WO2014086428A1

WO2014086428A1 - Multistage converter with additional module

Info

Publication number: WO2014086428A1
Application number: PCT/EP2012/074771
Authority: WO
Inventors: Herbert Gambach; Hans-Joachim Knaak; Dominik Schuster
Original assignee: Siemens Aktiengesellschaft
Priority date: 2012-12-07
Filing date: 2012-12-07
Publication date: 2014-06-12

Abstract

The invention relates to a device (24) for transmitting an electric power between an AC voltage network and a DC voltage network in the high-voltage range, comprising phase modules (2, 3, 4), each of which has at least one common DC voltage connection (7, 8) and a separate AC voltage connection (5), a phase module branch (9,...14) extending between each DC voltage connection (7, 8) and each AC voltage connection (5). The phase module branch has a series circuit of two-pole sub-modules (15), each of which has an energy store (16) and a power semiconductor circuit connected in parallel to the energy store such that either the voltage that drops at the energy store (16) or a zero voltage can be generated at the two connection terminals (20, 21) of each sub-module (15) depending on the actuation of the power semiconductor circuit (17). The aim of the invention is to produce such a device so as to allow a simple balancing of the energy stores and additionally be inexpensive. This is achieved in that an additional module (24) is provided without an AC voltage connection, said additional module having at least one power semiconductor circuit (17), at least one energy store (16), and at least one DC voltage connection (26, 27). Each DC voltage connection (26, 27) of the additional module (25) is connected to one of the common DC voltage connections (7, 8) of the phase modules (2, 3, 4), and control means are provided with which a circuit current can be generated that flows across the additional module (25) and one of the phase modules (2, 3, 4).

Description

description

The invention relates to a device for transmitting an electrical power between an AC voltage network and a DC voltage network in the high voltage range with phase modules, each having at least one common DC voltage connection and a separate AC voltage connection, between each DC voltage connection and each AC voltage terminal a Phasenmodulzweig extends, in which a series circuit of two-pole submodules is formed, each having an energy storage and the energy storage parallel power semiconductor circuit, so that depending on the control of the power semiconductor circuit either the voltage drop across the energy storage or zero - Voltage can be generated at the two terminals of each submodule.

The invention further relates to a method for controlling such a device.

Such a device and such a method are already known from DE 101 03 031 AI. The revealed there

Device discloses a so-called modular multi-stage converter with three parallel-connected phase modules, which extend between two poles of a DC voltage connection and thus form two common DC voltage connections. The phase modules represent three poles and form in addition to the said two DC voltage connections also a central AC voltage connection. Between each DC voltage terminal and the AC voltage terminal of each phase module, a phase module branch extends. The phase module branches can also be referred to as converter arms. They have a series circuit of bipolar submodules, each having an energy storage and a power semiconductor circuit. The power semiconductor circuit consists of two series-connected IGBTs, each with opposite freewheeling diode. Due to the selected circuit, either the voltage dropping across the energy store or else a zero voltage can be generated at the terminals of each submodule. By connecting the bipolar submodules in series, the voltage dropping across the DC terminals of the phase modules can be adjusted stepwise. The distributed over the submodules energy storage must be complex balanced. In this case, it is expedient to generate circulating currents which flow over and between the phase modules. However, such a circulating current always causes a charge change of the energy storage of other submodules. In addition, the energy storage of submodules are designed so large that they have sufficient energy for the control of transient

Can store upper and lower oscillations. However, these large energy stores, usually capacitors, add significantly to the cost and weight of such a device.

WO 2008/039120 A1 describes a high-voltage direct-current transmission system with two converters, which are connected to one another on the DC voltage side. The converters have three phase modules, each with an AC voltage connection, where the AC voltage connections are each connected to one phase of the connected AC mains. In addition, each phase module has two DC voltage connections. In order to be able to fully utilize a three-phase AC voltage line for DC transmission, the device has, in addition to the phase modules, a further module which is equipped with two DC voltage connections and a center connection. The additional module is like the phase modules connected at its two DC voltage terminals in each case with a phase conductor of the three-phase AC voltage line. The third conductor is connected to the middle connection of the module. With the help of this additional connection, the Capacitance of the AC line for high-voltage DC transmission can be better used.

