SUBMODULE AS A PARALLEL SERIAL FULL BRIDGE FOR A MODULAR MULTILEVEL CONVERTER

Abstract

A submodule for a modular multilevel converter has nine 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.

Claims

1.-5. (canceled)

6. A submodule for a modular multilevel power converter, comprising: a first semiconductor switch, a fourth semiconductor switch and an eighth semiconductor switch forming a first series connection between a first connector and a second connector of the submodule, with the first semiconductor switch connected to the fourth semiconductor switch at a first network node, and with the fourth semiconductor switch connected to the eighth semiconductor switch at a fourth network node, the first semiconductor switch configured to disconnect a current flowing from the first network node to the first connector, the fourth semiconductor switch configured to disconnect a current flowing from the first network node to the fourth network node, and the eighth semiconductor switch configured to disconnect a current flowing from the second connector to the fourth network node; a second semiconductor switch, a sixth semiconductor switch and a ninth semiconductor switch forming a second series connection between the first connector and the second connector and connected in parallel with the first series connection, with the second semiconductor switch connected to the sixth semiconductor switch at a second node, and with the sixth semiconductor switch connected to the ninth semiconductor switch at a fifth node, the second semiconductor switch configured to disconnect a current flowing from the second network node to the first connector, the sixth semiconductor switch configured to disconnect a current flowing from the second network node to the fifth network node, and the ninth semiconductor switch configured to disconnect a current flowing from the second connector to the fifth network node; a third semiconductor switch, a fifth semiconductor switch and a seventh semiconductor switch forming a third series connection between the first connector and the second connector and connected in parallel with the first and the second series connection, with the third semiconductor switch connected to the fifth semiconductor switch at a third node, and with the fifth semiconductor switch connected to the seventh semiconductor switch at a sixth node, the third semiconductor switch configured to disconnect a current flowing from the first connector to the third network node, the fifth semiconductor switch configured to disconnect a current flowing from the sixth network node to the third network node, and the seventh semiconductor switch configured to disconnect a current flowing from the sixth network node to the second connector; a first capacitor connected between the first node and the third node; a second capacitor connected between the second node and the third node; a third capacitor connected between the fourth node and the sixth node; and a fourth capacitor connected between the fifth node and the sixth node.

7. The submodule of claim 6, wherein the first, second, third, fourth, fifth, sixth, seventh, eighth and ninth semiconductor switches are connected so as to be able to connect and disconnect the current flow in a current flow direction, and to only conduct the current flow in a direction opposite to the current flow direction.

8. (canceled)

9. A modular multilevel power converter, comprising a plurality of the submodules of claim 6, 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.

10. The modular multilevel power converter of claim 9, wherein an end of the converter arm, which is remote from the phase connector, forms an intermediate circuit connector of the multilevel power converter.

11. A method for operating a submodule as claimed in claim 6, comprising generating different voltages between the first connector and the second connector by switching operations of the first, second, third, fourth, fifth, sixth, seventh, eighth and ninth semiconductor switches.

12. A method for producing a submodule as claimed in claim 6 from two part-modules, wherein a first of the two part modules comprises the first, third, fourth, fifth, seventh and eighth semiconductor switches, the first and the third capacitor and the second, third, fourth and the sixth network nodes, and wherein a second of the two part modules comprises the first, third, fifth, sixth, seventh and ninth semiconductor switches, the second and the fourth capacitor and the second, third, fifth and the sixth network nodes.

Description

[0025] The invention is further described and explained below with reference to the exemplary embodiments that are illustrated in the figures, in which:

[0026] FIG. 1 shows the construction of the submodule in accordance with the invention,

[0027] FIG. 2 shows the construction of the modular multilevel power converter, and

[0028] FIG. 3 shows switching states of the submodule.

[0029] FIG. 1 illustrates an exemplary embodiment of a submodule 1 in accordance with the invention. A component is arranged in each case between the individual network nodes N1 . . . N6. In this case, the individual components are arranged directly between the network nodes N1 . . . N6 and connects the respective two network nodes to one another or one of the network nodes N1 . . . N6 to one of the connectors 11, 12. The voltage between the connectors 11, 12 of the submodule 1 is referred to with U.sub.SM. In this case, in an advantageous manner the third semiconductor switch S3, the fifth semiconductor switch S5 and the seventh semiconductor switch S7 are dimensioned in each case for the full current-carrying capacity of the submodule 1. The remaining semiconductor switches S1, S2, S4, S6, S8, S9 are to be designed in each case to half of the current-carrying capacity.

