Multilevel converter arrangement for converting electrical energy, use of a multilevel converter arrangement, method and computer program product

Abstract

Multilevel converter arrangement (10) for converting electrical energy, comprising - an input (14) for supplying electrical energy to be converted and an output (15) for delivering the converted electrical energy, - a level generation unit (11) and a converter unit (12) which are arranged to generate a certain number of voltage levels (SL) at the output (15), wherein - the level generation unit (11) is formed from at least one submodule (13, 13', 13''), wherein - the at least one submodule (13, 13', 13'') is formed by an electrical circuit (16), comprising a first branch (17) with an active switching element (19) connected in series with at least one partial voltage source (20) and a second branch (18) with a first switching element (21) connected in parallel to the first branch (17), and wherein - the first branch (17) has at least one second switching element (22) which is connected in parallel to one of the partial voltage sources (20), wherein the multilevel converter arrangement (10) has a boost converter (30) which is designed to apply a partial voltage to each of the partial voltage sources (20), wherein the multilevel converter arrangement (10) is designed to detect a faulty partial voltage source (20f), and wherein the boost converter (30) is designed to apply an increased partial voltage to each of the functional partial voltage sources (20) which are different from the faulty partial voltage source (20f).

Description

[0001] The invention relates to a multilevel converter arrangement for converting electrical energy. The invention further relates to a use of a multilevel converter arrangement, a method, and a computer program product. Technological background

[0002] The embodiments described herein generally relate to the field of power conversion, i.e. the conversion of direct current (DC) to alternating current (AC), or DC voltage to AC voltage, and vice versa, more precisely to converters (inverters and rectifiers) with multiple levels (multilevel).

[0003] The increasing use of gate-controlled electronic instrumentation technologies has given rise to a wide variety of converters. Various types of power converters and transformers are used in a variety of industrial applications. Multilevel converters, in particular, offer high power quality, high efficiency, reduced total harmonic distortion (THD) of the output voltage, improved electromagnetic compatibility, and high-quality voltage waveforms close to a sinusoidal shape.

[0004] This type of power conversion is particularly useful for directly connecting generator systems for renewable energy systems, such as wind turbines or solar panels, to the grid. Due to the growing number of renewable energy systems that are directly connected to the grid without intermediate storage, the inconsistent feed-in to the grid has a significant impact on the grid voltage and frequency. It is therefore necessary to control the voltage curve and frequency at the output of the generator system. One or more voltage converters are therefore coupled to a generator to ensure an appropriate voltage and frequency for the grid.

[0005] Converters with a small number of output voltage levels, for example two levels, show disadvantages in terms of the quality of the output AC voltage and current, low efficiency, high voltage drop and a reduced power factor.

[0006] These disadvantages can be compensated for with multilevel converters, which are capable of providing more and / or higher output levels or voltage levels at their output. However, increasing the output levels significantly increases the number of power electronics components used.

[0007] Conventional multilevel converters can be classified into three main groups: cascading H-bridge converters (CHBs) or their derivatives, so-called flying capacitor converters (FCs), and neutral point clamped converters (NPCs). These multilevel converters are formed by a specific arrangement of power components and capacitors as voltage sources.

[0008] The voltage generated at the output has a stepped shape due to the different switching times of individual power switches. Depending on the number of power switches, the output voltage increases or decreases by adding the individual (partial) voltages of the capacitances contained in the circuits, also referred to in this context as partial voltage sources. This requires a large number of power switches, DC sources, and gate control circuits to provide the required number of voltage levels. This disadvantageously increases power loss, the size and weight of the device, and reduces efficiency. Last but not least, the additional requirement for power electronics components increases the manufacturing and operating costs of a conventional multilevel converter.Due to the high number of circuit breakers required, there is also a high probability that there is a defect in one of the circuit breakers or that a defect occurs during operation.

[0009] DE 10 2020 127 328 A1 discloses a multilevel converter for converting electrical energy. A plurality of submodules, each comprising a partial voltage source, are connected in series.

[0010] However, as with other electronic devices, a fault can occur, for example, due to aging or a defect in one or more partial voltage sources or capacitors, which can have a negative impact on the reliability of the multilevel converter, particularly on the generation of voltage levels and the reduction of harmonic deviation. To avoid or remedy a potential impact on the reliability of the multilevel converter, an aged or defective partial voltage source can be replaced. However, such a replacement is complex and would lead to the shutdown of the multilevel converter, which is not always effectively possible.

[0011] Faults can occur in any switching element and / or any partial voltage source, i.e., capacitance. This can result in a complete interruption of the power supply and / or a voltage drop at the output. However, to provide a sinusoidal output current, the output voltage must not fall below the desired AC voltage.

[0012] The invention is based on the object of overcoming the disadvantages of the prior art, enabling fault-tolerant, reliable and continuous conversion of electrical energy, and avoiding shutdown of the converter arrangement.

[0013] The problem is solved by the subject matter of the independent patent claim. Preferred embodiments and further developments of the invention emerge from the features mentioned in the respective dependent claims, the drawings, and the associated description.

