Field bus communication method and device for high-voltage direct-current transmission control and protection system

Abstract

The invention belongs to the technical field of bus communication, and particularly relates to a field bus communication method and device for a high-voltage direct-current transmission control and protection system. The method comprises the steps that an Ethernet communication framework is established between a control system and IO equipment, and a field bus communication protocol frame format adopted by the Ethernet communication framework is obtained by improving application data of a goosePdu in an IEC61850GOOSE frame format, the improved application data comprises control words used for distinguishing uplink messages, downlink messages and transmitted data types; wherein the application data of the uplink message further comprises an input channel state quantity and any one of an event message and an analog quantity, and the application data of the downlink message further comprises time information, so that the communication rate of the field bus is improved, the cross-regional networking cost is relatively low, communication is performed between the control layer and the field IO layer based on an IEC61850 protocol, and the communication efficiency is improved. And the internationalized development requirements are met.

Description

Technical Field

[0001] The present invention belongs to the technical field of bus communication, and in particular relates to a field bus communication method and device for a high-voltage direct current transmission control and protection system. Background Art

[0002] Fieldbus is an important communication method in the control and protection system of high-voltage direct current transmission, which is directly related to the control efficiency and operation reliability of the control and protection system. The overall control and protection system of high-voltage direct current transmission consists of a three-layer architecture of operator control layer, control and protection layer and field IO layer; among them, the control and protection layer includes control systems such as pole control system, valve control system, DC station control system, AC station control system, and station power control system; the field IO layer includes IO devices such as measurement and control devices and valve interface units. Each control system and the IO device group connected to it jointly construct a high-voltage direct current transmission control and protection system. Each control system of the control and protection layer communicates in real time with the IO device connected to the field IO layer through the fieldbus to complete the core control functions of high-voltage direct current transmission, such as no-load pressurization, tap control, active power control, online valve group switching and reactive power control. Therefore, the communication reliability and real-time performance of the fieldbus between the control system and the IO device will directly affect the control performance and reliability indicators of the high-voltage direct current transmission control and protection system.

[0003] At present, the main fieldbus used in the HVDC transmission control and protection system is PROFIBUS DP bus or CAN bus. However, both Profibus DP bus and CAN bus belong to the technology of the last century. Compared with the current DC control and protection system requirements, the technical system has obvious deficiencies, which are mainly reflected in: (1) The communication rate is obviously insufficient. The maximum rate of PROFIBUS DP bus is 12Mbps, and the maximum rate of CAN bus is 1Mbps. The communication rate is low and cannot meet the application scenarios that require high-speed interconnection and communication in HVDC control and protection, such as AC filter fast switching. (2) Profibus DP bus requires a dedicated chip or protocol stack for communication. At present, it is mainly monopolized by some manufacturers. Cross-regional networking needs to be completed by dedicated equipment, and the engineering application cost is high; CAN bus has no application layer protocol support, requires user customization, and cannot support cross-regional networking. Due to the backward technology, the reliability of the two communication technologies in engineering applications is not high. (3) It does not meet the international standardization requirements of the power system. The international standard of the power system clearly requires the use of IEC61850 protocol at the station control layer and process layer. PROFIBUS DP bus and CAN bus are manufacturer protocols, which do not meet the requirements of international standardization development. Summary of the invention

[0004] The purpose of the present invention is to provide a field bus communication method and device for a high-voltage direct current transmission control and protection system, so as to solve the problems of low field bus communication rate, low cross-regional networking reliability and non-compliance with international standardization development requirements in the existing high-voltage direct current transmission control and protection system.

[0005] In order to solve the above technical problems, the present invention provides a field bus communication method for a high-voltage direct current transmission control and protection system, wherein an Ethernet communication architecture is established between a control system and an IO device, wherein a field bus communication protocol frame format adopted by the Ethernet communication architecture is obtained by improving the application data of goosePdu in the IEC61850 GOOSE frame format, wherein the improved application data includes a control word for distinguishing an uplink message, a downlink message and a data type of transmission; wherein the application data of the uplink message also includes an input channel state quantity, and any one of an event message and an analog quantity, and the application data of the downlink message also includes time information.

[0006] Furthermore, the control word of the uplink message includes a first control word and a second control word; the first control word of the uplink message includes an event group number, and the second control word includes a message type identifier for indicating the message type, and the message type includes an input event message, a system event message, an AC line analog message, and a DC analog message.

[0007] Furthermore, the first control word and the second control word of the uplink message occupy two bytes, and the control word is followed by the input channel status quantity; the input channel status quantity of the input event message and the system event message is followed by the event message; the input channel status quantity of the AC line analog message is followed by the analog quantity of the AC line; the input channel status quantity of the DC analog message is followed by the DC analog quantities of each channel; each input channel status quantity occupies one bit.

[0008] Furthermore, each event message includes an event identification ID and time information. The event identification ID is a two-byte form, and the highest bit indicates the event status; the time information is in a six-byte form.

[0009] Furthermore, the analog quantity of the AC line includes the effective value of three-phase voltage, the effective value of three-phase current, active power, reactive power, frequency and power factor parameter values. Each parameter value in the analog quantity of the AC line occupies two bytes; each DC analog quantity occupies two bytes.

[0010] Furthermore, the control words of the downlink message include a first control word, including the event group confirmation number of the control system and the primary or backup identifier of the control system corresponding to the current communication; when the IO device sends a new group of events, the event group number is transmitted, and after the control system receives the group of events, it writes the received event group number as a response into the corresponding bit field of the first control word as the event group confirmation number to indicate that the group of events has been received.

[0011] Furthermore, the downlink message also includes N relay outputs, each relay output occupies one bit, and the value range of N is 1-64.

[0012] Furthermore, the downlink message also includes a check code, and the check code is set at the last two bytes.

[0013] Furthermore, the control word of the downlink message also includes a second control word, which occupies one byte and is used to send a global scan command to the IO device.

[0014] The beneficial effects of the above technical solution are as follows: the present invention is a pioneering invention. The present invention performs bus communication based on Ethernet technology and does not rely on software and hardware of a specific manufacturer's protocol. The frame format of the field bus communication protocol adopted is obtained by improving the application data of goosePdu in the IEC61850 GOOSE frame format. For the master-slave architecture and data type of the high-voltage direct current transmission control and protection system, a control word is set to distinguish the uplink message, downlink message and the data type of the transmission. The control word is used to distinguish the data transmission direction and data type during direct current transmission, thereby realizing the application of IEC61850 GOOSE service in the direct current transmission control and protection system. This method improves the communication rate of the field bus, does not need to use monopolized hardware and protocols for communication, has a low cost for cross-regional networking, and the control layer and the field IO layer communicate based on the IEC61850 protocol, which meets the requirements of international development.

[0015] In order to solve the above technical problems, the present invention also provides a field bus communication device for a high-voltage direct current transmission control and protection system, which is respectively arranged at a control and protection layer and a field IO layer, and includes a processor and an Ethernet module, and the Ethernet module provides an Ethernet interface for accessing the equipment at the layer; the processor stores software, and the software includes an application layer protocol stack, and a field bus communication protocol is arranged in the application layer protocol stack to perform data transmission according to the field bus communication method of the high-voltage direct current transmission control and protection system as described above.

[0016] The beneficial effects of the above technical solution are as follows: the present invention is a pioneering invention. The present invention performs bus communication based on Ethernet technology and does not rely on software and hardware of a specific manufacturer's protocol. The frame format of the field bus communication protocol adopted is obtained by improving the application data of goosePdu in the IEC61850 GOOSE frame format. For the master-slave architecture and data type of the high-voltage direct current transmission control and protection system, a control word is set to distinguish the uplink message, downlink message and the data type of the transmission. The control word is used to distinguish the data transmission direction and data type during direct current transmission, thereby realizing the application of IEC61850 GOOSE service in the direct current transmission control and protection system. This method improves the communication rate of the field bus, does not need to use monopolized hardware and protocols for communication, has a low cost for cross-regional networking, and the control layer and the field IO layer communicate based on the IEC61850 protocol, which meets the requirements of international development. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic diagram of the IEC61850 communication and data model used in the AC control and protection system in the prior art;

[0018] Figure 2 It is a diagram of the architecture of a field bus communication device of a high voltage direct current transmission control and protection system of a device embodiment of the present invention;

[0019] Figure 3 is a real-time field bus networking schematic diagram of an embodiment of the device of the present invention;

[0020] Figure 4 is a software architecture diagram of an embodiment of the device of the present invention;

[0021] Figure 5 Schematic diagram of a first control word of a downlink message of an embodiment of the device of the present invention;

[0022] Figure 6 is a schematic diagram of a second control word of a downlink message of an embodiment of the device of the present invention;

[0023] Figure 7 It is a downlink message application data structure diagram of an embodiment of the device of the present invention;

[0024] Figure 8 It is a diagram of an uplink message application data structure of an embodiment of the device of the present invention;

[0025] Fig. 9 is a schematic diagram of a first control word of an uplink message of an embodiment of the device of the present invention;

[0026] Fig.10 It is a schematic diagram of the second control word of the uplink message of the device embodiment of the present invention. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical solutions and advantages of the present invention more clear, the specific implementation methods of the present invention are further described below in conjunction with the accompanying drawings.

[0028] The present invention performs bus communication based on Ethernet technology, does not rely on software and hardware of specific manufacturer protocols, and the frame format of the field bus communication protocol adopted is obtained by improving the application data of goosePdu in the IEC61850 GOOSE frame format. For the master-slave architecture and data type of the high-voltage direct current transmission control and protection system, a control word is set to distinguish the uplink message, the downlink message and the data type of the transmission, and the control word is used to distinguish the data transmission direction and data type during direct current transmission, thereby realizing the application of IEC61850 GOOSE service in the direct current transmission control and protection system. The method improves the communication rate of the field bus, does not need to use monopolized hardware and protocols for communication, has a low cost for cross-regional networking, and the control layer and the field IO layer communicate based on the IEC61850 protocol, which meets the requirements of international development.

[0029] Device Embodiment

[0030] IEC61850 is a universal communication protocol mainly used for data exchange and control in power systems. This protocol defines a standardized communication and data model to support data exchange and interoperability between devices and systems. Figure 1 As shown, the service implementation of the IEC61850 standard is mainly divided into three parts: MMS service, GOOSE service and SMV service. Among them, the MMS service is mainly used for data interaction between the device and the background; the GOOSE service is used for communication between devices; and the SMV service focuses on the transmission of sampled values. It usually transmits data based on Ethernet technology, and the transmission medium can be an electrical medium or an optical fiber medium, and the rate can usually support 10M-1Gbps. However, the IEC61850 communication technology is mainly used in AC protection, which requires model support, and its GOOSE service is the same-level communication between devices, while the high-voltage direct current transmission control and protection system is a master-slave communication architecture. A control system is connected to multiple slave IO devices, which cannot be directly applied, and is not conducive to application in the direct current transmission control and protection system. Therefore, in order to improve the rate of field bus communication of the high-voltage direct current transmission control and protection system, meet the requirements of international standards, and improve the versatility of bus cross-regional networking, the present invention is modified based on the standard IEC61850 GOOSE technology, and a field bus communication device of a high-voltage direct current transmission control and protection system that performs field bus communication through Ethernet is designed.

[0031] like Figure 2As shown, the field bus communication device of the high-voltage direct current transmission control and protection system is respectively arranged at the control protection layer and the field IO layer, including a processor (not shown in the figure) and an Ethernet module. The processor can communicate with the Ethernet module through its own Ethernet port, and the Ethernet module provides an Ethernet interface for accessing the equipment in the layer. The processor and the Ethernet module are arranged in the chassis, and the PICe backplane bus is arranged on the chassis backplane. Among them, the processor adopts a general-purpose CPU processor card, adopts a general-purpose architecture based on ARM A72, supports DDR4, expands Sata interface, NorFlash and other resources, and adopts an independent 4U standard plug-in. 4U refers to the height of the chassis is 4 U units, and 1 U unit is 1.75 inches. Furthermore, the device also includes a PICe backplane bus, and the processor and the Ethernet module can communicate using the PCIe bus, with a data transmission rate of 2.5Gbps, achieving extremely high data transmission and reducing data delay. The Ethernet module uses a dedicated fiber optic Ethernet card and provides several Ethernet interfaces, such as a dedicated fiber optic Ethernet card implemented with an ASIC chip to support 6-way full-duplex fiber optic communication. The communication rate can be configured to 100M or 1000M bps through a dial code, and an independent 4U standard plug-in is used. For example, the Ethernet module uses the WX1860 Gigabit Ethernet card, which provides 4 RJ45 network interfaces, so that Ethernet technology is used for data transmission. A signal modulation module (RT8521S in the figure) is correspondingly arranged between the Ethernet card and the RJ45 network interface to convert digital signals and analog signals. The device adopts a general hardware architecture of "general CPU processor card + PICe backplane + dedicated fiber optic Ethernet card" to establish an Ethernet communication architecture between the control system and IO devices, which does not rely on specific hardware and improves the versatility of cross-regional networking. It supports integrated design or distributed networking design. The control system layer and the field IO layer in the high-voltage direct current transmission control and protection system are respectively provided with this device, so that the control system and IO devices communicate through Ethernet technology. When there are many IO devices, the field bus networking method adopts distributed networking, such as Figure 3 As shown: a second-layer switch is arranged at the communication layer, and a high-voltage DC transmission control and protection system field bus communication device is arranged at the control system. Each Ethernet interface (gigabit optical fiber interface) of the device is connected to the first-layer switch, and a high-voltage DC transmission control and protection system field bus communication device is deployed on each switch at the second layer. The IO device is connected to the Ethernet interface provided by the device in the second-layer switch through a network cable or optical fiber, and the control and protection of DC transmission when there are multiple IO devices is realized through distributed networking.

[0032] The processor stores software, and the software architecture adopts the structure of "hardware driver + real-time operating system + runtime system + application layer protocol stack", such as Figure 4As shown. The driver mainly completes the driver design of the Ethernet module and PHY (i.e., physical layer IO device) of PCIe based on a specific real-time operating system; the real-time operating system includes the system kernel, file system, TCP / IP protocol stack, I / O system and runtime library, which are used for task scheduling, kernel and peripheral management of the operating system; the runtime system includes basic software functions such as multi-level cyclic task scheduling and distributed interrupt task scheduling; the application layer protocol stack includes the field bus communication protocol of the high-voltage direct current transmission control and protection system, which is designed based on the standard IEC61850 GOOSE technology and three typical application layer protocols for transmitting application data of the high-voltage direct current transmission control and protection system. Among them, the driver, real-time operating system and runtime system are all implemented using general technologies.

[0033] Since the GOOSE service is the same level communication between devices, and the high-voltage direct current transmission control and protection system is a master-multiple slave communication architecture, a control system is connected to multiple slave IO devices, and it cannot be directly applied. In addition, the standard IEC61850 GOOSE data set adopts the "tag-length-value" method, which requires at least 3 bytes to transmit a BOOL type variable, and the bytes required to transmit other types of variables may be more. When multiple state values ​​or analog quantities need to be transmitted in one frame, the efficiency is not high enough. Therefore, the present invention redesigns the data set part (goosePdu application data) of the GOOSE frame format according to the master-slave architecture of the field bus communication of the high-voltage direct current transmission control and protection system and the data type transmitted, and the format of other parts remains unchanged. The field bus communication protocol of the high-voltage direct current transmission control and protection system is obtained by setting the control word and compression coding. The data set part adopts the data transparent transmission method. The field bus frame format based on IEC61850 GOOSE is shown in Table 1. The goosePdu (protocol data unit) part in the frame format is different from the existing one, and the other parts are the existing GOOSE frame format.

[0034] Table 1

[0035]

[0036] The format of the application data part (i.e., "application data data 1, ..., application data data N" in Table 2) in goosePdu is redesigned, and the rest of the format is the same as the existing goosePdu format. The fieldbus goosePdu frame format based on IEC61850 GOOSE is shown in Table 2.

[0037] Table 2

[0038]

[0039]

[0040]

[0041] The data transmitted in the direction of the master station (control system)-slave station (IO device) is a downlink message, and the data transmitted in the direction of the slave station (IO device)-master station (control system) is an uplink message. The data types of the uplink message include events, state quantities and analog quantities, and the analog quantities include AC line analog quantities and DC analog quantities; the data types of the downlink message include relay outputs and may also include timing. In this embodiment, the AC line includes a first AC line and a second AC line, and the field bus communication protocol of the high-voltage direct current transmission control and protection system supports multiple input channels (such as 120 channels, which can be set according to needs), DC analog quantities and 2 AC analog quantity acquisition boards, and the supported functions are shown in Table 3.

[0042] Table 3

[0043]

[0044] The improved application data includes control words for distinguishing uplink messages, downlink messages and transmitted data types. The application data of uplink messages also includes channel status quantities, event messages and analog quantities. The application data of downlink messages also includes time information.

[0045] Specifically, the control word of the downlink message includes a first control word (control word 1), and the first control word occupies one byte. Each relay output in the downlink message occupies one bit. The downlink message also includes N relay outputs, each relay output occupies one bit, and the value range of N is 1-64. The time information is in the form of 6 bytes, including 2 bytes of days and 4 bytes of milliseconds, for example, the number of days since 1984.01.01 and the milliseconds from 00.00.00h of the day, which are arranged after the relay output. The H in the day represents the high bit, and the L represents the low bit, and the HH, HL, LH, and LL of the milliseconds represent from the highest bit to the lowest bit. Further, in order to improve the security of data transmission, the last two bytes of the downlink message are provided with a check code. The check code can be generated using existing encryption technology, such as generating a CRC check code based on the content of the transmission.

[0046] The first control word of the downlink message also includes the main or backup identification of the control system corresponding to the current communication, such as Figure 5As shown: 01 indicates that the control system currently communicating is required to be a backup system, 10 indicates that the control system currently communicating is required to be a primary system, 00 and 11 are illegal identifiers and will be ignored by the IO device. When the IO device is configured in dual-master mode, both communicating control systems are allowed to be required to be the primary system. The first control word also includes the event group confirmation number of the control system. When the IO device sends a new set of events, the event group number is transmitted. After the control system receives the group of events, it writes the received event group number as a response to the corresponding bit field as the event group confirmation number to indicate that the group of events has been received. The event group confirmation number of the slave system is not processed by the IO device. The first control word also includes a heartbeat bit, which jumps between 01 and 10 in each cycle. If the IO device does not receive a change in the heartbeat bit for more than the set time (which can be set according to requirements, such as 4 seconds), it is considered that the communication between the IO device and the control system is interrupted.

[0047] like Figure 6 As shown, the downlink message also includes a second control word (control word 2), which occupies one byte and is used to send a global scan command to the IO device. If the command is sent by the backup system, the global scan command will be ignored. According to the above settings, Figure 7 As shown, when supporting 64-channel relay control, the application data of the downlink message consists of 18 bytes of data.

[0048] like Figure 8 As shown, the uplink message includes event messages and analog messages, the event message includes input event messages and system event messages, the analog message includes AC line analog message and DC analog message, and the AC analog message includes the first AC line analog message and the second AC line analog message. All uplink messages include the first control word (control word 1) and the second control word (control word 2), the first control word and the second control word occupy two bytes, and the control word is followed by the input channel status quantity, and each input channel status quantity occupies one bit.

