CN111371663A - Ring network communication system and communication method for multi-level converter control system - Google Patents
Ring network communication system and communication method for multi-level converter control system Download PDFInfo
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L12/00—Data switching networks
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- H—ELECTRICITY
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- H04L12/00—Data switching networks
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Abstract
The invention discloses a ring network communication system and a communication method for a multilevel converter control system, which are applied to the control system of a modular multilevel converter, wherein the control system comprises a valve base controller VBC and N sub-module controllers SMC-1 to SMC-N; each SMC comprises 2 pairs of communication ports, and sub-module controllers SMC-1 to SMC-N are connected according to rules to form two independent unidirectional looped networks AB: the VBC is a master control device, simultaneously sends control commands to the SMC from the AB two ring network ports according to a fixed period, and receives state information sent by the SMC; the SMC always receives data of an upstream device, and sets transmission state information according to a fixed time slot in the cycle according to a received control command. The technical scheme can reduce the hardware complexity of the valve base control equipment, realize the control real-time performance close to 0 time delay, solve the problem of port conflict of the equipment in the ring network, and provide the redundant backup capability of a communication channel.
Description
Technical Field
The invention relates to a communication technology of a multi-level converter control system, in particular to a communication system and a communication method of the control system.
Background
Compared with high-voltage alternating current transmission and traditional high-voltage direct current transmission, the high-voltage flexible direct current transmission system has unique advantages and is more suitable for application occasions such as long-distance transmission, wind power integration, submarine transmission and the like. The modular multilevel converter system is the main solution of the current high voltage flexible direct current transmission system. The converter is generally formed by cascading a plurality of submodules, the number of the submodules cascaded by a single bridge arm is up to more than 200, and the number of the submodules cascaded by six three-phase bridge arms is larger in order to obtain better harmonic characteristics and provide enough redundancy for a system. Each Sub-module has a Sub-module Controller (SMC) for control and monitoring, and a Valve Base Controller (VBC) needs to communicate with all SMCs via a communication link.
However, in the related art, point-to-point communication is mainly achieved through VBC and SMC, for example, in the case where one VBC controls a single-arm SMC, the VBC has to have hundreds of pairs of communication interfaces to communicate with SMC through the same number of optical fibers. For a high-voltage flexible direct-current power transmission system with larger capacity and more SMC, the density of VBC device communication interfaces is further increased, and the complexity of hardware design and heat dissipation design is greatly increased.
In addition, a ring network networking scheme such as HSR or RSTP can theoretically reduce the number of communication interfaces and optical fibers, but the conventional ring network communication generally adopts a store and forward (store and forward) or cut-through (cut-through) mode; the store-and-forward mode can cause the problem that the delay of data forwarding through each network node is large, and the real-time transmission of important data is affected, while the direct-through mode is difficult to solve the problem of port collision of forwarding data and locally sent data. Therefore, the conventional ring network scheme is not suitable for systems requiring high real-time performance, such as a modular multilevel converter.
Disclosure of Invention
The invention aims to provide a ring network communication system and a communication method for a multilevel converter control system, which can reduce the hardware complexity of valve base control equipment, realize the control real-time performance of the time delay close to 0, solve the problem of port conflict of the equipment in the ring network and provide the redundant backup capability of a communication channel.
In order to achieve the above purpose, the solution of the invention is:
a multi-level converter control system looped network communication system is applied to a control system of a modular multi-level converter, and the control system comprises a valve base controller VBC and N sub-module controllers SMC-1 to SMC-N;
each SMC comprises 2 pairs of communication ports, which are marked as a communication port A and a communication port B, and sub-module controllers SMC-1 to SMC-N are connected according to the following rules to form two independent unidirectional ring networks:
the communication ports A are sequentially connected in series by each sub-module controller according to the ascending sequence of the serial number, and the two ends after being connected in series are connected with the VBC communication port A to form a unidirectional looped network A;
each sub-module controller connects the communication ports B in series according to the descending order of the serial number, and the two ends after the series connection are connected with the VBC communication port B to form a unidirectional looped network B;
the VBC is a master control device, simultaneously sends control commands to the SMC from the AB two ring network ports according to a fixed period, and receives state information sent by the SMC;
the SMC always receives data of an upstream device, and sets transmission state information according to a fixed time slot in the cycle according to a received control command.
