12 Transient overvoltage analysis method and device for pulsating valve commutation failure

Abstract

The present application provides a method and device for analyzing transient overvoltage during a 12-pulse commutation valve commutation fault. The method includes obtaining the fault type when the commutation fault occurs; obtaining the phase voltage, sequence impedance and the composite sequence network corresponding to the fault type before the commutation fault, and obtaining the sequence current relationship after the commutation fault according to the composite sequence network; calculating the equivalent transition resistance after the commutation fault; obtaining the commutation voltage based on the equivalent transition resistance calculation; calculating the phase difference according to the commutation voltage; obtaining the shutdown angle after the commutation fault according to the phase difference calculation; obtaining the shutdown angle control signal fluctuation trend according to the shutdown angle within a single cycle; obtaining the transient overvoltage change after the commutation fault according to the shutdown angle control signal fluctuation trend. The shutdown angle change trend is obtained by analyzing the phase angle difference analysis after an asymmetric fault, and combined with the transient reactive power characteristics of the rectifier during the commutation fault, the transient overvoltage changes under various faults are analyzed to effectively predict the overvoltage trend of the high-voltage DC system.

Description

Technical Field

[0001] The present application relates to the technical field of high-voltage direct current transmission engineering, and in particular to a method and device for analyzing transient overvoltage during a 12-pulse converter valve commutation fault. Background Art

[0002] When a commutation failure occurs on the inverter side of a traditional high-voltage DC system, the reactive power consumption of the rectifier will be greatly reduced and cause serious overvoltage at the sending end. Commutation failures caused by different types of faults on the inverter side will have an important impact on the reactive power characteristics of the rectifier. At present, most studies are conducted on the transient overvoltage characteristics of commutation failures caused by symmetrical faults. Most of the research methods are to establish a mathematical relationship between the commutation bus voltage on the rectifier side and the active and reactive power of the node, analyze the action logic of the DC control system, analyze the entire process of transient voltage changes at the sending end during commutation failure, establish the relationship between rectifier reactive power consumption and DC logic switching, and reveal the transient overvoltage characteristics of the sending end under symmetrical fault scenarios.

[0003] However, the above method does not consider the internal transient action of the LCC-HVDC (line-commutated converter HVDC) 12-pulse converter valve when analyzing the action logic of the high-voltage direct current system. As a result, the transient overvoltage change process at the sending end and the reactive power consumption process of the rectifier obtained on this basis ignore the zero-crossing deviation of the converter valve caused by the asymmetric fault, resulting in a significant difference between the transient overvoltage characteristic analysis results and the characteristic changes under the asymmetric fault.

[0004] Application Contents

[0005] In order to overcome the deficiencies of the above-mentioned prior art, the present application provides a method and device for analyzing transient overvoltage during commutation failure of a 12-pulse converter valve, which specifically adopts the following technical solutions:

[0006] The present application discloses a transient overvoltage analysis method for a 12-pulse converter valve commutation fault, which is used to analyze voltage changes when a commutation fault occurs in a high-voltage direct current system. The 12-pulse converter valve includes at least a YD-type converter transformer and a YY-type converter transformer, and the high-voltage direct current system includes at least a rectifier and an inverter. The method includes the following steps:

[0007] Acquire the fault type when the phase change fault occurs, wherein the fault type at least includes a single-phase grounding fault, a two-phase short circuit fault or a two-phase grounding fault;

[0008] Obtaining the phase voltage before the commutation fault, the corresponding sequence impedance and the composite sequence network corresponding to the fault type, and obtaining the sequence current relationship after the commutation fault according to the composite sequence network;

[0009] According to the sequence current relationship after the phase-changing fault, the equivalent transition resistance after the phase-changing fault of the corresponding fault type occurs is calculated;

[0010] Based on the equivalent transition resistance after the commutation fault, the commutation voltage of the YD type converter transformer and the commutation voltage of the YY type converter transformer under different fault types are calculated respectively;

[0011] Calculate the phase difference between the commutation voltages of two adjacent phases according to the commutation voltages of the two adjacent phases;

[0012] The shutdown angle of the high voltage DC system after a commutation fault is obtained by calculating the phase difference between the commutation voltages of two adjacent phases;

[0013] Obtaining a fluctuation trend of a turn-off angle control signal of the high-voltage direct current system within a single cycle according to the turn-off angle of the high-voltage direct current system within a single cycle;

[0014] The transient overvoltage change after commutation fault is obtained according to the fluctuation trend of the turn-off angle control signal of the high voltage DC system in a single cycle.

[0015] Optionally, the step of calculating and obtaining the commutation voltage of the YD type converter transformer and the commutation voltage of the YY type converter transformer under a single-phase grounding fault includes:

[0016] According to the composite sequence network corresponding to the single-phase grounding fault, the positive sequence, negative sequence and zero sequence current relationship after the commutation fault is obtained:

[0017] ;

[0018] in I 1 is the positive sequence current when a commutation fault occurs, I 2 is the negative sequence current when a commutation fault occurs, I 0 is the zero-sequence current when a commutation fault occurs, E is the phase voltage before the commutation fault occurs, Z 1 is the positive sequence impedance connected to the commutation bus, Z 2 is the negative sequence impedance connected to the commutation bus, Z 0 is the zero-sequence impedance connected to the commutation bus, is the transition resistance;

[0019] Calculate the equivalent transition resistance after the commutation fault of the corresponding fault type according to the sequence current relationship after the commutation fault Z f :

[0020] ;

[0021] The commutation voltage of the YY type converter transformer under a single-phase grounding fault is calculated based on the equivalent transition resistance after the commutation fault:

[0022] ;

[0023] in U Yab is the commutation voltage between phase a and phase b on the valve side of the YY type converter transformer; U Ybc is the commutation voltage between phase b and phase c on the valve side of the YY type converter transformer; U Yca is the commutation voltage between phase c and phase a on the valve side of the YY type converter transformer; U 1 is the positive sequence voltage in the composite sequence network after the commutation fault; U 2 is the negative sequence voltage in the composite sequence network after the commutation fault; a is the failure calculation coefficient;

[0024] The commutation voltage of the YD type converter transformer under a single-phase grounding fault is calculated based on the equivalent transition resistance after the commutation fault:

[0025] ;

[0026] in U Dab is the commutation voltage between phase a and phase b on the valve side of the YD type converter transformer; U Dbc is the commutation voltage between phase b and phase c on the valve side of the YD type converter transformer; U Dca is the commutation voltage between phase c and phase a on the valve side of the YD type converter transformer; U 1 is the positive sequence voltage in the composite sequence network after the commutation fault; U 2 is the negative sequence voltage in the composite sequence network after the commutation fault; a is the failure calculation coefficient, j is the symbol of the imaginary part.

[0027] Optionally: the step of calculating and obtaining the commutation voltage of the YD type converter transformer and the commutation voltage of the YY type converter transformer under a two-phase short circuit fault includes:

[0028] According to the composite sequence network corresponding to the two-phase phase-to-phase fault, the positive-sequence and negative-sequence current relationship after the commutation fault is obtained:

[0029] ;

[0030] in I 1 is the positive sequence current, I 2 is the negative sequence current, E is the phase voltage before the single-phase grounding fault occurs, Z 1 is the positive sequence impedance, Z2 is the negative sequence impedance, is the transition resistance;

[0031] According to the sequence current relationship after the phase-commutation fault, the equivalent transition resistance after the phase-commutation fault of the corresponding fault type is calculated:

[0032] ;

[0033] The commutation voltage of the YY type converter transformer under two-phase interphase fault is calculated based on the equivalent transition resistance after the commutation fault:

[0034] ;

[0035] in U Yab is the commutation voltage between phase a and phase b on the valve side of the YY type converter transformer; U Ybc is the commutation voltage between phase b and phase c on the valve side of the YY type converter transformer; U Yca is the commutation voltage between phase c and phase a on the valve side of the YY type converter transformer; U 1 is the positive sequence voltage in the composite sequence network after the commutation fault; U 2 is the negative sequence voltage in the composite sequence network after the commutation fault; a is the failure calculation coefficient;

[0036] The commutation voltage of the YD type converter transformer under two-phase interphase fault is calculated based on the equivalent transition resistance after the commutation fault:

[0037] ;

[0038] in U Dab is the commutation voltage between phase a and phase b on the valve side of the YD type converter transformer; U Dbc is the commutation voltage between phase b and phase c on the valve side of the YD type converter transformer; U Dca is the commutation voltage between phase c and phase a on the valve side of the YD type converter transformer; U 1 is the positive sequence voltage in the composite sequence network after the commutation fault; U 2 is the negative sequence voltage in the composite sequence network after the commutation fault; a is the failure calculation coefficient, j is the symbol of the imaginary part.

