DE102022109261B4 - Method for compensating modulation deviations in a modular multilevel converter - Google Patents

Abstract

The present invention relates to a method for controlling a modular multilevel converter, wherein the modular multilevel converter is controlled to generate an output signal by means of pulse width modulated control signals (1221, 1231, 1232, 1241, 1251, 1252) for the respective modules, a respective control signal (1221 , 1231, 1232, 1241, 1251, 1252) for a respective module based on a respective carrier signal, which has a phase shift related to the respective module, and is generated based on a modulation reference signal assigned to the respective module, according to a modulation deviation from an average Reference signal, the phase shift or a starting level of at least one carrier signal of the plurality of modules or at least one modulation reference signal of the plurality of modules are modified, while at the same time a time integral of the output signal (1211, 1212) is kept constant over a switching cycle, whereby at least one module is switched on a position of a rising and a falling signal edge changes. Furthermore, a modular multilevel converter with a control unit on which the method is implemented is claimed.

Description

The present invention relates to a method for compensating modulation deviations in control signals in a modular multilevel converter. Furthermore, a modular multilevel converter with a control unit on which the method is implemented is claimed.

Modular or cascaded inverters or converters are becoming increasingly important for both alternating current and direct current systems. In contrast to conventional inverters, modular multilevel converters have the advantage that they have a much larger number of quantized voltage levels available, which means they can generate virtually any output voltage by alternating switching between these levels.

A simple way to control modules of the converter is to use phase-shifted modulation of carrier signals, known in English as “phase-shifted carrier (PSC) modulation”. Such phase-shifted and overlapping but otherwise identical carrier signals represent one of the most commonly used modulation methods to generate and control switching pulses for all types of modular, offset or cascaded converters. Evenly phase-shifted carrier signals with individually set reference signals guarantee a uniform distribution of discharge or charging across all modules, especially if the carrier signals are designed as a sawtooth or triangular shape, but have disadvantages for controlling charge equalization between modules.

Different operating conditions of the modules, such as temperature or load variations or even disturbances, and different operating modes, such as the above-mentioned charge equalization between the modules, require different modulation reference signals for the individual modules. However, if a respective modulation reference signal differs from the reference signal averaged over all modules, this can lead to inequalities in the resulting switching pulses and/or voltage levels, which means that more than two voltage levels are present for a short time.

However, the task of modulation is to achieve the lowest possible switching effort for maximum output quality, i.e., for example, to only switch to an immediately adjacent voltage level per switching cycle. In general, switching across several voltage levels should be avoided, as this disadvantageously results in intermediate switching states with output voltages of low dynamics. However, conventional control methods have weaknesses here, especially as soon as different modulation reference signals occur for the modules.

The publication WO 2019/022745 A1 discloses a circuit diagram for a static synchronous compensator (STATCOM) with cascaded H-bridge converters. To generate a requested output voltage, individual H-bridges are switched active or passive.

In print WO 2014/023334 A1 A method for controlling a modular converter using pulse width modulated control signals is described. The control signals are generated based on carrier signals for the individual modules and at least one reference signal, the individual carrier signals being phase-shifted. The amounts of charge flowing through the modules are estimated and the individual modules are controlled in such a way that a desired energy storage voltage is achieved in the individual module.

The American publication US 2018/0006576 A1 discloses a method for controlling a modular converter using pulse width modulated control signals. Depending on whether a respective carrier signal for the individual modules is larger or smaller than a reference signal, the respective module is switched active or passive.

A fundamental assumption in conventional PSC is that all modules are completely balanced, an overall system encompassing all modules can be described ideally (i.e. without energy losses), and all modules have no faults. This results in the assumption of the same modulation reference signals, which results in accurately distributed, identical switching pulses. However, the reality is different, since the individual modules do not have the same properties in terms of voltage or impedance, they do not have the same charge states, and not all of them are available at all times.

The publication “H. AKAGI; L, MAHARJAN: A battery energy storage system based on a multilevel cascade PWM converter. 2009 Brazilian Power Electronics Conference, 2009, Conference Paper, IEEE” discloses an energy storage system based on a cascaded multilevel converter controlled by pulse duration modulation. The control implements a regulation of the state of charge compensation and is fault-tolerant.

The publication “M.HERZOG, AW EBENTHEUER;T. LAHLOU;H.-G. HERZOG: Management Algorithms for Cascaded H-Bridge Multilevel Inverters. In: 2018 53rd International Universities Power Engineering Conference (UPEC), 2018 , Conference Paper, IEEE” describes control algorithms for cascaded H-bridge multilevel inverters. The control algorithms are aimed at even distribution of energy between all battery modules.

Against this background, it is an object of the present invention to provide a method for controlling modules of a modular multilevel converter, which takes into account differences in operating conditions between individual modules, such as charge states, and different modulation reference signals, and only switching changes to adjacent voltage levels appear. Furthermore, a control unit of a modular multilevel converter should be provided on which the method can be carried out.

