Submodule as a hybrid cell of a modular multilevel converter

Abstract

The invention relates to a sub-module (1) for a modular, multi-stage converter (2), having ten turn-off semiconductor switches (S1, S2, S3, S4, S5, S6, S7, S8, S9, S10), four capacitors (C1.1, C1.2, C2.1, C2.2), six network nodes (N1, N2, N3, N4, N5, N6), two terminals (11, 12), wherein the components are arranged in such a way that different voltages are generated between the terminals (11, 12) of the sub-module (1) when the turn-off semiconductor switches are actuated. Here, the behavior of the converter and the sub-module (1) in the event of a fault is significantly improved.

Description

Technical Field

[0001] This invention relates to a submodule for a modular multi-stage converter. The invention also relates to a modular multi-stage converter. Furthermore, the invention relates to a method for operating such a submodule and a method for manufacturing such a submodule. Background Technology

[0002] A modular multistage converter is known from DE 101 03 031A1. Multistage converters are also called modular multistage converters, MMCs, or M2Cs. This type of converter has multiple sub-modules that can generate a stepped output voltage.

[0003] A modular multi-stage converter is a converter topology particularly suitable for high-voltage direct current (HVDC) applications and electric drives. The basic structure of a multi-phase converter includes two converter arms per phase, each implemented as a series connection of multiple submodules. Through this modular structure, each converter arm quantitatively mimics the desired voltage shape by either modulating a discrete voltage or short-circuiting a modulation terminal using each submodule. Here, the submodules can achieve regulation of different voltage levels.

[0004] Different submodule variants exist. The most common and known submodule types are half-bridge and full-bridge.

[0005] Here, the submodule contains switchable semiconductor switches, such as insulated-gate bipolar transistors (IGBTs), integrated gate commutated thyristors (IGCTs), gate turn-off thyristors (GTOs), and MOSFETs. Compared to thyristors, semiconductor switches can not only turn on current but also turn off current. Current turn-off can only be achieved in one current direction. In the opposite current direction, the turn-off semiconductor switch behaves like a diode. This behavior is either provided by the converter structure or achieved by means of a diode arranged in anti-parallel with the switching element of the semiconductor switch. Therefore, a turn-off semiconductor switch can turn current on and off in one current direction and conduct only in the other current direction. Therefore, current in the other current direction cannot be turned off. Summary of the Invention

[0006] The purpose of this invention is to improve the sub-modules of a modular multi-stage converter.

[0007] This invention is particularly based on the understanding that the proposed arrangement of semiconductor switches and capacitors can improve the erroneous behavior of submodules and modular multistage converters. Six switching states of the semiconductor switches can be defined, thereby generating five different output voltages at the terminals of the submodule. Furthermore, another switching state can be implemented, wherein, of course, different voltages are applied to the terminals through the submodule according to the current direction. Therefore, the six switching states described at the beginning for the regulation and control of submodules and modular multistage converters are particularly advantageous.

[0008] This circuit is used as a submodule in a modular multi-stage converter. Here, the submodule is used to actively switch six switching states relevant to normal operation, which result in different output voltages between the two terminals of the submodule. The first and second capacitors, as well as the third and fourth capacitors, are always connected in parallel accordingly. For a better overview, the modulated voltage of the parallel circuit consisting of the first and second capacitors will be referred to below as U. C1 Furthermore, the modulated voltage of the parallel circuit composed of the third and fourth capacitors is called U. C2 It can switch the following voltage states between the terminals of the submodule:

[0009] - The positive series connection of two capacitors in parallel corresponds to U C1 and U C2 sum

[0010] - Each single capacitor connected in parallel corresponds to U C1 or U C2 ,

[0011] - No voltage (terminal short circuit or freewheeling) and

[0012] -A parallel circuit of negative capacitors corresponds to -U C1 .

[0013] All of these states can be switched independently of the current direction, i.e., bidirectionally.

