DE102019120615B3 - Process and circuit for providing extended switching states for modular multilevel converters with half bridges - Google Patents

Abstract

The invention relates to a method for providing extended switching states in a modular multilevel converter with half bridges, in which the modular multilevel converter comprises at least one strand with a first outer module, a second outer module and at least one inner module, in which each module has a first side and a having second side, which each comprise a first module connection and a second module connection, in which each side has an outer and an inner half-bridge, each with a lower and an upper unidirectional semiconductor switch and a respective associated freewheeling diode, the respective outer half-bridges by an outer upper Busbar, the respective inner half-bridges are connected to one another by an inner upper busbar and all half-bridges are connected to one another by a lower busbar, with a first energy store between the inner upper busbar and the lower busbar and between A connection switch is arranged in the outer upper busbar and the inner upper busbar, with at least one serial and parallel connection of the first energy store of the respective module with the respective first energy stores of adjacent modules being made possible by a module formed in this way.

Description

The present invention relates to a method for providing extended switching states with an efficient skipping of a respective energy store in a modular multilevel converter, the modular multilevel converter having a plurality of half bridges as the base topology. A circuit for these efficient switching states is also claimed.

A modular multilevel converter system, for example an MMSPC described in " Goetz, SM; Peterchev, AV; Weyh, T., "Modular Multilevel Converter With Series and Parallel Module Connectivity: Topology and Control," Power Electronics, IEEE Transactions on, vol.30, no.1, pp.203,215, 2015. doi: 10.1109 / TPEL.2014.2310225 , generates voltage differences between two connection terminals, for example an energy network or a traction system of an electric car, by configuring an electrical connection of energy stores in modules and by switching modulation between switching states to form any intermediate states. If, for example, the modules generate a slightly lower voltage between two connection terminals than the terminals have, current and thus charge flow into the energy stores of the modules. If a few more modules are connected in series, current flows from the memories of these modules into the connection terminals. By means of targeted regulation, currents and voltages can be controlled very finely. In such a process, the energy stores behave like buckets that are temporarily filled or emptied from the outside. A controller can use a suitable selection of the switching states of each individual module, called scheduling, to decide which module is emptied, filled or not influenced by a current flowing into a multilevel converter.

The publication WO 2017/016601 A1 discloses a modular multilevel converter that has a bidirectional switch through which current can flow in both directions. The sub-modules of the modular multilevel converter described are also able to carry higher peak currents.

An essential goal in the operation of modular multilevel converters is to keep all energy stores similarly charged or at least to avoid that individual modules are overloaded or undercharged. This results in a first charge balancing mechanism: a respective energy content of the energy storage devices can be controlled and influenced by specifically switching modules into a current flow for charging (holding buckets in the water flow) or discharging them into the current flow (pouring buckets into the already flowing water jet) become). By measuring or estimating a state of charge or the voltage of each energy store, the controller can intervene accordingly.

Furthermore, charge and energy can be transferred from one module to another module in this way, for example by connecting one module positively in series and another module negatively in series, or, in the case of alternating current, one of the modules preferably with a positive one Half wave (in series connection) is used, but the module is preferably in a bypass mode in the case of a negative half wave. The other module is then treated in exactly the opposite way.

In the case of modular multilevel converters with the possibility of connecting modules in parallel, for example described in the US publication US 9,496,799 B2 , a second process of charge and energy transfer can also be used by temporarily connecting two or more modules with slightly differently charged energy stores in parallel. The equalizing currents from the full to the empty energy storage equalize the charge, voltage and / or energy accordingly.

However, energy between modules, and thus between their respective energy stores, can be exchanged only to a very limited extent or with high losses, although even during normal operation the modules can be loaded to different extents at times, in particular if different taps are used for different traction machines. In a multi-machine configuration, for example, this applies to the usual case that the individual traction machines are operated at different operating points, but also that due to the alternating voltage, a load per module can fluctuate with a frequency of the alternating voltage or its harmonics (in particular twice the frequency of the alternating voltage) . These fluctuations are not synchronized in time due to the time offset of the different phases and could compensate for an almost constant load if a substantial and efficient exchange of power between modules of different taps or lines would be possible.

The US publication US 2019/0052187 A1 discloses a method for controlling a multi-stage modular converter, the modules of which are formed with double submodules. An energy store arranged in each case in a submodule can be bypassed via two current paths, a parallel connection or an energy exchange of energy stores via one the respective double submodule is not possible.

The WO 2016/012 247 A1 relates to cascaded power converters with four-pole modules and realizes the principle that any modules in a line can be connected in parallel by bypassing energy storage in modules in between.

The DE 10 2015 106 196 B3 proposes in connection with two-pole modules to enable two parallel paths in bypass mode and to be able to separate the module energy storage from the module via a switch in series.

Against this background, it is an object of the present invention to provide a method which, in a modular multilevel converter, enables expanded switching states for an efficient skipping or bypassing of a respective energy store. It should also be possible to skip the respective energy store in several neighboring modules. Furthermore, a circuit with these efficient switching states will be presented.

