Methods, systems, equipment and media for predictive control of commutation failure in DC transmission systems

Abstract

This application discloses a method, system, equipment, and medium for predictive control of commutation failure in a DC transmission system, belonging to the field of DC transmission technology. The method includes: determining whether voltage distortion occurs on an AC bus that is not directly electrically connected to the inverter-side converter bus based on system parameters; when voltage distortion occurs, performing predictive control of commutation failure on the grid-commutated converter on the inverter side; the predictive control includes increasing the turn-off angle or decreasing the firing angle of the grid-commutated converter. This application utilizes the voltage of the AC bus that is not directly electrically connected to the inverter-side converter bus as an auxiliary prediction criterion, increasing the turn-off angle in advance before AC bus faults cause voltage distortion on the converter bus, thus preventing commutation failure.

Description

Technical Field

[0001] The embodiments of this application relate to the field of DC power transmission technology, and in particular to a method, system, device and medium for predictive control of commutation failure in DC power transmission systems. Background Technology

[0002] High-voltage direct current (HVDC) transmission systems employ thyristor-based grid-commutation converters. Since thyristors cannot be controlled to turn off, when a fault occurs in the AC system connected to the HVDC transmission system, existing technologies can quickly activate the commutation failure prediction function based on the voltage distortion of the converter bus, thus avoiding commutation failure when the AC system fault is not severe.

[0003] However, in addition to faults in the AC systems connected to the HVDC transmission system, faults in indirectly connected AC systems such as transformers can also affect the voltage of the converter bus. Due to the relatively large electrical distance, the voltage distortion of the converter bus is initially small, and the commutation failure prediction criterion based on the converter bus voltage cannot be activated. However, the voltage distortion will gradually increase over time, and commutation failure may occur before the commutation failure prediction criterion based on the converter bus voltage is activated, thus causing large fluctuations in the power of the HVDC transmission system. Summary of the Invention

[0004] The embodiments of this application provide a method, system, device, and medium for predicting and controlling commutation failure in a DC transmission system, in order to solve the technical problem in the prior art where voltage distortion caused by faults in high-voltage DC transmission systems leads to commutation failure.

[0005] To address the aforementioned technical problems, embodiments of this application disclose the following technical solutions:

[0006] Firstly, a method for predictive control of commutation failure in a DC transmission system is provided, applied to a DC transmission system including a rectifier side and an inverter side. The method includes:

[0007] Obtain system parameters for AC buses that are not directly electrically connected to the inverter-side converter bus, wherein the converter bus is the bus connected to the grid side of the inverter-side converter transformer;

[0008] Determine whether voltage distortion occurs on the AC bus based on the system parameters;

[0009] When voltage distortion occurs on the AC bus, commutation failure prediction control is performed on the grid commutation converter on the inverter side.

[0010] Wherein, the AC bus that is not directly electrically connected to the converter bus on the inverter side includes AC buses with the same voltage level connected to the converter bus on the inverter side via external lines and / or AC buses with different voltage levels connected via AC transformers and / or AC buses connected via external power grids; the commutation failure prediction control includes increasing the turn-off angle of the grid commutation converter or decreasing the firing angle of the grid commutation converter.

[0011] In conjunction with the first aspect, the system parameters of the AC bus include the zero-sequence voltage amplitude of the three-phase AC voltage and / or the amplitude of the three-phase AC voltage after Clarke transformation.

[0012] In conjunction with the first aspect, the method for determining whether voltage distortion occurs on the AC bus based on the system parameters includes:

[0013] The zero-sequence voltage amplitude of the three-phase AC voltage of the AC bus is compared with a first threshold.

[0014] If the zero-sequence voltage amplitude is greater than the first threshold, it indicates that voltage distortion has occurred on the AC bus.

[0015] In conjunction with the first aspect, the method for determining whether voltage distortion occurs on the AC bus based on the system parameters includes:

[0016] Obtain the Clarke-transformed amplitude of the three-phase AC voltage of the AC bus. Subtract the real-time value from the filtered Clarke-transformed amplitude of the three-phase AC voltage. If the difference is greater than the second threshold, it indicates that the AC bus has voltage distortion.

[0017] In conjunction with the first aspect,

[0018] The method for determining whether voltage distortion occurs on the AC bus based on the system parameters includes:

[0019] The change in any phase of the three-phase AC voltage of the AC bus per unit time is greater than the third threshold.

[0020] In conjunction with the first aspect, the method of increasing the turn-off angle or decreasing the firing angle of the grid commutator includes:

[0021] Obtain the firing angle command value of the power grid commutator;

[0022] The commutation failure prediction angle is calculated.

[0023] The firing angle of the grid commutation converter is obtained by subtracting the commutation failure prediction angle from the firing angle command value.

[0024] In conjunction with the first aspect, the method for calculating the commutation failure prediction angle includes:

[0025] Obtain the zero-sequence voltage amplitude of the three-phase AC voltage of the AC bus, and / or the amplitude of the three-phase AC voltage of the AC bus after Clarke transformation;

[0026] The commutation failure prediction angle is generated based on the magnitude of the zero-sequence voltage amplitude or the change in the three-phase AC voltage amplitude.

[0027] Specifically, the larger the zero-sequence voltage amplitude, the larger the commutation failure prediction angle, and a maximum value is set to limit it; the larger the amplitude change of the three-phase AC voltage after Clarke transformation, the larger the commutation failure prediction angle, and a maximum value is set to limit it.

[0028] Secondly, a commutation failure prediction and control system for a DC transmission system is provided, applied to a DC transmission system including a rectifier side and an inverter side, the commutation failure prediction and control system comprising:

[0029] The data acquisition module is used to acquire system parameters of AC busbars that are not directly electrically connected to the converter busbar on the inverter side, wherein the converter busbar is the busbar connected to the grid side of the converter transformer on the inverter side.

