Data transmission protocol, data transmission method and system for efficient communication in modular power electronics applications

Abstract

The invention relates to a data transmission protocol, a system and a method for efficient communication in multi-level converter systems. As shown in figure 1, the protocol comprises a command transmission phase (12), a diagnosis transmission phase (18) and a confirmation phase (20). A master sends control data to subscribers, which report back status information and send confirmation signals. The system implements this protocol in a multi-level converter, wherein energy storage modules act as subscribers. The master sends switching commands for voltage regulation, while the modules report their state. This enables dynamic load distribution and reconfiguration in the event of failures. The combination of protocol and application in multi-level converters addresses challenges of modern power electronics and represents an advance over the prior art, in particular with regard to the efficiency, reliability and adaptability of the system.

Description

DATA TRANSFER PROTOCOL, DATA TRANSFER METHOD AND SYSTEM FOR EFFICIENT COMMUNICATION IN MODULAR POWER ELECTRONICS APPLICATIONS FIELD OF THE INVENTION

[0001] The present invention relates to a data transmission protocol and systems and methods based thereon for efficient and reliable communication between a master and several participants in a network, in particular for use in modular power electronics applications, especially in multilevel converter systems, where precise control and monitoring of several components is required. BACKGROUND OF THE INVENTION

[0002] Data transmission protocols play a central role in modern communication systems, especially in applications that require precise control and monitoring of multiple components. In many industrial and technical fields, such as power electronics, efficient and reliable communication between a central control unit and multiple subordinate units is of great importance.

[0003] Conventional communication protocols, such as the widely used Controller Area Network (CAN), offer robust solutions for connecting control units and sensors. These protocols often use an acknowledgment method, where each receiver confirms the correct receipt of a message. While this method works well in many applications, it can lead to limitations in efficiency and scalability in systems with a large number of participants.

[0004] In complex systems, such as multilevel converters, where a large number of energy storage modules must be precisely controlled, conventional protocols often reach their limits. Real-time capability, synchronization, and fault tolerance pose particular challenges. Furthermore, the transmission of large amounts of data required for detailed monitoring and control can lead to delays and increased resource consumption.

[0005] Various approaches are known in the field of data transmission protocols for modular power electronics applications, particularly for multilevel converter systems. For example, US 2002 / 0002647 A1 discloses a data transmission protocol with a response field in which devices can return data. This protocol provides a basic structure for communication between a master and multiple nodes. However, it lacks an explicit division into separate phases for commands, diagnostics, and acknowledgment. Furthermore, the focus is not on determining the number of active nodes, which can be crucial in complex, modular systems.

[0006] US 2013 / 0139018 A1 describes a communication system with cyclic message transmission and an ACK (acknowledgment) field. This system offers improved reliability through the use of acknowledgment signals. However, it lacks a dedicated diagnostic transmission phase, which is important for efficient fault diagnosis and system optimization in modern power electronics applications. Furthermore, the acknowledgment phase is not primarily used to determine the number of active participants, which could provide valuable information for dynamic system adaptation.

[0007] US 5293571 A discloses a method for acknowledgment in multiplex transmission systems. This method places particular emphasis on the synchronization of the participants, which is of great importance for precisely controlled systems such as multilevel converters. However, it also lacks a clear division into separate phases for commands, diagnostics, and confirmation. Furthermore, the possibility of using the confirmation phase to determine the number of active participants is not explicitly addressed.

[0008] While existing solutions address individual aspects of communication in complex, modular systems, they do not offer a holistic solution that meets all the requirements of modern power electronics applications, especially multilevel converter systems. In particular, they lack an integrated approach that combines efficient command transmission, a dedicated diagnostic phase, and an innovative use of the confirmation phase for system monitoring. SUMMARY OF THE INVENTION

[0009] In view of the above considerations, the object of the invention is to provide a data transmission protocol, a system based thereon, and a control system that enables efficient and reliable communication in modular power electronics applications, particularly in multilevel converter systems. The protocol should ensure precise control and monitoring of multiple components, improve efficiency and scalability with a large number of participants, and simultaneously meet the requirements for real-time capability, synchronization, and fault tolerance.Preferred embodiments of the invention are intended, among other things, individually or cumulatively: to provide a clear structuring of the communication into separate phases for commands, diagnosis and confirmation, to implement an efficient method for determining the number of active participants, to integrate a dedicated diagnostic transmission phase for improved error diagnosis and system optimization, to use the confirmation phase innovatively for system monitoring and dynamic system adaptation, and to optimize the transmission of large amounts of data in order to minimize delays and resource consumption.

