Multi-level modulation

Abstract

There is provided a method for controlling a multilevel converter comprising a plurality of power converter modules, comprising:-for a first control cycle of a plurality of consecutive control cycles, associating a value of a first parameter that is a variable value with each power converter module; -determining, for the end point of the first control cycle, a characteristic of the conducting state of each power converter module, which is one of the first and second predetermined characteristics; obtaining a desired output signal of the power converter module for a second control period following a first control period of the plurality of consecutive control periods; for each change of the amplitude of the required output signal between the first and second amplitude levels, determining the amplitude of the required output signal based on a value of a first parameter associated with the at least one power converter module for the first control period and a characteristic of the conduction state of the at least one power converter module determined for the end point of the first control period; and controlling the conduction state of the at least one power converter module in the second control period.

Description

Technical Field

[0001] The present invention relates to the technical field of multi-level modulation, and more particularly to a multi-level converter and a method for controlling the multi-level converter. Background Art

[0002] A multilevel converter is a power conversion system that can generate a multistep voltage waveform from several DC input voltages. The multistep voltage waveform has at least three levels. The number of levels of a multilevel converter can be defined as the number of step or constant voltage levels that the multilevel converter can generate between the output and any internal reference node.

[0003] For example, a multilevel converter is described in the following document: J. Rodriguez et al., “Multilevel converters: An enabling technology for high-power applications,” IEEE Proceedings, Vol. 97, No. 11, pp. 1786-1817, 2009.

[0004] Multilevel converters are widely used in many technical fields, including the field of power conversion, such as the automotive field.

[0005] There are many different topologies of multilevel converters, for example, diode clamped multilevel converters, flying capacitors multilevel converters, and cascaded multilevel converters, and it is easy to use combinations and variations of these different topologies. Some of these topologies (such as flying capacitors multilevel converters and cascaded multilevel converters) have a modular structure consisting of multiple power converter modules (also called cells).

[0006] The output voltage of a multilevel converter is usually synthesized by a multilevel modulation technique. There are several multilevel modulation techniques applicable to multilevel converters. These modulation techniques can be classified into low switching frequency techniques and high switching frequency techniques according to the average switching frequency with which the modulation technique used for the multilevel converter operates. An example of a high frequency switching technique is multi-carrier pulse width modulation (PWM). Examples of multi-carrier PWM are phase shifted carrier PWM (PSCPWM) and level shifted carrier PWM (LSC PWM), which are one of the most popular modulation techniques.

[0007] These modulation techniques can be easily implemented on a microcontroller, field programmable gate array (FPGA) or application specific integrated circuit (ASIC).These multi-carrier PWM techniques use a carrier waveform signal for each power converter module of a multi-level converter.

[0008] Phase-shifted carrier PWM (PSC PWM) evenly distributes the on-time of each power converter module of a multi-level converter, effectively improving the effective output switching rate of the multi-level converter, but does not allow active control of the on-time of each power converter module to balance it in the workload distribution between the power converter modules.

[0009] Level-shifted carrier PWM (LSC PWM) does not evenly distribute the on-time of each power converter module, but utilizes carrier waveform signal exchange and a sequencing-based algorithm of each power converter module of a multi-level converter as a balancing algorithm.

[0010] Therefore, each modulation technique has its own disadvantages and advantages, and the modulation technique applied is highly dependent on the application area of ​​the multilevel converter. Therefore, the workload distribution between the individual power converter modules of a balanced multilevel converter is highly dependent on the modulation technique applied.

[0011] For example, US2021 / 0408935A1 describes a method for controlling a multilevel converter. However, the method described in US2021 / 0408935A1 is not applicable to multilevel pulse width modulation (PWM). In addition, the balance is completely dependent on feedback, which makes it produce potentially harmful low-frequency current ripple at the power converter module level.

[0012] Therefore, there is a need for improved modulation methods for multilevel converters.

[0013] It is therefore an object of the present invention to provide an improved modulation method for a multilevel converter. Summary of the invention

[0014] The above mentioned problems and disadvantages are solved by the subject matter of the independent claims. Further preferred embodiments are defined in the dependent claims.

[0015] In a first aspect of the present invention, there is provided a method for controlling a multilevel converter, the multilevel converter comprising a plurality of energy sources and a plurality of power converter modules, each power converter module comprising at least two switching elements, the method comprising:

[0016] - for a first control cycle from a plurality of consecutive control cycles, associating a value of a first parameter with each of a plurality of power converter modules, the value of the first parameter being a variable value;

[0017] - determining a characteristic of a conduction state of each of the plurality of power converter modules for an end point of the first control cycle, the characteristic of the conduction state being one of a first predetermined characteristic and a second predetermined characteristic;

[0018] - obtaining a desired output signal of the plurality of power converter modules for a second control cycle from the plurality of consecutive control cycles, the second control cycle being subsequent to the first control cycle;

[0019] -For each change in the amplitude of the desired output signal between the first amplitude level and the second amplitude level within the second control cycle, the conduction state of at least one power converter module within the second control cycle is controlled based on the value of a first parameter associated with at least one power converter module among the multiple power converter modules for the first control cycle and the characteristics of the conduction state of at least one power converter module determined for the end point of the first control cycle.

[0020] In a second aspect of the present invention, a multilevel converter is provided, the multilevel converter comprising a plurality of energy sources and a plurality of power converter modules, each power converter module comprising at least two switching elements, the multilevel converter comprising a device suitable for executing the steps of the method of the first aspect.

[0021] In a third aspect of the present invention, there is provided a computer program comprising instructions, which, when executed on a computer, causes the computer to perform the steps of the method of the first aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Embodiments of the present invention will now be described with reference to the accompanying drawings, which are presented for a better understanding of the inventive concept but should not be considered as limiting the present invention, in which:

[0023] Figure 1 schematically shows the required output signals of a multilevel converter and the arrangement of the individual power converter modules according to prior art solutions;

[0024] Figure 2 is a flowchart showing the steps of a method for controlling a multi-level converter according to an embodiment of the present invention;

[0025] Figure 3 is a schematic block diagram of a multilevel converter according to an embodiment of the present invention;

[0026] Figure 4A and Figure 4B shows information for controlling the conduction state of each power converter module according to an embodiment of the present invention;

[0027] Figure 5Schematically shows the required output signals of a multilevel converter and the arrangement of various power converter modules according to an embodiment of the present invention;

[0028] Figure 6 A control block diagram for executing a method for controlling a multi-level converter according to an embodiment of the present invention is shown;

[0029] Figure 7 A control block diagram for executing a method for controlling a multi-level converter according to an embodiment of the present invention is shown;

[0030] Figure 8 A control block diagram for executing a method for controlling a multi-level converter according to an embodiment of the present invention is shown;

[0031] Fig. 9 A control block diagram for executing a method for controlling a multilevel converter according to an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0032] In a multilevel converter, according to how the various power converter modules of the multilevel converter are connected together, the distribution of energy conversion (workload or load) between the different power converter modules of the multilevel converter can be controlled. For the distribution of energy conversion and therefore for the distribution of the workload (load) between the power converter modules of the multilevel converter, at least the following factors work: i) the modulation technique applied to the power converter modules of the multilevel converter, which includes determining how many power converter modules will participate in energy conversion, which in turn depends on the number of voltage levels required for the required output voltage of the multilevel converter, and ii) the arrangement of the various power converter modules of the multilevel converter to perform energy conversion, which includes determining which power converter modules will participate in the distribution of energy conversion (workload or load). Therefore, the distribution of the workload (load) between the various power converter modules of the multilevel converter is controlled.