[0014] Common multilevel converter arrangements are disclosed in B. ROOHOLAHI; R. SALOMON: New Series of Single-Phase Symmetric / Asymmetric Multilevel Inverter Topologies with Reduced Number of Power Switches, In: 2021 23rd European Conference on Power Electronics and Applications, (EPE'21 ECCE Europe) 2021, Conference Paper, Date of Conference: 6-10 Sept. 2021 and US 10 734 914 B2, whereby DE 10 2018 009 391 A1 discloses bridging of partial voltage sources in battery modules. Summary of the invention

[0015] One aspect of the invention relates to a multilevel converter arrangement for converting electrical energy, comprising an input for supplying electrical energy to be converted and an output for outputting the converted electrical energy, a level generation unit and a converter unit configured to generate a specific number of voltage levels at the output, wherein the level generation unit is formed from at least one submodule, wherein the at least one submodule is formed by an electrical circuit comprising a first branch with an active switching element connected in series with at least one partial voltage source and a second branch with a first switching element connected in parallel to the first branch, and wherein the first branch has at least one second switching element connected in parallel to one of the partial voltage sources, wherein the multilevel converter arrangement has a boost converter,which is configured to apply a partial voltage to each of the partial voltage sources, wherein the multilevel converter arrangement is configured to detect a faulty partial voltage source (20f), and wherein the boost converter is configured to apply an increased partial voltage to the functional partial voltage sources different from the faulty partial voltage source.

[0016] A further aspect of the invention relates to a method for converting electrical energy, comprising the following steps: providing a multilevel converter arrangement according to one aspect of the invention; and applying a partial voltage to each of the partial voltage sources.

[0017] A further aspect of the invention relates to a computer program comprising instructions which, when the program is executed by a computer, cause the computer to apply a partial voltage to each of the partial voltage sources (20) in a multilevel converter arrangement according to one aspect of the invention. Short description of the characters

[0018] The invention is explained in more detail below using an exemplary embodiment and the accompanying drawings. The figures show: Fig. 1 is a schematic representation of a multilevel converter arrangement; Fig. 2 is a detailed schematic representation of a multilevel converter arrangement according to the prior art; Fig. 3 is a schematic representation of a multilevel converter arrangement according to the prior art; Fig. 4 is a schematic diagram of a multilevel converter arrangement according to an embodiment of the invention; Fig. 5 is a schematic representation of simulation results of a simulation of a multilevel converter arrangement according to an embodiment of the invention; Fig. 6 is a schematic diagram of a multilevel converter arrangement according to another embodiment of the invention; Fig. 7 is a schematic block diagram of a use of a multilevel converter arrangement and / or a method according to an embodiment of the invention; and Fig. 8 Simulation results of a simulation of a multilevel converter arrangement according to an embodiment of the invention. Detailed description of the invention

[0019] A multilevel converter arrangement according to the invention is designed to convert electrical energy. The multilevel converter arrangement and its topology can be adapted for various industrial applications, in particular for DC / AC conversion of renewable energy sources using the multilevel converter arrangement for low, medium, and high voltage applications. Some advantageous applications include, for example, connecting renewable energy sources, preferably wind power or solar power, to a power grid. Furthermore, the proposed topologies can be advantageously used for vehicle electrical applications, in particular for controlling AC motors by converting battery DC voltage / current into high-quality AC voltage / current.Furthermore, the proposed topologies can be advantageously used to reduce the harmonics of the output voltage in applications where low total harmonic distortion (THD) is required. Furthermore, the proposed topologies can be advantageously used for active filtering and reactive power compensation.

[0020] The multilevel converter arrangement comprises an input for supplying electrical energy to be converted and an output for outputting the converted electrical energy. The input is a connection of the multilevel converter arrangement for supplying electrical energy to be converted. The output is a connection of the multilevel converter arrangement for outputting the converted electrical energy. The converted electrical energy output at the output is output according to a voltage level. For this purpose, the multilevel converter arrangement comprises a level generation unit and a converter unit. The level generation unit and the converter unit are configured to generate a specific number of voltage levels at the output.

[0021] The level generation unit is formed from at least one submodule. The level generation unit has a modular topology. The at least one submodule is formed by an electrical circuit. The at least one submodule comprises a first branch with an active switching element connected in series with at least one partial voltage source and a second branch with a first switching element connected in parallel to the first branch. Due to the partial voltage source provided for each submodule, the number of voltage levels that can be generated at the output is determined by the number of submodules. The modular design of the level generation unit and thus of the multilevel converter arrangement thus enables flexible and precise matching of the number of required submodules to the output voltage to be generated. The active switching element and the first switching element enable targeted and reliable switching of the partial voltage source of the respective submodule.The first switching element and the active switching element are power switches, whereby the output voltage is increased or decreased by adding individual switched (partial) voltages of the capacitances contained in the circuits.

