Current commutation system and current commutation method of power grid

Abstract

The invention relates to a current commutation system and a current commutation method of a power grid. The current commutation system comprises a first converter station, a second converter station and a coupling circuit, the first converter station comprises a first commutation module and a first external power supply circuit; the first reversing module comprises at least three first switch branches which are connected in parallel and at least three first full-bridge control circuits which are connected in parallel; the second converter station comprises a second commutation module and a second external power supply circuit; the second commutation module comprises at least three second switch branches which are connected in parallel and at least three second full-bridge control circuits which are connected in parallel; the first full-bridge control circuit is used for controlling the first switch branch to carry out current conduction in the first direction so as to enable the first converter station to carry out current commutation from the second direction; the first direction and the second direction are opposite directions; and the second full-bridge control circuit is used for controlling the second switch branch to carry out current conduction in the second direction, so that the second converter station carries out current commutation from the first direction.

Description

Technical Field

[0001] The present application relates to the technical field of power grid transmission, and in particular to a current commutation system and a current commutation method for a power grid. Background Art

[0002] With the steady increase in the penetration rate of renewable energy, the power grid transmission system faces severe challenges from the variability of renewable energy power output, and there is an urgent need to enhance the transmission flexibility of the power grid transmission system.

[0003] Line Commutated converter (LCC-HVDC) in the high-voltage direct current (HVDC) transmission system has been widely used around the world due to its mature technology and low cost and loss. In addition, with the increase in the flexibility of the transmission network, LCC-HVDC is also required to have a certain degree of flexibility, for example, LCC-HVDC needs to have a flexible current commutation function.

[0004] However, the current commutation circuits in power grids have the problem of poor current commutation flexibility. Summary of the invention

[0005] Based on this, it is necessary to provide a current commutation system and a current commutation method for a power grid that can flexibly implement current commutation in the power grid in order to address the above technical problems.

[0006] In a first aspect, the present application provides a current commutation system for a power grid, comprising: a first converter station, a second converter station and a coupling circuit;

[0007] The first converter station includes a first switching module and a first external power supply circuit; the first switching module includes at least three first switch branches connected in parallel and at least three first full-bridge control circuits connected in parallel; the second converter station includes a second switching module and a second external power supply circuit; the second switching module includes at least three second switch branches connected in parallel and at least three second full-bridge control circuits connected in parallel; one end of the first full-bridge control circuit is connected to the first switch branch, and the other end of the first full-bridge control circuit is connected to the input end of the coupling circuit; one end of the second full-bridge control circuit is connected to the second switch branch, and the other end of the second full-bridge control circuit is connected to the output end of the coupling circuit;

[0008] The input end of the first switching module is connected to the first external power supply circuit, the output end of the first switching module is connected to the input end of the coupling circuit, the output end of the coupling circuit is connected to the input end of the second switching module, and the output end of the second switching module is connected to the second external power supply circuit;

[0009] A first full-bridge control circuit is used to control the first switch branch to conduct current in a first direction, so that the first converter station performs current commutation in a second direction; the first direction and the second direction are opposite directions;

[0010] The second full-bridge control circuit is used to control the second switch branch to conduct current in the second direction, so that the second converter station performs current commutation from the first direction.

[0011] In one embodiment, the first switch branch includes a first group of switch circuits and a second group of switch circuits;

[0012] The first switch circuit comprises a first thyristor and a second thyristor connected in parallel, and the current conduction directions of the first thyristor and the second thyristor are opposite; the second switch circuit comprises a third thyristor and a fourth thyristor connected in parallel, and the current conduction directions of the third thyristor and the fourth thyristor are opposite;

[0013] The first thyristor and the third thyristor are connected in series, and the current conduction direction of the first thyristor and the third thyristor is the same; the second thyristor and the fourth thyristor are connected in series, and the current conduction direction of the second thyristor and the fourth thyristor is the same;

[0014] The second switch branch includes a third switch circuit group and a fourth switch circuit group;

[0015] The third switch circuit comprises a fifth thyristor and a sixth thyristor connected in parallel, and the current conduction directions of the fifth thyristor and the sixth thyristor are opposite; the fourth switch circuit comprises a seventh thyristor and an eighth thyristor connected in parallel, and the current conduction directions of the seventh thyristor and the eighth thyristor are opposite;

[0016] The fifth thyristor and the seventh thyristor are connected in series, and the current conduction direction of the fifth thyristor and the seventh thyristor is the same; the sixth thyristor and the eighth thyristor are connected in series, and the current conduction direction of the sixth thyristor and the eighth thyristor is the same.