To achieve the above object, a method for providing extended switching states in a modular multilevel converter with half bridges is proposed, in which the modular multilevel converter comprises at least one strand with a first outer module, a second outer module and at least one inner module. Each module has a first side and a second side, each of which comprises a first module connection and a second module connection. Each side has an outer and an inner half bridge, each with a lower and an upper unidirectional semiconductor switch and a respectively assigned freewheeling diode, the respective freewheeling diode in the flow direction from a source / emitter connection to a drain / collector connection of the respective unidirectional one Semiconductor switch is arranged. The respective lower semiconductor switch is connected with its drain / collector connection and the respective upper semiconductor switch with its source / emitter connection with the respective module connection on the respective side, the respective first module connection with the respective outer half bridge and the respective on each side each second module connection can be connected to the respective inner half bridge. The source / emitter connections of the respective lower semiconductor switches are by a lower busbar, the drain / collector connections of the respective outer half bridges by an outer upper busbar and the drain / collector connections of the respective inner half bridges are by an inner upper Busbar connected. A positive pole of a first energy store is connected to the inner upper busbar and a negative pole of the first energy store is connected to the lower busbar. A connection switch is arranged between the outer upper busbar and the inner upper busbar. A module formed in this way enables at least one serial and one parallel connection of the first energy store of the respective module with respective first energy stores of adjacent modules. A respective module is controlled by a control unit as a respective first switching unit. Finally, the current is conducted through at least one switching state of at least one first switching unit formed by an inner module via the respective outer upper busbar and the respective lower busbar, bypassing the respective first energy store of the at least one first switching unit.

Depending on the open or closed switch position, the connection switch arranged according to the invention enables two different sets of switching states which can be achieved with the half bridges, or can be switched back and forth between the two sets, similar to a register changeover, using the connection switch.

In the following, without restriction to this case, an inventive separation or division of a conceivable common upper busbar into the outer upper busbar and inner upper busbar with a connection switch arranged therebetween is considered. All of the disclosures set out below for this case apply analogously to the case also claimed: the lower busbar is separated or divided into an outer lower busbar and an inner lower busbar with a connection switch likewise arranged in between, the positive pole of the energy store now having all of them here Half-bridge common upper busbar and the negative pole of the energy store is connected to the inner lower busbar.

The respective energy store is selected as a DC voltage source or a DC voltage store at least from the following list: battery, battery pack, primary cell, secondary cell, capacitors of any type. In general, all energy sources or DC voltage storage devices providing DC voltage are conceivable.

The switching states of a module formed in one embodiment of the method according to the invention can include at least one serial-positive interconnection, ie interconnection of poles of the same name, one serial-negative interconnection, ie interconnection of poles of the same name, a parallel interconnection of the respective energy store Module with a respective energy storage of an adjacent module or bypassing or bypassing the respective energy storage of the module. The module formed in one embodiment of the method according to the invention advantageously has a module topology which enables switching states which are expanded compared to the prior art. Bypassing or bypassing the energy store of the respective inner module on two busbars is now possible, as a result of which transmission losses are reduced in comparison with a line through a single busbar. This also enables a new bypass switching state, here also referred to as “bypass boost”, in which the connection switch is open and, for example, when the inner upper semiconductor switches are open, all lower semiconductor switches and outer upper semiconductor switches of the respective inner module are closed and thus one In addition to the lower conductor rail, electricity can also be conducted via the outer upper conductor rail. With this bypass switching state, it is now also advantageously possible to skip the respective energy store of a number of adjacent modules, which is particularly important in the case of highly unevenly charged modules, in order to interconnect highly unevenly charged modules and the associated high short equalization currents and the energy losses resulting therefrom to avoid. Furthermore, a new parallel skip switching state is made possible for the respective inner module, in which a parallel connection of the respective energy stores is carried out between a left neighboring module and a right neighboring module, if such a neighboring module is not also in this parallel skipping switching state is formed, but the energy storage of the respective inner module is skipped. Both the bypass switching state made possible by the method according to the invention and the parallel skip switching state are therefore suitable for enabling a substantial and efficient power exchange between energy stores of different modules of a line or even different lines. In this way, an almost constant load balanced over a time course is also advantageously represented for the respective energy stores.

Dynamic reconfiguration of the interconnection of the respective energy stores of the modules advantageously enables a combination of at least three functions, namely firstly a charge exchange between the energy stores, for example to carry out conventional battery management, secondly bridging a defective module part without losing an overall function of the multilevel converter, and thirdly, generation of any output voltages and temporal current / voltage curves directly through the modular multilevel converter without the need for an additional power electronic converter.

The dynamic reconfiguration of the interconnection of the energy stores can directly generate an AC voltage and / or a multi-phase voltage for one or more consumers. A modulation index can advantageously be kept to a maximum for all amplitudes. Furthermore, the losses decrease even at low voltages, because an effective internal resistance drops due to the parallel connection of energy stores. Since levels between the voltages of two configurations can be kept very low, an almost distortion-free output voltage is generated. In addition, switching voltages can be used to modulate between such voltages in order to further smooth out.

It is conceivable that a respective semiconductor switch arranged in an embodiment of the method according to the invention is a low-voltage switch, i. That is to say that a maximum voltage for which the switch must be designed, for example in the switching units relevant to the respective switch, is significantly below an overall voltage provided by the multilevel converter.

In one embodiment of the method according to the invention, the connection switch is selected as a mechanical switch or a bidirectional semiconductor switch. The mechanical switch can be formed, for example, by a relay or a contactor and is used advantageously when a switching rate is very low or a very slow switching speed is desired. Alternatively, a bidirectional semiconductor switch can be used, which can be formed, for example, as a transistor that can be switched in both directions of current flow or from two unidirectional semiconductor switches with a respective free-wheeling diode. With such connection switches, the switching states of the inner module do not depend on the voltage conditions of the upper busbars.

