Method and system for preventing successive commutation failures in multi-infeed DC transmission systems

Abstract

The present invention discloses a method and system for preventing successive commutation failures in a multi-infeed DC transmission system. By taking into account the reactive power and harmonic interaction of the multi-infeed DC transmission system, the valve group at the receiving end of the faulty DC transmission line is triggered with a lag based on the reactive power influence of each faulty DC transmission line, and the valve group at the receiving end of the healthy DC transmission line is triggered in advance based on the harmonic distortion reference index of each healthy DC transmission line, thereby preventing successive commutation failures. The control method of the present invention is simple to implement and can be applied to a multi-infeed DC transmission system, effectively preventing successive commutation failures in the healthy DC transmission lines in the multi-infeed DC transmission system, and improving the system's stable operation capability and power transmission level.

Description

Technical Field

[0001] The invention relates to the technical field of high voltage direct current transmission, and in particular to a method and system for preventing successive commutation failures in multi-input direct current transmission. Background Art

[0002] Line Commutated Converter based High Voltage Direct Current (LCC-HVDC) is widely used in long-distance, large-capacity power transmission. Currently, there are multiple DC transmission systems that are closely connected to the same AC grid, namely multi-infeed high voltage direct current (MIDC) systems. Figure 1 The inverter side structure diagram of the multi-infeed DC transmission system is shown in Figure 1. The inverter side of the multi-infeed DC transmission system includes the inverter station converter, transformer, AC filter, receiving end AC system, and tie line impedance. The AC systems of each receiving end in the multi-infeed DC transmission system are connected through the tie line impedance, and the fault grounding impedance is set at the near end of the AC bus to simulate the occurrence of a fault.

[0003] Due to the interaction between the DC lines, there are more complex commutation failure (CF) phenomena in MIDC systems. In particular, if a local commutation failure (LCF) occurs on the faulty DC transmission line and a commutation failure occurs on the remote healthy DC transmission line, this phenomenon with a transfer nature is called successive commutation failure (SCF). Successive commutation failure may cause power outages and threaten the safe and stable operation of the power system. Therefore, considering the dynamic interaction between multiple DC lines, it is necessary to study the defense method of successive commutation failure in multi-infeed DC transmission systems.

[0004] Existing commutation failure prevention methods can be mainly divided into three categories: solutions based on converter topology improvement, solutions based on reactive power compensation devices, and solutions based on controller optimization. The solution based on converter topology improvement can effectively reduce the risk of commutation failure, but the LCC-HVDC engineering transformation is relatively complex. The solution based on reactive power compensation devices can effectively support the AC bus voltage at the receiving end, but its response speed is usually more than tens of milliseconds, which limits the prevention effect of successive commutation failures. Regarding the controller optimization scheme, existing literature (Li Chenghao, Tan Yangchen, Xiong Yongxin, Zhan Jin, Yao Wei, Ai Xiaomeng, Rao Yufei, Wen Jinyu. Coordinated control for preventing commutation failures in ultra-high voltage DC multi-infeed systems [J]. Power System Technology, 2019, 43(10): 3532-3542.) takes into account the influence of the parameters of the predictive control module (Commutation failure prevention, CFPREV) on the commutation process of adjacent sound DC transmission lines, and thus proposes a coordinated control strategy for preventing commutation failures. However, the degree of reactive power influence of each DC system is not comprehensively considered, and the influence of harmonics is not taken into account. Therefore, the effectiveness of preventing commutation failures still needs to be further improved. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a method and system for preventing successive commutation failures in a multi-infeed DC transmission system in view of the shortcomings of the prior art, so as to improve the prevention effect of successive commutation failures, thereby improving the stable operation capability and power transmission level of the multi-infeed DC transmission system.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is: a method for preventing successive commutation failures in a multi-infeed DC transmission system, which comprises the following steps: when a local commutation failure occurs in a faulty DC transmission line of the multi-infeed DC transmission system, based on the reactive power influence degree of each faulty DC transmission line, the receiving-end valve group of the faulty DC transmission line is triggered with a delay; based on the harmonic distortion reference index of each sound DC transmission line, the receiving-end valve group of the sound DC transmission line is triggered in advance.

