UHVDC power transmission system ice melting circuit and control method and control device thereof

Abstract

The application provides an ice melting circuit of an extra-high voltage direct current transmission system and a control method and a control device thereof. The extra-high voltage direct current transmission system comprises at least two converter stations, the converter station comprises double direct current poles, the direct current pole comprises at least two valve groups, each valve group comprises at least one converter, the circuit comprises a first current path and a second current path, one direct current pole of a station forms the first current path through two direct current lines and a metal bus of a counter station or two direct current poles connected with each other of the counter station, any converter station is taken as a station, another converter station corresponding to the station is a counter station, two valve groups of one direct current pole of the two direct current poles of the counter station are isolated through bypass switches, the converters of the two valve groups of another direct current pole of the station are reversely connected in terms of cathode and anode, and the other direct current pole of the station is connected in parallel to the two direct current lines to form the second current path.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of high-voltage direct current transmission, in particular to an ice-melting circuit of an ultra-high-voltage direct current transmission system and a control method and a control device thereof. BACKGROUND

[0002] An ultra-high-voltage direct current transmission line is long in distance, and needs to have an anti-icing and de-icing function when crossing a region prone to icing disasters. Ice-melting of the ultra-high-voltage direct current transmission line includes two modes: anti-icing, which is to apply a direct current near a rated value of a direct current transmission system on the direct current line to prevent formation of icing on the line; and ice-melting, which is to apply a direct current beyond the rated value by a certain range to the direct current line to quickly melt the icing already formed on the line.

[0003] A current ice-melting scheme for an ultra-high-voltage direct current transmission project is as follows: a small number of connecting lines and disconnectors are added to each of sending and receiving converter stations, and the conventional series operation of the converter is switched to parallel operation of multiple converters to achieve multiple rated value current operation, so as to achieve the purpose of ice-melting of the direct current line. In the above parallel ice-melting operation mode, the two stations need to be configured with dedicated connecting lines and disconnectors, and the direct current transmission system must transmit sufficient direct current power to perform ice-melting, and power fluctuation will occur if a fault occurs during ice-melting, which will affect the safety of the power grid.

[0004] Since icing disasters can only occur under certain climatic conditions, the actual occurrence probability is not high, and considering the construction cost and later maintenance cost of the dedicated connecting lines and switch disconnectors configured in the two stations, the economy of the scheme is not high. SUMMARY

[0005] An embodiment of the present application provides an ice-melting circuit of an ultra-high-voltage direct current transmission system, the ultra-high-voltage direct current transmission system including at least two converter stations, the converter station including double direct current poles, the direct current pole including at least two valve groups, each valve group including at least one converter, the circuit including a first current path and a second current path, one direct current pole of a station being connected to two direct current lines and a metal bus of a counter station or two direct current poles of the counter station to form the first current path, any converter station being the station, and another converter station corresponding to the station being the counter station, two valve groups of one direct current pole of the counter station being isolated by a bypass disconnector; converters of two valve groups of another direct current pole of the station being reversely connected, the other direct current pole of the station being connected in parallel to the two direct current lines and the metal bus of the counter station or the two direct current poles of the counter station to form the second current path.

[0006] According to some embodiments, only one of the station or the counter station is grounded.

[0007] According to some embodiments, the two DC lines include a DC line of one DC pole of the local station and a DC line of another DC pole of the local station.

[0008] According to some embodiments, the second current path includes a valve area de-icing switch, a first pole area de-icing switch, and a third pole area de-icing switch, the valve area de-icing switch being used to reverse the connection between the cathode and the anode of the converter of two valve groups of another DC pole of the local station, the first pole area de-icing switch connecting a pole bus of another DC pole of the local station and a DC line of one DC pole of the local station, and the third pole area de-icing switch connecting a DC line of another DC pole of the local station and a pole neutral bus.

[0009] According to some embodiments, one DC pole of the local station forms the first current path through two DC lines and a metal bus of the opposite station, and the first current path includes two valve groups of one DC pole of the local station, connecting lines of the two valve groups of one DC pole of the local station, a pole bus of one DC pole of the local station, a pole neutral bus, a DC line, and a metal bus of two DC poles of the opposite station; one DC pole of the local station forms the first current path through two DC lines and two DC poles of the opposite station, and the first current path includes two valve groups of one DC pole of the local station, connecting lines of the two valve groups of one DC pole of the local station, a pole bus of one DC pole of the local station, a pole neutral bus, a DC line, bypass switches of two valve groups of one DC pole of two DC poles of the opposite station, and one or two valve groups of another DC pole of two DC poles of the opposite station.

[0010] According to some embodiments, another DC pole of the local station is connected in parallel to the two DC lines and a metal bus of the opposite station to form the second current path, and the second current path includes two valve groups of another DC pole of the local station, connecting lines of the two valve groups of another DC pole of the local station, a pole bus of another DC pole of the local station, a pole neutral bus, de-icing connecting lines of the valve area de-icing switch, the first pole area de-icing switch, and the third pole area de-icing switch, a DC line, and a metal bus of two DC poles of the opposite station; another DC pole of the local station is connected in parallel to the two DC lines and two DC poles of the opposite station to form the second current path, and the second current path includes two valve groups of another DC pole of the local station, connecting lines of the two valve groups of another DC pole of the local station, a pole bus of another DC pole of the local station, a pole neutral bus, de-icing connecting lines of the valve area de-icing switch, the first pole area de-icing switch, and the third pole area de-icing switch, a DC line, bypass switches of two valve groups of one DC pole of two DC poles of the opposite station, and one or two valve groups of another DC pole of two DC poles of the opposite station.

[0011] According to some embodiments, the valve group is a current source type valve group or a voltage source type valve group, the current source type valve group comprising a line commutated converter, and the voltage source type valve group comprising a voltage source converter.

[0012] The application also provides a control method of an ice melting circuit of an UHVDC power transmission system, the UHVDC power transmission system comprising at least two converter stations, each of the converter stations comprising two DC poles, each of the DC poles comprising at least two valve groups, each of the valve groups comprising at least one converter, the control method comprising: controlling a DC pole of a current station to form a first current path through two DC lines and a metal bus of a counter station or two DC poles of the counter station, the current station being any of the converter stations, and the counter station being another converter station corresponding to the current station, wherein two valve groups of one of the two DC poles of the counter station are isolated by a bypass switch, and the bypass switch is controlled to be conductive; controlling two valve groups of another DC pole of the current station to form a second current path through the two DC lines and the metal bus of the counter station or the two DC poles of the counter station, the two valve groups of the another DC pole of the current station being connected in parallel to the two DC lines and the metal bus of the counter station; and controlling the converters of the first current path and the converters of the second current path to generate DC currents in the first current path and the second current path respectively, and melting ice in the DC lines.

[0013] According to some embodiments, if the DC current required for ice melting is greater than the maximum allowable current of a switch, a switch or a connecting line of the metal bus of the counter station and the two DC poles of the counter station, the metal bus of the counter station and the two DC poles of the counter station are controlled to flow current at the same time.