In a further embodiment of the method according to the invention, the connection switch is selected as a unidirectional semiconductor switch with a free-wheeling diode, the free-wheeling diode being switched in the “reverse direction” to the current flow which occurs when the unidirectional semiconductor switch is closed. In contrast to the prior art, for example in the publication mentioned US 9,496,799 B2 , which absolutely requires bidirectional transistors in order not to connect energy stores or modules that are not directly adjacent in parallel, are now also sufficient in the module formed according to this further embodiment of the method according to the invention, and explicitly not used as a substitute as oppositely arranged Series connection for a bidirectional transistor. The arrangement of the unidirectional semiconductor switch with free-wheeling diode, however, forces a voltage condition between the two upper busbars, since depending on the direction of the free-wheeling diode, one of the two voltages of the respective upper busbars may be lower than the other, but a higher voltage can be found in the free-wheeling diode other track would discharge. In this further embodiment with a unidirectional semiconductor switch, the bypass switching state associated with a reduced power loss according to the invention is therefore used depending on the voltage potential of the energy store that may have to be skipped and a particular orientation of the unidirectional semiconductor switch.

In a further continued embodiment of the method according to the invention, the unidirectional semiconductor switch with free-wheeling diode is connected with its source / emitter connection to the outer upper busbar and with its drain / collector connection to the inner upper busbar and the associated free-wheeling diode is connected accordingly from the outer upper busbar towards the inner upper busbar in the forward direction. In normal operation with the connection switch closed, the outer upper and the inner upper busbar are at the same potential. When the connection switch is open, the bypass switching state is always available, and the parallel skip switching state is only available if a voltage potential of the energy store that is possibly to be skipped is higher than the voltage potential of the closest non-skipped parallel energy store. This is the case, for example, in the case of a current which charges the energy store to be skipped.

In a still further embodiment of the method according to the invention, the unidirectional semiconductor switch with free-wheeling diode is connected with its source / emitter connection to the inner upper busbar and with its drain / collector connection to the outer upper busbar, and the associated free-wheeling diode is connected accordingly by the If the inner upper busbar is arranged towards the outer upper busbar in the forward direction, the bypass switching state can no longer be used, but the parallel skip switching state if a voltage potential of the energy store that is possibly to be skipped is lower than the voltage potential of the nearest non-skipped one energy storage connected in parallel. This is the case, for example, in the case of a current that discharges the energy store that is possibly to be skipped.

In a further embodiment of the method according to the invention, a field-effect transistor is selected as the respective semiconductor switch with a free-wheeling diode, the field-effect transistor intrinsically having a body diode which assumes the function of the free-wheeling diode. The field effect transistor can be a MOSFET, for example.

In yet another embodiment of the method according to the invention, a second energy store is additionally arranged between the outer upper busbar and the lower busbar. Without this additionally arranged second energy store, intermediate circuits are conceivable which “run freely” without being loaded on the first energy store, ie. H. are freely interconnectable. As an alternative to this, however, two intermediate circuits are conceivable by arranging a second energy store in the respective module, a first intermediate circuit being formed by the inner half bridges and the first energy store and the second intermediate circuit being formed by the outer half bridges and the second energy store. In this case, the first energy store and the second energy store can be formed, for example, as a capacitor or as a battery cell or as a combination of both, and can also have a different voltage storage capacity. The respective connection switch can temporarily connect these two energy stores of the respective module in parallel or separate them from one another.

In a still further embodiment of the method according to the invention, in which the additional second energy store has been arranged, the connection switch is replaced by a double rectifier. The double rectifier is formed by connecting an inductance to the upper upper busbar and to it the source / emitter connection of a first unidirectional semiconductor switch, and further connecting its drain / collector connection to the inner upper busbar, and between the inductance and the first unidirectional semiconductor switch, a drain / collector connection of a second unidirectional semiconductor switch is connected, the source / emitter connection of which is connected to the lower busbar. Instead of a binary interconnection or disconnection, a targeted current and / or voltage regulation, ie a targeted power exchange, is advantageously possible between the first energy store and the second energy store of the respective module. For example, the one energy store can be connected in parallel with at least one right-hand module, and the other energy store can be connected in parallel with at least one left-hand module if, for example, they have similar voltage relationships. The one that forms in this arrangement Double rectifiers can even be used for controlled power exchange against a voltage direction. In addition to this embodiment of an arrangement of the double rectifier according to the invention, which is also referred to as a unidirectional buck-boost arrangement and requires that a voltage of the first energy store is higher than a voltage of the second energy store, other topologies are also for the power exchange of energy stores in intermediate circuits conceivable, for example a bidirectional buck-boost topology with four switches. Regardless of this, such an integral rectifier stage can be operated in current, voltage or current-voltage regulation.

In a further embodiment of the method according to the invention, a respective second switching unit is formed by a respective module without the two half bridges on its left side, but together with the two half bridges on the left side of a module adjacent to the right side of the respective module. This is possible because a respective module boundary can be shifted in the at least one strand of modules to form a respective switching unit. A so-called current commutation, i. H. the redirection of the current path must be carried out in particular between the half bridges. Since an intermediate state, for example between a serial switching state and a parallel switching state of the respective module, can lead to short circuits, a high degree of synchronicity in the switching of the individual switches of a switching unit formed in each case is usually necessary here. For this reason, it can be advantageous to change the module limits according to this further embodiment to the second switching unit according to the invention. A synchronicity requirement for the implementation of a respective switching state is advantageously reduced or a respective time frame can be adhered to more easily, since the (at least one) energy store to be connected in each case by the second switching unit is on one side - here the right side of the second switching unit - and which, for example, form a commutation arrangement belonging to a semiconductor switch belonging to the second switching unit, which are immediately adjacent. As a result, the semiconductor switches, for example belonging to a commutation group, which must be controlled at the same time or at least within a very narrow time frame, are no longer separated by the respective (at least one) energy store, which is why it is advantageous that switching units no longer differ, i.e. H. in the first switching unit, a module with a central (at least one) energy store must be synchronized with one another. Instead, all semiconductor switches that have to be activated simultaneously for a commutation of a current path are located in the same (second) switching unit. The time frame for controlling this respective second switching unit extends from a nanosecond range to a microsecond range or even beyond. In the same way, it is conceivable to form a third switching unit with the respective energy storage on the right, analogous to the second switching unit with the respective (at least one) energy store on the left.

