A method and system for monitoring voltage of thyristor valve section of converter

Abstract

A method and system for monitoring the thyristor valve section voltage of a converter determines the monitoring interval corresponding to the voltage curve of the single valve under test within a power frequency cycle based on the state of the single valve under test in the converter; and calculates the valve section voltage of the single valve under test within each monitoring interval. Dividing the power frequency cycle of the single valve into monitoring intervals and testing the single valve voltage within the monitoring interval can address the blindness of planned testing. By monitoring voltage within different set intervals, it can also address potential faults caused by inaccurate monitoring due to the voltage and current stresses on the valve section during planned maintenance being lower than those under actual operating conditions.

Description

Technical Field

[0001] The present invention relates to the field of thyristor voltage monitoring, and in particular to a method and system for monitoring the voltage of a thyristor valve section of a converter. Background Art

[0002] Thyristor-based HVDC transmission systems, with their mature technology, low losses, and low costs, offer significant advantages for long-distance, high-capacity power transmission and grid interconnection. Due to my country's uneven energy distribution and wide disparity in economic development, HVDC technology plays a crucial role in the country's "West-to-East Power Transmission and National Networking" strategy. In recent years, numerous HVDC transmission lines have been connected to the grid and put into operation. With the trend of economic development and energy restructuring, the number of DC transmission lines is expected to increase significantly in the future.

[0003] Due to the characteristics of thyristor converters, both the rectifier and inverter undergo commutation during HVDC transmission. Since the inverter's trigger angle α must be greater than 90°, commutation failure is prone to occur during the inverter's commutation process. Therefore, during the actual operation of thyristor converter valves, accurately monitoring the valve section voltage during a power frequency cycle helps improve valve reliability. During actual operation, equipment in the valve tower can be damaged by factors such as overvoltage or overcurrent, causing the valve voltage to deviate from the ideal curve, ultimately reducing valve reliability. Current valve condition monitoring systems detect the establishment of positive and negative thyristor voltages, focusing on providing signals for triggering the thyristors. They lack real-time online monitoring of the valve section voltage, particularly the commutation voltage during the valve's shutdown process. This commutation process can severely impact the efficient and stable operation of the converter valve. The reliability of the converter valve system determines the reliability of the entire HVDC transmission system, which in turn impacts the overall power transmission efficiency. Summary of the Invention

[0004] In order to solve the problem in the prior art of lacking voltage monitoring of a single thyristor valve in a converter valve during the commutation process, the present invention provides a method and system for monitoring the voltage of a thyristor valve section of a converter.

[0005] The technical solution provided by the present invention is:

[0006] A method for monitoring the voltage of a thyristor valve section of a converter, comprising:

[0007] According to the state of the single valve to be tested in the converter, the monitoring interval corresponding to the voltage curve of the single valve to be tested within one power frequency cycle is determined;

[0008] Calculate the valve section voltage of the single valve to be tested in each monitoring interval.

[0009] Preferably, determining the monitoring interval corresponding to the voltage curve of the single valve to be tested within a power frequency cycle according to the state of the single valve to be tested in the converter includes:

[0010] Determine the state interval of the single valve to be tested in the converter according to the preset electrical angle of the single valve to be tested, wherein the state interval includes an on state interval and an off state interval;

[0011] When the single valve to be tested is in the conduction state interval, this interval is used as a monitoring interval;

[0012] When the single valve to be tested is in the off state interval, the off state interval is optimized according to the working state of the converter.

[0013] Preferably, the working state includes a commutation state and a non-commutation state.

[0014] The optimizing the shutdown state interval according to the working state of the converter includes:

[0015] The moment when two single valves located on different lines except the line where the single valve to be tested is located are simultaneously in the on state is used as the starting moment of the off state interval, and the converter is controlled to switch between the two working states;

[0016] The voltage curve corresponding to the time from the start of the shutdown state interval to the moment before the converter switches between the two working states is a monitoring interval; the switching moment of the converter between the two working states is the starting moment of triggering the next monitoring interval, until all single valves in the converter except the single valve to be tested are triggered to turn on and all phase lines in the converter have passed the commutation state.