[0014] According to some embodiments, the control method further comprises: controlling the two valve groups of the DC pole of the current station to form the first current path through the two DC lines and the metal bus of the counter station, and controlling the two valve groups of the another DC pole of the current station to form the second current path through the two DC lines and the metal bus of the counter station, and the control of the converters of the first current path and the converters of the second current path comprises: controlling the converters of the two valve groups of the DC pole of the current station to operate in rectification and inversion states respectively, and controlling the DC currents of the converters of the two valve groups of the DC pole of the current station; and controlling the converters of the two valve groups of the another DC pole of the current station to operate in rectification and inversion states respectively, and controlling the DC currents of the converters of the two valve groups of the another DC pole of the current station.

[0015] According to some embodiments, the control of the first current path and the second current path includes: controlling the two valve groups of the one DC pole of the local converter station to operate in rectification and inversion states respectively, and controlling the DC current of the two valve groups of the one DC pole of the local converter station; controlling the two valve groups of the other DC pole of the local converter station to operate in rectification and inversion states respectively, and controlling the DC current of the two valve groups of the other DC pole of the local converter station; and controlling the two valve groups of the other DC pole of the unisolated converter station to operate in rectification and inversion states respectively, and controlling the DC current of the two valve groups of the other DC pole of the unisolated converter station.

[0016] The embodiment of the present application further provides a control device of the UHV DC power transmission system ice melting circuit, which applies the control method of the UHV DC power transmission system ice melting circuit as described above. The device includes a detection unit and a control unit. The detection unit is used to detect the operating parameters of the UHV DC power transmission system. The control unit controls the first current path formed by the two DC lines and the metal bus of the opposite converter station or the two DC poles of the opposite converter station based on the operating parameters of the UHV DC power transmission system, wherein the any converter station is taken as the local converter station, and the other converter station corresponding to the local converter station is taken as the opposite converter station. The two valve groups of the one DC pole of the opposite converter station are isolated by a bypass switch. The bypass switch is controlled to be turned on. The two valve groups of the other DC pole of the local converter station are controlled to have the cathode and the anode reversed. The second current path is formed by the two DC lines and the metal bus of the opposite converter station or the two DC poles of the opposite converter station. The control of the first current path and the second current path controls the operation of the converter of the first current path and the operation of the converter of the second current path to generate DC currents in the first current path and the second current path respectively, and performs ice melting on the DC lines.

[0017] According to some embodiments, the operating parameters of the UHV DC power transmission system include the position signal of the switch or the switch, the DC current, the DC voltage and the AC voltage.

[0018] According to some embodiments, if the direct current of the ice-melting demand is greater than the maximum allowable current of the switch, the knife switch or the connecting wire of the metal bus of the two direct current poles of the station, the control unit controls the metal bus of the station and the two direct current poles of the station to flow current at the same time.

[0019] The technical scheme provided by the embodiments of the present application only adds a direct current field switch or a knife switch for ice melting in a single station of the UHVDC power transmission system, and the UHVDC power transmission system does not need to transmit direct current power during the ice melting process. By controlling the operation mode of the converter of the two stations, the ice melting function of the UHVDC power transmission system can be realized. BRIEF DESCRIPTION OF DRAWINGS

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0021] Figure 1 is a schematic diagram of a main circuit of a UHVDC power transmission system provided by the present application.

[0022] Figure 2 is a schematic diagram of an ice melting circuit of a UHVDC power transmission system provided by the present application.

[0023] Figure 3 is a schematic diagram of another ice melting circuit of a UHVDC power transmission system provided by the present application.

[0024] Figure 4 is a schematic diagram of a control method flow of an ice melting circuit of a UHVDC power transmission system provided by the present application.

[0025] Figure 5 is a schematic diagram of another control method flow of an ice melting circuit of a UHVDC power transmission system provided by the present application.

[0026] Figure 6 is a schematic diagram of a control device of an ice melting circuit of a UHVDC power transmission system provided by the present application. DETAILED DESCRIPTION

[0027] The technical solutions in the embodiments of the present application will be described clearly and completely in combination with the drawings of the embodiments of the present application. Obviously, the described embodiments are some embodiments of the present application, not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0028] It should be understood that the terms "comprise" and "comprising" used in the specification and claims of the application indicate the presence of the described features, integers, steps, operations, elements, and / or components but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0029] Figure 1 is a schematic diagram of a main circuit of an ultra-high voltage direct current power transmission system provided by the present application.

[0030] The main circuit of the ultra-high voltage direct current power transmission system includes, but is not limited to, a rectifier station 100, an inverter station 200, a first direct current line 150, a second direct current line 160, a rectifier station grounding pole line 114, a rectifier station grounding pole 115, and an inverter station grounding pole line 214, an inverter station grounding pole 215. The rectifier station 100 is connected in parallel with the inverter station 200 through the first direct current line and the second direct current line. The rectifier station 100 is connected to the rectifier station grounding pole 115 through the rectifier station grounding pole line 114. The rectifier station 200 is connected to the inverter station grounding pole 215 through the inverter station grounding pole line 214.

[0031] The rectifier station 100 includes a first direct current pole I 110, a second direct current pole II 120, a first alternating current filter group 118, a first alternating current system 140, a converter transformer incoming line switch, a metal return line transfer switch 113, a ground return line transfer switch 190, bipolar neutral area isolation knife switches 174, 175, 184 and 185, valve area deicing knife switches 35, 36, 45 and 46, first pole area deicing knife switches 191, 192 and third pole area deicing knife switches 193. The first alternating current system 140 is connected to the first alternating current filter group 118. The first direct current pole I 110 is connected to the first alternating current system 140 through the converter transformer incoming line switch 131, 132. The second direct current pole II 120 is connected to the first alternating current system 140 through the converter transformer incoming line switch 133, 134. The rectifier station 100 is connected to the rectifier station grounding pole line 114 through the bipolar neutral area isolation knife switches 174, 175, 184 and 185 and the direct current line transfer switch 113. The rectifier station 100 is connected to the direct current line through the bipolar neutral area isolation knife switches 174, 175, 184 and 185 and the ground return line transfer switch 190.

[0032] The first DC pole I 110 includes a first high-end valve group 111, a first low-end valve group 112, a first high-end converter transformer 116, a first low-end converter transformer 117, a first DC pole neutral bus switch 119, a first DC filter 93, a first smoothing reactor 91, a first DC filter isolation knife switch 171, a first pole bus isolation knife switch 172, and a first metal return line isolation knife switch 173. The first high-end valve group 111 and the first low-end valve group 112 are connected in series. The first high-end valve group 111 is connected to the converter transformer incoming line switch 131 through the first high-end converter transformer 116. The first low-end valve group 112 is connected to the converter transformer incoming line switch 132 through the first low-end converter transformer 117. The first high-end valve group 111 is connected to the first DC line 150 through the first smoothing reactor 91 and the first pole bus isolation knife switch 172. The first low-end valve group 112 is connected to the bipolar neutral area isolation knife switch 174, 175 through the first DC pole neutral bus switch 119. The end of the first smoothing reactor 91 not connected to the first high-end valve group 111 is connected to the first DC filter 93 through the first DC filter isolation knife switch 171 and the end of the first DC pole neutral bus switch 119 not connected to the first low-end valve group 112. The first DC line 150 and the second DC line 160 are connected through the first DC line isolation knife switch 173 and the second DC line isolation knife switch 183.