[0039] Optionally: the step of calculating and obtaining the commutation voltage of the YD type converter transformer and the commutation voltage of the YY type converter transformer under a two-phase grounding fault includes:

[0040] According to the composite sequence network corresponding to the two-phase grounding fault, the positive sequence, negative sequence and zero sequence current relationship after the commutation fault is obtained:

[0041] ;

[0042] ;

[0043] ;

[0044] in I 1 is the positive sequence current when a commutation fault occurs, I 2 is the negative sequence current when a commutation fault occurs, I 0 is the zero-sequence current when a commutation fault occurs, E is the phase voltage before the commutation fault occurs, Z 1 is the positive sequence impedance connected to the commutation bus, Z 2 is the negative sequence impedance connected to the commutation bus, Z 0 is the zero-sequence impedance connected to the commutation bus, is the transition resistance

[0045] Calculate the equivalent transition resistance after the commutation fault of the corresponding fault type according to the sequence current relationship after the commutation fault Z f1 and Z f2 :

[0046] ;

[0047] ;

[0048] The commutation voltage of the YY type converter transformer under two-phase grounding fault is calculated based on the equivalent transition resistance after the commutation fault:

[0049] ;

[0050] in U Yab is the commutation voltage between phase a and phase b on the valve side of the YY type converter transformer; U Ybc is the commutation voltage between phase b and phase c on the valve side of the YY type converter transformer; U Yca is the commutation voltage between phase c and phase a on the valve side of the YY type converter transformer; U 1 is the positive sequence voltage in the composite sequence network after the commutation fault; U 2 is the negative sequence voltage in the composite sequence network after the commutation fault; a is the failure calculation coefficient;

[0051] The commutation voltage of the YD type converter transformer under a two-phase grounding fault is calculated based on the equivalent transition resistance after the commutation fault:

[0052] ;

[0053] in U Dab is the commutation voltage between phase a and phase b on the valve side of the YD type converter transformer; U Dbc is the commutation voltage between phase b and phase c on the valve side of the YD type converter transformer; U Dca is the commutation voltage between phase c and phase a on the valve side of the YD type converter transformer; U 1 is the positive sequence voltage in the composite sequence network after the commutation fault; U 2 is the negative sequence voltage in the composite sequence network after the commutation fault; a is the failure calculation coefficient, j is the symbol of the imaginary part.

[0054] Optionally, the step of obtaining the transient overvoltage characteristics after a commutation fault according to the fluctuation trend of the turn-off angle control signal within a cycle includes:

[0055] Get the rectifier external characteristic equation:

[0056] ;

[0057] According to the external characteristic equation of the rectifier, the time derivative is obtained to obtain the derivative result:

[0058] ;

[0059] in Q dr Reactive power is consumed by the rectifier. I dr is the DC current of the rectifier, U dr0 is the no-load voltage of the rectifier, U dr is the voltage of the rectifier;

[0060] According to the derivative result of the rectifier external characteristic equation and the fluctuation trend of the turn-off angle control signal within the cycle, the transient overvoltage fluctuation trend after the commutation fault is obtained, among which the transient overvoltage peak fluctuation trend is negatively correlated with the turn-off angle control signal fluctuation trend.

[0061] Optionally, in a single cycle of the single-phase grounding fault, the fluctuation trend of the cut-off angle control signal obtained according to the cut-off angle of the high voltage direct current system is:

[0062] The turn-off angle control signal of the high-voltage DC system under a single-phase grounding fault presents two troughs in a single cycle, and as the transition resistance decreases, the trough fluctuation of the turn-off angle control signal of the high-voltage DC system becomes larger;

[0063] According to the fluctuation trend of the turn-off angle control signal of the single-phase grounding fault, the transient overvoltage change trend after the commutation fault is obtained as follows:

[0064] The transient overvoltage under a single-phase grounding fault presents two peaks in a single cycle, and as the transition resistance decreases, the peak fluctuation of the transient overvoltage becomes larger.

[0065] Optionally: In a single cycle of the two-phase short circuit fault, the fluctuation trend of the cut-off angle control signal obtained according to the cut-off angle of the high voltage direct current system is:

[0066] The turn-off angle control signal of the high-voltage DC system under a two-phase short-circuit fault presents two peaks in a single cycle, and as the transition resistance decreases, the peak fluctuation of the turn-off angle control signal of the high-voltage DC system becomes larger;

[0067] According to the fluctuation trend of the turn-off angle control signal of the two-phase short-circuit fault, the transient overvoltage change trend after the commutation fault is obtained as follows:

[0068] The transient overvoltage under a two-phase short-circuit fault presents two troughs in a single cycle, and as the transition resistance decreases, the trough fluctuation of the transient overvoltage becomes larger.

[0069] Optionally, in a single cycle of the two-phase grounding fault, the fluctuation trend of the cut-off angle control signal obtained according to the cut-off angle of the high voltage direct current system is:

[0070] The cut-off angle control signal of the high-voltage DC system under a two-phase grounding fault presents two peaks in a single cycle, and as the transition resistance decreases or increases, the peak of the cut-off angle control signal of the high-voltage DC system does not fluctuate;

[0071] According to the fluctuation trend of the turn-off angle control signal of the two-phase grounding fault, the transient overvoltage change trend after the commutation fault is obtained as follows:

[0072] The transient overvoltage under a two-phase grounding fault presents two troughs in a single cycle, and the trough of the transient overvoltage does not fluctuate as the transition resistance decreases or increases.

[0073] Optionally, the step of calculating and obtaining the turn-off angle of the high voltage DC system after a commutation fault according to the phase difference between the commutation voltages of two adjacent phases includes:

[0074] Get the phase difference between the commutation voltages of two adjacent phases after a commutation fault:

[0075] ;

[0076] in is the phase difference between the commutation voltages of two adjacent phases; n =1,2,...,6; for U Yab and U Dab The phase difference, for U Dab and U Ybc The phase difference, for U Ybc and U Dbc The phase difference, for U Dbc and U Yca is the phase difference, for U Yca and U Dca The phase difference, for U Dca and U Yca The phase difference; U Y After a commutation fault Corresponding to one of the commutation voltages of two adjacent phases; U D After a commutation fault Corresponding to the other commutation voltage of the adjacent two-phase commutation voltage; After a commutation fault The phase of one commutation voltage corresponding to two adjacent phase commutation voltages; After a commutation fault The phase of the other commutation voltage corresponding to the adjacent two-phase commutation voltage; To obtain the complex argument function;

[0077] The shutdown angle of the high-voltage DC system after a commutation fault is calculated based on the phase difference between the commutation voltages of two adjacent phases:

[0078] ;

[0079] in is the turn-off angle of the HVDC system after a commutation fault; is the initial value of the turn-off angle of the high voltage DC system.

[0080] The present application also discloses a method and device for analyzing transient overvoltage during commutation failure of a 12-pulse converter valve, the device comprising:

[0081] A first acquisition module is used to acquire the fault type when a commutation fault occurs, wherein the fault type at least includes a single-phase grounding fault, a two-phase short circuit fault or a two-phase grounding fault;

[0082] A second acquisition module is used to acquire the phase voltage before the commutation fault, the corresponding sequence impedance and the composite sequence network corresponding to the fault type, and acquire the sequence current relationship after the commutation fault according to the composite sequence network;

[0083] An equivalent resistance calculation module is used to calculate the equivalent transition resistance after a commutation fault of a corresponding fault type occurs according to the sequence current relationship after the commutation fault;

[0084] The commutation voltage calculation module is used to obtain the phase voltage and the corresponding sequence impedance before the commutation fault, and calculate the commutation voltage of the YD type converter transformer and the commutation voltage of the YY type converter transformer under different fault types in combination with the sequence current relationship after the commutation fault;

[0085] A phase difference calculation module, used for calculating the phase difference between the commutation voltages of two adjacent phases according to the commutation voltages of the two adjacent phases;

[0086] A cut-off angle calculation module is used to calculate the cut-off angle of the high-voltage DC system after a commutation fault according to the phase difference between the commutation voltages of two adjacent phases;

[0087] A signal analysis module, used for obtaining a fluctuation trend of a cut-off angle control signal within a cycle according to a cut-off angle of the high voltage DC system within the cycle;

[0088] The result output module is used to obtain the transient overvoltage characteristics after the commutation fault according to the fluctuation trend of the turn-off angle control signal within the cycle.

