MMC device

Abstract

The invention relates to an MMC device designed as a modular multilevel converter having a single-phase side (S), which comprises two lines (4), and having a multi-phase side (M), which comprises a plurality of lines (4), each line (4) on the single-phase side (S) being connected to each line (4) on the multi-phase side (M) via control elements (2) which form a system of phase arms (AP), and each control element (2) having a plurality of switching modules (3), the MMC device (1) comprising: - a compensation arm (AC) having a control element (2) that has a plurality of switching modules (3), the control element (2) being connected between the two lines (4) on the single-phase side (S), - a measuring system (5) designed to measure a reactive power Qb on the single-phase side (S), - a control unit (6) designed to control the switching states of the switching modules (3) of all of the control elements (2) in such a way that the measured reactive power Qb is divided between the compensation arm (AC) on the one hand and the phase arms (AP) on the other hand on the basis of a predefined ratio x. The invention also relates to a method.

Description

[0001]202322254 MMC device The invention relates to an MMC device and a method for controlling a voltage converter. MMC devices are widely known in the art. An MMC device is a modular multilevel converter. Multilevel converters (MLCs) have been known for a long time and are commonly used to generate high-voltage waveforms from low-voltage components. Modular multilevel converters (MMCs) have existed since the 2000s (see, for example, Marquardt et al. “An innovative modular multi-level Converter Topology for a Wide Power Range”, IEEE Power Tech Conference, Bologna, Italy, June 2003 or Tricoli et al. “Efficiency assessment of modular multilevel converters for battery electric vehicles”, IEEE Transactions on Power Electronics. 32 (3): 2041–2051; March 2017). Such converters convert AC or DC voltages into other AC or DC voltages.MMCs typically have a single-phase side with two lines (for AC or DC) and a multi-phase side with typically two or three lines ("phases"). The lines of the multi-phase side are typically connected to each line of the single-phase side via so-called "actuators" (or "arms"). Each actuator consists of several switching modules connected in series. For example, an MMC device for converting an HV DC voltage to an AC voltage is designed to switch the switching modules in "waves" to form the desired waveform. In an architecture with three phase lines on the multi-phase side, an MMC device comprises a total of six actuators (6 "phase arms"). Typically, each switching module of the actuators (or "arms") consists of two or four switches (e.g., thyristors), often connected in pairs in series and connected in parallel with a capacitor.Traditionally, three-phase to single-phase voltage conversion for DC-frequency operation is performed using a three-phase AC-DC MMC (consisting of 6 arms) cascaded with a DC-to-single-phase AC-MMC topology (consisting of 4 arms). Therefore, the conventional approach requires 10 arms for three-phase and single-phase DC-frequency operation, which is costly. 202322254 Alternatively, a direct AC-AC MMC topology (consisting of 6 arms) can be used for DC-frequency operation, but this topology contains more switching modules per arm compared to the conventional topology. However, the converter dimensioning increases significantly due to the load- and source-side reactive currents in the MMC.Load and source reactive currents are unavoidable during fault operation, so the dimensioning of the direct MMC for equal-frequency operation is mainly determined by the source and load PQ diagrams and the magnitude of the reactive current during fault operation, which increases costs and degrades efficiency. Serious disadvantages of conventional MMC devices include the overall system cost, the burden of arm currents, and the power loss, especially in the direct AC-AC MMC topology for three-phase and single-phase frequency applications, especially during load or source operation with poor power factor and fault conditions. Major problems are the reactive power and the currents due to higher harmonics. It is an object of the present invention to provide an MMC device and a method for controlling an MMC device that avoid the disadvantages described above.This object is achieved by an MMC device according to claim 1 and a method according to claim 10. An MMC device according to the invention is designed as a modular multilevel converter with a single-phase side comprising two lines and a multi-phase side comprising