[0033] The first high-end valve group 111 includes a first high-end converter 1, a first high-end valve group first bypass switch 11, a first high-end valve group second bypass switch 12, a first high-end valve group bus switch 13, and a first high-end valve group valve group switch 14. The first low-end valve group 112 includes a first low-end converter 2, a first low-end valve group first bypass switch 21, a first low-end valve group second bypass switch 22, a first low-end valve group valve group switch 23, and a first low-end valve group bus switch 24. The first high-end converter 1 is connected in parallel with the first high-end valve group second bypass switch 12. The two ends of the first high-end valve group first bypass switch 11 are respectively connected to the first high-end valve group bus switch 13 and the first high-end valve group valve group switch 14, and then connected in parallel with the first high-end valve group second bypass switch 12. The first low-end converter 2 is connected in parallel with the first low-end valve group second bypass switch 22. The two ends of the first low-end valve group first bypass switch 21 are respectively connected to the first low-end valve group valve group switch 23 and the first low-end valve group bus switch 24, and then connected in parallel with the first low-end valve group second bypass switch 22.

[0034] The first high-end converter 1 and the first low-end converter 2 include at least one of a line-commutated converter or a voltage source converter. The line-commutated converter includes at least one of a six-pulse bridge circuit or a twelve-pulse bridge circuit. The pulse bridge circuit includes, but is not limited to, a non-blockable semi-controlled power semiconductor device, generally a thyristor device.

[0035] The voltage source converter includes, but is not limited to, at least one of a two-level converter, a diode clamped multi-level converter, a modular multi-level converter MMC, a hybrid multi-level converter HMC, a two-level cascaded converter CSL, a cascaded two-level converter CTL, which include, but are not limited to, a turn-off, fully controlled power semiconductor device. The modular multi-level converter MMC includes, but is not limited to, at least one of a modular multi-level converter MMC of a half-bridge sub-module structure, a modular multi-level converter MMC of a full-bridge sub-module structure, a modular multi-level converter MMC of a half-bridge and full-bridge hybrid sub-module structure.

[0036] The second DC pole II 120 includes a second low-end valve group 121, a second high-end valve group 122, a second low-end converter transformer 126, a second high-end converter transformer 127, a second DC pole neutral bus switch 129, a second DC filter 94, a second smoothing reactor 92, a second DC filter isolation switch 181, a second pole bus isolation switch 182, and a second metal return line isolation switch 183. The second low-end valve group 121 and the second high-end valve group 122 are connected in series. The second high-end valve group 122 is connected to the converter transformer incoming line switch 134 through the second high-end converter transformer 127. The second low-end valve group 121 is connected to the converter transformer incoming line switch 133 through the second low-end converter transformer 126. The second high-end valve group 122 is connected to the second DC line 160 through the second smoothing reactor 92 and the second pole bus isolation switch 182. The second low-end valve group 121 is connected to the bipolar neutral area isolation switch 184, 185 through the second DC pole neutral bus switch 129. The end of the second smoothing reactor 92 not connected to the second high-end valve group 122 is connected to the second DC filter 94 through the second DC filter isolation switch 181 between the end of the second DC pole neutral bus switch 129 not connected to the second low-end valve group 121.

[0037] The second low-end valve group 121 includes a second low-end converter 3, a second low-end valve group first bypass switch 31, a second low-end valve group second bypass switch 32, a second low-end valve group bus switch 33, and a second low-end valve group valve group switch 34. The second high-end valve group 122 includes a second high-end converter 4, a second high-end valve group first bypass switch 41, a second high-end valve group second bypass switch 42, a second high-end valve group valve group switch 43, and a second high-end valve group bus switch 44. The second low-end converter 3 and the second high-end converter 4 include at least one of a line-commutated converter or a voltage source converter. The second high-end converter 4 is connected in parallel with the second high-end valve group second bypass switch 42. The second high-end valve group first bypass switch 41 is connected across the second high-end valve group bus switch 44 and the second high-end valve group valve group switch 43, and is connected in parallel with the second high-end valve group second bypass switch 42. The second low-end converter 3 is connected in parallel with the second low-end valve group second bypass switch 32. The second low-end valve group second bypass switch 32 is connected across the second low-end valve group valve group switch 34 and the first low-end valve group bus switch 33, and is connected in parallel with the second low-end valve group second bypass switch 32.

[0038] The inversion station 200 includes a third DC pole I 210, a fourth DC pole II 220, a second AC filter group 218, a second AC system 240, and a converter transformer feeder switch, a ground pole line isolation switch 213, a metal return line isolation switch 290, bipolar neutral zone isolation switches 274, 275, 284, and 285. The second AC system 240 is connected with the second AC filter group 218. The third DC pole I 210 is connected with the second AC system 240 through the converter transformer feeder switches 231, 232. The fourth DC pole II 220 is connected with the second AC system 240 through the converter transformer feeder switches 233, 234. The inversion station 200 is connected with the rectification station ground pole line 214 through the bipolar neutral zone isolation switches 274, 275, 284, and 285 and the DC line transfer switch 213.

[0039] The third DC pole I 210 includes a third high-end valve group 211, a third low-end valve group 212, a third high-end converter transformer 216, a third low-end converter transformer 217, a third DC pole neutral bus switch 219, a third DC filter 97, a third smoothing reactor 95, a third DC filter isolation knife switch 271, a third pole bus isolation knife switch 272, and a third metal return line isolation knife switch 273. The first high-end valve group 111 and the first low-end valve group 112 are connected in series. The third high-end valve group 211 and the third low-end valve group 212 are connected in series. The third high-end valve group 211 is connected to the converter transformer incoming line switch 231 through the third high-end converter transformer 216. The third low-end valve group 212 is connected to the converter transformer incoming line switch 232 through the third low-end converter transformer 217. The third high-end valve group 211 is connected to the first DC line 150 through the third smoothing reactor 95 and the third pole bus isolation knife switch 272. The third low-end valve group 212 is connected to the bipolar neutral area isolation knife switch 274, 275 through the third DC pole neutral bus switch 219. The end of the third smoothing reactor 95 not connected to the third high-end valve group 211 is connected to the third DC filter 97 through the third DC filter isolation knife switch 271 and the end of the third DC pole neutral bus switch 219 not connected to the third low-end valve group 212. The first DC line 150 and the second DC line 160 are connected through the third DC line isolation knife switch 273 and the fourth DC line isolation knife switch 283.

[0040] The third high-end valve group 211 includes a third high-end converter 5, a third high-end valve group first bypass switch 51, a third high-end valve group second bypass switch 52, a third high-end valve group bus switch 53, and a third high-end valve group valve group switch 54. The third low-end valve group 212 includes a third low-end converter 6, a third low-end valve group first bypass switch 61, a third low-end valve group second bypass switch 62, a third low-end valve group valve group switch 63, and a third low-end valve group bus switch 64. The third high-end converter 5 and the third low-end converter 6 include at least one of a line-commutated converter or a voltage source converter. The third high-end converter 5 is connected in parallel with the third high-end valve group second bypass switch 52. The two ends of the third high-end valve group first bypass switch 51 are respectively connected to the third high-end valve group bus switch 53 and the third high-end valve group valve group switch 54, and then connected in parallel with the third high-end valve group second bypass switch 52. The third low-end converter 6 is connected in parallel with the third low-end valve group second bypass switch 62. The two ends of the third low-end valve group first bypass switch 61 are respectively connected to the third low-end valve group valve group switch 63 and the third low-end valve group bus switch 64, and then connected in parallel with the third low-end valve group second bypass switch 62.