To solve the above-mentioned problem, a method for controlling a modular multilevel converter is proposed, wherein the modular multilevel converter comprises a plurality of modules with at least one energy storage unit and a plurality of controllable switches. Starting from a connection to a voltage source, the large number of modules are interconnected to form at least one strand. The modular multilevel converter is controlled to generate an output signal using pulse width modulated control signals for the respective modules. A respective control signal for a respective module is generated based on a respective carrier signal, which has a phase shift related to the respective module, and based on a modulation reference signal assigned to the respective module. By comparing a signal curve of the respective carrier signal with the respective modulation reference signal based on a size comparison, a connection duration of the at least one energy storage unit of the respective module is triggered to a load current. According to a modulation deviation from a mean reference signal, the phase shift or a starting level of at least one carrier signal of the plurality of modules is modified while at the same time a time integral of the output signal is kept constant over a switching cycle. As a result, the position of a rising and a falling signal edge changes when at least one module is switched on.

A control unit controls that the time integral of the output signal is kept constant over the switching cycle, or that a value of a modulation reference signal averaged over the switching cycle remains unchanged.

In one embodiment of the method according to the invention, signal edge positions of at least one switching period are changed step by step, while at the same time a sum of the position changes of the signal edges of all modules is kept constant. This is done by modifying the phase shift of at least one carrier signal in order to take into account the deviation of at least one modulation reference signal from the average reference signal.

Keeping the sum of the position changes of the signal edges of all modules constant is particularly important for charge balancing between energy storage units of individual modules. Changes in modulation emanating from the control unit in order to achieve this charge equalization can cause switching processes over more than two adjacent voltage levels, but this is advantageously solved by the method according to the invention.

If dm(i) is a change value for a pulse width or pulse duration of an i-th switching pulse, which is modified to dm'(i), the following applies to N modules or N carrier signals in the at least one strand: $$dm\text{'}\left(i\right)=dm\left(i\right)-{\displaystyle \sum {}_{j=1}^N}dm\left(j\right).$$

geändert werden und entsprechend einer Verschiebung bei der fallenden Signalflanke die Phasenverschiebung des jeweiligen Trägersignals um $dm\text{'}\times \frac{2\pi }{N}$

geändert werden.First, it is determined which pulse widths are caused by changes according to Eq. (1) are affected. Next, it is determined which signal edges opposite in the respective switching pulse belong to which carrier signal. In this carrier signal, the phase shift is, so to speak, adjusted in the opposite direction, that is, while dm changes the value of the pulse width by shifting the rising or falling signal edge, the phase shift of the respective carrier signal must be adjusted in accordance with a shift in the rising signal edge $-dm\text{'}\times \frac{2\pi }{N}$

can be changed and the phase shift of the respective carrier signal corresponding to a shift on the falling signal edge $dm\text{'}\times \frac{2\pi }{N}$

be changed.

It is possible that rising and falling signal edges of several switching pulses are complementary to one another. This occurs, for example, when a rising signal edge of a first switching pulse and a falling signal edge of a second switching pulse go back to a first carrier signal, and at the same time a rising signal edge of the second switching pulse and a falling signal edge of the first th switching pulse goes back to a second carrier signal.

Sometimes it can also happen that both rising and falling signal edges of a switching pulse can be traced back to a single carrier signal. In such a case, all other carrier signals must then be shifted in order to achieve a better distribution of the switching pulses

In a further embodiment of the method according to the invention, a rising signal edge in the connection duration of a respective module is brought into line with a falling signal edge in the connection duration of the module that was previously immediately adjacent in the at least one strand. This is done by cyclically iterating over all modules in the at least one strand and modifying the phase shifts of these neighboring modules.

und $$Edg{e}_{-,i}=\left(m\left(i\right)\right)\times 2\pi$$

First, the positions of the rising (Edge _+,i ) and falling (Edge _-,i ) signal edges of the switch-on duration or the voltage pulse of the i-th module are calculated without phase shift: $$EdG{e}_{+,i}=\left(1-m\left(i\right)\right)\times \pi$$

and $$EdG{e}_{-,i}=\left(m\left(i\right)\right)\times 2\pi$$

und $$Pul{s}_{end}=\mathrm{0,}$$

sowie $${\phi }_{i+1}=Pul{s}_{end}-Edg{e}_{+,i},$$

und $$Pul{s}_{end}=Pul{s}_{end}+Edg{e}_{-,i},$$

The phase shifts of the respective carrier signals are then calculated in such a way that the falling signal edge of a voltage pulse in the preceding module coincides with the rising signal edge of the voltage pulse in the immediately following module, whereby absolute order is not important. So you don't have to start with the first module in the strand, but this is done here - without limiting generality - to simplify the notation: $${\mathrm{<figure-callout\; id="1"\; label="\phi "\; filenames="DE102022109261B4\_0020.png,DE102022109261B4\_0021.png"\; state="\{\{state\}\}">\phi </figure-callout>}}_1=-\left(1-m\left(1\right)\right)\times \pi ,$$

and $$Pul{s}_{end}=\mathrm{0,}$$

as well as $${\phi }_{i+1}=Pul{s}_{end}-EdG{e}_{+,i},$$

and $$Pul{s}_{end}=Pul{s}_{end}+EdG{e}_{-,i},$$

If step-by-step changes occur in the modulations, the changes in the phase shift of the respective carrier signals are taken into account by the affected modules. Since such changes are linear, they can be easily calculated and compensated for: $$d{\phi }_i={\displaystyle \sum {}_{j=i}^{i-1}}\left(dm\left(j\right)\right)\times 2\pi -dm\left(i\right)\times \pi .$$

