WO2018113926A1

WO2018113926A1 - Power converter

Info

Publication number: WO2018113926A1
Application number: PCT/EP2016/081950
Authority: WO
Inventors: Daniel BÖHME; Ingo Euler; Thomas KÜBEL; Steffen PIERSTORF; Daniel Schmitt; Frank Schremmer; Torsten Stoltze; Marcus Wahle
Original assignee: Siemens Aktiengesellschaft
Priority date: 2016-12-20
Filing date: 2016-12-20
Publication date: 2018-06-28

Abstract

The invention relates to a power converter (1) comprising a plurality of modules (1_1... 6_n), each of which includes at least two electronic switching elements (202, 206) and an electric energy store (210). The modules (1_1... 6_n) are in each case provided with a surge arrester (A1_1... A6_n).

Description

The invention relates to a power converter with a plurality of modules, each having at least two electronic

Have switching elements and an electrical energy storage. Furthermore, the invention relates to a method for protecting modules of a power converter from overvoltage.

Power converters are power electronic circuits for converting electrical energy. With converters, AC can be used in DC, DC in AC, AC in AC of other frequency and / or

Amplitude or DC to be converted into DC other voltage. Power converters may include a plurality of the above-mentioned similar modules (also referred to as sub-modules) which are electrically connected in series. Such converters are referred to as modular multilevel converters and belong to the VSC power converters (VSC = voltage sourced converter). The electrical series connection of the modules can achieve high output voltages. The converters are easily adaptable to different voltages (scalable) and a desired output voltage can be generated relatively accurately. Modular multilevel converters are often used in the high voltage range, for example as

Power converters for high-voltage direct current transmission systems.

When operating such converters, overvoltages can occur which can damage the modules. It is conceivable to protect the input and the output of the converter each with a surge arrester. This Überspannungsabieiter must then on the respective

Operating voltage of the converter to be matched. For modular power converters (designed by selecting the number of modules for different operating voltages this means that for each desired

Operating voltage of the power converter must be used a surge arrester with a different threshold voltage. This requires producing or stocking a large number of different surge arresters. In addition, surge arresters designed for high voltages require a lot of space, for example, to meet the required voltage ranges. This results in relatively high expenses and costs for the

Overvoltage protection.

The invention has for its object to provide a power converter and a method in which the

Surge protection can be realized easily and inexpensively.

This object is achieved by a

Power converter and by a method according to the independent claims. Advantageous embodiments of the

Converter and the method are specified in the dependent claims.

Disclosed is a power converter with a plurality of

Modules, each containing at least two electronic

Have switching elements and an electrical energy storage, the modules each with a

Überspannungsabieiter are provided. It is advantageous that the modules are each provided with a (only the respective module assigned) surge arrester. As a result, each module is customized by means of its own

Surge arrester protected. Parasitic electrical variables of the converter (for example parasitic resistances, parasitic inductances or parasitic capacitances, which may occur, for example, due to conductor tracks of the converter or the design of the converter hall)

do not affect the surge protection. The

Surge arresters are installed at the module level. The

Modules is thus each a separate protective element in shape assigned to the respective surge arrester. As a result, the surge arrester can be optimally adapted to the module, for example by selecting a suitable threshold voltage for the module. If a power converter is built with a higher operating voltage and therefore more modules are connected in series, then no other surge arresters need to be used because the individual surge arresters only have to fit to the respective module, but not to the operating voltage of the module

Inverter.

Furthermore, it is advantageous that instead of a few large surge arresters (which are each designed for a large voltage) now many small Überspannungsabieiter (each designed for a small voltage) are used. Due to their small size, the many small surge arresters can be more easily integrated into the power converter than a few large ones

Surge. In addition, large numbers of surge arresters with low threshold voltage

less expensive on the market than single pieces of large surge arresters with high threshold voltage. Due to economies of scale, the

Overvoltage protection therefore cost-effective. The power converter can in particular be a modular

Be multilevel converter. The modules may in particular be bipolar modules. The surge arresters can also be used as decentralized modular surge arresters or as decentralized modular multilevel surge arresters

be designated.

