Method and device for damping of LCL filter during start-up of an electronic appliance

1. An electronic appliance comprising an LCL filter on a grid side of the electronic appliance and an active front end rectifier (AFE) on a load side of the electronic appliance, wherein the LCL filter comprises grid side inductors and the active front end rectifier (AFE) is connected to the LCL filter, wherein damping components are provided in parallel to the grid side inductors, wherein the damping components are connectable to grid side ends of the grid side inductors via switches, and wherein the damping components are disconnected from the grid side ends of the grid side inductors as soon as the active front end rectifier (AFE) has synchronized to the grid.

2. The electronic appliance according to claim 1 , wherein the damping components comprise damping resistors, secondary windings with a switch or the modification of a magnetic core with a switch.

3. The electronic appliance according to claim 1 , wherein the resistance R damp of the damping components is close to an impedance of the grid side inductors L 1 , L 2 , and L 3 at a resonance frequency (f res ) of a LC circuit with the grid, fulfilling the equation

| R damp |≈|2π f res L 1,2,3 |.

4. The electronic appliance according to claim 1 , wherein the damping components are only connected to the grid side ends of the grid side inductors when the electronic appliance is connected to the grid via grid switches and the active front end rectifier (AFE) is not modulating.

5. The electronic appliance according to claim 1 , wherein the damping components connected to the grid side ends of the grid side inductors during start-up of the electronic appliance for 0 ms-500 ms.

6. The electronic appliance according to claim 1 , wherein the damping components are directly connected to all inductors of the LCL filter.

7. The electronic appliance according to claim 1 , wherein the resistance of the damping components is between 0.1 ohm and 100 ohm.

8. The electronic appliance according to claim 2 , wherein the resistance R damp of the damping components is close to the impedance of the grid side inductors at the resonance frequency (f res ) of the LC circuit with the grid, fulfilling the equation

| R damp |≈|2π f res L 1,2,3 |.

9. The electronic appliance according to claim 2 , wherein the damping components are only connected to the grid side ends of the grid side inductors when the electronic appliance is connected to the grid via grid switches and the active front end rectifier (AFE) is not modulating.

10. The electronic appliance according to claim 2 , wherein the damping components are disconnected from the grid side ends of the grid side inductors as soon as the active front end rectifier (AFE) has synchronized to the grid.

11. The electronic appliance according to claim 3 , wherein the damping components are disconnected from the grid side ends of the grid side inductors as soon as the active front end rectifier (AFE) has synchronized to the grid.

12. The electronic appliance according to claim 4 , wherein the damping components are disconnected from the grid side ends of the grid side inductors as soon as the active front end rectifier (AFE) has synchronized to the grid.

13. The electronic appliance according to claim 2 , wherein the damping components are connected to the grid side ends of the grid side inductors during start-up of the electronic appliance for 0 ms-500 ms.

14. The electronic appliance according to claim 3 , wherein the damping components are connected to the grid side ends of the grid side inductors during start-up of the electronic appliance for 0 ms-500 ms.

15. The electronic appliance according to claim 4 , wherein the damping components are connected to the grid side ends of the grid side inductors during start-up of the electronic appliance for 0 ms-500 ms.

16. An electronic appliance according to claim 1 , wherein the electronic appliance is a low harmonic drive, an active rectifier, or a grid converter.

17. An electronic appliance according to claim 1 , wherein the electronic appliance is an active front end or grid converter.

18. The electronic appliance according to claim 1 , wherein the resistance R damp of the damping components is close to an impedance of the grid side inductors L 1 , L 2 , and L 3 at a resonance frequency (f res ) of a LC circuit with the grid, fulfilling the equation

| R damp |≈(1±0,1)×|2π f res L 1,2,3 |.

19. A method for damping of an LCL filter during start-up of an electronic appliance an LCL filter, wherein a converter is a two-level, a three-level or a multilevel inverter, comprising an LCL filter on the grid side of the electronic appliance and an active front end rectifier (AFE) on the load side of the electronic appliance, wherein an LCL filter comprises grid side inductors and an active front end rectifier (AFE) is connected to the LCL filter, wherein damping components are provided in parallel to the grid side inductors, wherein the damping components are connectable to grid side ends of the grid side inductors via switches, the method comprising the steps of

connecting the electronic appliance to the grid via grid switches;

connecting the damping components to the grid side ends of the grid side inductors via switches when the active front end rectifier (AFE) is not modulating; and

disconnecting the damping components from the grid side ends of the grid side inductors as soon as the active front end rectifier (AFE) has synchronized to the grid.

20. The method according to claim 19 , wherein the damping components are connected to the grid side ends of the grid side inductors in a default state of the electronic appliance.