Furthermore, a circuit for providing extended switching states in a modular multilevel converter with half bridges is claimed, the modular multilevel converter comprising at least one line with a first outer module, a second outer module and at least one inner module. Each module has a first side and a second side, each of which comprises a first module connection and a second module connection. Each side has an outer and an inner half bridge, each with a lower and an upper unidirectional semiconductor switch and a respectively assigned freewheeling diode, the respective freewheeling diode in the flow direction from a source / emitter connection to a drain / collector connection of the respective unidirectional one Semiconductor switch is arranged and the respective lower semiconductor switch with its drain / collector connection and the respective upper semiconductor switch with its source / emitter connection is connected to a respective first or second module connection on the respective side, the respective first module connection on each side is connected to the respective outer half bridge and the respective second module connection is connected to the respective inner half bridge. The source / emitter connections of the respective lower semiconductor switches are connected by a lower busbar. The drain / collector connections of the respective outer upper semiconductor switch are connected by an outer upper current rail and the drain / collector connections of the respective inner upper semiconductor switch are connected by an inner upper current rail. A positive pole of a first energy store is connected to the inner upper busbar and a negative pole of the first energy store is connected to the lower busbar, a connection switch being arranged between the outer upper busbar and the inner upper busbar. A module formed in this way enables at least one serial and one parallel connection of the first energy store of the respective module with respective first energy stores of adjacent modules. The circuit further comprises a control unit which is configured to control at least the respective first switching units. Finally, at least one switching state of at least one first switching unit formed by an inner module is configured to transmit the current via the respective outer upper busbar and the to conduct the respective lower busbar together bypassing the respective energy store of the at least one first switching unit.

In one configuration of the circuit according to the invention, the circuit additionally has a second energy store, which is arranged between the outer upper busbar and the lower busbar.

In a further embodiment of the circuit according to the invention, the connection switch is replaced by a double rectifier, the double rectifier being formed by connecting an inductance to the outer upper busbar and to it the source / emitter connection of a first unidirectional semiconductor switch, and furthermore its drain / Collector connection is connected to the inner upper busbar, and between the inductor and the first unidirectional semiconductor switch a drain / collector connection of a second unidirectional semiconductor switch is connected, the source / emitter connection of which is connected to the lower busbar.

In a still further embodiment of the circuit according to the invention, a respective second switching unit is formed by a respective module without the two half bridges on its left side, but together with the two half bridges on the left side of a module adjacent to the right side of the respective module.

Further advantages and refinements of the invention result from the description and the accompanying drawings.

It goes without saying that the features mentioned above and those yet to be explained below can be used not only in the combination specified in each case, but also in other combinations or on their own without departing from the scope of the present invention.

• 1 zeigt eine Modulschaltung als eine erste Schalteinheit zu einer Ausführungsform des erfindungsgemäßen Verfahrens.
• 2 zeigt eine Modulschaltung mit einem unidirektionalen Halbleiterschalter als Verbindungsschalter zu einer weiteren Ausführungsform des erfindungsgemäßen Verfahrens.
• 3 zeigt einen Bypass-Schaltzustand zu einer weiter fortgesetzten Ausführungsform des erfindungsgemäßen Verfahrens.
• 4 zeigt einen Parallel-Überspring-Schaltzustand zu einer noch weiter fortgesetzten Ausführungsform des erfindungsgemäßen Verfahrens.
• 5 zeigt eine Modulschaltung mit einem bidirektionalen Halbleiterschalter als Verbindungsschalter zu einer noch weiteren Ausführungsform des erfindungsgemäßen Verfahrens.
• 6 zeigt eine Modulschaltung mit einem umgekehrt angeordneten unidirektionalen Halbleiterschalter als Verbindungsschalter zu einer fortgesetzt weiteren Ausführungsform des erfindungsgemäßen Verfahrens.
• 7 zeigt eine Modulschaltung mit einer zweiten Schalteinheit zu einer fortgesetzt noch weiteren Ausführungsform des erfindungsgemäßen Verfahrens.
• 8 zeigt eine explizite Modulschaltung als zweite Schalteinheit zu der fortgesetzt noch weiteren Ausführungsform des erfindungsgemäßen Verfahrens.
• 9 zeigt eine Modulschaltung mit einem zusätzlichen zweiten Energiespeicher zu einer weiteren Ausführungsform des erfindungsgemäßen Verfahrens.
• 10 zeigt eine Modulschaltung mit einem Doppelgleichrichter zu einer noch weiteren Ausführungsform des erfindungsgemäßen Verfahrens.
• 11 zeigt eine Modulschaltung mit einem Doppelgleichrichter in bidirektionaler Buck-Boost-Topologie zu einer fortgesetzt noch weiteren Ausführungsform des erfindungsgemäßen Verfahrens.

The figures are described coherently and comprehensively, the same components are assigned the same reference numerals.

