Control protection device and method for C-NPC type topology converter

Abstract

The invention discloses a control protection device and method for a C-NPC type topological converter. The control protection device comprises a dual station control layer, a dual pole control layer and a valve control layer, the station control layer is used for issuing a received start-stop instruction issued by a system scheduling end and a control target to the pole control layer; the pole control layer is used for performing outer ring control algorithm processing and device-level protection function operation based on the start-stop instruction and the control target, and issuing active and reactive reference instructions obtained through calculation to the valve control layer; the valve control layer is used for performing inner ring control algorithm processing and sub-module level protection function operation based on active and reactive reference instructions, and issuing generated IGBT trigger pulses to each C-NPC sub-unit; according to the invention, a layered architecture is adopted, so that the control protection device is clear in function and higher in flexibility; during operation, only the pole control layer needs to issue active and reactive reference instructions to the valve control layer, the reliability of the device is higher, the independence is higher, and the requirement for the real-time performance of control and protection is lower.

Description

Technical Field

[0001] The present invention relates to the field of power systems, and in particular to a control and protection device and method for a C-NPC topology converter. Background Art

[0002] In order to solve the problems of power grids in remote areas and islands, such as mismatch between operating capacity and load, large intermittent power supply, poor power quality, and long black start time, it is necessary to carry out research on the use of flexible DC transmission technology for distribution network power supply. Flexible DC transmission technology based on MMC technology has the advantages of bidirectional flow, high power quality, and low loss, but the converter valve is expensive and large in size.

[0003] The flexible direct current distribution network adopting the cascaded three-level converter (Cascade Neutral Point Clamped Converter, C-NPC) topology is composed of several three-level power module units directly connected in series on the DC side and connected in parallel on the AC side through a multi-winding transformer, which realizes the improvement of system-level converter capacity and withstand voltage level. It has the characteristics of high switching frequency, good power quality, high power density, small footprint, good economy, and can supply power to passive networks. Each C-NPC power module unit is equipped with a composite bypass unit on the DC side to ensure automatic bypass exit in the event of a serious fault in the power module, which can maximize the reliability of system operation. At present, the application of flexible direct current distribution network projects with C-NPC topology architecture is relatively small, especially the control and protection system architecture for flexible direct current distribution network has no mature solution. Summary of the invention

[0004] In order to solve the problem that there is a lack of control and protection system for flexible direct current distribution network suitable for C-NPC topology architecture in the prior art, the present invention proposes a control and protection device for C-NPC topology converter, the control and protection device is connected to the system dispatching end and several C-NPC subunits through Ethernet and optical fiber respectively; the control and protection device includes: a dual station control layer, a dual pole control layer and a valve control layer;

[0005] The station control layer is used to send the start and stop instructions and control targets sent by the system dispatching end to the pole control layer;

[0006] The pole control layer is used to perform outer loop control algorithm processing and device-level protection function operation based on the start-stop command and control target, and send the calculated active and reactive reference commands to the valve control layer;

[0007] The valve control layer is used to perform inner loop control algorithm processing and submodule level protection function operation based on the active and reactive reference instructions, and send the generated IGBT trigger pulse to each C-NPC subunit.

[0008] Preferably, the station control layer is specifically used for:

[0009] Receive the start / stop instructions and control targets issued by the system dispatcher based on Ethernet;

[0010] Based on the start-stop instructions and control targets, the measurement and control functions of the switch and the switch opening and closing in the control station are operated, and the start-stop instructions and control targets are sent to the pole control layer.

[0011] Preferably, the polar control layer is specifically used for:

[0012] Execute the start and stop control of the positive or negative electrode and the device-level protection function operation based on the start and stop command and the control target;

[0013] Based on the start-stop command and the control target, an outer loop control algorithm is processed to calculate active and reactive reference commands;

[0014] The active and reactive power reference instructions are sent to the valve control layer.

[0015] Preferably, the valve control layer is specifically used for:

[0016] Perform submodule-level protection function operations based on the electrical quantities and state quantities of the converter;

[0017] Based on the active and reactive reference instructions, an inner loop control algorithm is processed to calculate a three-phase voltage modulation wave;

[0018] Performing modulation based on the three-phase voltage modulation wave to obtain an IGBT trigger pulse;

[0019] The IGBT trigger pulse is sent to each C-NPC sub-unit through an optical fiber for triggering.

