Modular energy store for bridging voltage drops in electric drives

Abstract

The invention relates to a power converter circuit (4), in particular an M2C converter having at least two sub-converters, a first sub-converter, in particular a rectifier bridge, and a second sub-converter, in particular an inverter bridge, wherein at least the second sub-converter has at least one phase module (8), which has an upper and a lower branch, and the positive connections (P) of which are electrically conductively connected to a positive busbar (PS) and the negative connections (N) of which are electrically conductively connected to a negative busbar (NS) and thus form an intermediate circuit, in particular a DC intermediate circuit (7), wherein a connection point of the electrically series-connected branches of each phase module (8) forms an AC voltage connection (L), wherein each branch of the phase module (8) has two or more bipolar sub-modules (12) electrically connected in series, wherein each bipolar sub-module (12) has a storage capacitor (17) to which a series circuit of two controllable electronic semiconductor switches (13, 14), each having a diode (15, 16) connected in anti-parallel, is electrically connected in parallel, and wherein a connection of the storage capacitor (17) and a connection point of said two controllable electronic switches (13, 14) each form a terminal (I, II or II, I), wherein the intermediate circuit, in particular DC intermediate circuit (7), has at least one storage branch (9) with at least two sub-modules (12), wherein these sub-modules (12) each have an energy store (10) which is electrically connected in parallel with the, in particular internal, energy store (17) of the sub-module (12).

Description

[0001] Description

[0002] Modular energy storage for bridging voltage drops in electric drives

[0003] The invention relates to a modular energy storage device for bridging voltage drops in electric drives.

[0004] In drive technology, a variety of converter circuits are known for the low-loss conversion of electrical energy into mechanical work. Especially in the higher power range, these converter circuits are used to control the energy flow between dynamoelectric machines and power grids, especially in variable-speed drives.

[0005] Modular converters with an intermediate circuit, as shown in FIGS. 1 and 2, can be used as known circuits in the higher power and voltage range. These converters are described in more detail in the figure description. The modular design with cell modules enables higher voltages to be achieved than would be possible with other circuits.

[0006] In the event of voltage dips in the supply network, pulse-controlled inverters with diode feed-in (DFE) of the intermediate circuit - depending on the extent of the dip - result in a reduced output voltage at the motor and thus in a loss of output power or even in active braking of the motor load.

[0007] With an active feed-in of the intermediate circuit (Active Front End, AFE), reduced power can still be provided in the event of dips with residual voltage, but deep voltage dips in the supply network can even lead to the AFE being switched off.

[0008] This is particularly critical for modular converter circuit topologies, such as the M2C topology, which is also known from DE 101 03 031 B4. For a description and explanation of the M2C topology, please refer to this source. If a shutdown has occurred, restarting the converter is not always possible without prior precharging and formatting. In this case, the converter and thus the entire drive train fails for several seconds. In practice, therefore, there is a choice between a shutdown-robust variant without residual torque using DFE and a less robust variant with residual torque using AFE.

[0009] A robust variant with available residual torque is not known.

[0010] There has long been a proposal to integrate energy storage into the converter cells. However, this has several disadvantages:

[0011] For example, when storage devices are directly integrated into the module's intermediate circuits, the available voltage swing of the storage device is reduced because the minimum module voltage is limited. This is particularly disadvantageous when capacitors are used as energy storage devices.

[0012] Furthermore, scaling the memory is difficult because the number of modules is usually specified directly by the application.

[0013] In addition, these storage devices must also be charged during pre-charging if they are not connected via DC / DC converters.

[0014] It is known to provide a capacitor or a series connection of capacitor banks in the intermediate circuit of a so-called U-converter having a DC voltage intermediate circuit.

[0015] Increasing the size of the capacitor bank for energy storage purposes brings with it several disadvantages:

[0016] In the event of a short circuit in the DC link, extremely high discharge currents flow from the DC-side capacitor arrangement, which can cause destruction due to extremely high mechanical forces and / or the arc effect.

[0017] The very small leakage inductance of the capacitor arrangement required for the semiconductor switches of the U-converter increasingly conflicts with a mechanically short-circuit-proof and insulation-safe design as the voltage level and energy content increase.