several lines. Each line of the single-phase side is connected to each line of the multi-phase side via actuators, which form a system of phase arms, each actuator having several switching modules.The MMC device comprises the following components: - a compensation arm with a controller with several switching modules, the controller being connected between the two lines of the single-phase side, - a measuring system designed to measure a reactive power Qb on the single-phase side, - a control unit designed to control the switching states of the switching modules of all controllers such that the measured reactive power Qb is distributed between the compensation arm on the one hand and the phase arms on the other hand based on a 202322254 predefined ratio x. As already mentioned above, the architecture and operation of an MMC device without a compensation arm are already known. In particular, the control of a controller is known when a specific current or voltage or a predetermined power is to be transmitted. For example,a certain power can be specified and if this does not exceed the maximum achievable power, a mode can be specified in which the switching modules of a controller are to be switched. It should be noted that both the single-phase side and the multi-phase side can serve as the input (the other side would then be the output). The respective output side can then contain a load or be connected to a power grid. The cables can be normal power cables, e.g. in a car or a locomotive, or even feeders to overhead lines. The only important thing here is that the cables are electrically conductive. The compensation arm is the core of the invention. This connects the two cables on the single-phase side and serves to divert reactive power and currents caused by harmonic waves past the phase arms. This compensates for excessive loading of the phase arms.With regard to an advantageous architecture, it is preferred that reactive powers or currents are distributed in such a way that the same number of switching modules can be arranged in each controller (of the phase arms and the compensation arm). The measuring system creates the prerequisites for controlling the compensation arm (its controller or its switching modules). It measures at least the reactive power Qb on the single-phase side, but preferably also the reactive power Qa on the multi-phase side and also the voltages on both sides. The measurement of powers, in particular reactive powers, and voltages, as well as suitable measuring devices, are known in the art. The control unit is designed to control the switching states of the switching modules of all controllers in such a way that the measured reactive power Qb is distributed based on the ratio x, 202322254, i.e., e.g., into the reactive power components Q1 and Q2, between the compensation arm on the one hand and the phase arms on the other hand, e.g.with Q1 = (x-1)∙Qb and Q2 = x∙Qb. The invention can contribute to increasing the power density or reducing the overall dimensioning of the MMC device, e.g., for operation with the same two- or three-phase and single-phase frequency (fb = fa) using the additional compensation arm (can be considered an additional phase) in a conventional MMC (four-arm or six-arm). Each arm can contain an additional choke ("filter" or "L-filter"). A method according to the invention is used to control an MMC device according to the invention and comprises the following steps: - measuring a reactive power Qb on the single-phase side using the measuring system of the MMC device, - controlling the switching states of the switching modules of all controllers so that the measured reactive power Qb is distributed between the compensation arm on the one hand and the phase arms on the other, based on a predefined ratio x using the control unit of the MMC device.Basically, the control of a conventional MMC device is known in the prior art. The method according to the invention also includes the control of the compensation arm, or rather its controller. First, values ​​are measured, at least the reactive power Qb on the single-phase side, and then the switching modules of all controllers of the phase arms and the compensation arm are controlled according to the measured values. The steps of the method can be applied in many ways, i.e., measured values ​​can be continuously recorded and then controlled according to the measured values. The control can thus also correspond to a closed-loop control. It is important that the ratio x according to which the reactive power is distributed among the arms has been selected beforehand. The ratio x is preferably constant throughout