GFL
Grid-following inverter
An inverter that tracks an existing network voltage with a phase-locked loop and injects controlled current into it.
SLD
Symbols · 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.
In plain English
What does Grid-forming inverter mean?
A grid-forming inverter controls its output as a voltage source behind an impedance, setting voltage magnitude and frequency itself rather than measuring and following them. This lets it start a dead microgrid, share load with other sources through droop or virtual synchronous machine control, and respond instantly to load steps.
A simple example
Single-line diagrams use the inverter symbol, a box with DC and AC marks, with a GFM label, a voltage-source note or a sine source mark to show the control mode. On microgrid drawings at least one grid-forming source must be available whenever the system is islanded.
What the drawings help you do
Hardware alone does not decide grid-forming behaviour; many converters can switch modes in software. The symbol does not show current limits during faults, which are usually far lower than a synchronous machine, so protection based on fault current needs checking.
This particular reference
An inverter controlled as a voltage source that sets its own voltage and frequency, able to energise and hold up an island. A grid-forming inverter sets voltage and frequency; a grid-following inverter injects current synchronised to a voltage that something else provides.
- DC
- Direct current: electricity flowing in one direction.
- AC
- Alternating current: electricity whose direction changes periodically.
- Signal
- Electrical information passed between devices, rather than necessarily the main power supply.
Read the source: Quattro official product and documents · Reliable hybrid power and microgrid solutions
SLD · GFM
What it represents
A grid-forming inverter controls its output as a voltage source behind an impedance, setting voltage magnitude and frequency itself rather than measuring and following them. This lets it start a dead microgrid, share load with other sources through droop or virtual synchronous machine control, and respond instantly to load steps.
Single-line diagrams use the inverter symbol, a box with DC and AC marks, with a GFM label, a voltage-source note or a sine source mark to show the control mode. On microgrid drawings at least one grid-forming source must be available whenever the system is islanded.
Hardware alone does not decide grid-forming behaviour; many converters can switch modes in software. The symbol does not show current limits during faults, which are usually far lower than a synchronous machine, so protection based on fault current needs checking.
How to read it
- Look for GFM or voltage-source notes; the box itself is the same as any inverter.
- Confirm that a grid-forming source is present in every islanded operating case.
Information to show or reference
- State control mode and droop settings.
- Show island and grid-connected switching.
- Reference fault current capability.
A distinction that matters
A grid-forming inverter sets voltage and frequency; a grid-following inverter injects current synchronised to a voltage that something else provides.
Sources you can follow
These public references support the explanation and provide further detail. Their graphics and downloadable files remain with their publishers.
Quattro official product and documents
Public inverter-charger documentation describing island operation.
Reliable hybrid power and microgrid solutions
Public hybrid microgrid context in which a forming source sets voltage and frequency.
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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