[0030] The judgment module is used to determine whether voltage distortion occurs on the AC bus based on the system parameters;

[0031] The control module is used to perform commutation failure prediction control on the AC bus when voltage distortion occurs.

[0032] Wherein, the AC bus that is not directly electrically connected to the converter bus on the inverter side includes AC buses of the same voltage level connected to the converter bus on the inverter side via external lines and / or AC buses of different voltage levels connected via AC transformers and / or AC buses connected via external power grids; the commutation failure prediction control includes increasing the turn-off angle of the grid commutation converter or decreasing the firing angle of the grid commutation converter.

[0033] Thirdly, a computer device is provided, including a memory and a processor, wherein the memory stores a computer program, and the processor executes the computer program to implement the DC transmission system commutation failure prediction and control method as described in any one of the first aspects.

[0034] Fourthly, a computer-readable storage medium is provided storing a computer program that, when executed by a processor, implements the DC transmission system commutation failure prediction and control method as described in any one of the first aspects.

[0035] One of the above technical solutions has the following advantages or beneficial effects:

[0036] Compared with existing technologies, this application provides a commutation failure prediction and control method for DC transmission systems, applied to DC transmission systems including a rectifier side and an inverter side. The method includes: acquiring system parameters of an AC bus that is not directly electrically connected to the inverter side's converter bus; determining whether voltage distortion occurs on the AC bus based on the system parameters; and when voltage distortion occurs on the AC bus, performing commutation failure prediction and control on the grid-commutated converter on the inverter side. The AC bus includes AC buses of the same voltage level connected to the inverter side's converter bus via external lines and / or AC buses of different voltage levels connected via AC transformers and / or AC buses connected via an external power grid. The commutation failure prediction and control includes increasing the turn-off angle or decreasing the firing angle of the grid-commutated converter. The method provided in this application can predict potential commutation impacts in advance based on AC bus faults that are not directly electrically connected, thereby reducing the probability of commutation failure in the DC transmission system and improving the reliability of the DC transmission system.

[0037] This application discloses a commutation failure prediction and control system for a DC transmission system, applied to a DC transmission system including a rectifier side and an inverter side. The system includes: a data acquisition module for acquiring system parameters of the AC bus of the converter bus on the inverter side; a judgment module for determining whether voltage distortion has occurred on the AC bus based on the system parameters; and a control module for performing commutation failure prediction and control on the AC bus when voltage distortion occurs. The AC bus includes AC buses of the same voltage level connected to the converter bus on the inverter side via external lines and / or AC buses of different voltage levels connected via AC transformers and / or AC buses connected via an external power grid. The system parameters are acquired through a grid-connected commutator on the inverter side. The commutation failure prediction and control includes increasing the turn-off angle or decreasing the firing angle of the grid-connected commutator. The system provided in this application can predict potential commutation effects in advance based on AC bus faults that are not directly electrically connected, thereby reducing the probability of commutation failure in the DC transmission system and improving its reliability. Attached Figure Description

[0038] The technical solution and other beneficial effects of this application will become apparent from the following detailed description of specific embodiments in conjunction with the accompanying drawings.

[0039] Figure 1 This is a schematic diagram of the method flow structure provided in the embodiments of this application;

[0040] Figure 2 This is a schematic diagram of the circuit structure of a DC power transmission system provided in an embodiment of this application;

[0041] Figure 3 This is a schematic diagram of the commutation failure prediction and control function provided in the embodiments of this application;

[0042] Figure 4 This is a schematic diagram of the system structure provided in an embodiment of this application.

[0043] The attached figures are labeled as follows:

[0044] 91-First smoothing reactor, 92-Second smoothing reactor, 93-First DC filter, 94-Second DC filter, 95-Third smoothing reactor, 96-Fourth smoothing reactor, 97-Third DC filter, 98-Fourth DC filter, 100-Rectifier station, 110-First DC pole, 111-First converter, 113-Metallic return line changeover switch, 114-Rectifier station grounding electrode line, 115-Rectifier station grounding electrode, 116-First converter transformer, 118-First AC filter bank, 119-First DC pole neutral bus switch, 120-Second DC pole, 121-Second converter, 126- Second converter transformer, 129 - Second DC pole neutral bus switch, 131 - First converter transformer incoming switch, 133 - Second converter transformer incoming switch, 140 - First converter bus, 150 - First DC line, 160 - Second DC line, 171 - First DC filter isolating switch, 172 - First pole bus isolating switch, 173 - First metallic return isolating switch, 174 - First isolating switch, 175 - Second isolating switch, 181 - Second DC filter isolating switch, 182 - Second pole bus isolating switch, 183 - Second metallic return isolating switch, 184 - Third isolating switch, 185 - Fourth Isolating switch, 190-Ground return transfer switch, 200-Inverter station, 210-Third DC pole, 211-Third converter, 213-Grounding electrode line isolating switch, 214-Inverter station grounding electrode line, 215-Inverter station grounding electrode, 216-Third converter transformer, 218-Second AC filter bank, 219-Third DC pole neutral bus switch, 220-Fourth DC pole, 221-Fourth converter, 226-Fourth converter transformer, 229-Fourth DC pole neutral bus switch, 231-Third converter transformer incoming switch, 232-Filter switch, 233-Fourth converter transformer incoming switch, 234- 235 - First bus tie switch, 236 - Second bus tie switch, 240 - AC transformer, 241 - Second converter bus, 242 - Third AC bus, 243 - Fifth AC bus, 271 - Third DC filter isolating switch, 272 - Third pole bus isolating switch, 273 - Third metallic return isolating switch, 274 - Fifth isolating switch, 275 - Sixth isolating switch, 281 - Fourth DC filter isolating switch, 282 - Fourth pole bus isolating switch, 283 - Fourth metallic return isolating switch, 284 - Seventh isolating switch, 285 - Eighth isolating switch, 290 - Metallic return isolating switch. Detailed Implementation

[0045] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. In the description of this application, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the accompanying drawings and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of the stated features. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0046] Therefore, obtaining information about AC bus faults that are not directly electrically connected to the grid side of the converter transformer within the station in advance will help improve the response speed to commutation failures and allow for proactive measures.

