Submodule as a parallel series full-bridge for modular multilevel converter

Abstract

The invention relates to a sub-module (1) for a modular, multi-stage power converter (2), having nine switchable semiconductor switches (S1, S2, S3, S4, S5, S6, S7, S8, S9), four capacitors (C 1.1 , C 1.2 , C 2.1 , C 2.2 ), six network nodes (N1, N2, N3, N4, N5, N6), two interfaces (11, 12), wherein the components are arranged in such a way that different voltages arise between the interfaces (11, 12) of the sub-module (1) when the switchable semiconductor switches are actuated. Here, the behavior of the power converter and the sub-module (1) in the event of a fault can be significantly improved.

Description

Technical Field

[0001] This invention relates to a submodule for a modular multistage power converter. The invention also relates to a modular multistage power 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 power converter is known from DE 101 03 031 A1. This multistage power converter is also called a modular multistage converter, MMC, or M2C. This type of power converter has multiple sub-modules that can generate a stepped output voltage.

[0003] A modular multi-stage power converter is a converter topology particularly suitable for HVDC applications and electric drives. The basic structure of a multiphase power converter includes two converter arms per phase, each configured as a series circuit of multiple submodules. By modulating discrete voltages or short-circuiting modulation terminals using each submodule, the desired voltage shape is quantitatively simulated by each converter arm through the modular structure. Here, the submodules achieve regulation of different voltage levels.

[0004] There are different variations of submodules. The most common and known submodule types are half-bridge and full-bridge.

[0005] Here, the submodule includes a switchable semiconductor switch, such as an IGBT, IGCT, GTO, MOSFET, etc. Compared to a thyristor, this semiconductor switch can not only turn on current but also turn off current. Current interruption can only occur in one current-carrying direction. In the opposite current-carrying direction, the interruptible semiconductor switch behaves like a diode. This behavior has been provided by a power converter structure or achieved by means of a diode arranged in anti-parallel with the switching element of the semiconductor switch. Therefore, the interruptible semiconductor switch turns on and off current in one current-carrying direction and conducts only in the other current-carrying direction. Therefore, it is impossible to interrupt current in the other current-carrying direction. Summary of the Invention

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

[0007] This objective is achieved by a submodule having the features of the present invention. Furthermore, this objective is achieved by a modular multi-stage power converter having the features of the present invention. This objective is also achieved by a method for operating such a submodule having the features of the present invention and by a method for manufacturing such a submodule having the features of the present invention.

[0008] This invention is particularly based on the understanding that the proposed device using semiconductor switches and capacitors can improve the fault behavior of submodules and modular multistage power converters. Eight switching states of the semiconductor switches can be defined, thereby generating seven different output voltages at the interface of the submodule. Furthermore, another switching state can be implemented, in which different voltages are applied to the interface through the submodule according to the current flow direction. Therefore, the six switching states mentioned earlier for the regulation and control of submodules and modular multistage power converters are particularly advantageous.

[0009] This circuit serves as a submodule in a modular multi-stage power converter. Here, the submodule enables the active switching of eight switching states relevant to normal operation, resulting in different output voltages between the two interfaces of the submodule. The first and second capacitors, as well as the third and fourth capacitors, are always connected in parallel. For better overview, the modulated voltage of the parallel circuit consisting of the first and second capacitors will be referred to as U in the following text. C1 Furthermore, the modulated voltage of the parallel circuit consisting of the third and fourth capacitors is called U. C2 It can switch the following voltage states between the interfaces of the submodules:

[0010] - The positive series connection of two capacitors in parallel corresponds to U C1 and U C2 The sum of, i.e., U C1 +U C2 ,

[0011] - Each individual positive capacitor is connected in parallel, corresponding to U C1 or U C2 ,

[0012] - No voltage (terminal short circuit or freewheeling).

[0013] - Negative capacitors connected in parallel, corresponding to -U C1 or -U C2 ,and

[0014] - The negative series connection of two capacitors in parallel corresponds to U C1 and U C2 The negative sum, i.e. -(U C1 +U C2 ).