• 1 shows a module circuit as a first switching unit to an embodiment of the inventive method.
• 2nd shows a module circuit with a unidirectional semiconductor switch as a connection switch to a further embodiment of the method according to the invention.
• 3rd shows a bypass switching state to a further continued embodiment of the inventive method.
• 4th shows a parallel skip switching state to a still further embodiment of the method according to the invention.
• 5 shows a module circuit with a bidirectional semiconductor switch as a connection switch to yet another embodiment of the method according to the invention.
• 6 shows a module circuit with a reversed unidirectional semiconductor switch as a connection switch to another embodiment of the inventive method.
• 7 shows a module circuit with a second switching unit to a still further embodiment of the inventive method.
• 8th shows an explicit module circuit as a second switching unit to the still further embodiment of the method according to the invention.
• 9 shows a module circuit with an additional second energy storage for a further embodiment of the inventive method.
• 10th shows a module circuit with a double rectifier to yet another embodiment of the method according to the invention.
• 11 shows a module circuit with a double rectifier in bidirectional buck-boost topology to a still further embodiment of the method according to the invention.

samt jeweiliger Freilaufdiode 111, 112, 113, 114, 115, 116, 117, 118, hier als Feldeffekttransistor mit intrinsischer Bodydiode dargestellt. Zwei Modulanschlüsse 101, 102 stellen eine Verbindung zu einem linken Nachbarmodul und zwei Modulanschlüsse 103, 104 stellen eine Verbindung zu einem rechten Nachbarmodul her. Zwischen einem Drain-Anschluss des oberen unidirektionalen Halbleiterschalters $Q_{\alpha }^{\left(i\right)}$

111 der äußeren Halbbrücke der linken Seite und dem Drain-Anschluss des oberen unidirektionalen Halbleiterschalters $Q_{\eta }^{\left(i\right)}$

117 der äußeren Halbbrücke der rechten Seite verläuft eine äußere obere Stromschiene 105. Zwischen einem Drain-Anschluss des oberen unidirektionalen Halbleiterschalters $Q_{\gamma }^{\left(i\right)}$

113 der inneren Halbbrücke der linken Seite und dem Drain-Anschluss des oberen unidirektionalen Halbleiterschalters $Q_{\epsilon }^{\left(i\right)}$

115 der inneren Halbbrücke der rechten Seite verläuft eine innere obere Stromschiene 106. Zwischen allen Source-Anschlüssen der unteren unidirektionalen Halbleiterschalter $Q_{\beta }^{\left(i\right)}\mathrm{112,}{Q}_{\sigma }^{\left(i\right)}\mathrm{114,}{Q}_{\varsigma }^{\left(i\right)}\mathrm{116,}{Q}_{\theta }^{\left(i\right)}118$

der Halbbrücken verläuft eine untere Stromschiene 107. Zwischen beiden oberen Stromschienen 105, 106 ist ein Schalter $Q_l^{\left(i\right)}$

110, der ein mechanischer Schalter oder ein Halbleiterschalter sein kann, als ein Verbindungsschalter angeordnet. Schließlich ist zwischen der inneren oberen Stromschiene 106 und der unteren Stromschiene 107 ein Energiespeicher 109, hier dargestellt als gepolter Elektrolytkondensator 109 der Kapazität $C_m^{\left(i\right)}$

mit einem Spannungspotential $V_m^{\left(i\right)}$

108, angeordnet. In einem modularen Multilevelkonverter mit mindestens einem Strang aus N Modulen bildet ein erstes Modul ein erstes äußeres Modul und ein N-tes Modul ein zweites äußeres Modul, und das i-te Modul mit 1 <i<N ein inneres Modul als eine erste Schalteinheit. In einer Ausführungsform des erfindungsgemäßen Verfahrens werden nun durch einen mit der Modulschaltung 100 realisierbaren neuen Bypass-Schaltzustand und einen neuen Parallel-Überspring-Schaltzustand vorteilhaft die äußere obere und die untere Stromschiene 105, 107 als ein jeweiliger Strompfad mit gegenüber dem Stand der Technik reduzierten Durchleitungsverlusten genutzt.In 1 becomes a module circuit 100 shown for an i-th module for an embodiment of the method according to the invention. On both sides there is an outer and an inner half bridge, each with two unidirectional semiconductor switches $Q_{\alpha }^{\left(i\right)},Q_{\beta }^{\left(i\right)},Q_{\gamma }^{\left(i\right)},Q_{\delta }^{\left(i\right)},Q_{\epsilon }^{\left(i\right)},Q_{\varsigma }^{\left(i\right)},Q_{\eta }^{\left(i\right)},Q_{\theta }^{\left(i\right)},$

including the respective freewheeling diode 111 , 112 , 113 , 114 , 115 , 116 , 117 , 118 , shown here as a field effect transistor with an intrinsic body diode. Two module connections 101 , 102 connect to a left neighboring module and two module connections 103 , 104 establish a connection to a right neighboring module. Between a drain connection of the upper unidirectional semiconductor switch $Q_{\alpha }^{\left(i\right)}$

111 the outer half-bridge on the left side and the drain connection of the upper unidirectional semiconductor switch $Q_{\eta }^{\left(i\right)}$

117 An outer upper busbar runs along the outer half-bridge on the right-hand side 105 . Between a drain connection of the upper unidirectional semiconductor switch $Q_{\gamma }^{\left(i\right)}$

113 the inner half-bridge on the left side and the drain connection of the upper unidirectional semiconductor switch $Q_{\epsilon }^{\left(i\right)}$

115 An inner upper busbar runs along the inner half-bridge on the right side 106 . Between all source connections of the lower unidirectional semiconductor switches $Q_{\beta }^{\left(i\right)}\mathrm{112,}{Q}_{\sigma }^{\left(i\right)}\mathrm{114,}{Q}_{\varsigma }^{\left(i\right)}\mathrm{116,}{Q}_{\theta }^{\left(i\right)}118$

a lower busbar runs along the half-bridges 107 . Between the two top tracks 105 , 106 is a switch $Q_l^{\left(i\right)}$

