Abstract: A turbocharger system comprises: a gas input for receiving exhaust gases from an engine; a first turbocharger comprising a first compressor driven by a first turbine, arranged to be driven by received exhaust gases and providing a compressed air output defining a boost pressure a second turbocharger, arranged to be driven by exhaust gases passing through the first turbocharger or exhaust gases received at the gas input and being coupled to an electrical generator operative to provide electrical power, the first turbine not being coupled to an electrical generator; and a controller. A diversion mechanism may be configured to affect the flow of exhaust gases between the gas input and the first turbocharger. The controller may be configured to adjust the operation of the electrical generator independently from the operating mode of the associated engine, to affect the boost pressure.

Abstract: Exhaust gases can bypass a turbocharger to reduce its speed, but energy in the gases is then lost. A brake for a turbocharger can be implemented using at least one rotor driven by the turbocharger rotatable shaft and at least one stator. Either the rotor or stator are magnetic, the other being ferrous, such that rotation of the shaft induces eddy currents in the ferrous part, thereby extracting energy from the shaft. The magnetic field experienced by the ferrous part can be adjusted in response to an input parameter to control the level of braking.