In a still further embodiment of the method according to the invention, signal edge positions of at least one switching period are changed cyclically iteratively across all modules in the at least one strand, while at the same time a sum of the position changes of the signal edges of all modules is kept constant. This is done by modifying the phase shift of the carrier signal in the previously adjacent module in cyclic sequence in view of a change in position in a respective module in order to take into account the deviation of at least one modulation reference signal from the average reference signal.

The following applies to the changes in the switching pulses: $$dm\text{'}\left(i\right)=dm\left(i\right)-{\displaystyle {\sum }_{j=1}^N\frac{dm\left(j\right)}{N}}.$$

It is first determined which pulse widths are caused by changes according to Eq. (1) are affected. Next, adjacent carrier signals, i.e. the respective carrier signal of the preceding module and the next module under periodic boundary conditions (module 1 precedes module N), are determined. This is followed by a gradual adjustment of the phase shifts of the respective carrier signals $$d{\phi }_i=\text{sgn}\times dm\text{'}\left(i-1\right)\times \frac{2\pi }{N}-\text{sgn}\times dm\text{'}\left(i+1\right)\times \frac{2\pi }{N}.$$

und $$dm\text{'}\left(i\right)=0.$$

In a still further embodiment of the method according to the invention, a distribution of starting levels of the respective carrier signals is changed step by step, while at the same time the respective connection duration is kept constant. If, for example, there is only a single modulation reference signal, all necessary changes are achieved by vertical shifts of the respective carrier signals. This means: $$d\delta \text{'}\left(i\right)=-dm\left(i\right)+{\displaystyle {\sum }_{j=1}^N\frac{dm\left(j\right)}{N}},$$

and $$dm\text{'}\left(i\right)=0.$$

The changes result from modifying the phase shift of at least one carrier signal of the plurality of modules in order to take into account the deviations (dδ'(i)) of the starting levels from the average deviation value (δ). Here it is first determined which pulse widths are caused by changes according to Eq. (11) are affected. Next, it is found out which signal edge on the opposite side of the respective switching pulse belongs to which carrier signal. Now the phase shifts of these carrier signals are adjusted accordingly in order to compensate for the vertical deviations.

In another embodiment of the method according to the invention, a modulation index assigned to the respective module is reduced to zero for a respective inactive module. Corresponding to a number of inactive modules, the phase shift of the respective carrier signal and the respective modulation reference signals of the active modules are modified for all active modules to compensate for a failed connection duration caused by the respective inactive module.

A changed phase difference between two consecutive carrier signals caused by a failure of inactive modules is 2π/(N - N _f ), where N _f is a number of inactive modules. Starting from the first active module, the modified phase shifts of the remaining active modules are given by: $${\phi }_i=i\times \frac{2\pi }{N-N_f}.$$

The modifications of the modulation reference signals of the active modules result in: $$m\text{'}\left(i\right)=m\left(i\right)+{\displaystyle {\sum }_{j=1}^{N_f}\frac{m\left(j\right)}{N-N_f}}.$$

In yet another embodiment of the method according to the invention, for a respective inactive module, a starting level of the carrier signal assigned to the respective module is increased to one. Corresponding to a number of inactive modules, the phase shift of the respective carrier signal and the respective starting levels of the active modules are modified for all active modules to compensate for a failed connection period caused by the respective inactive module.

A changed phase difference between two consecutive carrier signals caused by a failure of inactive modules is 2π/(N - N _f ). Starting from the first active module, the modified phase shifts of the remaining active modules are given by: $${\phi }_i=i\times \frac{2\pi }{N-N_f},$$

The modifications to the starting levels to compensate for the inactive modules result in: $$\delta \text{'}\left(i\right)=\delta \left(i\right)-{\displaystyle {\sum }_{j=1}^{{\mathrm{<figure-callout\; id="1"\; label="N\; f"\; filenames="DE102022109261B4\_0020.png,DE102022109261B4\_0021.png"\; state="\{\{state\}\}">N</figure-callout>}}_f}\frac{1-\delta \left(j\right)-m\left(j\right)}{N-N_f}}.$$