110 , which may be a mechanical switch or a semiconductor switch, arranged as a connection switch. Finally, between the inner top track 106 and the bottom track 107 an energy storage 109 , shown here as a polarized electrolytic capacitor 109 of capacity ${\mathrm{C.}}_m^{\left(i\right)}$

with a potential for tension $V_m^{\left(i\right)}$

108 , arranged. In a modular multilevel converter with at least one strand of N modules, a first module forms a first outer module and an Nth module forms a second outer module, and the i-th module with 1 <i <N an inner module as a first switching unit. In one embodiment of the method according to the invention, a module circuit is used 100 realizable new bypass switching state and a new parallel skip switching state advantageous the outer upper and lower busbar 105 , 107 used as a respective current path with reduced transmission losses compared to the prior art.

In 2nd becomes a module circuit 200 with a unidirectional semiconductor switch 210 as a connection switch 210 shown to a further embodiment of the method according to the invention. In normal operation with the connection switch closed 210 are the outer top track 105 and the inner top track 106 at the same potential. With the connection switch open 210 the bypass switching state is always available, the parallel skip switching state only when a voltage potential 108 of the energy storage to be skipped if necessary 109 is higher than the voltage potentials of the closest non-skipped energy storage devices connected in parallel.

In 3rd becomes a module circuit with a bypass switching state 300 , 399 shown to a further continued embodiment of the method according to the invention. This is the module circuit 200 out 2nd Shown as a middle module with a left-adjacent module with module connections 301 , 302 , Semiconductor switches 311 , 312 , 313 , 314 , 315 , 316 , 317 , 318 , Connection switch 310 and energy storage 319 , and with a right-adjacent module with module connections 303 , 304 , Semiconductor switches 321 , 322 , 323 , 324 , 325 , 326 , 327 , 328 , Connection switch 320 and energy storage 329 connected is. A respective switch position of the semiconductor switch 111 , 112 , 113 , 114 , 115 , 116 , 117 , 118 , 210 , 310 , 315 , 316 , 317 , 318 , 320 , 321 , 322 , 323 , 324 is indicated by a small symbol of an open or closed switch, with a "v" as a logical ampersand expressing that both switch positions are permitted. The switch positions of the outermost semiconductor switches 311 , 312 , 313 , 314 , 325 , 326 , 327 , 328 are not specified because these, together with the modules that follow further outwards, can enter into any connections that do not influence the state of the modules shown with one another. With the switch positions shown, an additional bypass boost current path is shown in the middle module, in the figure by an upper and lower dashed line 306 shown, for a bypass switching state, for example, bypass boost around the energy store 109 generated around. The middle module does not increase the voltage of the line, but conducts any current of the line with less losses than a previously known bypass mode that only uses the lower (or outer upper) busbar alone. The bypass boost does not require a bidirectional connection switch because the electrical potential of the outer upper busbar corresponds approximately to that of the lower busbar and the voltage is therefore automatically lower than or equal to the voltage of the energy store 109 is. The freewheeling diode is therefore at the connection switch 210 not conductive. For clarification, the bypass boost is also in one for the circuit arrangement 300 equivalent equivalent circuit 399 shown, in addition to that between the lower busbar between the module connections 302 and 304 located connection of the energy storage 210 from an outer upper bypass current path around the connection switch 210 is bypassed.

In 4th becomes a module circuit with a parallel skip switching state 400 , 499 shown to a still further embodiment of the method according to the invention. Here, as with a dashed parallel skip current path 406 shown, the energy storage 319 of the module on the left and the energy storage 329 of the module on the right and connected in parallel and the energy storage 109 skipped the middle module. It is conceivable to skip a number of modules, just as it is conceivable to include other modules that are adjacent to the parallel connection of the energy storage devices 319 and 329 to involve. Would this be a bidirectional switch 110 out 1 done the potential relationships in the respective busbars would not matter. In the unidirectional version of the connection switch shown here 210 becomes the middle energy storage 109 however only skipped if the voltage potential of the external energy storage 319 and 329 are lower than the voltage potential of the middle energy store 109 . For the sake of clarity, the parallel skip switching state is also in one for the circuit arrangement 400 equivalent equivalent circuit 499 shown in which the energy storage 210 through which is between the module connections 302 and 304 located lower connection and that between the module connections 301 and 303 located upper connection is bypassed.

In 5 becomes a module circuit 500 shown with a bidirectional semiconductor switch as a connection switch to yet another embodiment of the method according to the invention. The connection switch 110 out 1 is in this embodiment by two anti-serial unidirectional semiconductor switches 510 , 520 realized with respective freewheeling diode.

In 6 becomes a module circuit 600 with a reversed unidirectional semiconductor switch 610 shown as a connection switch to another embodiment of the method according to the invention. The unidirectional semiconductor switch 610 with free-wheeling diode is with its source connection with the inner upper busbar 106 and with its drain connection to the outer upper busbar 105 connected.

The associated freewheeling diode is correspondingly from the inner upper busbar 106 towards the outer top track 105 arranged in the forward direction. With this arrangement, the bypass switching state can no longer be used, but the parallel skip switching state if a voltage potential 108 of the energy store to be skipped 109 is lower than the voltage potentials of the nearest non-skipped energy stores connected in parallel with one another.