The communication port of the VBC of the valve base controller sends two states: no data is sent in state P1, and control command is sent in state P2; the VBC controls the transmit port to switch between state P1 and state P2.
The communication port of each sub-module controller SMC sends two states: state Q1 is a signal for forwarding the corresponding receiving port, and state Q2 is the state information data of the transmission own SMC; the SMC controls the transmitting port to switch between state Q1 and state Q2. When the SMC is in Q1, the upstream signal is delayed by SMC forwarding so as to delay the routing of the SMC internal hardware signal.
Based on the communication method of the multi-level converter control system ring network communication system, the connection mode of the N sub-module controllers SMC-1 to SMC-N is as follows:
a communication port A of the SMC-i transmits and is connected with a communication port A of the SMC- (i +1), the communication port A of i-1, …, N-1, SMC-N transmits and is connected with a VBC communication port A, the communication port A of the SMC-1 receives and is connected with the VBC communication port A, and a unidirectional ring network A is formed;
the communication port B of SMC-i receives and transmits and links with the communication port B of SMC- (i +1), i is 1, …, N-1, the communication port B of SMC-N receives and transmits and links with VBC communication port B, the communication port B of SMC-1 transmits and receives and links with VBC communication port B, make up unidirectional looped network B;
the VBC sends control commands to the SMC from the AB two ring network ports at the same time according to a fixed period and receives state information sent by the SMC; the control command is in a broadcast form and comprises control commands for all SMCs in the ring network;
the SMC always receives data of an upstream device, and sets transmission state information according to a fixed time slot in the cycle according to a received control command.
The control command sent by the valve base controller VBC and the status information data sent by the sub-module controller SMC contain type identifiers with distinguishable types, and the SMC distinguishes the control command from the status information according to the type identifiers in the analyzed and received data.
The time length of the fixed period is greater than the sum of the transmission time of the control command and the time of sending the state information by all the SMCs in the ring.
The communication port of the VBC sends two states: no data is sent in state P1, and a control command is sent in state P2; the VBC controls the transmit port to switch between state P1 and state P2;
the communication port of the SMC sends two states: state Q1 is a signal for forwarding the corresponding receiving port, and state Q2 is the state information data of the transmission own SMC; the SMC controls the transmitting port to switch between state Q1 and state Q2. When the SMC is in Q1, the upstream signal is delayed by SMC forwarding so as to delay the routing of the SMC internal hardware signal.
The fixed period is divided into a plurality of time slots according to the number of SMCs in the ring network, the time slot 0 is a VBC sending time slot, the VBC is in a state P1 at the moment, and all SMCs are in a state Q2; the time slots 1-N are SMC transmission time slots, with the SMC of the corresponding sequence number in state Q1, VBC in state P2, and other SMCs in state Q2.
And when the sub-module controller SMC sends the state information, the state information is sent to the AB two unidirectional ring networks at the same time.
The control command and the state information are organized according to frames, the frame format comprises four fields of a lead code, frame overhead, frame content and frame check, wherein the lead code is used for extracting data clock information from the signals by the equipment at the receiving side and analyzing the frame content by using the clock information; the frame overhead comprises a frame type identifier and frame sequence number information, and whether the received data is a control command or state information is distinguished by analyzing the frame overhead; the frame content contains the specific content of the device command or status information for implementing the application function; the frame check is a cyclic redundancy check code comprising frame overhead and frame content, and the integrity of the currently received frame is determined according to a frame check result.
After the scheme is adopted, the system comprises the valve base controller VBC and N sub-module controllers SMC. SMC is connected with communication medium in series through communication port, and both ends are connected with VBC and form one-way ring network. The SMC has two pairs of independent communication ports to form two unidirectional ring networks with opposite directions. And the VBC sends a control command according to a fixed time period, and the SMC selects to forward a received signal or send local information according to the time when the control command is received and a preset time slot.
By implementing the scheme of the invention, the communication function of 2 pairs of communication ports for VBC and all SMCs in the ring network can be realized, so that the number of communication interfaces can be reduced by using the scheme of the invention for the same total number of the SMCs, thereby reducing the complexity of hardware design and the system power consumption. In addition, by implementing the topology and the method, the data transmission with near zero time delay can be realized, and the real-time performance of control is improved. Thirdly, the equipment in the ring network has a definite time-sharing transmission mechanism without port conflict. Fourthly, because two independent unidirectional ring network topologies are adopted, the communication function of other normal SMCs and VBCs can not be influenced by a single fault in the network.