[0041] The fourth DC pole II 220 includes a fourth low-end valve group 221, a fourth high-end valve group 222, a fourth low-end converter transformer 226, a fourth high-end converter transformer 227, 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 metal return line isolation switch 283. The fourth low-end valve group 221 and the fourth high-end valve group 222 are connected in series. The fourth high-end valve group 222 is connected to the converter transformer incoming line switch 234 through the fourth high-end converter transformer 227. The fourth low-end valve group 221 is connected to the converter transformer incoming line switch 233 through the fourth low-end converter transformer 226. The fourth high-end valve group 222 is connected to the second DC line 160 through the fourth smoothing reactor 96 and the fourth pole bus isolation switch 282. The fourth low-end valve group 221 is connected to the bipolar neutral area isolation switch 284, 285 through the fourth DC pole neutral bus switch 229. The fourth smoothing reactor 96 is connected to the fourth DC filter 98 through the fourth DC filter isolation switch 281 between the end of the fourth high-end valve group 222 not connected to the fourth DC pole neutral bus switch 229 and the end of the fourth low-end valve group 221 not connected to the fourth DC pole neutral bus switch 229.

[0042] The fourth low-end valve group 221 includes a fourth low-end converter 7, a fourth low-end valve group first bypass switch 71, a fourth low-end valve group second bypass switch 72, a fourth low-end valve group bus switch 73, and a fourth low-end valve group valve group switch 74. The fourth high-end valve group 222 includes a fourth high-end converter 8, a fourth high-end valve group first bypass switch 81, a fourth high-end valve group second bypass switch 82, a fourth high-end valve group valve group switch 83, and a fourth high-end valve group bus switch 84. The fourth low-end converter 7 and the fourth high-end converter 8 include at least one of a line-commutated converter or a voltage source converter. The fourth high-end converter 8 is connected in parallel to the fourth high-end valve group second bypass switch 82. The fourth high-end valve group first bypass switch 81 is connected in parallel to the fourth high-end valve group second bypass switch 82 after being connected to the fourth high-end valve group bus switch 84 and the second high-end valve group valve group switch 83, respectively. The fourth low-end converter 7 is connected in parallel to the fourth low-end valve group second bypass switch 72. The fourth low-end valve group second bypass switch 72 is connected in parallel to the fourth low-end valve group second bypass switch 72 after being connected to the fourth low-end valve group valve group switch 74 and the fourth low-end valve group bus switch 73, respectively.

[0043] The various switches mentioned above include at least one of a mechanical switch, a switch, a DC circuit breaker, and a thyristor valve group, but are not limited thereto.

[0044] If the high-end converter and the low-end converter of the DC pole of the rectifier station 100 and the inverter station 200 are both line-commutated converters, it is a conventional UHVDC power transmission system.

[0045] If the high-end converter and the low-end converter of the DC pole of the rectifier station 100 and the inverter station 200 are all voltage source converters, it is a flexible UHVDC power transmission system.

[0046] If the first high-end converter 1, the first low-end converter 2, the second high-end converter 4 and the second low-end converter 3 of the first DC pole I110 and the second DC pole II120 of the rectifier station 100 are all line commutated converters, and the third high-end converter 5, the third low-end converter 6, the fourth high-end converter 8 and the fourth low-end converter 7 of the third DC pole I210 and the fourth DC pole II220 of the inverter station 200 are all voltage source converters, it is a hybrid UHVDC power transmission system with inter-station mixing.

[0047] If the first high-end converter 1, the first low-end converter 2, the second high-end converter 4 and the second low-end converter 3 of the first DC pole I110 and the second DC pole II120 of the rectifier station 100 are all line commutated converters, and the third high-end converter 5 and the fourth high-end converter 8 of the third DC pole I210 and the fourth DC pole II220 of the inverter station 200 are line commutated converters, and the third low-end converter 6 and the fourth low-end converter 7 are voltage source converters, it is a hybrid UHVDC power transmission system with intra-pole mixing.

[0048] The rectifier station 100 is connected to the grounding pole 115 through the grounding pole line 114. The inverter station 200 is connected to the grounding pole 215 through the grounding pole line 214. When the power is sent positively, the first AC system 140 of the rectifier station 100 converts the AC power into DC power through the first high-end converter 1, the first low-end converter 2, the second high-end converter 4 and the second low-end converter 3, and sends the DC power to the inverter station 200 through the first DC line 150 and the second DC line 160. The inverter station 200 converts the DC power into AC power through the third high-end converter 5, the third low-end converter 6, the fourth high-end converter 8 and the fourth low-end converter 7, and sends the AC power to the second AC system 240 of the inverter station 200, thereby realizing the positive sending of DC power. The converters of the rectifier station generally operate in current control, and the converters of the inverter station generally operate in voltage control or maximum trigger angle control (AMAX). It should be pointed out that the maximum trigger angle control (AMAX) is only applicable to line commutated converters, but not to voltage source converters.

[0049] The analog signals collected by the rectifier station 100 and the inverter station 200 include: high-voltage bus current IDC1P of the high-end converter DC side, low-voltage bus current IDC1N, high-voltage bus current IDC2P of the low-end converter DC side, low-voltage bus current IDC2N, pole bus current IDL, pole neutral bus current IDNC, DC filter head current IZT1, grounding pole current IDEL, pole bus voltage UDL and pole neutral bus voltage UDN; optionally, the analog signals collected by the rectifier station 100 or the inverter station 200 further include pole midpoint voltage UDM. The digital signals collected include: position signals of all switches or disconnectors.

[0050] Figure 2 is a schematic diagram of an ice melting circuit of an ultra-high voltage DC power transmission system provided by the present application.

[0051] The ultra-high voltage DC power transmission system includes at least two converter stations, the converter station includes double DC poles, the DC pole includes at least two valve groups, each valve group includes at least one converter, and the parallel ice melting circuit of the high-voltage DC power transmission system includes a first current path and a second current path.

[0052] A DC pole of the station forms the first current path through two DC lines and a metal bus of the opposite station, any converter station as the station, and the other converter station corresponding to the station as the opposite station. The two valve groups of one of the two DC poles of the opposite station are isolated by a bypass disconnector. The converters of the two valve groups of the other DC pole of the station are reversely connected, and the other DC pole of the station is connected in parallel to the two DC lines and forms the second current path with the metal bus of the opposite station.

[0053] The station or the opposite station has and only has one converter station grounding. The two DC lines include a DC line of one DC pole of the station and a DC line of the other DC pole of the station. The second current path includes a valve area ice melting disconnector, a first pole area ice melting disconnector and a third pole area ice melting disconnector, and the reversely connection of the converter cathode and anode of the two valve groups of the other DC pole of the station is realized through the valve area ice melting disconnector. The first pole area ice melting disconnector connects the pole bus of the other DC pole of the station and the DC line of the other DC pole of the station. The third pole area ice melting disconnector connects the DC line of the other DC pole of the station and the pole neutral bus.

[0054] In the embodiment, the first current path includes two valve groups of one DC pole of the station, connection lines of the two valve groups of one DC pole of the station, a pole bus of one DC pole of the station, a pole neutral bus, a DC line and metal buses of two DC poles of the opposite station.