The object of the invention is therefore to provide a device and a method of the type mentioned above, which allow a simple balancing of the energy storage and which are also inexpensive.

The invention achieves this object on the basis of the aforementioned device by an additional module without AC voltage connection, which has at least one power semiconductor circuit, at least one energy store and at least one DC voltage connection, each DC voltage connection of the additional module being connected to one of the common DC voltage connections of the phase modules and Control means are provided, with which a circular current can be generated, which flows through the additional module and one of the phase modules. Based on the method mentioned above, the invention achieves this object by virtue of the fact that in a device which has phase modules with at least one common DC voltage connection and in each case a separate AC voltage connection, a voltage is applied between each DC voltage connection and each AC voltage connection

Phase module branch extends, in which is formed by a series circuit of two-pole submodules, each having an energy storage and the energy storage parallel-connected power semiconductor circuit, so that depending on the control of the power semiconductor switch either the voltage drop across the energy storage or zero voltage at the two terminals of a each submodule can be generated, wherein an additional module without an AC voltage connection is provided which has at least one power semiconductor circuit, at least one energy store and at least one DC voltage connection, each DC voltage connection of the additional module being connected to one of the common DC voltage connections of the phase modules and no An AC terminal, the power semiconductor circuits of a phase module and the additional module are driven so that a circular current is generated, which flows between and the add-on module and one of the phase modules and on this.

The device according to the invention has, in addition to the phase modules whose number corresponds to the number of phases of the connected AC voltage connection, an additional module. The additional module has no AC voltage connection and therefore can not be connected to the AC voltage network connected to the inverter. The additional installation of an additional module seems at first glance to be extra work. However, requirements are conceivable which justify the additional expense of savings elsewhere in the device. Thus, within the scope of the invention, it is possible to generate circulating currents which flow only via one of the phase modules, with the return current taking place via the additional module. In addition, if necessary, the additional module can provide active power supplies which, for example, are used to compensate for transient harmonics for balancing in the case of asymmetrical network errors of the phase affected by an error. In addition, it is also possible to absorb or emit energy in the event of an imbalance between the inverters. Finally, a controlled short circuit at the DC voltage terminals of the inverter is possible. The additional module can also serve to balance the DC voltages that are present in the DC voltage network. As a result, conventional transformers can be used, which are much cheaper than the DC transformers otherwise used, which generally have to contend with high DC voltage components and are therefore costly. As energy storage, a capacitor is preferably used. The configuration of the additional module is in principle initially arbitrary within the scope of the invention. It is essential that at least one energy store, and a power semiconductor circuit are provided, with which a control of the charge state of the or the energy storage is enabled. In other words, the power semiconductor circuit is connected to the energy storage device (s) such that, depending on the activation of the power semiconductor switch, the energy storage device (s) are charged or discharged.

In the context of the invention, it is preferred that the additional module has a series arrangement of two-pole submodules, which are each equipped with a power semiconductor circuit and with one of these parallel-connected energy storage, so that depending on the control of the power semiconductor circuit, either the voltage dropping to an energy store or a zero voltage can be generated between the two terminals of each submodule. In other words, the additional module also has a modular multi-level structure, with two-pole submodules connected in series with one another. In this case, each submodule again comprises an energy store and a power semiconductor circuit arranged parallel to the energy store. According to this advantageous development of the structure of the additional module is based on the structure of the phase modules. The submodules of

Add-on modules may be identical to or different from the submodules of the phase modules. It is essential in this exemplary embodiment that in this way a circulating current can be generated between the additional module and one of the phase modules of one of the inverters.