[0089] Beneficial Effects

[0090] The technical solution of this application has the following beneficial effects:

[0091] The analysis method of the present application analyzes the phase difference of the voltage of adjacent commutation lines of the 12-pulse converter valve after an asymmetric fault, analyzes and obtains the trend of the switch-off angle change of the high-voltage DC system under different fault types, and performs characteristic analysis based on the switch-off angle change trend corresponding to each fault type, revealing the process in which various faults cause the high-voltage DC system to periodically enter constant current control in advance. Combined with the transient reactive power characteristics of the rectifier during the commutation fault caused by each fault type, the transient overvoltage changes of the high-voltage DC system under various faults are analyzed, effectively predicting the overvoltage trend of the high-voltage DC system during operation, and providing guidance for subsequent voltage suppression or recovery. BRIEF DESCRIPTION OF THE DRAWINGS

[0092] Figure 1 It is a flow chart of the transient overvoltage analysis method when 12 pulsating converter valves fail in the embodiment of the present application.

[0093] Figure 2 It is a structural schematic diagram of the transient overvoltage analysis method when 12 pulsating converter valves fail in the embodiment of the present application.

[0094] Figure 3 Schematic diagram of the change of the commutation voltage phase difference with the transition resistance under a single-phase grounding fault in an embodiment of the present application.

[0095] Figure 4 Schematic diagram of the change of the commutation voltage phase difference with the transition resistance under a two-phase short circuit fault in an embodiment of the present application.

[0096] Figure 5 Schematic diagram of the change of the commutation voltage phase difference with the transition resistance under a two-phase grounding fault in an embodiment of the present application.

[0097] Figure 6 Schematic diagram of the change in the shutdown angle fluctuation trend under a single-phase grounding fault in an embodiment of the present application.

[0098] Figure 7 Schematic diagram of the change in the turn-off angle fluctuation trend under a two-phase short-circuit fault in an embodiment of the present application.

[0099] Figure 8 Schematic diagram of the change in the shutdown angle fluctuation trend under a two-phase grounding fault in an embodiment of the present application.

[0100] Fig. 9 It is the DC operation curve of the transient voltage of the sending-end AC system caused by various asymmetric faults in the embodiment of the present application.

[0101] Fig.10 This is a comparison diagram of transient voltage peak and DC current corresponding to asymmetric and symmetric faults in the embodiment of the present application. Fig.10 (a) is a schematic diagram of the transient overvoltage peak value of a single-phase grounding fault occurring at 4.012s; Fig.10 (b) is a schematic diagram of the DC current response process of a single-phase grounding fault occurring at 4.012s; Fig.10 (c) is a schematic diagram of the transient overvoltage peak value of a single-phase grounding fault occurring at 4.006s; Fig.10 (d) is a schematic diagram of the DC current response process of a single-phase grounding fault occurring at 4.006s.

[0102] Fig.11 This is a comparison diagram of DC control signals corresponding to asymmetric and symmetric faults in the embodiment of the present application. Fig.10(a) is a schematic diagram of the DC control signal response process when a single-phase ground fault occurs at 4.012s; Fig.10 (b) is a schematic diagram of the DC control signal response process when a symmetrical fault occurs at 4.012s; Fig.10 (a) is a schematic diagram of the DC control signal response process when a single-phase ground fault occurs at 4.006s; Fig.10 (a) is a schematic diagram of the DC control signal response process when a symmetrical fault occurs at 4.006s.

[0103] Fig.12 It is a schematic diagram of the peak value of transient overvoltage at the sending end under three-phase grounding fault, single-phase grounding fault, two-phase short circuit fault and two-phase grounding fault in the embodiment of the present application. DETAILED DESCRIPTION

[0104] The technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all of the embodiments. Therefore, it should be appreciated by those of ordinary skill in the art that various changes and modifications may be made to the embodiments described herein without departing from the scope and spirit of the present disclosure. Similarly, for the sake of clarity and conciseness, the description of well-known functions and structures is omitted in the following description. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of the present application.

[0105] Since line-commutated converter HVDC (LCC-HVDC) has the advantages of large transmission capacity, low transmission loss, and flexible power regulation, it has been widely used in long-distance and large-capacity transmission. When the HVDC transmission system transmits power, the reactive power consumed by the converter valve is about 40%-60% of the transmitted active power. This reactive power is generally compensated on-site by the AC filter system of the converter station. Commutation failure is one of the most common events in traditional HVDC transmission systems. After the inverter fails due to a short-circuit fault in the receiving system, the DC voltage and current on the rectifier side will undergo a significant change, resulting in a change in the reactive power consumed by the rectifier, which in turn causes voltage fluctuations in the AC system at the sending end. At present, the proportion of new energy in the power system is increasing. However, new energy such as wind turbines and photovoltaics will be disconnected from the grid when the terminal voltage exceeds 1.3pu. Therefore, it is urgent to conduct in-depth research on the transient overvoltage at the sending end during the commutation failure to quickly and accurately predict the transient overvoltage changes.

[0106] However, most current studies do not explain the differences in rectifier reactive power characteristics caused by different fault types, and lack a systematic description of the differences in transient overvoltages caused by various faults (especially asymmetric faults). At present, asymmetric faults occur frequently in new power systems, and there is an urgent need to deeply analyze the transient overvoltage generation mechanism and differential impact of various asymmetric faults.

[0107] Specifically, Figure 1 As shown, the embodiment of the present application discloses a transient overvoltage analysis method for a 12-pulse converter valve commutation fault, which is used to analyze voltage changes when a commutation fault occurs in a high-voltage direct current system. The 12-pulse converter valve includes at least a YD-type converter transformer and a YY-type converter transformer, and the high-voltage direct current system includes at least a rectifier and an inverter. The method includes the following steps:

[0108] Step 1: Obtain the fault type when the commutation fault occurs, wherein the fault type at least includes a single-phase grounding fault, a two-phase short circuit fault or a two-phase grounding fault;

[0109] Step 2: obtaining the phase voltage before the commutation fault, the corresponding sequence impedance and the composite sequence network corresponding to the fault type, and obtaining the sequence current relationship after the commutation fault according to the composite sequence network;

[0110] Step 3: Calculate the equivalent transition resistance after the commutation fault of the corresponding fault type according to the sequence current relationship after the commutation fault;

[0111] Step 4: Based on the equivalent transition resistance after the commutation fault, the commutation voltage of the YD type converter transformer and the commutation voltage of the YY type converter transformer under different fault types are calculated respectively;

[0112] Step 5: Calculate the phase difference between the commutation voltages of two adjacent phases according to the commutation voltages of the two adjacent phases;

[0113] Step 6: Calculate and obtain the turn-off angle of the high voltage DC system after the commutation fault according to the phase difference between the commutation voltages of two adjacent phases;

[0114] Step 7: obtaining a fluctuation trend of a turn-off angle control signal of the high voltage direct current system in a single cycle according to the turn-off angle of the high voltage direct current system in a single cycle;

[0115] Step 8: Obtain the transient overvoltage change after the commutation fault according to the fluctuation trend of the turn-off angle control signal of the high voltage DC system in a single cycle.

[0116] The present application analyzes the phase angle difference of the adjacent commutation line voltages of the 12-pulse converter valve after an asymmetric fault, obtains the trend of the turn-off angle change of the high-voltage DC system under different fault types, performs feature analysis based on the turn-off angle change trend corresponding to each fault type, reveals the process in which the high-voltage DC system periodically enters constant current control in advance due to various faults, and combines the transient reactive power characteristics of the rectifier when the commutation fault is caused by each fault type to obtain the transient overvoltage change of the high-voltage DC system under various faults, effectively predicting the overvoltage trend of the high-voltage DC system during operation.

[0117] This application further verifies the above method by analyzing the dynamic process of the voltage at the sending end during the commutation failure caused by asymmetric faults. Specifically, when the high-voltage DC system fails to commutate, its DC voltage and current will change dramatically. The external characteristic equation of the rectifier is as follows, which shows that the reactive power consumed by the rectifier is closely related to the DC voltage and DC current:

[0118] ;

[0119] According to the external characteristic equation of the rectifier, the time derivative is obtained to obtain the derivative result:

[0120] ;

[0121] in Q dr Reactive power is consumed by the rectifier. I dr is the DC current of the rectifier, U dr0 is the no-load voltage of the rectifier, U dr is the voltage of the rectifier. According to the above formula, the transient reactive power characteristics of the rectifier are related to the DC voltage, current and their change rate on one side of the rectifier during the commutation failure.