[0055] In the embodiment, the first current path includes two valve groups of one DC pole of the station, connection lines of the two valve groups of one DC pole of the station, a pole bus of one DC pole of the station, a pole neutral bus, a DC line and metal buses of two DC poles of the opposite station. Figure 2For example, the first high-end valve group 111 and the first low-end valve group 112 of the first DC pole I110 of the rectifier station 100, the connecting line of the two valve groups, the pole bus (including the first pole bus isolating switch 172), the pole neutral bus (including the first DC pole neutral bus switch 119), the metal return connecting line (including the bipolar neutral zone isolating switch 175, the ground return transfer switch 190, and the second metal return isolating switch 183), the first DC line 150, the second DC line 160, and the metal bus of the two DC poles of the inverter station 200 (including the third metal return isolating switch 273 and the fourth metal return isolating switch 283) constitute the first current path.

[0056] In this embodiment, the second current path includes two valve groups of the other DC pole of this station, the connecting line of the two valve groups of the other DC pole of this station, the pole bus of the other DC pole of this station, the pole neutral bus, the de-icing connection line of the valve area de-icing knife switch, the first pole area de-icing knife switch and the third pole area de-icing knife switch, the DC line, and the metal bus of the two DC poles of the opposite station.

[0057] by Figure 2 For example, the second low-end valve group 121 and the second high-end valve group 122 of the second DC pole II120, the connecting line of the two valve groups, the pole bus (including the second pole bus isolating switch 182), the pole neutral bus (including the second DC pole neutral bus switch 129), the de-icing connection line composed of valve area de-icing switches 35, 36, 45 and 46 (to realize the reverse connection of the cathode and anode of the second low-end converter 3 and the second high-end converter 4), the de-icing connection line composed of the first pole area de-icing switch 191 and the third pole area de-icing switch 193, the first DC line 150, the second DC line 160, and the metal bus of the two DC poles of the inverter station 200 (including the third metal return line isolating switch 273 and the fourth metal return line isolating switch 283) form the second current path.

[0058] Optionally, the valve assembly can be a current source valve assembly or a voltage source valve assembly. The current source valve assembly includes a grid phase-switching converter, and the voltage source valve assembly includes a voltage source converter, but is not limited thereto.

[0059] The pole bus connection lines of the two DC poles of the inverter station 200 (including the third metal return isolation switch 273 and the fourth metal return isolation switch 283) form the only branch of the de-icing circuit.

[0060] Figure 3 This is a schematic diagram of another ice-melting circuit for an ultra-high voltage direct current transmission system provided in this application.

[0061] The ultra-high voltage direct current transmission system includes at least two converter stations, each converter station includes two DC poles, each DC pole includes at least two valve groups, each valve group includes at least one converter, and the parallel de-icing circuit of the high voltage direct current transmission system includes a first current path and a second current path.

[0062] The DC pole of this station forms the first current path through two DC lines and the metal busbar of the opposite station. Any converter station is considered this station, and the other converter station corresponding to this station is the opposite station. The two valve groups of one of the DC poles of the opposite station are isolated by a bypass switch. The converter cathodes and anodes of the two valve groups of the other DC pole of this station are reversed. The other DC pole of this station is connected in parallel to the two DC lines, forming the second current path with the two DC poles of the opposite station. Only one converter station (this station or the opposite station) is grounded. The two DC lines include the DC line of the DC pole of this station and the DC line of the other DC pole of this station. The second current path includes a valve area de-icing switch, a first pole area de-icing switch, and a third pole area de-icing switch. The valve area de-icing switch enables the reverse connection of the converter cathodes and anodes of the two valve groups of the other DC pole of this station; the first pole area de-icing switch connects the pole busbar and the DC line of the other DC pole of this station; the third pole area de-icing switch connects the DC line of the other DC pole of this station and the neutral busbar.

[0063] In this embodiment, the first current path includes two valve groups of one DC pole of this station, the connecting line of the two valve groups of one DC pole of this station, the pole bus of one DC pole of this station, the neutral bus, the DC line, and the metal bus of the two DC poles of the opposite station.

[0064] by Figure 3 For example, the first high-end valve group 111 and the first low-end valve group 112 of the first DC pole I110 of the rectifier station 100, the connecting line of the two valve groups, the pole bus (including the first pole bus isolating switch 172), the pole neutral bus (including the first DC pole neutral bus switch 119), the metal return connecting line (including the bipolar neutral zone isolating switch 175, the ground return transfer switch 190, and the second metal return isolating switch 183), and the metal bus of the two DC poles of the inverter station 200 (including the third metal return isolating switch 273 and the fourth metal return isolating switch 283) constitute the first current path.

[0065] In this embodiment, the second current path includes two valve groups of the other DC pole of this station, the connecting line of the two valve groups of the other DC pole of this station, the pole bus of the other DC pole of this station, the neutral bus, the de-icing connection line of the valve area de-icing switch, the first pole area de-icing switch and the third pole area de-icing switch, the DC line, the bypass switch of the two valve groups of one of the two DC poles of the opposite station, and one or two valve groups of the other DC pole of the opposite station.

[0066] byFigure 3 For example, the second low-end valve group 121 and the second high-end valve group 122 of the second DC pole II 120, the connection line of the two valve groups, the pole bus (including the second pole bus isolation knife switch 182), the pole neutral bus (including the second DC pole neutral bus switch 129), the ice melting connection line of the ice melting knife switches 35, 36, 45 and 46 (realizing the cathode and anode reverse connection of the second low-end converter 3 and the second high-end converter 4), the ice melting connection line of the first pole area ice melting knife switch 191 and the third pole area ice melting knife switch 193, the first DC line 150, the second DC line 160, the fourth low-end valve group 221 and the fourth high-end valve group 222 of the fourth DC pole II 220 of the inverter station 200, the connection line of the two valve groups, the pole bus (including the fourth pole bus isolation knife switch 282) and the pole neutral bus connection line (including the fourth DC pole neutral bus switch 229), the third high-end valve group first bypass switch 51 and the third low-end valve group first bypass switch 71 of the third DC pole I 210, the pole bus (including the fourth pole bus isolation knife switch 272) and the pole neutral bus connection line (including the fourth DC pole neutral bus switch 219) form the second current path.

[0067] Figure 4 is a control method flow diagram of an ice melting circuit of an extra-high voltage DC power transmission system provided by the present application, which is suitable for Figure 2 the ice melting circuit shown in the figure.

[0068] In S110, one DC pole of the station is connected to the DC line.

[0069] Taking the rectifier station 100 as an example, the first DC pole I 110 of the rectifier station 100 is connected to the DC line. Specifically, the bipolar neutral area isolation knife switch 175, the second metal return line isolation knife switch 183, the ground return line transfer switch 190, the first DC pole neutral bus switch 119 and the first pole bus isolation knife switch 172 are closed, and the first DC pole I 110 is connected to the DC line.

[0070] Before connecting the DC line, the valve group needs to be charged and connected. Specifically, the first high-end converter transformer incoming line switch 131 is closed, and the first high-end valve group 111 is charged; the first high-end valve group bus switch 13 and the first high-end valve group valve group switch 14 are closed, the first high-end valve group first bypass switch 11 and the first high-end valve group second bypass switch 12 are separated, and the first high-end valve group 111 is connected. The first low-end converter transformer incoming line switch 132 is closed, and the first low-end valve group 112 is charged; the first low-end valve group bus switch 23 and the first low-end valve group valve group switch 24 are closed, the first low-end valve group first bypass switch 21 and the first low-end valve group second bypass switch 22 are separated, and the first low-end valve group 112 is connected.