[0018] Before commissioning the converter, a current-limited pre-charging of the capacitor bank to a voltage equal to or higher than the operating voltage is generally necessary, as otherwise an uncontrolled, short-circuit-like charging of the capacitor bank from the AC or three-phase side may occur. The auxiliary circuits for this pre-charging are complex, as they must be designed for the high (operating) voltage.

[0019] These disadvantages are particularly serious at high voltages, which require series connection of power semiconductors.

[0020] Based on this, the object of the invention is to provide a power converter of an electric drive, in particular a pulse-controlled inverter in modular topology, which maintains a residual torque during robust shutdown and thereby avoids, among other things, the disadvantages mentioned above.

[0021] This object is achieved according to the invention with the features of the independent claim.

[0022] Advantageous embodiments can be found in the dependent claims.

[0023] A power converter circuit according to the invention is to be understood in particular as a power converter circuit which consists of a series connection of half-bridge or full-bridge modules, wherein the modules contain energy storage devices which have a greater energy density than electrolytic capacitors, e.g. supercapacitors or accumulators, and which is connected to the intermediate circuit of at least one three-phase converter, hereinafter referred to as partial converter, in such a way that energy can be exchanged between the converter(s) and the described series connection. This series connection of modules provided with storage devices is hereinafter referred to as the storage branch. The intermediate circuit can be designed as a DC voltage or AC voltage intermediate circuit. The energy storage devices contained in the modules can either be connected directly to the respective module intermediate circuit or to this intermediate circuit via a DC / DC converter.

[0024] In an advantageous development of the invention, the partial converter is a power converter circuit, also known as a modular multilevel converter (M2C). The number of submodules provided in the storage branch depends on various factors, such as the required energy storage capacity or the redundancy requirements of the overall system. In an advantageous development of the invention, the storage branch is connected to the common intermediate circuit of two partial converters, with the first partial converter being coupled to a supply network and the second partial converter supplying a load such as a drive or a second network.

[0025] In this arrangement, the storage branch can fulfill several advantageous functions. This makes it possible to bridge even deep dips in the supply network at the first sub-converter.

[0026] This applies both when the first converter section is designed as a diode bridge – here the storage branch maintains the intermediate circuit voltage so that the second converter can continue to supply the load – and when the first converter is designed as an M2C – here the storage branch relieves the load on the first converter, so that a mains voltage that is too low or a voltage change that is too large is less likely to lead to shutdown. Furthermore, the storage branch can also store energy, which is necessary, for example, during braking when energy cannot or may not be fed back into the supply network, such as when a diode bridge is used as the first converter section. This means that a controlled resistor, often referred to as a chopper, is no longer required for braking operation.

[0027] The storage branch thus offers the possibility of supplying or receiving energy to a load or a power grid in a regulated or controlled manner. At the same time, the storage branch is capable of supporting the voltage of the intermediate circuit. This can, for example, eliminate or at least significantly reduce flicker phenomena in a power grid. Furthermore, it is possible to significantly reduce power oscillations, such as those that occur in a single-phase grid, and reliably prevent mechanical vibrations from a motor connected to the power converter.

[0028] In other words: The power converter has two sub-converters. A first sub-converter on the AC side or three-phase side (usually the mains side) to, in particular, the DC intermediate circuit; it can be designed as a rectifier bridge. A second sub-converter from, in particular, the DC intermediate circuit to the AC side or three-phase side (usually the load side); it can be designed as an inverter bridge. The power converter therefore has an intermediate circuit that is electrically connected via the first and second sub-converters (rectifier bridge and inverter bridge) to the load side and, if applicable, the mains side as the AC side. These terms refer in particular to the energy supply from the mains. For example, when the drive is braking, in addition to charging the storage branch modules in the DC intermediate circuit, energy can also be fed back into the mains - depending on the design of the first sub-converter.

[0029] A phase module is provided for each potential connection on the AC side. The phase module, in turn, has two converter branches, with the connection point of the two series-connected converter branches representing the output-side potential connection. Furthermore, at least the majority of the phase modules have at least one branch choke to reduce circulating current harmonics. The converter branches comprise a series connection of submodules. The submodules, in turn, have an internal capacitor unit, also called a storage capacitor.

