Maintaining grid stability is paramount, particularly in the context of the growing deployment of variable renewables such as PV and wind. Aaron Philipp Gerdemann explores some of the grid-forming technologies emerging as alternatives to traditional solutions for safeguarding the grid.
This is an extract of a feature article that originally appeared in Vol.39 of PV Tech Power, Solar Media''s quarterly journal covering the solar and storage industries. Every edition includes ''Storage & Smart Power'', a dedicated section contributed by the Energy-Storage.news team, and full access to upcoming issues as well as the 10-year back catalogue are included as part of a subscription to Energy-Storage.news Premium.
In the quest for stable power systems, ensuring grid stability is paramount, particularly with the increasing integration of volatile renewable generators such as PV and wind. Grid stability relies on the dependable provision of essential grid services such as frequency response (FRT), voltage stability, and inertia.
Traditionally, synchronous generators provided these reserves at the transmission system level. However, the emergence of large-scale battery storage technology presents an alternative solution.
Battery storage offers rapid delivery of stored power and energy, outperforming conventional synchronous power plants in terms of response time and efficiency. With its impressive technical performance and increasing commercial competitiveness, battery storage is poised to play a pivotal role in future power systems with 100% renewable penetration.
Global solar inverter manufacturer SMA has utilised advanced power conversion systems (PCS) and control technologies that have significantly contributed to grid stability by encompassing inverters, medium voltage solutions, plant control and engineering services.
The provision of grid-following inverters proved instrumental in maintaining operational continuity and ensuring an uninterrupted power supply during severe grid disturbances in Odessa in 2021 and 2022.
Additionally, advanced grid-following controls have proven effective even in weak grid environments, as demonstrated in the West Murray region of Australia.
This article explores the pivotal role of advanced inverter and control technology, especially concerning grid stability.
Developing the grid-forming solution was not merely about replicating a synchronous generator; instead, the focus was on preserving relevant features and emphasising beneficial capabilities. This approach diverged from the conventional term “virtual synchronous machine,” as the goal was to enhance functionality beyond traditional methods.
In the initial stages of discussions, there were doubts about the feasibility of grid-forming technology. Demonstrators, such as the one on the island of St. Eustatius in the Caribbean Sea, played a crucial role in dispelling these concerns.
Software (SW) plays a pivotal role in grid-forming operation, where grid parameters are stabilised in response to deviations. This involves adapting island grid SW to react to frequency gradients instead of frequencies for grid-tied operation, resulting in a unique combination of droop and inertia control. This approach ensures stability and resilience, allowing inverters to emulate the behaviour of synchronous machines effectively.
Hardware (HW) enhancements are also integral to grid-forming solutions. Given that grid-following inverters typically offer limited short-circuit level (SCL) contributions compared to synchronous condensers, SMA’s Large Scale Hardware incorporates a short-term boost capability. This involves improving thermal management and providing design headroom for short-term overload, ensuring grid-friendly behaviour across various operational conditions.
By harnessing the stability and flexibility of battery energy storage systems, grid-forming solutions offer a pathway to a more sustainable and reliable energy future.
These solutions for grid-forming on-grid applications ensure seamless integration of renewable energy sources while maintaining grid stability. The emergence of additional stability services like inertia, system strength, and islanding capabilities underscores the necessity for grid-forming (GFM) controls at both inverter and plant levels.
Australia’s ambitious federal goal of achieving 82% renewable energy generation by 2030 has propelled the nation to the forefront of renewable energy adoption. With a vast potential for wind and solar energy, Australia faces the challenge of integrating these intermittent energy sources into its grid seamlessly. Battery energy storage systems (BESS) equipped with grid-forming technology have emerged as essential components to enable the required grid-hosting capacity for renewable energy.
Australia’s unique energy landscape offers valuable insights into the future of energy supply and grid stability. As an islanded power system with extensive distances for power transmission and high renewable energy penetration, Australia encounters challenges that other regions may face in the future.
