(1)Full Professor and Integrated Researcher, Dept. Industrial Electronics - University of Minho & ALGORITMI Research Centre & LASI
(2)Full Professor, Director of INESC Coimbra, Dept. of Electrical and Computer Engineering, University of Coimbra
(3)Full Professor, Dept. of Industrial Electronics, University of Minho & ALGORITMI Research Centre & LASI
(4)Senior Researcher, INESC TEC
In recent decades, power electronics technologies have contributed to important developments in electrical power systems, in terms of electricity generation, transmission, distribution and end-use, culminating in the advent of smart grids and microgrids, which are essential to enable the integration of generation from renewables with energy storage technologies and their coordinated operation.
Power Electronics
Power electronics is the technological area associated with the use of electrical and electronic components for the conversion, control, and conditioning of electrical energy. By using systems that employ power electronics, it is possible to process the power flow from the production to the loads and vice-versa, allowing, in both cases, a highly efficient and reliable operation. In particular, power electronics is used when the aim is to change the way that electrical energy is made available, either in the conversion of alternating current (AC) to direct current (DC) (using rectifiers) or from DC to AC (using inverters), either to change the amplitude of voltages and currents, both in DC (using switched power supplies), and in AC (using voltage regulators or dimmers), or even to change the frequency value (using cycloconverters or by combining rectifiers and inverters). Power electronics technologies can be used for a wide range of applications, from solutions of low-power applications (e.g., in the order of mW in mobile communication systems) to solutions of high-power applications (e.g., in the order of GW in high-voltage DC power transmission systems). Due to the technological evolution, it is possible to design power electronics solutions with lower costs, greater efficiency, and increased functionalities, including fault-tolerant operation. Power electronics will remain crucial to support new technological solutions (Figure 1): systems for energy production from renewable sources; energy storage systems; load management systems; green hydrogen production systems; electric mobility systems (including rail, road, maritime and aerospace transportation); telecommunications systems; systems for improving power quality and power flow control (including active power conditioners and solid-state transformers), and energy-use systems in industries and homes (automation and robotics, motor control systems, lighting, air conditioning, household appliances, etc.) (AFONSO, 2020) (AFONSO, 2021).
Smart Grids and microgrids
The decarbonisation of the economy, combined with the need to renew the electricity grids, triggered a paradigm shift in electrical power systems, increasing the capacity to integrate decentralised production based on renewable energy sources and new services and markets that promote the active participation of consumers (LOPES, 2019).
Only one third of the energy use is associated with driven systems (e.g., compressed air, ventilation, refrigeration), which are already mainly powered by electricity. The main energy need, covering the other two thirds, is in the form of thermal energy for processes and other thermal needs.
This led to the emergence of the smart grid concept, which is understood as an active grid capable of dealing with the greater complexity of the electrical power grid operation, through new monitoring, automation, and control solutions. These new solutions aim to ensure a safer and more efficient power grid operation from a technical and economic point of view, enabling new services to consumers, producers, and prosumers. More specifically, smart grids involve the integration of diverse technologies into the power grid that establish a bidirectional flow of information on its operation and performance - from the generation to the transmission, distribution and end-user systems.
Power electronics technologies take on a special relevance in several applications (Figure 2) associated with electric vehicles, decentralised renewable energy generation and energy storage solutions. These interfaces must ensure the optimal connection to the power grid, while minimising the impact of these technologies on its operation
Power electronics converters, commonly identified as smart inverters, currently enable the integration of local control algorithms to support voltage and frequency regulation, as well as communication and remote control (IEEE, 2018). With these monitoring and communication technologies for information collection and remote actuation, the inverter can locally adjust its power operation according to the power grid conditions, avoiding the unwanted disconnection of renewable-based production units, while allowing for their integration into energy management and grid optimisation systems.
The flexibility of the inverters and their interoperability allows to explore strategies concerning active consumption management with benefits for the consumer, the energy communities and the power grid operation. For example, in the case of an electric vehicle, when connected to the grid, it can charge in a controlled manner when operating in G2V (grid-to-vehicle) mode, also supporting the power grid or even the home where it is connected, by operating in V2G (vehicle-to-grid) or V2H (vehicle-to-home) modes (MONTEIRO, 2016)(GOUVEIA, 2013).
The flexibility of smart inverters is also essential to microgrids, aiming at fault detection and protection strategies, as well as reliable operation with high standards of power quality. Defined as a distribution power grid that integrates distributed generation, electrical energy storage and flexible loads that operate in a controlled and coordinated way, the microgrid can operate interconnected to the distribution power grid or islanded from the main grid (ANDRE, 2017).
The new regulatory frameworks for collective self-consumption, together with concerns about the electrical power system security of supply and resilience, have led to a growing interest in microgrids. At the same time, the flexibility of smart inverters has also contributed to the definition of different microgrid topologies (DC, for example) and the integration of different technologies (from conventional generators to electrolysers), enabling different business models, ranging from rural and remote electrification, energy communities and data centres.
