Method and charging system for charging an electrical energy storage device of an electrically driven vehicle

A charging system (1) for charging an electrical energy storage device (4) of an electrically driven vehicle (3), comprising:

• a charging source (2) external to the electrically driven vehicle (3) for providing a charging voltage;
• a charging port (5) of the electrically driven vehicle (3) for coupling the electrically driven vehicle (3) to the charging source (2) external to the vehicle (3);
• a charging device (6) of the electrically driven vehicle (3) for performing a charging process of the electrical energy storage device (4);
• a determination device (16) for determining a battery voltage (UBatt) of the electrical energy storage device (4) during the charging process;
• an evaluation unit (17) which is configured to compare the battery voltage (UBatt) of the electrical energy storage device (4) with the charging voltage of the charging source (2) external to the electrically driven vehicle (3);
• and
• a voltage transformer (7) of the charging device (6) for providing a choke current (ID) lower than the charging current (IL) in dependence on a comparison between the battery voltage (UBatt) and the charging voltage;
• wherein the charging device (6) has a bypass circuit (8) for charging the electrical energy storage device (4) in dependence on the charging current (IL);
• wherein the bypass circuit (8) is connected between a positive potential of the charging source (2) external to the electrically driven vehicle (3) and a positive potential of the electrical energy storage device (4) and is connected between a negative potential of the charging source (2) external to the electrically driven vehicle (3) and a negative potential of the electrical energy storage device (4);
• wherein the charging device (6) is configured such that, in a first phase of the charging process of the electrical energy storage device (4), the electrical energy storage device (4) can be charged in dependence on a charging current (IL) of the charging source (2) external to the electrically driven vehicle (3) with a first direct voltage (U1) as charging voltage of the charging source (2) external to the electrically driven vehicle (3) of the electrical energy storage device (4) via the bypass circuit (8);
• wherein the charging device (6) is configured such that, in a second phase of the charging process following the first phase, the electrical energy storage device (4) is charged in dependence on the choke current (ID) of the voltage transformer (7) with a second DC voltage (U2) of the voltage transformer (7) which is higher than the charging voltage;
• wherein in the second phase of the charging process the bypass circuit (8) is switched current-free by an isolating element (9), as a result of which the current flow of the charging current (IL) of the charging source (2) external to the electrically driven vehicle (3) to the electrical energy storage device (4) via the bypass circuit (8) is interrupted and the charging current (IL) flows from the charging source (2) via the voltage transformer (7) such that the electrical energy storage device (4) can be charged indirectly via the voltage transformer (7);
• wherein the charging current (IL) of the charging source external to the electrically driven vehicle (3) can be adapted in dependence on the choke current (ID), wherein a current value of the charging current (IL) can be adapted to a current value of the choke current (Ip).