• • den modularen Multilevelkonverter zur Erzeugung eines Ausgangssignals mittels pulsweitenmodulierter Steuersignale für die jeweiligen Module anzusteuern,
• • ein jeweiliges Steuersignal basierend auf einem jeweiligen Trägersignal, welches eine auf das jeweilige Modul bezogene Phasenverschiebung aufweist, und basierend auf einem dem jeweiligen Modul zugewiesenen Modulationsreferenzsignal zu erzeugen,
• • durch einen auf einem Größenvergleich basierenden Vergleich eines Signalverlaufs des jeweiligen Trägersignals mit dem jeweiligen Modulationsreferenzsignal eine Zuschaltdauer der mindestens einen Energiespeichereinheit des jeweiligen Moduls zu einem Laststrom zu triggern, und
• • gemäß einer Modulationsabweichung von einem mittleren Referenzsignal die Phasenverschiebung oder ein Startniveau mindestens eines Trägersignals der Vielzahl von Modulen zu modifizieren und
• • gleichzeitig ein Zeitintegral des Ausgangssignals über einen Schaltzyklus konstant zu halten,

wodurch sich bei einer Zuschaltdauer mindestens eines Moduls eine Lage einer steigenden und einer fallenden Signalflanke verschiebt.Furthermore, a control unit for a modular multilevel converter is claimed, wherein the modular multilevel converter comprises a plurality of modules with at least one energy storage unit and a plurality of controllable switches. Starting from a connection to a voltage source, the large number of modules are interconnected to form at least one strand. The control unit is configured to

• • to control the modular multilevel converter to generate an output signal using pulse width modulated control signals for the respective modules,
• • generate a respective control signal based on a respective carrier signal, which has a phase shift related to the respective module, and based on a modulation reference signal assigned to the respective module,
• • to trigger a connection duration of the at least one energy storage unit of the respective module to a load current by comparing a signal curve of the respective carrier signal with the respective modulation reference signal based on a size comparison, and
• • modify the phase shift or a starting level of at least one carrier signal of the plurality of modules according to a modulation deviation from a mean reference signal and
• • at the same time to keep a time integral of the output signal constant over a switching cycle,

whereby a position of a rising and a falling signal edge shifts when at least one module is switched on.

In one embodiment of the control unit according to the invention, the control unit is additionally configured to simultaneously keep a sum of the position changes of the signal edges of all modules constant and to gradually change signal edge positions of at least one switching period by modifying the phase shift of at least one carrier signal in order to accommodate the deviation of at least one modulation reference reference signal from the average reference signal.

In a further embodiment of the control unit according to the invention, the control unit is additionally configured to bring a rising signal edge in the connection duration of a respective module into agreement with a falling signal edge in a connection duration of the module that was previously immediately adjacent in the at least one strand, by cyclically iterating over all Modules in which at least one strand, the phase shifts of these neighboring modules are modified.

In a still further embodiment of the control unit according to the invention, the control unit is additionally configured to simultaneously keep a sum of the position changes of the signal edges of all modules constant and to change signal edge positions of at least one switching period cyclically iteratively across all modules in the at least one strand in view of a change in position in a respective module, the phase shift of the carrier signal in the previously adjacent module in cyclic sequence is modified in order to take into account the deviation of at least one modulation reference signal from the average reference signal.

In a further embodiment of the control unit according to the invention, the control unit is additionally configured to simultaneously keep the respective connection duration constant and to gradually change a distribution of starting levels of the respective carrier signals by modifying the phase shift of at least one carrier signal of the plurality of modules in order to achieve this Deviations of the starting levels from the average deviation value must be taken into account.

In another embodiment of the control unit according to the invention, the control unit is additionally configured to reduce a modulation index assigned to the respective module to zero for a respective inactive module and, in accordance with a number of inactive modules, to reduce the phase shift of the respective carrier signals and the modulation reference signals of the active modules for all active modules to compensate for a missing connection time caused by a respective inactive module.

In yet another embodiment of the control unit according to the invention, the control unit is additionally configured to increase a starting level of the carrier signal assigned to the respective module to one for a respective inactive module, and to increase the phase shift of the respective carrier signals and the corresponding to a number of inactive modules for all active modules to modify the respective start levels of the active modules to compensate for a failed connection duration caused by a respective inactive module.

Furthermore, a modular multilevel converter is claimed, wherein the modular multilevel converter comprises a control unit according to the invention and is configured to carry out a method according to the invention.

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

It is understood that the features mentioned above and those to be explained below can be used not only in the combination specified in each case, but also in other combinations or alone, without departing from the scope of the present invention.

• 1a zeigt ein erstes Steuerungsschema in einer Ausführungsform des erfindungsgemäßen Verfahrens.
• 1b zeigt graphisch einen ersten Signalverlauf in der Ausführungsform des erfindungsgemäßen Verfahrens.
• 1c zeigt graphisch einen zweiten Signalverlauf in der Ausführungsform des erfindungsgemäßen Verfahrens.
• 2a zeigt ein zweites Steuerungsschema in einer weiteren Ausführungsform des erfindungsgemäßen Verfahrens.
• 2b zeigt graphisch einen dritten Signalverlauf in der weiteren Ausführungsform des erfindungsgemäßen Verfahrens.
• 3a zeigt ein drittes Steuerungsschema in einer noch weiteren Ausführungsform des erfindungsgemäßen Verfahrens.
• 3b zeigt ein Kreisschema zur Abfolge einer Signalmodifikation in der noch weiteren Ausführungsform des erfindungsgemäßen Verfahrens.
• 3c zeigt graphisch einen vierten Signalverlauf in der noch weiteren Ausführungsform des erfindungsgemäßen Verfahrens.
• 4 zeigt ein viertes Steuerungsschema in einer fortgesetzt noch weiteren Ausführungsform des erfindungsgemäßen Verfahrens.
• 5a zeigt ein fünftes Steuerungsschema in einer anderen Ausführungsform des erfindungsgemäßen Verfahrens.
• 5b zeigt graphisch einen fünften Signalverlauf in der anderen Ausführungsform des erfindungsgemäßen Verfahrens.
• 6 zeigt ein sechstes Steuerungsschema in einer noch anderen Ausführungsform des erfindungsgemäßen Verfahrens.