[0071] After connecting the DC line, the first DC filter 93 is connected. Specifically, the first DC filter isolation knife switch 171 is closed.

[0072] In S120, the converter cathode and anode of the two valve groups of the other DC pole of the station are controlled to be reversed, and the DC line of the other DC pole of the station is controlled to be connected to one DC pole of the station.

[0073] Taking the rectifier station 100 as an example, the valve area deicing knife switches 35, 36, 45 and 46 are closed, the second low-end valve group bus switch 33, the second low-end valve group valve group switch 34, the second high-end valve group valve group switch 43 and the second high-end valve group bus switch 44 are separated; the second pole area deicing knife switch 192 is separated, the first metal return line isolation knife switch 173, the second DC pole neutral bus switch 129, the first pole area deicing knife switch 191 and the third pole area deicing knife switch 193 are closed.

[0074] Before the above operation, the valve groups are charged and connected. Specifically, the second high-end converter transformer incoming line switch 134 is closed, and the second high-end valve group 122 is charged; the second high-end valve group bus switch 44 and the second high-end valve group valve group switch 43 are closed, the second high-end valve group first bypass switch 41 and the second high-end valve group second bypass switch 42 are separated, and the second high-end valve group 122 is connected. The second low-end converter transformer incoming line switch 133 is closed, and the second low-end valve group 121 is charged; the second low-end valve group bus switch 33 and the second low-end valve group valve group switch 34 are closed, the second low-end valve group first bypass switch 31 and the second low-end valve group second bypass switch 32 are separated, and the fourth low-end valve group 121 is connected.

[0075] In S130, the metal bus of the station is controlled to be connected to two DC poles. The station or the opposite station is controlled to be connected to the ground.

[0076] Taking the inverter station 200 as an example, the third metal return line isolation knife switch 273 and the fourth metal return line isolation knife switch 283 are closed.

[0077] After the metal bus is connected to the two DC poles, the rectifier station 100 or the inverter station 200 can be connected to the ground pole or the station ground. Taking the rectifier station 100 connected to the ground pole as an example, the bipolar neutral area isolation knife switch 174 and the metal return line transfer switch 113 are closed.

[0078] It should be noted that S110-S130 have no strict order, and the order provided in the embodiment is relatively optimal; in each step, the order of closing the switch or the knife switch can be adjusted.

[0079] In S140, the converters of the two valve groups of one DC pole of the station are controlled to operate in rectification and inversion states respectively, and the converters of the two valve groups of the other DC pole of the station are controlled to operate in rectification and inversion states respectively.

[0080] For example, the first low-end converter 2 of the first DC pole I110 of the rectifier station 100 is controlled to operate in the rectification state, and the first high-end converter 1 is controlled to operate in the inversion state. The second low-end converter 3 of the second DC pole I120 of the rectifier station 100 is controlled to operate in the rectification state, and the second high-end converter 4 is controlled to operate in the inversion state.

[0081] Before unlocking, the first AC filter group 118 needs to be connected.

[0082] In S150, the DC currents of the two valve groups of the converter of the DC pole of the station are controlled, the DC currents of the two valve groups of the converter of the other DC pole of the station are controlled, and the DC line between the station and the opposite station is deiced.

[0083] Specifically, the DC current of the first DC pole I110 of the rectifier station 100 is controlled, the DC current of the second DC pole I120 of the rectifier station 100 is controlled, and the DC current of the fourth DC pole II220 of the inversion station 200 is controlled to deice. A more preferred working condition is that the DC current of the first DC pole I110 of the rectifier station 100 is 0.8pu, the DC current of the second DC pole I120 of the rectifier station 100 is 0.8pu, and the current of the metal bus of the inversion station 200 is 1.6pu, which requires that the maximum allowable current flowing through the third metal return line isolation switch 273, the fourth metal return line isolation switch 283 and the connecting line thereof is greater than or equal to 1.6pu.

[0084] The DC current measurement value can be the high-voltage bus current IDC1P and the low-voltage bus current IDC1N on the DC side of the high-end converter, the high-voltage bus current IDC2P and the low-voltage bus current IDC2N on the DC side of the low-end converter, the pole bus current IDL or the pole neutral bus current IDNC.

[0085] Figure 5 is another control method flow diagram of the ice melting circuit of the UHVDC power transmission system provided by the present application, which shows an ice melting control method of the ice melting required DC current being greater than the maximum allowable current of the switch, switch or connecting line for the metal bus of the two DC poles of the opposite station, and is applicable to Figure 3 the ice melting circuit shown in the figure.

[0086] Taking the main circuit shown in Figure 1 as an example, the ice melting required DC current is greater than the third metal return line isolation switch 273 and the fourth metal return line isolation switch 283 for the metal bus.

[0087] In S210, one DC pole of the station is connected to the DC line.

[0088] For example, the first DC pole I110 of the rectifier station 100 is connected to the DC line by closing the bipolar neutral zone isolation switch 175, the second metal return line isolation switch 183, the ground return line transfer switch 190, the first DC pole neutral bus switch 119 and the first pole bus isolation switch 172.

[0089] Before connecting the DC line and the ground, the valve groups need to be charged and connected. Specifically, the first high-end converter transformer incoming line switch 131 is closed, the first high-end valve group 111 is charged; the first high-end valve group bus switch 13 and the first high-end valve group switch 14 are closed, the first high-end valve group first bypass switch 11 and the first high-end valve group second bypass switch 12 are separated, and the first high-end valve group 111 is connected. The first low-end converter transformer incoming line switch 132 is closed, the first low-end valve group 112 is charged; the first low-end valve group bus switch 23 and the first low-end valve group switch 24 are closed, the first low-end valve group first bypass switch 21 and the first low-end valve group second bypass switch 22 are separated, and the first low-end valve group 112 is connected.

[0090] After connecting the DC line and the ground, the first DC filter 93 is connected. Specifically, the first DC filter isolation switch 171 is closed.

[0091] In S220, the converter cathode and anode of the two valve groups of the other DC pole of the station are controlled to be reversed, and the other DC pole of the station is controlled to be connected in parallel to the DC line of one DC pole of the station.

[0092] For example, the rectifier station 100 is closed, the valve area deicing switch 35, 36, 45 and 46 is closed, the second low-end valve group bus switch 33, the second low-end valve group switch 34, the second high-end valve group switch 43 and the second high-end valve group bus switch 44 are separated; the second pole area deicing switch 192 is closed, the first metal return line isolation switch 173, the second DC pole neutral bus switch 129, the first pole area deicing switch 191 and the third pole area deicing switch 193 are closed.

[0093] Before the above operation, the valve groups need to be charged and connected. Specifically, the second high-end converter transformer incoming line switch 134 is closed, the second high-end valve group 122 is charged; the second high-end valve group bus switch 44 and the second high-end valve group switch 43 are closed, the second high-end valve group first bypass switch 41 and the second high-end valve group second bypass switch 42 are separated, and the second high-end valve group 122 is connected. The second low-end converter transformer incoming line switch 133 is closed, the second low-end valve group 121 is charged; the second low-end valve group bus switch 33 and the second low-end valve group switch 34 are closed, the second low-end valve group first bypass switch 31 and the second low-end valve group second bypass switch 32 are separated, and the fourth low-end valve group 121 is connected.

[0094] In S230, the metal bus of the station is connected to two DC poles.

