Power supporting arrangement for a power grid

1. A power supporting arrangement for a power grid, the power supporting arrangement comprising:

first, second, third and fourth voltage source converters, each voltage source converter having a respective AC side and a respective DC side;

a DC link interconnecting the DC sides of the first, second, third and fourth voltage source converters;

first and second switching arrangements, each switching arrangement having a number of settable positions;

a first synchronous machine; and

a second synchronous machine;

wherein the AC side of the second voltage source converter is connected to the power grid and the first switching arrangement is connected between the first synchronous machine, the AC side of the first voltage source converter and the power grid, thereby making the first voltage source converter into a machine side converter and the second voltage source converter into a grid side converter;

wherein the AC side of the fourth voltage source converter is connected to the power grid and the second switching arrangement is connected between the second synchronous machine, the AC side of the third voltage source converter and the power grid, thereby making the third voltage source converter into a machine side converter and the fourth voltage source converter into a grid side converter;

wherein the first switching arrangement is operable to selectively connect the first synchronous machine to the power grid in a first configuration and to the AC side of the first voltage source converter in a second configuration, wherein the first synchronous machine is connected to the power grid in a first settable position of the first switching arrangement in the first configuration and to the AC side of the first voltage source converter in a second settable position of the first switching arrangement in the second configuration; and

wherein the second switching arrangement is operable to selectively connect the second synchronous machine to the power grid in a first configuration and to the AC side of the third voltage source converter in the second configuration, wherein the second synchronous machine is connected to the power grid in a first settable position of the second switching arrangement in the first configuration and to the AC side of the third voltage source converter in a second settable position of the second switching arrangement in the second configuration.

2. The power supporting arrangement according to claim 1 , wherein, when the first switching arrangement is set in the second settable position, the power supporting arrangement is configured to provide reactive power and inertia support to the power grid, where the inertia is delivered from the first synchronous machine via the first and second voltage source converters and the DC link.

3. The power supporting arrangement according to claim 1 , wherein, when the first switching arrangement is set in the first settable position, the first synchronous machine is configured to supply reactive power and inertia to the power grid in parallel with the second voltage source converter providing reactive power support.

4. The power supporting arrangement according to claim 3 , wherein the first voltage source converter is configured to provide reactive power support to the power grid in parallel with the second voltage source converter and in parallel with the inertia and reactive power from the first synchronous machine.

5. The power supporting arrangement according to claim 1 , wherein, when the second switching arrangement is set in the second settable position, the power supporting arrangement is configured to provide reactive power and inertia support to the power grid, where the inertia is delivered from the second synchronous machine via the third and fourth voltage source converters and the DC link.

6. The power supporting arrangement according to claim 1 , wherein, when the second switching arrangement is set in the first settable position, the second synchronous machine is configured to supply inertia and reactive power to the power grid in parallel with the fourth voltage source converter providing reactive power support.

7. The power supporting arrangement according to claim 6 , wherein the third voltage source converter is configured to provide reactive power support to the power grid in parallel with the second voltage source converter and in parallel with the inertia and reactive power from the second synchronous machine.

8. The power supporting arrangement according to claim 1 , where the first and second settable positions of the second switching arrangement are set in the same way as in the first switching arrangement.

9. The power supporting arrangement according to claim 1 , wherein the first and second settable positions of the second switching arrangement are set in the opposite way compared with the first and second settable positions of the first switching arrangement.

10. The power supporting arrangement according to claim 1 , further comprising an energy storage system connected to the DC link via a further converter for supplying or receiving active power supporting the power grid.

11. A power supporting arrangement for a power grid, the power supporting arrangement comprising:

first, second, third and fourth voltage source converters, each voltage source converter having a respective AC side and a respective DC side;

a DC link interconnecting the DC sides of the first, second, third and fourth voltage source converters;

a first transformer for connection of each grid side voltage source converter to the power grid;

first and second switching arrangements, each switching arrangement having a number of settable positions;

a first synchronous machine; and

a second synchronous machine;

wherein the AC side of the second voltage source converter is connected to the power grid and the first switching arrangement is connected between the first synchronous machine, the AC side of the first voltage source converter and the power grid, thereby making the first voltage source converter into a machine side converter and the second voltage source converter into a grid side converter;