[0007] The present invention takes into account the interactive influence of reactive power and harmonics of a multi-infeed DC transmission system, performs delayed triggering of a receiving-end valve group of a faulty DC transmission line based on the reactive influence degree of each faulty DC transmission line, and performs early triggering of a receiving-end valve group of a sound DC transmission line based on a harmonic distortion reference index of each sound DC transmission line, thereby effectively avoiding successive commutation failures of sound DC transmission lines in a multi-infeed DC transmission system and improving the system's stable operation capability and power transmission level.

[0008] In the present invention, based on the reactive power influence degree of each faulty DC transmission line, the specific implementation process of delaying triggering the valve group at the receiving end of the faulty DC transmission line includes:

[0009] 1) Obtain the high-level flag Flag_LCF of the local commutation failure of the faulty DC transmission line f , set the high level flag Flag_LCF f After extending the first setting time, the low level flag Flag_F is obtained through the NOT gate f The three-phase AC voltage of the faulty DC transmission line is input into the first prediction control module CFPREV, and the first prediction control module CFPREV outputs an angle α CFPf Multiply by Flag_F f , get the first prediction control module CFPREV correction angle α′ CFPf , where the subscript f represents the variable of the f-th fault DC transmission line;

[0010] 2) Calculate the DC reactive power impact index RPII of the f-th fault DC transmission line f : where δ self_f is the reactive power consumption ratio of the fth faulty DC transmission line in the multi-infeed DC transmission system, δ inter_f is the measure of the impact of the restoration of the f-th fault DC transmission line on other DC lines, δ AC_f is the AC grid support capacity measurement index of the f-th fault DC transmission line, is the impact of the trigger angle control of the f-th fault DC transmission line on the reactive power consumption of the converter, Q f is the reactive power consumption of the inverter station converter, β f is the Echizen trigger angle, β f0 is the steady-state value of the Echizen trigger angle, f=1,2,…,k, k is the number of faulty DC transmission lines;

[0011] 3) Sort the DC reactive power impact indexes of all faulty DC transmission lines obtained in step 2) in ascending order, according to RPII f The ranking in the ascending sequence shows that the ranking number of the reactive power impact degree of the f-th fault DC transmission line is R f , where R f =1,2,…,k;

[0012] 4) Based on the ranking value R of the DC reactive power impact degree of the f-th fault DC transmission line in step 3) f , in Flag_F f When the delay module is in the low level flag position, the PI controller proportional coefficient k in the fixed cut-off angle controller in the CIGRE standard model is pγ Modified to k′ pγ =k pγ R f / (k+1), after adjustment by the fixed cut-off angle controller of the CIGRE standard model, the CIGRE control output angle α is obtained CIGf ;

[0013] 5) Change the CIGRE control output angle α in step 4) CIGf Subtract the correction angle α′ of the first predictive control module CFPREV in step 1) CFPf , and the faulty DC transmission line trigger angle α is obtained f ;

[0014] 6) Based on the trigger angle α of the faulty DC transmission line in step 5) f Trigger and control the valve group at the receiving end of the faulty DC transmission line.

[0015] The above-mentioned faulty DC transmission line trigger angle calculation process takes into account the reactive power influence degree of multiple faulty DC transmission lines, so that each faulty DC transmission line can evenly adjust the reactive power characteristics of the converter, and the calculation process does not require complex sampling processing, and is relatively simple to implement, which is beneficial to the defense against successive commutation failures of multi-input DC transmission systems.

[0016] In the present invention, the reactive power consumption ratio of the fth fault DC transmission line in the multi-infeed DC transmission system is Among them, Q f is the reactive power consumption of the inverter station of the f-th fault DC transmission line, Q i is the reactive power consumption of the inverter station converter of the i-th DC system, and n is the number of DC branches in the multi-infeed DC transmission system. Among them, P di is the power of the ith DC system, M IIFif is the mutual influence factor between the i-th DC system and the f-th faulty DC transmission line. The AC grid support capacity measurement index of the f-th faulty DC transmission line Among them, S acf is the short-circuit capacity of the commutation busbar of the f-th fault DC transmission line, Q Cf The reactive power provided by the filter, P df is the power of the f-th fault DC transmission line. The impact of the trigger angle control of the f-th fault DC transmission line on the reactive power consumption of the converter is measured by the index Among them, B f is the number of converter bridges in the inverter station converter, i df is the DC current, v f is the AC voltage, T f is the transformer ratio, X Tf is the commutation reactance.

[0017] In the present invention, based on the harmonic distortion reference index of each healthy DC transmission line, the specific implementation process of triggering the receiving-end valve group of the healthy DC transmission line in advance includes:

[0018] A) Calculate the harmonic distortion reference index VDI of the hth round of sound DC transmission line h : in are the instantaneous three-phase voltages v of the AC busbar of the sound DC transmission line calculated by discrete Fourier analysis. h The maximum value of DC component, 1st, 2nd and 3rd order voltages, They are the maximum voltage amplitude of the DC component of the AC bus voltage, the minimum fundamental voltage amplitude, the maximum voltage amplitude of the second-order harmonic, and the maximum voltage amplitude of the third-order harmonic, which are calculated based on the commutation voltage area theory; VDI h Multiply by the harmonic distortion component gain factor k VDI , get CM_VDI output angle α VDI0 ; The subscript h represents the hth round of sound DC transmission line variables;

[0019] B) Change the CM_VDI output angle α in step A) VDI0 After the limiting module; the h-th round of the three-phase AC voltage of the DC transmission line is input into the second prediction control module CFPREV, and the second prediction control module CFPREV outputs an angle α CFPh Compare with 0 to obtain the second prediction control module CFPREV control start high level flag, extend the high level flag for the second set time, and obtain the low level flag Flag_H through the NOT gate h ; Set α VDI0 The limit output is multiplied by Flag_H h , and obtain the corrected angle α of the advance triggering of the sound DC transmission line VDIh ;

[0020] C) Trigger the correction angle α of the sound DC transmission line in step B) in advance VDIh The second predictive control module outputs an angle α CFPh The actual advance trigger angle of the sound DC transmission line is obtained by superposition; the CIGRE control output angle α CIGh Subtract the actual advance trigger angle to obtain the healthy DC transmission line trigger angle α h .

[0021] D) Based on the trigger angle α of the DC transmission line in step C) h Trigger control of the valve group at the receiving end of the sound DC transmission line.

[0022] The above-mentioned sound DC transmission line trigger angle calculation process takes into account the harmonic distortion degree of each sound DC transmission line, and the calculation process has a short control delay and a fast system response speed, which is beneficial to the defense against successive commutation failures of multi-infeed DC transmission systems.

[0023] As an inventive concept, the present invention also provides a multi-infeed DC transmission system successive commutation failure protection system, which includes a processor and a memory; the memory is used to store a computer program, and the processor is configured to execute the computer program; the computer program is configured to implement the steps of the above-mentioned method of the present invention.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows: the present invention provides a method for preventing successive commutation failures in a multi-infeed DC transmission system, comprehensively considering the influence of reactive interaction and harmonic interaction, and triggering the receiving-end valve group of the faulty DC transmission line with a lag based on the reactive influence degree of each faulty DC transmission line, and triggering the receiving-end valve group of the healthy DC transmission line in advance based on the harmonic distortion reference index of each healthy DC transmission line. The present invention can be applied to a multi-infeed DC transmission system, and can effectively prevent successive commutation failures in the healthy DC transmission lines in the multi-infeed DC transmission system, thereby improving the system's stable operation capability and power transmission level. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is the inverter side structure diagram of the multi-infeed DC transmission system;

[0026] Figure 2 This is a flow chart of a method for preventing successive commutation failures in multi-infeed DC transmission according to an embodiment of the present invention;

[0027] FIG3 is a control principle diagram of a method for preventing successive commutation failures in multi-infeed DC transmission according to an embodiment of the present invention;

[0028] FIG4(a) shows the change of the DC shutdown angle of each loop after a three-phase inductive grounding fault occurs near the AC bus of the first loop DC system in the fed-in DC transmission system of the third embodiment of the present invention; FIG4(b) shows the change of the advance triggering angle of each loop DC; FIG4(c) shows the change of the advance triggering angle of each fault DC CIGRE output;

[0029] FIG5(a) shows the change of the shutdown angle of each DC circuit after a three-phase inductive grounding fault occurs near the AC bus of the first DC system in the DC transmission system fed into the DC power transmission system according to the third embodiment of the present invention after the method of the present invention is introduced; FIG5(b) shows the change of the advance triggering angle of each DC circuit after the method of the present invention is introduced; FIG5(c) shows the change of the advance triggering angle of each faulty DC CIGRE output after the method of the present invention is introduced. DETAILED DESCRIPTION

