TURBO COMPOUND SYSTEM CONTROL DEVICE

An object is to enable low fuel-consumption operation of an engine by controlling a back pressure and a power generation amount taking account of a trade-off relationship between deterioration of fuel efficiency due to an increase in pumping loss due to a back-pressure rise of the engine and improvement of fuel efficiency due to recovery of exhaust energy by a turbo compound. A control system includes: a turbocharger 5; a turbine generator 7; a power-generation-amount control unit 51 of the turbine generator 7; a back-pressure control unit 53 configured to control a back pressure of the engine; and a turbo controller 17 including a power-generation-mode setting unit 31 to set the turbine generator to a low fuel-consumption mode, the turbo controller 17 being configured to, in the low fuel-consumption mode, control the power-generation-amount control 51 unit and the back-pressure control unit 53 so that the engine 3 continues low fuel-consumption operation, on the basis of a relationship between an increase in pumping loss due to a back-pressure rise for rotating the turbine generator 7 and a recovery amount of exhaust energy by the turbine generator 7.