Ancillary Services in Hybrid AC/DC Low Voltage Distribution Networks

In the last decade, distribution systems are experiencing a drastic transformation with the advent of new technologies. In fact, distribution networks are no longer passive systems, considering the current integration rates of new agents such as distributed generation, electrical vehicles and energy storage, which are greatly influencing the way these systems are operated. In addition, the intrinsic DC nature of these components, interfaced to the AC system through power electronics converters, is unlocking the possibility for new distribution topologies based on AC/DC networks. This paper analyzes the evolution of AC distribution systems, the advantages of AC/DC hybrid arrangements and the active role that the new distributed agents may play in the upcoming decarbonized paradigm by providing different ancillary services.Ministerio de Economía y Competitividad ENE2017-84813-RUnión Europea (Programa Horizonte 2020) 76409

Distributed consensus-based secondary control of multi-terminal DC railway systems

Electrification of the transportation sector is one of the main pillars of the future decarbonized society. In this context, high-speed railway corridors are expected to reduce as much as possible their environmental impact while maintaining the safety and quality of service with minimum investments. In pursuing those objectives, the multi-terminal DC railway system may become the preferred paradigm. In contrast to conventional AC railway electrification schemes, the multi-terminal DC railway system requires the adoption of a control algorithm to establish suitable references for the power converters. This paper elaborates on a new consensus-based secondary control strategy, which can be implemented in a distributed fashion. In this approach, each power converter controller receives information from its nearest neighbors to adjust its operating point. A 600-km railway system, subject to realistic train traffic, is used to compare the performance of the proposed control strategy with that of purely local controllers. Numerical simulations evidence that the proposed distributed control scheme provides a compromise solution in terms of voltage drops and equalization of power converter loading, surpassing the performance of conventional state-of-the art controllers

A model-less control algorithm of DC microgrids based on feedback optimization

This work addresses the problem of the optimal real-time control of a DC microgrid without relying on its corresponding network model. The main goal of such a controller is to keep the nodal network voltages within the regulatory limits while offering current sharing capability between the different controllable generators powering the DC microgrid. The proposed model-less methodology is based on feedback optimization, which takes advantage of the available real-time measurements to update the setpoints of the DC generation assets. The optimal control variables are determined in an iterative manner by applying a primal–dual saddle-point method, which guarantees appropriate convergence features. The paper details both centralized and distributed implementations which are compared through simulations. The results evidence a good dynamic performance and an optimal steady-state operation as the proposed control algorithm converges to the solution provided by a conventional model-based Optimal Power Flow.Universidad de Sevilla VI PPIT-USUnión Europea - Horizonte 2020 No 764090Ministerio de Economía ENE2017-84813-RCentro para el Desarrollo Tecnológico Industrial HySGrid+ CER-2019101

Provision of Primary Frequency Response as Ancillary Service From Active Distribution Networks to the Transmission System

This paper deals with the provision of primary frequency response (PFR) as ancillary service (AS) from active distribution networks (ADNs) to the transmission system (TS). In particular, two methodologies are developed. The first one aims to quantify the PFR capability range of the ADN. This range is defined by determining the range of the aggregated, i.e., equivalent, active power - frequency P(f ) droop curves that can be provided at the point of interconnection (POI) with the TS. The second one targets to optimally control P(f ) droop curves of individual distributed energy resources (DERs), installed in the premises of the ADN, to guarantee specific frequency regulation characteristic at the POI. This frequency regulation characteristic is expressed by means of a P(f ) droop curve. Both methods are tested on two discrete distribution systems. Several test cases are examined to demonstrate their implementation. Additionally, comparisons against conventional approaches and time series simulations are conducted to evaluate the performance of the proposed methods.Unión Europea Subvención 76409

Short-term energy recovery control for virtual inertia provision by renewable energy sources

The proliferation of Converter-Interfaced Renewable Energy Sources (CIRES), which are inertia-less, and the gradual decommissioning of synchronous generation have posed several challenges to the electric power system. This has motivated a complete a shift in the CIRES design and its corresponding control philosophy. Integrating Energy Storage Systems (ESS) within CIRES enables the implementation of different operating modes allowing them to provide ancillary services (AS) in a similar way to the synchronous generation. In order to tackle with those short-term response AS, such as virtual inertia, fast ESS (FESS) solutions with high power-to-energy ratio, particularly flywheels and supercapacitors, are preferred. In spite of several control algorithms have been proposed to provide such fast AS, very little research effort has been paid on the proper FESS energy recovery after the AS provision. This task is particularly challenging, since supercapacitors must be operated at a certain state of charge to guarantee that the required AS can be provided within its operational limits. This paper aims to fill this gap by proposing a new energy recovery control scheme for supercapacitors after the provision of short-term AS, such as virtual inertia. The proposed control is validated via simulations which clearly highlights its adequate performance.Horizonte 2020 (Unión Europea) 764090Ministerio de Economía y Competitividad (MINECO). España ENE2017-84813-R

