The innovation here is in the packaging, fitting the brushless inductive power coupling for the field excitation inside the shaft. T
he idea of using a high frequency rotating transformer or inductive coupler to transmit current to the field winding without using brushes and slip rings has been investigated by a number of companies, universities, and national labs.

A good survey paper of excitation systems for wound field synchronous machines or electrically excited synchronous machines is.

J. K. Nøland, S. Nuzzo, A. Tessarolo and E. F. Alves, "Excitation System Technologies for Wound-Field Synchronous Machines: Survey of Solutions and Evolving Trends," in IEEE Access, vol. 7, pp. 109699-109718, 2019, doi: 10.1109/ACCESS.2019.2933493.

An example of a high frequency transformer or inductive coupling developed by General Motors is detailed for example in the following paper.

C. Stancu, T. Ward, K. M. Rahman, R. Dawsey and P. Savagian, "Separately Excited Synchronous Motor With Rotary Transformer for Hybrid Vehicle Application," in IEEE Transactions on Industry Applications, vol. 54, no. 1, pp. 223-232, Jan.-Feb. 2018, doi: 10.1109/TIA.2017.2757019.

Below is some work done by Oak Ridge National Lab on rotating high frequency transformers for field excitation.

T. Raminosoa, R. H. Wiles and J. Wilkins, "Novel Rotary Transformer Topology With Improved Power Transfer Capability for High-Speed Applications," in IEEE Transactions on Industry Applications, vol. 56, no. 1, pp. 277-286, Jan.-Feb. 2020, doi: 10.1109/TIA.2019.2955050.

The field excitation current is typically provided using a single phase high frequency transformer (20 to 100 kHz switching frequency) which is then rectified by a rotating full bridge rectifier.

Just to clear up some of the misconceptions in the comments. In state-of-the-art electric vehicles there are basically three main machine topologies that are used for the main traction machine.

- Interior permanent magnet synchronous machines (IPMSMs): A large number of OEMs and suppliers use/supply this motor topology, e.g., General motors, Tesla model 3, Ford, etc.

- Induction machines (IMs): Also used by a large number of OEMs and suppliers, e.g., Tesla model S and X, G.M. for assist motors, etc.

- Wound field synchronous machines (WFSMs) [in Europe more commonly known as electrically excited synchronous machines (EESMs) but they are the same thing] - Currently used in Renault and some BMW models. A large number of suppliers are developing them.

Each of the machine topologies has tradeoffs compared to the others, cost, manufacturing CapEx, supply chain risk, drive cycle efficiency, difficulty of control, failure modes, cooling complexity, etc.

WFSMs or EESMs have some potential advantages over IPMSMs or IMs for some applications.

- They don't contain rare earth permanent magnets eliminating the supply chain and price volatility associated with them.

- In terms of drive cycle efficiency generally they are more efficient than IMs and if the drive cycle is dominated by moderate torques and highspeeds they can exceed the drive cycle efficiencies of IPMSMs.

- They are very easy to field weaken and theoretically can have an infinite constant power speed range.

- The field excitation can be controlled to provide unity power factor potentially allowing the stator inverter to be downsized.

The main negatives of WFSMs or EESMs compared to IPMSMs or IMs are:

- The field excitation is more complicated and requires power electronics either for brushes and slip rings or inductive power transfer approaches.

- The cooling of the field winding is difficult and typically spray/jet cooling of the end turns or at a minimum through shaft cooling.

- The control of WFSMs or EESMs is considerably more complicated than IPMSMs or IMs.