[0033] Figure 1 An example of a desired output signal of a multi-level converter is schematically shown in the upper part. More specifically, Figure 1The example of the required output voltage of multilevel converter is schematically shown in the upper part. In this example, the required output voltage of multilevel converter is modulated between the second voltage level (2lvl) and the third voltage level (3lvl). Vertical dotted line represents the boundary between each control cycle Ti, Ti+1, Ti+2... In other words, each independent control cycle Ti extends between two vertical dotted lines. In this example, in each control cycle, the required output voltage has a baseline 50 corresponding to the second voltage level (2lvl) and a step 60 to the third voltage level (3lvl). In this example, the step occurs at the beginning of each control cycle Ti and the duration is a small part of the control cycle Ti. The control cycle Ti can be regarded as the cycle corresponding to the required output signal.

[0034] Figure 1 The lower part of FIG. 1 shows the arrangement of the individual power converter modules of the multilevel converter according to the prior art solution, so as to Figure 1 The desired output voltage of the multilevel converter is achieved within each control period (Ti) shown in the upper part of . Figure 1 The arrangement of the individual power converter modules is shown for the case of four power converter modules (M1, M2, M3 and M4).

[0035] According to prior art solutions, for each control cycle Ti, Ti+1, Ti+2 ..., select a new combination of power converter modules to be placed in an active state (represented by filling slashes) or vice versa from an inactive state, or keep an active state or inactive state from the immediately preceding control cycle. The selection of power converter modules is usually based on at least one parameter, such as, the temperature of power converter modules or the output voltage of power converter module strings. If power converter modules actively participate in the energy conversion in the multilevel converter, they are in an active state (therefore being arranged for energy conversion), otherwise they are considered to be in an inactive state.

[0036] For control period Ti, control power converter module M1 and M3 are in active state in the whole length of control period Ti. These power converter modules (M1 and M3) realize the baseline 50 corresponding to the second voltage level (2lvl) in the required output voltage. Control power converter module M4 is in active state only in a small part of control period Ti, thereby realizes the step 60 from the second voltage level (2lvl) to the 3rd voltage level (3lvl) in the required output voltage, and the length of this small part corresponds to the duration of step 60. Control power converter module M2 is in inactive state in the whole length of control period Ti.

[0037] For subsequent control cycle Ti+1, according to prior art solutions, a new combination of power converter modules is selected based on at least one of the above-mentioned at least one parameter again to achieve the required output voltage in the subsequent control cycle Ti+1. In the control cycle Ti+1, the control power converter modules M2 and M4 are in an active state in the entire length of the control cycle Ti+1, thereby achieving the baseline 50 corresponding to the second voltage level (2lvl) in the required output voltage, and the control power converter module M1 is in an active state only in a small part of the control cycle Ti, thereby achieving the step 60 of the required output voltage from the second voltage level (2lvl) to the third voltage level (3lvl), the length of which corresponds to the duration of the step 60. The control power converter module M3 is in an inactive state in the entire length of the control cycle Ti+1.

[0038] from Figure 1 As can be seen in FIG, between control period Ti and Ti+1, three power converter modules (i.e., power converter modules M2, M3 and M4) switch conduction state between active state and inactive state. This increases the switching loss in the multilevel converter according to the prior art solution. In addition, it is difficult to achieve the balance of conduction time between different power converter modules.

[0039] The present invention proposes a modulation technique for a multilevel converter, which is not to arrange power converter modules for each control cycle, but to arrange power converter modules for events in each control cycle. When arranging for events in each control cycle, the present invention prioritizes the power converter modules to be used and distinguishes between the power converter modules based on the conduction state of the power converter modules in the previous control cycle. This achieves a balance of conduction time between different power converter modules and reduces the number of switching times of the conduction state of each power converter module between control cycles, thereby reducing switching losses.

[0040] The event in each control cycle in the sense of the present invention is a change of the desired output signal of the multilevel converter between the first amplitude level of the desired output signal of the multilevel converter and the second amplitude level of the desired output signal of the multilevel converter. The output signal of the multilevel converter is usually a voltage signal. The desired output signal can correspond to or represent the desired (desired or required) voltage of the multilevel converter. Therefore, the first amplitude level and the second amplitude level can correspond to the voltage level of the desired voltage of the multilevel converter.

[0041] Figure 2 is a flow chart showing steps of a method for controlling a multilevel converter according to an embodiment of the present invention.

[0042] Figure 3A schematic block diagram of a multilevel converter 1 according to an embodiment of the present invention is shown. The multilevel converter 1 includes multiple energy sources 11 and multiple power converter modules 10_1, 10_2, 10_3, ..., 10_i, ..., 10_n (i = 1....n). Each power converter module 10_i includes at least two switching elements 12. Each of the at least two switching elements 12 can be a solid-state switching element, for example, a two-terminal solid-state switch or a three-terminal solid-state switch. Examples of two-terminal solid-state switches include PiN (positive-intrinsic-negative) diodes and Schottky diodes, which do not limit the present invention. Examples of three-terminal solid-state switches include MOSFET, JFET, IGBT, BJT and thyristor, which do not limit the present invention.

[0043] It should be understood that although Figure 3 Each energy source 11 is shown to be connected to a corresponding one of power converter modules 10_1, 10_2, 10_3, ..., 10_i, ..., 10_n (i is an index, replacing any one of 1 to n), but this is not restrictive, and other connection configurations are also possible. Energy source 11 can be any type of energy source, such as a battery, a photovoltaic cell, a fuel cell, an electromechanical power converter or a capacitive energy source. It should also be understood that the present invention is not limited to the specific topology of multilevel converter 1. For example, power converter modules 10_1, 10_2, 10_3, ..., 10_n can be connected in series, and a plurality of such series can be arranged in multilevel converter 1. Each series can represent a phase or an arm of multilevel converter 1.

[0044] According to the method for controlling a multilevel converter 1 of an embodiment of the present invention, the method comprises: in step S100, for the first control cycle from a plurality of continuous control cycles, the value of the first parameter is associated with each of a plurality of power converter modules 10_1, 10_2, 10_3, ..., 10_n. The value of the first parameter is a variable value. In one or more embodiments of the present invention, the value of the first parameter can be a variable value.

[0045] The method further includes: in step S200, for the end point of the first control cycle, determining the characteristic of the conduction state of each of the plurality of power converter modules 10_1, 10_2, 10_3, ..., 10_n. The characteristic of the conduction state is one of a first predetermined characteristic and a second predetermined characteristic.

[0046] In one or more embodiments of the present invention, the end point of the first control cycle may correspond to the actual end time point of the first control cycle, while in other embodiments of the present invention, the end point of the first control cycle may be a time point within a time period of a predetermined length and is an end point corresponding to the actual end time point of the first control cycle, so the end point of the first control cycle may be a time point before the actual end time point of the first control cycle. In other words, in one or more embodiments of the present invention, the definition of the end point of the first control cycle may depend on the accuracy of the determination of the end point of the first control cycle, and the accuracy of the determination of the end point of the first control cycle may depend on the processing accuracy and processing speed (e.g., clock cycle) of one or more hardware components responsible for determining the end point of the first control cycle.

[0047] The method also includes: in step S 300, for the second control cycle from a plurality of continuous control cycles, obtain the required output signal of a plurality of power converter modules 10_1, 10_2, 10_3, ..., 10_n. The second control cycle is after the first control cycle. The second control cycle can be a continuous cycle of the first control cycle, but this is not necessary. As mentioned above, the required output signal can correspond to or represent the required (desired or required) voltage (signal) of multilevel converter 1.

[0048] The method also includes: in step S 400, for each change of the amplitude of the desired output signal between the first amplitude level and the second amplitude level within the second control cycle, based on the value of a first parameter associated with at least one power converter module among the multiple power converter modules 10_1, 10_2, 10_3, ..., 10_n for the first control cycle and the characteristics of the conduction state of the at least one power converter module determined for the end point of the first control cycle, controlling the conduction state of the at least one power converter module within the second control cycle.