[0030] Each submodule can provide at least the voltage applied to its capacitor or a zero voltage at its output terminals. The phase modules of the power converter are connected at one end to a first, for example, positive potential terminal. The other end of the phase modules is connected to a second, preferably negative, potential terminal. The difference between these two potentials represents the voltage on the intermediate circuit side, or the DC link. The output AC voltage, or the output three-phase system, is formed from the output-side potentials.

[0031] According to the invention, one or more energy storage devices, in particular supercapacitors, are now integrated into the storage branches implemented with submodules, either in addition to or as a replacement for existing internal energy storage devices or storage capacitors of the submodules. The voltage of the energy storage devices can be adapted to the requirements of the submodule by connecting individual storage elements in series, and the energy content can be varied by connecting them in parallel.

[0032] Supercapacitors according to the invention are electrochemical capacitors. These are only suitable for pure DC applications, e.g., in the DC intermediate circuit. Compared to rechargeable batteries, they have a longer service life, significantly higher power density, and high peak current carrying capacity. Furthermore, they exhibit comparatively significantly greater cycle stability with maintenance-free operation.

[0033] A direct electrical connection of the storage device to the respective module intermediate circuit without an intermediate DC / DC converter allows for a larger number of series-connected storage modules and a larger voltage swing of the individual storage elements. The minimum total storage voltage of a storage branch should be greater than the maximum DC intermediate circuit voltage or the peak value of the maximum AC intermediate circuit voltage.

[0034] In an advantageous development of the invention, the storage branch can be separated from the intermediate circuit by means of a switch, allowing it to either absorb or release energy independently, for example, during pre-charging. Since no switching under load is required, i.e., essentially only currentless switching occurs, the switch can be designed as a disconnector with minimal effort.

[0035] Depending on the application, parallel connection of several storage branches in the DC link is also advantageously possible. This allows for scaling the energy content by varying both the number of storage modules connected in series in each storage branch and the number of storage branches connected in parallel. From a control engineering perspective, it is advisable, but not absolutely necessary, to decouple the parallel connection using chokes. The branch chokes used in the phase modules of the M2C can also be used here.

[0036] The SuperCaps can also be replaced by batteries, with compromises in terms of energy content-related performance and peak current load capacity.

[0037] This results in an optimal operating behavior of electric drives, especially in conjunction with a suitable control unit - even in the case of the above-mentioned network disturbances - by providing storage branches according to the invention with submodules containing, for example, supercaps on the intermediate circuit.

[0038] In pulse-controlled inverters with diode feed-in (DFE) of the DC link, the output voltage at the motor remains constant even during voltage drops in the supply network. This prevents a loss of output power or even active braking of the motor load.

[0039] The structure of the memory branches allows for modular expandability for almost any number of series connections of identical submodules and thus their memories, especially with SuperCaps.

[0040] Furthermore, the invention provides at least reduced error propagation in the event of failure or incorrect control of semiconductor switches of the submodules in the storage branches compared to a storage device installed directly in the intermediate circuit. This means that even with a large number of submodules, especially in the storage branches, there is a reliable option for utilizing redundancy within the respective storage branch, for example, by using bypass switches on the submodule terminals.

[0041] The inventive design of the storage branches, together with appropriate control, ensures a uniform voltage distribution across the energy storage devices or their SuperCap modules.

[0042] The invention is not limited to the use of storage branches in M2C technology. Such storage branch modules can also be used as storage in other DC intermediate circuits.

[0043] Such storage branch modules can also be arranged in AC intermediate circuits with appropriate adaptations if necessary.

[0044] The energy storage devices designed as supercapacitors can replace the existing capacitor, in particular the film capacitor of the submodule, or can be present in addition to it.

[0045] The supercaps are also optionally available with a snubber.

[0046] Spatially speaking, the supercaps are arranged outside the submodule or integrated into the submodule.

