Method and device for charging an electric energy storage system in a vehicle

A method for the control of a charge operation and the State of Charge (SOC) of an electrical Energy Storage System (ESS) comprising a multitude of cells, the ESS electrically connected to a propulsion system of a vehicle in order to power an Electric Motor (EM), the method comprising the steps of:

• Charging the ESS from an electrical power source, e.g. the grid, when the vehicle is at standstill,
• Stop the charging when the SOC level of the ESS (SOCESS) is above a maintenance limit for the SOC level of the ESS (SOCML),
• Monitoring the ESS and/or performing a balance operation of the ESS after the ESS has been charged to a SOC level above the maintenance limit for the SOC level of the ESS (SOCML),
• Deliberately discharging the ESS to lower the SOC level, wherein the SOC level of the ESS (SOCESS) is reduced to a take-off limit for the SOC level of the ESS (SOCTOL) before there is an upshift from the starting gear when the vehicle is started and driven after the charging, the take-off limit for the SOC level of the ESS (SOCTOL) being set such that the increase of SOC level of the ESS (SOCESS) due to charging of the ESS by regenerative braking of the EM during the upshift does not cause the SOC level of the ESS (SOCESS) to reach a driving limit for the SOC level of the ESS (SOCDL), wherein the driving limit for the SOC level of the ESS (SOCDL) is preferably set such that the ESS does not deteriorate.