[0015] The states can be switched independently of the current direction, i.e., bidirectionally.

[0016] The submodule according to the invention is functionally comparable to two full-bridge series circuits. Here, the same voltage state can be switched between the interfaces of the submodule. If the respective semiconductor switches are designed accordingly in the proposed device and in the two full-bridge series circuits, the same number of semiconductors is obtained. If it is assumed that the same capacitor energy is installed in the proposed device and the two full-bridge series circuits, then in the event of a semiconductor failure in the device according to the invention, only half the energy is discharged. If this semiconductor switch fails, only one capacitor in the parallel capacitors is always short-circuited. Therefore, only half the energy can be safely controlled in the submodule or power converter.

[0017] The same fault behavior can be achieved by configuring the two sub-modules as parallel circuits in a series circuit of the full bridge. However, in this case, at least sixteen switches must be installed instead of the nine switches in the device according to the invention. Therefore, the goal of lower fault energy, i.e., energy in fault conditions, can be achieved with a significantly fewer number of semiconductors and semiconductor drive devices. This makes the multi-stage power converter with modular sub-modules significantly less complex, less costly, and easier to control and / or regulate.

[0018] The basic structure of a submodule can be composed of two submodules because the submodules have 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 submodules include an interface, a first semiconductor switch, a third semiconductor switch, a fourth semiconductor switch, a fifth semiconductor switch, a seventh semiconductor switch, and an eighth 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.

[0019] The third, fifth, and seventh semiconductor switches are formed by a parallel circuit consisting of one semiconductor switch from each of the two sub-modules, allowing the semiconductor switches to be designed to be smaller, for example, with half the current carrying capacity.

[0020] In the proposed structure, the third, fifth, and seventh semiconductor switches are designed for the full current-carrying capacity of submodule 1. The remaining semiconductor switches are each designed for only half the current-carrying capacity. Since the third, fifth, and seventh semiconductor switches are implemented as parallel circuits consisting of two semiconductor switches in the two submodules, the semiconductor switches within each submodule are designed for only half the current-carrying capacity. This allows all semiconductor switches in each submodule to be constructed with the same structure.

[0021] 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 drive signals are driven synchronously.

[0022] 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.

[0023] The features and advantages can be summarized as follows. Through a symmetrical structure, particularly when using two or more sub-modules, the current path obtained through the sub-modules is essential for the invention, as it provides two or more parallel current paths. 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 comparable redundancy by simultaneously providing comparable voltages via different switching states. Simultaneously, the parallel circuits of the capacitors allow for the design of smaller capacitances of each capacitor, 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 more easily controlled because the existing stored energy is significantly lower. Furthermore, by using fewer semiconductors, the proposed structure can be manufactured in a substantially simpler and less costly manner. Moreover, the failure probability is significantly reduced by using fewer semiconductors. This leads to high availability of the sub-modules and the resulting multi-stage power converters. Attached Figure Description

[0024] The invention will now be described and explained in more detail with reference to the embodiments shown in the accompanying drawings. These drawings illustrate:

[0025] Figure 1 The structure of the submodule according to the present invention is shown.

[0026] Figure 2 This illustrates the structure of a modular multi-stage power converter, and

[0027] Figure 3 This indicates the on / off status of the submodule. Detailed Implementation

[0028] Figure 1An 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 to one of interfaces 11, 12. The voltage between interfaces 11, 12 of submodule 1 is called U. SM Here, the third semiconductor switch S3, the fifth semiconductor switch S5, and the seventh semiconductor switch S7 are each designed in an advantageous manner to accommodate the full current-carrying capacity of submodule 1. The remaining semiconductor switches S1, S2, S4, S6, S8, and S9 are each designed to carry half of the current.