[0049] In step S 400, controlling the conduction state of at least one power converter module in a plurality of power converter modules 10_1, 10_2, 10_3, ..., 10_n may include any one of the following: switching the conduction state of at least one power converter module, placing at least one power converter module in a parallel configuration state, placing at least one power converter module in a bypass state, and reversing the output voltage of at least one power converter module. The term "placed" should be understood as controlling at least one power converter module to be in a parallel configuration state or a bypass state, or issuing one or more commands for controlling at least one power converter module to be in a parallel configuration state or a bypass state.

[0050] Reversing the output voltage of at least one power converter module may include: before controlling at least one power converter module to reverse the output voltage, controlling at least one power converter module to generate a voltage opposite to the generated voltage. In other words, in the example, reversing the output voltage of at least one power converter module 10_i may correspond to reversing the output voltage of at least one power converter module 10_i from +20V to -20V. Therefore, the power converter module remains in an active on state, but its output voltage is reversed.

[0051] Switching the conductive state of the at least one power converter module may include switching between a conductive state and a non-conductive state of the at least one power converter module 10_i, or vice versa.

[0052] The non-conducting state of at least one power converter module 10_i does not necessarily mean that for at least one power converter module 10_i in a non-conducting state, each element of the power converter module 10_i is in a non-conducting state. For example, when at least one power converter module 10_i is in a non-conducting state, at least one of the two switch elements 12 of the power converter module 10_i can be in a conducting state, thereby bypassing the energy source 11 connected to the power converter module 10_i. Therefore, at least one power converter module 10_i being in a non-conducting state can be understood as at least one power converter module 10_i not (actively) participating in the distribution of energy conversion (workload, load) in the multi-level converter 1. The output signal of at least one power converter module 10_i in a non-conducting state can have a value of 0V. Therefore, at least one power converter module 10_i being in a non-conducting state can be understood as at least one power converter module 10_i not participating in the generation of the required output voltage of the multi-level converter 1 by adding the voltage level to the required output voltage. However, it is important to note that this does not exclude “unintentionally” generated voltages, such as parasitic voltages.

[0053] In an embodiment of the invention, the first predetermined characteristic of the conduction state may indicate an active conduction state, and the second predetermined characteristic of the conduction state may indicate an inactive conduction state.

[0054] The active on-state may also be referred to as the on-state. At least one power converter module 10_i being in the on-state may be understood as at least one power converter module 10_i (actively) participating in the distribution of energy conversion (workload, load) in the multilevel converter 1. More specifically, at least one power converter module 10_i being in the on-state may be understood as at least one power converter module 10_i (actively) participating in the generation of the required output voltage of the multilevel converter 1.

[0055] In an embodiment of the present invention, the inactive conducting state can be any one of the non-conducting state and the parallel configuration state. The power converter module 10_i in the parallel configuration state does not participate in the generation of the required output voltage of the multilevel converter 1, but can only share the current load with at least one other power converter module connected in parallel therewith. In an embodiment of the present invention, if the power converter module is placed in the bypass state, the power converter module can be in an inactive state.

[0056] Each power converter module may be placed in a parallel configuration state or placed from a conductive state to a bypass state as one possible way of controlling the conductive state of at least one of the plurality of power converter modules 10_1 , 10_2 , 10_3 , . . . , 10_n.

[0057] In an embodiment of the present invention, the first parameter may indicate the priority of the corresponding power converter module, which is used to select the power converter module 10_i to control the conduction state of the corresponding selected power converter module 10_i in the second control cycle. Therefore, according to the method for controlling the multilevel converter 1 of the embodiment of the present invention, based on the value of the first parameter associated with at least one power converter module 10_i of the plurality of power converter modules 10_1, 10_2, 10_3, ..., 10_n for the first control cycle and the characteristics of the conduction state of at least one power converter module 10_i determined for the end point of the first control cycle, controlling the conduction state of at least one power converter module 10_i in the second control cycle may include: based on at least one power converter module 10_1, 10_2, 10_3, ..., 10_n of the plurality of power converter modules 10_1, 10_2, 10_3, ..., 10_n 0_i and the characteristics of the conduction state of at least one power converter module 10_i determined for the end point of the first control cycle, select at least one power converter module 10_i, and control the conduction state of at least one power converter module selected from multiple power converter modules 10_1, 10_2, 10_3, ..., 10_n within the second control cycle by any one of the following methods: switching the conduction state of at least one power converter module, placing at least one power converter module in a parallel configuration state, placing at least one power converter module in a bypass state, and reversing the output voltage of at least one power converter module.

[0058] The priority of the conduction state of the selected power converter module 10_i for selecting the power converter module 10_i of the corresponding power converter module 10_i can depend on the actual application and application environment of the multilevel converter 1. Therefore, the priority can be determined based on various parameters depending on the actual application and application environment of the multilevel converter 1. For example, the priority can depend on the current direction in the system (for example, the battery system to which the multilevel converter 1 can be applied). When the battery system is charging or discharging, the priority can be determined based on the state of charge of the energy source. When the battery system is discharging, the power converter module 10_i with the highest state of charge can have the highest priority for selecting it to control its conduction state in the second control cycle, and when the battery system is charging, the power converter module 10_i with the lowest state of charge can have the highest priority for selecting it to control its conduction state in the second control cycle. In other applications or application environments, priority can be determined based on the temperature of the energy source. For example, the power converter module with the highest temperature may have the lowest priority for selecting the power converter module 10_i to control the conduction state of the corresponding power converter module 10_i during the second control cycle.

[0059] In one embodiment of the present invention, the first parameter associated with each of a plurality of power converter modules 10_1, 10_2, 10_3, ..., 10_n and the characteristics of the conduction state of each of a plurality of power converter modules 10_1, 10_2, 10_3, ..., 10_n can be stored in one or more lists or tables. In other words, in one embodiment of the present invention, for the first control cycle, the value of the first parameter and the association of each of a plurality of power converter modules 10_1, 10_2, 10_3, ..., 10_n can be performed by using a list or table. Lists or tables can also store each state (or information indicating the conduction state) of a plurality of power converter modules 10_1, 10_2, 10_3, ..., 10_n at the end point of the first control cycle.

[0060] The characteristic of the conduction state of each of the multiple power converter modules 10_1, 10_2, 10_3, ..., 10_n for the end point of the first control cycle can be performed based on the control command sent to each of the multiple power converter modules 10_1, 10_2, 10_3, ..., 10_n or based on any one of the output current or voltage of the power converter modules 10_1, 10_2, 10_3, ..., 10_n strings for the end point of the first control cycle. The control command can be sent for the entire first cycle, or for a small part of the first cycle, or even for several control cycles in advance.

[0061] In an embodiment of the present invention, the control command sent to each of a plurality of power converter modules 10_1, 10_2, 10_3, ..., 10_n may include the conduction time of the corresponding power converter module 10_i in the first control cycle. The conduction time may indicate that the corresponding power converter module 10_i will (actively) participate in or will not (actively) participate in the time period of the distribution of energy conversion (workload, load) in the multilevel converter 1 in the first control cycle. Therefore, the characteristic of the conduction state of each of the plurality of power converter modules 10_1, 10_2, 10_3, ..., 10_n determined for the end point of the first control cycle may be performed based on the conduction time of the corresponding power converter module 10_i in the first control cycle. However, this should not be considered as limitation of the present invention.

[0062] Figure 4A and Figure 4B Exemplary embodiments for storing the first parameter and the characteristics of the conduction state in one and two tables are shown. In these embodiments of the invention, the multilevel converter 1 comprises four power converter modules, however, this does not limit the invention.