[0047] The specific implementation methods of this application are illustrated below through examples:

[0048] like Figure 1 As shown, this application provides a method for predictive control of commutation failure in a DC transmission system. The DC transmission system includes a rectifier side, an inverter side, a converter bus, and an AC bus. The AC bus includes AC buses of the same voltage level connected to the converter bus on the inverter side via external lines and / or AC buses of different voltage levels connected via AC transformers and / or AC buses connected via an external power grid. The method of this application includes:

[0049] S1: Obtain system parameters for AC buses that are not directly electrically connected to the converter bus on the inverter side.

[0050] The AC busbars not directly electrically connected to the inverter-side converter busbar include AC buses of the same voltage level connected to the inverter-side converter busbar via external lines and / or AC buses of different voltage levels connected via AC transformers and / or AC buses connected via external power grids. The system parameters of the AC busbars include the zero-sequence voltage amplitude of the three-phase AC voltage and / or the amplitude after Clarke transformation of the three-phase AC voltage. Specifically, whether a fault has occurred on the AC busbar can be determined by the zero-sequence voltage amplitude or the amplitude after Clarke transformation of the three-phase AC voltage; therefore, only one parameter needs to be considered during the judgment. Through Clarke transformation, the three-phase AC signal can be converted from a time-domain representation to a vector-domain representation, representing the voltage signals of the three phases as the amplitude and phase angle of a single vector.

[0051] S2: Determine whether voltage distortion occurs on the AC bus based on system parameters.

[0052] Specifically, the methods include:

[0053] The zero-sequence voltage amplitude of the three-phase AC voltage of the AC bus is compared with the first threshold.

[0054] The comparison method includes: obtaining the zero-sequence voltage amplitude of the three-phase AC voltage of the AC bus; if the zero-sequence voltage amplitude is greater than a first threshold, it indicates that a fault has occurred on the AC bus. A single-phase ground fault on the AC bus is simulated to find the critical value at which the zero-sequence voltage amplitude causes commutation failure in the high-voltage direct current transmission system, and this critical value is used as the first threshold.

[0055] The method also includes:

[0056] The amplitude of the three-phase AC voltage after Clarke transformation of the AC bus is compared with the second threshold.

[0057] The comparison method includes: obtaining the Clarke-transformed amplitude of the three-phase AC voltage of the AC bus; subtracting the real-time value from the filtered Clarke-transformed amplitude of the three-phase AC voltage; if the difference is greater than a second threshold, it indicates that voltage distortion has occurred on the AC bus. By simulating a three-phase ground fault on the AC bus, the critical value at which changes in the Clarke-transformed amplitude of the three-phase AC voltage cause commutation failure in the high-voltage direct current transmission system is identified, and this critical value is used as the second threshold.

[0058] The method also includes:

[0059] The change in any phase of the three-phase AC voltage of the AC bus per unit time is greater than the third threshold.

[0060] The comparison method includes: obtaining the unit-time changes of the first, second, and third amplitudes of the three-phase AC voltage of the AC bus; if the unit-time change of the first, second, or third amplitude is greater than a third threshold, it indicates that voltage distortion has occurred on the AC bus. By simulating single-phase, two-phase, and three-phase ground faults on the AC bus, the critical value at which the unit-time change of the first, second, or third amplitude causes commutation failure in the HVDC transmission system is identified, and this critical value is used as the third threshold.

[0061] S3: When voltage distortion occurs on the AC bus, commutation failure prediction control is performed on the grid commutator on the inverter side; wherein, the commutation failure prediction control includes increasing the turn-off angle of the grid commutator or decreasing the firing angle of the grid commutator.

[0062] Methods to increase the turn-off angle or decrease the firing angle of a grid-commutated converter include:

[0063] Obtain the firing angle command value of the commutation converter; calculate the commutation failure prediction angle; subtract the commutation failure prediction angle from the firing angle command value to increase the turn-off angle of the grid commutation converter, or subtract the commutation failure prediction angle from the firing angle command value to obtain the firing angle of the grid commutation converter.

[0064] The calculation methods for the prediction angle of power grid commutation failure include:

[0065] Obtain the zero-sequence voltage amplitude of the three-phase AC voltage of the AC bus, and / or the amplitude of the three-phase AC voltage of the AC bus after Clarke transformation;

[0066] The commutation failure prediction angle is generated based on the magnitude of the zero-sequence voltage amplitude or the magnitude of the three-phase AC voltage after Clarke transformation.

[0067] The larger the zero-sequence voltage amplitude, the larger the commutation failure prediction angle, and a maximum value is set to limit it, such as 8°; the larger the amplitude change of the three-phase AC voltage after Clarke transformation, the larger the commutation failure prediction angle, such as 8°.

[0068] like Figure 2 As shown in the figure, this application embodiment also provides a schematic diagram of the commutation circuit structure of a DC transmission system. In this embodiment, the grid commutation converter adopts a twelve-pulse bridge circuit, including twelve bridge arms, each of which includes thyristors connected in series. X1 and X2 represent the cathode and anode terminals on the DC side of the grid commutation converter, respectively.