[0017] Preferably, the calculating of the valve section voltage of the single valve to be tested in each monitoring interval includes:

[0018] When the single valve to be tested is in the on state, the valve section voltage of the single valve to be tested is 0;

[0019] When the single valve to be tested is in the off state, the valve section voltage of the single valve to be tested is calculated according to the voltage between the circuits where the single valve to be tested is located.

[0020] Preferably, the step of calculating the valve section voltage of the single valve to be tested based on the voltage between the circuits where the single valve is connected includes:

[0021] Determine the working state of the converter, wherein the working state includes a commutation process and a non-commutation process;

[0022] If the converter is in a non-commutation state, the valve section voltage of the single valve to be tested is the voltage difference between the circuits where the single valve is turned on;

[0023] If the converter is in a commutation state, the valve section voltage of the single valve to be tested is the average value of the sum of the voltages between the circuits where the single valves are turned on.

[0024] Preferably, if the converter is in a non-commutation state, the valve section voltage of the single valve to be tested is the voltage difference between the circuits where the single valve is turned on, including:

[0025] When the first single valve in the B-phase circuit of the converter is connected to the first single valve in the C-phase circuit, the voltage difference between the A-phase circuit and the B-phase circuit of the single valve to be tested is determined;

[0026] When the first single valve in the B-phase circuit of the converter is connected to the second single valve in the A-phase circuit, the voltage difference between the A-phase circuit and the B-phase circuit of the single valve to be tested is determined;

[0027] When the second single valve in the A-phase circuit of the converter is connected to the second single valve in the C-phase circuit, the voltage difference between the A-phase circuit and the C-phase circuit of the single valve to be tested is determined;

[0028] When the second single valve in the C-phase circuit of the converter is connected to the second single valve in the B-phase circuit, the voltage difference between the A-phase circuit and the C-phase circuit of the single valve to be tested is determined.

[0029] Preferably, when the single valve to be tested is in a phase-changing state, the single valve voltage is determined by the following formula:

[0030]

[0031] in, is the valve section voltage of the single valve to be tested, u ab is the voltage difference between phase A and phase B; u ac is the voltage difference between phase A and phase C.

[0032] Preferably, if the converter is in a commutation state, the valve section voltage of the single valve to be tested is the average value of the sum of the voltages between the circuits where the single valves are turned on, including:

[0033] When the second single valve in the A-phase circuit of the converter, the first single valve in the B-phase circuit, and the first single valve in the C-phase circuit are turned on, the voltage of the single valve to be tested is determined by the average value of the voltage difference between the A-phase and B-phase lines and the voltage difference between the B-phase and C-phase lines;

[0034] When the second single valve in the A-phase circuit of the converter, the first single valve in the B-phase circuit, and the second single valve in the C-phase circuit are turned on, the voltage of the single valve to be tested is determined by the average value of the voltage difference between the A-phase and B-phase lines and the voltage difference between the A-phase and C-phase lines;

[0035] When the second single valve in the A-phase circuit, the second single valve in the B-phase circuit and the second single valve in the C-phase circuit of the converter are turned on, the voltage of the single valve to be tested is determined by the average value of the A-phase B-phase line voltage difference and the B-phase C-phase line voltage difference.

[0036] Preferably, the voltage of the single valve to be tested when the converter is in a commutation state is determined by the following formula:

[0037]

[0038] in, is the valve section voltage of the single valve to be tested, u ab is the voltage difference between phase A and phase B; u ac is the voltage difference between phase A and phase C; u cb is the voltage difference between phase C and phase B; u bc is the voltage difference between phase B and phase C.