The power converter can be designed so that

- The Überspannungsabieiter the respective module

is connected in parallel. This allows the

Surge Absieiter be arranged spatially close to the respective module.

The power converter can be designed so that - The surge arrester is low inductively connected to the respective module. This allows the surge arrester to quickly perform its protective function in the event of overvoltage. The power converter can also be designed so that

- The surge arrester each a metal oxide surge arrester, in particular a metal oxide varistor, is. The power converter can be designed so that

- The two electronic switching elements of the modules are arranged in a half-bridge circuit, or

- The modules each have the two electronic switching elements and two other electronic switching elements, wherein the two electronic switching elements and the two other electronic switching elements in one

Full bridge circuit are arranged.

In the case of the first alternative, such a module also becomes a half-bridge module or a half-bridge submodule

designated. In the case of the second alternative, a

such module also referred to as a full bridge module or as a full bridge submodule.

Also disclosed are a high-voltage DC transmission system and a reactive power

Compensation system with a power converter according to

variants described above.

Disclosed is still a method for protecting

Modules of a power converter against overvoltage, the

Converter has a plurality of modules and each module has at least two electronic switching elements and an electrical energy storage, wherein in the

method

- When an overvoltage occurs on one of the modules of this module is electrically bridged by means of a

Surge arrester assigned (exclusively) to this module. In other words, each module has a first terminal and a second terminal, and the first terminal and the second terminal become electrically conductive (when an overvoltage occurs) by means of the surge absorber (exclusively) associated with this module

shorted.

In the event that overvoltage occurs simultaneously on several modules of the power converter, the following method is disclosed:

A method for protecting modules of a power converter from overvoltage, wherein the power converter has a plurality of modules and each module has at least two electronic modules

Switching elements and an electrical energy storage

wherein in the method

- When an overvoltage occurs on several modules, these modules are each electrically bridged by means of a surge arrester, which is (exclusively) associated with the respective module.

The described power converter and the described methods have the same or similar advantages.

The invention is further illustrated by execution ^¬ examples. The same reference numbers refer to the same or equivalent elements. This is in

Figure 1 shows an embodiment of a power converter, which has a plurality of modules, in Figure 2 shows an embodiment of a module, in

Figure 3 shows another embodiment of a module, in

FIG. 4 shows an exemplary embodiment of a high-voltage

DC transmission systems, in

FIG. 5 shows an exemplary embodiment of a reactive power

Compensation system and in

FIG. 6 shows an exemplary sequence of the method for

Protecting modules of a power converter before Over voltage shown. In Figure 1, a power converter 1 in the form of a modular

Multilevel converter 1 (modular multilevel converter, MMC). This multi-level power converter 1 has a first AC voltage connection 5, a second alternating voltage terminal ^¬ 7 and a third AC voltage terminal. 9 The first AC voltage terminal 5 is electrically connected to a first phase module branch 11 and a second phase module branch 13. The first phase module branch 11 and the second phase module branch 13 form a first phase module 15 of the power converter 1. The end of the first one facing away from the first AC voltage connection 5

Phase module branch 11 is electrically connected to a first DC voltage connection 16; that the first

AC voltage connection 5 opposite end of the second

Phase module branch 13 is connected to a second

DC voltage terminal 17 electrically connected. The first DC voltage terminal 16 is a positive one

DC voltage connection; the second DC voltage terminal 17 is a negative DC voltage terminal. Between the first DC voltage connection 16 and the second

DC voltage terminal 17 is applied to a DC voltage Ud.