[0069] exist Figure 2In this context, the DC transmission equipment is a high-voltage DC transmission equipment. The main circuit of the high-voltage DC transmission equipment includes a rectifier station 100 (i.e., the rectifier side), an inverter station 200 (i.e., the inverter side), a first DC line 150, a second DC line 160, a rectifier station grounding electrode line 114, a rectifier station grounding electrode 115, an inverter station grounding electrode line 214, and an inverter station grounding electrode 215. The rectifier station 100 and inverter station 200 are connected via a first DC line 150 and a second DC line 160, respectively. The rectifier station 100 includes a first DC pole 110, a second DC pole 120, a first AC filter bank 118, a first converter bus 140, a first converter transformer incoming line switch 131, a second converter transformer incoming line switch 133, a metallic return line changeover switch 113, a ground return line changeover switch 190, a first isolating switch 174, a second isolating switch 175, a third isolating switch 184, and a fourth isolating switch 185. The first isolating switch 174, the second isolating switch 175, the third isolating switch 184, and the fourth isolating switch 185 are all bipolar neutral zone isolating switches. The first AC filter bank 118 is connected to the first converter bus 140. DC pole 110 is connected to the first converter bus 140 via the first converter transformer incoming line switch 131. DC pole 120 is connected to the first converter bus 140 via the second converter transformer incoming line switch 133. The first isolating switch 174 and the second isolating switch 175 are connected in parallel, with one end connected to the first DC pole 110 and the other end connected to the metallic return line changeover switch 113. The other end of the metallic return line changeover switch 113 is connected to one end of the rectifier station grounding electrode line 114, and the other end of the rectifier station grounding electrode line 114 is connected to the rectifier station grounding electrode 115. The third isolating switch 184 and the fourth isolating switch 185 are connected in parallel, with one end connected to the earth return line changeover switch 190 and the other end connected to the second DC pole 120. The other end of the earth return line changeover switch 190 is connected to the first DC line 150.

[0070] exist Figure 2In the first DC pole 110, there are a first converter 111, a first converter transformer 116, a first DC pole neutral bus switch 119, a first DC filter 93, a first smoothing reactor 91, and a first DC filter isolation switch 171. The input terminal of the first converter transformer 116 is connected to the first converter bus 140 via a first converter transformer input switch 131. Both output terminals of the first converter transformer 116 are connected to the first converter 111. The first output terminal of the first converter 111 is connected to the first smoothing reactor 91. One end of the smoothing reactor 91 and the second output terminal of the first converter 111 are respectively connected to the first DC neutral bus switch 119 and the first DC filter 93. The other end of the first DC filter 93 is connected to the other end of the first smoothing reactor 91 through the first DC filter isolation switch 171. The other end of the first smoothing reactor 91 is also connected to one end of the first pole bus isolation switch 172. The other end of the first pole bus isolation switch 172 is respectively connected to the first metallic return isolation switch 173 and the first DC line 150. It should be noted that the first converter 111 is a grid-commutated converter. Grid-commutated converters include, but are not limited to, at least one of a six-pulse bridge circuit and a twelve-pulse bridge circuit. Pulse bridge circuits include, but are not limited to, non-turn-off semi-controlled power semiconductor devices, generally thyristor devices.

[0071] exist Figure 2 In the second DC pole 120, there are a second converter 121, a second converter transformer 126, a second DC pole neutral bus switch 129, a second DC filter 94, a second smoothing reactor 92, and a second DC filter isolation switch 181. The input terminal of the second converter transformer 126 is connected to the first converter bus 140 via a second converter transformer input switch 133. Both output terminals of the second converter transformer 126 are connected to the second converter 121. The first output terminal of the second converter 121 is connected to the second smoothing reactor 92. One end of the smoothing reactor 92 and the second output terminal of the second converter 121 are respectively connected to the second DC neutral bus switch 129 and the second DC filter 94. The other end of the second DC filter 94 is connected to the other end of the second smoothing reactor 92 through the second DC filter isolating switch 181. The other end of the second smoothing reactor 92 is also connected to one end of the second bus isolating switch 182. The other end of the second bus isolating switch 182 is connected to the second metallic return isolating switch 183 and the first DC line 150. It should be noted that the second converter 121 is also a grid-commutated converter.

[0072] exist Figure 2In the inverter station 200, there are a third DC pole 210, a fourth DC pole 220, a second AC filter bank 218, a second converter bus 240, a third converter transformer incoming line switch 231, a fourth converter transformer incoming line switch 233, a third AC bus 241, a fourth AC bus 242, a fifth AC bus 243, an AC transformer 236, a grounding electrode line isolating switch 213, a metallic return line isolating switch 290, a fifth isolating switch 274, a sixth isolating switch 275, a seventh isolating switch 284, and an eighth isolating switch 285. The second converter bus 240 and the third AC bus 241 are connected via the first bus tie switch 234, and are at the same voltage level. The second converter bus 240 is connected to the fourth AC bus 242 and the fifth AC bus 243 via AC transformers 236, and are at different voltage levels. The AC transformers 236 are connected to the second converter bus 240 via the second bus tie switch 235. The third DC pole 210 and the fourth DC pole 220 are connected to the second converter bus 240 via the third converter transformer inlet switch 231 and the fourth converter transformer inlet switch 233, respectively. The second AC filter bank 218 is connected to the second converter bus 240 via a filter switch 232. The fifth isolating switch 274 and the sixth isolating switch 275 are connected via... All ends are connected to the third DC pole 210. The other end of the fifth isolating switch 274 is connected to one end of the seventh isolating switch 284 and one end of the grounding line isolating switch 213. The other end of the grounding line isolating switch 213 is connected to the inverter station grounding line 214 and the inverter station grounding pole 215. The other end of the seventh isolating switch 284 is connected to the fourth DC pole 220. The other end of the sixth isolating switch 275 is connected to one end of the eighth isolating switch 285. The other end of the eighth isolating switch 285 is connected to the fourth DC pole 220. One end of the metal return line isolating switch 290 is connected to the connection between the eighth isolating switch 285 and the sixth isolating switch 275. The other end of the metal return line isolating switch 290 is connected to the third pole bus isolating switch 272 and the fourth pole bus isolating switch 282 through the third metal return line isolating switch 273 and the fourth metal return line isolating switch 283, respectively.

[0073] exist Figure 2In the middle, the third DC pole 210 includes a third converter 211, a third converter transformer 216, a third DC pole neutral bus switch 219, a third DC filter 97, a third smoothing reactor 95, a third DC filter isolation switch 271, a third pole bus isolation switch 272, and a third metallic return line isolation switch 273. The input terminal of the third converter transformer 216 is connected to the second converter bus 240 via the third converter transformer incoming line switch 231. Both output terminals of the third converter transformer 216 are connected to the third converter 211. The first output terminal of the third converter 211 is connected to one end of the third smoothing reactor 95. The second output terminal of the third converter 211 is connected to the third DC neutral bus switch 219 and the third DC filter 97, respectively. The other end of the third DC filter 97 is connected to the other end of the third smoothing reactor 95 via the third DC filter isolating switch 271. The other end of the third smoothing reactor 95 is also connected to one end of the third pole bus isolating switch 272. The other end of the third pole bus isolating switch 272 is connected to the first DC line 150. It should be noted that the third converter 211 is also a grid-commutated converter.

[0074] exist Figure 2 In the fourth DC pole 220, there are a fourth converter 221, a fourth converter transformer 226, a fourth DC pole neutral bus switch 229, a fourth DC filter 98, a fourth smoothing reactor 96, a fourth DC filter isolation switch 281, a fourth pole bus isolation switch 282, and a fourth metallic return line isolation switch 283. The input terminal of the fourth converter transformer 226 is connected to the second converter bus 240 via the fourth converter transformer incoming switch 233. Both output terminals of the fourth converter transformer 226 are connected to the fourth converter 221. The first output terminal of the fourth converter 221 is connected to one end of the fourth smoothing reactor 96. The second output terminal of the fourth converter 221 is connected to the fourth DC neutral bus switch 229 and the fourth DC filter 98, respectively. The other end of the fourth DC filter 98 is connected to the other end of the fourth smoothing reactor 96 via the fourth DC filter isolating switch 281. The other end of the fourth smoothing reactor 96 is also connected to one end of the fourth pole bus isolating switch 282. The other end of the fourth pole bus isolating switch 282 is connected to the first DC line 150. It should be noted that the fourth converter 221 is also a grid-commutated converter. Furthermore, the various switches mentioned above include, but are not limited to, at least one type of mechanical switch, disconnector, or DC circuit breaker.

[0075] exist Figure 2In this configuration, rectifier station 100 is connected to rectifier station grounding electrode 115 via rectifier station grounding electrode line 114. Inverter station 200 is connected to inverter station grounding electrode 215 via inverter station grounding electrode line 214. During power forward transmission, the first converter bus 140 of rectifier station 100 converts AC power to DC power through its first converter 111, and transmits it to inverter station 200 via the first DC line 150 and the second DC line 160. Inverter station 200 then converts the DC power back to AC power through its third converter 211 and sends it to its second converter bus 240, thus achieving DC power forward transmission. The converter of rectifier station 100 generally operates under current control, while the converter of inverter station 200 generally operates under voltage control or maximum firing angle control (α). MAX ).

[0076] exist Figure 2 In the process, the analog signals collected by rectifier station 100 and inverter station 200 are: high voltage bus current IDH, low voltage bus current IDNC, pole bus current IDL, pole neutral bus current IDNE, DC filter head current IZT1, grounding electrode current IDDL, pole bus voltage UDL and pole neutral bus voltage UDN on the DC side of the converter, star valve side current IVY and angle valve side current IVD on the AC side of the converter, and AC bus voltage UAC1 of the first converter bus 140, AC bus voltage UAC2 of the second converter bus 240, AC bus voltage UAC3 of the third AC bus 241, AC bus voltage UAC4 of the fourth AC bus 242, and AC bus voltage UAC5 of the fifth AC bus 243.

[0077] exist Figure 2 In the process, the first DC pole 110 and the third DC pole 210 form pole I of the high voltage DC transmission, and the second DC pole 120 and the fourth DC pole 220 form pole II of the high voltage DC transmission.

[0078] In some embodiments, the parameters of the DC transmission system include the AC bus voltage UAC, star valve side current IVY and angle valve side current IVD on the AC side, the high voltage bus current IDH, the low voltage bus current IDNC, the pole bus current IDL, the pole neutral bus current IDNC, the grounding pole current IDEL, the pole bus voltage UDL and the pole neutral bus voltage UDN on the DC side, and the metallic return line current IDME.

[0079] exist Figure 2 In this configuration, the AC busbars include the third AC busbar 241 (with the first bus tie switch 234 disconnected), the fourth AC busbar 242, and the fifth AC busbar 243. Therefore, the zero-sequence voltage amplitudes of the third AC busbar 241, the fourth AC busbar 242, and the fifth AC busbar 243 are calculated as follows:

[0080] U 03=UAC3_L1+UAC3_L2+UAC3_L3;

[0081] U 04 =UAC4_L1+UAC4_L2+UAC4_L3;

[0082] U 05 =UAC5_L1+UAC5_L2+UAC5_L3;

[0083] U 03 U represents the zero-sequence voltage amplitude of the third AC bus 241. 04 U represents the zero-sequence voltage amplitude of the fourth AC bus 242. 05 This represents the zero-sequence voltage amplitude of the fifth AC bus 243;

[0084] The amplitude of the three-phase AC voltage after Clarke transformation of the third AC bus 241 is calculated as follows:

[0085] U α3 =2 / 3·UAC3_L1-1 / 3(UAC3_L2+UAC3_L3),

[0086] U β3 =sqrt(3) / 3·(UAC3_L2-UAC3_L3),

[0087] U m3 =sqrt(U α3 ^2+U β3 ^2);