[0063] Figure 4A An embodiment of the present invention is shown, wherein, for the end point of the first control cycle, the first parameter of each of a plurality of power converter modules 10_1, 10_2, 10_3, ..., 10_n and the characteristics of the on-state are stored in a table. Each power converter module is assigned a power converter module identification, also referred to as "module ID". For example, each power converter module is assigned a module ID, including "module 1", "module 2", "module 3", "module 4". Therefore, the table includes three columns. In the first column, the module ID of each power converter module is stored. In the second column, the first parameter associated with each power converter module is stored. The first parameter may also be referred to as "cost". "Cost" can be seen as the cost of using the corresponding power converter module energy conversion (workload distribution) in the multilevel converter 1. The characteristics of the on-state may also be referred to as "state", and are stored in the third column. In this embodiment of the present invention, the power converter modules are arranged in the table in a descending order based on "cost".

[0064] Figure 4B An embodiment of the present invention using two tables is shown. One table is used for a power converter module whose characteristic of the on-state at the end point of the first control cycle is a first predetermined characteristic, and the other table is used for a power converter module whose characteristic of the on-state at the end point of the first control cycle is a second predetermined characteristic.

[0065] In an embodiment of the present invention, the method may also include sorting multiple power converter modules 10_1, 10_2, 10_3, ..., 10_n based on the value of the first parameter associated with each of the multiple power converter modules 10_1, 10_2, 10_3, ..., 10_n for the first control cycle. Sorting multiple power converter modules 10_1, 10_2, 10_3, ..., 10_n based on the value of the first parameter may include: sorting multiple power converter modules 10_1, 10_2, 10_3, ..., 10_n according to the descending or ascending order of the corresponding value of the first parameter. However, sorting is optional.

[0066] exist Figure 4A and Figure 4B In the embodiment of the present invention shown, the sorting of multiple power converter modules 10_1, 10_2, 10_3, ..., 10_n based on the value of the first parameter is sorted in descending order of the corresponding value of the first parameter, but this is not restrictive. In the present invention, the first parameter indicates the priority of the corresponding power converter module 10_i for selecting the power converter module, so as to control the conduction state of the corresponding power converter module 10_i in the second control cycle. In the embodiment, the power converter modules 10_1, 10_2, 10_3, ..., 10_n are sorted in descending order of priority.

[0067] In another embodiment of the present invention, a table (for example, Figure 4A ) or two tables (for example, Figure 4B Each row in the two tables shown in (shown in) is assigned to a specific power converter module 10_i. The one or two tables can then be searched to identify the power converter module in ascending or descending order according to the value of the first parameter. Therefore, in this embodiment of the present invention, the value based on the first parameter can be omitted to sort multiple power converter modules 10_1, 10_2, 10_3, ..., 10_n.

[0068] In an embodiment of the present invention, the first amplitude level is lower than the second amplitude level. For example, the first amplitude level may correspond to Figure 1 The second voltage level (2lvl) in the upper part of the second amplitude level can correspond to the third voltage level (3lvl).

[0069] For each change in the amplitude of the desired output signal from a first amplitude level to a second amplitude level, the method may include: controlling the conduction state of one or more power converter modules of the plurality of power converter modules 10_1, 10_2, 10_3, ..., 10_n whose conduction state characteristic is a second predetermined characteristic. The control may include selecting one or more power converter modules of the power converter modules 10_1, 10_2, 10_3, ..., 10_n whose conduction state characteristic is a second predetermined characteristic in the order from the value of the first parameter indicating the highest priority to the value of the first parameter indicating the lowest priority, to control the conduction state of the selected one or more power converter modules 10_1, 10_2, 10_3, ..., 10_n. In an embodiment of the present invention, in which multiple power converter modules 10_1, 10_2, 10_3, ..., 10_n are sorted in one or two tables based on the value of a first parameter associated with each of the multiple power converter modules 10_1, 10_2, 10_3, ..., 10_n, the sorting can simplify the identification and selection of one or more of the power converter modules 10_1, 10_2, 10_3, ..., 10_n.

[0070] For each change in the amplitude of the desired output signal from the second amplitude level to the first amplitude level, the method may include: controlling the conduction state of one or more power converter modules in the power converter modules 10_1, 10_2, 10_3, ..., 10_n whose conduction state characteristic is a first predetermined characteristic. The control may include selecting one or more power converter modules 10_1, 10_2, 10_3, ..., 10_n whose conduction state characteristic is a first predetermined characteristic in the order from the value of the first parameter indicating the lowest priority to the value of the first parameter indicating the highest priority, so as to control the conduction state of the selected one or more power converter modules 10_1, 10_2, 10_3, ..., 10_n. Again, in an embodiment of the present invention in which multiple power converter modules 10_1, 10_2, 10_3, ..., 10_n are sorted in one or two tables based on the value of a first parameter associated with each of the multiple power converter modules 10_1, 10_2, 10_3, ..., 10_n, the sorting can simplify the identification and selection of one or more of the power converter modules 10_1, 10_2, 10_3, ..., 10_n.

[0071] In one or more embodiments of the present invention, controlling the conduction state of one or more power converter modules whose conduction state characteristic is a first predetermined characteristic in power converter modules 10_1, 10_2, 10_3, ..., 10_n may include: reversing the output voltage of one or more power converter modules whose conduction state characteristic is a first predetermined characteristic in power converter modules 10_1, 10_2, 10_3, ..., 10_n. This may be the case with a full-bridge power converter module. In a full-bridge power converter module, by reversing or changing the output voltage of a power converter module whose conduction state characteristic is a first predetermined characteristic, the required output voltage can be reduced from a second amplitude level to a first amplitude level (especially when the first amplitude level and the second amplitude level differ by one or two voltage levels).

[0072] Figure 5 Schematically shows the example of the required output signal (required output voltage) of the multilevel converter 1 in the embodiment of the present invention, and shows the arrangement of each power converter module 10_1,10_2,10_3,...,10_n of the multilevel converter 1 according to the embodiment of the present invention, to realize the required output signal of the multilevel converter 1. In this embodiment of the present invention, the arrangement for four power converter modules (M1, M2, M3 and M4) is shown, but this is not restrictive. The multilevel converter 1 can only include four power converter modules, but it can include more than four power converter modules.

[0073] In this embodiment of the present invention, the required output voltage of the multilevel converter 1 is modulated between the second voltage level (2lvl) and the third voltage level (3lvl). However, the present invention is not limited thereto.

[0074] The vertical dotted lines represent the boundaries between the various control cycles Ti, Ti+1, Ti+2, Ti+3, Ti+4... In other words, each individual control cycle Ti extends between two vertical dotted lines. In this embodiment of the present invention, in each control cycle, the desired output voltage has a baseline 50 corresponding to the second voltage level (2lvl) and a step 60 to the third voltage level (3lvl). In this embodiment of the present invention, the step 60 appears at the beginning (starting point) of each control cycle Ti, and the duration is a small part of the control cycle Ti. However, this is not restrictive, and the step may appear, for example, in the middle of each control cycle or at the end of the control cycle, such as a step to the second voltage level (2lvl) can be aligned with the end point of the control cycle. Preferably, the portion corresponding to the third voltage level (3lvl) in the desired output voltage can be aligned with the middle of the control cycle (center alignment). In addition, in an embodiment of the present invention, within the control cycle, the desired output signal can have more than one step. The control cycle Ti can be regarded as corresponding to the cycle of the desired output signal.

[0075] The second voltage level (2lvl) may correspond to the first amplitude level described above, and the third voltage level (3lvl) may correspond to the second amplitude level described above.

[0076] The change of the desired output voltage from the second voltage level (2lvl) to the third voltage level (3lvl) may also be referred to as a rising edge, and the change of the voltage from the third voltage level (3lvl) to the second voltage level (2lvl) may also be referred to as a falling edge of the desired output voltage. Therefore, in this embodiment of the present invention, within each control cycle, two events occur in the desired output signal: a rising edge at the beginning of each control cycle and a falling edge within each control cycle. However, the present invention is not limited thereto. In other words, the rising edge does not have to be at the beginning of each control cycle, and in each control cycle, the desired output signal may have more than one rising edge and / or falling edge. The falling edge may also be at the end of the control cycle.