[0049] like Fig. 9 As shown: The first control word of the uplink message includes an event group number. Whenever a new group of events is transmitted, the event group number is increased by 1 after the last event group number confirmed by the control system. The event group number cycles between 1-15. Once the new group of events is confirmed by the control system, the corresponding bit field is set to 0000 (unless there is a new event group to be transmitted). The first control word also includes a heartbeat bit, which is usually the same as the heartbeat bit data in the first control word of the received control system, and jumps between 01 and 10 in each cycle, so that the control system monitors the communication status with the IO device. The first control word also includes the primary or backup identification of the control system corresponding to the current communication: 01 indicates that the control system of the current communication is the primary system, and 10 indicates that the control system of the current communication is the backup system.

[0050] The second control word of the uplink message includes a message type identifier used to indicate the message type, such as Fig.10 As shown: 000 indicates an input event message, 010 indicates a system event message, 100 indicates a first AC line analog message, 101 indicates a second AC line analog message, and 110 indicates a DC analog message. The second control word of the uplink message also includes a device failure indication, 1 indicates a device failure, corresponding to system event -144; the second control word also includes a cache flag, indicating that there are system events or input events to be sent in the event cache area of ​​the IO device; the second control word also includes an IO device heartbeat bit, which jumps between 0 and 1 in each cycle; the second control word also includes a local mode flag, when the corresponding bit field is 1, it indicates that the IO device is in local mode, corresponding to system event -146.

[0051] Among them, the event message follows the input channel status of the input event message and the system event message. The input event consists of the input state and the state change event. Each event message includes an event ID and time information. The event ID is a double-byte, and the highest bit indicates the event state, 1 indicates generation, and 0 indicates disappearance; the time information is in the form of 6 bytes, including 2 bytes of days and 4 bytes of milliseconds, for example, the number of days since 1984.01.01 and the milliseconds from 00.00.00h of the day.

[0052] The analog quantity of the AC line analog quantity message is followed by the analog quantity of the AC line, wherein the analog quantity of the first AC line analog quantity message is followed by the analog quantity of the first AC line, the analog quantity of the second AC line analog quantity message is followed by the analog quantity of the second AC line, and the analog quantity of each DC line (such as 8-way DC analog quantity) is followed by the analog quantity of each DC line after the input channel state quantity of the DC analog quantity message. The three types of analog quantities are sent alternately in the analog quantity message. The analog quantity of the AC line includes the effective value of the three-phase voltage, the effective value of the three-phase current, active power, reactive power, frequency and power factor. Each data in the AC analog quantity occupies 2 bytes; the data of each DC analog quantity occupies 2 bytes. Furthermore, in order to ensure the consistency of a frame of the message, the last byte of the uplink message is also provided with a second control word. The receiver will determine whether the second control words at two positions in a frame of the message are consistent. Inconsistency indicates that the data is damaged and needs to be discarded.

[0053] When there are system events or input events in the local cache of the IO device, 1 frame of analog message and 2 frames of event messages in the buffer area will be transmitted in every 3 frames of messages until they are confirmed by the control system, otherwise they will continue to be transmitted, for example, in the order of the first AC line analog message L1, buffer area event message S1, buffer area event message S1, second AC line analog message L2, buffer area event message S1, buffer area event message S1, DC analog message DC1, buffer area event message S1, buffer area event message S1, first AC line analog message L1, the transmission interval of the analog quantity is 9 cycles. When there are no system events and input events, the IO device only transmits analog messages to the control system, and the three analog messages are sent in turn.

[0054] Method Embodiment

[0055] A field bus communication method for a high-voltage direct current transmission control and protection system of the present invention establishes an Ethernet communication architecture between the control system and the IO device. The field bus communication protocol frame format adopted by the Ethernet communication architecture is the field bus goosePdu frame format based on IEC61850GOOSE in the field bus communication protocol of the high-voltage direct current transmission control and protection system described in the above-mentioned device embodiment, which will not be described in detail here.