The second AC voltage terminal 7 is electrically connected to one end of a third phase module branch 18 and to one end of a fourth phase module branch 21. The third phase module branch 18 and the fourth phase module branch 21 form a second phase module 24. The third alternating voltage ^terminal 9 is connected to one end of a fifth

Phase module branch 27 and with one end of a sixth

Phase module branch 29 electrically connected. The fifth

Phase module branch 27 and the sixth phase module branch 29 form a third phase module 31. The second AC terminal 7 opposite end of the third phase module branch 18 and the third

AC terminal 9 opposite end of the fifth

Phase module branch 27 are electrically connected to the first DC voltage connection 16. The second AC terminal 7 remote from the end of the fourth phase ^¬ module branch 21 and the third AC terminal 9 opposite end of the sixth phase module branch 29 are electrically connected to the second DC voltage terminal 17. The first phase module branch 11, the third phase module branch 18 and the fifth phase module branch 27 form a positive-side converter element 32; the second phase module branch 13, the fourth phase module branch 21 and the sixth phase module branch 29 form a negative-side converter element 33.

Each phase module branch has a plurality of modules (1_1, 1_2, 1_3, ... l_n; 2_1 ... 2_n; etc.) which are electrically connected in series (by means of their galvanic current connections). Such modules are also referred to as submodules. In the exemplary embodiment of FIG. 1, each phase module branch has n modules. The number of means of their galvanic

Power connections electrically connected in series modules can be very different, at least two modules are connected in series, but it can also be, for example, 3, 50, 100 or more modules connected electrically in series. in the

Embodiment is n = 36: the first phase module branch 11 thus has 36 modules 1_1, 1_2, 1_3, ... 1_36. The other phase module branches 13, 18, 21, 27 and 29 are of similar construction.

From a control device (not shown) of the

Power converter 1 are optical messages or optical signals via an optical communication link (for example via an optical waveguide) to the individual

Transfer modules 1_1 to 6_n. For example, the control device sends one to the individual modules

Setpoint for the amount of output voltage that the respective module should provide. The modules 1_1 to 6_n are each with a

Surge Arrester Al_l to A6_n provided. Everyone

Surge arrester is assigned to exactly one module. For example, module 3_2 is exactly that

Overvoltage arrester A3_2 assigned. In other words, each module is a separate one

Assigned surge arrester. The surge arrester is connected in parallel to the respective module. Of the

Überspannungsabieiter is electrically low inductively connected to the respective module. This is due to a short and winding-free electrical connection between the

Surge arrester and the respective module realized. The surge arrester in the exemplary embodiment is a metal oxide surge arrester, in particular a

Metal oxide varistor.

If an overvoltage occurs on a module, the threshold voltage of the respective surge arrester is exceeded. As a result, the electrical increases

Conductance of the surge arrester quickly, whereby on the one hand large currents are conducted past the module and on the other hand, the voltage drop across the module decreases. This will protect the module from overvoltage. If overvoltage occurs only on one module or on some modules, then only at the respectively assigned one

Surge absorber or at the respectively assigned

Surge arresters exceeded the threshold voltage and these surge arresters each bypass the module affected by the overvoltage. But if at all

In the case of overvoltage modules, the surge voltage is exceeded for all surge arresters and all surge arresters bridge the modules affected by the surge voltage.

The method for protecting modules of the power converter 1 against overvoltage thus runs so that when an overvoltage occurs on one of the modules of this module by means of (exclusively or exclusively) this module associated surge arrester is electrically bridged. at

If an overvoltage occurs at several modules, these modules are each electrically bridged by means of a respective surge arrester, which is assigned (exclusively) to the respective module.