The figures are described coherently and comprehensively; the same components are assigned the same reference numbers.

• 1a shows a first control scheme in an embodiment of the method according to the invention.
• 1b graphically shows a first signal curve in the embodiment of the method according to the invention.
• 1c graphically shows a second signal curve in the embodiment of the method according to the invention.
• 2a shows a second control scheme in a further embodiment of the method according to the invention.
• 2 B graphically shows a third signal curve in the further embodiment of the method according to the invention.
• 3a shows a third control scheme in yet another embodiment of the method according to the invention.
• 3b shows a circuit diagram for the sequence of a signal modification in the yet further embodiment of the method according to the invention.
• 3c graphically shows a fourth signal curve in the still further embodiment of the method according to the invention.
• 4 shows a fourth control scheme in a further embodiment of the method according to the invention.
• 5a shows a fifth control scheme in another embodiment of the method according to the invention.
• 5b graphically shows a fifth signal curve in the other embodiment of the method according to the invention.
• 6 shows a sixth control scheme in yet another embodiment of the method according to the invention.

In 1a a first control scheme 110 is shown in an embodiment of the method according to the invention. A controller 111 provides at least one modulation reference signal 101 to a first control unit 112. The first control unit 112 is configured to simultaneously keep a sum of position changes of signal edges of all modules constant and to gradually change signal edge positions for at least one switching period. A phase shift of at least one carrier signal is modified in order to take into account the deviation of at least one modulation reference signal from the average reference signal. The step-by-step adjustments of the at least one phase shift 103 are fed to a phase shift counter 113, which provides multiple, each phase-shifted carrier signals 104 for a signal addition 115. A connection duration control unit 114 also provides carrier signals 105 with adapted signal edges for at least one connection duration for signal addition 115. The signal addition 115 supplies modified carrier signals 106 to a comparator 116. At the same time, the first control unit 112 generates compensated modulation reference signals 102 and supplies a single modulation reference signal 108 to the comparator 116 in accordance with the respective module. The comparator 116 compares the individual modulation reference signal 108 with the respective modified carrier signal 106, and provides respective switching pulses 107 to the respective assigned modules.

In 1b A first signal curve 120 is shown graphically in the embodiment of the method according to the invention. An overall signal curve 121 of voltage signals 1211, 1212, for example for supplying an electric traction machine, is plotted in the top panel over a time curve 129 of a complete switching cycle. The overall signal curve 121 is generated with the (control) signal curves 122, 123, 124, 125 from four modules in this example. By modulating the respective control signals 1221, 1231, 1241, 1251, for example in order to equalize the charge of energy storage devices, a voltage signal 1211 (dashed line) is created which disadvantageously extends over three voltage levels. Through the embodiment of the method according to the invention, the control signals 1232, 1252 are modified in such a way that a voltage signal 1212, which extends exclusively over two adjacent voltage levels, is advantageously composed of four voltage pulses of the same pulse width. The method according to the invention thus achieves a qualitatively better distribution of the voltage pulses.

In 1c A second signal curve 130 is shown graphically in the embodiment of the method according to the invention. An overall signal curve 131 of voltage signals 1311, 1312 is composed of the signal curves 132, 133, 134, 135 of the four modules. According to the invention, the original control signals 1321, 1331, 1341, 1351 are converted into modified control signals 1332, 1352, so that the resulting voltage signal 1312 advantageously has four evenly distributed voltage pulses with improved quality.

In 2a a second control scheme 210 is shown in a further embodiment of the method according to the invention. The controller 111 off 1 now directs the individual modulation reference signal 108 to the comparator 116. The second control unit 212 is configured to bring a rising signal edge in the connection duration of a respective module into agreement with a falling signal edge in a connection duration of the module that was previously immediately adjacent in the at least one strand. The phase shifts of these neighboring modules are modified cyclically iterating across all modules in the at least one strand. The step-by-step adjustments of the at least one phase shift 103 and the carrier signals 105 with adjusted signal edges are made according to the GIn. (2) to (7) calculated.

In 2 B A third signal curve 220 is shown graphically in the further embodiment of the method according to the invention. An overall signal curve 221 of voltage signals 2211, 2212 is generated with the signal curves 222, 223, 224, 225 of four modules. By modulating the respective control signals 2221, 2231, 2241, 2251, for example in order to equalize the charge of energy storage devices, a voltage signal 2211 (dashed line) and different pulse widths are created which disadvantageously extends over three voltage levels. Through the further embodiment of the method according to the invention, the control signals 2222, 2232, 2242, 2252 are modified in such a way that they advantageously form a voltage signal 2212 with two voltage pulses that extends exclusively over two adjacent voltage levels.