[0122] The following is an analysis of the transient reactive power characteristics of the rectifier under asymmetric faults based on the variation rules of DC voltage and DC current during commutation failure, and further explains the voltage variation of the sending-end AC system caused by various asymmetric faults. Fig. 9 As shown in the figure, this paper divides the transient voltage change at the sending end into three stages:

[0123] Phase 1:

[0124] In this stage, after an asymmetric fault occurs near the inverter, the AC voltage on one side of the inverter decreases, causing the inverter to fail to commutate. The DC voltage on the other side of the inverter decreases significantly, and the DC current increases. At the same time, the low-voltage current limiting device (VDCOL) starts, which reduces the DC voltage on one side of the rectifier by increasing the trigger angle on one side of the rectifier to suppress the growth of the DC current and reduce the DC current to the set minimum value. ,generally 0.4 pu That is, the DC current on the rectifier side in stage 1 will increase first and then decrease, such as Fig. 9 As shown, the DC operating point will quickly pass through point B to point C. When the reactive power consumed by the rectifier is reduced to less than the rated reactive power consumption At this time , the rectifier side begins to return reactive power to the sending-end AC system, and when the reactive power consumed by the rectifier is reduced to a minimum value, the reactive power returned by the high-voltage DC system to the sending-end AC system reaches a maximum value, and a transient overvoltage peak will appear in the sending-end AC system. Since this process is extremely rapid, there is no obvious difference between the overvoltage peaks caused by asymmetric faults and symmetric faults.

[0125] Phase 2:

[0126] During the asymmetric short circuit fault on the inverter side in phase 2, the DC voltage on the inverter side is maintained at about 0, and the DC voltage on the rectifier side is also maintained at about 0, such as Fig. 9 As shown, the DC operating point is maintained near point C. The DC current on one side of the rectifier is maintained at ,In this stage 2, the reactive power consumed by the rectifier is basically unchanged, but since the DC active power transmission is blocked during the commutation failure, the AC voltage at the sending end is maintained at a high level due to the active power surplus.

[0127] Phase 3:

[0128] In stage 3, after the fault on the inverter side is cleared, the inverter resumes normal operation, and the DC voltage on the inverter side increases. Since the DC voltage on the rectifier side does not have time to change, the DC current decreases. The VDCOL device increases the DC voltage on the rectifier side by reducing the trigger angle on the rectifier side to suppress the reduction of DC current. At this time, the output of the fixed turn-off angle control continues to decrease, and the output of the constant current control continues to increase. When the DC current decreases to the reference current value of the constant current control, the inverter side will switch from the fixed turn-off angle control to the constant current control, such as Fig. 9As shown, the DC system operating point will move from point C to point D. In this stage 3, due to the continuous decrease of DC current and the continuous decrease of reactive power consumption of the rectifier, a second transient overvoltage peak will appear at the sending end. And because the DC current will drop to the lowest point at this time, the second overvoltage peak will be greater than the first overvoltage peak.

[0129] However, when an asymmetric fault occurs on one side of the inverter, the set value generated by the fixed turn-off angle control is in a periodic fluctuation state during the recovery process of the high-voltage DC system. At this time, if the set value of the fixed turn-off angle control is in a periodic reduction stage, after the high-voltage DC system runs to stage 3, the output of the fixed turn-off angle control on the inverter side is also continuously decreasing, and the change trends of the two are the same. The high-voltage DC system can quickly complete the switch from fixed turn-off angle control to constant current control. In this case, the high-voltage DC system is equivalent to entering the constant current control earlier than the three-phase symmetrical fault scenario, that is, the DC current is reduced to the constant current control reference current value in a shorter time, such as Fig. 9 As shown in dI dr / dt reduce, dQ dr / dt Reduced, during this period of time, the rectifier consumes less reactive power, and the rectifier returns a large amount of reactive power to the sending-end AC system, which causes a more serious transient overvoltage problem than a three-phase short circuit. And as the control signal is further reduced, the high-voltage DC system is more likely to enter the constant current control in advance, and the transient overvoltage problem caused is more serious. If the high-voltage DC system is in the periodic increase stage of the DC cut-off angle signal at this time, it is reduced at this time, and the change trends of the two are opposite. The high-voltage DC system cannot immediately complete the switch from fixed cut-off angle control to constant current control, and may even lag in entering the constant current control. The DC current will not drop quickly, and the corresponding rectifier consumption reactive power decline trend is alleviated, and the transient overvoltage peak on the rectifier side is reduced accordingly. As the control signal further increases, it is more difficult for the high-voltage DC system to enter the constant current control, and the transient overvoltage peak caused by the asymmetric fault is also reduced accordingly. In summary, in the DC control signal falling interval, the transient overvoltage peak caused by asymmetric faults increases; in the DC control signal rising interval, the transient overvoltage peak caused by asymmetry decreases. That is, the fluctuation trend of the transient overvoltage peak is exactly the opposite to the fluctuation trend of the high-voltage DC system control signal.

[0130] Embodiment 1:

[0131] Specifically, the present application analyzes and verifies the transient overvoltage of the high voltage DC system under a single-phase grounding fault. A Phase transition resistance R f Taking grounding as an example for analysis, set the phase voltage before the fault E A=E B =E C =E The positive sequence, negative sequence and zero sequence impedances connected to the inverter side commutation bus are Z 1. Z 2. Z 0. In detail, its single-phase grounding fault YD The commutation voltage of the converter transformer and YY The commutation voltage of the converter transformer is calculated as follows:

[0132] First, the positive sequence, negative sequence and zero sequence current relationship after the commutation fault is obtained according to the composite sequence network corresponding to the single-phase grounding fault:

[0133] ;

[0134] in I 1 is the positive sequence current when a commutation fault occurs, I 2 is the negative sequence current when a commutation fault occurs, I 0 is the zero-sequence current when a commutation fault occurs, E is the phase voltage before the commutation fault occurs, Z 1 is the positive sequence impedance connected to the commutation bus, Z 2 is the negative sequence impedance connected to the commutation bus, Z 0 is the zero-sequence impedance connected to the commutation bus, is the transition resistance; usually Z 1= Z 2.

[0135] Secondly, according to the sequence current relationship after the phase-changing fault, the equivalent transition resistance after the phase-changing fault of the corresponding fault type is calculated. Z f :

[0136] ;

[0137] The commutation voltage of the YY type converter transformer under a single-phase grounding fault is calculated again based on the equivalent transition resistance after the commutation fault:

[0138] ;

[0139] in U Yab is the commutation voltage between phase a and phase b on the valve side of the YY type converter transformer; U Ybc is the commutation voltage between phase b and phase c on the valve side of the YY type converter transformer; U Yca is the commutation voltage between phase c and phase a on the valve side of the YY type converter transformer;U 1 is the positive sequence voltage in the composite sequence network after the commutation fault; U 2 is the negative sequence voltage in the composite sequence network after the commutation fault; a is the failure calculation coefficient;

[0140] The commutation voltage of the YD type converter transformer under a single-phase grounding fault is calculated based on the equivalent transition resistance after the commutation fault:

[0141] ;

[0142] in U Dab is the commutation voltage between phase a and phase b on the valve side of the YD type converter transformer; U Dbc is the commutation voltage between phase b and phase c on the valve side of the YD type converter transformer; U Dca is the commutation voltage between phase c and phase a on the valve side of the YD type converter transformer; U 1 is the positive sequence voltage in the composite sequence network after the commutation fault; U 2 is the negative sequence voltage in the composite sequence network after the commutation fault; a is the failure calculation coefficient, j is the symbol of the imaginary part.

[0143] Then, the phase difference between the commutation voltages of the two adjacent phases is calculated according to the commutation voltages of the two adjacent phases. The calculation formula of the phase difference is:

[0144] ;

[0145] in is the phase difference between the commutation voltages of two adjacent phases; n =1,2,...,6; for U Yab and U Dab The phase difference, for U Dab and U Ybc The phase difference, for U Ybc and U Dbc The phase difference, for U Dbc and U Yca is the phase difference, for U Yca andU Dca The phase difference, for U Dca and U Yca The phase difference; U Y After a commutation fault Corresponding to one of the commutation voltages of two adjacent phases; U D After a commutation fault Corresponding to the other commutation voltage of the adjacent two-phase commutation voltage; After a commutation fault The phase of one commutation voltage corresponding to two adjacent phase commutation voltages; After a commutation fault The phase of the other commutation voltage corresponding to the adjacent two-phase commutation voltage; To obtain the complex argument function;

[0146] at this time It is no longer equal to the phase difference of 30° between adjacent commutation voltages during normal operation. R f The phase difference between the YD type converter transformer and the YY type converter transformer under single-phase grounding fault is 0-200Ω, and the phase difference between the YD type converter transformer and the YY type converter transformer under single-phase grounding fault is substituted into the above phase difference calculation formula, and the following can be obtained: Figure 3 The phase difference trend diagram shown is from Figure 3 It can be seen that after a single-phase grounding fault occurs, the adjacent commutation voltage angles deviate, and there are three repeated commutation differences among the six commutation angles. In the case of a single-phase grounding fault, the commutation difference decreases with the increase of the transition resistance and gradually tends to 30°.