[0039] A thyristor valve section voltage monitoring system for a converter, the system comprising:

[0040] Monitoring interval confirmation module: determines the monitoring interval corresponding to the voltage curve of the single valve to be tested within a power frequency cycle according to the status of the single valve to be tested in the converter;

[0041] Voltage calculation module: calculates the valve section voltage of the single valve to be tested in each monitoring interval.

[0042] Preferably, the monitoring interval confirmation module includes:

[0043] Logical division submodule: determines the state interval of the single valve to be tested in the converter according to the preset electrical angle of the single valve to be tested, wherein the state interval includes an on state interval and an off state interval;

[0044] Judgment submodule: when the single valve to be tested is in the on-state interval, the interval is used as a monitoring interval; when the single valve to be tested is in the off-state interval, the off-state interval is optimized according to the working state of the converter;

[0045] The working state of the converter includes a commutation state and a non-commutation state.

[0046] Preferably, the judgment submodule includes:

[0047] The first optimization unit controls the converter to switch between the two working states, taking the moment when two single valves located on different lines other than the line where the single valve to be tested is located at the same time in the on state as the starting moment of the off state interval;

[0048] Second optimization unit: The voltage curve corresponding to the time from the start of the shutdown state interval to the moment before the converter switches between the two working states is a monitoring interval; the switching moment of the converter between the two working states is the starting moment of triggering the next monitoring interval, until all single valves except the single valve to be tested in the converter are triggered to turn on and all phase lines in the converter have passed the commutation state.

[0049] Compared with the existing technology, the present invention has the following advantages: This solution determines the monitoring interval corresponding to the voltage curve of the single valve under test within a power frequency cycle based on the state of the single valve under test in the converter; and calculates the valve section voltage of the single valve under test within each monitoring interval. Dividing the power frequency cycle of the single valve into monitoring intervals and testing the single valve voltage within the monitoring interval can solve the blindness of planned testing. By monitoring voltage within different set intervals, it can also solve the potential fault problem of inaccurate monitoring caused by the voltage and current stresses on the valve section during planned maintenance being lower than those under actual operating conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 This is a flow chart of a method for monitoring voltage of a single valve of a converter according to the present invention;

[0051] Figure 2 This is a wiring diagram of a single valve in the converter of the present invention;

[0052] Figure 3 This is a periodic waveform diagram of a single valve with the highest conduction priority according to the present invention. DETAILED DESCRIPTION

[0053] In order to better understand the present invention, the present invention is further described below with reference to the accompanying drawings and examples.

[0054] Example 1:

[0055] A method for monitoring voltage of a single valve of a converter, a flow chart of the method, as shown in FIG. Figure 1 shown.

[0056] S1: According to the state of the single valve to be tested in the converter, determine the monitoring interval corresponding to the voltage curve of the single valve to be tested within a power frequency cycle.

[0057] HVDC transmission systems utilize grid-commutated technology, with a six-pulse converter composed of semi-controlled thyristors as the basic commutation unit. In this project, the converter operates as a valve tower within a valve hall. During actual operation, each individual valve acts as a unit, and the entire valve is simultaneously in either the on or off state. Failure or maintenance of any individual valve will cause the entire converter to shut down, reducing the reliability of the converter valve.

[0058] Whether it is a rectifier or an inverter, there is a commutation process during the operation of the converter. During the commutation process, the voltage at both ends of the valve will have commutation teeth, and commutation failure may occur during the commutation process. The probability of commutation failure in the inverter is relatively high.

[0059] Determine the state interval of the single valve to be tested in the converter according to the preset electrical angle of the single valve to be tested, wherein the state interval includes an on state interval and an off state interval;

[0060] When the single valve to be tested is in the conduction state interval, this interval is used as a monitoring interval;

[0061] When the single valve to be tested is in the off state interval, the off state interval is optimized according to the working state of the converter;

[0062] The working state of the converter includes a commutation state and a non-commutation state.

[0063] Figure 2 The figure shows a single valve wiring diagram. In actual engineering, the 12-pulse converter unit is also composed of two 6-pulse converter units connected in series. In the figure, the six thyristors V1, V2, V3, V4, V5 and V6 are triggered and turned on in sequence. At any time, at least two single valves are turned on at the same time. During the commutation period, three single valves will be in the on state at the same time. In one power frequency cycle, the electrical angle of the single valve on is 120°+μ, and the electrical angle of the single valve off is 240°-μ, where μ is the commutation angle of the thyristor. Figure 3 The voltage waveform diagram of the single valve 1 within the cycle shown divides the state of the single valve 1 during the off period into 7 different intervals. The off state of the single valve 1 is uniformly divided into interval 8, which is the conduction interval. At this time, the valve section voltage of the single valve to be tested is 0.

[0064] The shutoff interval is optimized by taking the time when two single valves on different lines other than the line where the single valve to be tested is simultaneously in the on state as the start time of the shutoff state interval, and controlling the converter to switch between the two working states;

[0065] The voltage curve corresponding to the time from the start of the shutdown state interval to the moment before the converter switches between the two working states is a monitoring interval; the switching moment of the converter between the two working states is the starting moment of triggering the next monitoring interval, until all single valves in the converter except the single valve to be tested are triggered to turn on and all phase lines in the converter have passed the commutation state.

[0066] Based on the above interval optimization, a total of 7 intervals are obtained: intervals 1-7 are 7 different states during the closing period of single valve 1. Among them, the electrical angle of intervals 1, 3, 5 and 7 is 60°-μ, and the electrical angle of intervals 2, 4 and 6 is the commutation angle μ. The specific single valve that is turned on in each interval and the voltage expression across the valve in this state are analyzed as follows:

[0067] S2: Calculate the valve section voltage of the single valve to be tested in each monitoring interval.

[0068] Interval 8 contains five different combinations of single valve 1 conduction:

[0069] (1) V1, V5 and V6 are turned on, and V5 switches phase to V1;

[0070] (2) V1 and V6 are turned on;

[0071] (3) V1, V2 and V6 are turned on, and V6 switches phase to V2;

[0072] (4) V1 and V2 are turned on;

[0073] (5) V1, V2 and V3 are turned on, and V1 switches phase to V3;

[0074] During the conduction period of a single valve, the voltage across the valve is 0, that is,

[0075] In interval ①: V2 and V3 are conducting, the voltage across the valve

[0076] In interval ②: V2, V3 and V4 are on at the same time, V2 switches to V4, and the voltage across the valve

[0077] In interval ③: V3 and V4 are conducting, the voltage across the valve

[0078] In interval ④: V3, V4 and V5 are on at the same time, V3 switches to V5, and the voltage across the valve

[0079] In interval ⑤: V4 and V5 are conducting, the voltage across the valve

[0080] In interval ⑥: V4, V5 and V6 are on at the same time, V4 switches to V6, and the voltage across the valve

[0081] In interval ⑦: V5 and V6 are turned on, the voltage across the valve

[0082] In actual HVDC transmission projects, a single valve consists of n (the number of valve segments used in different projects varies) valve segments connected in series. Therefore, the voltage borne by each valve segment is 1 / n of the single valve voltage. The thyristor converter valve segment voltage online monitoring system proposed in the present invention can monitor the valve segment voltage in real time and perform segmented monitoring, dividing the valve segment voltage within a power frequency cycle into 8 intervals. It can accurately compare and analyze the real-time monitored voltage value with the ideal threshold in real time, timely monitor converter valve faults, and formulate maintenance plans in a timely manner, reducing the risk of frequent maintenance of HVDC transmission thyristor converter valves.

[0083] The online monitoring system for the valve terminal voltage of the thyristor commutator valve proposed in the present invention can solve the blindness of planned maintenance and the potential fault problem of inaccurate monitoring caused by the voltage and current stresses on the valve section during planned maintenance being lower than the actual operating conditions.