In 7 becomes a module circuit 700 with a second switching unit 706 shown for a still further embodiment of the method according to the invention. In a string of modules, a module limit of an individual module, that is to say where the cut between two modules is made to form a switching unit, can be chosen relatively freely. So-called current commutation, ie redirection of the current path, must be carried out in particular between the half bridges. Since intermediate states, for example between a serial switching state and a switching state immediately following it, can lead to short circuits, a high degree of synchronism in the switching of the individual semiconductor switches of a commutation unit or switching unit is usually necessary here. For this reason, it may be advantageous not to change the module limits as with the first switching unit 705 to choose where the energy storage 109 is surrounded by the respective half bridges on the left and right side, but the module limits as in the second switching unit 706 to choose where the energy storage 319 directly on one of the module boundaries, here on the left.

In 8th becomes an explicit module circuit 800 as a second switching unit (reference number 706 out 7 ) to the still further embodiment of the method according to the invention. The selected module limits create three module connections 801 , 802 , 803 on the left and three module connections 804 , 805 , 806 On the right side. The energy storage 319 as module memory with voltage potential 808 is located here on the left. As an alternative to this, it is conceivable to set the module boundaries in such a way that, for example, the energy store 109 a module memory with voltage potential 108 on the right side.

In 9 becomes a module circuit with an additional second energy storage 909 shown to a further embodiment of the method according to the invention. There is a second energy store in an intermediate circuit formed by the outer half bridges 909 arranged, possibly with the first energy store 109 Can operate current or voltage exchange. The connection switch 110 can both energy storage 109 , 909 temporarily connect in parallel with each other or separate from each other again.

In 10th becomes a module circuit 1000 shown with a double rectifier to yet another embodiment of the method according to the invention. For this purpose, a first unidirectional semiconductor switch 1010 with an inductance 1030 serially between the inner upper busbar 106 and the outer top track 105 arranged. Together with a second unidirectional semiconductor switch 1020 a double rectifier in a so-called unidirectional buck-boost arrangement is thus formed, which exchanges power between the two energy stores 109 and 909 can regulate. However, this requires that the energy storage device has a voltage potential 909 is lower than the voltage potential of the energy store 109 .

In 11 becomes a module circuit 1100 shown with a double rectifier in bidirectional buck-boost topology to a still further embodiment of the inventive method. The two additionally arranged unidirectional semiconductor switches 1110 , 1120 enable the regulation of the exchange of power between the two energy stores 109 , 909 regardless of their respective tension ratios.

Claims (13)

