Resonant electrical machine

An electrical machine and driving circuitry for an electrical machine, wherein the electrical machine has one or more electromagnetic resonant frequencies based on the connection of a source of a three-phase driving signal to respective phases of the stator winding via respective capacitors of a plurality of capacitors arranged in series, wherein the respective capacitors are housed within a rotor of the electrical machine. The rotor 400 includes a rotor shaft 410, a rotor body 415 mounted to the rotor shaft 410, and rotor windings 490 mounted to the rotor body. Capacitors 420A-C are located within the rotor of the electrical machine. The rotor 400 may also include switching devices 430 for connecting an inverter 470 (i.e. a source of a three-phase driving signal) to stator windings 480 via the capacitors. The switching devices may allow switching between a first arrangement wherein the three-phase driving signal is connected to the stator windings via the respective associated capacitors, and one or more other arrangements wherein the driving signal is connected to the stator windings without the respective associated capacitors. The switching devices may comprise slip rings.