the process, but x can also be changed dynamically during the process.A preferred constant value for the ratio x is 0.5, so that the reactive power is divided equally between the compensation arm and the phase arms. 202322254 There are various methods for controlling actuators in a conventional MMC device, e.g. the "Method 7" or the "Method 12". When controlling the compensation arm, care should be taken to ensure that the components Q1 and Q2 of the reactive power divided according to the ratio x are passed through the arms with the correct phase relationship to one another. The invention can be implemented in particular in the form of a computer unit with suitable software. The computer unit can, for example, have one or more cooperating microprocessors or the like for this purpose. In particular, it can be implemented in the form of suitable software program components in the computer unit.A largely software-based implementation has the advantage that even previously used computer units can be easily retrofitted by means of a software or firmware update to operate in the manner according to the invention. In this respect, the object is also achieved by a corresponding computer program product with a computer program that can be loaded directly into a memory device of a computer unit, with program sections to carry out all steps of the method according to the invention when the program is executed in the computer unit. Such a computer program product can, in addition to the computer program, optionally comprise additional components such as documentation and / or additional components, including hardware components such as hardware keys (dongles, etc.) for using the software.A computer-readable medium, for example a memory stick, a hard disk, or another portable or permanently installed data storage device, on which the program sections of the computer program that can be read and executed by a computer unit are stored, can be used for transport to the computer unit and / or for storage on or in the computer unit. Further, particularly advantageous embodiments and developments of the invention emerge from the dependent claims and the following description, wherein the claims of one claim category can also be developed analogously to the claims and description parts to form another claim category, and in particular, individual features of different embodiments or variants can be combined to form new embodiments or variants.202322254 In a preferred MMC device, the measuring system is designed to measure a reactive power component Qa and a voltage Va on the multi-phase side and a voltage Vb on the single-phase side. Preferably, the MMC device, in particular its control unit, is designed to divide the reactive power Qb based on the ratio x and Qa, Va and Vb. Preferably, the reactive power Qb is divided such that a first part of the power Q1 flows through the compensation arm and a second part of the power Q2 flows through the phase arms, based on the calculation:^^1 ൌ ^x െ 1^ ^ Qb െ a ^ ^Vb / Va^ଶ ^ Qa and Q2 ൌ x ^ Qb െ a ^ ^Vb / Va^ଶ ^ QaThe constant factor a is less than 1 and preferably 1 / 4.Preferably, the method comprises the additional steps of: - measuring a reactive power Qa and a voltage value Va on the multi-phase side, - measuring a voltage value Vb on the single-phase side, wherein in the control step the switching states of the switching modules of all actuators are controlled such that the reactive power Qb is divided based on the ratio x and Qa, Va and Vb, preferably into the reactive power components Q1 and Q2 based on the calculation:^^1 ൌ ^x െ 1^ ^ Qb െ a ^ ^Vb / Va^ଶ ^ Qa and Q2 ൌ x ^ Qb െ a ^ ^Vb / Va^ଶ ^ Qa.In a preferred MMC device, each line on the multi-phase side comprises a first phase arm connected to one of the lines on the single-phase side and a second phase arm connected to the other line on the single-phase side. Each “phase” on the phase side is therefore connected to both lines on the single-phase side via an actuator (or arm).If the multi-phase side has N phases (lines), the MMC device together with the (one) compensation arm has 2N+1 arms. Preferably, the MMC device is a converter with five phase arms, comprising the compensation arm and two lines on the multi-phase side with two controllers per line, or a converter with seven phase arms, comprising the compensation arm and three lines on the multi-phase side with two controllers per line. 202322254 A preferred MMC device comprises a compensation choke for the compensation arm, which is arranged in series with the controller of the compensation arm, wherein the phase arms are connected in parallel with the