Recognising the importance of grid-forming technology in enhancing grid stability and resilience, the Australian Renewable Energy Agency (ARENA) has allocated substantial funding to support grid-connected BESS projects with GFM capabilities.
The deployment of robust GFM technology is crucial for the Australian grid’s progression, as outlined in the Integrated System Plan released by the Australian Energy Market Operator (AEMO).
With a shift towards renewable energy sources connected to the grid through inverter-based resources (IBR), traditional IBR without grid-forming technology fall short in providing adequate grid support services. Grid-forming functionality is essential to address this gap, enabling IBR coupled with BESS to contribute to network strength and stability.
Grid-forming inverters offer several advantages over traditional synchronous generators. Firstly, they behave similarly to synchronous machines, acting as a voltage source behind an impedance without the physical constraints associated with rotating machinery.
This enables them to independently create their own three-phase voltage vector with a balanced sinusoidal waveform, reacting promptly to grid disturbances. Unlike grid-following assets, grid-forming inverters represent a true voltage source rather than a current source.
One significant advantage lies in the control capabilities of grid-forming inverters. Advanced grid-forming controls enable these inverters to exhibit synchronous, inertial, and damping behavior of the voltage vector. This results in an instantaneous, delay-free power response to grid events.
Moreover, the parameters of this response, including voltage amplitude, phase angle, and frequency, are adjustable. This flexibility allows for tuning of characteristics such as damping behaviour over the lifetime of the asset, enhancing its performance and adaptability.
Additionally, integrating electrochemical battery storage with grid-forming inverters further enhances their versatility and cost-effectiveness. Battery storage replaces the rotating mass traditionally used for mechanical storage in synchronous machines.
As a result, grid-forming inverters combined with battery storage can provide not only inertia and short-circuit-level (SCL) but also capacity for congestion management and other ''traditional'' energy services. This multi-purpose functionality makes grid-forming inverters with battery storage a highly efficient and adaptable asset.
Furthermore, the introduction of current boost capability by SMA eliminates the last remaining advantage of synchronous condensers, ensuring a high firm response at rated power. This capability enhances the performance of grid-forming inverters, making them even more competitive and suitable for various applications.
A world first, the Blackhillock project stands as a groundbreaking initiative in Scotland, spearheaded by developer Zenobē Energy, to propel the UK towards a net-zero economy.
The project’s state-of-the-art inverters, power stations, and advanced control systems deliver vital grid services, marking a significant advancement in renewable energy integration.
The primary aim of the Blackhillock project is to enhance system stability in the most cost-effective manner for consumers. Leveraging grid-forming technology and battery energy storage, the project targets to boost grid resilience, curtail carbon emissions, and reduce consumer bills. Additionally, it aims to bolster inertia and short-circuit levels at crucial interconnection nodes, thereby enhancing the overall reliability of the electricity grid.
Phase 1 of the Blackhillock project, comprising 200MW is planned to be commissioned in the summer of 2024, with Phase 2, an additional 100MW, slated for completion in the latter half of 2026. Upon completion, it will be the largest transmission-connected battery in Europe, offering a comprehensive suite of active and reactive power services. By facilitating greater integration of wind power into the transmission network, the project is projected to prevent approximately 2.3 million tonnes of CO2 emissions over 15 years.
SMA supplied critical components for the project, including 62 medium-voltage power stations boasting 333MWs of inertia and 84 MVA of SCL. Collaborating with industry leaders like Wärtsilä and H&MV, Zenobē ensured the successful implementation of the project, setting new benchmarks in grid stability and renewable energy integration.
Zenobē, SMA and Wärtsilä are partnering again for a comparable project located in South Kilmarnock, also Scotland. This new endeavor aims to surpass previous performance with an impressive power output of 300MW, coupled with 1,314MWs of inertia and 249MVA of SCL capacity.
The Blackhillock project not only represents a significant milestone in maintaining grid stability based on inverter-based resources (IBRs) but also in the UK''s journey towards achieving net-zero emissions.
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