[0017] In one embodiment, the first full-bridge control circuit comprises a first control component and a first inductor, one end of the first control component is connected to a common connection end of the first group of switch circuits and the second group of switch circuits, the other end of the first control component is connected to one end of the first inductor, and the other end of the first inductor is connected to an input end of the coupling circuit;

[0018] The second full-bridge control circuit includes a second inductor and a second control component, one end of the second inductor is connected to the output end of the coupling circuit, the other end of the second inductor is connected to one end of the second control component, the other end of the second control component is connected to the common connection end of the third group of switch circuits and the fourth group of switch circuits, and the common connection end of the third group of switch circuits and the fourth group of switch circuits is connected to the second external power supply circuit.

[0019] In one embodiment, the first converter station further includes a third commutation module, and the second converter station further includes a fourth commutation module; the third commutation module and the first commutation module are connected in parallel between the input end of the coupling circuit and the first external power supply circuit; the second commutation module and the fourth commutation module are connected in parallel between the output end of the coupling circuit and the second external power supply circuit;

[0020] The third switching module includes at least three third switch branches connected in parallel and at least three third full-bridge control circuits connected in parallel; the fourth switching module includes at least three fourth switch branches connected in parallel and at least three fourth full-bridge control circuits connected in parallel; one end of the third full-bridge control circuit is connected to the third switch branch, and the other end of the third full-bridge control circuit is connected to the input end of the coupling circuit; one end of the fourth full-bridge control circuit is connected to the fourth switch branch, and the other end of the fourth full-bridge control circuit is connected to the output end of the coupling circuit;

[0021] The input end of the third switching module is connected to the first external power supply circuit, the output end of the third switching module is connected to the input end of the coupling circuit, the output end of the coupling circuit is connected to the input end of the fourth switching module, and the output end of the fourth switching module is connected to the second external power supply circuit;

[0022] A third full-bridge control circuit is used to control the third switch branch to conduct current in the first direction, so that the third commutation module performs current commutation in the second direction;

[0023] The fourth full-bridge control circuit is used to control the fourth switch branch to conduct current in the second direction, so that the fourth commutation module performs current commutation in the first direction.

[0024] In one embodiment, the third switch branch includes a fifth switch circuit group and a sixth switch circuit group;

[0025] The fifth switch circuit comprises a ninth thyristor and a tenth thyristor connected in parallel, and the current conduction directions of the ninth thyristor and the tenth thyristor are opposite; the sixth switch circuit comprises an eleventh thyristor and a twelfth thyristor connected in parallel, and the current conduction directions of the eleventh thyristor and the twelfth thyristor are opposite;

[0026] The ninth thyristor and the eleventh thyristor are connected in series, and the current conduction directions of the ninth thyristor and the eleventh thyristor are the same; the tenth thyristor and the twelfth thyristor are connected in series, and the current conduction directions of the tenth thyristor and the twelfth thyristor are the same;

[0027] The fourth switch branch includes a seventh switch circuit group and an eighth switch circuit group;

[0028] The seventh switch circuit includes a thirteenth thyristor and a fourteenth thyristor connected in parallel, and the current conduction directions of the thirteenth thyristor and the fourteenth thyristor are opposite; the eighth switch circuit includes a fifteenth thyristor and a sixteenth thyristor connected in parallel, and the current conduction directions of the fifteenth thyristor and the sixteenth thyristor are opposite;

[0029] The thirteenth thyristor and the fifteenth thyristor are connected in series, and the current conduction direction of the thirteenth thyristor and the fifteenth thyristor is the same; the fourteenth thyristor and the sixteenth thyristor are connected in series, and the current conduction direction of the fourteenth thyristor and the sixteenth thyristor is the same.

[0030] In one embodiment, the third full-bridge control circuit includes a third control component and a third inductor, one end of the third control component is connected to the common connection end of the fifth group of switch circuits and the sixth group of switch circuits, the other end of the third control component is connected to one end of the third inductor, and the other end of the third inductor is connected to the input end of the coupling circuit;

[0031] The fourth full-bridge control circuit includes a fourth inductor and a fourth control component, one end of the fourth inductor is connected to the output end of the coupling circuit, the other end of the fourth inductor is connected to one end of the fourth control component, the other end of the fourth control component is connected to the common connection end of the seventh group of switch circuits and the eighth group of switch circuits, and the common connection end of the seventh group of switch circuits and the eighth group of switch circuits is connected to the second external power supply circuit.