compensation choke or in series with the compensation choke. Preferably, the choke is arranged between the compensation arm and the phase arms.In a preferred MMC device, the compensation arm is controlled such that during a cycle, a portion of the reactive current flows through the compensation arm, preferably wherein the compensation arm is controlled such that the current is divided equally (at x = 0.5), i.e., the same current flows through the compensation arm and the phase arms. A preferred MMC device is a high-voltage converter. Preferably, the MMC device is an AC-AC MMC device. Preferably, the controller of the compensation arm comprises as many switching modules as a controller of a phase arm. Alternatively or additionally, all controllers of the phase arms preferably comprise the same number of switching modules. This results in a very cost-effective architecture. A preferred MMC device additionally comprises a resonant filter arranged to filter a desired harmonic component of the current on the single-phase side.The filter is preferably designed such that the filtered harmonic has the same frequency as the common-mode voltage of the MMC device on the multiphase side. The resonant filtering can be implemented, in particular, in software or using a digital or analog measurement system for measuring harmonics. It should be noted that there can be multiple harmonics (each with an N-fold (N = 1, 2, 3,...), often a 2N+1-fold, of a fundamental frequency). The first harmonic often has the largest amplitude. It is preferred that at least the first harmonic (at least) be passed through the compensation arm to a portion z. For this purpose, the resonant filter is preferably designed to filter out the first harmonic. A further harmonic can also be filtered out. This can then be mixed with the first harmonic, in particular by subtraction.A preferred MMC device additionally comprises a proportional resonance controller for controlling the harmonic current flowing into the phase arms. The proportional resonance controller is preferably designed to pass the harmonic current completely or partially through the compensation arm. It is particularly preferred to first filter out one or more harmonics using a resonance filter (superimposing them if necessary) and then use the resulting signal to the resonance filter to control the harmonic current flowing into the phase arms.A preferred method comprises the additional steps: - diverting at least part of a harmonic current on the single-phase side through the compensation arm so that the harmonic current does not flow or only partially flows within the phase arms, wherein the diverted harmonic current preferably has the same frequency as the common-mode voltage and / or preferably wherein the diverted harmonic current serves as a reference and a harmonic current through the compensation arm serves as a feedback signal. The invention is explained in more detail below with reference to the attached figures using exemplary embodiments. In the various figures, identical components are provided with identical reference numerals. The figures are generally not to scale.4 shows a preferred example of a method according to the invention for controlling an MMC device. 202322254 Figure 1 shows an MMC device 1 according to the prior art. It is designed as a three-phase modular multilevel converter and has two lines 4 on its single-phase side S (left) and three lines 4 on its multi-phase side M (right), one for each phase. By means of controllers 2, each of the two lines 4 of the single-phase side S is connected to each line 4 (phase) of the multi-phase side M. A system of six phase arms can be seen, which additionally comprise a choke L per controller 2.On the far right it is indicated that each controller 2 is made up of several switching modules 3, and that each switching module is made up of several switching components, here four thyristors equipped with diodes, and a capacitor. Figure 2 shows general control structures of the six-arm MMC device 1 from Figure 1. The phase-arm controllers 2 regulate the six arm energies of the MMC device 1 by generating a suitable reference arm and source-side currents as output. The MMC device 1 can draw energy from either the three-phase or the single-phase system, depending on how the arms are controlled. The controllers 2 supply a three-phase reference current when the MMC device 1 draws active power from the three-phase system, and they supply a single-phase reference current when the single-phase side of the MMC device behaves as a source.The actuators 2 regulate the currents according to the command of an arm energy