A power control device is provided for controlling an electric machine in a vehicle trailer. The electric machine is coupled to at least one wheel of the vehicle trailer to be able to convert mechanical rotation power at the wheel and electric power at the electric machine into one another. The power control device is configured to control a mechanical power output and/or a mechanical power input of the electric machine and is configured to control the mechanical power output and/or the mechanical power input of the electric machine as a function of a present driving condition of a towing vehicle pulling the vehicle trailer.