[0022] Preferably, the voltage levels at the output can be adjusted by the multilevel converter arrangement comprising a number of submodules that can be assigned to the voltage levels. The multilevel converter arrangement is single-phase, but can preferably also be formed as a single phase of a multiphase converter. In principle, the multilevel converter arrangement makes it possible to provide direct energy coupling on the output side to a power supply network without the need for additional, for example, known coupling devices based on the use of multiple inverters and isolating transformers. The serial modular design offers the possibility of easily increasing the voltage levels by combining various submodules according to the invention.This significantly reduces the conversion effort, increases efficiency and output quality, and reduces costs, installation space and control complexity.

[0023] According to the invention, the first branch has at least one second switching element. The second switching element is connected in parallel to one of the partial voltage sources. The second branch is thus branched into two sub-branches connected in parallel. The second switching element ensures that in the event of a fault, for example a defect, insufficient voltage, and / or failure of the partial voltage source, a current flows through the submodule in order to maintain the series connection of several submodules and / or partial voltage sources and / or the current flow through the submodule. Thus, by structurally changing the topology of the submodule, a fault-tolerant multilevel converter arrangement is provided that can address various fault scenarios and compensate for errors. This enables fault-tolerant, reliable, and continuous conversion of electrical energy.

[0024] Preferably, the second switching element has a forward direction and is arranged such that the second switching element forms a passive bypass for the partial voltage source connected in parallel with the second switching element. The active switching element connected in series with the partial voltage source can be switched in the forward direction. The two sub-branches of the second branch of the submodule are thus connected in parallel to one another such that the second switching element is passive in the case of an intact partial voltage source that provides a voltage and a current, while the second switching element conducts a current through the second branch in the case of a defective or non-operating partial voltage source. This prevents the entire submodule and thus the entire multilevel converter arrangement from failing in the event of a fault in the partial voltage source.The active switching element can be switched such that the active switching element and the second switching element have the same conduction direction to ensure current flow through the submodule. This allows, for example, an intact partial voltage source in the submodule to be connected to the defective partial voltage source to generate the output voltage.

[0025] Preferably, the second switching element has a forward direction and is arranged such that the first switching element of the second branch can be switched in parallel with the forward direction. This prevents the entire submodule, and thus the entire multilevel converter arrangement, from failing in the event of a fault in the partial voltage source. The first switching element can be switched such that the active switching element and the first switching element have the same forward direction in order to ensure current flow through the submodule. This allows, for example, an intact partial voltage source in the submodule to be switched in conjunction with the defective partial voltage source to generate the output voltage.

[0026] The multilevel converter arrangement preferably comprises a plurality of second switching elements, and the second switching elements are connected such that a second switching element is connected in parallel with each of the partial voltage sources. This ensures that for each of the partial voltage sources, one of the second switching elements is passive in the case of an intact partial voltage source that provides a voltage and a current, while the respective second switching element conducts a current through the second branch in the case of a defective or non-operating partial voltage source. Thus, in the event of a fault in one of the partial voltage sources, any other of the partial voltage sources in the submodule can be connected to generate the output voltage.

[0027] The multilevel converter arrangement preferably comprises a boost converter configured to supply a partial voltage to each of the partial voltage sources. The boost converter, also called a boost converter, is configured to charge the partial voltage sources, i.e., to generate a respective partial voltage of the partial voltage sources. Accordingly, the boost converter is electrically connected to the partial voltage sources. This embodiment recognizes that the output voltage results from the sum of the partial voltages, and a failure of one or more partial voltage sources can be at least partially compensated.For this purpose, the boost converter is designed to charge an intact partial voltage source in the case of one or more faulty partial voltage sources in such a way that the intact partial voltage source provides a partial voltage that is higher than the partial voltage of the intact partial voltage source in a case with fewer or no faulty partial voltage sources, i.e. in a case in which more or all partial voltage sources are intact.

[0028] The multilevel converter arrangement is preferably configured to detect a faulty partial voltage source. For this purpose, the multilevel converter arrangement preferably has a detection device and / or detection circuit configured to detect the partial voltages of the partial voltage sources. Based on the partial voltage, a conclusion is drawn as to whether the partial voltage source is intact or faulty. An intact or functional partial voltage source is a partial voltage source that has a predetermined partial voltage and / or a partial voltage within a predetermined first range. A faulty partial voltage source is a partial voltage source that has no partial voltage and / or a partial voltage within a predetermined second range.The boost converter is designed to apply an increased partial voltage to the functional partial voltage sources different from the faulty partial voltage source in order to compensate for a fault in the faulty partial voltage source.

[0029] Preferably, the boost converter has a duty cycle, and the boost converter is configured to change the duty cycle to change the partial voltage in order to be able to charge a partial voltage source accordingly in such a way that a possible error in a faulty partial voltage source is compensated. The partial voltage depends on the duty cycle. The duty cycle is optionally adjusted depending on the error by pulse width modulation in order to achieve a specific partial voltage, an increase, or a decrease in the partial voltage.

