Patent ID: 8564981

Claim:
A device for converting a DC voltage into an AC voltage and vice versa comprising at least one phase leg, each phase leg having a first voltage source and a first passive energy storage element connected in series between a first DC terminal and a first AC terminal and a second passive energy storage element and a second voltage source connected in series between the first AC terminal and a second DC terminal, where each of the voltage sources comprises at least a first and a second submodule in series-connection, each submodule comprising at least two power electronic switches connected in parallel with at least one capacitor, a passive electronic filter comprising passive energy storage elements is arranged between the first and second voltage sources as well as the first AC terminal, said filter comprising said first and second energy storage elements, a third energy storage element connected in series between the first and second energy storage elements, a fourth energy storage element having two ends, a first end connected to a junction between the first energy storage element and the third energy storage element and a second end coupled to the AC terminal and a fifth energy storage element having two ends, a first end connected to a junction between the second energy storage element and the third energy storage element and a second end coupled to the AC terminal, wherein the energy storage elements comprise elements of two different types, capacitive and inductive energy storage elements, with values selected to provide reduction of frequency components at three times the fundamental frequency of the AC voltage, wherein the energy storage elements comprise elements with values selected to provide reduction of frequency components at two times the fundamental frequency of the AC voltage, and at least one capacitive element of the filter is a DC blocking element for stopping DC components from reaching the AC terminal.