Drawings
Fig. 1 is a schematic diagram of a network topology of a ring network communication method according to the present invention;
FIG. 2 is a functional diagram of the SMC controlling the transmission of a communication port according to the present invention;
the system comprises a communication module, a local state information sending controller, an SMC communication module receiving port 201, an SMC communication module sending port 202 and an SMC sending controller 211, wherein the local state information is sent; 212 is an SMC receiving controller, 213 is a delay controller, and 214 is a 1-out-of-2 gate for sending signals;
FIG. 3 is a schematic diagram of control cycle allocation, with the circle representing the cycle period time length and the sector representing the fractional occupancy time;
wherein 301 is a VBC sending time slot and is marked as TS 0; 302 sends a slot for SMC1, labeled TS 1; 303 is the slot time in two transmit slots; reference numeral 304 denotes the time interval between the end of TS6 in a cycle and the start of the next cycle.
Detailed Description
The technical solution and the advantages of the present invention will be described in detail with reference to the accompanying drawings.
The invention provides a ring network communication system of a multilevel converter control system, which is applied to the control system of a modular multilevel converter, wherein the control system comprises a valve base controller VBC and 1 st sub-module controllers SMC-1 to Nth SMC-N, wherein,
each SMC comprises 2 pairs of communication ports, which are marked as a communication port A and a communication port B, and sub-modules SMC-1 to SMC-N are connected according to the following rules to form two independent unidirectional ring networks:
the communication port A of the SMC-1 is connected with the SMC-2 communication port A in a receiving mode, the communication port A of the SMC-2 is connected with the SMC-3 communication port A in a receiving mode, and the like, namely, the communication ports A are sequentially connected in series by each sub-module controller according to the ascending sequence of the sequence number, and the two ends of the sub-module controller are connected with the VBC communication port A in the receiving and sending mode to form a unidirectional looped network A.
Similarly, each sub-module controller connects the communication ports B in series according to the descending order of the serial number, and the two ends are connected with the VBC communication port B to form a unidirectional ring network B.
The VBC is a master control device, simultaneously sends control commands to the SMC from the AB two ring network ports according to a fixed period, and receives state information sent by the SMC; the control command is in a broadcast form and comprises control commands for all SMC in the ring network; the fixed period time length is larger than the sum of the control command transmission time and the time for all SMC in the ring to send state information.
The SMC always receives data of an upstream device, and sets transmission state information according to a fixed time slot in the cycle according to a received control command.
The control command sent by the VBC and the state information data sent by the SMC contain type identifiers with distinguishable types, and the SMC distinguishes the control command and the state information according to the type identifiers in the analyzed and received data;
the communication port of the VBC sends two states: in state 1, only the signal of the port is received, and in state 2, a control command is transmitted. The VBC may control the transmit port to switch between state 1 and state 2.
The communication port of the SMC sends two states: state 1 is to forward a signal corresponding to the receiving port, and state 2 is to transmit the state information data of the present SMC. The SMC can control the transmitting port to switch between a state 1 and a state 2, and in the state 1, the SMC directly copies a receiving port signal to the transmitting port in a hardware signal direct driving mode, and the forwarding delay is hardware signal delay.
The fixed period is divided into a plurality of time slots according to the number of SMCs in the ring network, the time slot 0 is a VBC sending time slot, the VBC is in a state 1 at the moment, and all the SMCs are in a state 2; the time slots 1-N are SMC sending time slots, the SMC corresponding to the sequence number is in a state 1, and the VBC and other SMCs are in a state 2.
The VBC is not overlapped with the sending time slots of the SMCs in the ring in terms of time, idle time is reserved among the time slots, and the idle time is larger than the sum of the forwarding delays of all the SMCs in the ring network.
The invention also provides a communication method, the control command has a fixed forwarding sequence in the two unidirectional ring networks, and for the control command, the control command issued by the VBC communication port A follows the path of the unidirectional ring network A and sequentially reaches SMC-1 and SMC-2 … … SMC-N; and the control command issued by the VBC communication port B follows the path of the unidirectional ring network B and sequentially reaches SMC-N … … SMC-2 and SMC-1.
In the method, when the SMC sends the state information, the SMC sends the state information to the A/B two unidirectional ring networks at the same time. Taking SMC-1 as an example, the state information sent by the ring network A is sequentially forwarded by SMC-2 … … SMC-N and finally reaches the communication port A of the VBC; the state information sent by the ring network B directly reaches the communication port B of the VBC.
In the method of the invention, the VBC receives the control command arriving through the ring network and directly discards the control command; SMC state information arriving through a ring network is received and transmitted to an application layer for processing; the VBC does not forward any data.
In the method, the control command and the state information are organized according to frames, and the frame format comprises four fields of a lead code, frame overhead, frame content and frame verification. The lead code is used for the receiving side equipment to extract data clock information from the signal and analyze the frame content by using the clock information; the frame overhead comprises a frame type identifier and frame sequence number information, and whether the received data is a control command or state information can be distinguished by analyzing the frame overhead; the frame content contains the specific content of the device command or status information for implementing the application function; the frame check is a cyclic redundancy check code including frame overhead and frame content, and the integrity of the currently received frame can be determined according to a frame check result.
In the method of the invention, the minimum period of the system can be determined according to the transmission time of the control command frame and the state information frame. The minimum period needs to include at least the following three parts: 1. broadcast control command frame transmission time; 2. the sum of the transmission time of all SMC state information frames in the ring network; 3. the frame gap time.
In the method of the invention, the communication port of the SMC sends two states: state 1 is to forward a signal corresponding to the receiving port, and state 2 is to transmit the state information data of the present SMC. The SMC may control the sending port to switch between state 1 and state 2.
In the method, when the SMC is in the state 1, a hardware signal direct driving mode is adopted to directly forward the signals of the receiving port to the corresponding sending port, and the forwarding delay on each level of SMC is very small. Therefore, when the SMCs in the ring are all in the state 1, the time points of the SMCs at any position in the ring network receiving the VBC control command from the two unidirectional ring networks are basically the same. The SMCs in the ring network may infer an identical cycle time starting point from the time when the control command frame is received and the transmission time of the control command frame. The time frame for the VBC to send the control command is referred to as TS 0.
In the method of the invention, each SMC in the ring network sequentially shifts to a state 2 according to the starting point of the cycle time, the pre-allocated SMC serial number and the sending time slot length, and simultaneously sends the state information of the SMC to two unidirectional ring networks.
In the method of the invention, only 1 device (including VBC and SMC) sends data to the ring network at any time in the period, and gaps are left between all sending time slots to adapt to the delay and uncertainty brought by hardware parameters.
In the method of the invention, the control command frame sent by the VBC reaches the corresponding receiving port of the VBC after being forwarded by the SMC, and the VBC does not process the control command frame and directly discards the control command frame.
In the method of the invention, the control command frame sent by the VBC can reach any SMC through two independent bidirectional ring networks, and the state information sent by the SMC can also reach the VBC along the directions of the two independent ring networks, so that the single fault on the path can not cause the communication function fault of the ring networks.
The technical solution of the present invention will be further described with reference to specific examples.
The whole multi-level converter control system consists of one VBC device and 18 SMC sub-modules. The SMC was divided into 3 groups on average, and each group had 6 SMCs. Each sub-module is connected in series to form the ring network, and two ends of each sub-module are connected with the VBC to form two independent unidirectional ring networks. Since the network topology formed by the three groups of SMCs and VBC is the same and the communication method is the same, in this embodiment, a network formed by a group of SMCs and VBC is described.
The system network topology in this embodiment is shown in fig. 1: the receiving and transmitting ports of the communication ports A of the 6 SMCs are connected in series end to end through optical fibers according to the ascending order of SMC serial numbers, and the two ends of the receiving and transmitting ports are respectively connected to the communication ports of the VBC to form a one-way ring network A; the receiving and transmitting ports of the communication ports B of the 6 SMCs are connected in series end to end through optical fibers according to the descending order of SMC serial numbers, and the two ends of the receiving and transmitting ports are respectively connected to the communication ports of the VBC to form a one-way ring network B.
In the embodiment, the signal forwarding sequence of the unidirectional ring network a is SMC1-SMC 2-SMC 3-SMC 4-SMC 5-SMC 6; the signal forwarding sequence of the unidirectional ring network B is opposite to that of the ring network A.
In the communication method, the VBC is a master control device, and sends a control command to the SMC in the ring network according to a fixed period of 50us, wherein the control command is in a broadcast form and contains control command information of all SMC in the ring network. The SMC receives the correct control command information and sequentially sends the state information to the VBC according to the pre-allocated time slot.