[0030] According to the invention, the multilevel converter arrangement is used to convert electrical energy. This enables fault-tolerant, reliable, and continuous conversion of electrical energy. The multilevel converter arrangement preferably comprises the features previously described as advantageous and / or optional in order to achieve the associated technical effects.

[0031] A method according to the invention for converting electrical energy comprises the following steps: providing the multilevel converter arrangement with the boost converter; and applying a partial voltage to each of the partial voltage sources. The multilevel converter arrangement preferably comprises the features previously described as advantageous and / or optional in order to achieve the associated technical effects. In particular, the method advantageously comprises detecting a faulty partial voltage source and / or changing a duty cycle to change a partial voltage.

[0032] A computer program according to the invention comprises instructions which, when executed by a computer, cause the computer to carry out the method according to the invention. Preferably, the computer program comprises instructions which, when executed by a computer, cause the computer to carry out the method, including optional and advantageous features, and to achieve the associated technical effects. In particular, the computer program comprises instructions which, when executed by a computer, cause the computer to detect a faulty partial voltage and / or change the duty cycle.

[0033] Fig. 1 shows a schematic representation of a multilevel converter arrangement 10. The schematic structure of the multilevel converter arrangement 10 is known in the prior art and corresponds to the structure of the multilevel converter arrangement 10 according to the invention.

[0034] The multilevel converter assembly 10 has an input 14 for supplying electrical energy to be converted and an output 15 for outputting the converted electrical energy. The input 14 is powered by a plurality of input voltage sources 40. Each of the input voltage sources 40 is, for example, a solar module, which is electrically connected to the multilevel converter assembly 10 via the input 14.

[0035] The multilevel converter arrangement 10 comprises a level generation unit 11. The level generation unit 11 comprises a plurality of submodules 13. The submodules 13 are in Fig. 1. The submodules 13 are fed through the input 14. Each of the input voltage sources 40 is electrically connected to the level generation unit 11. For example, each of the submodules 13 is electrically connected to one of the energy voltage sources 40. Each of the submodules 13 provides a partial voltage Vn. The submodules 13 are connected in series with one another. Therefore, an output voltage of the series connection of the submodules 13 results from the sum of the partial voltages Vn of the submodules 13. The output voltage of the series connection of the submodules 13 is applied to a DC voltage connection 25 of the multilevel converter arrangement 10 and is therefore referred to as voltage VL of the DC voltage connection 25.

[0036] The multilevel converter arrangement 10 comprises a converter unit 12. The level generation unit 11 is electrically connected to the converter unit 12 through the DC voltage connection 25.

[0037] In the embodiment shown, the converter unit 12 is an H-bridge converter and comprises four active power switches S1, S2, S3, and S4, referred to as converter switching elements 23. The H4-bridge converter unit 12 with four active power switches S1, S2, S3, and S4 is designed to switch in two half-cycles of the output frequency. Switches S1 and S4 switch in the positive half-cycle, and switches S2 and S3 switch in the negative half-cycle of the AC voltage of the supply network connected at output 15. The supply network is connected via output 15 to the multilevel converter arrangement 10, to which the output voltage Vout is applied. The output voltage Vout results from the voltage VL of the DC voltage connection 25 and the switching state of the converter switching elements 23.

[0038] As indicated by the vertically arranged sequence of dots, the number of submodules 13 and / or input voltage sources 40 can vary as desired to achieve a specific voltage level SL.

[0039] Fig. Figure 2 shows a detailed schematic representation of a multilevel converter arrangement 10 according to the prior art. The multilevel converter arrangement 10 according to Fig. 2 is described with reference to the multilevel converter arrangement 10 according to Fig. 1 described.

[0040] A plurality of submodules 13', 13'' are connected in series. Each of the submodules 13', 13'' comprises a first branch 17 and a second branch 18. The first branch 17 and the second branch 18 are connected in parallel. Each of the submodules 13', 13'' comprises an active switching element 19 and at least one partial voltage source 20 in the first branch 17. The submodules 13', 13'' differ in the number of partial voltage sources 20. The submodule 13' has one partial voltage source 20. The submodule 13'' has two partial voltage sources. The active switching elements 19 of the various submodules 13', 13'' are oriented similarly. Each of the submodules 13', 13'' comprises a first switching element 21 in the second branch 18. The first switching element 21 may, for example, comprise a diode or a transistor.

[0041] The level generation unit 11 comprises two further individual partial voltage sources 24, which are connected in series with the submodules 13', 13''. A bypass diode 26 enables the switching of the submodule 13' without the submodules 13''.

[0042] A DC voltage Vdc is applied as the total voltage at the input terminal 14 across the entire level generation unit 11. The sum of the individual partial voltages Vn of the partial voltage sources 20, 24 corresponds to the total voltage Vdc. The level generation unit 11 supplies N voltage levels SL to the DC voltage connection 25. With the converter unit 12, in such a configuration, a number N of voltage levels SL at the output 15 results from N = 2 x n + 1 = 4 x NS + 7, where n is the number of partial voltage sources 20, 24, and where NS is the number of submodules 13'' with two partial voltage sources 20.