In 3a A third control scheme 310 is shown in yet another embodiment of the method according to the invention. The third control scheme 310, otherwise the same as the second control scheme 210 2a , has a third control unit 312. This is configured to simultaneously keep a sum of the position changes of the signal edges of all modules constant and to change signal edge positions for at least one switching period cyclically iterating across all modules in the at least one strand. In view of the change in position in a respective module, the phase shift of the carrier signal in the module previously adjacent in cyclic sequence is modified in order to take into account the deviation of at least one modulation reference signal from the average reference signal. The step-by-step adjustments of the at least one phase shift 103 and the carrier signals 105 with adapted signal edges are according to Eqs. (9) and (10) are calculated.

In 3b a circuit diagram 320 is shown for the sequence of a signal modification in the yet further embodiment of the method according to the invention. The sequence of signal modification is periodically closed. That is, the carrier signal 321 of the first module is previously adjacent to the carrier signal 322 to the second module, while the carrier signal of the Nth module is previously adjacent to the carrier signal 321 to the first module.

In 3c A fourth signal curve 330 is shown graphically in the yet further embodiment of the method according to the invention. An overall signal curve 331 of voltage signals 3311, 3312 is generated with the signal curves 332, 333, 334, 335 from four modules. By modulating the respective control signals 3321, 3331, 3341, 3351, a voltage signal 3311 (dashed line) with different pulse widths is created which disadvantageously extends over three voltage levels. Through the yet further embodiment of the method according to the invention, the control signals 3332, 3352 are modified in such a way that a voltage signal 3312 with two voltage pulses that extends exclusively over two adjacent voltage levels is advantageously produced.

In 4 A fourth control scheme 400 is shown in a further embodiment of the method according to the invention. The fourth control scheme 400, otherwise the same as the second control scheme 210 2a , has a fourth control unit 412, which also provides compensated modulation reference signals 409 to the connection duration control unit 114. The fourth control unit 412 is configured to simultaneously keep the respective connection duration constant and to gradually change a distribution of starting levels of the respective carrier signals. The phase shift of at least one carrier signal of the plurality of modules is modified in order to take into account the deviations of the starting levels from the average deviation value. The step-by-step adjustments of the at least one phase shift 103 and the carrier signals 105 with adjusted signal edges are carried out according to Equations. (11) and (12) are calculated.

In 5a A fifth control scheme 510 is shown in another embodiment of the method according to the invention. The fifth control scheme 510, otherwise the same as the first control scheme 110 1a , has a fifth control unit 512. The fifth control unit 512 is configured to reduce a modulation index assigned to the respective module to zero for a respective inactive module and, in accordance with a number of inactive modules, to adjust the phase shift of the respective carrier signal and the modulation reference signals of the active modules for all active modules to compensate for one by one to compensate for the failed connection duration caused by the inactive module 102. The step-by-step adjustments of the at least one phase shift 103 and the modifications of the starting levels of the carrier signals 105 are carried out according to Equations. (13) and (14) are calculated.

In 5b A fifth signal curve 520 is shown graphically in the other embodiment of the method according to the invention. An overall signal curve 521 of voltage signals 5211, 5212 is generated with the signal curves 523, 524, 525 from three modules. A fourth module is inactive, so that its control signal 5221 is reduced to zero in signal curve 522. By modulating the respective control signals 5231, 5241, 5251, a voltage signal 5211 (dashed line) is created which disadvantageously extends over three voltage levels. Through the other embodiment of the method according to the invention, the control signals 5232, 5242, 5252 are modified in such a way that this advantageously results in a voltage signal 5212 which extends exclusively over two adjacent voltage levels and is composed of three equally distributed voltage pulses of the same pulse width.

In 6 A sixth control scheme 600 is shown in yet another embodiment of the method according to the invention. The sixth control scheme 600, otherwise the same as the fourth control scheme 400 4 , has a sixth control unit 612, which provides adapted phase shifts 603 to the phase shift counter 113 and compensated modulation reference signals 609 to the switch-on duration control unit 114. The sixth Control unit 612 is configured to increase a start level of the carrier signal assigned to the respective module to one for a respective inactive module, and in accordance with a number of inactive modules for all active modules, the phase shift of the respective carrier signal and the respective start levels of the active modules to compensate for one to modify the connection duration caused by an inactive module. The adjustments to the phase shifts 603 and the modifications to the starting levels of the carrier signals 105 are made according to the GIn. (15) and (16) are calculated.