[0147] After a single-phase grounding fault occurs on one side of the high-voltage DC system inverter, the corresponding shutdown angle of the high-voltage DC system can be expressed as follows:

[0148] ;

[0149] In the formula γ is the inverter side turn-off angle, I d is the DC current, X ic is the commutation reactance, U LL is the effective value of the commutation voltage, is the advance trigger angle of the converter valve. After sorting, the setting value of the cut-off angle of the high-voltage DC system can be expressed by the following formula:

[0150] ;

[0151] After sorting, we get:

[0152] ;

[0153] in is the turn-off angle of the HVDC system after a commutation fault; is the initial value of the turn-off angle of the high voltage DC system.

[0154] The phase difference is obtained by calculating the single-phase ground fault Substituting the turn-off angle of the HVDC system into The calculation formula of can be used to calculate the fluctuation trend of the turn-off angle of the high-voltage DC system in a single cycle under a single-phase grounding fault, as follows: Figure 6 As shown by Figure 6 It can be seen that, ignoring the influence of the high-voltage DC system control, a single-phase grounding fault on one side of the inverter will cause the shutdown angle of the high-voltage DC system to fluctuate periodically within a single cycle. Specifically, the shutdown angle of the high-voltage DC system shows a trend of first decreasing and then increasing twice within a single cycle, that is, two troughs appear, and the fluctuation becomes more intense as the transition resistance becomes smaller.

[0155] Since the 12-pulse converter valve on the inverter side expands the asymmetric component of the single-phase grounding fault into the HVDC system, the HVDC system periodically enters constant current control in advance. At this time, the transient overvoltage peak also presents a periodic time-space distribution characteristic, and its fluctuation trend is similar to that of the Figure 6 The control signal fluctuation trend of the high voltage DC system shown is opposite. Figure 6 From the analysis, it can be seen that the transient overvoltage peak value caused by a single-phase grounding fault will appear twice in a single cycle, which is greater than the transient overvoltage peak value caused by a symmetrical fault. The transient overvoltage peak value caused by a single-phase grounding fault appears at 1 / 4T and 3 / 4T cycles, and the transient overvoltage peak value caused by a single-phase grounding fault changes significantly with the transition resistance.

[0156] Therefore, in Example 1 of the present application, when a single-phase grounding fault occurs in a single cycle, the shutdown angle control signal of the high-voltage DC system presents two troughs in a single cycle, and as the transition resistance decreases, the trough fluctuation of the shutdown angle control signal of the high-voltage DC system becomes larger; the transient overvoltage under the single-phase grounding fault presents two peaks in a single cycle, and as the transition resistance decreases, the peak fluctuation of the transient overvoltage becomes larger.

[0157] Embodiment 2:

[0158] Specifically, the present application analyzes and verifies the transient overvoltage of the high voltage DC system under a two-phase short circuit fault. A Phase transition resistance R fTaking grounding as an example for analysis, set the phase voltage before the fault E A =E B =E C =E The positive sequence, negative sequence and zero sequence impedances connected to the inverter side commutation bus are Z 1. Z 2. Z 0. In detail, its response to two-phase short circuit fault YD The commutation voltage of the converter transformer and YY The commutation voltage of the type converter transformer is calculated.

[0159] First, the positive sequence, negative sequence and zero sequence current relationship after the commutation fault is obtained according to the composite sequence network corresponding to the two-phase short circuit fault:

[0160] ;

[0161] in I 1 is the positive sequence current, I 2 is the negative sequence current, E is the phase voltage before the single-phase grounding fault occurs, Z 1 is the positive sequence impedance, Z 2 is the negative sequence impedance, is the transition resistor.

[0162] Secondly, according to the sequence current relationship after the phase-changing fault, the equivalent transition resistance after the phase-changing fault of the corresponding fault type is calculated. Z ff :

[0163] ;

[0164] The commutation voltage of the YY type converter transformer under two-phase interphase fault is calculated based on the equivalent transition resistance after the commutation fault:

[0165] ;

[0166] in U Yab is the commutation voltage between phase a and phase b on the valve side of the YY type converter transformer; U Ybc is the commutation voltage between phase b and phase c on the valve side of the YY type converter transformer; U Yca is the commutation voltage between phase c and phase a on the valve side of the YY type converter transformer; U 1 is the positive sequence voltage in the composite sequence network after the commutation fault; U 2 is the negative sequence voltage in the composite sequence network after the commutation fault;a is the failure calculation coefficient;

[0167] The commutation voltage of the YD type converter transformer under two-phase interphase fault is calculated based on the equivalent transition resistance after the commutation fault:

[0168] ;

[0169] in U Dab is the commutation voltage between phase a and phase b on the valve side of the YD type converter transformer; U Dbc is the commutation voltage between phase b and phase c on the valve side of the YD type converter transformer; U Dca is the commutation voltage between phase c and phase a on the valve side of the YD type converter transformer; U 1 is the positive sequence voltage in the composite sequence network after the commutation fault; U 2 is the negative sequence voltage in the composite sequence network after the commutation fault; a is the failure calculation coefficient, j is the symbol of the imaginary part.

[0170] Subsequently, similarly to the first embodiment, the second embodiment calculates the phase difference between the commutation voltages of two adjacent phases according to the commutation voltages of the two adjacent phases, and the calculation formula of the phase difference is:

[0171] ;

[0172] in is the phase difference between the commutation voltages of two adjacent phases; n =1,2,...,6; for U Yab and U Dab The phase difference, for U Dab and U Ybc The phase difference, for U Ybc and U Dbc The phase difference, for U Dbc and U Yca is the phase difference, for U Yca and U Dca The phase difference, for UDca and U Yca The phase difference; U Y After a commutation fault Corresponding to one of the commutation voltages of two adjacent phases; U D After a commutation fault Corresponding to the other commutation voltage of the adjacent two-phase commutation voltage; After a commutation fault The phase of one commutation voltage corresponding to two adjacent phase commutation voltages; After a commutation fault The phase of the other commutation voltage corresponding to the adjacent two-phase commutation voltage; To obtain the complex argument function;

[0173] at this time It is no longer equal to the phase difference of 30° between adjacent commutation voltages during normal operation. R f The phase difference between the YD type converter transformer and the YY type converter transformer under two-phase short circuit fault is 0-200Ω, and the phase difference between the YD type converter transformer and the YY type converter transformer under two-phase short circuit fault is substituted into the above phase difference calculation formula, and the following can be obtained: Figure 4 The phase difference trend diagram shown is from Figure 4 It can be seen that after a two-phase short circuit fault occurs, the adjacent commutation voltage angles deviate, and there are three repeated commutation angles in the six commutation angles. In the case of a two-phase short circuit fault, the commutation difference decreases with the increase of the transition resistance and gradually tends to 30°.

[0174] Then, a two-phase short circuit fault occurs on one side of the HVDC system inverter, and the corresponding shutdown angle of the HVDC system can be expressed as:

[0175] ;

[0176] in is the turn-off angle of the HVDC system after a commutation fault; is the initial value of the turn-off angle of the high voltage DC system.

[0177] The phase difference is obtained by calculating the two-phase short-circuit fault Substituting the turn-off angle of the HVDC system into The calculation formula of can be used to calculate the fluctuation trend of the turn-off angle of the high-voltage DC system in a single cycle under a two-phase short-circuit fault, as shown in Figure 7 As shown by Figure 7It can be seen that, ignoring the influence of the high-voltage DC system control, a two-phase short-circuit fault on one side of the inverter will cause the turn-off angle of the high-voltage DC system to fluctuate periodically within a single cycle. Specifically, the turn-off angle of the high-voltage DC system increases and then decreases twice within a single cycle, that is, two peaks appear, and the fluctuation becomes more severe as the transition resistance decreases.

[0178] Since the 12-pulse converter valve on the inverter side expands the asymmetric component of the two-phase short-circuit fault into the HVDC system, the HVDC system periodically enters constant current control in advance. At this time, the transient overvoltage peak also presents a periodic time-space distribution characteristic, and its fluctuation trend is similar to Figure 7 The control signal fluctuation trend of the high voltage DC system shown is opposite. Figure 7 From the analysis, it can be seen that the transient overvoltage peak value caused by the two-phase short-circuit fault will appear twice in a single cycle, which is greater than the transient overvoltage peak value caused by the symmetrical fault. The transient overvoltage peak value caused by the two-phase short-circuit fault appears at 1 / 2T and 1T cycles, and the transient overvoltage peak value caused by the two-phase short-circuit fault changes significantly with the transition resistance.