controller (not shown here) and generate the reference arm voltages as output signals. The reference arm voltage can be realized by switching the switching modules 3 of each arm. Since the switching modules 3 are electrically floating, an additional sorting algorithm is used to distribute the arm energies evenly among their corresponding switching modules 3. The sorting algorithm is independent. Therefore, any sorting method can be selected to evenly distribute the energies of the switching modules. How the switching modules 3 are controlled to distribute the energy is well known in the art. Figure 2 shows different modes for controlling the MMC device for different applications.The top left corner shows the "Total Arm Energy Regulation", the top right corner the "Phase Energy Regulation", the bottom left corner the "Total Lower and Upper Arm Energy Regulation", and the bottom right corner the "Individual Arm Energy Regulation". In addition to the 202322254 converters, phase diagrams are also displayed, showing the phases of the voltages (dashed) and the currents (solid). The "Total Arm Energy Regulation" shows two possible phase diagrams depending on the mode (left "Method 7", right "Method 12"). Several methods for regulating the arm energy could be used, but only two methods for balancing the arm energy (Method 7 and Method 12) seem to be stable for operation with equal three-phase and single-phase frequencies (fb = fa), which do not cause harmonics to be injected into the source and load currents. In addition, the common-mode voltage (v. cm) and those with v cmIn-phase circulating currents are required for stable direct AC-AC MMC operation at the same frequency. The phasor diagram of the proposed Method-7 and Method-12 for arm energy balancing in the abc frame is shown in Figure 2 (top left). Method-7 is used when the three-phase side is the source, and Method-12 is used when the single-phase side is the source. Therefore, the three-phase active power (Pa) helps regulate the total arm energy (see top left of Figure 2) for Method-7, and the single-phase active power (Pb) balances the total energy for Method-12. The following equations (1) to (7) represent the instantaneous arm power equations for the six-arm MMC topology in an αβ0 frame, using the notations summation (Σ) and difference (Δ) (see, for example, G.K. Sah et al."Overview and Evaluation of Energy Balancing Techniques for MMCs with Various Input and Output Frequencies" 202224th European Conference on Power Electronics and Applications (EPE'22 ECCE Europe), Hanover, Germany, 2022, pp.1-10): ^^ஊ^ ൌ ^^୮^ ^ ^^୬^ ; ^^^^ ൌ ^^୮^ െ ^^୬^ (1). 202322254 with θ^ ൌ ω^t ; θ^ ൌ ω^t ^ ϕ^ ; θ^^ ൌ 3ω^t ^ π (8) The size i ad+ is the active power current component of the multiphase side, i bd+ the reactive current component of the multiphase side, i aq+ the circulating current component in phase with the multiphase voltage (the voltages on the multiphase side) and The single-phase current is in phase with the single-phase current. Circulating currents offer a further five degrees of freedom to exchange all average arm energies and regulate them to a specific point. Here, the circulating currents can each be in phase with the three-phase voltages (v b with i ad+), single-phase voltages (v b with ^^ ^ ^ ^ ஒ ) and the common mode voltages (v cm with ^^ ^ ^^ ^ ஒ ). Circulating currents flow only within the MMC and have no influence on the single-phase (i b ) and three-phase (i a123 ) currents. In a practical example, Vb = 2Va, f a = f b = 50 Hz, ϕ b = 60°. The frequencies on the multi-phase side and the single-phase side can be the same or different, a constant frequency operation (f b = f a ) is preferred. Equations (8) and (9) represent the general expressions of the instantaneous three-phase voltages in the αβ-frame (v aαβ ), the single-phase voltage (v b ) and the common mode voltage (v cm ) for operation at the same frequency (f a = f b). Here, ϕb = θb – θa represents the phase angle difference between the single-phase and three-phase voltage. 