[0077] In this embodiment of the present invention, it is assumed that the first control cycle and the second control cycle are continuous control cycles, but the present invention is not limited thereto. In addition, in this embodiment of the present invention, it is assumed that the inactive conductive state is a non-conductive state, and it is assumed that controlling the conductive state of at least one power converter module 10_i includes switching the conductive state of at least one power converter module from conductive to non-conductive state, and vice versa. Figure 5 At the bottom of the diagram, the active conduction states of each power converter module are indicated by slashes.

[0078] As described above, step S200 includes determining a characteristic of a conduction state of each of the plurality of power converter modules for an end point of the first control cycle, the characteristic of the conduction state being one of a first predetermined characteristic and a second predetermined characteristic.

[0079] For the control period Ti as the first control period, by applying step S200, the following is determined for the end point of the control period Ti (first control period):

[0080] M1-active state, M2-inactive state, M3-inactive state, M4-active state.

[0081] In this embodiment of the present invention, for the first control period Ti, the value of the first parameter associated with M3 indicates a higher priority than the value of the first parameter associated with M2, and for the first control period Ti, the value of the first parameter associated with M4 indicates a lower priority than the value of the first parameter associated with M1. The details of determining the value of the first parameter in an embodiment of the present invention are further described below.

[0082] For the rising edge of the desired output signal at the beginning of the second control period Ti+1, M3 is controlled so that its conductive state is switched at the rising edge (here, at the beginning of the second control period) by applying step S400. Since M1 and M4 maintain the conductive state of the first control period Ti at the beginning of the second control period Ti+1, M1, M3 and M4 generate the desired output voltage with a rising edge (step 60 of the desired output voltage) from the second voltage level to the third voltage level.

[0083] For the falling edge of the desired output signal in the second control period Ti+1, by applying step S 400, control M4, thereby switch its conduction state at the falling edge. Because M3 and M1 keep conduction state, therefore M1 and M3 produce the baseline 50 of required output voltage.Therefore, in the second control period Ti+1, two power converter modules (M3 and M4) switch conduction state between active state and inactive state.In prior art solution, as mentioned above, three power converter modules (M1, M3 and M4) switch conduction state between active state and inactive state.

[0084] For the control period Ti+2 as the second control period, by applying step S200, the following is determined for the end point of the control period Ti+1 (the first control period):

[0085] M1-active state, M2-inactive state, M3-active state, M4-inactive state.

[0086] In this embodiment of the present invention, for the first control period Ti+1, the value of the first parameter associated with M2 indicates a higher priority than the value of the first parameter associated with M4, while the value of the first parameter associated with M3 indicates a lower priority than the value of the first parameter associated with M1.

[0087] For the rising edge of the desired output signal at the starting point of the second control period Ti+2, M2 is controlled so that its conductive state is switched at the beginning (at the rising edge) of the second control period by applying step S400. Since M1 and M3 maintain the conductive state of the first control period Ti+1 at the rising edge of the second control period Ti+2, M1, M2 and M3 generate the desired output voltage with a rising edge (step 60 of the desired output voltage) from the second voltage level to the third voltage level.

[0088] For the falling edge of the desired output signal in the second control period Ti+2, by applying step S 400, control M3, thereby switch its conduction state at the falling edge. Because M1 and M2 keep conduction state, therefore M1 and M2 produce the baseline 50 of required output voltage.Therefore, in the second control period Ti+2, two power converter modules (M2 and M3) switch conduction state between active state and inactive state.In prior art solution, as mentioned above, three power converter modules (M1, M3 and M4) switch conduction state between active state and inactive state.

[0089] For the control period Ti+3 as the second control period, by applying step S200, the following is determined for the end point of the control period Ti+2 (the first control period):

[0090] M1-active state, M2-active state, M3-inactive state, M4-inactive state.

[0091] In this embodiment of the present invention, for the first control period Ti+2, the value of the first parameter associated with M3 indicates a higher priority than the value of the first parameter associated with M4, while the value of the first parameter associated with M1 indicates a lower priority than the value of the first parameter associated with M2.

[0092] For the rising edge of the desired output signal at the starting point of the second control period Ti+3, M3 is controlled so that its conductive state is switched at the beginning (at the rising edge) of the second control period by applying step S400. Since M1 and M2 maintain the conductive state of the first control period Ti+2 at the beginning of the second control period Ti+3, M1, M2 and M3 generate the desired voltage with a rising edge (a step 60 of the desired output voltage) from the second voltage level to the third voltage level.

[0093] For the falling edge of the desired output signal in the second control period Ti+3, by applying step S 400, control M1, thereby switch its conduction state at the falling edge. Because M2 and M3 keep conduction state, therefore M2 and M3 produce the baseline 50 of required output voltage.Therefore, in the second control period Ti+3, two power converter modules (M1 and M3) switch conduction state between active state and inactive state.In prior art solution, as mentioned above, three power converter modules (M1, M3 and M4) switch conduction state between active state and inactive state.

[0094] For the control period Ti+4 as the second control period, by applying step S200, the following is determined for the end point of period Ti+3 (the first control period):

[0095] M1-inactive, M2-active, M3-active, M4-inactive.

[0096] In this embodiment of the present invention, for the first control period Ti+3, the value of the first parameter associated with M1 indicates a higher priority than the value of the first parameter associated with M4, while the value of the first parameter associated with M2 indicates a lower priority than the value of the first parameter associated with M3.

[0097] For the rising edge of the desired output signal at the start point of the second control period Ti+4, M1 is controlled so that its conductive state is switched at the beginning (at the rising edge) of the second control period by applying step S400. Since M2 and M3 maintain the conductive state of the first control period Ti+3 at the beginning of the second control period Ti+4, M1, M2 and M3 generate the desired voltage with a rising edge (step 60 of the desired output voltage) from the second voltage level to the third voltage level.

[0098] For the falling edge of the desired output signal in the second control period Ti+4, by applying step S 400, control M2, thereby switch its conduction state at the falling edge. Because M1 and M3 keep conduction state, therefore M1 and M3 produce the baseline 50 of required output voltage.Therefore, in the second control period Ti+4, two power converter modules (M1 and M2) switch conduction state between active state and inactive state.In prior art solution, as mentioned above, three power converter modules (M1, M3 and M4) switch conduction state between active state and inactive state.

[0099] Therefore, one or more power converter modules that are in an inactive conducting state at the end point of the first control cycle and are associated with a value of a higher priority than other one or more power converter modules that are in an inactive conducting state at the end point of the first control cycle with the indication of the first parameter for the first control cycle are first utilized or arranged for the rising edge of the required output voltage in the second control cycle by being turned on or placed in an active state. On the other hand, one or more power converter modules that are in an active state at the end point of the first control cycle and are associated with a value of a lower priority than other one or more power converter modules that are in an active state at the end point of the first control cycle with the indication of the first parameter for the first control cycle are first disconnected or placed in an inactive state for the falling edge of the required output voltage in the second control cycle. For a modular multilevel converter with parallel connection, a power converter module with a value of a lower priority indicating a first parameter is first placed in a parallel configuration state or bypassed.

[0100] In each control cycle, zero or one or more rising edges and falling edges are accurately placed using counters or timers, thereby realizing pulse width modulation, to realize high output voltage resolution. Therefore, according to the present invention, the event (rising edge or falling edge) in the required output voltage is arranged. Only the inactive power converter module to be switched on and the active power converter module to be disconnected are selected to inherently reduce the switching loss to a minimum, thereby without considering the switching loss in the priority list, thereby reducing the computational workload and therefore reducing computing resources.

[0101] In one or more embodiments of the present invention, a control cycle may be executed for each control cycle. Figure 2 Steps of the method.