[0095] Taking the inverter station 200 as an example, the third metal return line isolation switch 273 and the fourth metal return line isolation switch 283 are closed.

[0096] In S240, the station or the opposite station is connected to the ground, and only one of the two DC poles of the opposite station is connected. The two valve groups of the opposite station are connected to the two DC poles, and the two valve groups of one of the two DC poles of the opposite station are isolated.

[0097] Taking the inverter station 200 as an example, the third DC pole I 210 and the fourth DC pole II 220 of the inverter station 200 are connected to the ground return line. Specifically, the ground pole line isolation switch 213, the bipolar neutral area isolation switch 274, the fourth DC pole neutral bus switch 219, and the fourth pole bus isolation switch 272 are closed, and the third DC pole I 210 is connected to the ground return line. The ground pole line isolation switch 213, the bipolar neutral area isolation switch 284, the fourth DC pole neutral bus switch 229, and the fourth pole bus isolation switch 282 are closed, and the fourth DC pole II 220 is connected to the ground return line.

[0098] The third DC pole II 120 of the inverter station 200 is isolated. Specifically, the third high-end valve group first bypass switch 51 is closed, the third high-end valve group valve group switch 54 and the third high-end valve group bus switch 53 are separated, and the third high-end valve group 211 is isolated. The third low-end valve group first bypass switch 61 is closed, the third low-end valve group bus switch 64 and the third low-end valve group valve group switch 63 are separated, and the third low-end valve group 212 is isolated.

[0099] Before connecting the ground return line, the valve group of the unisolated pole needs to be charged and connected. Specifically, the fourth high-end converter transformer incoming line switch 234 is closed, and the fourth high-end valve group 222 is charged. The fourth high-end valve group bus switch 84 and the fourth high-end valve group valve group switch 83 are closed, the fourth high-end valve group first bypass switch 81 and the fourth high-end valve group second bypass switch 82 are separated, and the fourth high-end valve group 222 is connected. The fourth low-end converter transformer incoming line switch 233 is closed, and the fourth low-end valve group 221 is charged. The fourth low-end valve group bus switch 73 and the fourth low-end valve group valve group switch 74 are closed, the fourth low-end valve group first bypass switch 71 and the fourth low-end valve group second bypass switch 72 are separated, and the fourth low-end valve group 221 is connected.

[0100] It should be noted that S210-S240 have no strict order, and the order provided in the embodiment is relatively optimal. In each step, the order of closing the switch or the switch can be adjusted.

[0101] In S250, the converters of the two valve groups of one DC pole of the station are controlled to run in rectification and inversion states respectively, and the converters of the two valve groups of the other DC pole of the station are controlled to run in rectification and inversion states respectively.

[0102] Taking the rectification station 100 as an example, the first low-end converter 2 of the first DC pole I110 of the rectification station 100 is controlled to run in a rectification state, and the first high-end converter 1 is controlled to run in an inversion state. The second low-end converter 3 of the second DC pole I120 of the rectification station 100 is controlled to run in a rectification state, and the second high-end converter 4 is controlled to run in an inversion state.

[0103] Before unlocking, the first AC filter group 118 also needs to be connected.

[0104] In S260, the converters of the two valve groups of the other of the two DC poles of the station are controlled to run in rectification and inversion states respectively.

[0105] Taking the inversion station 200 as an example, the fourth low-end converter 7 of the fourth DC pole II220 of the inversion station 200 is controlled to run in a rectification state, and the fourth high-end converter 8 is controlled to run in an inversion state.

[0106] Before unlocking, the second AC filter group 218 also needs to be connected.

[0107] In S270, the DC currents of the converters of the two valve groups of one DC pole of the station are controlled, the DC currents of the converters of the two valve groups of the other DC pole of the station are controlled, the DC currents of the converters of the two valve groups of the other DC pole of the station which is not isolated are controlled, and ice melting is performed on the DC lines between the station and the counter station.

[0108] Specifically, the DC currents of the first DC pole I110 of the rectification station 100 are controlled, the DC currents of the second DC pole I120 of the rectification station 100 are controlled, the DC currents of the fourth DC pole II220 of the inversion station 200 are controlled, and ice melting is performed. A more preferred working condition is that the DC current of the first DC pole I110 of the rectification station 100 is 0.8pu, the DC current of the second DC pole I120 of the rectification station 100 is 0.8pu, and the DC current of the fourth DC pole II220 of the inversion station 200 is 0.8pu. Since the DC current of the fourth DC pole II220 of the inversion station 200 is 0.8pu, the current of the metal bus of the inversion station 200 is also 0.8pu, and the DC currents of the two parallel branches are controllable.

[0109] The DC current measurement value can be the high-voltage bus current IDC1P and the low-voltage bus current IDC1N of the high-end converter DC side, the high-voltage bus current IDC2P and the low-voltage bus current IDC2N of the low-end converter DC side, the pole bus current IDL, or the pole neutral bus current IDNC.

[0110] Figure 6 is a structure schematic diagram of an ice melting control device 300 of an extra-high voltage direct current transmission system provided by the present application, and the device comprises a detection unit 310 and a control unit 320.

[0111] The detection unit 310 is used for detecting the operating parameters of the high-voltage direct current transmission system, including the high-voltage bus current IDC1P of the high-end converter DC side, the low-voltage bus current IDC1N, the high-voltage bus current IDC2P of the low-end converter DC side, the low-voltage bus current IDC2N, the pole bus current IDL, the pole neutral bus current IDNC, the DC filter head current IZT1, the grounding pole current IDEL, the pole bus voltage UDL and the pole neutral bus voltage UDN, and the switch and knife switch position signal.

[0112] The control unit 320 controls one DC pole of the station to connect the DC line based on the operating parameters of the high-voltage direct current transmission system, controls the converter cathode and anode of the two valve groups of the other DC pole of the station to be reversed, controls the other DC pole of the station to be connected to the DC line of one DC pole of the station, controls the two DC poles to be connected to the metal bus of the opposite station, controls the converters of the two valve groups of one DC pole of the station to operate in the rectification and inversion states respectively, controls the converters of the two valve groups of the other DC pole of the station to operate in the rectification and inversion states respectively, controls the DC current of the station and / or the opposite station to melt the ice of the DC line between the station and the opposite station. The station and the opposite station are connected to the ground, and the ground connection is the connection of the grounding pole or the ground inside the station. If the required DC current for ice melting is greater than the maximum allowable current of the switch, the knife switch or the connecting line of the metal bus of the two DC poles of the opposite station, the two DC poles of the opposite station are connected, the two valve groups of one of the two DC poles of the opposite station are isolated, and the converters of the two valve groups of the other of the two DC poles of the opposite station operate in the rectification and inversion states respectively.

[0113] The above embodiments are only used to illustrate the technical idea of the present application, and cannot be used to limit the protection scope of the present application. Any modification made on the basis of the technical idea of the present application falls within the protection scope of the present application.