[0020] Preferably, the device-level protection function operations include: AC overvoltage protection, AC undervoltage protection, AC overcurrent protection, converter station DC overvoltage protection, DC undervoltage protection, DC overcurrent protection and DC pole bus differential protection.

[0021] Preferably, the submodule protection function operations include: valve side AC overvoltage protection, AC undervoltage protection, overcurrent protection, DC overvoltage protection, DC undervoltage protection, DC overcurrent protection and midpoint overvoltage protection.

[0022] The hardware configuration of the control and protection device adopts a standardized board.

[0023] Based on the same inventive concept, the present invention also proposes a control and protection method for a C-NPC topology converter, comprising:

[0024] The start / stop command and control target issued by the system dispatching end received by the station control layer of the control protection device are sent to the pole control layer of the control protection device;

[0025] Based on the start-stop command and the control target, an outer loop control algorithm is processed and a device-level protection function is operated, and the calculated active and reactive reference commands are sent to the valve control layer of the control protection device;

[0026] Based on the active and reactive reference instructions, the inner loop control algorithm processing and the sub-module level protection function operation are performed, and the generated IGBT trigger pulse is sent to each C-NPC sub-unit.

[0027] Preferably, the start / stop instruction and the control target issued by the system dispatching end received by the station control layer of the control and protection device are sent to the pole control layer of the control and protection device, including:

[0028] Receive the start / stop instructions and control targets issued by the system dispatcher based on Ethernet;

[0029] Based on the start-stop instructions and control targets, the measurement and control functions of the switch and the switch opening and closing in the control station are operated, and the start-stop instructions and control targets are sent to the pole control layer.

[0030] Preferably, the outer loop control algorithm processing and device-level protection function operation are performed based on the start-stop instruction and the control target, and the calculated active and reactive reference instructions are sent to the valve control layer of the control protection device, including:

[0031] Execute the start and stop control of the positive or negative electrode and the device-level protection function operation based on the start and stop command and the control target;

[0032] Based on the start-stop command and the control target, an outer loop control algorithm is processed to calculate active and reactive reference commands;

[0033] The active and reactive power reference instructions are sent to the valve control layer.

[0034] Preferably, the inner loop control algorithm processing and submodule level protection function operation based on the active and reactive reference instructions, and the generated IGBT trigger pulse is sent to each C-NPC subunit, including:

[0035] Performing submodule level protection function operation based on the electrical quantity and state quantity of the converter;

[0036] Based on the active and reactive reference instructions, an inner loop control algorithm is processed to calculate a three-phase voltage modulation wave;

[0037] Performing modulation based on the three-phase voltage modulation wave to obtain an IGBT trigger pulse;

[0038] The IGBT trigger pulse is sent to each C-NPC sub-unit through an optical fiber for triggering.

[0039] Preferably, the device-level protection function operations include: AC overvoltage protection, AC undervoltage protection, AC overcurrent protection, converter station DC overvoltage protection, DC undervoltage protection, DC overcurrent protection and DC pole bus differential protection.

[0040] Preferably, the submodule protection function operations include: valve side AC overvoltage protection, AC undervoltage protection, overcurrent protection, DC overvoltage protection, DC undervoltage protection, DC overcurrent protection and midpoint overvoltage protection.

[0041] Compared with the prior art, the present invention has the following beneficial effects:

[0042] A control and protection device for a C-NPC topology converter, the control and protection device is connected to a system dispatching end and several C-NPC subunits through Ethernet and optical fiber respectively; the control and protection device comprises: a station control layer, a dual pole control layer and a valve control layer; the station control layer is used to send the start and stop instructions and control targets sent by the system dispatching end to the pole control layer; the pole control layer is used to perform outer loop control algorithm processing and device-level protection function operations based on the start and stop instructions and control targets, and send the calculated active and reactive reference instructions to the valve control layer; the valve control layer is used to perform inner loop control algorithm processing and submodule-level protection function operations based on the active and reactive reference instructions, and send the generated IGBT trigger pulses to each C-NPC subunit; the control and protection device in the present invention adopts a layered architecture, consisting of a station control layer, a pole control layer and a valve control layer, so that the function of the control and protection device is clear and the flexibility is higher; when the present invention is running, only the pole control layer needs to send active and reactive reference instructions to the valve control layer, and the device has higher reliability, stronger independence, and lower requirements for real-time control and protection;

