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

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

the electrically driven vehicle ( 3 ) is coupled to a charging source ( 2 ) external to the electrically driven vehicle ( 3 );

a charging process of the electrical energy storage device ( 4 ) is carried out with the coupled charging source ( 2 ) external to the electrically driven vehicle ( 3 ) and a charging device ( 6 ) of the electrically driven vehicle ( 3 );

a battery voltage (U Batt ) of the electrical energy storage device ( 4 ) is determined during the charging process;

the battery voltage (U Batt ) of the electrical energy storage device ( 4 ) is compared with a charging voltage of the charging source ( 2 ) external to the electrically driven vehicle ( 3 ) by the charging device ( 6 );

a voltage transformer ( 7 ) of the charging device ( 6 ) of the electrically driven vehicle ( 3 ) is operated in dependence on the comparison of the battery voltage (U Batt ) with the charging voltage;

wherein in a first phase of the charging process of the electrical energy storage device ( 4 ), the electrical energy storage device ( 4 ) is charged, in dependence on a charging current (I L ) of the charging source ( 2 ) external to the electrically driven vehicle ( 3 ), with a first DC voltage (U 1 ) as the charging voltage of the charging source ( 2 ) external to the electrically driven vehicle ( 3 );

wherein in the first phase of the charging process the electrical energy storage device ( 4 ) is coupled directly to the charging source ( 2 ) external to the electrically driven vehicle ( 3 ) by a bypass circuit ( 8 ) of the charging device ( 6 ) such that the charging current (I L ) of the charging source ( 2 ) external to the electrically driven vehicle ( 3 ) flows directly via the bypass circuit ( 8 ) to the electrical energy storage device ( 4 ), wherein the voltage transformer ( 7 ) is bypassed in the first phase of the charging process by the bypass circuit ( 8 );

wherein in a second phase of the charging process following the first phase, the electrical energy storage device ( 4 ) is charged, in dependence on a choke current (I D ) of the voltage transformer ( 7 ) which is lower than the charging current (I L ), with a second DC voltage (U 2 ) of the voltage transformer ( 7 ) which is higher than the charging voltage;

wherein the bypass circuit ( 8 ) is switched current-free by an isolating element ( 9 ) in the second phase of the charging process, as a result of which the current flow of the charging current (I L ) 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 (I L ) flows from the charging source ( 2 ) via the voltage transformer ( 7 ) such that the electrical energy storage device ( 4 ) is charged indirectly via the voltage transformer ( 7 );

wherein in the second phase of the charging process, the charging current (I L ) of the charging source external to the electrically driven vehicle ( 3 ) is adapted in dependence on the choke current (I D ), wherein a current value of the charging current (I L ) is adapted to a current value of the choke current (I D ).

2 . The method according to claim 1 , wherein the voltage transformer ( 7 ) is operated in dependence on the battery voltage (U Batt ) of the electrical energy storage device ( 4 ) such that the choke current (Ip) is impressed in a choke (L) of the voltage transformer ( 7 ) in dependence on the charging current (I L ).

3 . 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 (U Batt ) of the electrical energy storage device ( 4 ) during the charging process;

an evaluation unit ( 17 ) which is configured to compare the battery voltage (U Batt ) 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 (I D ) lower than the charging current (I L ) in dependence on a comparison between the battery voltage (U Batt ) 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 (I L );

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 (I L ) of the charging source ( 2 ) external to the electrically driven vehicle ( 3 ) with a first direct voltage (U 1 ) 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 (I D ) of the voltage transformer ( 7 ) with a second DC voltage (U 2 ) 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 (I L ) 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 (I L ) 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 (I L ) of the charging source external to the electrically driven vehicle ( 3 ) can be adapted in dependence on the choke current (I D ), wherein a current value of the charging current (I L ) can be adapted to a current value of the choke current (Ip).

4 . The charging system ( 1 ) according to claim 3 , wherein a first connection side of the bypass circuit ( 8 ) is connected to a primary side of the voltage transformer ( 7 ) and a second connection side of the bypass circuit ( 8 ) is connected to a secondary side of the voltage transformer ( 7 ).

5 . The charging system ( 1 ) according to claim 4 , wherein the isolating element ( 9 ) is connected between the first connection side of the bypass circuit ( 8 ) and the second connection side of the bypass circuit ( 8 ) and wherein the voltage transformer ( 7 ) can be bridged with the isolating element ( 9 ).

6 . The charging system ( 1 ) according to claim 3 , wherein the voltage transformer ( 7 ) is a current-controlled step-up converter.