[0179] Therefore, in Example 2 of the present application, when a two-phase short-circuit fault occurs in a single cycle, the turn-off angle control signal of the high-voltage DC system presents two peaks in a single cycle, and as the transition resistance decreases, the peak fluctuation of the turn-off angle control signal of the high-voltage DC system becomes larger; the transient overvoltage under the two-phase short-circuit fault presents two troughs in a single cycle, and as the transition resistance decreases, the trough fluctuation of the transient overvoltage becomes larger.

[0180] Embodiment 3:

[0181] Specifically, Example 3 of the present application analyzes and verifies the transient overvoltage of the high-voltage DC system under a two-phase grounding fault. BC Phase transition resistance R f Taking grounding as an example for analysis, set the phase voltage before the fault E A = E B =E C =E The positive sequence, negative sequence and zero sequence impedances connected to the inverter side commutation bus are Z 1. Z 2. Z 0. In detail, its response to two-phase grounding fault YD The commutation voltage of the converter transformer and YY The commutation voltage of the converter transformer is calculated as follows:

[0182] First, the positive sequence, negative sequence and zero sequence current relationship after the commutation fault is obtained according to the composite sequence network corresponding to the two-phase grounding fault:

[0183] ;

[0184] ;

[0185] ;

[0186] in I 1 is the positive sequence current when a commutation fault occurs, I 2 is the negative sequence current when a commutation fault occurs, I 0 is the zero-sequence current when a commutation fault occurs, E is the phase voltage before the commutation fault occurs, Z 1 is the positive sequence impedance connected to the commutation bus, Z 2 is the negative sequence impedance connected to the commutation bus, Z 0 is the zero-sequence impedance connected to the commutation bus, is the transition resistor.

[0187] Secondly, according to the sequence current relationship after the phase-changing fault, the equivalent transition resistance after the phase-changing fault of the corresponding fault type is calculated. Z f1 and Z f2 :

[0188] ;

[0189] ;

[0190] The commutation voltage of the YY type converter transformer under two-phase grounding fault is calculated based on the equivalent transition resistance after the commutation fault:

[0191] ;

[0192] in U Yab is the commutation voltage between phase a and phase b on the valve side of the YY type converter transformer; U Ybc is the commutation voltage between phase b and phase c on the valve side of the YY type converter transformer; U Yca is the commutation voltage between phase c and phase a on the valve side of the YY type converter transformer; U 1 is the positive sequence voltage in the composite sequence network after the commutation fault; U 2 is the negative sequence voltage in the composite sequence network after the commutation fault; a is the failure calculation coefficient;

[0193] The commutation voltage of the YD type converter transformer under a two-phase grounding fault is calculated based on the equivalent transition resistance after the commutation fault:

[0194] ;

[0195] in U Dab is the commutation voltage between phase a and phase b on the valve side of the YD type converter transformer; U Dbc is the commutation voltage between phase b and phase c on the valve side of the YD type converter transformer; U Dca is the commutation voltage between phase c and phase a on the valve side of the YD type converter transformer; U 1 is the positive sequence voltage in the composite sequence network after the commutation fault; U 2 is the negative sequence voltage in the composite sequence network after the commutation fault; a is the failure calculation coefficient, j is the symbol of the imaginary part.

[0196] Subsequently, similarly to the first embodiment, the third embodiment calculates the phase difference between the commutation voltages of two adjacent phases according to the commutation voltages of the two adjacent phases. The calculation formula of the phase difference is:

[0197] ;

[0198] in is the phase difference between the commutation voltages of two adjacent phases; n =1,2,...,6; for U Yab and U Dab The phase difference, for U Dab and U Ybc The phase difference, for U Ybc and U Dbc The phase difference, for U Dbc and U Yca is the phase difference, for U Yca and U Dca The phase difference, for U Dca and U Yca The phase difference;U Y After a commutation fault Corresponding to one of the commutation voltages of two adjacent phases; U D After a commutation fault Corresponding to the other commutation voltage of the adjacent two-phase commutation voltage; After a commutation fault The phase of one commutation voltage corresponding to two adjacent phase commutation voltages; After a commutation fault The phase of the other commutation voltage corresponding to the adjacent two-phase commutation voltage; To obtain the complex argument function.

[0199] at this time It is no longer equal to the phase difference of 30° between adjacent commutation voltages during normal operation. R f The phase difference between the YD type converter transformer and the YY type converter transformer under two-phase grounding fault is 0-200Ω, and the phase difference between the YD type converter transformer and the YY type converter transformer under two-phase grounding fault is substituted into the above phase difference calculation formula, and the following can be obtained: Figure 5 The phase difference trend diagram shown is from Figure 5 It can be seen from the figure that after a two-phase grounding fault occurs, the adjacent commutation voltage angles deviate, and there are three repeated commutation differences in the six commutation angles. In the case of a two-phase grounding fault, the commutation difference remains unchanged as the transition resistance increases.

[0200] Then, a two-phase grounding fault occurs on one side of the HVDC system inverter, and the corresponding shutdown angle of the HVDC system can be expressed as:

[0201] ;

[0202] in is the turn-off angle of the HVDC system after a commutation fault; is the initial value of the turn-off angle of the high voltage DC system.

[0203] The phase difference is obtained by calculating the two-phase ground fault Substituting the turn-off angle of the HVDC system into The calculation formula of can be used to calculate the fluctuation trend of the turn-off angle of the high-voltage DC system in a single cycle under a two-phase grounding fault, as shown in Figure 8 As shown by Figure 8 It can be seen that, ignoring the influence of the high-voltage DC system control, a two-phase grounding fault on one side of the inverter will cause the shutdown angle of the high-voltage DC system to fluctuate periodically within a single cycle. Specifically, the shutdown angle of the high-voltage DC system increases first and then decreases twice within a single cycle, that is, two peaks appear, but the change in transition resistance has no obvious effect on the fluctuation.

[0204] Since the 12-pulse converter valve on the inverter side expands the asymmetric component of the two-phase grounding fault into the HVDC system, the HVDC system periodically enters constant current control in advance. At this time, the transient overvoltage peak also presents a periodic time-space distribution characteristic, and its fluctuation trend is similar to Figure 8 The control signal fluctuation trend of the high voltage DC system shown is opposite. Figure 8 Analysis shows that the transient overvoltage peak value caused by a two-phase grounding fault will appear twice in a single cycle, which is greater than the transient overvoltage peak value caused by a symmetrical fault. The trough peak value of the transient overvoltage caused by a two-phase grounding fault appears at 1 / 2T and 1T cycles, and the fluctuation trend of the transient overvoltage peak value is negatively correlated with the fluctuation trend of the turn-off angle control signal. In addition, the transient overvoltage peak value caused by a two-phase grounding fault does not change significantly with the transition resistance.

[0205] Therefore, when a two-phase grounding fault occurs in Example 3 of the present application, the shutdown angle control signal of the high-voltage DC system presents two peaks in a single cycle, and as the transition resistance decreases or increases, the peak of the shutdown angle control signal of the high-voltage DC system does not fluctuate; the transient overvoltage under the two-phase grounding fault presents two troughs in a single cycle, and as the transition resistance decreases or increases, the trough of the transient overvoltage does not fluctuate.

[0206] Furthermore, the embodiment of the present application verifies the present method based on the CIGRE (International Conference on Large Electric Systems) standard DC model. Specifically, in the present application, based on the CIGRE standard DC model, a single-phase ground fault is imposed on the AC bus on one side of the inverter, and the transient overvoltage peak value at the AC bus at the sending end during the phase change failure is measured and recorded, and the fault duration is 0.1 seconds. Fig.10 It can be seen that when the fault occurs at 4.012s, the transient overvoltage peak value caused by the single-phase fault is lower than the transient overvoltage peak value caused by the three-phase fault, and when the fault occurs at 4.006s, the transient overvoltage peak value caused by the single-phase fault is higher than the transient overvoltage peak value caused by the three-phase fault. When the fault occurs at 4.006s, the DC current decreases faster in the third stage, corresponding to Fig.11 As shown, it can be seen that in the case of an asymmetric fault, the high voltage DC system enters constant current control earlier, which is consistent with the transient process analysis of the DC control signal in the asymmetric fault scenario.