202322254 Equations (10) to (14) illustrate the expressions for the three-phase current in the αβ frame (i aαβ ), the circulating current in the αβ frame (i bαβ ) and the single-phase current (i b ) for Method 7 and Method 12 for arm energy compensation. The three-phase voltage angle (θ a ) is used for the Park and inverse Park transformation. The currents i b ⊥b and I aq+are the single-phase and three-phase reactive current components (see also equation (15)). Figure 3 shows an MMC device according to the invention. It is similar to the MMC device 1 of Figure 1 with the important difference that it has an AC compensation arm with a controller 2 with several switching modules 3, where the controller 2 is connected between the two lines 4 of the single-phase side S. Arrows are drawn in the diagram, indicating the powers (denoted by "P") and the reactive powers (denoted by "Q") in the MMC device 1. The MMC device 1 comprises a measuring system 5, which serves to measure the reactive power Qb on the single-phase side S. Based on this measurement, the control unit 6 controls the switching modules 3 of all controllers 2. The control is carried out in such a way that the measured reactive power Qb is distributed between the AC compensation arm on the one hand and the phase arms AP on the other hand, based on a predefined ratio x.With the help of the compensation arm, the single-phase reactive power Q2 flowing through the six phase arms can be reduced. Reducing the reactive power flowing through the six phase arms can help reduce the load on I. cm bαβ and thus significantly increase the power density of the six phase arms. The ratio x defines the proportion of the single-phase reactive power Qb that flows into the six phase arms (Q2 = xQb). The remaining single-phase reactive power flows into the compensation arm (Q1 = (x–1)Qb). In addition, Q2 can contain an additional term to compensate for the three-phase reactive power Qa according to (Q2 = (Vb / 2Va) 2Qa+Qb). The general expression of Q2 and Q1 could then be: ^1 ≈ ^x ≈ 1 ^ ^ Qb ≈ a ^ ^Vb / Va^≤ ^ Qa and Q2 ≈ x ^ Qb ≈ a ^ ^Vb / Va^≤ ^ Qa. The following equations represent modified average expressions for the arm power of the six-arm direct AC-AC MMC (see equations (6) and (7)) for operation at equal frequencies: 202322254 and In contrast to the six-arm MMC topology, the total branch current and energy ripple of the six-arm MMC are reduced when the compensation arm supplies the full reactive power of the single-phase load (at x=0). However, this would result in higher current and higher oscillation components in the compensation arm. Therefore, preferential sharing of the load reactive power by the compensation arm and the six phase arms (Q1 = Q2) can help reduce the current load on the compensation arm. If the same switching modules are to be used for the compensation arm and the six phase arms, Qb can be shared by both the compensation arm and the six phase arms, thus reducing the load on the compensation arm. Furthermore, sharing the reactive power between the compensation arm and the six phase arms helps ensure optimal use of the switching modules under all load power factor conditions.Therefore, the proposed seven-arm direct AC-AC MMC offers various degrees of freedom in the design and control of the converter. This can contribute to reducing the overall system costs and dimensioning. Figure 4 shows a preferred example of an inventive method for controlling an MMC device, such as that shown in Figure 3, for example. In step I, the reactive power Qb on the single-phase side S is measured using the measuring system 5 of the MMC device 1 (see, for example, Figure 3). In addition, the reactive power component Qa and the voltage Va on the multi-phase side M and the voltage Vb on the single-phase side S are also measured. In step II, the reactive power Qb is divided into a first part of the power Q1, which should flow through the compensation arm AC, and a second part of the power Q2, which should flow through the phase arms AP. This is based, for example, onbased on the calculation^^1 ൌ ^x െ 1^ ^ Qb െ a ^ ^Vb / Va^ଶ ^ Qa and Q2 ൌ x ^ Qb െ a ^ ^Vb / Va^ଶ ^ Qa 202322254 with a predetermined ratio x. In step III, the switching states of the switching modules 3 of all actuators 2 are controlled by the control unit 6 of the MMC device 1 such that the measured reactive power Qb is divided between the compensation arm AC on the one hand and the phase arms AP on the other hand into the calculated components Q1 and Q2. Finally, it is pointed out again that the invention described in detail above only concerns exemplary embodiments which can be modified in many different ways by a person skilled in the art without departing from the scope of the invention. Furthermore, the use of the indefinite articles “a” or “an” does not exclude the possibility that the features in question can be present multiple times.Likewise, terms like "unit" do not exclude the possibility that the components in question consist of several interacting subcomponents, which may also be spatially distributed. The term "a number" should be read as "at least one." Regardless of the grammatical gender of a particular term, this includes persons with male, female, or other gender identities.

