Charging system of an internal combustion engine

A method for providing boost air (44) for cylinders (12) of an internal combustion engine (10), comprising:

• directing an exhaust gas mass flow (45) from the cylinders (12) to a first energy recovery turbine (25) and a second energy recovery turbine (26) that are connected in parallel so that the first and second energy recovery turbines (25, 26) receive selected proportions of the exhaust gas mass flow (45),
• using energy from the first energy recovery turbine (25) to rotate a first shaft (31) and to thereby operate a compressor (22) via the first shaft (31) to compress intake air (41) to compressed air (42) at a pressure that is higher than a boost pressure of the internal combustion engine (10),
• directing the compressed air to a boost air cooler (23) that cools the compressed air (42) compressed by the compressor (22) and thereby produces cooled air (43)
• using energy from the second energy recovery turbine (26) to rotate a second shaft (31), the second shaft (31) being connected to a cooling turbine (24) and to an energy sink so that energy from the second shaft (31) is used for further cooling the compressed air (42) from the boost air cooler (23) and then relaxing the compressed air (42) to the boost pressure and feeding a resulting boost air (44) directly from the cooling turbine (24) to the cylinders (12) and the energy from the second shaft (31) then is transmitted to the energy sink,
• wherein the proportion of exhaust gas mass flow (45) directed to the first energy recovery turbine (25) is selected to control compression of the intake air (41), and the proportion of the exhaust gas mass flow (45) directed to the second energy recovery turbine (26) rotates the second shaft (32) and rotational energy from the second shaft (32) controls the further cooling of the cooled air from the boost air cooler (23) by the cooling turbine (24) and the rotational energy from the second shaft (32) also is transmitted to the energy sink.