[0010] Ultimately, the invention aims to create a holistic approach that combines the advantages of known solutions while overcoming their limitations in order to meet the specific requirements of modern, complex power electronics applications.

[0011] The problem is solved by a data transmission protocol, a data transmission system, a method for transmitting data, and a data transmission system in a multilevel converter system having the features of the independent claims. Advantageous embodiments and further developments are the subject of the dependent claims.

[0012] According to the invention, the data transmission protocol for communication between a master and several participants in a network has the following features: a) A command transmission phase in which the master sends control data to the participants; b) A diagnostic transmission phase in which the participants report status information back to the master; c) An acknowledgment phase in which each active participant sends an individual acknowledgment signal to the master.

[0013] The protocol is configured to record the number of received acknowledgement signals during the acknowledgement phase and use this information to determine the number of active participants. This has the advantage of allowing the system to monitor the number of functional participants in real time and dynamically adapt to changes, increasing the reliability and efficiency of the overall system.

[0014] In a preferred embodiment, the data transmission protocol has a dominant-recessive bit pattern, where dominant bits can override recessive bits. This enables efficient arbitration and error detection in the communication system.

[0015] In a further embodiment, the data transmission protocol uses elements of a CAN protocol, in particular a bit arbitration method in which certain signal states can override others. This allows the proven robustness and reliability of the CAN protocol to be utilized while simultaneously making specific adaptations for the requirements of power electronics applications.

[0016] The data transmission protocol can also provide mechanisms for temporal synchronization of the participants. This enables precise coordination of the participants, which is particularly important in multilevel converter systems.

[0017] A data transmission system implementing this data transmission protocol comprises a communication bus, a master, at least two nodes connected to the master via the communication bus, and a device for exchanging data packets between the master and the nodes according to the data transmission protocol. This system architecture enables a flexible and scalable implementation of the protocol in various application scenarios.

[0018] The system can be configured to process and transmit data packets, each comprising a start bit, several data bits, and at least one stop bit. The data packets preferably contain timing information for synchronizing the participants. This improves synchronization and enables precise timing of the communication.

[0019] During the acknowledgment phase, the system can be configured to process and transmit a single acknowledgment bit per participant. This reduces communication overhead and increases protocol efficiency.

[0020] To enable efficient use of transmission bandwidth, the system can transmit multiple data packets at different times. This optimizes data transmission and reduces latency.

[0021] The system can be specifically configured to control energy storage modules in a multilevel converter system, with the energy storage modules acting as participants. This enables precise and efficient control of complex power electronics systems.

[0022] A method for transferring data in this system includes transferring control data in a command transfer phase from the master to the Participants, transferring diagnostic data from the participants to the master in a diagnostic transfer phase, performing an acknowledgment phase, where the number of processed acknowledgment signals corresponds to the number of active participants, and determining the number of active participants based on the received acknowledgment signals. This structured procedure enables efficient communication and system monitoring.

[0023] A central aspect of the invention, as set forth in claim 11, is the application of the novel data transmission protocol in a multilevel converter system. This combination directly addresses the complex requirements of modern power electronics applications. The system comprises a communication bus, a master, several energy storage modules as participants, and a device for exchanging data packets. This structure enables efficient and precise control of the energy storage modules, representing a significant advance over the known prior art. The system advantageously combines a novel data transmission protocol with a specific data transmission system and applies this combination to multilevel converter systems. This combination enables particularly efficient and reliable communication in complex power electronics applications.

[0024] The data transmission protocol, with its three phases—command transmission, diagnostic transmission, and confirmation—enables precise control and monitoring of the individual energy storage modules. The confirmation phase, used to determine the number of active devices, allows the system to dynamically adapt to changing conditions.

[0025] The application of this protocol in a data transmission system specifically configured for multilevel converter systems enables optimized control of the energy storage modules. This leads to improved efficiency and reliability of the overall system.

[0026] In particular, the ability of the master, based on the Diagnostic transmission phase received data the load distribution between the Optimizing active energy storage modules and reconfiguring them in the event of a module failure represents a significant advance over the current state of the art.

[0027] This combination of features enables an adaptive and robust control of multilevel converter systems that was previously unknown in this form and addresses the specific challenges of these complex systems.

[0028] In this system, the master can be configured to send switching commands to the energy storage modules during the command transmission phase to generate a desired output voltage of the multilevel converter system. This enables precise voltage regulation and improves the efficiency of the overall system.

[0029] The energy storage modules can be configured to transmit information about their state of charge, temperature, and / or voltage to the master during the diagnostic transmission phase. This enables comprehensive monitoring and optimized control of the system.

[0030] Based on the data received during the diagnostic transmission phase, the master can optimize load distribution between the active energy storage modules. This improves the service life and efficiency of the individual modules and the overall system.

[0031] Finally, the master can be configured to reconfigure the multilevel converter system upon detection of an energy storage module failure during the confirmation phase to compensate for the failure. This significantly increases the system's resilience and reliability.

[0032] The data transmission protocol can be called FAAD (Fast-Acknowledge-And-Data) protocol.

[0033] The data can consist of dominant and recessive bits. While a dominant 0 cannot be overwritten, a recessive 1 can. This principle is also known as arbitration. Arbitration regulates allocation to a bus system.

[0034] For example, a cycle of the data transmission protocol can last 50 ps. The cycle is divided into three different phases (also called sections): a command transmission phase (command stage), a diagnostic transmission phase (diagnostic stage), and an acknowledgment phase.

[0035] During the command transmission phase, a master, for example, can send its control data to the nodes. The control data can contain all the information a node needs, for example, to switch the correct cells on or off. The cells can be cells of a multilevel converter system, for example.

[0036] The multilevel converter system can be used, for example, in an electric vehicle. Accordingly, the invention also relates to an electric vehicle comprising the multilevel converter system according to the invention.

[0037] With regard to a possible application of the invention in multilevel converter systems, reference is additionally made to DE 10 2022 110 424 A1, the disclosure content of which is hereby incorporated by reference in its entirety in the countries whose national law permits it.

[0038] If a node fails to successfully receive the control data, it cannot participate in switching the correct cells. In this case, the node enters a fail-safe mode. Either the failed node would disrupt the entire system, which is undesirable, or the system would have to operate with one less node. In this case, the affected node does not participate in the confirmation phase, and the master can detect the failure of a node.

[0039] In a preferred embodiment, the following is provided in detail:

[0040] The data transfer protocol has a command transfer phase.

[0041] The data is transmitted from the master to the nodes. For example, the data can be sent from the master via a bus. In certain embodiments, the nodes themselves do not communicate with each other and / or are not directly connected.

[0042] During the command transmission phase, the master can, for example, send switching commands to the nodes. The length of the command transmission phase can depend on the number of nodes connected and the data reduction technology used. Since this phase can be safety-relevant, it is preferably designed so that errors can be detected and / or corrected. This can be achieved, for example, by using checksums, redundancies, or other error correction techniques. Furthermore, the phase can be designed to allow for retransmission if transmission errors occur.

[0043] Each command cycle can end with a known synchronization sequence. For example, a TDMA (Time Division Multiple Access) scheme can be used. Here, commands can be sent at full speed and / or without the need for arbitration. Each node can, for example, initiate a synchronization algorithm with the received command data.

[0044] The data transfer protocol includes a diagnostic transfer phase. This phase involves transferring data from the node to the master.

[0045] The diagnostic transmission phase begins with the data transmission between the nodes and the master. This phase serves as a feedback line from the nodes to the master, as all nodes need time to process the commands received during the command transmission phase. This time can be used to transmit their diagnostic data.

[0046] For example, an update rate of 100 Hz per node can be implemented. For example, with a control frequency of 20 kHz, 200 nodes can be processed. In an implementation with 72 nodes, each node would have two cycles to send its data, resulting in an update frequency of 139 Hz. The amount of data that can be sent depends on the command transmission phase and the confirmation phase, as these have a greater impact than the diagnostic transmission phase.

[0047] The data transmission protocol has an acknowledgement phase. The acknowledgement phase operates depending on the number of participants. During this phase, data is transferred from the participant to the master.

[0048] A feature of the FAAD protocol is the confirmation phase. This phase can be used, for example, to confirm the BUS system.

[0049] While previous CAN protocols use the acknowledgment phase to confirm received data regardless of the number of receivers and correct decoding, the FAAD protocol aims for acknowledgment from, say, up to 72 participants within the 50 ps cycle. The bit rate can be, for example, 8 Mbps. Each acknowledgment ensures correct reception and decoding of the data for each participant.

[0050] The data transmission protocol allows for confirmation from up to 72 nodes per cycle. This can be beneficial for error detection and additional communication between nodes. After each cycle (50 ps), the master can detect which node has failed and subsequently activate the fail-safe mechanism.

[0051] Because the confirmation phase depends on the number of participants, the amount of data can be reduced.

[0052] Further developments of the invention can also be found in the dependent claims, the description and the accompanying drawings.

[0053] According to one embodiment, the data transmission protocol is designed as a CAN protocol.

[0054] The term "CAN protocol" should be understood broadly here—as a kind of umbrella term. For example, it also includes CAN-FD (flexible data rate).

[0055] For example, a CAN FD transceiver with 8 Mbit / s can be used to achieve a high data bandwidth.

[0056] Since the data transmission protocol has little in common with a traditional CAN FD protocol and therefore does not need to be compatible with other CAN transceivers, the arbitration bit rate of 1 Mbit / s can be neglected. Furthermore, a specific control loop of 50 ps has the advantage of allowing a TDMA scheme to be used for data exchange. With a given TDMA scheme, arbitration is not required, as each participant has a specific time frame in which to exchange data. This allows for efficient bandwidth use.

[0057] According to another embodiment, the participants operate synchronously. The participants can be time-synchronized, e.g., in the nanosecond range. For example, a time signal can be included in the data packet.

[0058] The invention also relates to a system for data transmission using a data transmission protocol according to the invention.

[0059] The system has at least or exactly one, preferably time-based, bus, at least or exactly one master and at least two participants that are connected to the master via the bus.

[0060] Fermer the system has at least one data packet that can be exchanged between the master and the participants.

[0061] The participants can be connected to the master via a bus, for example. Preferably, however, the participants themselves do not communicate with each other and / or are not connected to each other.

[0062] According to one embodiment, the data packet is embodied as a UART (Universal Asynchronous Receiver and Transmitter) packet. A UART is an electronic circuit for digital serial interfaces.

[0063] For example, two data lines can be provided for communication, namely one for sending (TX - Transmit) and one for receiving (RX - Receive).

[0064] A clock is preferably not used for timing. Instead, so-called start bits (LOW) and stop bits (HIGH) are used. As soon as a device receives the start bit, it reads the data until it receives the stop bit.

[0065] For example, a UART packet consists of a start bit, eight information bits, an optional parity bit to detect transmission errors and at least or exactly one stop bit.

[0066] Depending on the application, other configurations are also conceivable, e.g. a start bit, five to a maximum of nine information bits, an optional parity bit and one or two stop bits.

[0067] According to a further embodiment, the data packet comprises a time signal.

[0068] Each node can store a timestamp of the control data. The timestamps can be used to synchronize the nodes. There are various options for synchronization. For example, to initiate synchronization, the master can terminate the command packets with a sync packet. After receiving the corresponding sync packet, all nodes enter sync mode and wait for the master's sync pulse. After a certain time, the master sends the sync pulse, which preferably consists of one bit, to all nodes.

