The increase of renewable energy sources has favored the connection of new non-conventional generation technologies in electrical power systems. Many of these technologies are connected to the network by means of power electronics causing, among other problems, reduction of the inertia constant of the power system, to the detriment of frequency stability. There are different alternatives to improve the inertial response, but an instantaneous power reserve is always needed. The adequate instantaneous power reserve depends on the mix of dispatched generators. Thus, a flexible tool for determining the required instantaneous power reserve for the day-ahead operation is developed in this work. Obtained results show that the developed tool calculates the required power reserve with great accuracy and speed. Therefore, it serves as support for decision-making regarding instantaneous power reserve dispatch.

En este artículo se presenta un algoritmo para la búsqueda manual del tap del transformador de distribución y la búsqueda de los valores óptimos para la configuración de los inversores inteligentes de la generación distribuida fotovoltaica (GD-FV). Mediante esta configuración optima se logra mitigar los problemas de tensión que se producen debido a una alta penetración de GD-FV en redes de distribución. Los inversores inteligentes tienen la capacidad de gestionar la potencia activa y reactiva usando curvas configurables con valores por defecto y mediante un rango de valores establecidos en la norma IEEE 1547-2018. El algoritmo de optimización está basado en el algoritmo genético y permite realizar la búsqueda del óptimo de entre el rango de valores establecidos en la norma. De las simulaciones obtenidas se muestra que el uso de valores optimizados juntamente con una selección adecuada del tap pueden llegar a reducir a cero los problemas de tensión frente al uso de los valores por defecto que recomienda la norma IEEE1547-2018.

Photovoltaic Distributed Generation (PV-DG) produces some technical, commercial, and regulatory challenges in distribution systems. The most important technical challenge are the overvoltages produced by a high PV-DG penetration, which modifies the voltage profiles along the network and disturbs the operation of conventional voltage regulation devices. Extensive research has been carried out using various regulation devices under different control schemes to mitigate this impact. This paper presents a review of the literature dedicated to mitigate these overvoltage problems, proposing the classification and definition of regulation devices and control schemes used.

Debido al creciente interés en el aprovechamiento de energías renovables como la solar fotovoltaica acompañado por la reducción constante de costos de estas tecnologías, la penetración de generación distribuida de fuentes renovables está en franco crecimiento en el mundo. La forma más eficiente y efectiva de penetración se logra en forma de bloques de generación y cargas, denominados microrredes eléctricas (MRE). Estos bloques requieren de sistemas de control y de almacenamiento, con el fin de mantener el balance de potencia instantánea y de brindar servicios al sistema de distribución. Actualmente, los sistemas de almacenamiento más aptos para MREs son del tipo electroquímico, más específicamente de tecnología de Litio, y se espera que siga siendo la tecnología más apta en el mediano plazo. La reducción de costos de estos sistemas es de vital importancia, y por esta razón, el estudio de la degradación de los almacenadores y de las formas de mitigarla cobran gran relevancia. La degradación depende en gran medida del estado de carga del almacenador (SOC) y de sus variaciones, los cuales pueden obtenerse de patrones de estado de carga, obtenidos durante la operación del almacenador como parte de la MRE. Existen distintas formas de analizar señales con el fin de detectar y cuantificar sus variaciones, sin embargo, cuando el objetivo final es el análisis de la fatiga y degradación de materiales, es de gran importancia la cuantificación de ciclos de carga y descarga. Por ese motivo, en este trabajo se presenta la aplicación del método de conteo Rainflow a través de uno de sus algoritmos más difundidos, el cual brinda como resultado un listado de los ciclos completos y semiciclos presentes en la señal de SOC obtenida durante la simulación de un modelo de MRE bajo distintas condiciones.

Frequency stability analysis of large power systems are extremely time consuming, laborious and may even exceed the computational capacity of modern computers. Hence, simplified power system models have being developed in the literature. These models are usually called System Frequency Response (SFR). In SFR models, generators are represented by transfer functions, nonlinearities are generally neglected and the grid is not taken into account. Conventional SFR models only contemplate the mechanical behavior of speed governors, turbines and synchronous machines of generators. This is because, a common simplification is to consider that frequency and voltage can be controlled independently. However, it is demonstrated that there is an interaction between them, so frequency can be affected by the effect of power system stabilizers (PSSs) over excitation system controllers. In this work, a modified SFR model is proposed, considering the influence of generators excitation control on frequency. Simulation results show an improvement of the accuracy in the estimation of frequency response of the power system.