wherein the AC side of the fourth voltage source converter is connected to the power grid and the second switching arrangement is connected between the second synchronous machine, the AC side of the third voltage source converter and the power grid, thereby making the third voltage source converter into a machine side converter and the fourth voltage source converter into a grid side converter;

wherein the first switching arrangement is operable to selectively connect the first synchronous machine to the power grid in a first configuration and to the AC side of the first voltage source converter in a second configuration, wherein the first synchronous machine is connected to the power grid in a first settable position of the first switching arrangement in the first configuration and to the AC side of the first voltage source converter in a second settable position of the first switching arrangement in the second configuration; and

wherein the second switching arrangement is operable to selectively connect the second synchronous machine to the power grid in a first configuration and to the AC side of the third voltage source converter in a second configuration, wherein the second synchronous machine is connected to the power grid in a first settable position of the second switching arrangement in the first configuration and to the AC side of the third voltage source converter in a second settable position of the second switching arrangement in the second configuration.

12. The power supporting arrangement according to claim 11 , wherein the first transformer is a single winding transformer.

13. The power supporting arrangement according to claim 11 , further comprising a second transformer for connecting each synchronous machine and each grid side converter to the power grid.

14. The power supporting arrangement according to claim 13 , wherein the second transformer is a three-winding transformer comprising a first group of windings connected to a first bus leading to each synchronous machine, a second group of windings connected to a second bus leading to each grid side converter and a third group of windings for connection to the power grid.

15. A power supporting arrangement for a power grid, the power supporting arrangement comprising:

first, second, third and fourth voltage source converters, each voltage source converter having a respective AC side and a respective DC side;

a DC link interconnecting the DC sides of the first, second, third and fourth voltage source converters;

first and second switching arrangements, each switching arrangement having a number of settable positions;

a first synchronous machine; and

a second synchronous machine;

wherein the AC side of the second voltage source converter is connected to the power grid and the first switching arrangement is connected between the first synchronous machine, the AC side of the first voltage source converter and the power grid, thereby making the first voltage source converter into a machine side converter and the second voltage source converter into a grid side converter;

wherein the AC side of the fourth voltage source converter is connected to the power grid and the second switching arrangement is connected between the second synchronous machine, the AC side of the third voltage source converter and the power grid, thereby making the third voltage source converter into a machine side converter and the fourth voltage source converter into a grid side converter;

wherein the first switching arrangement is operable to selectively connect the first synchronous machine to the power grid in a first configuration and to the AC side of the first voltage source converter in a second configuration, wherein the first synchronous machine is connected to the power grid in a first settable position of the first switching arrangement in the first configuration and to the AC side of the first voltage source converter in a second settable position of the first switching arrangement in the second configuration;

wherein the second switching arrangement is operable to selectively connect the second synchronous machine to the power grid in a first configuration and to the AC side of the third voltage source converter in a second configuration, wherein the second synchronous machine is connected to the power grid in a first settable position of the second switching arrangement in the first configuration and to the AC side of the third voltage source converter in a second settable position of the second switching arrangement in the second configuration;

wherein, when the first switching arrangement is set in the first settable position, the first synchronous machine is configured to supply reactive power and inertia to the power grid in parallel with the second voltage source converter providing reactive power support; and

wherein, when the first switching arrangement is set in the second settable position, the power supporting arrangement is configured to provide reactive power and inertia support to the power grid, where the inertia is delivered from the first synchronous machine via the first and second voltage source converters and the DC link.

16. The power supporting arrangement according to claim 15 , wherein, when the second switching arrangement is set in the second settable position, the power supporting arrangement is configured to provide reactive power and inertia support to the power grid, where the inertia is delivered from the second synchronous machine via the third and fourth voltage source converters and the DC link.

17. The power supporting arrangement according to claim 15 , wherein, when the second switching arrangement is set in the first settable position, the second synchronous machine is configured to supply inertia and reactive power to the power grid in parallel with the fourth voltage source converter providing reactive power support.

18. The power supporting arrangement according to claim 15 , where the first and second settable positions of the second switching arrangement are set in the same way as in the first switching arrangement.

19. The power supporting arrangement according to claim 15 , wherein the first and second settable positions of the second switching arrangement are set in the opposite way compared with the first and second settable positions of the first switching arrangement.

20. The power supporting arrangement according to claim 15 , further comprising an energy storage system connected to the DC link via a further converter for supplying or receiving active power supporting the power grid.