[0047] In a further advantageous embodiment of the invention, the submodules of the phase modules and the submodules of the storage branch are identical. It has been shown that the same submodules can be used in the storage branch as in the phase modules. This increases the number of common components in the converter circuit and allows for a cost-effective design. At the same time, maintenance costs are reduced because there is no need to keep different submodules in stock. Alternatively, it is also possible to arrange semiconductors in the submodules of the storage branch that have a higher blocking voltage than the semiconductors of the submodules of the phase module. This allows a more finely stepped voltage to be provided to the load. It has been shown that such fine grading is not necessary for the storage branch and has no influence on the control dynamics of the energy provided by the storage branch.Alternatively, it is also advantageous to arrange semiconductors in the submodules of the storage branch that have a lower blocking voltage than the semiconductors in the submodules of the phase module. These submodules can be connected to supercaps or ultracaps, which have a low operating voltage. In this case, the submodules of the storage branch can also be used to balance the voltages of the supercaps or ultracaps.

[0048] In a further advantageous embodiment of the invention, the capacity of the energy storage device is greater than the capacity of the internal energy storage device. In this embodiment, the energy storage devices of the sub-modules of the phase module can be designed with particularly low capacity if the support of the intermediate circuit voltage is taken over by the storage branch. Furthermore, the sub-modules of the phase modules do not have to contribute to maintaining or controlling / regulating the intermediate circuit voltage. This is achieved by the energy storage devices of the storage module. This leads to a smaller number of capacitors if the capacitance of the capacitors is concentrated in the storage branch. It has been shown that this results in a lower total capacitance required compared to an arrangement of capacitors for stabilizing the intermediate circuit voltage in the sub-modules of the phase modules.

[0049] In a further advantageous embodiment of the invention, the storage branch is designed to be branch-free. This achieves high dynamics in the regulation of the intermediate circuit voltage. Furthermore, the occurrence of major asymmetries is prevented. Branch-free means that there is neither a load connection nor parallel current paths in the storage branch.

[0050] The invention and further advantageous embodiments of the invention are explained in more detail using exemplary embodiments shown in principle, in which:

[0051] FIG 1 Converter circuit of a drive with diode feed (DFE) of a DC intermediate circuit,

[0052] FIG 2 Converter circuit of a drive with active supply of a DC intermediate circuit (Active Front End, AFE),

[0053] FIG 3, 4, 9 Schematic diagrams of submodules,

[0054] FIG 5 Phase module on rectifier or inverter side,

[0055] FIG 6 storage branch module,

[0056] FIG 7 Converter circuit of a drive with diode feed (DFE) of a DC intermediate circuit with storage branch module,

[0057] FIG 8 Converter circuit of a drive with active DC link feed (Active Front End, AFE) with storage branch module. For the sake of clarity, in some cases where components are present multiple times, not all components shown are provided with reference symbols.

[0058] The described embodiments can be combined in almost any way. Individual features of the respective embodiments can also be combined without departing from the essence of the invention.

[0059] FIG 1 shows a converter circuit with pulse-controlled inverters with diode feed (DFE). This modular multilevel converter is fed from a power grid, and the grid voltage is adjusted using a transformer arrangement 2. Using, for example, a diode bridge or rectifier bridge 5, the AC voltage of a busbar 1 of a power grid is converted into a DC voltage. The diodes, as components of the rectifier bridge 5, charge an intermediate circuit 7. An inverter bridge 6 is connected to the intermediate circuit 7. The inverter bridge 6 has phase modules 8, each with a plurality of submodules 12.

[0060] The submodules 12 of the modular multilevel power converter 4 generate an alternating voltage from this direct voltage for operating a dynamoelectric machine 3, in particular a motor. To control or regulate the motor 3, the alternating voltage generated by the submodules 12 of the inverter bridge 6 is adjusted in amplitude and frequency for the motor 3. The illustrated inductances 11 can be used to improve the control and / or regulation behavior of the modular multilevel power converter 4.

[0061] A phase module 8 has two branches, with the connection point of the two series-connected branches representing the AC voltage side potential connection. Each branch comprises a series connection of submodules 12. The submodules 12, in turn, each comprise an internal memory 17. A branch thus refers to a submodule 12 or the series connection of several submodules 12 with an inductor.

[0062] The inverter bridge 6 has three phase modules 8 which provide a three-phase system to a motor 3.