[0069] The confirmation sequence follows immediately after the synchronization pulse to keep the synchronization point precise. In this synchronization, all participants synchronize each cycle, typically with an accuracy of +-10 ns.

[0070] To avoid additional processing time, no additional code is preferably required.

[0071] Another way to synchronize is based on a method that uses DMA (Direct Memory Access) controllers.

[0072] DMA controllers are independent hardware controllers that operate separately from the main MCU (Microcontroller Unit). Unlike the MCU, DMA controllers are capable of processing data transfer requests in parallel without direct intervention from the MCU, meaning the MCU doesn't have to wait for each data transfer to complete.

[0073] The DMA controller can handle data transfer to offload the MCU. Each received UART packet triggers the DMA to write it to memory.

[0074] This trigger can be extended by modifying the DMA multiplexer register so that the current timestamp is written to a previously defined buffer. This timestamp process ensures that each UART packet is uniquely identified and can be precisely synchronized with other data. This allows all participants to synchronize to within + / - 20 ns, for example. To ensure correct synchronization, it can be checked at a later time. If synchronization fails or is triggered by an incorrect UART packet, an attempt is made to resynchronize or to enter fail-safe mode.

[0075] According to another embodiment, only one information bit is transmitted per participant during the confirmation phase. Additionally, a start bit and at least one stop bit can be transmitted. The minimum that can be sent is a UART packet, consisting of, for example, one start bit, one stop bit, and eight information bits.

[0076] In this case, only one information bit is transmitted per participant, indicating their confirmation. It would be a waste of bandwidth to transmit one bit and seven unused bits.

[0077] According to a further embodiment, several data packets are superimposed on one another.

[0078] Multiple UART packets can be overlaid so that the receiver receives only one message instead of several.

[0079] All embodiments and components of the devices described here are preferably designed to be operated, e.g., by means of a control device, according to the method described here. Furthermore, all embodiments of the devices described here, as well as all embodiments of the method described here, can be combined with one another, preferably independently of the specific embodiment in whose context they are mentioned.

[0080] Further details, features and advantages of the invention will become apparent from the following purely exemplary and non-limiting description of embodiments and the four drawings. SHORT DESCRIPTION OF THE DRAWING

[0081] Fig. 1 is a schematic representation of an embodiment of a data transmission protocol according to the invention.

[0082] Fig. 2 is a schematic representation of an embodiment of a section of a system according to the invention.

[0083] Fig. 3 is a schematic representation of an embodiment of a data overlay according to the invention.

[0084] Fig. 4 is a schematic representation of an embodiment of a system according to the invention. DESCRIPTION OF EMBODIMENTS

[0085] First, it should be noted that the embodiments presented are purely exemplary in nature. Individual features may be implemented not only in the combination shown, but also independently or in other technically feasible combinations. For example, the features of one embodiment may be combined with features of another embodiment. The number of participants may vary.

[0086] If a figure contains a reference symbol that is not explained in the immediately corresponding description, reference is made to the corresponding preceding or following explanations in the figure description. Thus, the same reference symbols are used for identical or comparable components in the figures and these are not explained again.

[0087] Fig. 1 shows a cycle of a data transmission protocol 10, which may last, for example, 50 ps.

[0088] In a command transmission phase 12, data is transmitted from a master 14 to a participant 16.

[0089] In a subsequent diagnostic transmission phase 18, data is transmitted from a participant 16 to a master 14.

[0090] Finally, in a subsequent confirmation phase 20, data is transferred from all participants 16 to a master 14.

[0091] Fig. 2 shows a system for data transmission using a data transmission protocol 10.

[0092] The master 14 is connected to the participant 16 via a bus 22.

[0093] Compensation of propagation delay is important for synchronization.

[0094] Therefore, it may be advantageous if the delay from the transmitter to the bus 22 is known so that each participant can compensate for its delay in order to achieve precise synchronization.

[0095] For example, there are four units: Participant Receive AR, Participant Transmit BT, Master Transmit AT, and Master Receive BR. These units represent the time delay in each part of the receiver.

[0096] To successfully compensate for the delay, each participant 16 needs to know their BT and AR, or their compensation factor. Unfortunately, BT and AR cannot be measured individually, but it is possible to compensate for the delay without knowing them.

[0097] As shown, the external paths are measurable for the node 16 or the master 14. A round trip with an internal or ideal delay of 0 ns takes approximately 240 ns. However, this is not feasible. Therefore, a predefined delay T 1 can be introduced between AR and BT.

[0098] The ping packet is sent and received with AT+AR+T1+BT+BR. If the master 14 queries each participant 16 using the same approach, it can determine which participants 16 can be compensated by which factor.

[0099] Since there is only one master 14 in the system, the propagation delay of AT and BR is irrelevant. Therefore, the master 14 calculates a compensation factor for each participant 16 and sends it to each participant 16.

[0100] The compensation factor is an individually set artificial delay that ensures compensation for the CAN transceiver used.

[0101] Runtime compensation can be performed during each startup phase to verify and / or ensure changing runtime due to an aging and / or changing environment.

[0102] Self-compensation can be implemented by measuring BT+AR during transmission and adjusting the compensation factor. Thus, each participant 16 can compensate and / or adjust its own factor.

[0103] Fig. 3 shows eight data packets S1 to S8 of the participants 16. Each data packet S1 to S8 contains only one information bit B1 to B8.

[0104] A start bit SA and a stop bit SO of the master 14 can overlap with the information bits B1 to B8.

[0105] The receiver (master) (shown on the far right) can then receive the following signal, for example: 0|0000|0000|1 .

[0106] The confirmation phase 20 therefore works depending on the number of participants 16.

[0107] The data transmission protocol according to the invention reduces the amount of data when transmitting the data.

[0108] Fig. 4 shows an example of a data transmission system. Several data packets S1 to S9 are exchanged between the participants 16 and the master 14.

[0109] This is illustrated by the three phases of an electric motor. However, this cannot be a multi-phase system.

[0110] Viewed from a different perspective, the invention can also be described, for example, in the following aspects:

[0111] 1. A data transmission protocol (10) with a dominant-recessive bit behavior, preferably with a dominant first signal edge, comprising: - a command transmission phase (12), - a diagnostic transmission phase (18), and - a confirmation phase (20), wherein the confirmation phase (20) operates depending on the number of participants (16).

[0112] 2. The data transmission protocol (10) according to the previous aspect can be designed as a CAN protocol.

[0113] 3. The data transmission protocol (10) according to one of the previous aspects, wherein the participants (16) operate synchronously.

[0114] 4. A system for transmitting data using a data transmission protocol (10) according to any one of the preceding aspects, the system comprising: - a bus (22), - a Master's degree (14), - at least two participants (16) connected to the master (14) via the bus (22), and - at least one data packet (S1 -S8) exchangeable between the master (14) and the participants (16).

[0115] 5. The system according to the previous aspect, wherein the data packet (S1 -S8) is designed as a UART packet.

[0116] 6. The system according to any one of the preceding aspects, wherein the data packet (S1-S8) comprises a time signal.

[0117] 7. The system according to one of the preceding aspects, wherein in the confirmation phase (20) only one information bit (B1-B8) is transmitted per participant (16).

[0118] 8. The system according to any one of the preceding aspects, wherein several data packets (S1 -S8) are superimposed on each other.

[0119] 9. The system according to any one of the preceding aspects, wherein the participants (16) are energy storage modules of a multilevel converter system.

[0120] 10. A method for transmitting data with a system according to any one of the preceding aspects, wherein the confirmation phase (20) operates depending on the number of participants (16).

[0121] The above ten aspects can be implemented individually or in combination to further improve the efficiency and flexibility of the data transmission protocol and the system based on it.

[0122] It is noted that "vorzugsweise" "bevorzugt" can be translated into English as "preferably." A feature introduced by "vorzugsweise" "bevorzugt" is purely optional, can be omitted, and does not constitute a limitation, for example, of the claims.

[0123] Within the scope of the invention defined by the claims, numerous modifications and further developments are possible, for example, relating to the implementation of the data transmission protocol, synchronization methods, or the configuration of the participants. The protocol can thus be used in various application areas, such as industrial control systems, automotive electronics, or smart home applications. The number of participants can vary depending on the application, and the system can be adapted to operate efficiently with a larger or smaller number of participants.