[0029] It can be seen that the structure of submodule 1 extends symmetrically to the axis formed by interfaces 11 and 12 of submodule 1. Therefore, it is feasible to construct submodule 1 from two identical partial modules 7, which are connected to each other at interfaces 11 and 12, at the third network node N3, and at the sixth network node N6, respectively. Here, the partial modules include interfaces 11 and 12, a first semiconductor switch, a third semiconductor switch, a fourth semiconductor switch, a fifth semiconductor switch, a seventh semiconductor switch, and an eighth semiconductor switch S1, S3, S4, S5, S7, and S8, a first capacitor, and a third capacitor C. 1.1 C 2.1 And the first network node, the third network node, the fourth network node, and the sixth network node N1, N3, N4, 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 interfaces 11, 12, the third network node N3, and the sixth network node N6, respectively.

[0030] In this configuration, the third semiconductor switch S3, the fifth semiconductor switch S5, and the seventh semiconductor switch S7 can also be designed to have half the current-carrying capacity of submodule 1. Thus, by constructing submodule 1, which consists of two submodules 7, the full current-carrying capacity is obtained from the parallel circuit. Consequently, all semiconductor switches within submodule 7 can be designed to have the same current-carrying capacity, especially. 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...S9, the manufacturing of the submodule is particularly cost-effective and reliable.

[0031] Figure 2 An embodiment of a modular multi-stage power converter 2 is shown, which is composed of the proposed submodule 1. To avoid repetition, refer to... Figure 1The description and reference numerals introduced therein are used. The submodule 1 is arranged in series in its interfaces 11, 12 and forms converter arms 3, which are shown in only one converter arm 3 for overview purposes. The two converter arms 3 arranged in series form converter phase 4. The connection points of the converter arms 3 form phase interfaces L1, L2, L3. Converter phase 4 is arranged between intermediate loop interfaces L+, L-. For better adjustability or controllability, it is advantageous to supplement the series circuit of the converter arms 3 with inductors 20, which are arranged in series between the converter arms 3 and the corresponding intermediate loop interfaces 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...S9.

[0032] This embodiment is configured as a three-phase modular multi-stage power converter 2.

[0033] Figure 3 This diagram illustrates the possible switching states of semiconductor switches S1...S9 and the resulting voltage U between interfaces 11 and 12 of submodule 1. SM To avoid repetition, please refer to... Figure 1 and Figure 2 The description and reference numerals in the accompanying drawings are provided. Here, the first and second semiconductor switches S1, S2, the fourth and sixth semiconductor switches S4, S6, the eighth and ninth semiconductor switches S8, S9 are driven in the same manner, i.e., turned on (identified by 1 in the table) or turned off (identified by 0). It is clear from this that only one drive unit is needed to implement submodule 1, which consists of two part modules 7, because the mirror-arranged semiconductor switches always exhibit the same switching state.

[0034] In the preferred switching states numbered sequentially from 1 to 8, the submodule voltage U is obtained regardless of the direction of current flow through submodule 1. SM Only the state of block (in which all semiconductor switches S1...S9 are turned off) provides different submodule voltages U depending on the current direction. SM Therefore, the state is preferably not used to control submodule 1.

[0035] In summary, the present invention relates to a submodule for a modular multi-stage power converter, the submodule having:

[0036] - Nine semiconductor switches that can cut off

[0037] - Four capacitors,

[0038] -Six network nodes

[0039] - Two interfaces,

[0040] The components are arranged such that different voltages are generated between the interfaces of the submodules when a semiconductor switch that can be turned off is driven. This significantly improves the behavior of the power converter and submodules in the event of a fault.