[0063] FIG 2 shows another converter circuit - with a mains-side converter designed as an AFE

[0064] Converter - a modular multilevel power converter, with phase modules 8 with a plurality of submodules 12 provided in both the rectifier bridge 5 (also referred to as the line-side inverter) and the inverter bridge 6 (also referred to as the load-side inverter). This modular multilevel power converter is fed from a power grid, and the input voltage is adjusted using a transformer arrangement 2. If the voltages more or less "match," chokes may also be sufficient.

[0065] With the help of a rectifier bridge 5 constructed from phase modules 8, the alternating voltage of a busbar 1 of a power supply network is converted into a direct voltage. The submodules 12 of the phase modules 8 in the inverter bridge 6 generate an alternating voltage from this direct voltage for operating a dynamoelectric machine, in particular a motor 3. To control or regulate the motor 3, the alternating voltage generated by the submodules 12 of the inverter bridge 6 for the motor 3 is adjusted in amplitude and frequency. The illustrated inductors 11 can be used to improve the control and / or regulation behavior of the modular multilevel power converter 2.

[0066] A phase module 8 has two branches, with the connection point of the two series-connected branches representing the AC-side potential connection to the load or the mains. Each branch has a series connection of submodules 12. The submodules 12, in turn, each have an internal memory 17.

[0067] Both the rectifier bridge 5 and the inverter bridge 6 each have three phase modules 8.

[0068] FIGS. 3 and 4 each show a submodule 12. The submodule 12 has at least two semiconductor switches 13, 14 arranged in series and an internal memory 17 arranged in parallel with the two semiconductor switches 13, 14 arranged in series. The terminals of the submodule 12 are referred to below as I and II. The potential difference between these terminals I, II is referred to as the terminal voltage.

[0069] The controllable semiconductor switches 13, 14 are implemented using semiconductors such as IGBTs or MOS field-effect transistors. The antiparallel diodes 15, 16 can be discrete components or—as with MOS field-effect transistors—integrated into the semiconductor structure of the controllable semiconductor switches 13, 14. The submodule 12 further comprises a storage 17 or a capacitor bank composed of several storage capacitors with a resulting capacitance. The semiconductor switches 13, 14 arranged in series generally do not carry the same current. This submodule 12 can be used to generate the "zero" voltage or the voltage at the storage 17 at terminals I, II of the submodule 12.

[0070] The semiconductor switch 13, 14 comprises, in addition to a switching element capable of switching a current in a first current flow direction, a diode 15, 16 capable of conducting a current in a second current flow direction opposite to the first current flow direction. This diode 15, 16 is also referred to as a freewheeling diode.

[0071] FIG 9 shows another possible variant of submodule 12. Specifically, this submodule 12 comprises at least two semiconductor switches 13, 14 arranged in series, at least two further semiconductor switches 13, 14 arranged in series, and an internal storage device 17 arranged in parallel with these series circuits. The terminals of submodule 12 are also referred to below as I and II, and the potential difference between these terminals I, II is referred to as the terminal voltage. Such a submodule 12 is also conceivable with an energy storage device 10, particularly in an AC intermediate circuit.

[0072] The submodules 12 have the following properties:

[0073] There are one or more switching states of submodule 12 in which the terminal voltage (except for the forward voltage drop of real power semiconductors) assumes the value zero, regardless of the terminal current direction. Furthermore, there are one or more switching states in which the terminal voltage of submodule 12 assumes values ​​other than zero, regardless of the terminal current direction, and submodule 12 can absorb or release energy from storage device 17, depending on the terminal current direction. Furthermore, depending on the design of submodule 12, there may be one or more switching states of submodule 12 in which the terminal voltage is zero, depending on the terminal current direction, so that submodule 12 neither releases nor absorbs any energy.

[0074] FIG 3 and FIG 4 represent functionally equivalent variants of a submodule 12.

[0075] FIG. 5 shows a somewhat more detailed representation of the phase module 8, which has five submodules 12 (according to FIG. 3 or FIG. 4) per branch. The inverter bridges 6 according to FIG. 1 or FIG. 2 and / or the rectifier bridges according to FIG. 2 are formed from three phase modules 8 each. FIG. 6 shows a storage branch arranged in the DC intermediate circuit 7 via the connection terminals 18 and 19. A further storage device 10, in particular a SuperCap module, is provided electrically parallel to the energy storage devices 17 of a submodule 12 of the storage branch 9.