[0088] Among them, U α3 U represents the amplitude of the three-phase AC voltage of the third AC bus 241 mapped onto the α-axis after Clarke transformation. β3 U represents the amplitude of the three-phase AC voltage of the third AC bus 241 mapped to the β axis after Clarke transformation. m3 This represents the amplitude of the three-phase AC voltage of the third AC bus 241 after Clarke transformation;

[0089] The change in three-phase AC voltage per unit time of the three AC busbar 241 is calculated as follows:

[0090] k A3 =d UAC3_L1 / dt,

[0091] k B3 =d UAC3_L2 / dt,

[0092] k C3 =d UAC3_L3 / dt;

[0093] Among them, k A3This represents the change in phase A voltage per unit time of the third AC bus 241; k B3 This represents the change in phase B voltage per unit time of the third AC bus 241; k C3 This represents the change in phase C voltage per unit time of the third AC bus 241;

[0094] The amplitude of the three-phase AC voltage after Clarke transformation of the fourth AC bus 242 is calculated as follows:

[0095] U α4 =2 / 3·UAC4_L1-1 / 3(UAC4_L2+UAC4_L3),

[0096] U β4 =sqrt(3) / 3·(UAC4_L2-UAC4_L3),

[0097] U m4 =sqrt(U α4 ^2+U β4 ^2);

[0098] Among them, U α4 U represents the amplitude of the three-phase AC voltage of the fourth AC bus 242 mapped onto the α-axis after Clarke transformation. β4 U represents the amplitude of the three-phase AC voltage of the fourth AC bus 242 mapped to the β axis after Clarke transformation. m4 This represents the amplitude of the three-phase AC voltage of the fourth AC bus 242 after Clarke transformation;

[0099] The change in three-phase AC voltage per unit time of the fourth AC bus 242 is calculated as follows:

[0100] k A4 =d UAC4_L1 / dt,

[0101] k B4 =d UAC4_L2 / dt,

[0102] k C4 =d UAC4_L3 / dt;

[0103] Where, k A4 This represents the change in phase A voltage per unit time of the fourth AC bus 242; k B4 This represents the change in phase B voltage per unit time of the fourth AC bus 242; k C4 This represents the change in phase C voltage per unit time of the fourth AC bus 242;

[0104] The Clarke transformation amplitude of the three-phase AC voltage of the fifth AC bus 243 is calculated as follows:

[0105] U α5 =2 / 3·UAC5_L1-1 / 3(UAC5_L2+UAC5_L3),

[0106] U β5 =sqrt(3) / 3·(UAC5_L2-UAC5_L3),

[0107] U m5 =sqrt(U α5 ^2+U β5 ^2);

[0108] Among them, U α5 U represents the amplitude of the three-phase AC voltage of the fifth AC bus 243 mapped onto the α-axis after Clarke transformation. β5 U represents the amplitude of the three-phase AC voltage of the fifth AC bus 243 mapped to the β axis after Clarke transformation. m5 This represents the amplitude of the three-phase AC voltage of the fifth AC bus 243 after Clarke transformation;

[0109] The change in three-phase AC voltage per unit time of the fifth AC bus 243 is calculated as follows:

[0110] k A5 =d UAC5_L1 / dt,

[0111] k B5 =d UAC5_L2 / dt,

[0112] k C5 =d UAC5_L3 / dt;

[0113] Among them, k A5 This represents the change in phase A voltage per unit time of the fifth AC bus 243; k B5 This represents the change in phase B voltage per unit time of the fifth AC bus 243; k C5 This represents the change in phase C voltage per unit time of the fifth AC bus 243.

[0114] like Figure 3 As shown in the illustration, this application provides a functional diagram of a commutation failure prediction control for a power grid commutator. By detecting the zero-sequence component and amplitude change of the AC bus voltage, commutation failure is predicted in advance, thereby enabling commutation failure prediction control and outputting the commutation failure prediction angle in advance. Specific steps include:

[0115] When any zero-sequence voltage amplitude U of the third AC bus 241, the fourth AC bus 242, or the fifth AC bus 243 03 U 04 or U 05If the absolute value of the per-unit value U0 is greater than A1 (the first threshold, based on the zero-order component criterion), Flag1 is set to 1, and the absolute value of U0 is selected to be within T. h The maximum value within the time window is maintained and multiplied by the commutation failure prediction proportional gain K1; or any voltage amplitude U of the third AC bus 241, the fourth AC bus 242, or the fifth AC bus 243. m3 U m4 or U m5 per unit value U m The value after filtering by the time constant T1 minus the real-time value U m If the value is greater than A2 (the second threshold, determined by the amplitude criterion), Flag2 is 1, and U is selected. m The value after filtering by the time constant T1 minus the real-time value in T h The maximum value within the time window is maintained and multiplied by the commutation failure prediction proportional gain K2. The maximum value of these two values ​​is then passed through a limiting circuit, a filtering circuit, and the inverted value is added to 1. This result is then processed using an inverse cosine function to obtain the commutation failure prediction angle Δα. Here, U0 multiplied by the voltage reference value equals the zero-sequence voltage amplitude, U... m Multiplying by the voltage reference value equals the amplitude of the three-phase AC voltage after Clarke transformation. Figure 3 In the diagram, U0 represents the amplitude of the zero-sequence voltage on the inverter-side AC bus, in per-unit value; U m Δα is the AC bus voltage amplitude on the inverter side, in per-unit value; Δα is the commutation failure prediction angle, in degrees (°); Flag1 is the ground fault action flag, 1 indicates an AC side ground fault has been detected, 0 indicates no AC side ground fault has been detected; Flag2 is the fault flag, 1 indicates an AC side fault has been detected, 0 indicates no AC side fault has been detected; MAX HOLD is used to obtain T h The maximum value within the time window is maintained; T1 is the filter time constant in seconds (s); K1 and K2 are the proportional gains for commutation failure prediction; A1 and A2 are the start-up voltage thresholds in per-unit values; T h is the width of the time window; T is the time constant when the input decreases, and is 0 when the input increases, in seconds (s).