Claims

1. A circuit for melting ice in an ultra-high voltage direct current power transmission system, the ultra-high voltage direct current power transmission system comprising at least two converter stations, each of the converter stations comprising two direct current poles, each of the direct current poles comprising at least two valve groups, each of the valve groups comprising at least one converter, the circuit comprising: a first current path, a direct current pole of a local station and a metal bus of an opposite station or two direct current poles of the opposite station constitute the first current path through two direct current lines, any of the converter stations is the local station, and another converter station corresponding to the local station is the opposite station, two valve groups of one of the two direct current poles of the opposite station are isolated by bypass breakers; a second current path, converters cathodes and anodes of two valve groups of another direct current pole of the local station are reversely connected, the two valve groups of the another direct current pole of the local station are connected in parallel to the two direct current lines and the metal bus of the opposite station or the two direct current poles of the opposite station constitute the second current path, wherein the second current path comprises: a valve area ice melting breaker, the converters cathodes and anodes of the two valve groups of the another direct current pole of the local station are reversely connected by the valve area ice melting breaker; a first pole area ice melting breaker, a pole bus of the another direct current pole of the local station and a direct current line of the direct current pole of the local station are connected by the first pole area ice melting breaker; and a third pole area ice melting breaker, a direct current line of the another direct current pole of the local station and a pole neutral bus are connected by the third pole area ice melting breaker. only one of the converter stations of the local station or the opposite station is grounded. the two direct current lines comprise a direct current line of one direct current pole of the local station and a direct current line of another direct current pole of the local station. the direct current pole of the local station and the metal bus of the opposite station constitute the first current path through the two direct current lines, the first current path comprises the two valve groups of the one direct current pole of the local station, connection lines of the two valve groups of the one direct current pole of the local station, a pole bus of the one direct current pole of the local station, a pole neutral bus, the direct current line, and the metal bus of the two direct current poles of the opposite station. the direct current pole of the local station and the two direct current poles of the opposite station constitute the first current path through the two direct current lines, the first current path comprises the two valve groups of the one direct current pole of the local station, connection lines of the two valve groups of the one direct current pole of the local station, a pole bus of the one direct current pole of the local station, a pole neutral bus, the direct current line, bypass breakers of the two valve groups of one of the two direct current poles of the opposite station, and one or two valve groups of another of the two direct current poles of the opposite station. the another direct current pole of the local station and the metal bus of the opposite station constitute the second current path through the two direct current lines, the second current path comprises the two valve groups of the another direct current pole of the local station, connection lines of the two valve groups of the another direct current pole of the local station, a pole bus of the another direct current pole of the local station, a pole neutral bus, ice melting connection lines composed of the valve area ice melting breaker, the first pole area ice melting breaker, and the third pole area ice melting breaker, the direct current line, and the metal bus of the two direct current poles of the opposite station. ​ ​ ​ ​ ​ 2. The circuit of claim 1, wherein, ​ 3. The circuit of claim 1, wherein, ​ 4. The circuit of claim 1, wherein, ​ ​ 5. The circuit of claim 1, wherein, ​ The other direct current pole of the local station is connected in parallel to the two direct current lines and the two direct current poles of the opposite station to form the second current path, and the second current path comprises two valve groups of the other direct current pole of the local station, connection lines of the two valve groups of the other direct current pole of the local station, a pole bus of the other direct current pole of the local station, a pole neutral bus, ice-melting connection lines composed of the valve area ice-melting switch, the first pole area ice-melting switch and the third pole area ice-melting switch, the direct current lines, a bypass switch of the two valve groups of one of the two direct current poles of the opposite station, and one or two valve groups of the other direct current pole of the opposite station.

6. The circuit of claim 1, wherein, The valve groups are current source type valve groups or voltage source type valve groups, the current source type valve groups comprise grid commutated converters, and the voltage source type valve groups comprise voltage source converters.

7. A control method for the ice-melting circuit of an UHVDC power transmission system as claimed in any one of claims 1-6, wherein, The control method comprises: controlling one direct current pole of the local station to form the first current path through the two direct current lines and the metal bus of the opposite station or the two direct current poles of the opposite station, and controlling the bypass switch to be turned on; controlling two valve groups of the other direct current pole of the local station to be reverse connected, the other direct current pole of the local station being connected in parallel to the two direct current lines and the metal bus of the opposite station or the two direct current poles of the opposite station to form the second current path; controlling the converters of the first current path and the converters of the second current path to generate direct current in the first current path and the second current path respectively, and performing ice-melting on the direct current lines.

8. The control method of claim 7, wherein, If the direct current required for ice-melting is greater than the maximum allowable current of the switch, the switch or the connection line of the metal bus of the two direct current poles of the opposite station, the metal bus of the opposite station and the two direct current poles of the opposite station are controlled to flow current simultaneously.

9. The control method of claim 7, wherein, The control of the one direct current pole of the local station to form the first current path through the two direct current lines and the metal bus of the opposite station, the other direct current pole of the local station being connected in parallel to the two direct current lines and the metal bus of the opposite station or the two direct current poles of the opposite station to form the second current path, and the control of the converters of the first current path and the converters of the second current path comprise: controlling the converters of the two valve groups of the one direct current pole of the local station to operate in rectification and inversion states respectively, and controlling the direct current of the converters of the two valve groups of the one direct current pole of the local station; controlling the converters of the two valve groups of the other direct current pole of the local station to operate in rectification and inversion states respectively, and controlling the direct current of the converters of the two valve groups of the other direct current pole of the local station.

10. The control method of claim 7, wherein, The control of one DC pole of the station is connected to the two DC lines and the metal bus of the opposite station to form the first current path, and the other DC pole of the station is connected in parallel to the two DC lines and the two DC poles of the opposite station to form the second current path, or the control of one DC pole of the station is connected to the two DC lines and the two DC poles of the opposite station to form the first current path, and the other DC pole of the station is connected in parallel to the two DC lines and the metal bus of the opposite station to form the second current path, and the control of the converter working of the first current path and the converter working of the second current path comprises: controlling the converter of the two valve groups of one DC pole of the station to operate in rectification and inversion states respectively, and controlling the DC current of the converter of the two valve groups of one DC pole of the station; controlling the converter of the two valve groups of the other DC pole of the station to operate in rectification and inversion states respectively, and controlling the DC current of the converter of the two valve groups of the other DC pole of the station; controlling the converter of the two valve groups of the other DC pole of the opposite station to operate in rectification and inversion states respectively, and controlling the DC current of the converter of the two valve groups of the other DC pole of the opposite station.

11. A control device of an ice melting circuit of an UHVDC power transmission system, applying the control method of the ice melting circuit of the UHVDC power transmission system according to any one of claims 7 to 10, the device comprising: a detection unit for detecting the operating parameters of the UHVDC power transmission system; a control unit for controlling one DC pole of the station to be connected to the two DC lines and the metal bus of the opposite station or the two DC poles of the opposite station to form the first current path, controlling the bypass switch to be conducted, controlling the converter of the two valve groups of the other DC pole of the station to have the cathode and the anode reversed, the other DC pole of the station being connected in parallel to the two DC lines and the metal bus of the opposite station or the two DC poles of the opposite station to form the second current path, and controlling the converter working of the first current path and the converter working of the second current path to generate DC current in the first current path and the second current path respectively, and performing ice melting of the DC lines.

12. The control device of claim 11, wherein, The operating parameters of the UHVDC power transmission system include the position signal of the switch or the switch, the DC current, the DC voltage and the AC voltage.

13. The control device of claim 11, wherein, If the DC current required for ice melting is greater than the maximum allowable current of the switch, the switch or the connecting line of the metal bus of the opposite station, the control unit controls the metal bus of the opposite station and the two DC poles of the opposite station to flow current at the same time.

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