Autonomous Control Strategy of DC Microgrid for Islanding mode using Power Line Communication

This paper proposes a DC-bus signaling (DBS) method for autonomous power management in a DC microgrid, used to improve its reliability. Centralized power management systems require communication between the power sources and loads. However, the DBS method operates based on the common DC-bus voltage and does not require communication. Based on the DC-bus voltage band, the DC-bus voltage can be used to inform the status of the DC-bus in various scenarios. The DC microgrid operates independently to maintain the system stably in the DC-bus voltage band. The DC microgrid can be divided into a grid-connected mode and an islanding mode. This paper proposes a control strategy based on power management of various independent components in islanding mode. In addition, the autonomous control method for switching the converter???s operation between grid-connected mode and islanding mode is proposed. A DC microgrid test bed consisting of a grid-connected AC/DC converter, a bidirectional DC/DC converter, a renewable energy simulator, DC home appliances and a DC-bus protector is used to test the proposed control strategy. The proposed autonomous control strategy is experimentally verified using the DC microgrid test bed

DFIG versus PMSG for marine current turbine applications

Emerging technologies for marine current turbine are mainly relevant to works that have been carried out on wind turbines and ship propellers. It is then obvious that many electric generator topologies could be used for marine current turbines. As in the wind turbine context, doubly-fed induction generators and permanent magnet generators seems to be attractive solutions to be used to harness the tidal current energy. In this paper, a comparative study between these two generators type is presented and fully analyzed in terms of generated power, maintenance and operation constraints. This comparison is done for the Raz de Sein site (Brittany, France) using a multi physics modeling simulation tool. This tool integrates, in a modular environment, the resource model, the turbine hydrodynamic model and the generators models

European White Book on Real-Time Power Hardware in the Loop Testing : DERlab Report No. R- 005.0

The European White Book on Real-Time-Powerhardware-in-the-Loop testing is intended to serve as a reference document on the future of testing of electrical power equipment, with specifi c focus on the emerging hardware-in-the-loop activities and application thereof within testing facilities and procedures. It will provide an outlook of how this powerful tool can be utilised to support the development, testing and validation of specifi cally DER equipment. It aims to report on international experience gained thus far and provides case studies on developments and specifi c technical issues, such as the hardware/software interface. This white book compliments the already existing series of DERlab European white books, covering topics such as grid-inverters and grid-connected storag

Generator Systems for Marine Current Turbine Applications: A Comparative Study

Emerging technologies for marine current turbines are mainly related to works that have been carried out on wind turbines and ship propellers. It is then obvious that many electric generator topologies could be used for marine current turbines. As in the wind turbine context, doubly-fed induction generators and permanent magnet generators seem to be attractive solutions for harnessing the tidal current energy. In this paper, a comparative study between these two generator types is presented and fully analyzed in terms of generated power, maintenance, and operation constraints. This comparison is done for the Raz de Sein site (Brittany, France) using a multiphysics modeling simulation tool. This tool integrates, in a modular environment, the resource model, the turbine hydrodynamicmodel, and generator models. Experiments have also been carried out to confirm the simulation results.Financement de thèse de Brest Métropole Océan

Power Management Strategies for a Wind Energy Source in an Isolated Microgrid and Grid Connected System