[0043] As indicated by the vertically arranged sequence of dots, the number of submodules 13', 13'' can vary arbitrarily (not shown) in order to achieve a specific voltage level SL or a specific number N of voltage levels SL.

[0044] A fault in one of the partial voltage sources 20, 24 leads to a reduced performance of the entire multilevel converter arrangement 10. If, for example, another partial voltage source 24 fails, this leads to a serious failure of all submodules 13'' with two partial voltage sources 20 due to the series connection.

[0045] Fig. Figure 3 shows a schematic representation of a multilevel converter arrangement 10 according to the prior art. The multilevel converter arrangement 10 according to Fig. 3 is described with reference to the multilevel converter arrangement 10 according to Fig. 1 and Fig. 2 described.

[0046] The level generation unit 11 comprises a submodule 13' with one partial voltage source 20, a submodule 13'' with two partial voltage sources 20, and two further individual partial voltage sources 24. The level generation unit 11 comprises five DC partial voltage sources 20, 24, three active switches 19, 21, also referred to as Sa, Sb, and Sc, and two diodes 26 to generate four positive voltage levels SL. The converter unit 12 is configured to change the polarity of the voltage levels SL. Accordingly, the multilevel converter arrangement 10 shown can generate four voltage levels SL with a positive polarity, four voltage levels SL with a negative polarity, and one zero voltage level SL. Table 1: Switching states of the active switches for generating the output levels. Ausgangsspannung Sa Sb Sc S1 S2 S3 S4 +5Vn 1 0 1 1 0 0 1 +4Vn 1 0 0 1 0 0 1 +3Vn 0 1 1 1 0 0 1 +2Vn 0 1 0 1 0 0 1 +1Vn 0 0 1 1 0 0 1 0 0 0 0 1 0 1 0 0 0 0 0 0 1 0 1 -1Vn 0 0 1 0 1 1 0 -2Vn 0 1 1 0 1 1 0 -3Vn 1 0 0 0 1 1 0 -4Vn 1 0 1 0 1 1 0 -5Vn 1 0 1 0 1 1 0

[0047] Table 1 shows how the seven switching elements 19, 21, 23 or Sa, Sb, Sc, S1, S2, S3, S4 must be controlled in order to generate eleven voltage levels SL at the output 15.

[0048] Faults can occur in any switching element 19, 21, 23, or Sa, Sb, Sc, S1, S2, S3, S4, and / or any partial voltage source 20, 24, i.e., capacitance. This can result in a complete interruption of the power supply and / or a voltage drop at output 15.

[0049] Fig. 4 shows a schematic representation of a multilevel converter arrangement 10 according to an embodiment of the invention. The multilevel converter arrangement 10 according to Fig. 4 is described with reference to the multilevel converter arrangement 10 according to Fig. 1 to 3. In particular, the differences to the multilevel converter arrangement 10 according to Fig. 2 and Fig. 3 according to the state of the art.

[0050] The multilevel converter arrangement 10 comprises a second switching element 22 for each of the partial voltage sources 20, 24. Each submodule 13, 13'' thus comprises at least one second switching element 22, which is connected in parallel to the partial voltage source(s) 20. The multilevel converter arrangement 10 comprises a further switching element 27, which is connected in parallel to the further partial voltage sources 24.

[0051] The second switching element 22 is a diode having a forward direction and is arranged such that the second switching element 22 forms a passive bypass for the partial voltage source 20 of the respective submodule 13', 13'', which is connected in parallel to the second switching element 22. The active switching element 19, connected in series with the partial voltage source 20, can be switched in the forward direction. The second switching element 22 of each submodule 13', 13'' is arranged such that the first switching element 21 of the second branch 18 can be switched in parallel to the forward direction.

[0052] The further switching element 27 is a diode which has a forward direction and is arranged such that the active switching element 19 connected in series with the partial voltage source 20 can be switched in the forward direction.

[0053] The multilevel converter arrangement 10 comprises a plurality of second switching elements 22 or further switching elements 27. A second switching element 22 or further switching element 27 is connected in parallel to each of the partial voltage sources 20, 24. This ensures uninterrupted power flow through the submodules 13', 13'' or through the level generation unit 11 in the event of a fault in one of the partial voltage sources 20, 24.

[0054] Fig. 5 shows a schematic representation of simulation results SE of a simulation of a multilevel converter arrangement 10 according to an embodiment of the invention. The simulated multilevel converter arrangement 10 is the multilevel converter arrangement 10 according to Fig. 4, i.e. a multilevel converter arrangement 10 with eleven producible voltage levels SL as with reference to Fig. 3 described.

[0055] As a result of simulations SE of the multilevel converter arrangement 10 using the PSCAD / EMTDC software, the Fig. 6 generated. Fig. 6 shows three different scenarios (a), (b), (c).

