How Converdan adapted a standard inverter platform to fit a fifty-year-old wind turbine no one else could match.
The legend behind Tvindkraft
Tvindkraft was built in response to the 1970s oil crisis and Denmark’s political debate over nuclear power. A group of teachers, students and local volunteers (average age 21) set out to demonstrate that wind energy was a viable alternative to fossil fuels and atomic energy. None of them had built a wind turbine before. No one had built one this size.
Construction began in 1975. Electricity first reached the local grid in March 1978. Along the way, the team pioneered or refined techniques that are now industry standard: fibreglass blades, pitch control, variable rotational speed, and a frequency converter designed by Professor Krabbe’s engineering students that allowed the turbine to produce grid-compatible AC at any wind speed.
Nearly fifty years on, Tvindkraft still turns. International engineers passing through Western Jutland still stop to see what is now known as the mother of all windmills.
Read Tvindkraft’s own history and listen to the BBC’s documentary on the turbine.
The challenge
By the early 2020s, the original analogue frequency converter was reaching the end of its life. Built with discrete components in an era before computer-controlled power electronics, its replacement parts had become nearly impossible to source. Without a modern alternative as a replacement that can be repaired, the turbine had a future measured in years rather than decades.
The replacement was not a matter of buying off the shelf. Tvindkraft’s generator had been acquired second-hand from a Swedish paper mill: built for industrial power generation, not wind. Modern digital frequency converters create voltage spikes that the generator’s insulation cannot absorb. Standard solutions would have burned it out within a handful of years.
Tvindkraft’s team approached several of Europe’s largest power electronics suppliers. The technical fit was not there. For a single, one-off installation at this specification, the economics did not work for organisations built around volume product lines.
Why Converdan
Tvindkraft’s network around the turbine led the team to Vojens. Converdan’s Thomas Slivsgaard had visited the mill several times over the years, and the technical conversation moved quickly.
“They can sit down at a table and figure out what to do.”
That, in Kim Hansen’s words, was the difference. Tvindkraft’s team had spent months talking to engineering departments organised to deliver standard products at scale. At Converdan, an engineer answered, and then engineers from both sides worked the problem together.
Custom & Standard, in practice
The starting point was Converdan’s AFE333KAC platform: the same hardware running in fast EV chargers and battery energy storage systems across the company’s customer base. The topology is bidirectional. It can pull power off the grid into a battery, or push power off a turbine onto the grid. The fundamentals were already proven.
What Tvindkraft needed was firmware. The standard platform supported up to 16 parallel modules; Tvindkraft’s 800 kW installation required 24, the largest single-site Converdan installation to date. Tvindkraft’s team brought the specifications of a turbine no one else operates in commercial wind today. Converdan adapted the AFE333KAC — input voltage behaviour, parallel-module control, dynamic braking — to match what Tvindkraft knew the turbine needed.
Each adjustment was a firmware change, not a hardware redesign. The hardware shipping to Tvindkraft was the same hardware Converdan ships every week.
That is the Custom & Standard approach in practice. A stable platform, customer-specific firmware, and a very agile engineering team that sits with the customer’s engineers and works out the details.
Scope of Converdan work
Platform & firmware:
- Adaptation of AFE333KAC inverter platform (24 parallel modules, 800 kW total)
- Custom firmware tuned to Tvindkraft’s specifications: parallel-module support, variable input voltage, dynamic braking
Engineering & support:
- System simulation and concept study
- On-site commissioning and firmware tuning
- Ongoing service and remote monitoring
Outcome
The 800 kW installation is operational, with ongoing optimisation between Converdan and Tvindkraft’s local team.
The modular design carries an advantage that matters for a turbine intended to last another half-century: individual converter modules can be removed and serviced while the turbine continues running at reduced power. A single module is light enough for one person to lift. The competing class of single-unit, megawatt-scale inverters would require a crane.
Tvindkraft remains a customer. Converdan’s product support team handles firmware updates and remote monitoring, and both sides expect the installation to keep evolving as the turbine’s testing programme progresses.
“Good Danish engineering craftsmanship and agility with their solutions. And quick on the trigger.”
Most converter requirements are not fifty-year-old wind turbines. But many of them arrive with a problem the volume suppliers cannot quite fit: an unusual specification, a non-standard operating envelope, a need that lands outside the off-the-shelf catalogue. Tvindkraft is what a standard platform can do when an engineering team is agile enough to adapt it.
If your requirement does not quite fit a standard data sheet, get in touch.
Tvindkraft and the 800 kW installation:
