High bandwidth modulation

Abstract

A control system for controlling a multi-level converter, the multi-level converter comprising a plurality of switching modules, each switching module connected to an energy source, the control system comprising: a central control unit; and one or more module control units wherein the central control unit is configured to transmit a command for controlling the plurality of switch modules to the one or more module control units before a pulse width modulation (PWM) cycle starts, each of the one or more module control units is configured to receive a command from the central control unit prior to the start of the PWM cycle and to apply the command to one or more of the plurality of switching modules during the PWM cycle.

Description

[0001] Cross-reference

[0002] This application claims priority to European Patent Application No. 23215794.1, filed on December 12, 2023, the entire disclosure of which is incorporated herein by reference. Technical Field

[0003] The present invention generally relates to a control system and a control method for controlling a multilevel converter. Background Art

[0004] A multilevel converter is a power conversion system that can generate a multi-step (multilevel) voltage waveform from several direct current (DC) input voltages. Multilevel converters have a wide range of applications in many technical fields, especially in the field of power conversion (e.g., power conversion in motor vehicles). A multilevel converter for alternating current (AC) applications is also referred to as an AC battery. When controlling a multilevel converter through a distributed control system of the multilevel converter, high-bandwidth modulation can be used to control the output of the multilevel converter, i.e., the output of the AC battery.

[0005] However, due to the physical size of the multilevel converter, it may be difficult to control the entire distributed control system through a single control unit. This is especially true for the control of the switching modules that interconnect the individual capacitor / battery modules of the multilevel converter in the distributed control system. Therefore, it may be necessary to control the switching of the switching modules through controllers that can be placed close to the switching modules.

[0006] At the same time, centralized calculation of the required module switching is needed in order to be able to consider many parameters. For example, the required state of a switching module at a specific point in time depends on the states of other modules for calculation and cannot be calculated separately by the corresponding controller of the switching module itself.

[0007] However, implementing such a configuration using conventional techniques may require a faster communication bus speed, or when using a standard bus speed, delay processing within the multilevel converter. Summary of the Invention

[0008] An object of the present invention is to provide an efficient control system for controlling a multilevel converter.

[0009] The present invention is defined by the subject matter of the independent claims. Preferred embodiments are given by the subject matter of the dependent claims. Other examples are provided to facilitate the understanding of the present invention.

[0010] According to an embodiment of the present invention, a control system for controlling a multilevel converter is provided. The multilevel converter includes a plurality of switching modules, and each switching module is connected to an energy source. The control system includes: a central control unit; and one or more module control units. Wherein, the central control unit is configured to transmit commands for controlling the plurality of switching modules to the one or more module control units before the start of a pulse width modulation (PWM) cycle. Wherein, each of the one or more module control units is configured to receive commands from the central control unit before the start of the PWM cycle and apply the commands to one or more of the plurality of switching modules within the PWM cycle.

[0011] According to another embodiment of the present invention, a control method for a control system of a multilevel converter is provided. The multilevel converter includes a plurality of switching modules, and each switching module is connected to an energy source. The control system includes a central control unit and one or more module control units. The control method includes: transmitting, by the central control unit, commands for controlling the plurality of switching modules to the one or more module control units before the start of a pulse width modulation (PWM) cycle; receiving, by each of the one or more module control units, commands from the central control unit before the start of the PWM cycle; and applying, by each of the one or more module control units, the commands to one or more of the plurality of switching modules within the PWM cycle.

[0012] According to the present invention, the required communication bus speed can be reduced. In other words, for a standard bus speed, a higher duty cycle resolution can be achieved. Therefore, the present invention can provide more time for message processing and more time for possible error handling in case a message is not correctly received. Description of the Drawings

[0013] Embodiments of the present invention will now be described with reference to the drawings, which are presented for a better understanding of the inventive concept but should not be regarded as limiting the present invention. In the drawings:

[0014] Figure 1 Schematically shows a control system with a distributed control unit according to an embodiment of the present invention;

[0015] Figure 2 Shows a schematic flowchart of a control method according to an embodiment of the present invention;

[0016] Figure 3 Shows the message transmission time and message processing time of a module control unit according to an example configuration;

[0017] Figure 4 Shows the message transmission time and message processing time of a module control unit according to an embodiment of the present invention; and

[0018] Figure 5 Shows an example of a voltage level change according to an embodiment of the present invention. Detailed implementation

[0019] In the following disclosure, the expression "AC battery" and the expression "multilevel converter" may be used interchangeably.