[0056] For each of the scenarios (a), (b), (c) a multilevel converter arrangement 10 according to the invention is shown on the left, with a description of which can be found on Fig. 3 and Fig. 4. A detailed description and the use of reference symbols are omitted for reasons of clarity.

[0057] For each of the scenarios (a), (b), and (c), the temporal development of the voltage at the output of the level generation unit 11, i.e., the voltage VL of the DC voltage connection 25, is shown in the center. The time unit is not indexed. The voltage VL of the DC voltage connection 25 is plotted on the ordinate, which is discretely obtained by connecting the partial voltage sources 20, 24.

[0058] For each of the scenarios (a), (b), (c) a diagram is shown on the right, in which a current curve I (I Output ) at the AC voltage terminal (output 15) of the eleven-level multilevel converter arrangement 10. The abscissa is a time axis indicating time. The output current I is plotted on the ordinate.

[0059] In scenario (a), the multilevel converter arrangement 10 is fault-free. This means that each of the partial voltage sources 20, 24 is functioning properly and is intact. Each of the partial voltage sources 20, 24 supplies the intended voltage Vn. The second switching elements 22 and further switching elements 27 provided as a bypass are passive. The generated voltage levels SL correspond to the voltage levels SL described in Table 1 and are discrete with a distance of Vn from each other. The course of the current I at the output 15 is approximately sinusoidal (see also Fig. 8).

[0060] In scenario (b), the partial voltage source 20f in the submodule 13'' marked with a cross or crossed out is faulty, in particular defective. As a result, the voltage source 20f can be damaged by the voltage source 20f in the submodule 13''. Fig. 3, not every voltage level SL can be achieved. The voltage levels +1 Vn, -1 Vn, +5 Vn, and -5 Vn are not switchable. The maximum voltage VL of the DC voltage connection 25 is lower than in scenario (a).

[0061] Current now flows through the second switching element 22, which is connected in parallel to the faulty partial voltage source 20, thus preventing a failure of the multilevel converter arrangement 10. In the prior art, such a fault would lead to a failure of the submodule 13''. However, with the multilevel converter arrangement 10 according to the invention, a largely sinusoidal curve of the current I is achieved at the output 15.

[0062] In scenario (c), the partial voltage source 20f in the submodule 13' marked with a cross or crossed out is faulty, in particular defective. As a result, the voltage source 20f can be Fig. 3, not every voltage level SL can be achieved. The voltage levels +3Vn, +1Vn, -1Vn, -3Vn, +5Vn, and -5Vn are not switchable. The maximum voltage VL of the DC voltage connection 25 is lower than in scenario (a). Current now flows through the second switching element 22 connected in parallel to the faulty partial voltage source 20, thus preventing failure of the submodule 13' of the multilevel converter arrangement 10. With the multilevel converter arrangement 10 according to the invention, a largely sinusoidal curve of the current I at the output 15 is achieved.

[0063] The results show that the current I at the output 15 follows a reference current (the current I in scenario (a)), even in fault scenarios. The multilevel converter arrangement 10 is thus particularly advantageously applicable when a current I applied to the output 15 or a voltage applied to the output 15 must be close to a sinusoidal shape. A nearly sinusoidal output current can be achieved even with faulty partial voltage sources 20, 24 or switching elements.

[0064] Fig. 6 shows a schematic representation of a multilevel converter arrangement 10 according to another embodiment of the invention. The multilevel converter arrangement 10 according to Fig. 6 is described with reference to the multilevel converter arrangement 10 according to Fig. 4. As described with reference to Fig. As described in Figure 5, the number of voltage levels SL and the maximum voltage VL of the DC voltage link 25 decrease depending on a fault in one or more of the partial voltage sources 20, 24. The amplitude of the voltage VL of the DC voltage link 25 increases with the number of intact partial voltage sources 20, 24. Without a fault, the amplitude of the voltage VL of the DC voltage link 25 is greater than or equal to the grid voltage. With a fault, the amplitude of the voltage VL of the DC voltage link 25 is smaller than the grid voltage.

[0065] In order to adjust, in particular to increase, the voltage VL of the DC voltage connection 25 in the event of a fault in one of the partial voltage sources 20, 24, the multilevel converter arrangement 10 comprises a plurality of boost converters 30, see Fig. 6. Each of the boost converters 30 is electrically connected to one of the partial voltage sources 20, 24. Each of the boost converters 30 is electrically connected to one of the input voltage sources 40 and is supplied with an input voltage ViB of the boost converter 30 by the input voltage sources 40. The input voltage ViB of the boost converter 30 is transmitted in a modulated manner to the respective partial voltage sources 20, 24 connected to the boost converter 30. Thus, the respective partial voltage sources 20, 24 can be charged such that the respective partial voltage Vn of the charged partial voltage sources 20, 24 exceeds a predetermined partial voltage Vn, in particular the partial voltage Vn that is present in a case where there is no fault, as with reference to scenario (a) in Fig. 5. The multilevel converter arrangement 10 charges the partial voltage sources 20 by the boost converters 30 accordingly. The method for charging the partial voltage sources 20 by the boost converters 30 is described with reference to Fig. 7 described.

[0066] It is also possible to control one, several, or each of the boost converters 30 in such a way that several or all of the partial voltage sources 20, 24 are charged, for example, to compensate for aging effects of the partial voltage sources 20, 24. Different partial voltage sources 20, 24 can be charged evenly for this purpose. Alternatively, partial voltage sources 20, 24 can be charged differently.

[0067] In an embodiment not shown, the multilevel converter arrangement 10 comprises a boost converter 30 configured to charge several or all of the partial voltage sources 20, 24. Thus, the described effects can be generated with only one or fewer boost converters 30.

[0068] Fig. 7 shows a schematic block diagram of a use of a multilevel converter arrangement 10 and / or a method according to an embodiment of the invention. Fig. 7 is related to Fig. 6. Schematically, Fig. 7 shows a boost converter 30.

[0069] The boost converter 30 has a duty cycle D. The duty cycle D of the boost converter 30 influences the voltage Vn of the partial voltage sources 20, 24. Since all partial voltage sources 20, 24 are connected in series, the sum of the partial voltages Vn of the partial voltage sources 20, 24 results in the amplitude of the DC voltage of the level generation unit 11, which is applied to the converter 12, i.e. the voltage VL of the DC voltage connection 25. If one of the partial voltage sources 20, 24 is faulty, the partial voltages Vn of the intact partial voltage sources 20, 24 are increased in order to compensate for the error of the faulty partial voltage source 20, 24. In this case, the boost converter 30 increases the partial voltages Vn applied to the (intact) partial voltage sources 20, 24. The increase in the partial voltages Vn is achieved by increasing the duty cycle D of the boost converter 30.

[0070] In this embodiment, the DC voltage connection 25 between the level generation unit 11 and the converter unit 12 is crucial for the duty cycle D of the boost converter 30 to be set. A voltage comparator 28 compares the voltage VL of the DC voltage connection 25 with a predetermined reference voltage Vref, for example, the voltage in the case of an intact multilevel converter arrangement 10. The reference voltage Vref is the voltage that must be provided to the converter unit 12 so that a sinusoidal output voltage can be generated. The difference between a reference voltage Vref and the peak voltage VL of the DC voltage connection 25 results in an error value F. If no error is present, an error value F is zero, F=0, and the duty cycle D remains unchanged and is set by appropriate pulse width modeling (PWM).

[0071] With nB boost converters 30 (see Fig. 6) With each input voltage ViB, the total output voltage of all boost converters 30 is VtB = nB x ViB / (1-D), because each of the boost converters 30 has an output voltage VoB = ViB / (1-D) that depends on the duty cycle D. The voltage VL of the DC voltage connection 25 is: VL = nx Vn. In the example according to Fig. 6, the numbers of boost converters 30 and partial voltage sources 20 are equal: n = nB. The output voltage VoB of each boost converter 30 is an input voltage of a partial voltage source 20, 24. It follows that an increasing duty cycle D implies an increasing output voltage VoB of each boost converter 30. This results in an increasing voltage Vn of the partial voltage sources 20 and thus an increasing voltage VL of the DC voltage link 25. Thus, the duty cycle D can be adjusted depending on the error value F.

[0072] If the error value is zero, F = 0, the duty cycle D of the boost converter 30 is correctly set. If the error value F is not zero, a further distinction must be made based on the sign of the error value F. If the error value F is greater than 0 (F>0), the duty cycle D is set to D+ε, where ε is a positive constant or a value dependent on F. If the error value F is less than 0 (F<0), the duty cycle D is set to D-ε. The procedure changes the duty cycle D until the error value is zero, F = 0.

[0073] At output 15, the current I is measured and compared with a reference current Iref by means of a current comparator 29, thus determining an error value F'. If the error value F' is not equal to zero, a further distinction must be made based on the sign of the error value F'. If the error value F' is greater than 0 (F'>0), the current I is increased by a current increment lup using a model predictive control MPC. If the error value F' is less than 0 (F'<0), the current I is decreased by a current decrement Idown using the model predictive control MPC.

[0074] The voltage comparator 28 and the current comparator 29 are part of a detection device of the multilevel converter arrangement 10. The pulse width modeling PWM and the model predictive control MPC are carried out with a data processing device (not shown) which is included in the multilevel converter arrangement 10 and is connected to the voltage comparator 28 and the current comparator 29 for data transmission.

[0075] Fig. Figure 8 shows simulation results of a simulation of a multilevel converter arrangement 10 according to an embodiment of the invention. The simulated multilevel converter arrangement 10 is the multilevel converter arrangement 10 according to Fig. 4, i.e. a multilevel converter arrangement 10 with eleven producible voltage levels SL as with reference to Fig. 3. As a result of simulations SE of the multilevel converter arrangement 10 using the PSCAD / EMTDC software, the Fig. 9, which the Fig. 6 added.