[0076] These supercapacitors are thus designed, in particular, as supercapacitor modules that can be easily attached to the submodules 12 and their storage devices 17. The supercapacitors or supercapacitor modules used as energy storage devices 10 can be individual capacitors or composed of several subcapacitors that have the effect of a single (overall) capacitor.

[0077] Furthermore, these SuperCaps are designed as electrochemical capacitors intended only for pure DC applications, e.g., in a module intermediate circuit or DC intermediate circuit 7. They offer significantly higher power density and a higher peak current capacity, while also having a longer service life than rechargeable batteries.

[0078] A power source (not shown in detail) is provided to precharge the energy storage devices 10 of the submodules 12 of the storage branches 9. This can be, for example, a power supply with current limitation, a battery with a series resistor, or a transformer with a secondary rectifier. If necessary, the precharging circuit can be expanded with a switch and / or a rectifier diode. A significant advantage, compared to a conventional voltage converter, is that the power source only needs to have a comparatively very low voltage.

[0079] To achieve this, each storage branch 9 can be controlled as follows to precharge its energy storage device 10. The energy storage devices 10 of each submodule 12 of a storage branch 9 are precharged sequentially or, in the case of multiple storage branches 9 connected in parallel, synchronously one after the other. With a higher available precharge voltage, several storage modules can also be charged simultaneously; with a lower precharge voltage, pulse width modulation in the storage branch can be used to boost the precharge voltage.

[0080] FIG 7 shows a power converter circuit with pulse-controlled inverters with diode feed (DFE) with a storage branch 9 in the DC intermediate circuit 7. FIG 8 shows a power converter circuit (AFE) of a modular multilevel power converter 4, wherein both in the rectifier bridge 5 and in the inverter bridge 6 phase modules 8 with a plurality of submodules 12 are provided and a storage branch 9 is connected in the DC intermediate circuit 7.

[0081] Particularly in conjunction with a suitable control unit 20, a storage branch 9 with submodules 12 containing supercaps is suitable for optimal control of electric drives.

[0082] In pulse-controlled inverters with diode feed-in (DFE) of the DC link 7, the output voltage at motor 3 remains constant even during voltage drops in the supply network. A loss of output power or even active braking of the motor load is avoided.

[0083] Even with active DC link feeding (Active Front End, AFE), voltage drops are virtually avoided and power can be provided almost undiminished, preventing a "worst-case scenario" such as the AFE shutting down.

[0084] The number of submodules 12 used in both the phase modules 8 and the storage branches 9 is determined by the application. Thus, two, three, four, five, or more submodules 12 can be provided per branch.

[0085] The converter circuit shown in FIGS. 7 and 8 can be broken down into individual, essentially identical phase modules 8, each of which has three terminals on the power side. These are designated as follows:

[0086] P: Positive terminal, which is to be connected to the positive busbar PS of the impressed DC voltage in the DC intermediate circuit.

[0087] N: Negative terminal, which is to be connected to the negative busbar NS of the impressed DC voltage in the DC link.

[0088] L: Load terminal which is to be connected to the AC side load - e.g. a phase of an AC or three-phase system.

[0089] Furthermore, these converter circuits have storage branch 9 with the following connections: P: positive connection, which is to be connected to the positive busbar PS of the impressed DC voltage in the DC intermediate circuit.

[0090] N: Negative terminal, which is to be connected to the negative busbar NS of the impressed DC voltage in the DC link.

[0091] The potential at load terminal L can be controlled by appropriately switching the respective submodules 12 to the potential of P or the potential of N. By continuously switching between these two switching states (pulse width modulation), any mean potential value between these limits can be set in a known manner. This process of setting a potential setpoint at load terminal L is also referred to as "voltage control."

[0092] The storage branch 9 arranged on the DC voltage side for supporting the DC voltage of the DC intermediate circuit 7 is directly connected to the DC voltage side connections P, N of all phase modules 8 via a system of busbars PS, NS.

[0093] The storage branches 9 contain internal energy storage devices that can be switched on and off, in particular supercaps.