[0020] Figure 1 Schematically shows a control system with a distributed control unit according to an embodiment of the present invention.

[0021] Figure 1 The control system is the control system 10 for controlling a multilevel converter. The multilevel converter includes a plurality of switch modules, and each switch module is connected to an energy source. The energy source can be understood as a battery module or a capacitor module.

[0022] As Figure 1 shown, the control system 10 includes a central control unit 1 and one or more module control units 2. One or more module control units 2-1, 2-2,... 2-N (N is the number of one or more module control units) can be collectively referred to as one or more module control units 2. The central control unit 1 is configured to transmit commands for controlling a plurality of switch modules 3 to one or more module control units 2 before the start of a pulse width modulation (PWM) cycle. A plurality of switch modules 3-1, 3-2,... 3-M (M is the number of a plurality of switch modules) can be collectively referred to as a plurality of switch modules 3. Each of the one or more module control units 2 is configured to receive commands from the central control unit 1 before the start of the PWM cycle and apply the commands to one or more of the plurality of switch modules 3 during the PWM cycle.

[0023] The central control unit 1 may be responsible for calculating the required states of the one or more module control units 2. The type of communication between the central control unit 1 and the one or more module control units 2 may be digital communication, which means that the messages to be communicated between the central control unit 1 and the one or more module control units 2 are written in bits. For example, the commands are written in bits.

[0024] The central control unit 1 is configured to transmit commands before the start of the PWM cycle, and preferably exactly before the start of the PWM cycle. In other words, the central control unit 1 may be configured to transmit commands for the (target) PWM cycle in the previous PWM cycle directly before the target PWM cycle. By transmitting commands to the one or more module control units 2 before the start of the PWM cycle, the one or more module control units 2 can receive the commands early enough in advance to apply the received commands at the start of the PWM cycle.

[0025] As Figure 1 shown, each of one or more module control units 2 is connected to one or more of the plurality of switch modules 3. For example, one module control unit may be connected to one switch module or multiple switch modules. The module control unit and the one or more switch modules corresponding to the module control unit may communicate through a logic signal input to the gate(s) of the one or more switch modules.

[0026] Each of one or more module control units 2 is configured to receive a command before the start of a PWM cycle and apply the command during the PWM cycle. In other words, each of one or more module control units 2 may not need to both receive and apply a command within one PWM cycle. Each of one or more module control units 2 may apply a command received in the previous PWM cycle during the PWM cycle.

[0027] The command transmitted from the central control unit 1 before the start of the PWM cycle and received by one or more module control units 2 may be processed by the one or more module control units 2 until the start of the PWM cycle.

[0028] More specifically, the command may be received and decoded by one or more module control units 2, and corresponding actions may be taken by the one or more module control units 2.

[0029] The length of the PWM cycle may be predetermined based on the switching frequency. The switching frequency may be a system parameter. The range of the switching frequency may be between 5 and 80 kHz. The switching parameters may be given by the output filter design. For example, in automotive applications, the switching frequency may be given by the motor specifications.

[0030] For example, the PWM cycle may be set such that the change in the voltage set point between two consecutive PWM cycles remains within a voltage level defined by an energy source. However, the present invention is not limited thereto, and the change in the voltage set point may also be multiple levels within one PWM cycle.

[0031] As Figure 1 shown, each switch module is connected to an energy source. The switch module is connected to the energy source via a DC link. It can be understood that the control system 10 for controlling the multilevel converter is connected to multiple energy sources. By controlling each of the multiple energy sources, in a more specific example, by controlling each of the multiple battery modules, a multilevel voltage output of the multilevel converter can be generated.

[0032] Figure 2FIG. shows a schematic flow chart of a control method according to an embodiment of the present invention. The control method can be understood corresponding to the control system 10.