[0030] It is apparent that the construction of the submodule 1 extends in a mirror-symmetrical manner with respect to an axis that is formed by the connectors 11, 12 of the submodule 1. As a consequence, it is possible to construct the submodule 1 from two identical part-modules 7 that are connected to one another in each case at the connectors 11, 12, at the third network node N3 and at the sixth network node N6. A part-module comprises in this case the connectors 11, 12, the first, third, fourth, fifth, seventh and eight semiconductor switches S1, S3, S4, S5, S7, S8, the first and the third capacitor C.sub.1,1, C.sub.2,1 and the first, third, fourth and the sixth network nodes N1, N3, N4, N6. In order to form a submodule 1 from two structurally identical part-modules 7, the two structurally identical part-modules 7 are connected to one another in an electrically conductive manner in each case at the connectors 11, 12, the third network node N3 and the sixth network node N6.

[0031] In this case, the third semiconductor switch S3, the fifth semiconductor switch S5 and the seventh semiconductor switch S7 can likewise be designed for half the current-carrying capacity of the submodule 1. The full current-carrying capacity then results from the parallel connection by virtue of the construction of the submodule 1 from the two part-modules 7. As a consequence, it is possible to design all the semiconductor switches within the part-module 7 as identical, in particular with regard to the current-carrying capacity. This increases the common parts and increases the ease of maintenance of the submodule 1. The production of the submodule is also particularly cost-effective and reliable by virtue of the large quantity of common parts in the case of the semiconductor switches S1 . . . S9.

[0032] FIG. 2 illustrates an exemplary embodiment of a modular multilevel power converter 2 that is constructed from the proposed submodules 1. In order to avoid repetitions, reference is made to the description with regard to FIG. 1 and also to the reference characters introduced there. These submodules 1 are arranged in series in their connectors 11, 12, which are only illustrated in one converter arm 3 for the sake of clarity, and said submodules form the converter arm 3. Two converter arms 3 that are arranged in series form the converter phase 4. The connecting point of the converter arms 3 forms the phase connector L1, L2, L3. The converter phases 4 are arranged between the intermediate circuit connectors L+, L−. In order to improve the ability to provide regulation or control, it has proven advantageous to supplement the series connection of the converter arms 3 by inductances 20 that are arranged in series between the converter arm 3 and the respective intermediate circuit connector L+, L−. In each case, the module voltage U.sub.SM prevails at the individual submodules 1 and the module voltage results from the switching states of the semiconductor switches S1 . . . S9.

[0033] The present exemplary embodiment is designed as a three-phase modular multilevel power converter 2.

[0034] FIG. 3 illustrates the possible switching states of the semiconductor switches S1 . . . S9 and the voltage U.sub.SM which then results between the connectors 11, 12 of the submodule 1. In order to avoid repetitions, reference is made to the description with regard to FIGS. 1 and 2 and also to the reference characters introduced there. In this case, the first and the second semiconductor switch S1, S2, the fourth and the sixth semiconductor switch S4, S6, the eighth and the ninth semiconductor switch S8, S9 in each case are actuated identically, in other words switched on, which is characterized in the table by a 1, or are switched off, which is characterized by a 0. As a consequence, it becomes clear that only one actuation unit is required for the realization of the submodule 1 from two part-modules 7, since the semiconductor switches that are arranged in a mirror-inverted manner always assume the same switching state.

[0035] In the preferred switching states that are numbered consecutively 1 to 8 the submodule voltage U.sub.SM results regardless of the current flow direction of the current through the submodule 1. Only the state BLOCK in which all the semiconductor switches S1 . . . S9 are switched off provides different submodule voltages U.sub.SM depending on the current flow direction with the result that this state is preferably not used for the control of the submodule 1.

[0036] In summary, the invention relates to a submodule for a modular multilevel power converter having:

[0037] nine semiconductor switches that can be switched off

[0038] four capacitors

[0039] six network nodes

[0040] two connectors,

wherein the components are arranged in such a manner that different voltages are generated between the connectors of the submodule in the case of actuating the semiconductor switches that can be switched off. In this case, the behavior of the power converter and of the submodule can be considerably improved in the event of failure.