[0043] The hardware configuration of the control and protection device in the present invention adopts a standardized board, which is conducive to subsequent modularization, serialization design and production, can reduce the debugging workload of on-site construction, and has lower overall cost and smaller footprint than traditional flexible direct current control and protection systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 A diagram of a control and protection device for a C-NPC topology converter according to the present invention;

[0045] Figure 2 It is a layered diagram of the C-NPC control protection architecture of the present invention. DETAILED DESCRIPTION

[0046] In order to develop a solution for a flexible direct current control and protection system for a C-NPC topology distribution network, the present invention proposes a control and protection device for a C-NPC topology converter, which can meet the application requirements of a control and protection system for a flexible direct current distribution network with low cost, high reliability, small footprint and flexible functions. In order to better understand the present invention, the contents of the present invention are further explained below in conjunction with the accompanying drawings and embodiments of the specification.

[0047] Embodiment 1:

[0048] A control and protection device for a C-NPC topology converter, the control and protection device is connected to a system dispatching terminal and a plurality of C-NPC subunits through Ethernet and optical fiber respectively; the control and protection device comprises: a dual station control layer, a dual pole control layer and a valve control layer; the control and protection device integrates control and protection functions according to a layered architecture, such as Figure 1 As shown;

[0049] The station control layer is used to send the start and stop instructions and control targets sent by the system dispatching end to the pole control layer;

[0050] The pole control layer is used to perform outer loop control algorithm processing and device-level protection function operation based on the start-stop command and control target, and send the calculated active and reactive reference commands to the valve control layer;

[0051] The valve control layer is used to perform inner loop control algorithm processing and submodule level protection function operation based on the active and reactive reference instructions, and send the generated IGBT trigger pulse to each C-NPC subunit.

[0052] The station control layer is specifically used for:

[0053] Receive the start / stop instructions and control targets issued by the system dispatcher based on Ethernet;

[0054] Based on the start-stop instructions and control targets, the measurement and control functions of the switch and the switch opening and closing in the control station are operated, and the start-stop instructions and control targets are sent to the pole control layer.

[0055] Coordinated control of double-end and double-pole operation, the main functions are: coordinated control of double-end and double-pole start and stop, receiving remote adjustment target values; AC and DC field isolation / grounding knife control and interlocking, realizing measurement and control functions; controlling the opening and closing operations of DC busbar circuit breakers. Double-end refers to the sending end and the receiving end; bipolar refers to the positive and negative poles.

[0056] The pole control layer is specifically used for:

[0057] Execute the start and stop control of the positive or negative electrode and the device-level protection function operation based on the start and stop command and the control target;

[0058] Based on the start-stop command and the control target, an outer loop control algorithm is processed to calculate active and reactive reference commands;

[0059] The active and reactive power reference instructions are sent to the valve control layer.

[0060] The pole control layer controls the single-pole operation, corresponding to N C-NPC subunits, and its main functions include: AC system voltage phase-locked control and dq conversion; realization of active type outer loop control and reactive type outer loop control; start-up and shutdown control of the pole; protection functions of the pole and neutral pole, emergency shutdown control, etc.; control and status monitoring of the pole DC circuit breaker and neutral pole DC circuit breaker, control and status monitoring of the pole AC access circuit breaker, etc.; control and status monitoring of converter valve cooling and auxiliary systems. The pole refers to the positive or negative pole.

[0061] The valve control layer is specifically used for:

[0062] Perform submodule-level protection function operations based on the electrical quantities and state quantities of the converter;

[0063] Based on the active and reactive reference instructions, an inner loop control algorithm is processed to calculate a three-phase voltage modulation wave;

[0064] Performing modulation based on the three-phase voltage modulation wave to obtain an IGBT trigger pulse;

[0065] The IGBT trigger pulse is sent to each C-NPC sub-unit through an optical fiber for triggering.

[0066] The valve control layer controls the sub-unit, and its main functions include: DC side voltage control; AC side current control; taking the sum of the inner loop current target value sent by the pole control layer and the additional inner loop current target value as the final inner loop current control target value, generating a voltage modulation wave, and obtaining a three-phase voltage modulation wave after DQ inverse transformation; DC capacitor midpoint potential control, generating an additional midpoint potential control voltage modulation wave; by superimposing the DQ inverse transformed three-phase voltage modulation wave with the additional midpoint potential control voltage modulation wave, the final three-phase voltage modulation wave is obtained, which is used to generate IGBT trigger pulses after modulation; C-NPC sub-unit command sending and upload status monitoring; C-NPC sub-unit redundancy control, master-slave screening and following, etc. Valve control redundancy control: When there are N sub-units in one phase, when individual sub-units fail, the redundant number can be automatically bypassed if it allows, and the equipment will continue to operate. Master-slave screening: When the pole control is a dual-system configuration, there is one master and one slave; the valve control layer is a single-system configuration, and the valve control receives commands from the pole control dual system in the communication, and only executes the commands sent by the pole control master system after master-slave screening.

[0067] The device-level protection function operations include: AC overvoltage protection, AC undervoltage protection, AC overcurrent protection, converter station DC overvoltage protection, DC undervoltage protection, DC overcurrent protection and DC pole bus differential protection.

[0068] The submodule protection function operations include: valve side AC overvoltage protection, AC undervoltage protection, overcurrent protection, DC overvoltage protection, DC undervoltage protection, DC overcurrent protection and midpoint overvoltage protection.

[0069] The hardware configuration of the control and protection device adopts a standardized board.

[0070] Embodiment 2:

[0071] A control and protection method for a C-NPC topology converter, comprising:

[0072] Step 1: The start / stop instruction and control target issued by the system dispatching end are received by the station control layer of the control and protection device and sent to the pole control layer of the control and protection device;

[0073] Step 2: Perform outer loop control algorithm processing and device-level protection function operation based on the start-stop command and the control target, and send the calculated active and reactive reference commands to the valve control layer of the control protection device;

[0074] Step 3: Based on the active and reactive reference instructions, inner loop control algorithm processing and submodule level protection function operation are performed, and the generated IGBT trigger pulse is sent to each C-NPC subunit.

[0075] In step 1, the start / stop instruction and the control target issued by the system dispatching end received by the station control layer of the control and protection device are sent to the pole control layer of the control and protection device, including:

[0076] Receive the start / stop instructions and control targets issued by the system dispatcher based on Ethernet;

[0077] Based on the start-stop instructions and control targets, the measurement and control functions of the switch and the switch opening and closing in the control station are operated, and the start-stop instructions and control targets are sent to the pole control layer.

[0078] In step 2, the outer loop control algorithm processing and the device-level protection function operation are performed based on the start-stop command and the control target, and the calculated active and reactive reference commands are sent to the valve control layer of the control protection device, including:

[0079] Execute the start and stop control of the positive or negative electrode and the device-level protection function operation based on the start and stop command and the control target;

[0080] Based on the start-stop command and the control target, an outer loop control algorithm is processed to calculate active and reactive reference commands;

[0081] The active and reactive power reference instructions are sent to the valve control layer.

[0082] The device-level protection function operations include: AC overvoltage protection, AC undervoltage protection, AC overcurrent protection, converter station DC overvoltage protection, DC undervoltage protection, DC overcurrent protection and DC pole bus differential protection.

[0083] In step 3, the inner loop control algorithm processing and submodule level protection function operation are performed based on the active and reactive reference instructions, and the generated IGBT trigger pulse is sent to each C-NPC subunit, including:

[0084] Perform submodule-level protection function operations based on the electrical quantities and state quantities of the converter;

[0085] Based on the active and reactive reference instructions, an inner loop control algorithm is processed to calculate a three-phase voltage modulation wave;

[0086] Performing modulation based on the three-phase voltage modulation wave to obtain an IGBT trigger pulse;

[0087] The IGBT trigger pulse is sent to each C-NPC sub-unit through an optical fiber for triggering.

[0088] The submodule protection function operations include: valve side AC overvoltage protection, AC undervoltage protection, overcurrent protection, DC overvoltage protection, DC undervoltage protection, DC overcurrent protection and midpoint overvoltage protection.

[0089] Embodiment 3:

[0090] The present invention is described in detail below by taking the information interaction between the control protection device and the C-NPC subunit as an example.

[0091] The control and protection device for flexible direct current in distribution network proposed in this embodiment is applied to C-NPC topology converter, and the control and protection device is respectively connected to the system dispatching end and several C-NPC subunits; the control and protection device and the subunits communicate through optical fiber.

[0092] The control and protection device adopts a layered structure, consisting of a station control layer, a pole control layer, and a valve control layer. Figure 2 shown.

[0093] The control and protection device adopts a dual configuration, including two sets of station control devices, A and B, and two sets of pole control devices, A and B, configured in duplicate for each pole. There is no cross-connection between the station control and pole control A\B systems. The pole control layer device receives the start and stop commands, control targets and other instructions issued by the dispatcher from the station control layer through optical fiber, and completes the outer loop control algorithm, device-level protection functions, etc. The valve control layer performs the inner loop control algorithm, submodule-level protection, redundant control, etc., and finally generates a PWM trigger pulse to send to the C-NPC subunit controller.

[0094] The station control device mainly realizes dual-station coordination, start-stop control, operation mode issuance, measurement and control functions, and logical interlocking; the pole control device mainly realizes positive / negative pole start-stop, active / reactive power control, AC / DC zone protection and other functions; the valve control device includes VBC1 and VBC2, which realize sub-unit equalization of voltage and current, pulse distribution, valve protection, redundancy and other functions.

[0095] At the beginning, the station control device A\B system receives the start and stop instructions, control targets, etc. issued by the dispatching layer through Ethernet. After receiving the instructions issued by the dispatching layer, the station control device completes the measurement and control functions such as the opening and closing of the knife switches and switches in the control station, and controls the start and stop instructions, control targets, etc. to be sent to the pole control layer A\B system of the two poles through optical fiber; the pole control layer A\B system of each pole executes the specific start and stop logic according to the received operating mode and start and stop instructions, performs outer loop control algorithm processing and device-level protection functions, and sends the calculated active and reactive reference instructions to the valve control device; after the valve control device performs master-slave screening, it performs inner loop control algorithm processing and sub-module-level protection functions according to the received outer loop control instructions, and finally generates a three-phase voltage modulation wave and an IGBT trigger pulse, which are sent to the sub-unit controller board of each C-NPC through optical fiber; after receiving the instructions, the C-NPC sub-unit control board controls the IGBT to trigger, and feeds back the sub-unit status through the uplink optical fiber.

[0096] At this point, the data interaction between the control and protection device and the C-NPC submodule is completed through a hierarchical control and protection device technology.

[0097] Since the C-NPC control and protection device has a layered structure, consisting of a station control layer, a pole control layer, and a valve control layer, its functions are clear and its flexibility is high. When the device is running, only the pole control layer needs to send an outer loop command to the valve control layer. The control algorithm and protection function of each C-NPC submodule are completely completed by an independent valve control layer board. There is no correlation between the modules, so it has high reliability, strong independence, and low requirements for real-time control and protection. In addition, the hardware configuration of the entire C-NPC control and protection system is a standardized board, which is conducive to subsequent modularization, serialization design and production. The workload of on-site construction and debugging is small, and it has an advantage in comprehensive cost compared to traditional flexible direct current control and protection systems, with a small footprint and low cost.

[0098] Those skilled in the art will appreciate that embodiments of the present invention may be provided as methods, systems, or computer program products. Therefore, the present invention may take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0099] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0100] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0101] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0102] The above are merely embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention are included in the scope of the claims of the present invention to be approved.

Claims

1. A control and protection device for a C-NPC topology converter, characterized in that: The control and protection device is connected to the system dispatching end and several C-NPC subunits through Ethernet and optical fiber respectively; the control and protection device includes: a duplicated station control layer, a duplicated pole control layer and a valve control layer; The station control layer is used to send the start and stop instructions and control targets sent by the system dispatching end to the pole control layer; The pole control layer is used to perform outer loop control algorithm processing and device-level protection function operation based on the start-stop command and control target, and send the calculated active and reactive reference commands to the valve control layer; The valve control layer is used to perform inner loop control algorithm processing and submodule level protection function operation based on the active and reactive reference instructions, and send the generated IGBT trigger pulse to each C-NPC subunit.

2. The device according to claim 1, characterized in that: The station control layer is specifically used for: Receive the start / stop instructions and control targets issued by the system dispatcher based on Ethernet; Based on the start-stop instructions and control targets, the measurement and control functions of the switch and the switch opening and closing in the control station are operated, and the start-stop instructions and control targets are sent to the pole control layer.

3. The device according to claim 1, characterized in that: The pole control layer is specifically used for: Execute the start and stop control of the positive or negative electrode and the device-level protection function operation based on the start and stop command and the control target; Based on the start-stop command and the control target, an outer loop control algorithm is processed to calculate active and reactive reference commands; The active and reactive power reference instructions are sent to the valve control layer.

4. The device according to claim 1, characterized in that: The valve control layer is specifically used for: Perform submodule-level protection function operations based on the electrical quantities and state quantities of the converter; Based on the active and reactive reference instructions, an inner loop control algorithm is processed to calculate a three-phase voltage modulation wave; Performing modulation based on the three-phase voltage modulation wave to obtain an IGBT trigger pulse; The IGBT trigger pulse is sent to each C-NPC sub-unit through an optical fiber for triggering.

5. The device according to claim 3, characterized in that: The device-level protection function operations include: AC overvoltage protection, AC undervoltage protection, AC overcurrent protection, converter station DC overvoltage protection, DC undervoltage protection, DC overcurrent protection and DC pole bus differential protection.

6. The device according to claim 4, characterized in that: The submodule protection function operations include: valve side AC overvoltage protection, AC undervoltage protection, overcurrent protection, DC overvoltage protection, DC undervoltage protection, DC overcurrent protection and midpoint overvoltage protection.

7. The device according to claim 1, characterized in that: The hardware configuration of the control and protection device adopts a standardized board.

8. A control and protection method for a C-NPC topology converter, characterized in that: include: The start / stop command and control target issued by the system dispatching end received by the station control layer of the control protection device are sent to the pole control layer of the control protection device; Based on the start-stop command and the control target, an outer loop control algorithm is processed and a device-level protection function is operated, and the calculated active and reactive reference commands are sent to the valve control layer of the control protection device; Based on the active and reactive reference instructions, the inner loop control algorithm processing and the sub-module level protection function operation are performed, and the generated IGBT trigger pulse is sent to each C-NPC sub-unit.

9. The method according to claim 8, characterized in that: The station control layer based on the control and protection device receives the start and stop instructions and control targets issued by the system dispatching end and sends them to the pole control layer of the control and protection device, including: Receive the start / stop instructions and control targets issued by the system dispatcher based on Ethernet; Based on the start-stop instructions and control targets, the measurement and control functions of the switch and the switch opening and closing in the control station are operated, and the start-stop instructions and control targets are sent to the pole control layer.

10. The method according to claim 8, characterized in that: The outer loop control algorithm processing and device-level protection function operation are performed based on the start-stop command and the control target, and the calculated active and reactive reference commands are sent to the valve control layer of the control protection device, including: Execute the start and stop control of the positive or negative electrode and the device-level protection function operation based on the start and stop command and the control target; Based on the start-stop command and the control target, an outer loop control algorithm is processed to calculate active and reactive reference commands; The active and reactive power reference instructions are sent to the valve control layer.

11. The method according to claim 8, characterized in that: The inner loop control algorithm processing and submodule level protection function operation are performed based on the active and reactive reference instructions, and the generated IGBT trigger pulse is sent to each C-NPC subunit, including: Perform submodule-level protection function operations based on the electrical quantities and state quantities of the converter; Based on the active and reactive reference instructions, an inner loop control algorithm is processed to calculate a three-phase voltage modulation wave; Performing modulation based on the three-phase voltage modulation wave to obtain an IGBT trigger pulse; The IGBT trigger pulse is sent to each C-NPC sub-unit through an optical fiber for triggering.

12. The method according to claim 10, characterized in that: The device-level protection function operations include: AC overvoltage protection, AC undervoltage protection, AC overcurrent protection, converter station DC overvoltage protection, DC undervoltage protection, DC overcurrent protection and DC pole bus differential protection.

13. The method according to claim 11, characterized in that: The submodule protection function operations include: valve side AC overvoltage protection, AC undervoltage protection, overcurrent protection, DC overvoltage protection, DC undervoltage protection, DC overcurrent protection and midpoint overvoltage protection.

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