Reference symbol list

101

Modulation reference signals

102

Compensated modulation reference signal

103

Incremental adjustments of phase shifts

104

Multiple carrier signals

105

Carrier signal adjustments

106

Modified carrier signals

107

Multiple switching pulses

108

Single modulation reference signal

110

First control scheme

111

Regulator

112

First control unit

113

Phase shift counter

114

Switch-on duration control unit

115

Signal addition

116

comparator

120

First waveform example

121

Overall signal curve

1211

Original overall signal

1212

Modified overall signal

122

Signal curve first module

1221

Control signal

123

Signal curve second module

1231

Original control signal

1232

Modified control signal

124

Third module signal curve

1241

Control signal

125

Signal curve fourth module

1251

Original control signal

1252

Modified control signal

129

over time

130

Second waveform example

131

Overall signal curve

1311

Original overall signal

1312

Modified overall signal

132

Signal curve first module

1321

Control signal

133

Signal curve second module

1331

Original control signal

1332

Modified control signal

134

Third module signal curve

1341

Control signal

135

Signal curve fourth module

1351

Original control signal

1352

Modified control signal

210

Second control scheme

212

Second control unit

220

Third waveform example

221

Overall signal curve

2211

Original overall signal

2212

Modified overall signal

222

Signal curve first module

2221

Original control signal

2222

Modified control signal

223

Signal curve second module

2231

Original control signal

2232

Modified control signal

224

Third module signal curve

2241

Original control signal

2242

Modified control signal

225

Signal curve fourth module

2251

Original control signal

2252

Modified control signal

310

Second control scheme

312

Third control unit

320

Circle scheme

321

Carrier signal first module

322

Carrier signal second module

329

Carrier signal Nth module

330

Fourth waveform example

331

Overall signal curve

3311

Original overall signal

3312

Modified overall signal

332

Signal curve first module

3321

Control signal

333

Signal curve second module

3331

Original control signal

3332

Modified control signal

334

Third module signal curve

3341

Control signal

335

Signal curve fourth module

3351

Original control signal

3352

Modified control signal

400

Fourth control scheme

409

Compensated vertical positions

412

Fourth control unit

510

Fifth control scheme

512

Fifth control unit

520

Fifth waveform example

521

Overall signal curve

5211

Original overall signal

5212

Modified overall signal

522

Signal curve first module

5221

Control signal

523

Signal curve second module

5231

Original control signal

5232

Modified control signal

524

Third module signal curve

5241

Original control signal

5242

Modified control signal

525

Signal curve fourth module

5251

Original control signal

5252

Modified control signal

600

Sixth control scheme

603

Phase shift adjustments

609

Modified vertical images

612

Sixth control unit

Claims (15)