[0033] In other words, the control system 10 controls a multilevel converter including a plurality of switch modules, wherein each switch module is connected to an energy source, and the control system 10 includes a central control unit 1 and one or more module control units. The control method for controlling the control system 10 includes: step (S1), the central control unit 1 transmits commands for controlling the plurality of switch modules 3 to one or more module control units 2 before the start of a pulse width modulation (PWM) cycle; step (S2), each of the one or more module control units 2 receives commands from the central control unit 1 before the start of the PWM cycle; and step (S3), each of the one or more module control units 2 applies the commands to one or more of the plurality of switch modules 3 during the PWM cycle.

[0034] Figure 3 and Figure 4 FIG. shows the message transmission time and message processing time of the module control unit in two different configurations.

[0035] Figure 3 FIG. shows the message transmission time and message processing time of the module control unit according to an example configuration. In a conventional implementation, once the central control unit 1 calculates the required state of the module control unit, the required state is communicated to the module control unit, and the module control unit applies the required state as soon as possible. Therefore, once the module state changes, that is, the state of the module to be applied, it takes at least the time amount required for message transmission to switch the corresponding module control unit to another state. This is shown in Figure 3 FIG. The box marked with stripes represents tTrans, that is, the message transmission time, and the box marked black represents tProcess, that is, the message processing time. The message contains data of the state change at only one time point (i.e., the current time).

[0036] As Figure 3 can be seen in FIG., in order to change the state based on message 1, it may take time to calculate the state, transmit "message 1" to the module control unit, and process "message 1" in the module control unit. When the next state change is to be dealt with, even if the state calculation of "message 2" is carried out while transmitting and processing "message 1", it still takes at least the message transmission time and message processing time of "message 2" to change the state based on "message 2".

[0037] In other words, if a rapid state change is desired, there is a limitation in that the change may not be able to be performed faster than the time difference of at least tTrans + tProcess between two state changes. This can be a severe limitation because it may mean that a high-speed communication bus is required and / or the duty cycle resolution should be lower.

[0038] Figure 4 The message transmission time and message processing time of a module control unit according to an embodiment of the present invention are shown. In the embodiment, a command including the required states of all state changes of an entire PWM cycle, which includes the timing of each state change, can be sent instead of sending a command including only the required state at one time point. Further, the command is sent in advance, preferably, in the previous PWM cycle immediately before the PWM cycle. Information about the timing can be in many forms and is not limited to a specific type. Preferably, the information about the timing can be derived from the duty cycle of the PWM cycle.

[0039] Figure 4 Three PWM cycles are shown, namely, PWM cycle k, PWM cycle k + 1, and PWM cycle k + 2. In PWM cycle k, the state is calculated by the central control unit 1, represented by the white box of PWM cycle k. Then, within PWM cycle k, the calculated state is transmitted to the module control unit, represented by the striped box of PWM cycle k. When the module control unit receives the state, the state is still processed by the module control unit within PWM cycle k, represented by the black box of PWM cycle k. The state is the state that will become / be applied in the next PWM cycle (i.e., PWM cycle k + 1). Since the state has been processed before the start of PWM cycle k + 1, the state can be applied at the required timing within PWM cycle k + 1 without any delay due to transmission and / or processing.

[0040] Information about the timing can be included in the command. Therefore, since the command has been transmitted and processed by the module control unit, the required state change included in the command can be applied at the corresponding timing included in the command.

[0041] Applying a state change does not necessarily mean a state change of the module control unit. If the desired state and the current state of the module control unit are the same, the module control unit may not change its state by applying the state change. If the desired state and the current state of the module control unit are different, the module control unit can change its state by applying the state change.

[0042] In addition, the state of the module control unit may refer to changing the internal state of one or more corresponding switch modules. Thus, it can be understood that the state(s) of the corresponding one or more switch modules is / are controlled / switched according to the state of the module control unit. In other words, the state of the corresponding one or more switch modules may follow the state of the module control unit.

[0043] In one embodiment, within a PWM period, only one of the one or more module control units 2 may be configured to control the corresponding one or more switch modules to change the output voltage of the multilevel converter at a time.

[0044] In this embodiment, the length of the PWM period is set such that the change in the voltage setpoint between two consecutive PWM periods remains within one voltage level defined by an energy source. The voltage setpoint is the desired average voltage level of the output voltage of the multilevel converter within a PWM period.