Electric power systems (EPS) are greatly impacted by renewable energy sources (RES) in modern days due to the environmental advantages that they bring when compared to conventional generation technologies, but it is well known that they also bring challenges to the operation and planning of the EPS due to the inherent uncertainties of weather conditions, low inertia, among others. This negatively impacts the reliability of the EPS and the effects of such uncertainties increase as the level of RES penetration rises. This problem is addressed by operators and planners with the operating reserves, that need to ensure the reliability of the EPS. This work presents a review of the current approaches found in the literature that address the problem of operating reserves in the context of operation and planning.

This article presents a Levelized Cost of Storage (LCOS) analysis for lithium batteries in different applications. A battery degradation model is incorporated into the analysis, which estimates the reduction in economic income due to the decrease in energy capacity. Another factor considered is the residual value attributed to the batteries, once they have completed their first stage of degradation and can be reused in second life applications. The Present Value of Throughput (PVT) metric is used to estimate the health factor of repurposed batteries and then calculate an attractive and reasonable selling price. All the analysis are made for the year 2020, and based on studies of the evolution of technology costs, the LCOS is projected for the year 2030. The results show that the most significant component of LCOS for all applications is investment, due to the high cost of this type of storage technology. Even for the year 2030, the LCOS is significantly reduced, capital expenditures continue to predominate, while the residual value represents an important role in the economic income at the end of the project life.

The connection of wind power generation (WPG) into ac microgrids (MGs) is steadily increasing. This incorporation can bring problems onto the power quality and dynamics of the electrical grid due to the lack of controllability over the wind and by the type of generation system implemented. This work presents a study of the impact on voltage and frequency of a MG operating in island mode when an important fault occurs. The study is carried out considering different penetration levels of centralized or distributed WPG, and the operation or non-operation of energy storage devices (SDs). For the SDs, a multi-level control scheme is suggested. This scheme includes two control modes of operation of the SD. The first one is used to maintain constant the voltage at the point of common coupling. And the second one is used to contribute to the frequency control when important faults arise in the system. Results show that the models and developed control algorithms of the proposed SDs work satisfactorily. The SD contributes to the recovery of the frequency and enhances the voltage profile when significant disturbances occur in the MG. Therefore, with the SD and control modes proposed, the power quality and the operation security of the MG with high penetration levels of WPG are improved. Moreover, it is observed that the behavior of the frequency is practically the same, either centralized or distributed systems, and a better voltage profile is observed for the distributed system.

This paper presents a methodology for determining the optimal size and location of Vanadium Redox Flow Battery (VRFB) which supplies load frequency control in electrical power systems. The objective is to achieve the optimal investment for installing a VRFB while considering its impact on the power system. Through stochastic optimization, the proposed methodology allows computing the variable operative costs and VRFB investment costs. To achieve this, a primal-dual interior point algorithm embedded in a meta-heuristic algorithm within an exhaustive search is used. In order to analyse the influence of the VRFB on frequency quality of the power system, statistical index is proposed such as the new factor used in dimensioning the secondary reserve.

The emerging potential of distributed generation (DG) is feasible to be conducted through microgrids implementation. A microgrid is a portion of the electrical system which views generation and associated loads as a subsystem, with the ability to operate both grid connected or islanded from grid, thus maintaining a high level of service and reliability. The existing grid infrastructure, the distributed energy resources to be integrated, as well as specific customer-oriented requirements will determine the best fitting architecture to constitute a microgrid. In this review, most common microgrids architectures based on ac, dc and hybrid ac/dc buses are analyzed. Furthermore, their advantages and disadvantages are discussed, describing their major components and most used control strategies.

Several control schemes specifically designed to operate inverter-based industrial microgrids during voltage sags have been recently proposed. This paper first classifies these control schemes in three categories and then performs a comparative analysis of them. Representative control schemes of each category are selected, described and used to identify the main features and performance of the considered category. The comparison is based on the evaluation of several indexes, which measure the power quality of the installation and utility grid during voltage sags, including voltage regulation, reactive current injection and transient response. The paper includes selected simulation results from a 500 kVA industrial microgrid to validate the expected features of the considered control schemes. Finally, in view of the obtained results, the paper proposes an alternative solution to cope with voltage sags, which includes the use of a static compensator in parallel with the microgrid. The novelty of this proposal is the suitable selection of the control schemes for both the microgrid and the static compensator. The superior performance of the proposal is confirmed by the analysis of the quality indexes. Its practical limitations are also revealed, showing that the topic studied in this paper is still open for further research.