[0124] Alternatively or additionally, various error correction and data integrity techniques can be implemented to increase transmission reliability. This may include the use of advanced coding methods or adaptive transmission rates. Synchronization methods can be enhanced to function precisely even in environments with strong electromagnetic interference. Furthermore, the system can be enhanced with functions for dynamically adapting the network topology, allowing it to respond flexibly to changes in the configuration of the participants. The integration of security mechanisms, such as encryption or authentication, can also be considered to protect data transmission against unauthorized access. LIST OF REFERENCE SYMBOLS 10 Data transfer protocol 12 Command transmission phase 14 Master 16 participants 18 Diagnosis transmission phase 20 Confirmation phase 22 buses AR Participant Reception BT Participant Send AT Master Send BR Master Receive S1 to S9 data package B1 to B8 information bit SA start bit SO stop bit

Claims

CLAIMS 1 . A data transmission protocol for communication between a master and multiple participants in a network, comprising: a) a command transmission phase in which the master sends control data to the participants; b) a diagnostic transmission phase in which the participants report status information back to the master; c) an acknowledgment phase in which each active participant sends an individual acknowledgment signal to the master; wherein the protocol is configured to record the number of acknowledgment signals received in the acknowledgment phase and use this information to determine the number of active participants.

2. Data transmission protocol according to claim 1, characterized in that it has a dominant-recessive bit behavior in which dominant bits can overwrite recessive bits.

3. Data transmission protocol according to claim 1 or 2, characterized in that it uses elements of a CAN protocol, in particular a method for bit arbitration in which certain signal states can overwrite others.

4. Data transmission protocol according to one of claims 1 to 3, characterized in that it provides mechanisms for the temporal synchronization of the participants.

5. A data transmission system implementing a data transmission protocol according to any one of the preceding claims, comprising: a communication bus, a master, at least two participants connected to the master via the communication bus, and a device for exchanging data packets between the master and the participants according to the data transmission protocol.

6. System according to claim 5, characterized in that it is configured to process and transmit data packets each comprising a start bit, several data bits and at least one stop bit, wherein the data packets preferably contain time information for synchronizing the subscribers.

7. System according to one of claims 5 or 6, characterized in that it is configured to process and transmit a single confirmation bit per participant in the confirmation phase.

8. System according to one of claims 5 to 7, characterized in that it is configured to transmit several data packets in a staggered manner in order to enable efficient use of the transmission bandwidth.

9. System according to one of claims 5 to 8, characterized in that it is configured to control energy storage modules in a multilevel converter system, wherein the energy storage modules act as participants.

10. A method for transmitting data in a system according to one of claims 5 to 9, comprising: a) transmitting control data in a command transmission phase from the master to the participants, b) transmitting diagnostic data in a diagnostic transmission phase from the participants to the master, c) performing an acknowledgment phase, wherein the number of processed acknowledgment signals corresponds to the number of active participants, and d) determining the number of active participants based on the received acknowledgment signals. 11 . System for data transmission in a multilevel converter system, comprising: a communication bus, a master, several energy storage modules as participants, which are connected to the master via the communication bus, a device for exchanging data packets between the master and the energy storage modules according to a data transmission protocol according to one of claims 1 to 4.

12. System according to claim 11, characterized in that the master is configured to send switching commands to the energy storage modules in the command transmission phase in order to generate a desired output voltage of the multilevel converter system.

13. System according to claim 11 or 12, characterized in that the energy storage modules are configured to transmit information about their state of charge, their temperature and / or their voltage to the master in the diagnostic transmission phase.

14. System according to one of claims 11 to 13, characterized in that the master is configured to optimize a load distribution between the active energy storage modules based on the data received in the diagnostic transmission phase.

15. System according to one of claims 11 to 14, characterized in that the master is configured to perform a reconfiguration of the multilevel converter system upon detection of a failure of an energy storage module in the confirmation phase in order to compensate for the failure.

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