[0207] Secondly, the present application sets three-phase grounding, single-phase grounding, two-phase short circuit and two-phase grounding faults at the same fault position on the inverter side. By changing the fault occurrence time within a cycle, the peak value of transient overvoltage at the sending end is counted. The grounding resistance is set to 0.01Ω, and the statistical results are as follows Fig.12 As shown. Fig.12It can be seen that the transient overvoltage peak value caused by a single-phase grounding fault has two peaks in one cycle, which appear at 1 / 4T and 3 / 4T cycles respectively (T is the length of a single cycle), and its magnitude is greater than the transient overvoltage peak value caused by a three-phase grounding fault; two-phase short circuit and two-phase grounding have two troughs in one cycle, and their peaks appear at 1 / 2T and 1T cycles respectively (T is the length of a single cycle), and their magnitude is also greater than the transient overvoltage peak value caused by a three-phase grounding fault, causing more serious safety hazards, and its fluctuation law is opposite to the fluctuation law of the DC control signal caused by asymmetric faults. Therefore, the results obtained by this method are consistent with the analysis results of the dynamic whole process of the sending end voltage during the phase change failure caused by asymmetric faults. Therefore, the transient overvoltage analysis method during the phase change failure of the 12-pulse converter valve in this application can accurately analyze the transient overvoltage changes under various asymmetric faults and effectively predict the overvoltage conditions of the high-voltage DC system.

[0208] Combination Figure 2 As shown, the present application also discloses a transient overvoltage analysis method and device for a 12-pulse converter valve commutation fault, the device comprising:

[0209] A first acquisition module is used to acquire the fault type when a commutation fault occurs, wherein the fault type at least includes a single-phase grounding fault, a two-phase short circuit fault or a two-phase grounding fault;

[0210] A second acquisition module is used to acquire the phase voltage before the commutation fault, the corresponding sequence impedance and the composite sequence network corresponding to the fault type, and acquire the sequence current relationship after the commutation fault according to the composite sequence network;

[0211] An equivalent resistance calculation module is used to calculate the equivalent transition resistance after a commutation fault of a corresponding fault type occurs according to the sequence current relationship after the commutation fault;

[0212] The commutation voltage calculation module is used to obtain the phase voltage and the corresponding sequence impedance before the commutation fault, and calculate the commutation voltage of the YD type converter transformer and the commutation voltage of the YY type converter transformer under different fault types in combination with the sequence current relationship after the commutation fault;

[0213] A phase difference calculation module, used for calculating the phase difference between the commutation voltages of two adjacent phases according to the commutation voltages of the two adjacent phases;

[0214] A cut-off angle calculation module is used to calculate the cut-off angle of the high-voltage DC system after a commutation fault according to the phase difference between the commutation voltages of two adjacent phases;

[0215] A signal analysis module, used for obtaining a fluctuation trend of a cut-off angle control signal within a cycle according to a cut-off angle of the high voltage DC system within the cycle;

[0216] The result output module is used to obtain the transient overvoltage characteristics after the commutation fault according to the fluctuation trend of the turn-off angle control signal within the cycle.

[0217] The device provided in the embodiment of the present application can achieve Figure 1 To avoid repetition, the various processes implemented by the method embodiment will not be described again here.

[0218] The above is only a preferred implementation of the present application. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present application. These improvements and modifications should also be regarded as the scope of protection of the present application.

Claims

1. A transient overvoltage analysis method for a 12-pulse converter valve commutation fault, used for analyzing voltage changes when a commutation fault occurs in a high-voltage direct current system, wherein the 12-pulse converter valve comprises at least a YD-type converter transformer and a YY-type converter transformer, and the high-voltage direct current system comprises at least a rectifier and an inverter, characterized in that: The method comprises the following steps: Acquire the fault type when the phase change fault occurs, wherein the fault type at least includes a single-phase grounding fault, a two-phase short circuit fault or a two-phase grounding fault; Obtaining the phase voltage before the commutation fault, the corresponding sequence impedance and the composite sequence network corresponding to the fault type, and obtaining the sequence current relationship after the commutation fault according to the composite sequence network; According to the sequence current relationship after the phase-changing fault, the equivalent transition resistance after the phase-changing fault of the corresponding fault type occurs is calculated; Based on the equivalent transition resistance after the commutation fault, the commutation voltage of the YD type converter transformer and the commutation voltage of the YY type converter transformer under different fault types are calculated respectively; Calculate the phase difference of the commutation voltages of two adjacent phases according to the commutation voltages of the two adjacent phases; The shutdown angle of the high voltage DC system after a commutation fault is obtained by calculating the phase difference between the commutation voltages of two adjacent phases; According to the cut-off angle of the high-voltage DC system in a single cycle, the fluctuation trend of the cut-off angle control signal of the high-voltage DC system in a single cycle is obtained: Get the rectifier external characteristic equation: According to the external characteristic equation of the rectifier, the time derivative is obtained to obtain the derivative result: Where Q dr Reactive power consumed by the rectifier, I dr is the DC current of the rectifier, U dr0 is the no-load voltage of the rectifier, U dr is the voltage of the rectifier; According to the derivative result of the rectifier external characteristic equation and the fluctuation trend of the turn-off angle control signal within the cycle, the transient overvoltage fluctuation trend after the commutation fault is obtained, wherein the transient overvoltage peak fluctuation trend is negatively correlated with the turn-off angle control signal fluctuation trend; The transient overvoltage change after commutation fault is obtained according to the fluctuation trend of the turn-off angle control signal of the high voltage DC system in a single cycle.

2. The transient overvoltage analysis method for 12-pulse converter valve commutation fault according to claim 1 is characterized in that: The steps of calculating and obtaining the commutation voltage of the YD type converter transformer and the commutation voltage of the YY type converter transformer under a single-phase grounding fault include: According to the composite sequence network corresponding to the single-phase grounding fault, the positive sequence, negative sequence and zero sequence current relationship after the commutation fault is obtained: Where I1 is the positive sequence current when the commutation fault occurs, I2 is the negative sequence current when the commutation fault occurs, I0 is the zero sequence current when the commutation fault occurs, E is the phase voltage before the commutation fault occurs, Z1 is the positive sequence impedance connected to the commutation bus, Z2 is the negative sequence impedance connected to the commutation bus, Z0 is the zero sequence impedance connected to the commutation bus, R f is the transition resistance; According to the sequence current relationship after the phase-changing fault, calculate the equivalent transition resistance Z after the phase-changing fault of the corresponding fault type f : The commutation voltage of the YY type converter transformer under a single-phase grounding fault is calculated based on the equivalent transition resistance after the commutation fault: Among them U Yab is the commutation voltage between phase a and phase b on the valve side of the YY type converter transformer; U Ybc is the commutation voltage between phase b and phase c on the valve side of the YY type converter transformer; U Yca is the commutation voltage between phase c and phase a on the valve side of the YY type converter transformer; U1 is the positive sequence voltage in the composite sequence network after the commutation fault; U2 is the negative sequence voltage in the composite sequence network after the commutation fault; a is the fault calculation coefficient; The commutation voltage of the YD type converter transformer under a single-phase grounding fault is calculated based on the equivalent transition resistance after the commutation fault: Among them U Dab is the commutation voltage between phase a and phase b on the valve side of the YD type converter transformer; U Dbc is the commutation voltage between phase b and phase c on the valve side of the YD type converter transformer; U Dca is the commutation voltage between phase c and phase a on the valve side of the YD type converter transformer; U1 is the positive sequence voltage in the composite sequence network after the commutation fault; U2 is the negative sequence voltage in the composite sequence network after the commutation fault; a is the fault calculation coefficient, and j is the sign of the imaginary part.

3. The transient overvoltage analysis method for 12-pulse converter valve commutation fault according to claim 1 is characterized in that: The steps of calculating and obtaining the commutation voltage of the YD type converter transformer and the commutation voltage of the YY type converter transformer under a two-phase short circuit fault include: According to the composite sequence network corresponding to the two-phase phase-to-phase fault, the positive-sequence and negative-sequence current relationship after the commutation fault is obtained: Where I1 is the positive sequence current, I2 is the negative sequence current, E is the phase voltage before the single-phase grounding fault occurs, Z1 is the positive sequence impedance, Z2 is the negative sequence impedance, R f is the transition resistance; According to the sequence current relationship after the phase-commutation fault, the equivalent transition resistance after the phase-commutation fault of the corresponding fault type is calculated: The commutation voltage of the YY type converter transformer under two-phase interphase fault is calculated based on the equivalent transition resistance after the commutation fault: Among them U Yab is the commutation voltage between phase a and phase b on the valve side of the YY type converter transformer; U Ybc is the commutation voltage between phase b and phase c on the valve side of the YY type converter transformer; U Yca is the commutation voltage between phase c and phase a on the valve side of the YY type converter transformer; U1 is the positive sequence voltage in the composite sequence network after the commutation fault; U2 is the negative sequence voltage in the composite sequence network after the commutation fault; a is the fault calculation coefficient; The commutation voltage of the YD type converter transformer under two-phase interphase fault is calculated based on the equivalent transition resistance after the commutation fault: Among them U Dab is the commutation voltage between phase a and phase b on the valve side of the YD type converter transformer; U Dbc is the commutation voltage between phase b and phase c on the valve side of the YD type converter transformer; U Dca is the commutation voltage between phase c and phase a on the valve side of the YD type converter transformer; U1 is the positive sequence voltage in the composite sequence network after the commutation fault; U2 is the negative sequence voltage in the composite sequence network after the commutation fault; a is the fault calculation coefficient, and j is the sign of the imaginary part.