[0030] Figure 2 This is a flow chart of a method for preventing successive commutation failures in multi-input DC transmission according to an embodiment of the present invention. Specifically, it includes the following steps:

[0031] 1) After determining that the faulty DC transmission line has a local commutation failure LCF, Flag_F f Set to 0, shield the output of the faulty DC transmission line prediction control module CFPREV (first prediction control module), and modify the proportional coefficient of the PI controller in the fixed shutdown angle controller according to the reactive power impact index sorting module RM_RPII;

[0032] 2) Before the healthy DC transmission line prediction control module CFPREV (the second prediction control module) is started, the output angle of the harmonic distortion reference index calculation module CM_VDI (the execution flow of the harmonic distortion reference index calculation module CM_VDI module is shown in Figure 3(b)) is limited and added to the advance trigger angle; when the healthy DC transmission line CFPREV is started, Flag_H h Set to 0 to block CM_VDI output;

[0033] 3) Get the faulty DC transmission line trigger angle α f and the trigger angle α of the sound DC transmission line h .

[0034] Fig. 3 is a control principle diagram of the method for preventing successive commutation failures in multi-infeed DC transmission according to an embodiment of the present invention. After a local commutation failure occurs in a faulty DC transmission line, the receiving-end valve group of the faulty DC transmission line is triggered with a delay based on the reactive power influence degree of each faulty DC transmission line, and the receiving-end valve group of the healthy DC transmission line is triggered in advance based on the harmonic distortion reference index of each healthy DC transmission line, so as to solve the problem of successive commutation failures in the healthy DC transmission lines in the multi-infeed DC transmission system.

[0035] In the embodiment of the present invention, the process of using the trigger angle to trigger the thyristor is referenced from the book: Zhao Wanjun. High Voltage Direct Current Transmission Engineering Technology [M]. Beijing: China Electric Power Press, 2011: 8-9.

[0036] The control principle diagram of the valve group at the receiving end of the faulty DC transmission line is shown in FIG3(a) based on the reactive power influence degree of each faulty DC transmission line. The specific implementation method includes the following steps:

[0037] 1) Based on the fault detection, the high-level flag Flag_LCF of the local commutation failure LCF of the faulty DC transmission line is obtained f , extend it for 20ms (that is, after detecting the local commutation failure, this level needs to be maintained for at least 20ms), and then pass through the NOT gate to obtain the low level flag Flag_F f; Output angle α of the prediction control module CFPREV CFPf Multiply Flag_F f , and obtain the correction angle α′ of the prediction control module CFPREV CFPf ;

[0038] 2) Assume that there are k faulty DC transmission lines among n DC transmission lines, calculate the DC reactive power impact index RPII of the f-th faulty DC transmission line. f , whose expression is:

[0039]

[0040] where δ self_f is the reactive power consumption ratio of the fth faulty DC transmission line in the multi-infeed DC transmission system, δ inter_f is the measure of the impact of the restoration of the f-th fault DC transmission line on other DC lines, δ AC_f is the AC grid support capacity measurement index of the f-th fault DC transmission line, is the impact of the trigger angle control of the f-th fault DC transmission line on the reactive power consumption of the converter, Q f is the reactive power consumption of the inverter station of the f-th fault DC transmission line, β f is the Echizen trigger angle, β f0 is the steady-state value of the Echizen trigger angle;

[0041] in, Q i is the reactive power consumption of the inverter station converter of the i-th DC system (i.e., the reactive power consumed by the inverter station converter of the i-th DC system), and n is the number of DC branches in the multi-infeed DC transmission system; P di is the power of the ith DC system, M IIFif is the mutual influence factor between the i-th DC system and the f-th fault DC transmission line (reference for mutual influence factor: B. Davies, A. Williamson, AMGole et al., “Systems with multiple DC infeed,” in CIGRE Working Group B4.41, Dec. 2008, Publ. 364.); S acf is the short-circuit capacity of the commutation busbar of the f-th fault DC transmission line, Q Cf The reactive power provided by the filter, P df is the power of the f-th fault DC transmission line; B f is the number of converter bridges in the inverter station converter, i df is the DC current, vf is the AC voltage, T f is the transformer ratio, X Tf is the commutation reactance;

