation. Experimental results validate the designed control logic in various operating cases, including warning and failure cases. Additionally, the experimental results show the correct operation in the different states of the plant, analyzing the evolution of the hydrogen flow pressure and temperature. The capacity of the developed PEM electrolysis plant is probed regarding its production rate, wide operating power range, reduced pressurization time, and high efficiency.

Novel modified phase‐shift modulation strategy for isolated AC–DC power converters

Different power converter topologies are used to perform the energy exchange between an AC grid and a DC source belonging to a hybrid electric micro-grid. A single-phase single-stage isolated AC–DC power converter is one of them. Moreover, this power converter can operate under different modulation strategies. The phase-shift modulation (PSM) strategy is capable of varying the phase between the voltages applied to the high-frequency transformer terminals of the power converter in order to control the energy flow in both directions. Based on the PSM strategy, this study presents a novel modified PSM strategy capable of controlling the power flow in both directions and obtaining a current with low total harmonic distortion and a power factor close to 1 for the entire operating range on the AC side. Considering the novel modulation strategy to be proposed, a comparison of three PSM-based modulation strategies was carried out taking into account the total harmonic distortion of current injected into the AC grid, the power factor and the average power transferred. A theoretical analysis was carried out and the results obtained were validated by means of experimental results.

Stochastic optimal integration of decentralized heat pumps in a smart thermal and electric micro-grid

Heat pumps represent a link between different energy vectors and their application in thermal and electrical grids can improve the overall operational flexibility of the system. In this work, the optimal integration of electrically driven heat pumps within a hybrid distributed energy system is investigated. A multi-objective stochastic optimization methodology is proposed to evaluate the integrated optimal sizing and operation of the energy systems under uncertainties in climate, space occupancy, energy loads, and fuel costs. A case study is considered, namely a University campus, and two different configurations, with and without heat pumps, are compared. Both configurations include a cogeneration system, photovoltaic and solar thermal panels, and a wind turbine. The results show how the integration of heat pumps can reduce the operational cost of the system, increase the renewables share, provide a more robust design of the system, and moderate the risk of the investment. Indeed, the configuration with heat pumps entails a 50% higher expected value of the energy savings, a 28% increase of the renewable energy production, and higher energy savings in the worst-case scenario (13% vs. 5%).

Inrush current estimation and hot-swapping for safe parallel battery pack

ABSTRACT Batteries used in electric vehicles and microgrid applications use battery modules connected in series to satisfy the voltage required for each system, and battery modules are connected in parallel to increase capacity. In this parallel connected system, in order to disconnect and reconnect a specific battery module or to reconnect a new battery module, the battery module to be newly connected should have a small state of charge (SOC) difference from the existing battery modules. In particular, when a new battery is to be connected under a load current, there is a problem that excessive inrush current may occur in a specific battery module due to the load current distributed to each module and the current due to the SOC difference. Therefore, in this paper, we propose a method of estimating the inrush current through an equivalent electrical modelling analysis for the case where a battery module is newly added in a system in which the battery modules are connected in parallel. In addition, the power management algorithm for the battery pack system with inrush current estimation is presented. The proposed method is validated through simulations and experiments of a battery pack system in which 10 battery modules of 710V and 120Ah are connected in parallel.

Energy Management in PV Based Microgrids Designed for the Universidad Nacional de Colombia

Stand-alone Electrical microgrids (MGs) require power management strategies to extend the life-time of their devices and to guarantee the global power balance of non-critical loads such as lighting of small sections of an university campus or individual air conditioning systems. This paper proposes an energy management strategy (EMS) for an isolated DC microgrid formed by a photovoltaic system (PVS), an energy storage system (battery), and a noncritical load. This configuration enables the photovoltaic system to control the power generation and ensures that the storage element does not exceed the safe limits of the state of charge. To control the generation of the photovoltaic system, two operating modes based on the perturb and observe (P&O) algorithm are implemented. The first one performs a maximum power point tracking (MPPT) action, while the second one regulates the power generated by the PVS to match the load requirement (power demand tracking, PDT). The management strategy also considers different operating states for ensuring the battery safety: normal operation, overcharge (at the maximum state of charge), and bulk charge (at the minimum state of charge); in those states the disconnection/connection of both the battery and the load is also considered. The main contribution of this work is to design and test a control strategy for an EMS aimed at regulating a standalone microgrid based on a PV system and an energy storage device. This solution is validated using detailed MG circuital simulations, which includes the PV source model (single-diode model), lithium-ion battery model, constant power load model and the DC/DC converters equations; moreover, realistic power generation and demand from Universidad Nacional de Colombia, located at Medellín-Colombia, are considered. The results obtained demonstrate the effectiveness of the energy management strategy, and in this way, enable to extend the battery lifetime and reduce the costs associated to the maintenance and disconnection of the microgrid in educational buildings or other applications focused on this type of DC microgrid.