This thesis focuses on the development of power management control strategies for a direct drive permanent magnet synchronous generator (PMSG) based variable speed wind turbine (VSWT). Two modes of operation have been considered: (1) isolated/islanded mode, and (2) grid-connected mode. In the isolated/islanded mode, the system requires additional energy sources and sinks to counterbalance the intermittent nature of the wind. Thus, battery energy storage and photovoltaic (PV) systems have been integrated with the wind turbine to form a microgrid with hybrid energy sources. For the wind/battery hybrid system, several energy management and control issues have been addressed, such as DC link voltage stability, imbalanced power flow, and constraints of the battery state of charge (SOC). To ensure the integrity of the microgrid, and to increase its flexibility, dump loads and an emergency back-up AC source (can be a diesel generator set) have been used to protect the system against the excessive power production from the wind and PV systems, as well as the intermittent nature of wind source. A coordinated control strategy is proposed for the dump loads and back up AC source. An alternative control strategy is also proposed for a hybrid wind/battery system by eliminating the dedicated battery converter and the dump loads. To protect the battery against overcharging, an integrated control strategy is proposed. In addition, the dual vector voltage control (DVVC) is also developed to tackle the issues associated with unbalanced AC loads. To improve the performance of a DC microgrid consisting wind, battery, and PV, a distributed control strategy using DC link voltage (DLV) based control law is developed. This strategy provides simpler structure, less frequent mode transitions, and effective coordination among different sources without relying on real-time communication. In a grid-connected mode, this DC microgrid is connected to the grid through a single inverter at the point of common coupling (PCC). The generated wind power is only treated as a source at the DC side for the study of both unbalanced and balanced voltage sag issues at a distribution grid network. The proposed strategy consists of: (i) a vector current control with a feed-forward of the negative-sequence voltage (VCCF) to compensate for the negative sequence currents; and (ii) a power compensation factor (PCF) control for the VCCF to maintain the balanced power flow between the system and the grid. A sliding mode control strategy has also been developed to enhance the overall system performance. Appropriate grid code has been considered in this case. All the developed control strategies have been validated via extensive computer simulation with realistic system parameters. Furthermore, to valid developed control strategies in a realistic environment in real-time, a microgrid has been constructed using physical components: a wind turbine simulator (WTS), power electronic converters, simulated grid, sensors, real-time controllers and protection devices. All the control strategies developed in this system have been validated experimentally on this facility. In conclusion, several power management strategies and real-time control issues have been investigated for direct drive permanent magnet synchronous generator (PMSG) based variable speed wind turbine system in an islanded and grid-connected mode. For the islanded mode, the focuses have been on microgrid control. While for the grid-connected mode, main consideration has been on the mitigation of voltage sags at the point of common coupling (PCC)

Contributions to smart grids based on renewable energy sources with hydrogen as backup system. Energy management system: design, modeling and physical implementation based on model predictive control theory