Claims

1. A submodule (1) for a modular multi-stage power converter (2), the submodule having: - Nine semiconductor switches that can be cut off (S1, S2, S3, S4, S5, S6, S7, S8, S9). - Four capacitors (C 1.1 C 1.2 C 2.1 C 2.2 ), - Six network nodes (N1, N2, N3, N4, N5, N6). -The two interfaces (11, 12) of the submodule (1). in, The first semiconductor switch (S1) of the nine disconnectable semiconductor switches is arranged between the first interface (11) of the two interfaces and the first network node (N1) of the six network nodes, thereby enabling the interruption of current from the first network node (N1) to the first interface (11). Among them, the second semiconductor switch (S2) of the nine disconnectable semiconductor switches is arranged between the first interface (11) and the second network node (N2) of the six network nodes (N2), thereby being able to cut off the current from the second network node (N2) to the first interface (11). Among them, the third semiconductor switch (S3) of the nine disconnectable semiconductor switches is arranged between the first interface (11) and the third network node (N3) of the six network nodes, thereby enabling the current from the first interface (11) to the third network node (N3) to be cut off. Among them, the fourth semiconductor switch (S4) of the nine disconnectable semiconductor switches is arranged between the first network node (NI) and the fourth network node (N4) of the six network nodes, thereby enabling the interruption of current from the first network node (N1) to the fourth network node (N4). Among them, the fifth semiconductor switch (S5) of the nine disconnectable semiconductor switches is arranged between the third network node (N3) and the sixth network node (N6) of the six network nodes, thereby being able to cut off the current from the sixth network node (N6) to the third network node (N3). The sixth semiconductor switch (S6) of the nine disconnectable semiconductor switches is arranged between the second network node (N2) and the fifth network node (N5) of the six network nodes, thereby enabling the interruption of current from the second network node (N2) to the fifth network node (N5). Of the nine disconnectable semiconductor switches, the seventh semiconductor switch (S7) is arranged between the second interface (12) and the sixth network node (N6) of the two interfaces, thereby enabling the interruption of current from the sixth network node (N6) to the second interface (12). The eighth semiconductor switch (S8) of the nine disconnectable semiconductor switches is arranged between the second interface (12) and the fourth network node (N4), thereby enabling it to cut off the current from the second interface (12) to the fourth network node (N4). Of the nine disconnectable semiconductor switches, the ninth semiconductor switch (S9) is arranged between the second interface (12) and the fifth network node (N5), thereby enabling the interruption of current from the second interface (12) to the fifth network node (N5). Among them, the first capacitor (C) of the four capacitors 1.1 The network node (N1) is positioned between the first network node (N2) and the third network node (N3). Among them, the second capacitor (C) of the four capacitors 1.2 The network node (N2) is positioned between the second network node (N3) and the third network node (N3). Among them, the third capacitor (C) of the four capacitors 2.1 The network node is positioned between the fourth network node (N4) and the sixth network node (N6). Among them, the fourth capacitor (C) of the four capacitors 2.2 The network node is positioned between the fifth network node (N5) and the sixth network node (N6). The corresponding semiconductor switches (S1, S2, S3, S4, S5, S6, S7, S8, S9) that can be cut off are capable of connecting and disconnecting current in one current flow direction and are capable of conducting current only in another current flow direction.

2. A modular multi-stage power converter (2) having multiple sub-modules (1) according to claim 1, wherein, The series circuit of at least two sub-modules (1) forms the converter arm (3) of the multi-stage power converter (2), wherein the series circuit of the two converter arms (3) forms the converter phase (4), wherein the connection point of the two converter arms (3) forms the phase interface (L1, L2, L3) of the multi-stage power converter (2).

3. The modular multi-stage power converter (2) according to claim 2, wherein, The end of the converter arm (3) away from the phase interface (L1, L2, L3) forms the intermediate loop interface (L+, L-) of the multi-stage power converter (1).

4. A method for operating a submodule (1) according to claim 1 or a modular multi-stage power converter (2) according to claim 2 or 3, wherein, Different voltages are generated between the interfaces (11, 12) of the submodule (1) by means of the switching operation of the turn-off semiconductor switches (S1, S2, S3, S4, S5, S6, S7, S8, S9).

5. A method for manufacturing a submodule (1) according to claim 1 from two partial modules (7), wherein, Partial module (7) includes interfaces (11, 12), a first semiconductor switch, a third semiconductor switch, a fourth semiconductor switch, a fifth semiconductor switch, a seventh semiconductor switch, and an eighth semiconductor switch (S1, S3, S4, S5, S7, S8), a first capacitor, and a third capacitor (C). 1.1 C 2.1 The submodule (1) is formed by connecting two structurally identical partial modules (7) to each other at the interfaces (11, 12), the third network node (N3), and the sixth network node (N6), respectively.

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