Grid forming with grid-forming inverters

string inverters Grid Forming active control over voltage and frequency in the grid – thereby ensuring reliable supply security. This has been ensured for decades by large power plants. Their Synchronous generators possess rotating flywheels that maintain a constant grid frequency and voltage even during sudden fluctuations – this is referred to as Current reserve or „inertia.“.

With the growing share of renewable energies, this situation is fundamentally changing: photovoltaic and wind power plants feed their electricity via Power electronics one. While this is very efficient, it brings no natural flywheel mass into the grid. This means: The more conventional power plants are shut down, the fewer classic stability mechanisms are available. Without additional measures, this can lead to Security of supply and Grid stability endanger.

Grid-forming through innovative inverter technology now enables renewable energy systems in conjunction with Large battery storage systems self net-forming function. This means: instead of just following an existing network signal, the plants actively take on tasks that were previously reserved for synchronous generators—they provide voltage and frequency, ensure virtual inertia and thus stabilize the grid. This makes grid forming a central component of the energy transition.

How does grid forming work?

While conventional grid-following inverters rely on an existing grid signal, grid-forming inverters, in conjunction with Energy management systems (EMS) even take on the role of „network conductor.“ They actively create their own reference for voltage and frequency, thereby providing the foundation for stable grid operation, even when there are no longer any rotating generators.

Virtual Inertia – Software Instead of Flywheel Mass

Conventional synchronous generators stabilize the power grid through their physical inertia. When loads are suddenly removed or added, the rotating mass of these generators buffers short-term frequency fluctuations. Grid-forming inverters take over this task in conjunction with renewable energies and storage systems on a purely software-based level. They transfer the role of synchronous generators to modern power electronics and can thus supply or absorb energy within milliseconds.

Due to the extremely short reaction time, these systems behave like conventional flywheels, even though there is no physical movement. This is made possible by control methods such as the Droop Control or the concept of Virtual Synchronous Machine (VSM), which react lightning-fast to frequency changes. This way, a momentary reserve is provided that effectively absorbs all frequency deviations. This even allows for a complete Black start with battery storage.

Voltage generation – active control instead of pure following

In addition to frequency stabilization, grid-forming inverters also actively control grid voltage. Unlike conventional grid-following systems, they act as Voltage source and can independently specify voltage level and quality. Using methods such as Voltage droop control continuously adapt their performance to current grid conditions. This keeps the voltage stable even in dynamic situations. Even in severe grid disturbances, such as Short-circuiting, are the systems able to continue to support the grid. This ability is called Fault Ride Through is designated and is a central building block for the resilience of future power grids.

Intelligent Real-Time Control

The foundation of grid forming is a highly dynamic measurement and control technology. Grid-forming systems continuously monitor all relevant grid parameters such as current, voltage, and frequency. With the help of Feedback loops they can adapt their behavior in real-time, thus reacting immediately to changes. Whether by limiting currents, supporting frequency, or stabilizing voltage – the systems operate with a speed and precision superior to conventional generators. This enables stable grid operation even in scenarios where only power electronic generators such as photovoltaic, wind power plants, and battery storage systems are involved.

Difference between Grid Forming and Grid Following

To understand how grid forming works, it's useful to compare it to the classic principle of Grid-following inverter helpful. Grid-following systems rely on „following“ an existing grid signal. They feed their power in synchronously to an already existing frequency and voltage and can only operate when a stable grid signal is present.

Grid-forming inverters, on the other hand, take on a significantly more active role: they „form“ the grid themselves by independently generating a reference for voltage and frequency. Conventional synchronous generators, which set the pace for frequency and voltage, thus become redundant.

While grid-following reliably functions in stable grids with sufficient conventional power plants and represents an important tool for feeding in renewable energies, grid-forming is therefore indispensable for modern, future-proof, and renewable energy-based power systems.

Comparison: Grid Forming vs. Grid Following

Technical Implementation & Areas of Application

The technical implementation of grid forming is fundamentally achieved through grid-forming inverters or converters in conjunction with an EMS. The hardware must be capable of autonomously dictating voltage and frequency, as well as taking over all physical functions. The EMS, as software, controls the operating mode, orchestrates the deployment of grid-forming hardware, and decides, for example, on island operation, load prioritization, or resynchronization.

Inverter as Hardware

Grid-forming inverters perform the physical task of grid forming. They actively provide voltage and frequency and can keep them stable in the grid. This forms the basis for functions such as island operation or black start capability. Their task is to precisely implement the setpoints specified by the software and to react quickly to changes in the grid.