[0042] 3) Introduce the reactive power impact index sorting module RM_RPII, that is, sort the DC reactive power impact indexes of the k faulty DC transmission lines in step 2) in ascending order, and then sort them according to RPII. f The ranking in the ascending sequence shows that the ranking number of the reactive power impact degree of the f-th fault DC transmission line is R f , where R f =1,2,…,k;

[0043] An example of the reactive power impact degree sequence of faulty DC transmission lines is as follows: There are three faulty DC transmission lines, the reactive power impact degree of LCC-HVDC1 is RPII1, the reactive power impact degree of LCC-HVDC2 is RPII2, and the reactive power impact degree of LCC-HVDC3 is RPII3. Assuming that the ascending sequence is obtained by sorting by size: {RPII1, RPII3, RPII2}, then according to the reactive power impact degree index RPII of each DC line, f The corresponding ascending sequence subscript values ​​can be obtained as follows: the DC reactive power influence degree sequence of the faulty DC transmission line {R1, R2, R3} is: {1, 3, 2}.

[0044] 4) Based on the ranking value R of the DC reactive power impact degree of the f-th fault DC transmission line in step 3) f , in Flag_F f When the delay module (delay time constant T0 is 2ms) is in the low level flag position, the PI controller proportional coefficient k in the fixed turn-off angle controller in the CIGRE standard model is pγ Modified to Further, after adjusting the fixed cut-off angle controller of the CIGRE standard model (for the CIGRE standard model, see: MO Faruque, Y. Zhang and V. Dinavahi, “Detailed modeling of CIGRE HVDC benchmark system using PSCAD / EMTDC and PSB / SIMULINK,” IEEE Trans. Power Del., vol. 21, no. 1, pp. 378–387, Jan. 2006.), the CIGRE control output angle α is obtained. CIGf ;

[0045] ) The CIGRE control output angle α in step 4) CIGf Subtract the CFPREV module correction angle α′ in step 1) CFPf, and the faulty DC transmission line trigger angle α is obtained f .

[0046] The control principle diagram of triggering the receiving-end valve group of the healthy DC transmission line in advance based on the harmonic distortion reference index of each healthy DC transmission line is shown in FIG3( b ). The specific implementation method includes the following steps:

[0047] 1) Introduce the harmonic distortion reference index calculation module CM_VDI, first calculate the harmonic distortion reference index VDI of the hth round of sound DC transmission line h , whose expression is:

[0048]

[0049] in are the instantaneous three-phase voltage v of the AC busbar of the sound DC transmission line calculated by discrete Fourier analysis DFT. h The maximum value of DC component, 1st, 2nd and 3rd order voltages, They are the maximum voltage amplitude of the DC component of the AC bus voltage, the minimum fundamental voltage amplitude, the maximum voltage amplitude of the second-order harmonic, and the maximum voltage amplitude of the third-order harmonic calculated based on the commutation voltage area theory (References on commutation voltage area theory: Jing Liuming, Wang Bin, Dong Xinzhou, et al. A review of research on continuous commutation failure of high-voltage DC transmission system [J]. Electric Power Automation Equipment, 2019, 39(9): 116-123.); VDI h Multiply by the harmonic distortion component gain factor k VDI Get CM_VDI output angle α VDI0 ;

[0050] 2) Set the CM_VDI output angle α in step 1) VDI0 After the limit module, the reactive power consumption of the inverter station is increased due to too much early triggering angle, where the upper limit is 10° (= 0.175 rad) and the lower limit is 0; the CFPREV output angle α CFPh Compare with 0 to get the CFPREV control start high level flag, extend it for 20ms, and then pass through the NOT gate to get the low level flag Flag_H h ; Set α VDI0 The limit output is multiplied by Flag_H h , and obtain the corrected angle α of the advance triggering of the sound DC transmission line VDIh ;

[0051] 3) Trigger the correction angle α of the DC transmission line in step 2) in advance VDIh The angle α output by CFPREV CFPhThe actual advance trigger angle of the sound DC transmission line is obtained by superposition; the CIGRE control output angle α CIGh Subtracting the actual advance trigger angle, the healthy DC transmission line trigger angle α can be obtained. h .