In a preferred embodiment, the submodules of the add-on module are designed as a half-bridge circuit. Deviating from this, however, it is possible to design the submodules as a full bridge circuit. In addition, it is possible to form the submodules as both half and full bridge modules. In the case of a submodule designed as a half bridge, either a zero voltage or the voltage dropping across the energy store can be generated at the output terminals of each submodule. The half-bridge circuit has only two power semiconductor switches, for example IGBTs, GTOs, IGCTs or the like, which are reverse-conducting or to which in each case a freewheeling diode is connected in parallel in opposite directions. The series circuit of the two power semiconductor switches is connected in parallel to the energy store. A terminal of the submodule is connected to a pole of the energy storage. The other terminal is connected to the potential point between the power semiconductor switches.

In a full bridge circuit, not only the energy storage voltage dropping across the energy store and a zero voltage at the two terminals of each submodule can be generated. Rather, the generation of the inverse energy storage voltage is also possible. For this purpose, the full bridge circuits have a total of four power semiconductor switches, wherein two series circuits each consisting of two power semiconductor switches are each connected in parallel to the energy store. One connection terminal is connected to the potential point between the power semiconductor switches of the first series circuit and the second connection terminal is connected to the potential point between the two power semiconductor switches of the second connection terminal. A possible with the use of Vollbrückensubmodulen negative voltage to the additional module can be used to extinguish arcs, which arise for example on a line of the DC network. In a further expedient development of the invention, the submodules moreover have at least one ohmic resistance, with which the electrical power is erroneous. can be reversibly converted into heat and released into the atmosphere.

In addition, it may be expedient that the additional module has at least one throttle. The throttle serves, for example, to connect a series circuit of submodules to one pole of the DC voltage network. Conveniently, two throttles are provided, which are arranged between the series connection of submodules and each pole of the DC voltage circuit.

Furthermore, it is possible for the additional module to have a center connection. The center connection can serve, for example, for earthing the entire system and for balancing the voltages in the DC intermediate circuit.

According to a preferred embodiment, the number of submodules of the additional module corresponds to the number of submodules of a phase module branch of a phase module. Thus, the add-on module can only have half as many submodules as one

Phase module connected to one phase of the connected AC mains. In this way the costs are reduced. Further expedient embodiments and advantages of the invention are the subject matter of the following description of embodiments of the invention with reference to the figures of the drawing, wherein like reference numerals refer to like-acting components and wherein

FIG. 1 shows an equivalent circuit diagram of a previously known modular multistage converter,

FIG. 2 shows a submodule designed as a half bridge for a multi-stage converter according to FIG. 1,

Figure 3 is designed as a full bridge submodule

the multi-stage converter according to FIG. 1, Figure 4 is an equivalent circuit diagram of a first embodiment of the device according to the invention and

Figure 5 show a further embodiment of the device according to the invention.

FIG. 1 shows a converter 1 according to the prior art. It can be seen that the converter has three phase modules 2, 3 and 4 which are each connected to a first common DC voltage connection 7 and a second common DC voltage connection 8. Furthermore, each phase module 2, 3, 4 has a separate AC voltage connection 7, which serves to connect one of the phases 6 of an otherwise not further clarified AC voltage network. The first common DC voltage connection 7 is connected to the positive pole and the second common DC voltage connection 8 to the negative pole of a DC voltage network. The inverter 1 is used to convert AC voltage to DC voltage or vice versa, depending on the direction of the power flow. The phase modules 2, 3 and 4 each have two phase module branches 9 to 14, which each extend between the respective AC voltage connection 5 and one of the DC voltage connections 7 or 8. In this case, each phase module branch 9 to 14 consists of a series connection of two-pole submodules 15 whose equivalent circuit diagrams are shown by way of example in FIGS. 2 and 3.

FIG. 2 shows a submodule 15 embodied as a half-bridge circuit. It can be seen that this submodule 15 has an energy store 16 and a power semiconductor circuit 17, which is implemented in FIG. 2 as a series circuit 22 which consists of two power semiconductor switches 18, each of which has a freewheeling diode 19 is connected in parallel in opposite directions. The power semiconductor switches 18 are power semiconductor switches which can be switched on and off such as IGBTs, GCTs or the like. The submodule 15 according to FIG. 2 has a first connection terminal 20, which is connected to the potential point between the power semiconductor switches 18, and via a second connection terminal 21, which is connected to a pole of the energy accumulator 16. Depending on the control of the power semiconductor switch 18, either the voltage dropping across the energy store Uc or the voltage zero can thus be generated at the connection terminals 20 and 21.