[0032] In one embodiment, the first external power supply circuit includes an input circuit and a first voltage conversion circuit, and the second external power supply circuit includes a second voltage conversion circuit and an output circuit;

[0033] The output end of the input circuit is connected to the input end of the first switching module, the output end of the first switching module is connected to the input end of the coupling circuit, the output end of the coupling circuit is connected to the input end of the second switching module, the output end of the second switching module is connected to the input end of the second transformer circuit, and the output end of the second transformer circuit is connected to the output circuit.

[0034] In one embodiment, the coupling circuit includes a fifth inductor, a first resistor, a second resistor, a sixth inductor and a capacitor;

[0035] The first end of the fifth inductor is connected to the output end of the first switching module and the output end of the third switching module, the second end of the fifth inductor is connected to the first end of the first resistor, the second end of the first resistor is connected to the first end of the second resistor and the first end of the capacitor, the second end of the capacitor is grounded, the second end of the second resistor is connected to the first end of the sixth inductor, and the second end of the sixth inductor is connected to the input end of the second switching module.

[0036] In a second aspect, the present application further provides a commutation method of a current commutation system of a power grid, the method being applied to the current commutation system of the power grid as described in the first aspect above, the commutation method comprising:

[0037] Controlling a first full-bridge control circuit in the current commutation system to conduct current in a first direction in a first switch branch in the current commutation system, so that the first converter station performs current commutation in a second direction; the first direction and the second direction are opposite directions;

[0038] The second full-bridge control circuit in the current commutation system is controlled to conduct current in the second direction in the second switch branch of the current commutation system, so that the second converter station performs current commutation from the first direction.

[0039] In one embodiment, controlling the first full-bridge control circuit to conduct current in a first direction in a first switch branch of the current commutation system includes:

[0040] Determine a first voltage according to the first direction, and control each first full-bridge control circuit to output the first voltage to the first common terminal of the corresponding first switch branch, so that the voltage at the first common terminal is greater than the voltage at the first output terminal of the first switch branch, and the voltage at the first common terminal is less than the voltage at the second output terminal of the first switch branch;

[0041] Correspondingly, controlling the second full-bridge control circuit to conduct current in the second direction in the second switch branch of the current commutation system includes:

[0042] The second voltage is determined according to the second direction, and each second full-bridge control circuit is controlled to output the second voltage to the first common terminal of the corresponding second switch branch, so that the voltage at the second common terminal is less than the voltage at the first output terminal of the second switch branch, and the voltage at the second common terminal is greater than the voltage at the second output terminal of the second switch branch.

[0043] The current commutation system and current commutation method of the above-mentioned power grid, the above-mentioned current commutation system comprises: a first converter station, a second converter station and a coupling circuit; the first converter station comprises a first commutation module and a first external power supply circuit; the first commutation module comprises at least three first switch branches connected in parallel and at least three first full-bridge control circuits connected in parallel; the second converter station comprises a second commutation module and a second external power supply circuit; the second commutation module comprises at least three second switch branches connected in parallel and at least three second full-bridge control circuits connected in parallel; one end of the first full-bridge control circuit is connected to the first switch branch, and the other end of the first full-bridge control circuit is connected to the input end of the coupling circuit; one end of the second full-bridge control circuit is connected to the second full-bridge control circuit; The second switch branches are connected, and the other end of the second full-bridge control circuit is connected to the output end of the coupling circuit; the input end of the first switching module is connected to the first external power supply circuit, the output end of the first switching module is connected to the input end of the coupling circuit, the output end of the coupling circuit is connected to the input end of the second switching module, and the output end of the second switching module is connected to the second external power supply circuit; the first full-bridge control circuit is used to control the first switch branch to conduct current in the first direction so that the first converter station performs current commutation from the second direction; the first direction and the second direction are opposite directions; the second full-bridge control circuit is used to control the second switch branch to conduct current in the second direction so that the second converter station performs current commutation from the first direction. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] In order to more clearly illustrate the technical solutions in the embodiments of the present application or related technologies, the drawings required for use in the embodiments of the present application or related technical descriptions will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0045] Figure 1 is a schematic diagram of a current commutation system in one embodiment;