[0052] The effectiveness of the control method of the embodiment of the present invention is verified by PSCAD simulation. The simulation system includes three DC transmission lines, each with a rated power of 1000MW, a rated DC voltage and a DC current of 500kV and 2kA, and a receiving-end AC bus voltage level of 230kV. The short-circuit ratio of the receiving-end AC power grid of the first DC system is 2.5, the short-circuit ratio of the receiving-end AC power grid of the second DC system is 3.5, and the short-circuit ratio of the receiving-end AC power grid of the third DC system is 3.5. The length of the interconnection line between the first and second DC systems is 120km, the length of the interconnection line between the second and third DC systems is 120km, the length of the interconnection line between the first and third DC systems is 50km, and the line impedance is 0.028+j0.271Ω / km. A 0.337H three-phase inductive grounding fault is set at the near end of the AC bus of the first DC system, the fault time is 1.0s, and the fault duration is 0.2s.

[0053] Referring to FIG. 4(a), after the ground fault occurs, the turn-off angle of the first DC system drops rapidly to 0 within 5ms, i.e., local commutation failure occurs; due to the short distance between the tie line between the third DC and the first DC, the turn-off angle of the third DC system also drops rapidly to 0, i.e., local commutation failure occurs; due to the long distance between the tie line between the second DC and the first DC, the turn-off angle of the second DC system drops to 0 about 14ms after the fault occurs, i.e., successive commutation failure occurs. Referring to FIG. 4(b), the prediction control module of the first and third DC is started about 6ms after the fault occurs, and the advance trigger angle is generated earlier; due to the slow drop of the AC bus voltage of the second DC system, the prediction control module is started about 12ms after the fault occurs, and the advance trigger angle is generated slower. Referring to FIG. 4(c), after the local commutation failure occurs in the first and third faulty DC transmission lines, the CIGRE output of the faulty DC transmission line increases rapidly.

[0054] Referring to FIG. 5(a), after the method of the present invention is introduced, the cut-off angles of the first and third DC circuits drop rapidly to 0 after a fault occurs, i.e., a local commutation failure occurs; the cut-off angle of the second DC circuit is reduced but does not drop to 0, i.e., no successive commutation failure occurs. Referring to FIG. 5(b), after the method of the present invention is introduced, the CFPREV output is shielded after a local commutation failure occurs in the first and third DC circuits, thereby reducing the reactive power consumption of the converter of the faulty DC transmission line; compared with the CFPREV prediction control module, the harmonic distortion reference index calculation module CM_VDI outputs the advance trigger angle earlier about 3ms after the fault occurs in the second DC circuit, which is beneficial to suppress the successive commutation failure of the healthy DC transmission line. Referring to FIG. 5(c), after the method of the present invention is introduced, after the local commutation failure occurs in the first and third DC circuits, the proportional coefficient of the PI controller in the fixed shutdown angle controller is reduced based on the reactive power impact index sorting module RM_RPII, thereby reducing the CIGRE output forward trigger angle and reducing the reactive power consumption of the faulty DC transmission line converter, which is beneficial to suppressing the successive commutation failures of the sound DC transmission lines.

Claims

1. A method for preventing successive commutation failures in a multi-infeed DC transmission system, characterized in that: The following steps are involved: When a local commutation failure occurs in a faulty DC transmission line of a multi-infeed DC transmission system, the receiving-end valve group of the faulty DC transmission line is triggered with a delay based on the reactive power impact of each faulty DC transmission line; Based on the harmonic distortion reference index of each healthy DC transmission line, the receiving-end valve group of the healthy DC transmission line is triggered in advance; Based on the harmonic distortion reference index of each healthy DC transmission line, the specific implementation process of triggering the valve group at the receiving end of the healthy DC transmission line in advance includes: A) Calculate the harmonic distortion reference index VDI of the hth round of sound DC transmission line h : in are the instantaneous three-phase voltages v of the AC busbar of the sound DC transmission line calculated by discrete Fourier analysis. h The maximum value of DC component, 1st, 2nd and 3rd order voltages, They are the maximum voltage amplitude of the DC component of the AC bus voltage, the minimum fundamental voltage amplitude, the maximum voltage amplitude of the second-order harmonic, and the maximum voltage amplitude of the third-order harmonic, which are calculated based on the commutation voltage area theory; VDI h Multiply by the harmonic distortion component gain factor k VDI , get CM_VDI output angle α VDI0 ; Wherein, the subscript h represents the hth round of sound DC transmission line variables; B) The CM_VDI output angle α VDI0 After the limiting module; the h-th round of the three-phase AC voltage of the DC transmission line is input into the second prediction control module CFPREV, and the second prediction control module CFPREV outputs an angle α CFPh Compare with 0 to obtain the second prediction control module CFPREV control start high level flag, extend the high level flag for the second set time, and obtain the low level flag Flag_H through the NOT gate h ; Set α VDI0 The limit output is multiplied by Flag_H h , and obtain the corrected angle α of the advance trigger of the sound DC transmission line VDIh ; C) triggering the corrected angle α of the healthy DC transmission line in advance VDIh The second predictive control module outputs an angle α CFPh The actual advance trigger angle of the sound DC transmission line is obtained by superposition; the DC current and the cut-off angle of the hth round of sound DC transmission line are input into the CIGRE standard model, and the control output angle α of the CIGRE standard model is CIGh Subtract the actual advance trigger angle to obtain the healthy DC transmission line trigger angle α h ; D) Based on the trigger angle α of the healthy DC transmission line h Trigger control of the valve group at the receiving end of the sound DC transmission line.