[0045] Therefore, the control system 10 according to this embodiment is optimized to change one voltage level by switching only one module control unit. In other words, an optimized and efficient control system can be achieved by changing one voltage level by switching only one module control unit.

[0046] Figure 5 An example of voltage level change according to an embodiment of the present invention is shown. On the left PWM period, the voltage level when the voltage setpoint is slightly less than "voltage level 2" is shown. On the middle PWM period, the voltage level when the voltage setpoint is slightly greater than "voltage level 2" is shown. In the middle PWM period, three voltage changes in one PWM period can be observed. The first voltage change is at the start of the PWM period, i.e., when "voltage level 1" changes to "voltage level 2", the second voltage change is when "voltage level 2" changes to "voltage level 3", and the third voltage change is when "voltage level 3" changes to "voltage level 2". The unit of the voltage level can be determined by the energy source. From now on, "voltage level X" may be abbreviated as "X".

[0047] In an embodiment, the central control unit 1 may be configured to determine a command such that the voltage setpoint in each PWM period corresponds to the desired average voltage level of the output voltage of the multilevel converter.

[0048] For example, in Figure 5Among them, the expected average voltage level of the middle PWM period can be "2.1". In this case, by setting the voltage level at the start of the middle PWM period to "2" and having a voltage level of "3" between the second voltage change and the third voltage change, and the time length between the second voltage change and the third voltage change can be 10% of the PWM period, then the expected average voltage level "2.1" can be achieved by calculating "2" * 90% + "3" * 10%.

[0049] Therefore, commands can be determined such that the voltage setpoints after all voltage changes within the PWM period will result in the expected average voltage level of the PWM period.

[0050] In one embodiment, module identifiers can be assigned to each of one or more module control units 2. The module identifiers can be included in the command. When each of one or more module control units 2 receives the command, each of one or more module control units 2 can obtain the part corresponding to each of one or more module control units 2 in the command. With this configuration having module identifiers, the central control unit 1 can generate only one command for all one or more module control units because one or more module control units 2 can obtain the corresponding parts of the command through the module identifiers.

[0051] The command can include configuration information of the PWM period to be applied by one or more module control units 2 that receive the command.

[0052] The command can include the module identifier of each of one or more module control units 2. In other words, one or more module control units 2 can obtain their respective module information from the configuration information of the command.

[0053] The command can be adapted to the type of PWM. For example, the PWM can be center - aligned PWM, left - aligned PWM, or right - aligned PWM. In center - aligned PWM, the change of the output voltage of the multilevel converter is center - aligned within the PWM period. In left - aligned PWM, the change of the output voltage of the multilevel converter is left - aligned within the PWM period. In right - aligned PWM, the change of the output voltage of the multilevel converter is right - aligned within the PWM period.

[0054] For left - aligned PWM or right - aligned PWM, the configuration information can include at least one of the following: information for determining the existence and type of state changes of each of one or more module control units 2 within the PWM period, and information for determining the timing of the state changes.

[0055] For center-aligned PWM, the configuration information may include at least one of the following: information for determining the presence and type of a first state change and a second state change for each of one or more module control units 2 within a PWM period, and information for determining the timing of the first state change and the second state change.

[0056] For example, in center-aligned PWM, the command may include a first vector of the states of one or more module control units 2 at the start of the PWM period, a second vector of the states of one or more module control units 2 applied when a first voltage level changes, a third vector of the states of one or more module control units 2 applied when a second voltage level changes, and a duty cycle.

[0057] In center-aligned PWM, the first voltage level change and the second voltage level change are symmetric about the center of the PWM period within the PWM period.

[0058] If the value of the duty cycle is 0, the second vector and the third vector are not used. This means that there will be no output voltage level change within the PWM period except at the start of the PWM period (where there may be one or more voltage level changes).

[0059] Each of one or more module control units 2 may obtain corresponding information based on its module identification. For example, a module control unit with a module identification of "1" may obtain the "1" element from each of the first vector, the second vector, and the third vector.

