Energy conversion apparatus comprising: an electrical machine including a rotor arranged to rotate about an axis, the rotor defining a first cavity therein; power electronic circuitry arranged at least partially around the axis and defining a second cavity therein, the power electronic circuitry being positioned adjacent to the electrical machine; a heat pipe positioned within the first cavity of the rotor and within the second cavity defined by the power electronic circuitry, the heat pipe being arranged to receive thermal energy from the rotor; and a cooling arrangement positioned at least partially within the second cavity and arranged to receive thermal energy from the power electronic circuitry and from the heat pipe.