Mejoramiento de la Estabilidad de Tensión con un DSTATCOM en una Microrred Integrada por GD Solar Fotovoltaica y Convencional

En la actualidad el posicionamiento de los sistemas de Generación Distribuida (GD) y Microrredes Eléctricas (MREs) han tomado connotadas participaciones alrededor del mundo. Por lo tanto, las necesidades investigativas en torno al control, operación, estabilidad y resiliencia de estos sistemas han marcado un nuevo paradigma de los sistemas de suministro de energía eléctrica. El objetivo de este artículo es mejorar la estabilidad de tensión mediante la inclusión de un dispositivo DSTATCOM de tecnología FACTS en una MRE integrada por GD de tipo Solar Fotovoltaica y Convencional. La metodología desarrollada se aplica en el sistema de prueba de MRE de la CIGRÉ, con la premisa de analizar dos escenarios operativos en relación a la ocurrencia de una contingencia, con lo cual la MRE operará en forma aislada. El análisis se realiza a través de simulaciones dinámicas en el domino del tiempo, donde se analiza y evalúa el comportamiento dinámico de la tensión, después de que los sistemas red-MRE han sido sometidos a perturbaciones, desencadenando la operación en isla eléctrica de la MRE. Los resultados muestran que los modelos y algoritmos de control desarrollados operan satisfactoriamente, además se demuestra la aplicabilidad y beneficios en la instalación de dispositivos FACTS tipo DSTATCOM en sistemas de MREs para mejorar las condiciones operativas en especialmente en términos de estabilidad de tensión.

Load/Frequency Control in the presence of Renewable Energy Systems: a Reference-Offset Governor approach.

In this paper a supervisory strategy for load/frequency control problems in networked multi-area electrical micro-grids in the presence of Renewable Energy Systems (RES) is presented. The proposed strategy exploits a recently developed constrained supervision methodology known in the literature as the Reference-Offset Governor (ROG) approach. Here, the ROG approach is extended to operate in the presence of rate-bounded disturbances acting as non-manipulable inputs on the plant. The main aim is at adequately orchestrating, during the on-line operations, the switching among different ROG configurations, suitably calibrated on the intensity of the disturbances, to efficiently satisfy the prescribed constraints. It is shown that the use of a bank of ROGs, instead of a single one, can remarkably reduce the conservativeness of the solution and improve the overall performance if the disturbance intensity changes. The effectiveness of the proposed approach is demonstrated on a two-area power system subject to coordination constraints on maximum frequency deviations, exchanged and generated powers and injected power from local RESs.

Impact of Smart Restoration and Energy Storage Systems on the Reliability of Electric Microgrid

In this paper, the impact of smart restoration and the integration of energy storage units on the reliability of the wind and solar-based microgrid (MG) are investigated. Since the early development and utilization of renewable energy sources (RES), especially wind and solar, they are being given increasing consideration owing to many reasons, such as the enhanced public awareness and the growing concerns regarding the potential impact of conventional energy systems on the environment. However, the random and intermittent nature of RES can affect their reliability in electrical networks. In the twenty-first century, the concept of a smart grid has become a major research area that addresses the challenges of the future power systems. One of the main characteristics of smart grids is the smart self-healing. The main objective of self-healing control is to monitor the real-time network operation, predict the power grid state, and detect and isolate the faults in the system without human intervention. We focus at smart restoration and investigate the integration of energy storage units on the reliability of wind- and solar-based MG. Two models are examined to reduce the effects of uncertainty in wind- and solar-generated power: the ARMA model for wind speed and the triple exponential smoothing model for solar energy prediction. This study was conducted on a Roy Billinton Test System.

Impact of Adaptive Protections in Electric Microgrids, Challenges and Future Trends

Impact of Adaptive Protections in Electric Microgrids, Challenges and Future Trends

A visualization approach to performing task analysis of time series event log data from a microworld simulation

This paper presents a novel visualization technique to perform a task analysis using only information from data logs collected from users interacting with the system. Traditional task analysis includes data acquired from system specifications, observations of the user interacting with the system, and interviews with the user. There are however situations, in which this information is not available such as forensic investigations. In situations in which these other data sources are available, the visualization approach provides an additional tool the analysist can use to further their understanding of the system and begin qualitatively and quantitatively describing a user’s behavior. As a demonstration of this technique, data logs from a microworld simulator, the Grid Game, were analyzed using a custom designed python based graphing tool. The Grid Game is a gamified and simplified simulation of an electric microgrid. Teams of players compete by maintaining and optimizing their grid configuration in the presence of cyber-attacks. Several different visualization graphing techniques were examined to identify their suitability for representing the grid event data in a format capable to support an analyst performing a task analysis. The most suitable graphing technique for this particular use case was a discrete event graphing technique including a common time dimension to provide performance based context to the graphical depiction of logged simulation events.