FIG. 3 shows a submodule 15, which is referred to as a so-called full bridge circuit. The full-bridge circuit also has energy stores 16 and a power semiconductor circuit 17 connected in parallel therewith, which has a first series circuit 22 and a second series circuit 23, each consisting of two power semiconductor switches 18 which can be switched on and off. The first series circuit 22 and the second series circuit 23 are both connected in parallel to the energy store 16. The first connection terminal 20 of the submodule 15 is connected to the potential point between the power semiconductor switches 18 of the first series circuit 22 and the second submodule connection terminal 21 is connected to the potential point between the power semiconductor switches 18 of the second series circuit 23. Thus, both the energy storage voltage Uc dropping across the energy store 16, in this case a capacitor, a zero voltage or else the inverse energy storage voltage Uc can be generated at the connection terminals 20 and 21 of the submodule 15 according to FIG.

There are known inverter 1, the submodules 15 are all formed as a half-bridge circuit. In addition, as known in Figure 1 inverter known, which form only submodules in full bridge circuit according to Figure 3. Finally, inverters 1 have been proposed which are both

Full and half-bridge circuits in their phase module branches have. In FIG. 1, dashed lines and arrows schematically illustrate that the currents flowing through the phase module branches 9 to 14 can have both alternating voltage components Iac flowing, for example, from a phase 6 of the alternating voltage network, to both sides via the phase module branches of a common phase module. In addition, DC components Idc are also recognizable which flow, for example, from the negative DC voltage connection of the phase module 2 via the phase module branches 10 and 9 to the positive DC voltage connection. Finally, circular currents Ici are also possible, which arise, for example, when voltage differences occur between the phase module voltages generated by the phase modules 3 and 4. The circulating currents Ici flow between the phase modules 3 and 4 and via the phase modules 3 and 4.

FIG. 4 shows an exemplary embodiment 24 of the device 24 according to the invention, which has an inverter 1 according to FIG. 1 and an additional module 25. The additional module 25 has two DC voltage terminals 26 and 27, which are connected to the common DC voltage terminals 7 and 8 of the phase modules 2, 3 and 4. The additional module 25 also has a series connection of submodules 15, which are all designed either as a half-bridge circuit according to FIG. 2 or all as a full-bridge circuit according to FIG. In addition, it is also possible to provide submodules both as half and full bridge circuits in the series connection of the additional module 25. In a further development of the embodiment shown in FIG. 4, which is not illustrated in FIG. 4, an inductance in the shape of a choke, coil or the like is arranged between the series connection of the submodules 15 and each of the DC voltage terminals 26 and 27 of the additional module 25.

FIG. 5 shows a further exemplary embodiment of the device 24 according to the invention, the additional module 25 of which has a A first additional module branch 28 and between the middle branch 30 and the DC voltage connection 27 a second additional module branch 29 extend between the middle connection 30 and the DC voltage connection 26. Each of the additional module branches 28, 29 in turn consists of a series connection of submodules 15 according to FIG. 2 and / or FIG. 3. The middle connection 30 is connected, for example, to the ground potential. With the aid of the additional module 25, it is possible within the scope of the invention to generate circulating currents Ici between only one of the phase modules, eg phase module 4, and the additional module 25, the remaining phase module branches 2 and 3 being unloaded from said circulating current. Such a circulating current Ici is illustrated in FIG. In this way, for example, an asymmetric load of the connected AC voltage network can be compensated. In addition, it is possible for the power stored in the energy stores of the additional module 25 to be made available for the converter 1 at short notice in the event of need. The energy storage 16 of the phase modules 2, 3, 4 of the inverter 1 can thus be made smaller and therefore less expensive.

The additional module 25 can be arranged in the immediate vicinity of the converter 1. In the context of the invention, however, a greater distance between the additional module 25 and inverter 1 is possible.