Claims

202322254 Patent claims 1. MMC device (1) designed as a modular multilevel converter with a single-phase side (S) comprising two lines (4) and a multi-phase side (M) comprising a plurality of lines (4), wherein each line (4) of the single-phase side (S) is connected to each line (4) of the multi-phase side (M) via actuators (2) which form a system of phase arms (AP), wherein each actuator (2) has a plurality of switching modules (3), the MMC device (1) comprising: - a compensation arm (AC) with an actuator (2) with a plurality of switching modules (3), wherein the actuator (2) is connected between the two lines (4) of the single-phase side (S), - a control unit (6) which is designed to control the switching states of the switching modules (3) of all actuators (2) such that the measured reactive power Qb is based on a predefined ratio x to the Compensation arm (AC) on the one hand and the phase arms (AP) on the other. 2.

4. The MMC device (1) according to claim 1, wherein the measuring system (5) is configured to measure a reactive power component Qa and a voltage Va on the multi-phase side (M) and a voltage Vb on the single-phase side (S), and wherein the MMC device (1) is configured to divide the reactive power Qb based on the ratio x and Qa, Va and Vb.

5. The MMC device (1) according to claim 2, configured to divide the reactive power Qb such that a first part of the power Q1 flows through the compensation arm (AC) and a second part of the power Q2 flows through the phase arms (AP), based on the calculation: Qa ≡ x ≡ 1 Qb ≡ a Vb / Va ≡ ^ Qa and Qb ≡ x ≡ Qb ≡ a Vb / Va ≡ ^ Qa ≡MMC device (1) according to one of the preceding claims, wherein each line (4) on the multi-phase side (M) comprises a first phase arm (AP) connected to one of the lines (4) of the single-phase side (S) and a second phase arm (AP) connected to the other line (4) of the single-phase side (S), preferably wherein the MMC device (1). 202322254 - is a converter with five phase arms (AP), comprising the compensation arm (AC) and two lines (4) on the multi-phase side (M) with two actuators (2) per line (4), or - is a converter with seven phase arms (AP), comprising the compensation arm (AC) and three lines (4) on the multi-phase side (M) with two actuators (2) per line (4).

5. MMC device (1) according to one of the preceding claims, comprising a compensation choke (LC) for the compensation arm (AC), which is arranged in series with the actuator (2) of the compensation arm (AC), wherein the phase arms (AP) are connected in parallel with the compensation choke (LC) or in series with the compensation choke (LC), preferably wherein the choke (L) is arranged between the compensation arm (AC) and the phase arms (AP).MMC device (1) according to one of the preceding claims, wherein the compensation arm (AC) is controlled such that during a cycle a portion of the reactive current flows through the compensation arm (AC), preferably wherein the compensation arm (AC) is controlled such that the same current flows through the compensation arm (AC) and the phase arms (AP).

7. MMC device (1) according to one of the preceding claims, wherein the MMC device (1) is a high-voltage converter, preferably an AC-AC MMC device (1).

8. MMC device (1) according to one of the preceding claims, wherein the controller (2) of the compensation arm (AC) comprises as many switching modules (3) as an controller (2) of a phase arm (AP) and / or wherein all controllers (2) of the phase arms (AP) comprise the same number of switching modules (3). 9.MMC device (1) according to one of the preceding claims, additionally comprising: - a resonant filter arranged to filter a desired harmonic component of the current on the single-phase side (S), wherein the filter is preferably designed such that the filtered harmonic has the same frequency as the common-mode voltage of the MMC device on the multi-phase side (S), and / or. 202322254 - a proportional resonant controller for controlling the harmonic current flowing into the compensation arm (AC), preferably designed to conduct the harmonic current completely or partially through the compensation arm.

10. A method for controlling an MMC device according to one of the preceding claims, comprising the steps: - measuring a reactive power Qb on the single-phase side (S) with the measuring system (5) of the MMC device (1), - controlling the switching states of the switching modules (3) of all actuators (2) so that the measured reactive power Qb is distributed between the compensation arm (AC) on the one hand and the phase arms (AP) on the other hand, based on a predefined ratio x with the control unit (6) of the MMC device (1). 11.Method according to claim 10, comprising the additional steps of: - measuring a reactive power Qa and a voltage quantity Va on the multi-phase side (M), - measuring a voltage quantity Vb on the single-phase side (S), wherein in the control step the switching states of the switching modules (3) of all actuators (2) are controlled such that the reactive power Qb is divided based on the ratio x and Qa, Va and Vb, preferably into the reactive power components Q1 and Q2 based on the calculation:^^1 ൌ ^x െ 1^ ^ Qb െ a ^ ^Vb / Va^ଶ ^ Qa and Q2 ൌ x ^ Qb െ a ^ ^Vb / Va^ଶ ^ Qa12.Method according to claim 10 or 11, comprising the additional step: - diverting at least part of a harmonic current on the single-phase side (S) through the compensation arm (AC) so that the harmonic current does not flow or only partially flows within the phase arms (AP), wherein preferably the diverted harmonic current has the same frequency as the common-mode voltage and / or preferably wherein the diverted harmonic current serves as a reference and a harmonic current through the phase arms (AP) as a feedback signal.

13. A computer program product comprising instructions which, when the program is executed by a computer, cause the computer to carry out the steps of the method according to one of claims 10 to 12. 202322254 14. A computer-readable storage medium comprising instructions which, when executed by a computer, cause the computer to perform the steps of the method according to any one of claims 10 to 12.

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