A supercharging system (6) for an internal combustion engine includes a turbo charging device with a turbine (7) and a compressor (8), the compressor having a compressor shaft (8a); a planetary gear (25) coupled to the compressor shaft (8a) and a drive shaft (32); a clutch unit (18); a power transmission for connecting a crank shaft (4) of the combustion engine (1) to the drive shaft (32) via the clutch unit (18); and an electric motor or electric generator (20) connected to the drive shaft (32). The compressor shaft (8a) is at least on one end movably arranged between the compressor (8) and the planetary gear (25) to allow relative movements between the compressor (8) and the planetary gear (25).