[0102] Therefore, in one or more embodiments of the present invention, the method may further include: for the second control cycle, the updated value of the first parameter is associated with each of the plurality of power converter modules 10_1, 10_2, 10_3, ..., 10_n; and for the end point of the second control cycle, the characteristics of the conduction state of each of the plurality of power converter modules 10_1, 10_2, 10_3, ..., 10_n are determined. In the embodiment of the present invention, the plurality of power converter modules 10_1, 10_2, 10_3, ..., 10_n are sorted based on the value of the first parameter associated with each of the plurality of power converter modules 10_1, 10_2, 10_3, ..., 10_n for the first control cycle, the method may further include: for the second control cycle, the plurality of power converter modules 10_1, 10_2, 10_3, ..., 10_n are reordered based on the updated value of the first parameter.

[0103] For each subsequent control cycle, the following steps can be repeated: the updated value of the first parameter is associated with each of a plurality of power converter modules 10_1, 10_2, 10_3, ..., 10_n, and the end point for the corresponding subsequent control cycle determines the characteristics of the conduction state of each of a plurality of power converter modules 10_1, 10_2, 10_3, ..., 10_n. In the present invention, based on the value of the first parameter associated with each of a plurality of power converter modules 10_1, 10_2, 10_3, ..., 10_n, in the embodiment in which a plurality of power converter modules 10_1, 10_2, 10_3, ..., 10_n are sorted, the step of re-sorting a plurality of power converter modules 10_1, 10_2, 10_3, ..., 10_n can be repeated. Therefore, the value of the first parameter is variable because it can be re-evaluated for each subsequent control cycle. The re-evaluation may result in an updated value of the first parameter for a second control cycle that is different from the value of the first parameter for a previous control cycle, but the value of the first parameter for a control cycle may be the same as the value for a previous control cycle even after the re-evaluation.

[0104] In other embodiments of the present invention, the following steps can be performed for grouped control cycles: the updated value of the first parameter is associated with each of a plurality of power converter modules 10_1, 10_2, 10_3, ..., 10_n, the characteristics of the conduction state of each of the plurality of power converter modules 10_1, 10_2, 10_3, ..., 10_n are determined for the end point of the corresponding subsequent control cycle, and optionally, the plurality of power converter modules 10_1, 10_2, 10_3, ..., 10_n are reordered. Such grouped control cycles can form a control loop. For example, can perform the following steps once for three continuous control cycles and then repeat the following steps again for the next three continuous cycles: the updated value of the first parameter is associated with each of a plurality of power converter modules 10_1, 10_2, 10_3, ..., 10_n, determine the characteristic of the conduction state of each of a plurality of power converter modules 10_1, 10_2, 10_3, ..., 10_n for the end point of the corresponding subsequent control cycle, and optionally, reorder a plurality of power converter modules 10_1, 10_2, 10_3, ..., 10_n. In this example, three continuous control cycles can form a control loop. This can reduce computational load, but may affect the balance between different power converter modules. In other embodiments of the present invention, the following steps can be performed for each subsequent control cycle: determine the characteristics of the conduction state of each of the multiple power converter modules 10_1, 10_2, 10_3, ..., 10_n and / or the conduction time of each power converter module 10_i in each control cycle for the end point of the corresponding subsequent control cycle, but, for example, the following steps can be performed for every nth control cycle: the updated value of the first parameter is associated with each of the multiple power converter modules 10_1, 10_2, 10_3, ..., 10_n. The following steps can be performed for example for every nth control cycle (for example, once every 100 control cycles): the updated value of the first parameter is associated with each of the multiple power converter modules 10_1, 10_2, 10_3, ..., 10_n, which can save computing resources and can improve the speed of the control method.

[0105] The following will describe how to determine the value of the first parameter in an embodiment of the present invention.

[0106] Figure 6 A control block diagram for executing a method for controlling a multilevel converter according to an embodiment of the present invention is shown.

[0107] The control block diagram includes a control unit 500, a module control unit 501, a module selector unit 502, a voltage synthesizer unit 503, a first parameter unit 504 and a module evaluation unit 505. Different units can communicate with each other to exchange information. The communication can be unidirectional or bidirectional. In addition, Figure 6 A plurality of power converter modules 10_1 , 10_2 , 10_3 , 10_4 , 10_5 , 10_6 , . . . , 10_n of a multilevel converter 1 are shown.

[0108] The different units may simply be functions or logical units within one or more hardware units. Figure 6 In the embodiment of the present invention, the present invention is shown by dot-dash line 106, and different units form a unit set, which can be understood as representing the minimum number of units (functions or logic) for performing the steps of the method for performing an embodiment of the present invention. In other words, the set can be regarded as a set of units whose main purpose is to determine how to generate the required output voltage of the multi-level converter and select (or arrange) the power converter module for generating the output voltage of the multi-level converter. In any case, at least one processing unit can perform each or even all functions of the described unit.

[0109] At least one processing unit may be or include any suitable unit capable of performing computer processing. The processing unit may include any one of a microprocessing unit (MCU), a field programmable gate array (FPGA) or an application specific integrated circuit (ASIC), a complex programmable logic device (CPLD) or a combination thereof. The processing unit may include a storage unit, for example, a memory (not shown). Alternatively or additionally, in addition to the at least one processing unit, one or more memories may be provided. The one or more memories may store different information required for processing by the at least one processing unit.

[0110] The control unit 500 may be configured to generate information about the duty cycle of the desired output signal and send the generated information 507 to the module control unit 501. The control unit 500 may be configured to generate information 507 about the duty cycle based on the feedback information 506. The feedback 506 may include one or more feedback parameters obtained from one or more sensors distributed in the system (e.g., a battery system to which the multilevel converter 1 is applied). The one or more feedback parameters may include at least one of the voltage or current of the power converter module string, for example, the terminal current and / or terminal voltage of the power converter module. The terminal current is the current flowing into / out of the terminal of the last power converter module in the string. The terminal voltage is the voltage at the terminal of the last power converter module in the string. However, the feedback 506 may be optional. In some embodiments of the present invention, alternatively or additionally, the control unit 500 may use information about the switch configuration in the string to generate information about the duty cycle of the desired output signal, and send the generated information 507 to the module control unit 501. The switch configuration gives information about which power converter modules are exposed to current. For example, a power converter module that actively participates in the sharing of the workload is exposed to current. On the other hand, power converter modules placed in a parallel configuration are only exposed to a small portion of the current.

[0111] In addition to the feedback 506, the control unit 500 may selectively receive one or more other inputs (not shown), such as a desired voltage / current, active power / reactive power, etc. The control unit 500 may use the one or more other inputs to generate information about the duty cycle of the desired output signal.

[0112] The module control unit 501 can be configured to determine the number of required power converter modules for generating the required output voltage signal with the required duty cycle of the multilevel converter 1. The number of required power converter modules can correspond to the total number of the power converter modules of the multilevel converter 1, or can be a fraction of the total number of the power converter modules of the multilevel converter 1.

[0113] The module control unit 501 may be configured to generate information 508 about the number of required power converter modules and send the information to the module selector unit 502 .

[0114] The first parameter unit 504 can be configured to determine the first parameter of each power converter module, and associate the first parameter with each power converter module. This association can be performed by the mode of table or list, as described above in the embodiment of the present invention. The first parameter unit 504 can be configured to send information 509 to the module selector unit 502. Information 509 can be the first parameter determined for each power converter module, or the association of the first parameter with the corresponding power converter module, or indicate the first parameter or the associated information. The first parameter unit 504 can exchange information with the module evaluation unit 505 (receive and / or send information to the module evaluation unit 505 from the module evaluation unit 505). The module evaluation unit 505 can evaluate each power converter module based on one or more parameters specific to each power converter module. For example, the module evaluation unit 505 can evaluate the conduction time of each power converter module 10_1, 10_2, 10_3, ..., 10_n in one or more control cycles. The module evaluation unit 505 can also be configured to determine the characteristics of the conduction state of each power converter module. However, this function may also be performed by the module selector unit 502 .

