A DRIVE SYSTEM AND A METHOD FOR CONTROLLING A DRIVE SYSTEM OF A HYBRID WORKING MACHINE

A method for controlling a hybrid drive system in a working machine, the system comprising: an internal combustion engine; a torque converter having an input shaft operatively coupled to the engine and an output shaft operatively coupled to a gearbox; an energy storage system operatively coupled to the gearbox for providing power to and receiving power from a drive shaft via the gearbox, said drive shaft being operatively coupled to propulsion means of the working machine; and work hydraulics operatively connected to the engine; the method comprising: determining a torque converter slip; and if the torque converter slip is above a predetermined threshold level, discharging the energy storage system to provide energy stored in the energy storage system to the drive shaft for vehicle propulsion.