[0076] Fig. Figure 8 (a) shows the output voltage Vout at the output 15 of the multilevel converter arrangement 10 (as V AB referred to) as a function of time in the error-free scenario (a) of the Fig. 5. The discrete voltage levels SL can be seen, which follow a sinusoidal curve.

[0077] Fig. Figure 8 (b) shows the output current I at the output 15 of the multilevel converter arrangement 10 (as V S referred to) as a function of time with a sinusoidal reference current Iref in the fault-free scenario (a) of the Fig. 5. The inset shows an enlarged view. The output current I follows a sinusoidal curve.

[0078] Fig. Figure 8 (c) shows the total harmonic distortion (THD) of the output voltage Vout at the output 15 of the multilevel converter arrangement 10 as a function of time in the fault-free scenario (a) of the Fig. 5. The THD drops to less than 0.82%.

[0079] Fig. Figure 8 (d) shows the output voltage Vout at the output 15 of the multilevel converter arrangement 10 (as V AB referred to) as a function of time in the error scenario (b) of the Fig. 5. The discrete voltage levels SL can be seen, which follow a sinusoidal curve.

[0080] Fig. Figure 8 (e) shows the output current I at the output 15 of the multilevel converter arrangement 10 (as V S referred to) as a function of time with a sinusoidal reference current Iref in the fault scenario (b) of the Fig. 5. The inset shows an enlarged view. The output current I follows a sinusoidal curve. List of reference symbols 10 Multilevel converter arrangement 11 Level generation unit 12 Inverter unit 13 Submodul 13' submodule with a partial voltage source 13'' submodule with two partial voltage sources 14 Entrance 15 Exit 16 electrical circuit 17 first branch 18 second branch 19 active switching element 20 partial voltage source 20f faulty partial voltage source 21 first switching element 22 second switching element 23 Inverter switching element 24 individual partial voltage sources 25 DC connection 26 Bypass diode 27 additional switching element 28 Voltage comparator 29 Current comparator 30 boost converters 40 Input voltage source D test grade F, F' error value I Output current, current Idown power decrement Iref reference current lup current increment n Number of partial voltage sources N Number of voltage levels MPC Model Predictive Control PWM pulse width modeling SE simulation results SL voltage level Vdc input voltage ViB input voltage of a boost converter VtB output voltage of all boost converters Vn partial voltage of a submodule VL voltage of the DC connection VoB Output voltage of a boost converter Vout output voltage Vref reference voltage

Claims

[1] Multilevel converter arrangement (10) for converting electrical energy, comprising - an input (14) for supplying electrical energy to be converted and an output (15) for delivering the converted electrical energy, - a level generation unit (11) and a converter unit (12) which are arranged to generate a certain number of voltage levels (SL) at the output (15), wherein - the level generation unit (11) is formed from at least one submodule (13, 13', 13''), wherein - the at least one submodule (13, 13', 13'') is formed by an electrical circuit (16), comprising a first branch (17) with an active switching element (19) connected in series with at least one partial voltage source (20) and a second branch (18) with a first switching element (21) connected in parallel to the first branch (17), and wherein - the first branch (17) has at least one second switching element (22) which is connected in parallel to one of the partial voltage sources (20), wherein the multilevel converter arrangement (10) has a boost converter (30) which is designed to apply a partial voltage to each of the partial voltage sources (20), wherein the multilevel converter arrangement (10) is designed to detect a faulty partial voltage source (20f), and wherein the boost converter (30) is designed to apply an increased partial voltage to each of the functional partial voltage sources (20) which are different from the faulty partial voltage source (20f). [2] Multilevel converter arrangement according to claim 1, wherein the second switching element (22) has a forward direction and is arranged such that the second switching element (22) forms a passive bypass for the partial voltage source (20) connected in parallel to the second switching element (22), and wherein the active switching element (19) connected in series with the partial voltage source (20) is switchable in the forward direction. [3] Multilevel converter arrangement according to one of the preceding claims, wherein the second switching element (22) has a forward direction and is arranged such that the first switching element (21) of the second branch (18) can be switched parallel to the forward direction. [4] Multilevel converter arrangement according to one of the preceding claims, wherein the multilevel converter arrangement (10) comprises a plurality of second switching elements (22), and the second switching elements (22) are connected such that a second switching element (22) is connected in parallel to each of the partial voltage sources (20). [5] Multilevel converter arrangement according to claim 1, wherein the boost converter (30) has a duty cycle, and the boost converter (30) is arranged to change the duty cycle to change the partial voltage. [6] Use of a multilevel converter arrangement (10) according to one of the preceding claims for converting electrical energy. [7] A method for converting electrical energy, comprising the following steps: - providing a multilevel converter arrangement (10) according to one of claims 1 to 5; and - Applying a partial voltage to each of the partial voltage sources (20). [8] Computer program comprising instructions which, when executed by a computer, cause the computer to apply a partial voltage to each of the partial voltage sources (20) in a multilevel converter arrangement (10) according to one of claims 1 to 5.

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