Ancillary Services Market Design in Distribution Networks: Review and Identification of Barriers

The high proliferation of converter-dominated Distributed Renewable Energy Sources (DRESs) at the distribution grid level has gradually replaced the conventional synchronous generators (SGs) of the transmission system, resulting in emerging stability and security challenges. The inherent characteristics of the SGs are currently used for providing ancillary services (ASs), following the instructions of the Transmission System Operator, while the DRESs are obliged to o er specific system support functions, without being remunerated for these functions, but only for the energy they inject. This changing environment has prompted the integration of energy storage systems as a solution for transfusing new characteristics and elaborating their business in the electricity markets, while the smart grid infrastructure and the upcoming microgrid architectures contribute to the transformation of the distribution grid. This review investigates the existing ASs in transmission system with the respective markets (emphasizing the DRESs’ participation in these markets) and proposes new ASs at distribution grid level, with emphasis to inertial response, active power ramp rate control, frequency response, voltage regulation, fault contribution and harmonic mitigation. The market tools and mechanisms for the procurement of these ASs are presented evolving the existing role of the Operators. Finally, potential barriers in the technical, regulatory, and financial framework have been identified and analyzed.Unión Europea (Programa Horizonte 2020) 76409

A holistic model-less approach for the optimal real-time control of power electronics-dominated AC microgrids

This paper addresses the problem of optimally operating a set of grid-forming devices in an AC microgrid when a detailed network model is not available. The main aim of the approach is to maximize the power sharing of the controllable grid-forming devices and to maintain the frequency and the nodal voltages of the microgrid as close as possible to their corresponding references. The proposed control architecture is conformed by a local control layer in each grid-forming device that intends to emulate the performance of a synchronous machine and a centralized secondary controller composed of two complementary tools that coordinates the setpoints of the grid-forming devices: an online feedback optimization algorithm and an automatic generation control. The proposed method has been validated through simulations and hardware-in-the-loop tests, evidencing its good performance and robustness under different conditions

Ancillary Services Offered by Distributed Renewable Energy Sources at the Distribution Grid Level: An Attempt at Proper Definition and Quantification

Article number 7106The gradual displacement of synchronous generators driven by conventional power plants, due to the increasing penetration of distributed renewable energy sources (DRES) in distribution grids, is creating a shortage of crucial ancillary services (AS) which are vital for the frequency and voltage stability of the grid. These AS, and some new ones, could now be offered by the DRES, particularly those that are converter interfaced, in a coordinated way in order to preserve the grid stability and resilience. Although recent standards and grid codes specify that the DRES exhibit some system support functions, there are no specifications on how to measure and quantify (M & Q) them both at DRES level and in aggregated form. The M & Q of AS is crucial, since it would allow the AS to be treated as tradable AS in the current and future AS markets. This paper attempts to define a number of AS that can be offered by converter-interfaced DRES and suggests methods for their M & Q. The new AS addressed are: (1) inertial response; (2) primary frequency response; (3) active power smoothing (ramp-rate limitation); (4) exchange of reactive power for voltage regulation; (5) fault-ride-through (FRT) and contribution to fault clearing; (6) voltage harmonic mitigation. Additionally, a rough estimation of the additional investment and operational cost, as well as the financial benefits associated with each AS is provided in order to form the basis for the development of business models around each AS in the near future.Unión Europea Proyecto EASY-RES (Horizonte 2020) 76409

DC-bus energy management of a converter-interfaced renewable energy source comprising an energy storage system

The increasing penetration of renewable energy sources is strongly linked to the development of voltage source converters used in their connection to the grid. As a result, in the near future of an inverter-dominated power system it will be a requirement for renewable generation to provide ancillary services in order to compensate for the absence of synchronous generation. In this scenario, the use of energy storage systems along with advanced control algorithms mimicking the dynamic behaviour of the traditional generators will be of utmost importance. This paper deals with a renewable energy source interfaced with a voltage source converter and comprising an energy storage system in the DC bus. Particularly, a new energy management algorithm for the DC-bus based on a three levels hierarchical control is proposed, which is able to simultaneously provide ancillary services, maintain the state of charge of the storage system within the permissible limits and use it to control the DC bus voltage. The control strategy is validated experimentally using a prototype with results evidencing a reliable and stable operation.European Union (UE). H2020 76409

Metodología integral de aprendizaje en Teoría de Circuitos

Se describe un trabajo de innovación educativa basado en la utilización de varias técni­cas docentes que complementan a la metodología tradicional existente, para generar una metodología integral en el aprendizaje de Teoría de Circuitos. Se propone una innovación docente desde el punto de vista de la adquisición de competencias orien­ tada al Espacio Europeo de Educación Superior (EEES).A novel integrated methodology of teaching of Theory of Circuits based on the use of a few techniques that complement the traditional way is presented. The experience is focused on the student's skill acquisition, looking toward the European Higher Education Area (EHEA).al Instituto de Ciencias de la Educación de la Universidad de Sevilla: Convocatoria de ayuda a la docencia para la innovació