In this embodiment, the fixed period 50us is divided into 7 transmission slots denoted as TS0-TS7, and the intervals between the slots are referred to as G0-G7, respectively. TS0 is a time slot for VBC to send control command frame, TS1-TS6 are time slots for SMC1-SMC6 to send state information respectively; G0-G5 are the time gaps between transmission slots, and G6 is the time gap from the end of the last transmission slot TS6 to the start of the next cycle.
In this embodiment, a communication data interface with an effective bandwidth of 50Mbps is adopted, and the control command frame is similar to the state information frame in format and includes four fields, namely a preamble, a frame overhead, a frame content and a frame check. The length of the control command frame (including the checksum) is 20 bytes, and the time for sending one control command frame is 3.2 us; the length of the SMC status information frame is 16 bytes, and the time for sending one status information frame is 2.56 us.
In this embodiment, an fpga (field Programmable Gate array) device is used to implement a communication control unit of the SMC, a schematic logic block diagram of the communication control unit is shown in fig. 2, 201 is an optical receiving circuit driver of the SMC, the optical receiving circuit driver is directly connected to the receiving control module 212, the receiving control module decodes a received signal, and identifies whether a current frame belongs to a control command frame or a status information frame according to a field in a frame overhead. And 211, a sending controller of the SMC, which is responsible for collecting the status information, framing and sending. The signal source of the optical transmitter driver 202 is controlled by a multiplexer 214.
In this embodiment, when the SMC is in the state of forwarding the received signal, the received signal (201) directly drives the transmitting circuit 202, which is called state 1, and the SMC forwarding delay in state 1 is small, and actually measures less than 100ns, so the total forwarding delay of the ring network is less than 1 us. The SMC sends local state information, referred to as state 2. The switching between state 1 and state 2 is controlled by a delay controller 213, the starting point of the delay time of which is determined by the receiving controller 212, and the delay value is associated with the SMC sequence number.
In this embodiment, the length of each slot is determined according to the frame transmission time. Setting TS 0-5 us, TS1-TS 2-TS 3-TS 4-TS 5-TS 6-4 us; g0 ═ G1 ═ G2 ═ G3 ═ G4 ═ G5 ═ 2us, and G6 ═ 9 us. As shown in fig. 3, it can be seen that the transmission timing of each VBC and each SMC is as shown in the following table:
TABLE 1 time slot distribution in period
In this embodiment, since the forwarding delay of the ring network in state 1 is small, under normal conditions, the delay from two independent ring networks to the SMC in different directions depends on the hardware forwarding time of the multiple stages of SMCs, the absolute delay value is small, and the time difference between the two directions is also small. Therefore, the real-time performance of the control command can be effectively improved.
In this embodiment, the SMC can achieve the effects of communication and synchronization as long as it receives a control command frame arriving in any direction. The SMC performs an action of sending local state information to two ring networks simultaneously according to the existing logic. Additionally, the VBC may also receive the SMC status information in both directions. Therefore, the communication method in the embodiment has the channel redundancy backup capability, and any communication link fails without influencing the communication effect.
In this embodiment, only 1 device (including VBC and SMC) sends data to the ring network at any time in the period, and a gap is left between each sending time slot to adapt to the delay and uncertainty caused by hardware parameters.
In this embodiment, the control command frame sent by the VBC reaches the corresponding receiving port of the VBC after being forwarded by the SMC, and the VBC directly discards the control command frame without processing the control command frame. Therefore, any data in the ring network is forwarded after reaching the VBC, and the possibility of network storm in the ring network is avoided.
The VBC and the SMC form two unidirectional ring networks with different directions, the VBC simultaneously issues control commands along the two directions, and the SMC receives the control commands and sequentially sends state information according to preset time slots. The SMC obtains the control right of the transmitting port only in the transmitting time slot of the module, and directly transmits the received signal to the transmitting port in other time slots.
The above embodiments are only for illustrating the technical idea of the present invention, and the protection scope of the present invention is not limited thereby, and any modifications made on the basis of the technical scheme according to the technical idea of the present invention fall within the protection scope of the present invention.
