A method for operating a turbocharged internal combustion engine having an after-treatment device for treating exhaust gas discharged from the turbocharger, wherein exhaust gas from the engine is passed through a variable-geometry mechanism for regulating power produced by the turbine. The method comprises the steps of measuring a boost pressure of the air delivered to the intake of the engine, measuring a temperature of the exhaust gas delivered to the after-treatment device, causing the temperature of the exhaust gas delivered to the after-treatment device to substantially match a predetermined target temperature by controlling the variable-geometry mechanism of the turbine to control the amount of power extracted by the turbine, and causing the boost pressure to substantially match a predetermined target boost pressure by either inputting mechanical power into or extracting mechanical power from the turbocharger, as required, using a power addition/extraction device, such as a motor/generator, coupled to the turbocharger.