[0014] The submodule according to the invention is functionally similar to a series circuit of half-bridge and full-bridge. Here, the same voltage state can be switched between the terminals of the submodule. If the individual semiconductor switches are designed accordingly in the proposed arrangement and in the series circuit composed of half-bridge and full-bridge, the same number of semiconductors is obtained. If it is assumed that the same capacitor energy is installed in the proposed arrangement and in the series circuit composed of half-bridge and full-bridge, then the discharge amount in the event of a semiconductor failure in the arrangement according to the invention is only half that of the other two. If this semiconductor switch fails, only one capacitor in the parallel-connected capacitors is always short-circuited. Therefore, only half of the energy can be safely controlled in the submodule or converter.

[0015] The same erroneous behavior can be achieved by implementing the two submodules in parallel connection in both the half-bridge and full-bridge series connections. However, in this case, at least twelve switches must be installed instead of the ten switches in the arrangement according to the invention. Therefore, the goal of lower fault energy, i.e., energy in fault conditions, can be achieved using a significantly fewer number of semiconductor switches and semiconductor drivers. This makes the multi-stage converter, which is further modularized by submodules, significantly less complex, less expensive, and easier to control and regulate.

[0016] The basic structure of a submodule can be composed of two submodules because the submodule has mirror symmetry. Therefore, it is particularly advantageous that a submodule composed of two submodules can be constructed in a particularly simple and low-cost manner. Here, the submodule includes terminals, first, third, fourth, sixth, eighth, and ninth semiconductor switches, first and third capacitors, and first, third, fourth, and sixth network nodes.

[0017] The third and eighth semiconductor switches are formed by a parallel circuit consisting of one semiconductor switch from each of the two sub-modules, thus allowing the semiconductor switches to be designed to be smaller, for example, with half the current carrying capacity.

[0018] In the proposed structure, the third and eighth semiconductor switches can be designed for the full current-carrying capacity of submodule 1. The remaining semiconductor switches can be designed for only half the current-carrying capacity. Since the third and eighth semiconductor switches are implemented as a parallel circuit consisting of two semiconductor switches in the two submodules, the semiconductor switches in each submodule are designed for only half the current-carrying capacity. Therefore, all semiconductor switches in each submodule can be implemented with the same structure.

[0019] Furthermore, the semiconductor switches of these two modules can be driven in the same way. Therefore, for a submodule consisting of two modules, only one drive circuit can be used for six semiconductor switches, and the drive signals of the drive circuit are distributed in parallel to the two modules, so that the modules are driven synchronously.

[0020] A network node can be understood as a branch in an electronic circuit, also known as an electronic network. Therefore, at least three current paths meet at a network node.

[0021] The features and advantages can be summarized as follows. The symmetrical structure, particularly when using two or more sub-modules, is important for this invention as it generates two or more parallel current paths through the sub-modules. The number of parallel current paths is derived from the number of parallel sub-modules. Here, the first and second capacitors, as well as the third and fourth capacitors, form parallel circuits decoupled via diodes. This results in high availability because the sub-modules can continue to operate even if the semiconductors and / or capacitors fail. Significantly fewer semiconductors are required compared to increasing the number of modules to achieve similar redundancy while providing similar voltages across different voltage states. Simultaneously, the parallel connection of the capacitors allows for the design of smaller capacitances, especially half the size. In the event of damage, this reduces the potential for failure originating from the capacitors. In other words, as previously mentioned, failures in the capacitors are thus easier to handle because the existing stored energy is significantly lower. Furthermore, by using fewer semiconductors, the proposed structure can be manufactured significantly more simply and at a lower cost. Moreover, the failure probability is significantly reduced by using fewer semiconductors. This leads to high availability of the sub-modules and the multi-stage converters constituted therefrom. Attached Figure Description

[0022] The invention will now be described and explained in more detail with reference to the embodiments shown in the accompanying drawings. These drawings illustrate:

[0023] Figure 1 The structure of the submodule according to the present invention is shown.