[0056] The present invention adopts general technology to design a field bus communication method and device for a high-voltage direct current transmission control and protection system, which is independent of specific software and hardware, and because standard Ethernet technology is adopted, the communication rate is greatly improved compared with the original technology. The application layer protocol adopted can complete the communication between the control system and the IO device in the direct current transmission control and protection system, and also supports the communication between the control systems. Under the task cycle of 16ms of the control system, the transmission of the state quantity change of a round-trip cycle with the IO device only takes 31ms to complete, which meets the high-speed transmission requirements of various application scenarios of high-voltage direct current transmission.

Claims

1. A field bus communication method for a high voltage direct current transmission control and protection system, characterized in that: An Ethernet communication architecture is established between a control system and an IO device. The field bus communication protocol frame format adopted by the Ethernet communication architecture is obtained by improving the application data of goosePdu in the IEC61850 GOOSE frame format, wherein the improved application data includes a control word for distinguishing uplink messages, downlink messages and the data type of transmission; wherein the application data of the uplink message also includes an input channel state quantity, and either an event message or an analog quantity, and the application data of the downlink message also includes time information.

2. The field bus communication method for high voltage direct current transmission control and protection system according to claim 1, characterized in that: The control word of the uplink message includes a first control word and a second control word; the first control word of the uplink message includes an event group number, and the second control word includes a message type identifier used to indicate the message type, and the message types include input event messages, system event messages, AC line analog messages, and DC analog messages.

3. The field bus communication method for high voltage direct current transmission control and protection system according to claim 2, characterized in that: The first control word and the second control word of the uplink message occupy two bytes. The control word is followed by the input channel status quantity; the input channel status quantity of the input event message and the system event message is followed by the event message; the input channel status quantity of the AC line analog message is followed by the analog quantity of the AC line; the input channel status quantity of the DC analog message is followed by the DC analog quantities of each channel; Each input channel status quantity occupies one bit.

4. The field bus communication method for high voltage direct current transmission control and protection system according to claim 3, characterized in that: Each event message includes an event ID and time information. The event ID is a two-byte format, with the highest bit indicating the event status. The time information is in a six-byte format.

5. The field bus communication method for high voltage direct current transmission control and protection system according to claim 3, characterized in that: The analog quantities of the AC line include the effective value of the three-phase voltage, the effective value of the three-phase current, active power, reactive power, frequency and power factor parameter values. Each parameter value in the analog quantity of the AC line occupies two bytes; each DC analog quantity occupies two bytes.

6. The field bus communication method for high voltage direct current transmission control and protection system according to claim 1, characterized in that: The control words of the downlink message include a first control word, including the event group confirmation number of the control system and the primary or backup identification of the control system corresponding to the current communication; when the IO device sends a new group of events, the event group number is transmitted, and after the control system receives the group of events, it writes the received event group number as a response into the corresponding bit field of the first control word as the event group confirmation number to indicate that the group of events has been received.

7. The field bus communication method for high voltage direct current transmission control and protection system according to claim 1, characterized in that: The downlink message also includes N relay outputs, each relay output occupies one bit, and the value range of N is 1-64.

8. The field bus communication method for high voltage direct current transmission control and protection system according to claim 1, characterized in that: The downlink message also includes a check code; the check code is set at the last two bytes.

9. The field bus communication method for high voltage direct current transmission control and protection system according to claim 6, characterized in that: The control word of the downlink message also includes a second control word, which occupies one byte and is used to send a global scan command to the IO device.

10. A field bus communication device for a high voltage direct current transmission control and protection system, characterized in that: The device is respectively arranged at the control protection layer and the field IO layer, including a processor and an Ethernet module, the Ethernet module provides an Ethernet interface for accessing the equipment at the layer; the processor stores software, the software includes an application layer protocol stack, and the application layer protocol stack is provided with a field bus communication protocol to perform data transmission according to the field bus communication method of the high-voltage direct current transmission control and protection system as described in any one of claims 1 to 9.

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