[0115] The module selector unit 502 may be configured to select at least one power converter module to control the conduction state of the at least one power converter module within a second control period based on the information 509 received from the first parameter unit 504 and characteristics of the conduction state of the at least one power converter module.

[0116] The module selector unit 502 may be configured to generate information about the selected at least one power converter module and send the information 519 to the voltage synthesizer unit 503. The generated information may also be sent to the module evaluation unit 505 as information 511. The information 519 may be information representing or indicating the selected at least one power converter module in the upcoming control cycle, and may represent or indicate the arrangement of the selected at least one power converter module.

[0117] The voltage synthesizer unit 503 may be configured to generate a control signal 512 to be sent to at least one power converter module to control the conduction state of at least one power converter module selected by the module selector unit 502. For a power converter module that does not need to change the conduction state, the voltage synthesizer unit 503 may still be configured to generate a control signal 512 indicating that the corresponding power converter module does not need to change the conduction state.

[0118] The voltage synthesis unit 503 may be connected to the plurality of power converter modules 10_1 , 10_2 , 10_3 , 10_4 , 10_5 , 10_6 , . . . , 10 — n of the multilevel converter 1 via wires or a digital bus.

[0119] In this embodiment of the present invention, module evaluation unit 505 can be configured to evaluate these power converter modules based on the conduction time of power converter module in one or more previous control cycles or current control cycle.Module evaluation unit 505 can send information 510 indicating or representing the conduction time of power converter module to first parameter unit 504.First parameter unit 504 can be configured to determine the value of the first parameter of each of multiple power converter modules based on the conduction time of each in previous control cycle or current control cycle in multiple power converter modules.First parameter unit 504 can also arrange or sort power converter modules according to the ascending or descending order of the first parameter.For initial control cycle (for example, when multilevel converter 1 is turned on, when the operation cycle of multilevel converter 1 begins), in an embodiment of the present invention, the value of the first parameter can be preconfigured or determined based on the conduction time of each of multiple power converter modules in the previous operation cycle of multilevel converter 1.In another embodiment of the present invention, for initial state, all or some components of multilevel converter 1 can be checked and / or calibrated. This may involve determining parameters such as state of charge, state of health, temperature, voltage, steady state current, etc. Based on at least one of these parameters, a value of a first parameter may be determined.

[0120] Thus, module selector unit 502, first parameter unit 504, module evaluation unit 505 and voltage synthesizer unit 503 create a control mechanism (represented by dotted line 206) with control loop (also referred to as fast control loop), because necessary feedback (in this embodiment, is the on-time of each of a plurality of power converter modules in previous control cycle or current control cycle) is based on the information processed in the control loop to evaluate. In this embodiment of the present invention, due to considering the on-time when determining the first parameter, module evaluation unit 505 can balance between the on-times of different power converter modules, and can evaluate the power converter module when considering balance. For example, module evaluation unit 505 can phase shift the operation of each power converter module, to balance the on-time of different power converter modules. In this case, PWM can be regarded as phase-shift carrier PWM. PSC PWM enables effective output switching rate to increase.

[0121] This control method is also called an open-loop control method, because the output of the multilevel converter 1 does not affect the input of the control loop.

[0122] Figure 7 FIG. 1 is a control block diagram for executing a method for controlling a multilevel converter according to an embodiment of the present invention. Figure 6The same elements and the same information are used in the described embodiments.

[0123] In this embodiment of the present invention, Figure 6 The embodiment described differs in that the feedback 506 sent to the control unit 500 may also be sent to the module evaluation unit 505 as feedback 513. The feedback 506, 513 may include one or more feedback parameters obtained from one or more sensors distributed in the system applying the multilevel converter 1. The one or more feedback parameters may include at least one of the voltage or current of the power converter module string, for example, the terminal current and / or terminal voltage of the power converter module.

[0124] The module evaluation unit 505 can evaluate the power converter module based on the above-mentioned conduction time and / or based on at least one first feedback parameter, and the at least one first feedback parameter is determined based on one or more feedback parameters obtained from the power converter module string connected to the corresponding power converter module. The module evaluation unit 505 can send the information 510 indicating or representing the conduction time of the power converter module to the first parameter unit 504 and / or the first feedback parameter. The first parameter unit 504 can be configured to determine the value of the first parameter of each in a plurality of power converter modules based on the information 510 received from the module evaluation unit 505.

[0125] In this embodiment of the invention, the control loop of the control mechanism 207 can still be regarded as a fast feedback loop. Since the output of the multilevel converter 1 affects the input in the control loop, the feedback loop is also called a closed loop method.

[0126] Figure 8 A control block diagram for executing a method for controlling a multilevel converter 1 according to an embodiment of the present invention is shown. In this embodiment of the present invention, the same reference numerals denote Figure 7 and Figure 6 The same elements and the same information are used in the described embodiments.

[0127] In this embodiment of the present invention, the control block diagram includes a module load control unit 514 and an optimization routine unit 515. In addition, the module evaluation unit 505 can perform the function of observing the module utilization, and therefore in this embodiment of the present invention, it will be referred to as the utilization observation unit 505. In this embodiment of the present invention, the module load control unit 514 and the optimization routine unit 515 can be regarded as a unit or a different set (indicated by a dotted line 107) that is at least functionally or logically constructed different from the set indicated by the dotted line 106 described above.

[0128] In this embodiment of the present invention, the value of the first parameter of each of the plurality of power converter modules 10_1, 10_2, 10_3, 10_4, 10_5, 10_6, ..., 10_n can be determined based on at least one second feedback parameter. The at least one second feedback parameter can be determined based on one or more feedback parameters obtained from one or more of the plurality of energy sources 11. The one or more feedback parameters obtained from one or more of the plurality of energy sources 11 can include at least one of the state of charge, temperature, voltage, current and health state of one or more of the plurality of energy sources. More specifically, the module load control unit 514 can receive one or more feedback parameters obtained from one or more of the plurality of energy sources 11 as feedback information 517. The module load control unit 514 can generate information 516 based on the one or more feedback parameters received from one or more of the plurality of energy sources 11 and send the information 516 to the optimization routine unit 515. The generated information 516 can be or can represent one or more feedback parameters obtained from one or more of the plurality of energy sources 11. The optimization routine unit 515 can process the received information 515 and generate at least one second feedback parameter.

[0129] The generation of the at least one second feedback parameter may be considered a slow feedback process because the at least one second parameter is generated based on feedback information based on a parameter that changes at a slower rate than a period of the control process.

[0130] Optimization routine unit 515 can send at least one second feedback parameter generated as information 518 to utilization observer unit 505, and this utilization observer unit 505 can generate at least one first feedback parameter as above.Utility observer unit 505 can send at least one second feedback parameter and / or at least one first feedback parameter as information 510 to first parameter unit 504.Therefore, first parameter unit 504 can determine the value of the first parameter of each in a plurality of power converter modules based on at least one first feedback parameter and / or at least one second feedback parameter.This control mechanism 208 can be regarded as representing the closed-loop method with fast feedback and slow feedback.Slow feedback can be regarded as the correction to fast feedback.

[0131] Fig. 9 FIG. 1 is a control block diagram for executing a method for controlling a multilevel converter according to an embodiment of the present invention. Figure 6 , 7 The same units and the same information as those in the embodiment described in 8. Figure 8The difference of the embodiment shown is that, in this embodiment of the present invention, the value of the first parameter is determined based on at least one second feedback parameter independently of the on-time of each of the multiple power converter modules in the previous control cycle or the current conduction cycle and / or at least one first feedback parameter to determine the value of the first parameter. In other words, in this embodiment of the present invention, in the control mechanism 209, the first parameter unit 504 interacts with the optimization routine unit 515 independently of the utilization rate observer unit 505. Therefore, the slow loop interacts with the first parameter unit 504 independently of the fast loop. The control mechanism 209 can be regarded as a closed-loop method.