EMS as software

In the case of grid forming with the corresponding hardware, the EMS also controls the operating mode of the inverters and coordinates their interaction with storage systems and generators. It decides whether to activate island mode, how to prioritize loads, or when to resynchronize with the grid. This ensures the intelligent orchestration of the hardware and makes grid forming functional as a complete system.

Key application areas of grid forming

• Battery storage: In combination with powerful storage systems, grid-forming inverters can supply or absorb energy within milliseconds, thus compensating for short-term fluctuations in the grid. These systems are also suitable for black start scenarios, where a grid is restarted independently after a blackout.
• Microgrids and Islanded Grids: Grid-forming technologies are essential, especially in decentralized structures or regions without secure grid connections, to operate local grids reliably and independently.
• Integration of renewable energies: In large photovoltaic or wind farms, grid-forming inverters can take on tasks that were previously only possible with rotating generators. This allows for the direct integration of renewable energies into grid stability.
• Grid support in the integrated grid: Even in existing power systems with a decreasing share of conventional power plants, grid forming is becoming increasingly necessary to ensure frequency and voltage control and maintain system strength.

This opens up a variety of new possibilities for ensuring grid reliability and stability, even in highly renewable energy systems. Thus, the technology is not just a technical option, but a crucial component of the energy transition.

Challenges & Current Trends for Grid Forming

The widespread use of grid-forming is still in its early stages. Two main reasons for this have been insufficient digitalization the energy grids and the lack of widely implemented EMS. Without this digital control, grid-forming inverters cannot be fully coordinated. In addition, battery storage systems were comparatively expensive for a long time, making their economic deployment possible only in pilot projects.

However, both are currently changing significantly: With the increasing digitalization of the energy system, new EMS solutions, and falling costs for storage technologies, the widespread use of grid forming is moving within reach. This opens up new possibilities for reliably stabilizing frequency and voltage, even in a grid dominated by renewable energies.

Technical challenges

Grid-forming inverters must seamlessly integrate into existing grids with conventional synchronous generators. It's crucial to reliably maintain frequency and voltage, even with a high proportion of renewable energies, which requires grid-forming inverters to react very quickly and precisely to grid disturbances. The parallel use of different devices leads to complex control and protection technology, as instabilities caused by oscillations and interactions must be avoided. Furthermore, many solutions are still in the pilot stage, and the interoperability of different manufacturers, as well as validation in ongoing grid operation, present additional hurdles. Overall, grid-forming is significantly more complicated than conventional operation with synchronous generators and demands new, robust system concepts and standards.

Regulatory Framework

The European Network Codes, particularly EU Regulation 2016/631 (Requirements for Generators – RfG), form the basis for requirements concerning grid-forming properties. This regulation has been in force since 2016 and defines technical and operational requirements for generation facilities. In Germany, implementation is carried out through national Grid Codes and technical connection rules (TARs) from VDE/FNN as of July 2024, which are legally anchored and continuously developed. For the grid connection of new facilities, compliance with these rules is mandatory and must be demonstrated through certifications. The regulatory framework for battery storage is also evolving – but it is still far from being practical. Legal uncertainties are particularly evident for multi-use storage systems for grid forming, concerning electricity tax, grid fees, measurement concepts, construction progress notifications, redispatch, and balancing separation.

Current Developments and Pilot Projects

Grid-forming inverters in Germany are currently experiencing dynamic development, accelerated primarily by targeted research funding and regulatory impulses. In the spring of 2025, the Federal Network Agency will introduce concrete specifications for the market-based procurement of instantaneous reserve, meaning that systems with grid-forming capabilities will be compensated for the first time. Numerous pilot projects are exploring technical requirements, interoperability, and the use of battery storage and photovoltaic systems for stable grid operation. Field tests are being conducted at all voltage levels, system services are being tested, and the integration of decentralized systems for normal, island, and grid restoration operation is being validated. The goal is to be able to operate converter-dominated subnetworks stably and securely by 2028 and to directly incorporate the insights gained into standardization processes.

Grid Forming for Stability & Integration of Renewable Energies

Grid forming is far more than a technical option – it is the foundation for a stable energy system without conventional power plants. Grid-forming inverters take on tasks that were previously reserved for synchronous generators, thus making a reliable power supply possible even with a high proportion of renewable energies.

The previous obstacles – high costs for battery storage and a lack of digital control – are increasingly losing significance. With falling storage prices, powerful energy management systems, and clearer regulatory requirements, the technology is on the verge of market breakthrough.

This makes grid forming the crucial link between renewable generation, grid stability, and security of supply – and a key factor for the future energy system.