Electrical networks

ELECTRIC POWER SYSTEMS

Electric power systems are undergoing a change of paradigm with the massive integration of renewable energy generation systems, storage systems and other power electronic converters used for the transmission of energy (such as medium and high voltage direct current or HVDC links) and for improving the power quality (such as FACTS equipment).

The Electric Power Systems research group is focused on researching, developing and transferring solutions to the business fabric within the field of modern power systems, where the penetration of power electronic converters is significant.

The group focuses its activities primarily on 4 areas of research.

• Modeling, analysis, simulation and validation
• Control of power converters connected to the grid
• Planning and management of electric power systems
• Medium voltage and high-power systems

Research areas

Modeling, analysis, simulation and validation

Traditional electric power systems, which were dominated by the electromechanical dynamics of large synchronous generators, were modelled under the assumption that the frequency and voltage of the system were constant or nearly constant. However, due to the massive penetration of power converters in modern networks, this premise is no longer valid. Synchronous generators are progressively being replaced by converters that do not inherently respond to disturbances in the grid, resulting in much larger frequency and voltage swings.

To this end, at the research group we develop mathematical tools and behavioral models for modern electrical systems in order to analyze not only the electromechanical interactions, but also the electromagnetic dynamics associated with the passive elements and the fastest control strategies of converters (current and voltage regulation loops, etc.). The objective is to identify the origin of undesired oscillations and to evaluate the stability of these systems, in order to subsequently develop solutions to improve this behavior. Using these models, we also carry out (offline and real-time) time-domain simulations to evaluate the behavior of the system under various conditions.

We work with models or our own analytical tools based on Matlab/Simulink® and in Python, as well as with commercial tools on projects collaborating with the sector's industry. Specifically, we have two proprietary tools for studying modern electrical power systems. Firstly, the CSTEP® tool, programmed in Matlab, allows us to build analytical models in a semi-automatic way for analyzing the small-signal stability of power systems and to carry out time-domain simulations. We also use the DFPF tool, which is based on the Matlab/Simulink environment, to perform time-domain simulations of hours and even days of electrical power systems with a high penetration of converters. The advantage of this tool is that it represents the dynamics of the frequency and voltage, which makes it possible to develop and study control strategies for devices participating in the regulation of these variables.

Control of power converters connected to the grid

In this area, our activity is focused on different levels of control. On the one hand, we are working on developing "internal" control loops for regulating the current and voltage of the converters. In addition to these loops, we also develop strategies for synchronization with the power system. Furthermore, in addition to the classic grid-following, we develop higher level control loops to provide services to the network. We have an extensive experience with grid-supporting and grid-forming algorithms in order to provide frequency and voltage support to the grid, and we work on developing new techniques or adapting already developed techniques to improve the response of converters under imbalances, faults, the presence of harmonics, phase jumps, etc. We also develop algorithms to provide new functionalities such as islanding or black-start.

Generally speaking, we develop new control algorithsm, propose tuning criteria (using traditional methods or optimization algorithms), and evaluate the performance of these strategies under a variety of conditions or uncertainties in the system.

To evaluate the control strategies developed, we have an experimental Microgrid with photovoltaic generation systems, energy storage systems and programmable sources and loads. In addition, we are currently working on the development of Power Hardware-in-the-Loop (PHIL) platforms for both AC and DC systems.

Planning and management of electric power systems

The purpose of this area of research is to improve flexibility in the operation of electrical power systems where a large part of the generation is distributed physically. We work to develop strategies that allow us to make better use of the energy generated, stored and consumed in an electrical grid.

On the one hand, we develop energy generation and demand forecasting algorithms that allow us to make better decisions for operating the system. For example, they allow us to decide the optimal state of charge of a stationary storage system, to choose when the optimal time to activate certain assets is, or to determine the most appropriate network configuration to optimize power flows in the system.

On the other hand, we develop algorithms for coordinating energy assets of different types, for instance stationary batteries and thermal assets such as heat pumps and thermal accumulators. In this regard, we have an extensive knowledge of the regulatory mechanisms of the electricity markets, which has allowed us to work on numerous transfer projects involving the integration of devices into the grid in compliance with the country's local regulations.

Medium voltage and high-power systems

In this area, we focus on the development of infrastructure elements and equipment connected to electrical power systems. The activities are focused on the development and testing of interconnection elements in networks (mainly transformers), power conversion and generation equipment, protection devices, etc.

In particular, we have considerable experience in distribution transformers. In addition to modeling these devices with different levels of fidelity to evaluate aspects such as switching (inrush) currents and the interactions with generation equipment controls, we have an extensive expertise in developing transformers with high-speed tap changers, which serve to modify voltage levels dynamically and on-load. During the last few years we have also gained knowledge in the development and control of medium voltage and high-power converters based on modular topologies such as cascaded H-bridges and MMCs (modular multilevel converters).

In order to carry out experimental tests in close-to-reality environments, we have a unique Medium Voltage Laboratory. This laboratory has two independent test areas that can be rented to conduct medium voltage and high-power tests. As a recent example, Siemens-Gamesa Renewable Energy used the laboratory to test its wind generators for voltage dips in order to improve their performance before certifying the equipment for sale and installation.

Applications

The applications of interest to the research group are Energy Transport and Distribution, internal distribution systems and charging and connection infrastructure for Electric Traction Systems, Stationary Storage Systems and Renewable Generation Systems such as wind farms and photovoltaic parks.

In addition to working with different companies and research centers in the area and in other countries, the research group is also participating in various collaborative research projects in the Basque Country, Spain and Europe.

 

 

 

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