In FIG. 2, the structure of a module 201 is shown by way of example. This may be, for example, the module l_n of the first phase module branch 11 (or else one of the other modules illustrated in FIG. 1). The module is designed as a half-bridge module 201. The module 201 has a first on and off switchable electronic

Switching element 202 (first electronic switching element 202) with a first antiparallel-connected diode 204 (first freewheeling diode 204) on. Furthermore, the module 201 has a second switchable on and off electronic switching element 206 (second electronic switching element 206) with a second antiparallel-connected diode 208 (second

Freewheeling diode 208) and an electrical energy store 210 in the form of an electrical capacitor 210. The first electronic switching element 202 and the second electronic switching element 206 are each configured as an IGBT (insulated-gate bipolar transistor). The first electronic switching element 202 is electrically connected in series with the second electronic switching element 206. At the connection point between the two electronic switching elements 202 and 206, a first (galvanic) module connection 212

arranged. At the connection of the second switching element 206, which is opposite to the connection point, a second (galvanic) module connection 215 is arranged. The second module connection 215 is furthermore connected to a first connection of the energy store 210; a second terminal of the energy storage 210 is electrically connected to the

Connection of the first switching element 202, the

Connection point opposite. The energy storage 210 is therefore electrically parallel

switched to the series connection of the first

By switching the first switching element 202 and the second switching element 206 can be achieved that between the first module terminal 212 and the second

Module terminal 215 either the voltage of the energy storage 210 is output or no voltage is output (i.e., a zero voltage is output). By interaction of the modules of the individual phase module branches so the respective desired output voltage of the converter can be generated. The control of the first switching element 202 and the second switching element 206 takes place in the exemplary embodiment by means of the (above-mentioned) transmitted from the control device of the power converter to the module message or signal.

The surge arrester Al_n (see FIG. 1) connects the first module terminal 212 and the second module terminal 215. The surge arrester Al_n is therefore connected in parallel to the module 201 (here: parallel to the module I_n).

FIG. 3 shows a further exemplary embodiment of a module 301 of the modular multilevel converter. This module 301 can be, for example, the module 1_1 (or also one of the other modules shown in FIG. 1). In addition to the already known from Figure 2 first electronic switching element 202, second

electronic switching element 206, first freewheeling diode 204, second freewheeling diode 208 and energy storage 210, the module 301 shown in Figure 3, a third electronic switching element 302 with an antiparallel third free-wheeling diode 304 and a fourth electronic

Switching element 306 with a fourth anti-parallel connected freewheeling diode 308 on. The third electronic switching element 302 and the fourth electronic switching element 306 are each configured as an IGBT. In contrast to

2, the second module connection 315 is not electrically connected to the second electronic switching element 206 The module 301 of FIG. 3 is a so-called full-bridge module 301. This full-bridge module 301 is characterized in that, when appropriately controlled, it is connected to a center of an electrical series connection of the third electronic switching element 302 and the fourth electronic switching element 306 the four

electronic switching elements between the first

(galvanic) module connection 212 and the second

(Galvanic) module connection 315 selectively either the positive voltage of the energy storage 210, the negative voltage of the energy storage 210 or a voltage of zero (zero voltage) can be output. Thus, therefore, by means of the full bridge module 301, the polarity of the output voltage can be reversed. The power converter 1 can have either only half-bridge modules 201, only full-bridge modules 301 or also half-bridge modules 201 and full-bridge modules 301. Via the first module connection 212 and the second module connection 215, 315 flow large electrical currents of the power converter.

FIG. 4 schematically shows an exemplary embodiment of a high-voltage direct-current transmission system 401. This high-voltage DC transmission system 401 has two power converters 1, as shown in FIG. These two power converters 1 are electrically connected to one another on the DC voltage side via a high-voltage direct current connection 405. The two are positive

DC terminals 16 of the power converters 1 are electrically connected to each other by means of a first high-voltage DC line 405a; the two negative DC voltage connections 17 of the two power converters 1 are electrically connected to one another by means of a second high-voltage direct-current line 405b. By means of such

High voltage DC transmission system 401 can

electrical energy is transmitted over long distances; the high voltage direct current connection 405 then has a corresponding length. FIG. 5 shows an exemplary embodiment of a power converter 501, which is a reactive power compensator 501. This power converter 501 has only the three

Phase module branches 11, 18 and 27, which form three phase modules of the power converter. The number of phase modules

corresponds to the number of phases of an alternating voltage network 511 to which the power converter 501 is connected. The three phase modules 11, 18 and 27 are connected in a triangular manner, i. the three phase modules 11, 18 and 27 are connected in a delta connection. Each vertex of the delta connection is electrically connected to a respective phase line 515, 517 and 519 of the three-phase AC network 511. (In another embodiment, the three phase modules can also be connected in a star connection instead of in delta connection.) The converter 501 can supply the AC voltage network 511 with reactive power or remove reactive power from the AC voltage network 511.