Method for providing extended switching states (306, 406) in a modular multilevel converter with half bridges, in which the modular multilevel converter has at least one line with a first outer module (100, 200, 500, 600, 900, 1000, 1100), a second outer module (100, 200, 500, 600, 900, 1000, 1100) and at least one inner module (100, 200, 500, 600, 900, 1000, 1100), in which each module (100, 200, 500, 600, 900, 1000, 1100) has a first side and a second side, each comprising a first module connection (101, 103) and a second module connection (102, 104), in which each side has an outer and an inner half bridge, each with a lower one and an upper unidirectional semiconductor switch (111, 112, 113, 114, 115, 116, 117, 118) and a respectively assigned freewheeling diode, the respective freewheeling diode in the flow direction from a source / emitter connection to a drain / collector Connection of the respective u nidirectional semiconductor switch (111, 112, 113, 114, 115, 116, 117, 118) is arranged and the respective lower semiconductor switch (112, 114, 116, 118) with its drain / collector connection and the respective upper semiconductor switch (111 , 113, 115, 117) with its source / emitter connection are connected to a respective module connection (101, 102, 103, 104) on the respective side, the respective first module connection (101, 103) on each side with the respective outer half bridge and the respective second module connection (102, 104) is connected to the respective inner half bridge, in which the source / emitter connections of the respective lower semiconductor switches (112, 114, 116, 118) are connected by a lower busbar (107) in which the drain / collector connections of the respective outer upper semiconductor switches (111, 117) are connected by an outer upper busbar (105) and the drain / collector connections of the respective inner upper semiconductor switches (113, 117) 115) are connected by an inner upper busbar (106), in which a positive pole of a first energy store (109) is connected to the inner upper busbar (106) and a negative pole of the first energy store (109) to the lower busbar (107) A connection switch (110, 210) is arranged between the outer upper busbar (105) and the inner upper busbar (106), with a module (100, 200, 500, 600, 900, 1000, 1100) formed in this way at least one serial and one parallel connection of the first energy store (109) of the respective module (100, 200, 500, 600, 900, 1000, 1100) with respective first energy stores (319, 329) of adjacent modules is made possible, a respective module ( 100, 200, 500, 600, 900, 1000, 1100) is controlled by a control unit as a respective first switching unit (705), and at least one is controlled by at least one switching state by an inner module (100, 200, 500, 600, 9 00, 1000, 1100) formed first switching unit (705) the current via the respective outer upper busbar (105) and the respective lower busbar (107) together bypassing the respective first energy store (109) of the at least one first switching unit (100, 200, 500, 600, 900, 1000, 1100). Procedure according to Claim 1 , in which the connection switch is selected as a mechanical switch (110, 710) or a bidirectional semiconductor switch (510, 520). Procedure according to Claim 1 , in which the connection switch is selected as a unidirectional semiconductor switch (210, 310, 320, 610) with a freewheeling diode. Procedure according to Claim 3 , in which the unidirectional semiconductor switch (210, 310, 320) with free-wheeling diode is connected with its source / emitter connection to the outer upper busbar (105) and with its drain / collector connection to the inner upper busbar (106) . Procedure according to Claim 3 , in which the unidirectional semiconductor switch (610) with free-wheeling diode is connected with its source / emitter connection to the inner upper busbar (105) and with its drain / collector connection to the outer upper busbar (106). Method according to one of the preceding claims, in which the respective semiconductor switch (111, 112, 113, 114, 115, 116, 117, 118, 210, 310, 311, 312, 313, 314, 315, 316, 317, 318, 320 , 321, 322, 323, 324, 325, 326, 327, 328, 510, 520, 610, 1010, 1020, 1110, 1120) with free-wheeling diode a field effect transistor (111, 112, 113, 114, 115, 116, 117, 118, 210, 310, 311, 312, 313, 314, 315, 316, 317, 318, 320, 321, 322, 323, 324, 325, 326, 327, 328, 510, 520, 610, 1010, 1020, 1110, 1120) is selected, the field effect transistor (111, 112, 113, 114, 115, 116, 117, 118, 210, 310, 311, 312, 313, 314, 315, 316, 317, 318, 320, 321 , 322, 323, 324, 325, 326, 327, 328, 510, 520, 610, 1010, 1020, 1110, 1120) intrinsically has a body diode which assumes the function of the freewheeling diode. Procedure according to Claim 2 , in which a second energy store (909) is additionally arranged between the outer upper busbar (105) and the lower busbar (107). Procedure according to Claim 7 , in which the connection switch (110, 210, 310, 320, 510, 520, 610, 710) is replaced by a double rectifier, the double rectifier being formed by an inductance (1030) and the upper upper busbar (105) the source / emitter connection of a first unidirectional semiconductor switch (1010) is connected, and further its drain / collector connection is connected to the inner upper busbar (106), and between the inductor (1030) and the first unidirectional semiconductor switch ( 1010) a drain / collector connection of a second unidirectional semiconductor switch (1020) is connected, the source / emitter connection of which is connected to the lower busbar (107). Method according to one of the preceding claims, in which a respective module without the two half bridges (311, 312, 313, 314) on its left side, but together with the two half bridges (111, 112, 113, 114) on the left side a respective second switching unit (706, 800) is formed on a module (705) adjoining the right side of the respective module. Circuit (100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1100) for providing extended switching states (306, 406) in a modular multilevel converter with half bridges, the modular multilevel converter having at least one strand with a first outer module (100, 200, 500, 600, 900, 1000, 1100), a second outer module (100, 200, 500, 600, 900, 1000, 1100) and at least one inner module (100, 200, 500, 600 , 900, 1000, 1100), wherein each module (100, 200, 500, 600, 900, 1000, 1100) has a first side and a second side, each of which has a first module connection (101, 103) and a second module connection (102, 104), in which each side has an outer and an inner half bridge, each with a lower and an upper unidirectional semiconductor switch (111, 112, 113, 114, 115, 116, 117, 118) and a respectively assigned freewheeling diode, the respective freewheeling diode in the flow direction from a source / emitter connection s is arranged to a drain / collector connection of the respective unidirectional semiconductor switch (111, 112, 113, 114, 115, 116, 117, 118) and the respective lower semiconductor switch (112, 114, 116, 118) with its drain / Collector connection and the respective upper semiconductor switch (111, 113, 115, 117) with its source / emitter connection is connected to a respective module connection (101, 102, 103, 104) on the respective side, with on each side the each first module connection (101, 103) is connected to the respective outer half bridge and the respective second module connection (102, 104) is connected to the respective inner half bridge, in which the source / emitter connections of the respective lower semiconductor switches (112, 114, 116 , 118) are connected by a lower busbar (107), in which the drain / collector connections of the respective outer upper semiconductor switches (111, 117) are connected by an outer upper busbar (105) and the drain / collector connections the respective The inner upper semiconductor switch (113, 115) are connected by an inner upper busbar (106), in which the inner upper busbar (106) is a positive pole of a first energy store (109) and the lower busbar (107) is a negative pole of the first energy store (109), a connection switch (110, 210) being arranged between the outer upper busbar (105, 106) and the inner upper busbar (106), with a module (100, 200, 500 , 600) at least one serial and one parallel connection of the first energy store (109) of the respective module (100, 200, 500, 600) with respective first energy stores (319, 329) of adjacent modules are made possible, the circuit further comprising a control unit, which is configured to control at least the respective first switching units (705), and wherein at least one switching state (306, 406) at least one is controlled by an inner module (100 , 200, 500, 600, 900, 1000, 1100) formed first switching unit (705) is configured to conduct the current via the respective outer upper busbar and the respective lower busbar together bypassing the respective energy store of the at least one first switching unit . Circuit (900, 1000, 1100) after Claim 10 , in which the circuit additionally has a second energy store (909) which is arranged between the outer upper busbar (105) and the lower busbar (107). Circuit (1000, 1100) according to one of the Claims 10 or 11 , in which the connection switch (110, 210, 310, 320, 510, 520, 610, 710) is replaced by a double rectifier, the double rectifier being formed by an inductance (1030) and thereon with the outer upper busbar (105) the source / emitter connection of a first unidirectional semiconductor switch (1010) is connected, and further its drain / collector connection is connected to the inner upper busbar (106), and between the inductor (1030) and the first unidirectional semiconductor switch ( 1010) a drain / collector connection of a second unidirectional semiconductor switch (1020) is connected, the source / emitter connection of which is connected to the lower busbar (107). Circuit (800) according to one of the Claims 10 to 12th , with a respective module without the two half bridges (311, 312, 313, 314) on its left side, but together with the two half bridges (111, 112, 113, 114) on the left side one on the right side of the respective Module adjacent module (705), a respective second switching unit (706, 800) is formed.

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