[0084] The thyristor commutator valve segment voltage online monitoring system proposed in the present invention is used to monitor the voltage across the thyristor valve segment in real time, determine whether the valve segment voltage is within the normal operating range, and then determine whether one or more valve segments are in a faulty state, so as to detect the fault in time and replace it, thereby improving the reliability of the commutator valve.

[0085] In this embodiment, the valve section voltage of a single valve in the converter can also be calculated based on the ideal voltage calculation of each phase line in the converter, so that the actual detection value can be compared with the ideal threshold in real time, so that the life of the single valve in the converter can be predicted by comparing the changing trend of the actual value with the ideal value.

[0086] Example 2:

[0087] This embodiment provides a thyristor valve section voltage monitoring system for a converter, including:

[0088] Monitoring interval confirmation module: determines the monitoring interval corresponding to the voltage curve of the single valve to be tested within a power frequency cycle according to the status of the single valve to be tested in the converter;

[0089] Voltage calculation module: calculates the valve section voltage of the single valve to be tested in each monitoring interval.

[0090] The monitoring interval confirmation module includes:

[0091] Logical division submodule: determines the state interval of the single valve to be tested in the converter according to the preset electrical angle of the single valve to be tested, wherein the state interval includes an on state interval and an off state interval;

[0092] Judgment submodule: when the single valve to be tested is in the on-state interval, the interval is used as a monitoring interval; when the single valve to be tested is in the off-state interval, the off-state interval is optimized according to the working state of the converter;

[0093] The working state of the converter includes a commutation state and a non-commutation state.

[0094] The judgment submodule includes:

[0095] The first optimization unit controls the converter to switch between the two working states, taking the moment when two single valves located on different lines other than the line where the single valve to be tested is located at the same time in the on state as the starting moment of the off state interval;

[0096] Second optimization unit: The voltage curve corresponding to the time from the start of the shutdown state interval to the moment before the converter switches between the two working states is a monitoring interval; the switching moment of the converter between the two working states is the starting moment of triggering the next monitoring interval, until all single valves except the single valve to be tested in the converter are triggered to turn on and all phase lines in the converter have passed the commutation state.

[0097] The voltage calculation module includes:

[0098] Conductivity state calculation submodule: when the single valve to be tested is in the conduction state, the valve section voltage of the single valve to be tested is 0;

[0099] Off-state calculation submodule: When the single valve to be tested is in the off state, the valve section voltage of the single valve to be tested is calculated based on the voltage between the lines where the single valve to be conducted is located.

[0100] The conduction state calculation submodule includes:

[0101] A judging unit is configured to judge the working state of the converter, wherein the working state includes a commutation process and a non-commutation process;

[0102] The first voltage calculation unit: if the converter is in a non-commutation state, the valve section voltage of the single valve to be tested is the voltage difference between the circuits where the single valve is turned on;

[0103] The second voltage calculation unit: if the converter is in a commutation state, the valve section voltage of the single valve to be tested is the average value of the sum of the voltages between the circuits where the single valves are turned on.

[0104] The first voltage calculation unit includes:

[0105] The first pressure difference calculation subunit: when the first single valve in the B-phase circuit of the converter is connected to the first single valve in the C-phase circuit, the voltage difference between the A-phase circuit and the B-phase circuit of the single valve to be tested is determined;

[0106] The second pressure difference calculation subunit: when the first single valve in the B-phase circuit of the converter and the second single valve in the A-phase circuit are connected, the voltage difference between the A-phase circuit and the B-phase circuit of the single valve to be tested is determined;

[0107] The third pressure difference calculation subunit: when the second single valve in the A-phase circuit of the converter and the second single valve in the C-phase circuit are connected, the voltage difference between the A-phase circuit and the C-phase circuit of the single valve to be tested is determined;

[0108] The fourth pressure difference calculation subunit: The first voltage calculation unit calculates the valve section voltage of the single valve to be tested by the following formula:

[0109]

[0110] in, is the valve section voltage of the single valve to be tested, u ab is the voltage difference between phase A and phase B; u ac is the voltage difference between phase A and phase C.