Atendiendo al concepto de Smart Grid (Red Inteligente), estos sistemas están íntimamente relacionados con el uso de los sistemas de generación renovable. A pesar de los beneficios de esta tecnología, su dependencia de los recursos ambientales hace imposible garantizar el balance de energía entre generación y demanda en todo momento. Para ello, la hibridación de sistemas, así como el uso de sistemas basados en hidrógeno, se muestra como una solución técnica viable para resolver o mitigar los problemas asociados a este tipo de tecnologías. El empleo de este tipo de sistemas híbridos plantea una mayor complejidad en materia de gestión debido a la elevada cantidad de parámetros y factores a tener en cuenta de cara a garantizar un óptimo reparto energético en función de la aplicación y el estado energético del sistema. En este sentido, han de considerarse ciertos aspectos asociados a la operación real de los sistemas, tales como la topología del sistema, costes de operación y mantenimiento, la necesidad de un control de tensión de carga para baterías, la degradación de los equipos, la dinámica de cada sistema, las pérdidas asociadas al punto de trabajo, o parámetros relacionados con la calidad del suministro eléctrico. A tenor de lo anterior, es necesario el empleo de estrategias de gestión de la energía que permitan determinar el reparto energético entre dispositivos, con el objetivo de optimizar la respuesta del sistema desde el punto de vista técnico y económico, planteándose por lo tanto un problema de optimización multiobjetivo. Para dar respuesta al problema de optimización multiobjetivo propuesto, en la presente Tesis, se hace uso de una arquitectura de control distribuida, compuesta en un primer nivel por controladores locales, y en el nivel superior, se propone el uso de un controlador supervisor basado en técnicas de control predictivo (MPC). La función principal del controlador propuesto es determinar la consigna de operación de cada uno de los equipos que componen la Smart Grid, dando respuesta a la función objetivo propuesta de acuerdo a los criterios de diseño del sistema. Las ventajas de la utilización de técnicas de control predictivo respecto a otro tipo de técnicas son claras; permite el empleo de técnicas de control multivariable, permitiendo plantear problemas de optimización multiobjetivo con restricciones; así como implementar una estrategia de control basado en un horizonte de predicción, lo que permite al sistema adaptar la respuesta del controlador en base a acontecimientos futuros, mejorando la respuesta del sistema frente a técnicas de control meramente pasivas. Como base de conocimientos del controlador propuesto, en esta tesis se presenta un modelo lineal discreto generalista de la planta, calculado en cada periodo de muestreo, en base a una linealización recursiva, lo que permite aument ar la calidad del modelo respecto a soluciones basadas en torno a un único punto de linealización. El modelo incluye todos los parámetros necesarios para el control de una planta real, incluyendo los términos asociados al estado energético del sistema, tensión de operación de baterías, así como los parámetros técnicos y económicos. tales como degradación. oérdidas o coste de operación con el obietivo de definir una función de coste del sistema que permita su generalidad para cualquier tipo de aplicación u objetivo de diseño. Atendiendo al diseño del controlador propuesto, y con el objetivo de garantizar la generalidad requerida en todo el proceso, en la presente tesis se propone una metodología de diseño basado en el modelo propuesto y una función de coste que incluye todos los parámetros técnicos y económicos necesarios para resolver el problema de optimización multiobjetivo propuesto, independientemente de la aplicación y topología del sistema. Esta función objetivo permite establecer un problema de tracking de acuerdo al balance de potencia instantáneo del sistema, a la vez que son considerados los parámetros técnicos y económicos asociados a la respuesta del sistema, véase degradación y rendimiento de equipos, límites y dinámica de operación, costes de operación y mantenimiento, criterios de carga de baterías, etc. Para garantizar la generalidad del controlador propuesto, fomentando así su uso, independientemente de la aplicación y topología del sistema, en la presente tesis se propone una metodología de diseño y tuning de los parámetros del controlador, de acuerdo a la función objetivo propuesta y los criterios de diseño en materia de prioridad de uso y distribución de energía entre equipos. La propuesta metodológica está basada en las relaciones causa-efecto entre los distintos parámetros, las cuales permiten definir el comportamiento del sistema de acuerdo a la estrategia de gestión de la energía y objetivos de diseño propuestos. De forma similar, con el objetivo de considerar la optimización a corto y largo plazo del sistema, limitada por el concepto de horizonte deslizante propio de las técnicas de control predictivo, se hace uso de técnicas de control adicionales, las cuales actúan directamente sobre el proceso de ajuste de los parámetros del controlador. En este sentido, en base a la historia del sistema, se recalculan los parámetros del controlador, en caso de que sea necesario, actuándose directamente sobre los parámetros de ponderación, de tal forma que permita adaptar la respuesta dinámica o reparto energético de acuerdo a los criterios de diseño del controlador. Finalmente, la metodología de diseño y el controlador propuesto fueron validados sobre la micro red experimental del grupo de investigación TEP-192. Para ello, fue necesario el diseño, desarrollo e implementación de toda la electrónica de control, adquisición y electrónica de potencia para la correcta operación e integración de los equipos.Attending to the concept of Smart Grid, these systems are closely related to the use of renewable generation systems. Despite the benefits of this technology, its dependence on environmental resources makes it impo ssible to guarantee the balance of energy between generation and demand at all times. Far this, the hybridization of systems, as well as the use of hydrogen-basedsystems, is shown as a viable technical solution to salve or mitigate the probel ms associated with this type of technologies. The use of this type of hybrid systems poses a greater compel xity in terms of managementdue to the high number of parameters and factors to be taken into account in arder to guarantee an optimal energy distribution dependingon the application and the energy status of the system. In this sense, certain aspects associated with the actual operation of the systems, such as the topology, the operating and maintenance costs, the need far a charge voltage control far batterie s, the degradation of equipment, dynamics of each system, the lossesassociated with the working point, or parameters related to the quality of the electricity supply.In the light of the above, it is necessary to use energy management strategies to determine the energy distribution between devices, in arder to optimize the response of the system from a technicaland economic point of view, thereforeposing a multi-objective optimization problem. In arder to respond to the proposed multiobjective optimization problem, in this Thesis, a distributed control architecture is used, composed of local controllers at th e first level, and at the top level, the use of a supervisory controlel r based on predictive control techniques (MPC). The main function of the proposed controlel r is to det ermine the operating setpoint of each of the equipment that makes up the Smart Grid, responding to the proposed objective function accordingto the system design criteria. The advantages of using predictive control techniques over other types of techniques are clear; allows the use of multivariable control techniques, allowing multiobjective optimization in constrained problems; as well as implementing a control strategy based on a prediction horizon, which allows the system to adapt the response of the controller based on future events, improvingthe response of the system against merely passive control techniques. As a knowledge base of the proposed controller, this Thesis presents a general discrete linear model of the plant, calculated in each sampling period, based on a recursive linearization, which allows to increase the quality of the model with respectto solutions based on lathe to a singlepoint of linearization. The model includes all the necessary parameters far the control of a real plant, including the terms associated with the energy status of the system, battery operating voltage, as well as technical and economic parameters, such as degradation, losses or operating cost, with the objective of defining a system cost function that allows its generality far any type of application or design objective. Based on the design of the proposed controller, and with the objective of guaranteeing the generality required throuqhout the orocess. in this Thesis a desian methodoloav basedon the orooosed model and a cost function that includes ali the necessary technical and economic parameters are proposed to solve the proposed multiobjective optimization problem, regardless of the application and system topology. This objective function allows to establish a tracking problem according to the instantaneous power balance of the system, while the technical and economic parameters associated with the system response are considered, see equipment degradation and performance, limits and operating dynamics, operation and maintenance costs, battery charging criteria, etc. To guarantee the generality of the proposed controller, thus promoting its use, regardless of the application and topology of the system, this Thesis proposes a design and tuning methodology of the controller parameters, according to the proposed objective function and the design criteria in terms of priority of use and energy distribution. The methodological proposal is based on the cause-effect relationships between the different parameters, which allow defining the behavior of the system according to the energy management strategy and proposed design objectives. Similarly, in order to consider the short and long-term optimization of the system, limited by the concept of the sliding horizon typical of predictive control techniques, additional control techniques are used, which act directly on the process of adjustment of the parameters of the controller. In this sense, based on the history of the system, the parameters of the controller are recalculated, if necessary, acting directly on the weighting parameters, in such a way that it allows adapting the dynamic response or energy distribution according to the controller design criteria. Finally, the design methodology and the proposed controller were validated on the experimental micro grid of the TEP-192 research group. For this, it was necessary to design, develop and implement ali the control, acquisition and power electronics for the correct operation and integration of the equipment