[0046] Figure 2 is a schematic diagram of a current commutation system in one embodiment;

[0047] Figure 3 is a schematic diagram of a current commutation system in one embodiment;

[0048] Figure 4 is a schematic diagram of a current commutation system in one embodiment;

[0049] Figure 5 is a schematic diagram of a current commutation system in one embodiment;

[0050] Figure 6 is a schematic diagram of a current commutation system in one embodiment;

[0051] Figure 7 is a schematic diagram of a current commutation system in one embodiment;

[0052] Figure 8 is a schematic diagram of a current commutation system in one embodiment;

[0053] Fig. 9 is a schematic diagram of a current commutation system in one embodiment;

[0054] Fig.10 is a control schematic diagram of a current commutation system in one embodiment;

[0055] Fig.11 is a control schematic diagram of a current commutation system in one embodiment;

[0056] Fig.12 is a control schematic diagram of a current commutation system in one embodiment;

[0057] Fig.13 is a schematic diagram of a current commutation system in one embodiment;

[0058] Fig.14 is a schematic diagram of a current commutation system in one embodiment;

[0059] Fig.15 is a schematic diagram of a current commutation system in one embodiment;

[0060] Fig.16 is a schematic flow chart of a current commutation method in one embodiment;

[0061] Fig.17 is a schematic diagram of a direct current in one embodiment;

[0062] Fig.18 is a schematic diagram of a trigger angle on the rectifier side in one embodiment;

[0063] Fig.19 is a schematic diagram of the inverter side trigger angle in one embodiment;

[0064] Fig. 20 is a schematic diagram of a DC voltage in one embodiment;

[0065] Fig.21 is a schematic diagram of reactive power of S1 in one embodiment;

[0066] Fig. 22 is a schematic diagram of reactive power of S2 in one embodiment;

[0067] Fig.23 FIG. 4 is a schematic diagram of active power on the DC side in an embodiment.

[0068] Description of Figure Numbers:

[0069] 10-first converter station; 100-first commutation module;

[0070] 101-a first external power supply circuit; 1000-a first switch branch;

[0071] 1001-a first full-bridge control circuit; 10000-a first set of switch circuits;

[0072] 10001-the second switch circuit; 100000-the first thyristor;

[0073] 100001-the second thyristor; 100010-the third thyristor;

[0074] 100011- fourth thyristor; 10010- first control component;

[0075] 10011-first inductor; 1010-input circuit;

[0076] 1011-a first voltage transformation circuit;

[0077] 20-second converter station; 200-second commutation module;

[0078] 201-a second external power supply circuit; 2000-a second switch branch;

[0079] 2001-the second full-bridge control circuit; 20000-the third switch circuit;

[0080] 20001-the fourth switch circuit; 200000-the fifth thyristor;

[0081] 200001-sixth thyristor; 200010-seventh thyristor;

[0082] 200011-eighth thyristor; 20010-second inductor;

[0083] 20011-second control component; 2010-second voltage conversion circuit;

[0084] 2011-output circuit;

[0085] 300-third switching module; 3000-third switch branch;

[0086] 3001-the third full-bridge control circuit; 30000-the fifth switch circuit;

[0087] 30001-sixth switch circuit; 300000-ninth thyristor;

[0088] 300001-the tenth thyristor; 300010-the eleventh thyristor;

[0089] 300011- twelfth thyristor; 30010- third control component;

[0090] 30011-third inductor;

[0091] 400- fourth switching module; 4000- fourth switch branch;

[0092] 4001-the fourth full-bridge control circuit; 40000-the seventh switch circuit;

[0093] 40001-eighth switch circuit; 400000-thirteenth thyristor;

[0094] 400001-the fourteenth thyristor; 400010-the fifteenth thyristor;

[0095] 400011-the sixteenth thyristor; 40010-the fourth inductor;

[0096] 40011-fourth control component;

[0097] 30-coupling circuit; 600-fifth inductor;

[0098] 601-a first resistor; 602-a second resistor;

[0099] 603-sixth inductor; 604-capacitor. DETAILED DESCRIPTION

[0100] In order to make the purpose, technical solution and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0101] With the steady increase in the penetration rate of renewable energy, the power grid transmission system faces severe challenges from the variability of renewable energy power output, and there is an urgent need to enhance the transmission flexibility of the power grid transmission system.