On the DC voltage network, which is connected to the DC voltage connections 7 and 8, are usually connected to at least two inverters. In addition, however, it is also possible in multi-terminal applications, multiple inverters by, for example, meshed

DC voltage networks to connect with each other. In the context of the invention it is therefore possible to equip all interconnected by the DC voltage network inverter 1 with such an additional module. However, an additional module can also be shared by several inverters. Also It is possible, for example, to use a plurality of additional modules for a plurality of inverters, wherein the number of phase modules is less than the number of inverters that are connected to the DC voltage network.

Claims

claims

1. Device (24) for transmitting an electrical power between an AC voltage network and a DC voltage network in the high voltage range with phase modules

(2,3,4), each having at least one common DC voltage connection (7,8) and a separate AC voltage connection (5), wherein between each DC voltage connection (7,8) and each AC voltage connection (5) a phase module branch (9,... 14), which has a series connection of bipolar submodules (15), each having an energy store (16) and a power semiconductor circuit connected in parallel to the energy store, so that depending on the drive of the power semiconductor circuit ( 17) either the voltage dropping across the energy store (16) or a zero voltage at the two terminals (20, 21) of each submodule (15) can be generated,

marked by

an additional module (24) without AC voltage connection, which has at least one power semiconductor circuit (17), at least one energy store (16) and at least one DC voltage terminal (26, 27), each DC voltage terminal (26, 27) of the additional module (25) with one of the common DC voltage connections (7, 8) of the phase modules

(2,3,4) is connected and control means are provided, with which a circular current can be generated, which flows via the additional module (25) and one of the phase modules (2,3,4).

2. Device (24) according to claim 1,

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

the additional module (25) has a series connection of bipolar submodules (15) which are each equipped with a power semiconductor circuit (7) and with an energy store (16) connected in parallel, so that depending on the activation of the power semiconductor circuit (17) either the at the energy storage (16) falling voltage or but a zero voltage between the two terminals (20,21) of each submodule (15) can be generated.

3. Device (24) according to claim 1 or 2,

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

each submodule (15) forms a half-bridge circuit.

4. Device (24) according to claim 2,

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

each submodule (15) forms a full bridge circuit.

5. Device (24) according to claim 2,

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

the sub-modules (15) form both half-bridge and full-bridge circuits.

6. Apparatus (24) according to any one of claims 2 to 5, d a d c h e c e n e c e s in that

the submodules (15) are at least partially equipped with ohmic resistors for the thermal dissipation of electrical power.

7. Device (24) according to one of the preceding claims, characterized in that a

Each additional module (25) is equipped with at least one throttle.

8. Device (24) according to one of the preceding claims, characterized in that a

the additional module (25) has a center connection (30).

9. Device (24) according to claim 2, wherein:

the number of submodules (15) of the additional module (25) corresponds to the number of submodules (15) of a phase module branch (9, ... 14) of a phase module (2, 3, 4).

10. A method for controlling a device (24), the phase modules (2,3,4) with at least one common DC voltage connection (7,8) and each having an AC voltage terminal (5), wherein between each DC voltage connection (7 , 8) and each AC voltage terminal (5) a Phasenmodulzweig (9, ... 14) extends, which has a series circuit of bipolar submodules (15), each having an energy storage and the energy storage (16) in parallel power semiconductor circuit (17) Depending on the control of the power semiconductor circuit (17), either the voltage dropping across the energy store (16) or a zero voltage at the two terminals (20, 21) of each submodule (15) can be generated, with an additional module ( 25) is provided, which has at least one power semiconductor circuit (17), at least one energy store (16) and at least one DC voltage connection (26, 27), each of which DC terminal (26,27) of the additional module (25) is connected to one of the common DC terminals of the phase modules and wherein the additional module has no AC terminal, in which the power semiconductor circuits of one of the phase modules (2,3,4) and the additional module (25) be controlled so that a circular current Ici flows between and over the additional module (25) and one of the phase modules (2,3,4).