Take Charge! Putting the e in eVTOL

A team of British researchers devise a new method to assess battery power capabilities

August 24, 2024 | Dave Clarke

In their research paper, “Novel battery power capability assessment for improved eVTOL aircraft landing,” researchers Ollie Hatherall, Anup Barai, Mona Faraji Niri, and James Marco from the Energy Innovation Centre, WMG, University of Warwick, Coventry, United Kingdom and Zeyuan Wang from Vertical Aerospace Group Ltd in Bristol, United Kingdom sought to find innovative ways to develop a power testing capability testing framework. They sought a means to measure the lowest state-of-charge (SoC) at which a constant power pulse can be fully completed. By testing battery cells to their minimum discharge voltage limit, the scientists believe they can ascertain the maximum amount the cell can be discharged before the power necessary for landing cannot be provided.

They performed their tests using various operating conditions, with the aim of replicating the conditions a cell may be subjected to under eVTOL landing (extended high-power discharge at low SoC). The study replicated an eVTOL landing by performing a high-power discharge pulse for an extended duration at low SoC. By doing so, the information gleaned from the testing model can indicate the SoC region necessary for reserve flight.

Ascertaining remaining battery power is crucial to safe eVTOL operations.

[subhed] 7.5%, 14%, 27%

What the testing methodology produced is a three-dimensional characteristic map using pulse power, pulse duration, and temperature inputs to output the lowest SoC at which a constant power pulse can be fully completed. The study was able to distinguish between both calendar-aged and cycle-aged cells. This new method yields an average maximum absolute percentage error which doesn’t exceed 7.5%.

In worst case landing scenarios, the lowest SoC for calendar aged cells is 14%; for cycle aged cells the lowest SoC is 27%. Doing so highlights the substantial loss in power capability from cycle ageing and highlights the need to track battery health to increase performance and safety.