[0024] Figure 2 This illustrates the structure of a modular multi-stage converter and

[0025] Figure 3 This indicates the on / off status of the submodule. Detailed Implementation

[0026] Figure 1 An embodiment of submodule 1 according to the present invention is shown. Components are arranged between each network node N1...N6. Here, each component is directly arranged between network nodes N1...N6 and connects the corresponding two network nodes, or one of network nodes N1...N6 is interconnected with terminals 11, 12. The voltage between terminals 11, 12 of submodule 1 is marked as U. SM Here, advantageously, the third semiconductor switch S3 and the eighth semiconductor switch S8 are designed for the full current-carrying capacity of submodule 1. The remaining semiconductor switches S1, S2, S4, S5, S6, S7, S9, and S10 can each be designed for half current-carrying capacity.

[0027] It can be seen that the structure of submodule 1 is mirror-symmetrical about the axis formed by terminals 11 and 12 of submodule 1. This allows submodule 1 to be composed of two identical partial modules 7, which are interconnected at terminals 11 and 12, at the third network node N3, and at the sixth network node N6. Here, a partial module includes terminals 11 and 12, first, third, fourth, sixth, eighth, and ninth semiconductor switches S1, S3, S4, S6, S8, and S9, and first and third capacitors C. 1.1 C 2.1 And the first, third, fourth and sixth network nodes N1, N3, N4 and N6. In order to form a submodule 1 from two structurally identical partial modules 7, the two structurally identical partial modules 7 are electrically connected to each other at terminals 11 and 12, at the third network node N3 and at the sixth network node N6, respectively.

[0028] In this configuration, both the third semiconductor switch S3 and the eighth semiconductor switch S8 can be designed for half the current-carrying capacity of submodule 1. Thus, the full current-carrying capacity is obtained from the parallel circuit by submodule 1, which consists of two submodules 7. Consequently, all semiconductor switches within submodule 7 can be designed to be identical, particularly in terms of current-carrying capacity. This increases the number of identical components and improves the maintainability of submodule 1. Due to the large number of identical components in semiconductor switches S1...S10, the manufacturing of the submodule is also particularly low-cost and reliable.

[0029] Figure 2 An embodiment of a modular multi-stage converter 2 is shown, which consists of the proposed submodule 1. To avoid repetition, refer to... Figure 1 The description and reference numerals introduced therein are used. The submodule 1 is arranged in series in its terminals 11, 12, and forms a converter arm 3, wherein, for clarity, only one converter arm 3 is shown as a terminal. The two converter arms 3 arranged in series form a converter phase 4. The connection points of the converter arms 3 form phase terminals L1, L2, L3. The converter phase 4 is arranged between intermediate loop terminals L+, L-. For better adjustability or controllability, it has proven advantageous to supplement the series circuit of the converter arms 3 with an inductor 20, which is arranged in series between the converter arm 3 and the corresponding intermediate loop terminals L+, L-. A module voltage U is applied at each submodule 1. SM The module voltage is derived from the switching states of semiconductor switches S1...S10.

[0030] This embodiment is configured as a three-phase modular multi-stage converter 2.

[0031] Figure 3 This illustrates the possible switching states of semiconductor switches S1...S10 and the resulting voltage U between terminals 11 and 12 of submodule 1.SM To avoid repetition, please refer to... Figure 1 and 2 The description, and reference to the accompanying reference numerals, are provided. Here, the first and second semiconductor switches S1, S2, the fourth and fifth semiconductor switches S4, S5, the sixth and seventh semiconductor switches S6, S7, and the ninth and tenth semiconductor switches S9, S10 are driven in the same manner, i.e., turned on (represented by 1 in the table), or turned off (represented by 0). It is thus clear that only one drive unit is needed to implement the submodule 1 consisting of two part modules 7, because the mirror-arranged semiconductor switches always exhibit the same switching state.

[0032] In the preferred switching states numbered sequentially from 1 to 6, regardless of the direction of the current flowing through submodule 1, a submodule voltage U is generated. SM The block, where all semiconductor switches S1...S10 are off, provides different submodule voltages U depending on the current direction. SM This makes it preferable not to use this state for controlling submodule 1.

[0033] In summary, the present invention relates to a submodule for a modular multi-stage converter, the submodule having:

[0034] - Ten switchable semiconductor switches

[0035] - Four capacitors

[0036] -Six network nodes

[0037] - Two terminals,

[0038] The components are arranged such that different voltages are generated between the terminals of the submodule when the turn-off semiconductor switch is driven. This significantly improves the behavior of the converter and submodule in the event of a failure.