[0116] Simulations were conducted on single-phase ground faults on the third AC bus 241, the fourth AC bus 242, and the fifth AC bus 243 to identify the critical value at which the zero-sequence voltage amplitude caused commutation failure in the HVDC transmission system. This critical value was then used as the first threshold value for each of the three AC buses 241, 242, and 243. Simulations were also conducted on three-phase ground faults on the same three AC buses 241, 242, and 243 to identify the critical value at which the amplitude change of the three-phase AC voltage after Clarke transformation caused commutation failure in the HVDC transmission system. This critical value was then used as the second threshold value for each of the three AC buses 241, 242, and 243.

[0117] To prevent misjudgments in the commutation failure prediction and control method due to maintenance outages of the third AC bus 241, the fourth AC bus 242, or the fifth AC bus 243, multiple comprehensive criteria for AC buses are adopted. For example, if the voltage distortion criteria for the fourth AC bus 242 and the fifth AC bus 243 are both determined to meet the conditions, the grid commutation converter will then be activated to use the commutation failure prediction and control function of the AC bus voltage. Among these, A1 and A2 in the voltage distortion criteria for the fourth AC bus 242 and the fifth AC bus 243 can be selected with different values.

[0118] To prevent misjudgment due to excessive electrical distance between the third AC bus 241, the fourth AC bus 242, or the fifth AC bus 243 and the second converter bus 240, a comprehensive criterion for multiple AC buses is adopted. For example, if the amplitude criterion for both the third AC bus 241 and the second converter bus 240 is satisfied, the commutation failure prediction control function of the grid commutator using AC bus voltage is then activated. The action threshold value of the commutation failure prediction criterion for the second converter bus 240 is set lower than the action threshold value of the commutation failure prediction criterion for the second converter bus 240 alone.

[0119] After obtaining the commutation failure prediction angle Δα, the commutation failure prediction angle Δα is subtracted from the trigger angle command calculated by the maximum trigger angle control or voltage control, thereby triggering the control pulse of the grid commutation converter in advance and increasing the turn-off angle of the grid commutation converter.

[0120] When the second converter bus 240 fails, the commutation failure prediction function of the third AC bus 241, the fourth AC bus 242, or the fifth AC bus 243 is turned off, and the commutation failure is suppressed by the commutation failure prediction function of the second converter bus 240; or the commutation failure prediction angle of the second converter bus 240 and the third AC bus 241, the fourth AC bus 242, or the fifth AC bus 243 is increased to suppress the commutation failure.

[0121] It should be understood that although the steps in the flowchart above are shown sequentially as indicated by the arrows, these steps are not necessarily executed in the order indicated by the arrows. Unless otherwise explicitly stated herein, there is no strict order restriction on the execution of these steps, and they can be executed in other orders. Moreover, at least some steps in the flowchart above may include multiple steps or stages, which are not necessarily completed at the same time, but can be executed at different times. The execution order of these steps or stages is not necessarily sequential, but can be performed alternately or in turn with other steps or at least some of the steps or stages of other steps.

[0122] like Figure 4 As shown in the embodiments of this application, a commutation failure prediction and control system for a DC transmission system is also provided, applied to a DC transmission system including a rectifier station and an inverter station. The commutation failure prediction and control system includes:

[0123] The data acquisition module is used to acquire the system parameters of the AC bus of the converter bus on the inverter side.

[0124] The judgment module is used to determine whether voltage distortion occurs on the AC bus based on system parameters.

[0125] The control module is used to predict and control commutation failure of the AC bus when voltage distortion occurs.

[0126] The AC bus includes the inverter-side converter bus connected to the same voltage level via external lines and / or AC buses of different voltage levels connected via AC transformers and / or AC buses connected via external power grids; system parameters are obtained through the grid-commutated converter on the inverter side; commutation failure prediction control includes increasing the turn-off angle of the grid-commutated converter or decreasing the firing angle of the grid-commutated converter.

[0127] It should be noted that the DC transmission system commutation failure prediction and control system of this application is a system corresponding to the DC transmission system commutation failure prediction and control method described above. The functional modules in the system correspond to the respective steps in the judgment method. The DC transmission system commutation failure prediction and control system of this application can be implemented in conjunction with the DC transmission system commutation failure prediction and control method. Accordingly, the relevant technical details mentioned in the DC transmission system commutation failure prediction and control system of this application can also be applied to the aforementioned DC transmission system commutation failure prediction and control method.

[0128] It should be noted that the aforementioned functional modules can be fully or partially integrated into a single physical entity, or they can be physically separated. Furthermore, these modules can be implemented entirely in software via processing element calls; they can be fully implemented in hardware; or some modules can be implemented by processing element calls to software, while others are implemented in hardware. Additionally, these modules can be fully or partially integrated together, or implemented independently. The processing element here can be an integrated circuit with signal processing capabilities. During implementation, some or all steps of the above method, or the aforementioned functional modules, can be completed through integrated logic circuits in the hardware of the processor element or through software instructions.

[0129] This application also provides a computer device with control computing capabilities; a computer program is stored in a memory, and when the computer program is executed by a processor, it implements the DC transmission system commutation failure prediction and control method provided in any of the above claims. The memory includes a computer storage medium and an internal memory. The computer storage medium is a non-volatile storage medium that stores an operating system and a computer program, and the internal memory provides an environment for the operation of the operating system and the computer program. The communication interface of the computer device is used for wired or wireless communication with external terminals, and the wireless communication can be achieved through WIFI, mobile cellular networks, etc.

