Submodule as a hybrid cell for a modular multilevel converter
A submodule for a modular multilevel converter has ten semiconductor switches that can be switched off, four capacitors, six network nodes, and two terminals. The components are mounted such that different voltages are generated between the terminals of the submodule by controlling the semiconductor switches. This arrangement of components substantially improves the behavior of the converter and of the submodule in the event of a fault.
1. A submodule for a modular multilevel power converter, comprising:
a first semiconductor switch, a fourth semiconductor switch and a ninth semiconductor switch forming a first series connection between a first terminal and a second terminal of the submodule, with the first semiconductor switch directly connected in a forward direction to the fourth semiconductor switch at a first network node, and with the fourth semiconductor switch directly connected in the forward direction to the ninth semiconductor switch at a fourth network node, and the ninth semiconductor switch directly connected in the forward direction to the second terminal,
a second semiconductor switch, a fifth semiconductor switch and a tenth semiconductor switch forming a second series connection between the first terminal and the second terminal and connected in parallel with the first series connection, with the second semiconductor switch directly connected in a reverse direction to the fifth semiconductor switch at a second network node, and with the fifth semiconductor switch directly connected in the forward direction to the tenth semiconductor switch at a fifth network node, and the tenth semiconductor switch directly connected in the forward direction to the second terminal,
a third semiconductor switch directly connected in the forward direction between the first terminal and a third network node,
a sixth semiconductor switch directly connected in the forward direction between the fourth network node and the third network node,
a seventh semiconductor switch directly connected in the forward direction between the fifth network node and the third network node,
an eighth semiconductor switch directly connected in the reverse direction between a sixth network node and the second terminal,
a first capacitor directly connected between the first network node and the third network node,
a second capacitor directly connected between the second network node and the third network node,
a third capacitor directly connected between the fourth network node and the sixth network node, and
a fourth capacitor directly connected between the fifth network node and the sixth network node.
2. The submodule of claim 1 , wherein the first, second, third, fourth, fifth, sixth, seventh, eighth, ninth and tenth semiconductor switches are constructed so as to be able to conduct as well as disconnect current flow in the forward direction, while only being able to conduct current flow in the reverse direction.
3. The submodule of claim 1 , wherein the first series connection is constructed identically to the second series connection.
4. A modular multilevel power converter, comprising a plurality of submodules, each of the plurality of the submodules constructed as set forth in claim 1 , with at least two of the plurality of the submodules connected in series to form a converter arm of the modular multilevel power converter and two converter arms connected in series at a connection point forming a converter phase, wherein the connection point forms a phase connector of the modular multilevel power converter.
5. The modular multilevel power converter of claim 4 , wherein an end of the converter arm, which is remote from the phase connector, forms an intermediate circuit connector of the multilevel power converter.
6. A method for operating a submodule constructed as set forth in claim 1 , comprising generating different voltages between the first terminal and the second terminal by switching operations of the first, second, third, fourth, fifth, sixth, seventh, eighth, ninth and tenth semiconductor switches.
7. The submodule of claim 1 constructed from two part-modules, wherein a first of the two part modules comprises the first, third, fourth, sixth, eighth and ninth semiconductor switches, the first and the third capacitor and the first, third, fourth and the sixth network nodes, and wherein a second of the two part modules comprises the second, third, fifth, seventh, eighth and tenth semiconductor switches, the second and the fourth capacitor and the second, third, fifth and the sixth network nodes.