[0094] The switching states used by the control unit 20 to connect and disconnect these energy storage devices, i.e., the SuperCaps 10, are designed to absorb energy in the event of overvoltages in the DC link 7 between the PS and LV busbars. However, uncontrolled energy release, particularly in the event of short circuits between PS and LV, is prevented.

[0095] In order to control the current or energy flow into or out of the storage branch 9, the control unit 20 can adjust the control level with the aim of achieving a specific total voltage.

[0096] According to the invention, the storage branches 9 prevent sudden discharges of energy storage devices 17 of the submodules 12 even in the event of possible short circuits between the busbars PS, NS of the DC intermediate circuit 7.

[0097] In addition, this storage structure on the DC intermediate circuit 7 enables the parallel operation of almost any number of storage branches 9 without disturbing compensating currents occurring between storage branches 9 and / or phase modules 8 on the DC intermediate circuit 7, which could lead, among other things, to energy losses.

[0098] A feature of the circuit arrangements according to the invention on the DC intermediate circuit 7 is, among other things, that it is possible to regulate, among other things, the energy flow by means of the control unit 20, ie by selecting corresponding switching states of the submodules 12 of the respective storage branch 9 and / or, if applicable, the phase modules 8.

[0099] The controllability of the energy flow can be used in an extremely advantageous manner to keep the voltage constant, especially at motor 3, in the event of transient or periodic fluctuations in the power flow (e.g. the power flow between the two alternating current or three-phase networks).

[0100] In each storage branch 9, the voltages across the supercapacitors are balanced using suitable methods. This is done, for example, by measuring the voltage at the energy storage device 10 and by detecting the current direction in the individual branches to determine the direction of the change tendency of each of the voltages at the energy storage device 10.

[0101] The submodules 12 of phase modules 8 and storage branches 9 do not have to be identical, but they can also be implemented differently (different voltage levels of the submodules, which of course must be suitable for the DC voltage together, different circuits of the submodules, e.g. full bridge / half bridge modules, different semiconductors with different current carrying capacity, different storage controls...).

[0102] Each submodule 12 can provide at least the voltage applied to the capacitor or a zero voltage at its output terminals.

[0103] The switching states of the submodules 12 of the storage branches 9 and / or the phase modules 8 as well as the charge states of their respective energy storage devices are adapted via the control unit 20 to the required operating states, e.g., of the motor 3.

[0104] In the submodule 12 according to FIGS. 3 and 4, a first of the two semiconductor switches 13, 14 is arranged between the terminals of the submodule 12, with a second of the two semiconductor switches 13, 14 being arranged between one of the terminals of the submodule 12 and the internal capacitor 17. To generate the first switching state, for example, the first semiconductor switch 13 is controlled such that it is conductive and the second semiconductor switch 14 is controlled such that it is blocking. Furthermore, the first switching state can also be achieved if neither of the two semiconductor switches 13, 14 is controlled.

[0105] The case in which no semiconductor switch 13, 14 is switched to the conducting state is also referred to as pulse blocking of submodule 12. Depending on the direction of current flow, one of the freewheeling diodes 15, 16 is then conductive. In this state, the internal capacitor 17 and the supercapacitor can only charge and not discharge due to the direction of current flow.

[0106] The energy storage device 10 does not have to be present in addition to the capacitor 17 of the submodule 12; it can also replace it if necessary, e.g., using supercapacitors instead of film capacitors, possibly equipped with an additional snubber. In any case, the energy storage device 10 can also be structurally integrated into the submodule 12.

[0107] In one embodiment of the invention, the error of a memory 10, 17 is detected, inter alia, by the magnitude of the voltage of the memory 10, 17 exceeding a predeterminable upper limit value or falling below a predeterminable lower limit value.

[0108] The semiconductor switches 13, 14, as well as a disconnector 22 are controlled by a control unit 20, which thus knows, among other things, both the switching states of the semiconductor switches 13, 14 and the switching state of the submodule 12.

[0109] The design of an M2C converter with storage branches 9 according to the invention is also suitable for controlled energy exchange between two three-phase networks, e.g., a HVDC close coupling.

[0110] The M2C converter could also be integrated into a HVDC transmission system to store energy, e.g., for minute reserve, or to mitigate fluctuations in wind farms.