In FIG. 6, the method for protecting modules of a power converter against overvoltage is shown once again by means of a flowchart.

Step 602:

Occurrence of overvoltage on one (or more) of the modules. Step 604:

Electrical bridging of the one module by means of

exclusively assigned to this module

Überspannungsabieiters (or each electrical bridging the plurality of modules by means of one each

Surge arrester, which is assigned exclusively to the respective module). It was a power converter with a plurality of modules and a method for protecting modules of the

Power converter before overvoltage described. Each module is assigned a (separate) surge arrester, which protects only the respective module against overvoltage. The

Surge arresters are installed at the module level. The

Surge arresters are thus distributed over the modules to be protected. As a result, the surge arresters are arranged adjacent to the respective module to be protected, ie spatially close to the respective module to be protected. The arrangement of the surge arrester has a number of advantages:

- Space saving and cheap design of the inverter, because many small Überspannungsabieiter better in the

Integrate power converter system than a few large ones

Surge.

Optimal voltage design of the surge arrester is possible, i. optimum adaptation of the threshold voltage of the surge arrester to the voltage of the modules.

- Parasitic influences of the hall and converter construction can be eliminated.

Claims

claims

1. power converter (1) having a plurality of modules (1_1 ... 6_n), each having at least two electronic

Switching elements (202, 206) and an electrical

Energy store (210), wherein

- The modules (1_1 ... 6_n) each with a

Surge Arrester (Al_l ... A6_n) are provided.

2. Converter according to claim 1,

d a d u r c h e c e n c i n e s that

- The surge arrester (A3_2) is connected in parallel to the respective module (3_2).

3. power converter according to claim 1 or 2,

d a d u r c h e c e n c i n e s that

- The surge arrester (A3_2) is low inductively connected to the respective module (3_2).

4. Converter according to one of the preceding claims, d a d u c h e c e n e c e s e s that

- The surge arrester each a metal oxide surge arrester (Al_l ... A6_n), in particular a

Metal oxide varistor (Al_l ... A6_n), is.

5. A power converter according to one of the preceding claims, characterized in that a

- The two electronic switching elements (202, 206) of

Modules (201) are arranged in a half-bridge circuit, or

- The modules (301) each have the two electronic

Switching elements (202, 206) and two further electronic switching elements (302, 306), wherein the two

electronic switching elements (202, 206) and the two

further electronic switching elements (302, 306) are arranged in a full bridge circuit.

6. High-voltage direct current transmission system (401) with a power converter (1) according to one of claims 1 to 5.

7. Reactive Power Compensation System (501) with a

Power converter according to one of claims 1 to 5.

8. Method for Protecting Modules (1_1 ... 6_n) of a

Power converter (1) against overvoltage, wherein the power converter (1) has a plurality of modules (1_1 ... 6_n) and each module has at least two electronic switching elements (202, 206) and an electrical energy store (210), wherein in the method

- If an overvoltage occurs on one of the modules (3_2), this module (3_2) is electrically bridged (604) by means of a surge arrester (A3_2) serving this module

assigned.

9. The method according to claim 8,

d a d u r c h e c e n c i n e s that

- When an overvoltage occurs on a plurality of modules (3_2, 5_1), these modules (3_2, 5_1) are each electrically bridged by means of one surge arrester (A3_2, A5_l), which is assigned to the respective module (3_2, 5 1).