[0111] The second voltage calculation unit includes:

[0112] First average value calculation subunit: when the second single valve in the A-phase circuit of the converter, the first single valve in the B-phase circuit, and the first single valve in the C-phase circuit are turned on, the voltage of the single valve to be tested is determined by the average value of the voltage difference between the A-phase and B-phase lines and the voltage difference between the B-phase and C-phase lines;

[0113] Second average value calculation subunit: when the second single valve in the A-phase circuit of the converter, the first single valve in the B-phase circuit, and the second single valve in the C-phase circuit are turned on, the voltage of the single valve to be tested is determined by the average value of the A-phase and B-phase line voltage difference and the A-phase and C-phase line voltage difference;

[0114] The third average value calculation subunit: when the second single valve in the A-phase circuit of the converter, the second single valve in the B-phase circuit and the second single valve in the C-phase circuit are turned on, the voltage of the single valve to be tested is determined by the average value of the A-phase B-phase line voltage difference and the B-phase C-phase line voltage difference.

[0115] The second voltage calculation unit calculates the terminal voltage of the single valve to be tested by the following formula:

[0116]

[0117] in, is the valve section voltage of the single valve to be tested, u ab is the voltage difference between phase A and phase B; u ac is the voltage difference between phase A and phase C; u cb is the voltage difference between phase C and phase B; u bcis the voltage difference between phase B and phase C.

[0118] Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0119] Those skilled in the art will appreciate that the embodiments of the present application can be provided as methods, systems, or computer program products. Therefore, the present application can adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment in combination with software and hardware. Moreover, the present application can adopt the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to magnetic disk storage, CD-ROM, optical storage, etc.) that contain computer-usable program code.

[0120] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes 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 steps in the process. 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.

[0121] These computer program instructions may also be stored in a computer readable memory that can direct a computer or other programmable data processing device to work 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 The function specified in one or more boxes.

[0122] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operational steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing the instructions executed on the computer or other programmable device for implementing the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0123] 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 method for monitoring the voltage of a thyristor valve section of a converter, characterized in that: include: According to the state of the single valve to be tested in the converter, the monitoring interval corresponding to the voltage curve of the single valve to be tested within a power frequency cycle is determined, including: Determine the state interval of the single valve to be tested in the converter according to the preset electrical angle of the single valve to be tested, wherein the state interval includes an on state interval and an off state interval; When the single valve to be tested is in the conduction state interval, this interval is used as a monitoring interval; When the single valve to be tested is in the off state interval, the off state interval is optimized according to the working state of the converter, including: The working state includes a commutation state and a non-commutation state; The moment when two single valves located on different lines except the line where the single valve to be tested is located are simultaneously in the on state is used as the starting moment of the off state interval, and the converter is controlled to switch between the two working states; The voltage curve corresponding to the time from the start of the shutdown state interval to the moment before the converter switches between the two working states is a monitoring interval; the switching moment of the converter between the two working states is the starting moment of triggering the next monitoring interval until all single valves in the converter except the single valve to be tested are triggered to conduct and all phase lines in the converter have passed the phase change state; Calculate the valve section voltage of the single valve to be tested in each monitoring interval, including: When the single valve to be tested is in the on state, the valve section voltage of the single valve to be tested is 0; When the single valve to be tested is in the off state, the valve section voltage of the single valve to be tested is calculated based on the voltage between the lines where the single valve to be tested is located, including: Determine the working state of the converter, wherein the working state includes a commutation state and a non-commutation state; If the converter is in a non-commutation state, the valve section voltage of the single valve to be tested is the voltage difference between the circuits where the single valve is turned on; If the converter is in a commutation state, the valve section voltage of the single valve to be tested is the average value of the sum of the voltages between the circuits where the single valves are turned on.