2. The method for preventing successive commutation failures in a multi-infeed DC power transmission system according to claim 1, characterized in that: Based on the reactive power impact of each faulty DC transmission line, the specific implementation process of delayed triggering of the receiving-end valve group of the faulty DC transmission line includes: 1) Obtain the high-level flag Flag_LCF of the local commutation failure of the faulty DC transmission line f , set the high level flag Flag_LCF f After extending the first setting time, the low level flag Flag_F is obtained through the NOT gate f The three-phase AC voltage of the faulty DC transmission line is input into the first prediction control module CFPREV, and the first prediction control module CFPREV outputs an angle α CFPf Multiply by Flag_F f , get the first prediction control module CFPREV correction angle α′ CFPf , where the subscript f represents the variable of the f-th fault DC transmission line; 2) Calculate the DC reactive power impact index RPII of the f-th fault DC transmission line f : where δ self_f is the reactive power consumption ratio of the fth faulty DC transmission line in the multi-infeed DC transmission system, Q f is the reactive power consumption of the inverter station of the f-th fault DC transmission line, Q i is the reactive power consumption of the inverter station in the i-th DC system, n is the number of DC branches in the multi-infeed DC transmission system; δ inter_f is the indicator for measuring the impact of the restoration of the f-th faulty DC transmission line on other DC lines, P di is the power of the ith DC system, M IIFif is the mutual influence factor between the i-th DC system and the f-th fault DC transmission line; δ AC_f is the AC grid support capacity measurement index of the f-th fault DC transmission line, S acf is the short-circuit capacity of the commutation busbar of the f-th fault DC transmission line, Q Cf The reactive power provided by the filter, P df is the power of the f-th fault DC transmission line; is the measurement index of the impact of the trigger angle control of the f-th fault DC transmission line on the reactive power consumption of the converter, B f is the number of converter bridges in the inverter station converter, i df is the DC current, v f is the AC voltage, T f is the transformer ratio, X Tf is the commutation reactance, β f is the Echizen trigger angle, β f0 is the steady-state value of the Echizen trigger angle, f=1,2,…,k, k is the number of faulty DC transmission lines; 3) Sort the DC reactive power impact indicators of all faulty DC transmission lines in ascending order, according to RPII f The ranking in the ascending sequence shows that the ranking number of the reactive power impact degree of the f-th fault DC transmission line is R f , where R f =1,2,…,k; 4) Based on the ranking value R of the DC reactive power impact degree of the f-th fault DC transmission line f , in Flag_F f When the delay module is in the low level flag position, the PI controller proportional coefficient k in the fixed cut-off angle controller in the CIGRE standard model is pγ Modified to k′ pγ =k pγ R f / (k+1), after adjustment by the fixed cut-off angle controller of the CIGRE standard model, the CIGRE control output angle α is obtained CIGf ; 5) The CIGRE controls the output angle α CIGf Subtract the first prediction control module CFPREV correction angle α′ CFPf , and the trigger angle α of the faulty DC transmission line is obtained f ; 6) Based on the faulty DC transmission line trigger angle α f Trigger and control the valve group at the receiving end of the faulty DC transmission line.

3. A system for preventing successive commutation failures in a multi-infeed DC transmission system, characterized in that: It comprises a processor and a memory; the memory is used to store a computer program, and the processor is configured to execute the computer program; the computer program is configured to implement the steps of the method according to claim 1 or 2.

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