Method for controlling a modular multilevel converter, wherein the modular multilevel converter comprises a plurality of modules with at least one energy storage unit and a plurality of controllable switches, the plurality of modules being interconnected to form at least one strand starting from a connection to a voltage source, the modular Multilevel converter for generating an output signal using pulse width modulated control signals (1221, 1231, 1232, 1241, 1251, 1252, 1321, 1331, 1332, 1341, 1351, 1352, 2221, 2222, 2231, 2232, 2241 , 2242, 2251, 2252, 3321 , 3331, 3332, 3341, 3351, 3352, 5221, 5231, 5232, 5241, 5242, 5251, 5252) is controlled for the respective modules, with a respective control signal (1221, 1231, 1232, 1241, 1251, 125 2, 1321 , 1331, 1332, 1341, 1351, 1352, 2221, 2222, 2231, 2232, 2241, 2242, 2251, 2252, 3321, 3331, 3332, 3341, 3351, 3352, 5221, 5231, 5232, 5241, 5242, 5251 , 5252) for a respective module based on a respective carrier signal (106), which has a phase shift (104) related to the respective module, and is generated based on a modulation reference signal (108) assigned to the respective module, by means of a size comparison Based on a comparison of a signal curve of the respective carrier signal (106) with the respective modulation reference signal (108), a connection duration of the at least one energy storage unit of the respective module is triggered to a load current, the phase shift (104) or a starting level (409) being determined according to a modulation deviation from a mean reference signal , 609) of at least one carrier signal (106) of the plurality of modules are modified, while at the same time a time integral of the output signal (1211, 1212, 1311, 1312, 2211, 2212, 3311, 3312, 5511, 5512) is kept constant over a switching cycle, whereby the position of a rising and a falling signal edge changes when at least one module is switched on. Procedure according to Claim 1 , wherein, while at the same time a sum of the position changes of the signal edges of all modules is kept constant, signal edge positions of at least one switching period are gradually changed by modifying the phase shift (104) of at least one carrier signal (106) in order to correspond to the deviation of at least one modulation reference signal (108). from the average reference signal. Procedure according to Claim 1 , whereby a rising signal edge during the connection duration of a respective module with a falling signal edge during the connection duration of the one immediately adjacent in the at least one strand Module is brought into agreement by cyclically iterating over all modules in the at least one strand and modifying the phase shifts (104) of these neighboring modules. Procedure according to Claim 1 , whereby, while at the same time a sum of the position changes of the signal edges of all modules is kept constant, signal edge positions of at least one connection period are changed cyclically iteratively across all modules in the at least one strand by changing the phase shift (104) of the carrier signal in view of a change in position in a respective module (106) is modified in the previously adjacent module in cyclic sequence (320) in order to take into account the deviation of at least one modulation reference signal (108) from the average reference signal. Procedure according to Claim 1 , wherein, while at the same time the respective connection duration is kept constant, a distribution of start levels of the respective carrier signals is changed step by step by modifying the phase shift (104) of at least one carrier signal (106) of the plurality of modules in order to accommodate the deviations of the start levels (409). the average deviation value must be taken into account. Procedure according to Claim 1 , wherein for a respective inactive module, a modulation index assigned to the respective module is reduced to zero, with the phase shift (104) of the respective carrier signal (106) and the respective modulation reference signals (108) of the active modules corresponding to a number of inactive modules for all active modules Compensation for a failed connection duration caused by the respective inactive module can be modified. Procedure according to Claim 1 , wherein for a respective inactive module, a starting level of the carrier signal assigned to the respective module is increased to one, with the phase shift (104) of the respective carrier signal (106) and the respective starting levels (609) of the active ones corresponding to a number of inactive modules for all active modules Modules can be modified to compensate for a failed connection time caused by the respective inactive module. Control unit for a modular multilevel converter, wherein the modular multilevel converter comprises a plurality of modules with at least one energy storage unit and a plurality of controllable switches, the plurality of modules being interconnected to form at least one strand starting from a connection to a voltage source, the control unit being configured to do so is, the modular multilevel converter for generating an output signal using pulse width modulated control signals (1221, 1231, 1232, 1241, 1251, 1252, 1321, 1331, 1332, 1341, 1351, 1352, 2221, 2222, 2231, 2232, 2241, 2242, 2251 , 2252, 3321, 3331, 3332, 3341, 3351, 3352, 5221, 5231, 5232, 5241, 5242, 5251, 5252) for the respective modules and a respective control signal (1221, 1231, 1232, 1241, 1251, 1252 , 1321, 1331, 1332, 1341, 1351, 1352, 2221, 2222, 2231, 2232, 2241, 2242, 2251, 2252, 3321, 3331, 3332, 3341, 3351, 3352, 5221, 5231, 5232, 5241, 5242 , 5251, 5252) based on a respective carrier signal (106), which has a phase shift (104) related to the respective module, and based on a modulation reference signal (108) assigned to the respective module, and by a comparison based on a size comparison a signal curve of the respective carrier signal (106) with the respective modulation reference signal (108) to trigger a connection duration of the at least one energy storage unit of the respective module to a load current, and according to a modulation deviation from a mean reference signal, the phase shift (104) or a starting level (409, 609 ) to modify at least one carrier signal (106) of the plurality of modules and at the same time to keep a time integral of the output signal (1211, 1212, 1311, 1312, 2211, 2212, 3311, 3312, 5511, 5512) constant over a switching cycle, whereby a switching period of at least one module shifts a position of a rising and a falling signal edge. control unit Claim 8 , wherein the control unit (112) is additionally configured to simultaneously keep a sum of the position changes of the signal edges of all modules constant and to gradually change signal edge positions of at least one switching period by modifying the phase shift (104) of at least one carrier signal (106). to take into account the deviation of at least one modulation reference signal (108) from the average reference signal. control unit Claim 8 , wherein the control unit (212) is additionally configured to bring a rising signal edge in the connection duration of a respective module into agreement with a falling signal edge in the connection duration of the module that was previously immediately adjacent in the at least one strand, by cyclically iterating over all modules in The phase shifts (104) of these adjacent modules are modified in the at least one strand. control unit Claim 8 , wherein the control unit (312) is additionally configured to simultaneously keep a sum of the position changes of the signal edges of all modules constant and to change signal edge positions of at least one switching period cyclically iteratively across all modules in the at least one strand, in view of a change in position in a respective one Module, the phase shift (104) of the carrier signal (106) is modified in the previously adjacent module in cyclic sequence (320) in order to take into account the deviation of at least one modulation reference signal (108) from the average reference signal. control unit Claim 8 , wherein the control unit (412) is additionally configured to simultaneously keep the respective connection duration constant and to gradually change a distribution of start levels of the respective carrier signals by modifying the phase shift (104) of at least one carrier signal (106) of the plurality of modules, to take into account the deviations of the starting levels (409) from the average deviation value. control unit Claim 8 , wherein the control unit (512) is additionally configured to reduce a modulation index assigned to the respective module to zero for a respective inactive module and, in accordance with a number of inactive modules, to reduce the phase shift (104) of the respective carrier signals (106) for all active modules and the To modify modulation reference signals (108) of the active modules to compensate for a failed connection duration caused by the respective inactive module. control unit Claim 8 , wherein the control unit (612) is additionally configured to increase a starting level of the carrier signal assigned to the respective module to one for a respective inactive module, and corresponding to a number of inactive modules for all active modules, the phase shift (104) of the respective carrier signals (106 ) and to modify the respective start levels (609) of the active modules to compensate for a failed connection duration caused by a respective inactive module. Modular multilevel converter, wherein the modular multilevel converter has a control unit (112, 212, 312, 412, 512, 612) according to one of Claims 8 until 14 comprises and is configured to implement a method according to one of Claims 1 until 7 to carry out.

Images