Wind generation (WG) is the most widespread renewable energy resource in the world. However, this implementation inevitably leads to an increase in the problems caused by WG, e.g. frequency oscillations, power fluctuations or voltage variations. To overcome these problems, the use of a power conditioning system (PCS) coupled with a vanadium redox flow battery (VRFB) is proposed in this study. The PCS is composed of a distribution static synchronous compensator connected to a dc/dc chopper. The PCS/VRFB detailed model is presented and a three-level control system is developed. This control system allows the PCS/VRFB to perform a decoupled reactive and active power flow control. The dynamic response of the PCS/VRFB is evaluated through simulation tests, and performance characteristics of the device are obtained by means of the variation of the power references. The results obtained demonstrate that the PCS/VRFB offers a good transient response and the control system proposed allows mitigating the problems caused by wind power generation.

Due to existing conflicts or natural disasters in many different parts of the world, refugee camps are established by different aid organizations in order to provide local humanitarian assistance. Nowadays, these camps are electrically supplied using diesel generators, which are not environmentally friendly and require huge amounts of not easily available fossil fuels. In this sense, Microgrids (MGs) may have an opportunity to provide efficient electrical energy including renewable energy resources. In this paper a refugee camp located in Juba, South Sudan was selected as simulation example. First, the proposed MG to replace the current refugee camp topology and to supply the required electric and heat power is presented. The MG here considered is composed of different commercially available technologies. An economic study of the benefit using this grid configuration is carried out in order to determine the fuel consumption savings due to the use of renewable energy resources based generation technologies. Then, the replacement of diesel by photovoltaic and wind generation results in a reduced system inertia which brings problems related to frequency stability. A control strategy derived from the equations of a synchronous machine is here used to operate converter-coupled units in order to improve the MG frequency stability.

Micro-grids (MG) are expected to be low inertia grids especially due to the deployment of power electronics used to connect distributed generation (DG) units. This issue brings consequences on the grid dynamics, reducing the frequency stability margins. To this end, the emulation of synchronous machines has been proposed as a possible alternative. This paper explores the benefits of this concept comparing the dynamic performance with respect to the conventional droop control.

Current electrical power systems are undergoing a transition process from the centralized generation paradigm to a decentralized one. In this sense power electronics can be seen as the key connecting both paradigms. However, the great deployment of power electronics also implies a negative impact on the grid dynamics. The main cause is represented by the reduction of inertial response. This paper presents the design of a control strategy based on the virtual synchronous machine concept to improve the incorporation of converter-coupled units. The application of this concept is extended to controllable and non-controllable generation as well as loads. The proposed control shows a great potential to improve frequency stability in systems with high penetration of power converters, especially in weak electrical systems such as Microgrids.

Due to the deployment of distributed generation, future grids will show reduced inertia resulting in higher dynamics and reduced frequency stability. This is especially true in microgrids (MGs). In this sense, the virtual synchronous generator (VSG) concept has been proposed as a promising solution. In this paper, the benefits of this concept are further explored studying the frequency stability improvement under simulation of different cases regarding the MG operation. Here, the analysis is carried out looking at the impact of the control parameters on the rate-of-change-of-frequency and on the average frequency deviation. The VSG concept shows a great potential to reduce both parameters improving the frequency stability.

The growth of electricity demand in Argentina leads to the system expansion in generation, transmission and distribution networks in that country. Regarding distribution networks, a typical problem arises when a distribution company or a large customer must choose the location of its electrical substations; because this decision will determine the total cost of the installation. With the aim of minimize these costs, this paper proposes a search algorithm in order to determine the optimal location of electrical substations. This algorithm is implemented in Matlab® and it is tested in two case studies.

Nowadays, Argentina is experiencing an energy crisis mainly due to an inadequate planning. On the other hand, several countries are beginning to consider social aspects in planning, such as the use of nuclear energy, which has sparked considerable controversy in recent years. Thus, in this paper a novel strategic planning methodology is used in order to determine the most appropriate power system for Argentina by the year 2050. The planning methodology jointly optimizes generation and transmission expansion alternatives considering renewable energy and energy storage, in order to minimize total costs. Technical and environmental aspects are considered by optimization model constraints. Results show how nuclear energy rejection technically and economically affects the Argentinean power system.