[0111] 1 busbar of the network

[0112] 2 Transformer arrangement

[0113] 3 dynamoelectric machine

[0114] 4 Converter circuit

[0115] 5 Rectifier bridge

[0116] 6 Inverter bridge

[0117] 7 DC link

[0118] 8 phase module

[0119] 9 Memory branch

[0120] 10 energy storage

[0121] 11 Inductance

[0122] 12 Submodul

[0123] 13 semiconductor switches

[0124] 14 semiconductor switches

[0125] 15 anti-parallel diode in the submodule

[0126] 16 anti-parallel diode in the submodule

[0127] 17 internal energy storage

[0128] 18 connection elements DC link

[0129] 19 Connection elements DC link

[0130] I, II terminals of the submodule

[0131] 20 control unit

[0132] 21 branch

[0133] 22 disconnectors

[0134] PS + busbar of the DC link

[0135] LV - Busbar of the DC link

[0136] P plus connection

[0137] N negative connection

[0138] L load connection

Claims

Patent claims 1. A power converter circuit (4), in particular an M2C converter with at least two partial converters, a first partial converter, in particular a rectifier bridge, and a second partial converter, in particular an inverter bridge, wherein at least the second partial converter has at least one phase module (8) having an upper and lower branch, the plus terminals (P) of which are electrically connected to a positive busbar (PS) and the minus terminals (N) of which are electrically connected to a negative busbar (NS), and thus form an intermediate circuit, in particular a DC intermediate circuit (7), wherein a connection point of the electrically series-connected branches of each phase module (8) forms an AC voltage connection (L), wherein each branch of the phase module (8) has two or more two-pole submodules (12) connected electrically in series, wherein each two-pole submodule (12) has a storage capacitor (17),in which a series circuit of two controllable electronic semiconductor switches (13, 14), each with an anti-parallel connected diode (15, 16), is electrically connected in parallel, and wherein a connection of the storage capacitor (17) and a connection point of these two controllable electronic switches (13, 14) each form a terminal (I, II or II, I), wherein the intermediate circuit, in particular DC intermediate circuit (7) has at least one storage branch (9) with at least two submodules (12), wherein these submodules (12) each have an energy store (10) which is electrically connected in parallel to the, in particular internal, energy store (17) of the submodule (12).

2. Power converter circuit (4), in particular an M2C converter according to claim 1, characterized in that the energy storage device (10) is designed as a supercap.

3. Power converter circuit (4), in particular an M2C converter according to claim 1, characterized in that the energy storage device (10) is designed as an accumulator.

4. Power converter circuit (4), in particular an M2C converter according to one of the preceding claims, characterized in that a storage branch (9) and / or the energy storage devices (10) of the respective submodules (12) can be switched by means of a switch in order to either absorb or release energy independently.

5. Power converter circuit (4), in particular an M2C converter according to claim 4, characterized in that the switch is designed as a disconnector (22).

6. Power converter circuit (4), in particular an M2C converter according to one of the preceding claims 4 or 5, characterized in that the isolating switch (22) is switched via a control unit (20).

7. Power converter circuit (4), in particular an M2C converter according to one of the preceding claims, characterized in that submodules (12) of the phase modules (8) are designed to be the same or different from the submodules (12) of the storage branches (9).

8. Power converter circuit (4), in particular an M2C converter according to one of the preceding claims, characterized in that the first partial converter, in particular the rectifier bridge (5) is designed as a diode feed or active feed.

9. Power converter circuit (4), in particular an M2C converter, according to one of claims 1 to 8, wherein the submodules (12) of the phase modules (8) and the submodules (12) of the storage branch (9) are identical.

10. Power converter circuit (4), in particular an M2C converter, according to one of claims 1 to 9, wherein the capacity of the energy storage device (10) is greater than the capacity of the internal energy storage device (17).

11. Power converter circuit (4), in particular an M2C converter, according to one of claims 1 to 10, wherein the storage branch (9) is designed to be branch-free.

12. Drive with a power converter circuit (4), in particular an M2C converter according to one of the preceding claims, wherein a motor (3) is electrically connected to the terminals of the second partial converter, in particular the inverter bridge (6).

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