Claims (10)
1. A multi-level converter control system looped network communication system is applied to a control system of a modular multi-level converter, and the control system comprises a valve base controller VBC and N sub-module controllers SMC-1 to SMC-N; the method is characterized in that:
each SMC comprises 2 pairs of communication ports, which are marked as a communication port A and a communication port B, and sub-module controllers SMC-1 to SMC-N are connected according to the following rules to form two independent unidirectional ring networks:
the communication ports A are sequentially connected in series by each sub-module controller according to the ascending sequence of the serial number, and the two ends after being connected in series are connected with the VBC communication port A to form a unidirectional looped network A;
each sub-module controller connects the communication ports B in series according to the descending order of the serial number, and the two ends after the series connection are connected with the VBC communication port B to form a unidirectional looped network B;
the VBC is a master control device, simultaneously sends control commands to the SMC from the AB two ring network ports according to a fixed period, and receives state information sent by the SMC;
the SMC always receives data of an upstream device, and sets transmission state information according to a fixed time slot in the cycle according to a received control command.
2. The communication system of claim 1, wherein: the communication port of the valve base controller VBC sends two states: no data is sent in state P1, and a control command is sent in state P2; the VBC controls the transmit port to switch between state P1 and state P2.
3. The communication system of claim 1, wherein: the communication port of each sub-module controller SMC sends two states: state Q1 is a signal for forwarding the corresponding receiving port, and state Q2 is the state information data of the transmission own SMC; the SMC controls the transmitting port to switch between state Q1 and state Q2.
4. The communication method of the ring network communication system of the multilevel converter control system according to claim 1, wherein:
the connection mode of the N sub-module controllers SMC-1 to SMC-N is as follows:
a communication port A of the SMC-i transmits and is connected with a communication port A of the SMC- (i +1), the communication port A of i-1, …, N-1, SMC-N transmits and is connected with a VBC communication port A, the communication port A of the SMC-1 receives and is connected with the VBC communication port A, and a unidirectional ring network A is formed;
the communication port B of SMC-i receives and transmits and links with the communication port B of SMC- (i +1), i is 1, …, N-1, the communication port B of SMC-N receives and transmits and links with VBC communication port B, the communication port B of SMC-1 transmits and receives and links with VBC communication port B, make up unidirectional looped network B;
the VBC sends control commands to the SMC from the AB two ring network ports at the same time according to a fixed period and receives state information sent by the SMC; the control command is in a broadcast form and comprises control commands for all SMCs in the ring network;
the SMC always receives data of an upstream device, and sets transmission state information according to a fixed time slot in the cycle according to a received control command.
5. The communication method of claim 4, wherein: the control command sent by the valve base controller VBC and the state information data sent by the sub-module controller SMC comprise type identifiers with distinguishable types, and the VBC and the SMC distinguish the control command from the state information according to the type identifiers in the analysis received data.
6. The communication method of claim 4, wherein: the time length of the fixed period is greater than the sum of the transmission time of the control command and the time of sending the state information by all SMCs in the ring.
7. The communication method of claim 4, wherein: the communication port of the VBC sends two states: no data is sent in state P1, and a control command is sent in state P2; the VBC controls the transmit port to switch between state P1 and state P2;
the communication port of the SMC sends two states: state Q1 is a signal for forwarding the corresponding receiving port, and state Q2 is the state information data of the transmission own SMC; the SMC controls the transmitting port to switch between state Q1 and state Q2.
8. The communication method of claim 7, wherein: the fixed period is divided into a plurality of time slots according to the number of SMCs in the ring network, the time slot 0 is a VBC sending time slot, the VBC is in a state P1 at the moment, and all the SMCs are in a state Q2; the time slots 1-N are SMC transmission time slots, with the SMC of the corresponding sequence number in state Q1, VBC in state P2, and other SMCs in state Q2.
9. The communication method of claim 4, wherein: and when the sub-module controller SMC sends the state information, the state information is sent to the AB two unidirectional ring networks at the same time.
10. The communication method of claim 4, wherein: the control command and the state information are organized according to frames, the frame format comprises four fields of a lead code, frame overhead, frame content and frame verification, wherein the lead code is used for extracting data clock information from signals by equipment at a receiving side and analyzing the frame content by using the clock information; the frame overhead comprises a frame type identifier and frame sequence number information, and whether the received data is a control command or state information is distinguished by analyzing the frame overhead; the frame content contains the specific content of the device command or status information for implementing the application function; the frame check is a cyclic redundancy check code comprising frame overhead and frame content, and the integrity of the currently received frame is determined according to a frame check result.
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