[0102] High-voltage direct current transmission (Line Commutated converter, LCC-HVDC) of the grid commutated converter in the high-voltage direct current transmission system (High-voltage direct current, HVDC) has been widely used around the world due to its mature technology and low cost and loss. In addition, with the increase in the flexibility of the transmission network, LCC-HVDC is also required to have a certain degree of flexibility. For example, LCC-HVDC is required to have a flexible current commutation function. However, the commutation circuit in the current power grid has the problem of poor current commutation flexibility. The present application provides a current commutation system capable of flexible commutation of the grid current, aiming to solve the above problems.

[0103] After introducing the background technology of the current commutation system of the power grid provided by the embodiment of the present application, the current commutation system of the power grid described in the present application will be introduced in detail below.

[0104] In an exemplary embodiment, Figure 1 As shown, a current commutation system 01 of a power grid is provided, comprising: a first converter station 10, a second converter station 20 and a coupling circuit 30;

[0105] The first converter station 10 includes a first commutation module 100 and a first external power supply circuit 101; the first commutation module 100 includes at least three first switch branches 1000 connected in parallel and at least three first full-bridge control circuits 1001 connected in parallel; the second converter station 20 includes a second commutation module 200 and a second external power supply circuit 201; the second commutation module 200 includes at least three second switch branches 2000 connected in parallel and at least three second full-bridge control circuits 2001 connected in parallel; one end of the first full-bridge control circuit 1001 is connected to the first switch branch 1000, and the other end of the first full-bridge control circuit 1001 is connected to the input end of the coupling circuit 30; one end of the second full-bridge control circuit 2001 is connected to the second switch branch 2000, and the other end of the second full-bridge control circuit 2001 is connected to the output end of the coupling circuit 30;

[0106] The input end of the first switching module 100 is connected to the first external power supply circuit 101, the output end of the first switching module 100 is connected to the input end of the coupling circuit 30, the output end of the coupling circuit 30 is connected to the input end of the second switching module 200, and the output end of the second switching module 200 is connected to the second external power supply circuit 201;

[0107] The first full-bridge control circuit 1001 is used to control the first switch branch 1000 to conduct current in a first direction, so that the first converter station 10 performs current commutation in a second direction; the first direction and the second direction are opposite directions;

[0108] The second full-bridge control circuit 2001 is used to control the second switch branch 2000 to conduct current in the second direction, so that the second converter station 20 performs current commutation from the first direction.

[0109] In an exemplary embodiment, see Figure 2 and Figure 3 , the first switch branch 1000 and the second switch branch 2000 can be further defined, wherein: (See Figure 2 ) The first switch branch 1000 comprises a first switch circuit 10000 and a second switch circuit 10001;

[0110] The first switch circuit 10000 includes a first thyristor 100000 and a second thyristor 100001 connected in parallel, and the current conduction directions of the first thyristor 100000 and the second thyristor 100001 are opposite; the second switch circuit 10001 includes a third thyristor 100010 and a fourth thyristor 100011 connected in parallel, and the current conduction directions of the third thyristor 100010 and the fourth thyristor 100011 are opposite;

[0111] The first thyristor 100000 and the third thyristor 100010 are connected in series, and the current conduction directions of the first thyristor 100000 and the third thyristor 100010 are the same; the second thyristor 100001 and the fourth thyristor 100011 are connected in series, and the current conduction directions of the second thyristor 100001 and the fourth thyristor 100011 are the same;

[0112] (See Figure 3 ) The second switch branch 2000 includes a third switch circuit group 20000 and a fourth switch circuit group 20001;

[0113] The third switch circuit 20000 includes a fifth thyristor 200000 and a sixth thyristor 200001 connected in parallel, and the current conduction directions of the fifth thyristor 200000 and the sixth thyristor 200001 are opposite; the fourth switch circuit 20001 includes a seventh thyristor 200010 and an eighth thyristor 200011 connected in parallel, and the current conduction directions of the seventh thyristor 200010 and the eighth thyristor 200011 are opposite;

[0114] The fifth thyristor 200000 and the seventh thyristor 200010 are connected in series, and the current conduction direction of the fifth thyristor 200000 and the seventh thyristor 200010 is the same; the sixth thyristor 200001 and the eighth thyristor 200011 are connected in series, and the current conduction direction of the sixth thyristor 200001 and the eighth thyristor 200011 is the same.