[0130] This application also provides a computer-readable storage medium storing a computer program. When executed by a processor, the computer program implements the DC transmission system commutation failure prediction and control method provided in any of the above embodiments. All or part of the processes in the methods of the above embodiments can be implemented by instructing related hardware through a computer program. The computer program can be stored in a non-volatile computer-readable storage medium. When executed, the computer program can include the processes of the embodiments of the above methods. Any references to memory, databases, or other media used in the embodiments provided in this application can include at least one of non-volatile and volatile memory. Non-volatile memory can include read-only memory (ROM), magnetic tape, floppy disk, flash memory, optical memory, high-density embedded non-volatile memory, resistive random access memory, etc. Volatile memory can include random access memory (RAM) or external cache memory, etc. By way of illustration and not limitation, RAM can be in various forms, such as static random access memory (SRAM) or dynamic random access memory (DRAM), etc.

[0131] The foregoing has provided a detailed description of a method, system, device, and medium for predicting and controlling commutation failure in a DC transmission system, as provided in the embodiments of this application. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the embodiments above are only for the purpose of helping to understand the technical solutions and core ideas of this application. Those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A method for predictive control of commutation failure in a DC transmission system, applied to a DC transmission system comprising a rectifier side and an inverter side, characterized in that, The method includes: Obtain the system parameters of the AC bus that is not directly electrically connected to the converter bus on the inverter side. The converter bus is the bus connected to the grid side of the converter transformer on the inverter side. The system parameters of the AC bus include the zero-sequence voltage amplitude of the three-phase AC voltage and / or the amplitude of the three-phase AC voltage after Clarke transformation. Determining whether voltage distortion occurs on the AC bus based on the system parameters includes: The zero-sequence voltage amplitude of the three-phase AC voltage of the AC bus is compared with a first threshold; if the zero-sequence voltage amplitude is greater than the first threshold, it indicates that voltage distortion has occurred on the AC bus. Alternatively, obtain the Clarke-transformed amplitude of the three-phase AC voltage of the AC bus, and subtract the real-time value from the filtered value of the Clarke-transformed amplitude of the three-phase AC voltage. If the difference is greater than the second threshold, it indicates that the AC bus has voltage distortion. Alternatively, the unit time change of any phase of the three-phase AC voltage of the AC bus is greater than the third threshold. When voltage distortion occurs on the AC bus, commutation failure prediction control is performed on the grid commutation converter on the inverter side. Wherein, the AC bus that is not directly electrically connected to the converter bus on the inverter side includes AC buses with the same voltage level connected to the converter bus on the inverter side via external lines and / or AC buses with different voltage levels connected via AC transformers and / or AC buses connected via external power grids; the commutation failure prediction control includes increasing the turn-off angle of the grid commutation converter or decreasing the firing angle of the grid commutation converter.

2. The method for predicting and controlling commutation failure in a DC transmission system as described in claim 1, characterized in that, The method for increasing the turn-off angle or decreasing the firing angle of the grid commutator includes: Obtain the firing angle command value of the power grid commutator; The commutation failure prediction angle is calculated. The firing angle of the grid commutation converter is obtained by subtracting the commutation failure prediction angle from the firing angle command value.

3. The DC transmission system commutation failure prediction and control method as described in claim 2, characterized in that, The calculation method for the commutation failure prediction angle includes: Obtain the zero-sequence voltage amplitude of the three-phase AC voltage of the AC bus, and / or the amplitude of the three-phase AC voltage of the AC bus after Clarke transformation; The commutation failure prediction angle is generated based on the magnitude of the zero-sequence voltage amplitude or the magnitude of the change in amplitude after Clarke transformation of the three-phase AC voltage. Specifically, the larger the zero-sequence voltage amplitude, the larger the commutation failure prediction angle, and a maximum value is set to limit it; the larger the amplitude change of the three-phase AC voltage after Clarke transformation, the larger the commutation failure prediction angle, and a maximum value is set to limit it.

4. A commutation failure prediction and control system for a DC transmission system, applied to a DC transmission system comprising a rectifier side and an inverter side, characterized in that, The commutation failure prediction and control system includes: The data acquisition module is used to acquire the system parameters of the AC bus that is not directly electrically connected to the converter bus on the inverter side. The converter bus is the bus connected to the grid side of the converter transformer on the inverter side. The system parameters of the AC bus include the zero-sequence voltage amplitude of the three-phase AC voltage and / or the amplitude of the three-phase AC voltage after Clarke transformation. The judgment module is used to determine whether voltage distortion occurs on the AC bus based on the system parameters. It compares the zero-sequence voltage amplitude of the three-phase AC voltage of the AC bus with a first threshold. If the zero-sequence voltage amplitude is greater than the first threshold, it indicates that voltage distortion occurs on the AC bus. Alternatively, it obtains the Clarke-transformed amplitude of the three-phase AC voltage of the AC bus, subtracts the real-time value from the filtered Clarke-transformed amplitude, and if the difference is greater than a second threshold, it indicates that voltage distortion occurs on the AC bus. Alternatively, the unit time change of any phase of the three-phase AC voltage of the AC bus is greater than the third threshold. The control module is used to perform commutation failure prediction control on the AC bus when voltage distortion occurs. Wherein, the AC bus that is not directly electrically connected to the converter bus on the inverter side includes AC buses of the same voltage level connected to the converter bus on the inverter side via external lines and / or AC buses of different voltage levels connected via AC transformers and / or AC buses connected via external power grids; the commutation failure prediction control includes increasing the turn-off angle of the grid commutation converter or decreasing the firing angle of the grid commutation converter.

5. A computer device comprising a memory and a processor, wherein the memory stores a computer program, characterized in that, When the processor executes the computer program, it implements the DC transmission system commutation failure prediction and control method as described in any one of claims 1 to 3.

6. A computer-readable storage medium storing a computer program, which, when executed by a processor, implements the DC transmission system commutation failure prediction and control method as described in any one of claims 1 to 3.

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