Grid-forming pilot
First grid-forming inverter trial on a 40 MW battery site.
Held frequency through
12 fault tests
Size
40 MW, 80 MWh
Location
Carrow Fen, eastern England
My role
Technical lead for the trial
Team
5 engineers, 1 inverter vendor
Duration
10 months, 2021 to 2022
01
The situation
Most battery inverters follow the grid. They read the frequency and copy it. That works while large power stations set the frequency for everyone. As those stations close, the grid needs inverters that can set the frequency themselves and hold it steady during a fault. These are called grid-forming inverters.
In 2021 Voltaic North had never installed one. The grid operator in eastern England was offering a new contract for sites that could prove the capability, and our 40 MW site at Carrow Fen was a candidate. Nobody in the company, including me, had tested grid-forming behaviour on a real site before.
02
What I did
I started with a computer model of the site in PSCAD and ran 140 fault cases on it. That told us which settings mattered and which tests were worth doing for real. I then agreed a test plan with the grid operator, who sent two engineers to witness every test on site.
You cannot cause a real fault on a public network, so we simulated one. We disconnected the site from the grid on purpose, with a 10 MW load bank attached, and watched whether the inverters held frequency on their own. We also played recorded fault signals into the controllers. There were 12 tests in total, run over three weeks.
03
What changed
The site passed all 12 tests. In the hardest one, a sudden loss of the grid with the load bank at full power, frequency dipped to 49.7 Hz and recovered within half a second. The agreed limit was 49.5 Hz. Carrow Fen became the first Voltaic North site to win a grid-forming contract.
I wrote up the method as a 20 page guide, and it was folded into the commissioning playbook the following year. Grid-forming is now specified on every new Voltaic North site. It is also the work I get asked about most. I have since explained it to more project managers than engineers.
12 of 12
Fault tests passed
Witnessed by the grid operator
49.7 Hz
Lowest frequency in the hardest test
Agreed limit was 49.5 Hz
40 MW
Site capacity under test
All inverters in grid-forming mode