4. The transient overvoltage analysis method for 12-pulse converter valve commutation fault according to claim 1 is characterized in that: The steps of calculating and obtaining the commutation voltage of the YD type converter transformer and the commutation voltage of the YY type converter transformer under a two-phase grounding fault include: According to the composite sequence network corresponding to the two-phase grounding fault, the positive sequence, negative sequence and zero sequence current relationship after the commutation fault is obtained: Where I1 is the positive sequence current when the commutation fault occurs, I2 is the negative sequence current when the commutation fault occurs, I0 is the zero sequence current when the commutation fault occurs, E is the phase voltage before the commutation fault occurs, Z1 is the positive sequence impedance connected to the commutation bus, Z2 is the negative sequence impedance connected to the commutation bus, Z0 is the zero sequence impedance connected to the commutation bus, R f is the transition resistance; According to the sequence current relationship after the phase-changing fault, calculate the equivalent transition resistance Z after the phase-changing fault of the corresponding fault type f1 and Z f2 : The commutation voltage of the YY type converter transformer under two-phase grounding fault is calculated based on the equivalent transition resistance after the commutation fault: Among them U Yab is the commutation voltage between phase a and phase b on the valve side of the YY type converter transformer; U Ybc is the commutation voltage between phase b and phase c on the valve side of the YY type converter transformer; U Yca is the commutation voltage between phase c and phase a on the valve side of the YY type converter transformer; U1 is the positive sequence voltage in the composite sequence network after the commutation fault; U2 is the negative sequence voltage in the composite sequence network after the commutation fault; a is the fault calculation coefficient; The commutation voltage of the YD type converter transformer under a two-phase grounding fault is calculated based on the equivalent transition resistance after the commutation fault: Among them U Dab is the commutation voltage between phase a and phase b on the valve side of the YD type converter transformer; U Dbc is the commutation voltage between phase b and phase c on the valve side of the YD type converter transformer; U Dca is the commutation voltage between phase c and phase a on the valve side of the YD type converter transformer; U1 is the positive sequence voltage in the composite sequence network after the commutation fault; U2 is the negative sequence voltage in the composite sequence network after the commutation fault; a is the fault calculation coefficient, and j is the sign of the imaginary part.

5. The transient overvoltage analysis method for 12-pulse converter valve commutation fault according to claim 1 is characterized in that: In a single cycle of the single-phase grounding fault, the fluctuation trend of the cut-off angle control signal obtained according to the cut-off angle of the high-voltage DC system is: The turn-off angle control signal of the high-voltage DC system under a single-phase grounding fault presents two troughs in a single cycle, and as the transition resistance decreases, the trough fluctuation of the turn-off angle control signal of the high-voltage DC system becomes larger; According to the fluctuation trend of the turn-off angle control signal of the single-phase grounding fault, the transient overvoltage change trend after the commutation fault is obtained as follows: The transient overvoltage under a single-phase grounding fault presents two peaks in a single cycle, and as the transition resistance decreases, the peak fluctuation of the transient overvoltage becomes larger.

6. The transient overvoltage analysis method for 12-pulse converter valve commutation fault according to claim 1 is characterized in that: In a single cycle of the two-phase short-circuit fault, the fluctuation trend of the cut-off angle control signal obtained according to the cut-off angle of the high-voltage DC system is: The turn-off angle control signal of the high-voltage DC system under a two-phase short-circuit fault presents two peaks in a single cycle, and as the transition resistance decreases, the peak fluctuation of the turn-off angle control signal of the high-voltage DC system becomes larger; According to the fluctuation trend of the turn-off angle control signal of the two-phase short-circuit fault, the transient overvoltage change trend after the commutation fault is obtained as follows: The transient overvoltage under a two-phase short-circuit fault presents two troughs in a single cycle, and as the transition resistance decreases, the trough fluctuation of the transient overvoltage becomes larger.

7. The transient overvoltage analysis method for 12-pulse converter valve commutation fault according to claim 1 is characterized in that: In a single cycle of the two-phase grounding fault, the fluctuation trend of the cut-off angle control signal obtained according to the cut-off angle of the high voltage DC system is: The cut-off angle control signal of the high-voltage DC system under a two-phase grounding fault presents two peaks in a single cycle, and as the transition resistance decreases or increases, the peak of the cut-off angle control signal of the high-voltage DC system does not fluctuate; According to the fluctuation trend of the turn-off angle control signal of the two-phase grounding fault, the transient overvoltage change trend after the commutation fault is obtained as follows: The transient overvoltage under a two-phase grounding fault presents two troughs in a single cycle, and the trough of the transient overvoltage does not fluctuate as the transition resistance decreases or increases.

8. The transient overvoltage analysis method for 12-pulse converter valve commutation fault according to claim 1 is characterized in that: The step of calculating and obtaining the turn-off angle of the high voltage DC system after a commutation fault according to the phase difference of the commutation voltages of two adjacent phases comprises: Get the phase difference between the commutation voltages of two adjacent phases after a commutation fault: in is the phase difference between the commutation voltages of two adjacent phases; where n=1,2,...,6; For U Yab with U Dab The phase difference, For U Dab with U Ybc The phase difference, For U Ybc with U Dbc The phase difference, For U Dbc with U Yca is the phase difference, For U Yca with U Dca The phase difference, For U Dca with U Yca The phase difference of U Y After a commutation fault Corresponding to one of the commutation voltages of the adjacent two phases; U D After a commutation fault Corresponding to the other commutation voltage of two adjacent phases; After a commutation fault The phase of one commutation voltage corresponding to two adjacent phase commutation voltages; After a commutation fault The phase of the other commutation voltage in the corresponding adjacent two-phase commutation voltage; arg() is to obtain the complex angle function; The shutdown angle of the high-voltage DC system after a commutation fault is calculated based on the phase difference between the commutation voltages of two adjacent phases: where γ (n)ref is the turn-off angle of the high-voltage DC system after a commutation fault; γ0 is the initial value of the turn-off angle of the high-voltage DC system.

9. A transient overvoltage analysis method and device for 12-pulse converter valve commutation fault, characterized in that: The device comprises: A first acquisition module is used to acquire the fault type when a commutation fault occurs, wherein the fault type at least includes a single-phase grounding fault, a two-phase short circuit fault or a two-phase grounding fault; A second acquisition module is used to acquire the phase voltage before the commutation fault, the corresponding sequence impedance and the composite sequence network corresponding to the fault type, and acquire the sequence current relationship after the commutation fault according to the composite sequence network; An equivalent resistance calculation module is used to calculate the equivalent transition resistance after a commutation fault of a corresponding fault type occurs according to the sequence current relationship after the commutation fault; The commutation voltage calculation module is used to obtain the phase voltage and the corresponding sequence impedance before the commutation fault, and calculate the commutation voltage of the YD type converter transformer and the commutation voltage of the YY type converter transformer under different fault types in combination with the sequence current relationship after the commutation fault; A phase difference calculation module, used for calculating the phase difference between the commutation voltages of two adjacent phases according to the commutation voltages of the two adjacent phases; A cut-off angle calculation module is used to calculate the cut-off angle of the high-voltage DC system after a commutation fault according to the phase difference between the commutation voltages of two adjacent phases; The signal analysis module is used to obtain the fluctuation trend of the cut-off angle control signal within the cycle according to the cut-off angle of the high-voltage DC system within the cycle: Get the rectifier external characteristic equation: According to the external characteristic equation of the rectifier, the time derivative is obtained to obtain the derivative result: Where Q dr Reactive power consumed by the rectifier, I dr is the DC current of the rectifier, U dr0 is the no-load voltage of the rectifier, U dr is the voltage of the rectifier; According to the derivative result of the rectifier external characteristic equation and the fluctuation trend of the turn-off angle control signal within the cycle, the transient overvoltage fluctuation trend after the commutation fault is obtained, wherein the transient overvoltage peak fluctuation trend is negatively correlated with the turn-off angle control signal fluctuation trend; The result output module is used to obtain the transient overvoltage characteristics after the commutation fault according to the fluctuation trend of the turn-off angle control signal within the cycle.

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