2. The method according to claim 1, wherein If the converter is in a non-commutation state, the valve section voltage of the single valve to be tested is the voltage difference between the circuits where the single valve is turned on, including: When the first single valve in the B-phase circuit of the converter is connected to the first single valve in the C-phase circuit, the voltage difference between the A-phase circuit and the B-phase circuit of the single valve to be tested is determined; When the first single valve in the B-phase circuit of the converter is connected to the second single valve in the A-phase circuit, the voltage difference between the A-phase circuit and the B-phase circuit of the single valve to be tested is determined; When the second single valve in the A-phase circuit of the converter is connected to the second single valve in the C-phase circuit, the voltage difference between the A-phase circuit and the C-phase circuit of the single valve to be tested is determined; When the second single valve in the C-phase circuit of the converter is connected to the second single valve in the B-phase circuit, the voltage difference between the A-phase circuit and the C-phase circuit of the single valve to be tested is determined.

3. The method according to claim 2, wherein When the single valve to be tested is in the commutation state, the single valve voltage is determined by the following formula: in, is the valve section voltage of the single valve to be tested, u ab is the voltage difference between phase A and phase B; u ac is the voltage difference between phase A and phase C.

4. The method according to claim 1, wherein If the converter is in a commutation state, the valve section voltage of the single valve to be tested is the average value of the sum of the voltages between the circuits where the single valves are turned on, including: When the second single valve in the A-phase circuit of the converter, the first single valve in the B-phase circuit, and the first single valve in the C-phase circuit are turned on, the voltage of the single valve to be tested is determined by the average value of the voltage difference between the A-phase and B-phase lines and the voltage difference between the B-phase and C-phase lines; When the second single valve in the A-phase circuit of the converter, the first single valve in the B-phase circuit, and the second single valve in the C-phase circuit are turned on, the voltage of the single valve to be tested is determined by the average value of the voltage difference between the A-phase and B-phase lines and the voltage difference between the A-phase and C-phase lines; When the second single valve in the A-phase circuit, the second single valve in the B-phase circuit and the second single valve in the C-phase circuit of the converter are turned on, the voltage of the single valve to be tested is determined by the average value of the A-phase B-phase line voltage difference and the B-phase C-phase line voltage difference.

5. The method according to claim 4, wherein The voltage of the single valve to be tested when the converter is in the commutation state is determined by the following formula: in, is the valve section voltage of the single valve to be tested, u ab is the voltage difference between phase A and phase B; u ac is the voltage difference between phase A and phase C; u cb is the voltage difference between phase C and phase B; u bc is the voltage difference between phase B and phase C.

6. A thyristor valve section voltage monitoring system for a converter, characterized in that: The system comprises: Monitoring interval confirmation module: Based on the status of the single valve to be tested in the converter, the module determines the monitoring interval corresponding to the voltage curve of the single valve to be tested within a power frequency cycle, including: Logical division submodule: determines the state interval of the single valve to be tested in the converter according to the preset electrical angle of the single valve to be tested, wherein the state interval includes an on state interval and an off state interval; Judgment submodule: When the single valve to be tested is in the on-state interval, the interval is used as a monitoring interval; when the single valve to be tested is in the off-state interval, the off-state interval is optimized according to the working state of the converter, including: The first optimization unit controls the converter to switch between the two working states, taking the moment when two single valves located on different lines other than the line where the single valve to be tested is located at the same time in the on state as the starting moment of the off state interval; Second optimization unit: The voltage curve corresponding to the time from the start of the shutdown state interval to the moment before the converter switches between the two working states is a monitoring interval; the switching moment of the converter between the two working states is the starting moment of triggering the next monitoring interval until all single valves in the converter except the single valve to be tested are triggered to conduct and all phase lines in the converter have passed the phase change state; The working state of the converter includes a commutation state and a non-commutation state; Voltage calculation module: calculates the valve section voltage of the single valve to be tested in each monitoring interval.

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