An innovative approach for energy generation from waves

Sustainable energy generation is becoming increasingly important due to the expected limitations in current energy resources and to reduce pollution. Wave energy generation has seen significant development in recent years. This paper describes an innovative system for generating energy from wave power. A complete description of the system is presented including the general concept, configurations, mechanical design, electrical system, simulation techniques and expected power output of the system. The results from the hydraulic linear wave simulator, using a real wave profiles captured at a location in the UK using an ultrasound system, it was seen that a ±0.8 m wave at 10 s time period, produced a conditioned power output of approximately 22 kW at optimum load conditions for the tested 3-phase 44 kW permanent magnet generator type STK500. The results indicate that this new technology could provide an efficient and low cost method of generating electricity from waves

The small wind turbine field lab extensive field tests for small wind turbines

This paper describes the research possibilities at the Small Wind Turbine Field Lab and the involved research groups of Ghent University, covering different aspects of a small wind energy system. In contrast to large and medium-sized wind turbines, small wind turbines are still plagued by relatively high production and purchase costs, and low reliability and energy yield. Furthermore, most of them have not been subjected to a field test program. Power-Link, the energy knowledge platform of Ghent University, has for three years operated a modest field test site for small wind turbines, that drew the attention of a lot of manufacturers of small wind turbines. In response, Ghent University decided to launch the Small Wind Turbine Field Lab (SWT Field Lab), to subject small wind turbines to more extensive field tests. Now not only the energy yield is tested, but also topics such as grid integration, structural strength, noise propagation, generator and drive train design and tower construction are studied. All of these parameters are correlated with meteorological data measured on-site

Influence of Negative Sequence Injection Strategies on Faulted Phase Selector Performance

Renewable power is expected to increase drastically in the coming years due to the energy transition. A large part of the newly installed generators will be connected to the power system through inverters and electronic converters, whose behaviour differs from the generators connected synchronously to the network. One of the main differences is the current contribution during symmetrical and asymmetrical faults which can affect protection systems. New grid codes establish requirements for fast current injection, but the converter’s maximum current limitations during faults make it difficult to establish control strategies for such current contribution. This paper studies the performance of faulted phase selector algorithm of a commercial relay under the current contribution from renewables before unbalanced faults. Two positive and negative sequence current injection strategies in compliance with new Spanish grid code requirements are proposed and tested under fault conditions in HiL (Hardware in the Loop). Test results show that the selected injection strategy affects the fault phase identification algorithm. Furthermore, the negative sequence injection requirements established in the new grid code improve the relay performance when line-to-line faults are applied, but they are not enough to identify all fault types