[0060] Generally, when the voltage setpoint is set to a rational number while the voltage levels definable by an energy source are integers, PWM can be used to obtain a smooth output. For example, when an energy source defines a voltage level, by connecting multiple energy sources, voltage levels such as "1", "2", "3", "4", etc. can be achieved. In this case, when the voltage setpoint is set to "1.5", it may not be possible to achieve the voltage setpoint of "1.5" by connecting only one or two energy sources. In this case, PWM can be used. To achieve the voltage setpoint of "1.5", PWM can be performed at a 50% duty cycle between "voltage level 1" and "voltage level 2". Then, the average output voltage can be calculated as 1.5 (according to 1*50% + 2*50%), thus achieving the desired voltage setpoint.

[0061] Since the desired voltage setpoint can be achieved by the average voltage within the PWM period, the change in the output voltage can be aligned at different positions. In the above example, in the case of a left-aligned change, the voltage output may be "2" at the start of the PWM period and drop to "1" after 50% of the PWM period has elapsed. In the case of a right-aligned change, the voltage output may be "1" at the start of the PWM period and change to "2" after 50% of the PWM period has elapsed. In the case of a center-aligned change, the voltage output may be "1" at the start of the PWM period, "2" between 25% and 75% of the PWM period, and drop back to "1" after 75% of the PWM period has elapsed.

[0062] Since the state of the module control unit can control the state(s) of the corresponding one or more switch modules, the state(s) of the corresponding one or more switch modules can be referred to as the switch state(s) to distinguish them from the state of the module control unit. The state of the module control unit and the switch state may or may not be in the same format.

[0063] In other words, each of the one or more module control units 2 is configured to control the one or more switch states of the corresponding one or more switch modules according to the state of each of the one or more module control units 2 in the configuration information.

[0064] In this sense, the first vector may include switch states corresponding respectively to the states of the one or more module control units 2 at the start of the PWM period. Similarly, the second vector may include switch states corresponding respectively to the states of the one or more module control units 2 applied when the first voltage level changes, and the third vector may include switch states corresponding respectively to the states of the one or more module control units 2 applied when the second voltage level changes.

[0065] The switch state of the switch module can be one of series plus, series minus, bypass plus, bypass minus, passive, and parallel. "Plus" and "minus" can indicate the polarity relative to a reference point. For example, in a three-phase system, the reference point can be specified as the neutral point of the three-phase system. In a single-phase system, the reference point can be specified as any terminal of the single-phase system.

[0066] In a series plus connection, the negative side of the battery module of the AC battery is connected to the reference point, or to the positive side of a battery module that is also connected in series plus and is closer to the reference point. In a series plus connection, the battery module can generate an output voltage that is positive relative to the reference point.

[0067] In a series negative connection, the positive side of a battery module of an AC battery is connected to a reference point, or to the negative side of a battery module that is also connected in series negative and is closer to the reference point. In a series negative connection, the battery module can generate an output voltage that is negative with respect to the reference point.

[0068] One or more module control units 2 may be configured to change the output voltage of the multilevel converter by switching corresponding ones of the one or more switch modules based on the respective switch states.

[0069] In an embodiment, the central control unit 1 and the one or more module control units 2 may be connected in a bus topology. In another embodiment, the central control unit 1 and the one or more module control units 2 may be connected in a star topology. However, the present invention is not limited to any type of topology, but rather any type of topology that facilitates efficient communication and synchronization between, for example, the central control unit 1 and the one or more module control units 2 may be employed.

[0070] Each of the one or more module control units 2 may be synchronized with the central control unit 1 and thus with each other. Although the one or more module control units 2 may initially have been synchronized with the central control unit 1, it is still important to continuously synchronize the central control unit 1 with each of the one or more module control units 2 because the clocks of the individual module control units may drift over time.

[0071] Synchronization can be achieved in a variety of ways. For example, a dedicated global lock signal may be used. Although this may provide more accurate synchronization, additional lines may be required. Therefore, message reception events that do not require additional lines may be used for synchronization. Alternatively, in the case where the bus used in the control system 10 provides a clock signal, the bus clock signal may be used for synchronization. These non-exhaustive ways of synchronization are given only as examples, and the present invention is not limited to any synchronization method.

[0072] In one embodiment, one or more module control units 2 may be configured to perform a cyclic redundancy check on commands received from the control unit. The cyclic redundancy check can detect errors in digital communication. In this way, the control system 10 is able to achieve more secure communication between the central control unit 1 and the one or more module control units 2.