Claims

1. A submodule (1) for a modular multi-stage converter (2), the submodule (1) having: - Ten semiconductor switches that can be turned off, - Four capacitors, -Six network nodes -The two terminals of the submodule (1), in, The first semiconductor switch among the ten turn-off semiconductor switches is arranged between the first terminal of the two terminals and the first network node among the six network nodes, thereby enabling the current from the first network node to the first terminal to be cut off. The second semiconductor switch among the ten turn-off semiconductor switches is arranged between the first terminal and the second network node among the six network nodes, thereby enabling the current from the second network node to the first terminal to be cut off. The third semiconductor switch among the ten turn-off semiconductor switches is arranged between the first terminal and the third network node among the six network nodes, thereby enabling the current from the first terminal to the third network node to be cut off. The fourth semiconductor switch among the ten turn-off semiconductor switches is arranged between the first and fourth network nodes in the six network nodes, thereby enabling the current from the first network node to the fourth network node to be cut off. The fifth semiconductor switch among the ten turn-off semiconductor switches is arranged between the second and fifth network nodes of the six network nodes, thereby enabling the current from the second network node to the fifth network node to be cut off. The sixth semiconductor switch among the ten turn-off semiconductor switches is arranged between the third network node and the fourth network node, thereby enabling it to cut off the current from the fourth network node to the third network node. The seventh semiconductor switch among the ten turn-off semiconductor switches is arranged between the third network node and the fifth network node, thereby enabling it to cut off the current from the fifth network node to the third network node. The eighth semiconductor switch among the ten turn-off semiconductor switches is arranged between the second terminal of the two terminals and the sixth network node among the six network nodes, thereby enabling it to cut off the current from the second terminal to the sixth network node. The ninth semiconductor switch among the ten turn-off semiconductor switches is arranged between the second terminal and the fourth network node, thereby enabling it to cut off the current from the fourth network node to the second terminal. The tenth semiconductor switch among the ten turn-off semiconductor switches is arranged between the second terminal and the fifth network node, thereby enabling it to cut off the current from the fifth network node to the second terminal. The first capacitor of the four capacitors is arranged between the first network node and the third network node. The second capacitor of the four capacitors is positioned between the second network node and the third network node. The third capacitor of the four capacitors is arranged between the fourth network node and the sixth network node. The fourth capacitor of the four capacitors is arranged between the fifth network node and the sixth network node.

2. The submodule (1) according to claim 1, wherein, The corresponding turn-off semiconductor switch can turn the current on and off in one current direction, and can only conduct current in the other current direction.

3. A modular multi-stage converter (2) having a plurality of sub-modules (1) according to claim 1 or 2, wherein, The series connection of at least two of the sub-modules (1) forms a converter arm (3) of the multi-stage converter (2), wherein the series connection of two of the converter arms (3) forms a converter phase (4), wherein the connection point of the two converter arms (3) forms a phase terminal of the multi-stage converter (2).

4. The modular multi-stage converter (2) according to claim 3, wherein, The end of the converter arm (3) facing away from the phase terminal forms the intermediate circuit terminal of the multi-stage converter (2).

5. A method for operating a submodule (1) according to claim 1 or 2, or a modular multi-stage converter (2) according to claim 3 or 4, wherein, Different voltages are generated between the terminals of the submodule (1) by means of the switching operation of a semiconductor switch that can be turned off.

6. A method for manufacturing a submodule (1) according to claim 1 or 2 from two partial modules (7), wherein, One of the said partial modules (7) has: a terminal, a first semiconductor switch, a third semiconductor switch, a fourth semiconductor switch, a sixth semiconductor switch, an eighth semiconductor switch and a ninth semiconductor switch, a first capacitor and a third capacitor, and a first network node, a third network node, a fourth network node and a sixth network node, wherein the sub-module (1) is formed by connecting two structurally identical partial modules (7) to each other at the terminal, the third network node and the sixth network node respectively.

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