GFM
Grid-forming inverter
An inverter controlled as a voltage source that sets its own voltage and frequency, able to energise and hold up an island.
SLD
Symbols · GFL
Grid-following inverter
An inverter that tracks an existing network voltage with a phase-locked loop and injects controlled current into it.
In plain English
What does Grid-following inverter mean?
A grid-following inverter measures the network voltage, locks to it with a phase-locked loop and injects a controlled current. Most rooftop and utility-scale solar inverters work this way. They need a stable voltage from the grid, a synchronous machine or a grid-forming inverter to operate, and they disconnect when that reference is lost.
A simple example
Drawings use the standard inverter symbol with a GFL note or a current-source annotation. Anti-islanding protection, often shown as a protection relay or a function list, is associated with this type so that it does not energise a dead network.
What the drawings help you do
In weak networks with high converter penetration, grid-following control can become unstable, so system strength studies are needed. The symbol does not show the phase-locked loop settings or the reactive power mode.
This particular reference
An inverter that tracks an existing network voltage with a phase-locked loop and injects controlled current into it. A grid-following inverter needs an external voltage reference; a grid-forming inverter provides that reference.
- Coil
- A wound conductor that can produce a magnetic field when energised.
- Phase
- One of the related AC waveforms in a power system.
- Rating
- A value stating the conditions for which equipment is specified.
Read the source: Photovoltaic technology and inverter functions · Solar electrical system architecture
SLD · GFL
What it represents
A grid-following inverter measures the network voltage, locks to it with a phase-locked loop and injects a controlled current. Most rooftop and utility-scale solar inverters work this way. They need a stable voltage from the grid, a synchronous machine or a grid-forming inverter to operate, and they disconnect when that reference is lost.
Drawings use the standard inverter symbol with a GFL note or a current-source annotation. Anti-islanding protection, often shown as a protection relay or a function list, is associated with this type so that it does not energise a dead network.
In weak networks with high converter penetration, grid-following control can become unstable, so system strength studies are needed. The symbol does not show the phase-locked loop settings or the reactive power mode.
How to read it
- Check that a forming source exists if the inverter is expected to run in an island.
- Anti-islanding settings are often listed as protection functions next to the inverter.
Information to show or reference
- State reactive power mode and ride-through settings.
- Show anti-islanding protection.
- Reference system strength assessment.
A distinction that matters
A grid-following inverter needs an external voltage reference; a grid-forming inverter provides that reference.
Sources you can follow
These public references support the explanation and provide further detail. Their graphics and downloadable files remain with their publishers.
Photovoltaic technology and inverter functions
Public photovoltaic inverter function context.
Solar electrical system architecture
Public solar electrical system architecture context.
About this graphic
This illustration was authored independently by Elora Grid to explain the concept. It is not reproduced from a customer drawing, an official standard graphic or a manufacturer CAD file. Its correspondence to an exact IEC or IEEE symbol identifier has not been certified.
SVG and DXF downloads contain this original artwork. DXF uses unscaled drawing units; a GA envelope supplies no product dimensions, clearances or fabrication information. Original artwork is available under CC BY 4.0. Third-party references retain their own terms.
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Put the reference into a drawing workflow.
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