[0073] Although detailed embodiments have been described, these embodiments are provided only to provide a better understanding of the present invention as defined by the independent claims and should not be considered as limiting the present invention.

Claims

1. A control system for controlling a multi-level converter, the multi-level converter comprising a plurality of switch modules, each switch module being connected to an energy source, the control system comprising: Central control unit; as well as one or more module control units; The central control unit is configured to transmit a command for controlling the plurality of switch modules to the one or more module control units before a pulse width modulation (PWM) cycle starts. wherein each of the one or more module control units is configured to receive the command from the central control unit before the start of the PWM cycle and apply the command to one or more switch modules among the plurality of switch modules during the PWM cycle, Wherein, within the PWM period, only one module control unit among the one or more module control units is configured to control the corresponding one or more switch modules to change the output voltage of the multi-level converter at a time, wherein the length of the PWM cycle is set so that the change in the voltage set point between two consecutive PWM cycles remains within a voltage level defined by an energy source, and The voltage set point is a desired average voltage level of the output voltage of the multi-level converter within one PWM cycle.

2. The control system according to claim 1, wherein: The central control unit is configured to determine the commands such that a voltage set point in each PWM period corresponds to a desired average voltage level of an output voltage of the multilevel converter.

3. The control system according to claim 1, wherein: A module identification is assigned to each of the one or more module control units.

4. The control system according to claim 1, wherein: The command includes configuration information of a PWM cycle to be applied by the one or more module control units receiving the command, and Wherein, within the PWM period, the change of the output voltage of the multi-level converter is center-aligned in center-aligned PWM, left-aligned in left-aligned PWM, or right-aligned in right-aligned PWM.

5. The control system according to claim 4, wherein: For the left-aligned PWM or the right-aligned PWM, the configuration information includes at least one of: information for determining the existence and type of a state change of each of the one or more module control units within the PWM period, and information for determining a timing of the state change; as well as For the center-aligned PWM, the configuration information includes at least one of: information for determining the existence and type of a first state change and a second state change of each of the one or more module control units within the PWM period, and information for determining the timing of the first state change and the second state change.

6. The control system according to claim 4, wherein: The one or more module control units are configured to obtain corresponding information from the configuration information of the command, and wherein each of the one or more module control units is configured to control one or more switch states of the corresponding one or more switch modules according to the state of each of the one or more module control units in the configuration information; The switch state is one of series positive, series negative, bypass positive, bypass negative, passive and parallel.

7. The control system according to claim 6, wherein: The one or more module control units are configured to change an output voltage of the multi-level converter by switching the corresponding one or more switch modules based on corresponding switch states.

8. The control system of claim 1, wherein: The communication between the central control unit and the one or more module control units is digital communication; as well as The communication between each of the one or more module control units and the corresponding one or more switch modules is a logic signal.

9. The control system according to claim 1, wherein: Commands transmitted from the central control unit before the start of the PWM cycle and received by the one or more module control units are processed until the start of the PWM cycle.

10. The control system according to claim 1, wherein: each of the one or more module control units is synchronized with the central control unit and thereby synchronized with each other, and The one or more module control units are configured to perform a cyclic redundancy check on commands received from the central control unit.

11. A control method for controlling a control system of a multi-level converter, the multi-level converter comprising a plurality of switch modules, each switch module being connected to an energy source, the control system comprising a central control unit and one or more module control units, the control method comprising: The central control unit transmits a command for controlling the plurality of switch modules to the one or more module control units before a pulse width modulation (PWM) cycle starts; each of the one or more module control units receives the command from the central control unit before the PWM cycle starts, and each of the one or more module control units applies the command to one or more switch modules among the plurality of switch modules during the PWM cycle, Wherein, in the PWM cycle, only one of the one or more module control units is controlled each time, and the output voltage of the multi-level converter is changed through the corresponding one or more switch modules, wherein the length of the PWM cycle is set so that the change in the voltage set point between two consecutive PWM cycles remains within a voltage level defined by an energy source, and The voltage set point is a desired average voltage level of the output voltage of the multi-level converter within one PWM cycle.

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