[0132] In one or more embodiments of the present invention, a third feedback parameter based on a combination of one or more first feedback parameters and / or one or more second feedback parameters and / or on-time may be acquired, and the value of the first parameter may be determined based on the third feedback parameter.

[0133] In one embodiment of the present invention, a multilevel converter 1 is provided, which includes multiple energy sources 11 and multiple power converter modules 10_1, 10_2, 10_3, ..., 10_n, each power converter module includes at least two switching elements, and the multilevel converter 1 includes a device suitable for executing the steps of the method of one or more of the above embodiments.

[0134] In addition, in one embodiment of the present invention, a computer program including instructions is provided, and when the program is executed by a computer, the computer performs the steps of the method of one or more embodiments described above. Such instructions can be stored in one or more memories.

[0135] Therefore, according to the present invention, a modulation technique for a multilevel converter is provided, which is not to utilize the arrangement of the power converter module in each control cycle, but to utilize the arrangement of the power converter module for the event in each control cycle. When arranging for the event in each control cycle, the present invention prioritizes the power converter module to be used, and distinguishes between the power converter modules based on the on-state of the power converter module in the previous control cycle. This realizes the balance of the on-time between different power converter modules, and reduces the switching number of the on-state of each power converter module, thereby reducing switching losses.

[0136] The present invention allows phase shift operation, thereby effectively increasing the effective output switching rate and introducing balancing capabilities, which cannot be achieved simultaneously by prior art modulation techniques. In addition, the proposed modulation technique does not introduce additional distortion in the power converter module switching rate and its harmonics.

[0137] Although detailed embodiments have been described, these embodiments are only intended to provide a better understanding of the invention as defined by the independent claims and therefore should not be considered limiting.

Claims

1. A method for controlling a multilevel converter, the multilevel converter comprising a plurality of energy sources and a plurality of power converter modules, each power converter module comprising at least two switching elements, the method comprising: - for a first control cycle from a plurality of consecutive control cycles, associating a value of a first parameter with each of the plurality of power converter modules, the value of the first parameter being a variable value; - determining a characteristic of a conduction state of each of the plurality of power converter modules for an end point of the first control period, the characteristic of the conduction state being one of a first predetermined characteristic and a second predetermined characteristic; - obtaining required output signals of the plurality of power converter modules for a second control cycle from the plurality of consecutive control cycles, the second control cycle being subsequent to the first control cycle; -For each change in the amplitude of the desired output signal between the first amplitude level and the second amplitude level within the second control cycle, the conduction state of the at least one power converter module among the multiple power converter modules is controlled within the second control cycle based on the value of the first parameter associated with at least one power converter module among the multiple power converter modules for the first control cycle and the characteristics of the conduction state of the at least one power converter module determined for the end point of the first control cycle.

2. The method according to claim 1, wherein: Controlling the conduction state of at least one power converter module among the multiple power converter modules includes any one of the following: switching the conduction state of the at least one power converter module, placing the at least one power converter module in a parallel configuration state, placing the at least one power converter module in a bypass state, and reversing the output voltage of the at least one power converter module.

3. The method according to any one of claims 1 and 2, wherein: The first parameter indicates a priority of a corresponding power converter module for selecting a power converter module to control a conduction state of the corresponding power converter module in the second control period.

4. The method according to claim 3, wherein: Controlling the conduction state of at least one power converter module among the multiple power converter modules during the second control cycle includes: selecting at least one power converter module among the multiple power converter modules based on the priority of the at least one power converter module and the characteristics of the conduction state of the at least one power converter module determined for the end point of the first control cycle.

5. The method according to any one of claims 1 to 4, wherein: The first predetermined characteristic of the conduction state indicates an active conduction state, and the second predetermined characteristic of the conduction state indicates an inactive conduction state, wherein the inactive conduction state is any one of a non-conducting state, a parallel configuration state, and a bypass state.

6. The method according to any one of claims 1 to 5, wherein: The first amplitude level is lower than the second amplitude level, wherein, for each change in the amplitude of the desired output signal from the first amplitude level to the second amplitude level, the method comprises: - controlling the conduction state of one or more power converter modules of the plurality of power converter modules whose characteristic of the conduction state is the second predetermined characteristic.

7. The method according to claim 6, wherein: The control includes: -Select one or more power converter modules in the power converter modules whose conduction state characteristic is the second predetermined characteristic in the order from the value of the first parameter indicating the highest priority to the value of the first parameter indicating the lowest priority, so as to control the conduction state of the selected one or more power converter modules.

8. The method according to any one of claims 1 to 7, wherein: The first amplitude level is lower than the second amplitude level, wherein, for each change in the amplitude of the desired output signal from the second amplitude level to the first amplitude level, the method comprises: - controlling the conduction state of one or more power converter modules whose characteristic of said conduction state in the power converter modules is said first predetermined characteristic.

9. The method according to claim 8, wherein: Controlling the conduction state of the one or more power converter modules whose characteristic of the conduction state in the power converter module is the first predetermined characteristic includes: reversing the output voltage of the one or more power converter modules whose characteristic of the conduction state in the power converter module is the first predetermined characteristic.

10. The method according to any one of claims 8 and 9, wherein: The control includes: -Selecting one or more power converter modules whose characteristic of the conduction state is the first predetermined characteristic in order from the value of the first parameter indicating the lowest priority to the value of the first parameter indicating the highest priority, so as to control the conduction state of the selected one or more power converter modules.

11. The method according to any one of claims 1 to 10, further comprising: - for the second control period, associating an updated value of the first parameter with each of the plurality of power converter modules; as well as - determining a characteristic of the conduction state of each of the plurality of power converter modules for an end point of the second control period.

12. The method according to claim 11, further comprising: -For each subsequent control cycle, repeat the following steps: associating the updated value of the first parameter with each of the multiple power converter modules, and determining the characteristics of the conduction state of each of the multiple power converter modules for the end point of the corresponding subsequent control cycle.

13. The method according to any one of claims 1 to 12, wherein: A value of a first parameter of each of the plurality of power converter modules is determined based on an on-time of each of the plurality of power converter modules in a previous control cycle or a current control cycle.

14. The method according to any one of claims 1 to 13, wherein: The value of a first parameter of each of the multiple power converter modules is also determined based on at least one first feedback parameter, and the at least one first feedback parameter is determined based on one or more feedback parameters obtained from a power converter module string to which the corresponding power converter module is connected, wherein, preferably, the one or more feedback parameters obtained from the power converter module string include at least one of the voltage or current of the power converter module string.

15. The method according to any one of claims 1 to 14, wherein: Determine a value of a first parameter of each of the plurality of power converter modules based on at least one second feedback parameter, wherein the at least one second feedback parameter is determined based on one or more feedback parameters obtained from one or more of the plurality of energy sources, wherein, preferably, the one or more feedback parameters obtained from the one or more of the plurality of energy sources include at least one of a charging state, a temperature, a voltage, a current and a health state of the one or more of the plurality of energy sources.

16. The method according to any one of claims 14 and 15, further comprising: A third feedback parameter is obtained based on a combination of the one or more first feedback parameters and / or the one or more second feedback parameters and / or the on-time, and a value of the first parameter is determined based on the third feedback parameter.

17. A multilevel converter comprising a plurality of energy sources and a plurality of power converter modules, each power converter module comprising at least two switching elements, the multilevel converter comprising means adapted to perform the steps of the method according to claim 1.

18. A computer program comprising instructions which, when executed on a computer, cause the computer to perform the steps of the method according to claim 1.

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