C2I 2023 Aerospace & Defence Winner: Retroflight Alpha (Future Flight Landing and Infrastructure - FFLP2)

The burgeoning market for electrified flight requires fast-charging facilities that will not overwhelm the electricity grid.


Category: Aerospace & Defence

Headline Sponsor: STFC

Project: Retroflight Alpha (Future Flight Landing and Infrastructure - FFLP2)

Partners: Petalite, Custom Interconnect Limited, Oxfordshire County Council, Midlands Aerospace Alliance, Vanti, ARC Aero Systems

The winners of the Aerospace category in the 2024 C2I awards epitomize everything that is positive and achievable when working in a collaborative team.

Based in Aston, Birmingham, Petalite is a scale-up that has developed a new form of electric vehicle charger that aims to disrupt the full bridge charger market with its patented SDC device.

According to company founder and CEO Leigh Purnell, current charging facilities are sold as a product into infrastructure with a two-to-five-year warranty. The economic case for these first-generation facilities is weak given the installation, maintenance and operational life of them.

Petalite’s SDC solution brings modularity and scalability to charging, and that includes recharging the electric vertical take-off and landing (eVTOL) aircraft that are set to criss-cross our skies in the near future.

However, before this futuristic scenario can take off the eVTOL operators will need the right charging infrastructure in place to accommodate frequent short flights and limited time to charge between them.

Furthermore, the aircraft will endure hundreds of charging cycles in their lifetime and require huge amounts of power and high reliability for vertical take-off and landing.

These are just two of the issues addressed in Retroflight Alpha (Future Flight Landing and Infrastructure - FFLP2) led by Petalite in collaboration with Custom Interconnect Limited, Oxfordshire County Council, Midlands Aerospace Alliance, Vanti (trading name RTS Technology Solutions Limited), ARC Aero Systems.

The aim of Retroflight-Alpha is to develop the physical and digital infrastructure to support eVTOL future flight objectives. This includes a 600kW charging capability at a site in Bicester utilising Petalite's 3-Phase SDC and Vanti's smart building operating system (Smart Core), which integrates proprietary technologies in buildings and is required to serve eVTOLs in high density urban environments.

Demonstration unit at Petalite

“With eVTOL you need to have reliable fast chargers that can be used on schedule, but because of the loading of those chargers it needs to be managed in the wider context of the community,” said Rob Nash, CTO at Petalite. “So when they charge you need it to be able to manage the local power in order to not overload the grid. This program was about understanding the trade-offs in installing that facility.”

Nash explained that Petalite’s core SDC (Sinusoidal DC) technology converts AC to DC for battery charging in a more efficient way. Part of the efficiency comes from using fewer components, so there’s less that can go wrong in the system.

“By doing that, it also allows us to implement power factor correction and power conversion in one stage,” he added. “This is possible because of… silicon carbide that allows the switch in frequencies. In addition, we have an advanced transformer design that allows for high power to be transferred across on the AC to DC side.”

Nash explained that most traditional converters are voltage-controlled DC-DC that take the AC, rectify it to create DC and then convert that DC to another DC level.

“In doing that, some of the critical components are not needed in our method that are needed in the traditional voltage control,” said Nash. “So that's the fundamental technology, we can do more with less, but that's because we started from ground up and actually designed a solution to the problem.”

Nash added that power converters are the weakest link in current charging set ups because they use more components, run hot, and are an adapted solution to a different problem. At Petalite, using fewer components – and more reliable components – means single point failures at the power stage are lower.

SDC’s modularity is another key enabler.

“When you do voltage-controlled inverters, they basically come in finite blocks, and those finite blocks have a limit how many you can parallel,” said Nash. “If you have one charger that charges 100kW you only need a single point failure and it takes out that 100kW charge capability.”

Nash continued: “In ours we have five 20kW chargers. If we lose one charger, we get 80 per cent capability rather than zero. By changing the modularity of the design, by using a new technology…implemented in a simpler way means that we not only have [something] more reliable, we have more modularity that gives us more redundancy.”

Another benefit of SDC is its ability to move charge around. As an example, Nash explained that with SDC, once the charge drops below 80 per cent then the additional 20kW can be moved somewhere else.

“As it drops below 60 you can move it,” said Nash. “So for example, on a 1MW charge, effectively we could probably give the same charging capability utilisation as a 2.5MW charge station, so we put less in get more out and therefore we are more reliable, more available.”

Retroflight-Alpha is currently in the build up to the demonstrator stage and Petalite is sourcing a manufacturer based on the demonstration of the modular power blocks.

Key to the project has been Innovate UK’s ability to assemble consortium partners to address specific challenges. Nash added that collaboration among the consortium partners was also key, as was collaboration with suppliers who, as Nash said, need to see that there is a future for this technology.  

Nash explained that getting support from multibillion pound suppliers can be difficult for a small, pre-revenue company, but being part of a consortium adds gravitas to what the project is trying to achieve.

“Everything about this is designed in a way that not only helps the adoption of electrification, it also does it in a way that is environmentally friendly for the future generations who have to inherit it,” he said. “That's the master concept of why Petalite agreed to lead this consortium.”

As CTO at Petalite, Nash himself brings a certain gravitas to proceedings, given his over 20-year career in leadership roles gained within companies including Continental and Zytek Automotive.

Past projects include developing the F1 Kinetic Energy Recovery Systems (KERS) for McLaren, and the Formula E Powertrain design for the three-time winner Renault e.DAMS in 2014, 15 and 16.