From a perspective of the power system resilience, the microgrids allow for local blackstart and can also be aggregated into clusters of microgrids, supplying the loads of a region through local strategies of service replacement (MONTEIRO, 2016). However, these operating modes require specific control strategies of the inverters and synchronisation mechanisms (GOUVEIA, 2013)(MONTEIRO, 2021).
Regarding power electronics applications in grid infrastructures, the main objective is to increase the transmission capacity and improve the power grid stability and power quality. However, due to high costs, its integration is mainly verified in power transmission networks, with the installation, for example, of FACTS (Flexible Alternating Current Transmission Systems) and STATCOM (STATic synchronous COMpensator). However, it is expected that, in the upcoming years, new solutions for the distribution power grid will emerge - where, in addition to congestion management, the use of such equipment will also foster improved voltage regulation capabilities and increase the flexibility of the power grid infrastructure (MONTEIRO, 2021) (ZHU, 2021).
In conclusion, given the goals of decarbonisation and the perspectives of technological evolution, the future electrical power grids will become systems largely dominated by power electronics technologies, from power generation to final consumption, including the power grid management. This new paradigm requires to the definition of control strategies that integrate all system components (individually or aggregated) in microgrids, as active elements in the optimisation, operation and reliability of the global power system. The contribution of power electronics technologies will also be essential to mitigate the estimated number of about 770 million people without access to electricity in the world (INTERNATIONAL ENERGY AGENCY, 2021), and about 3.5 billion suffering from connection to electrical grids with low power quality (AYABURI, 2020).
References
[1]AFONSO, J.; Tanta, M.; Pinto, J.; Monteiro, L.; Machado, L.; Sousa, T.; Monteiro, V. (2021) - A Review on Power Electronics Technologies for Power Quality Improvement. Energies, vol.14, no.24, pp.1-71
[2] AFONSO, J.; Cardoso, L.; Pedrosa, D.; Sousa, T.; Machado, L.; Tanta, M.; Monteiro, V. (2020) - A Review on Power Electronics Technologies for Electric Mobility. Energies, vol.13, no.23, pp.1-61.
[3] LOPES, J.; Madureira, A.; Matos, M.; Bessa, R.; Monteiro, V.; Afonso, J.; Santos, S.; Catalao, J.; Antunes, C.; Magalhães, P. (2019) - The Future of Power Systems: Challenges, Trends and Upcoming Paradigms. Wiley Interdisciplinary Reviews: Energy and Environment, vol.9, no.3, pp.1-16. Leal, R Teixeira. PoDIT: Portable device for Indoor Temperature Stabilization: Concept and Theoretical Performance Assessment. Energies 13 (22), 5982. 2020.
[4] Institute of Electrical and Electronics Engineers, Inc. (IEEE); IEEE Standard 1547(2018) “Standard for Interconnection and Interoperability of Distributed Energy Resources with Associated Electric Power Systems Interfaces”. https://standards.ieee.org/ieee/1547/5915/
[5] MONTEIRO, V.; Pinto, J.; Afonso, J. (2016) - Operation Modes for the Electric Vehicle in Smart Grids and Smart Homes: Present and Proposed Modes. Transactions on Vehicular Technology, vol.65, no.3, pp.1007-1020.
[6] GOUVEIA, C.; Moreira, C.; Lopes, J.; Varajão, D.; Araújo, R. (2013) - Service Restoration in Low Voltage MicroGrids with Plugged-in Electric Vehicles. Industrial Electronics Magazine, vol.7, no.4, pp.26-41.
[7] ANDRE, R.; Guerra, F.; Gerlich, M.; Metzger, M.; Rodriguez, S.; Gouveia, C.; Moreira, C.; Damásio, J.; Santos, R.; Gouveia, J. (2017) - Low Voltage Grid Upgrades enabling islanding operation”, CIRED 2017, Glasgow, Scotland.
[8] MONTEIRO, V.; Martins, J.; Fernandes, A.; Afonso, J. (2021) - Review of a Disruptive Vision of Future Power Grids: A New Path Based on Hybrid AC/DC Grids and Solid-State Transformers. Sustainability, vol.13, no.16, pp.1-24.
[9] ZHU, X.; Singh, A.; Mather, B. (2021) - Grid Value Investigation of Medium-Voltage Back-to-Back Converters. IEEE Power & Energy Society Innovative Smart Grid Technologies Conference (ISGT), 2021, pp. 1-5.
[10] International Energy Agency (2021) - World Energy Outlook.
[11] AYABURI, J.; Bazilian, M.; Kincer, J.; Moss, T. (2020) - Measuring “Reasonably Reliable” access to electricity services. The Electricity Journal, vol.33, no.7, pp.1-7.