[0115] In an exemplary embodiment, see Figure 4 , the first full-bridge control circuit 1001 and the second full-bridge control circuit 2001 can be further defined, wherein: the first full-bridge control circuit 1001 includes a first control component 10010 and a first inductor 10011, one end of the first control component 10010 is connected to the common connection end of the first group of switch circuits 10000 and the second group of switch circuits 100011, the other end of the first control component 10010 is connected to one end of the first inductor 10011, and the other end of the first inductor 10011 is connected to the input end of the coupling circuit 30;

[0116] The second full-bridge control circuit 2001 includes a second inductor 20010 and a second control component 20011, one end of the second inductor 20010 is connected to the output end of the coupling circuit 30, the other end of the second inductor 20010 is connected to one end of the second control component 20011, the other end of the second control component 20011 is connected to the common connection end of the third group of switch circuits 20000 and the fourth group of switch circuits 20001, and the common connection end of the third group of switch circuits 20000 and the fourth group of switch circuits 20001 is connected to the second external power supply circuit 201.

[0117] In an exemplary embodiment, see Figure 5 , the first converter station 10 and the second converter station 20 can be further defined, wherein: the first converter station 10 further includes a third commutation module 300, and the second converter station 20 further includes a fourth commutation module 400; the third commutation module 300 and the first commutation module 100 are connected in parallel between the input end of the coupling circuit 30 and the first external power supply circuit 101; the second commutation module 200 and the fourth commutation module 400 are connected in parallel between the output end of the coupling circuit 30 and the second external power supply circuit 201;

[0118] The third commutation module 300 includes at least three third switch branches 3000 connected in parallel and at least three third full-bridge control circuits 3001 connected in parallel; the fourth commutation module 400 includes at least three fourth switch branches 4000 connected in parallel and at least three fourth full-bridge control circuits 4001 connected in parallel; one end of the third full-bridge control circuit 3001 is connected to the third switch branch 3000, and the other end of the third full-bridge control circuit 3001 is connected to the input end of the coupling circuit 30; one end of the fourth full-bridge control circuit 4001 is connected to the fourth switch branch 4000, and the other end of the fourth full-bridge control circuit 400 is connected to the output end of the coupling circuit 30;

[0119] The input end of the third switching module 300 is connected to the first external power supply circuit 101, the output end of the third switching module 300 is connected to the input end of the coupling circuit 30, the output end of the coupled circuit 30 is connected to the input end of the fourth switching module 400, and the output end of the fourth switching module 400 is connected to the second external power supply circuit 201;

[0120] The third full-bridge control circuit 3001 is used to control the third switch branch 3000 to conduct current in the first direction, so that the third commutation module 300 performs current commutation in the second direction;

[0121] The fourth full-bridge control circuit 4001 is used to control the fourth switch branch 4000 to conduct current in the second direction, so that the fourth commutation module 400 performs current commutation in the first direction.

[0122] In an exemplary embodiment, see Figure 6 and Figure 7 , the third switch branch 3000 and the fourth switch branch 4000 can be further defined, wherein: (see Figure 6 ) The third switch branch 3000 includes a fifth switch circuit group 30000 and a sixth switch circuit group 30001;

[0123] The fifth switch circuit 30000 includes a ninth thyristor 300000 and a tenth thyristor 300001 connected in parallel, and the current conduction directions of the ninth thyristor 300000 and the tenth thyristor 300001 are opposite; the sixth switch circuit 30001 includes an eleventh thyristor 300010 and a twelfth thyristor 300011 connected in parallel, and the current conduction directions of the eleventh thyristor 300010 and the twelfth thyristor 300011 are opposite;

[0124] The ninth thyristor 300000 and the eleventh thyristor 300010 are connected in series, and the current conduction directions of the ninth thyristor 300000 and the eleventh thyristor 300010 are the same; the tenth thyristor 300001 and the twelfth thyristor 300011 are connected in series, and the current conduction directions of the tenth thyristor 300001 and the twelfth thyristor 300011 are the same;

[0125] (See Figure 7 ) the fourth switch branch 4000 includes a seventh switch circuit group 40000 and an eighth switch circuit group 40001;

[0126] The seventh switch circuit 40000 includes a thirteenth thyristor 400000 and a fourteenth thyristor 400001 connected in parallel, and the current conduction directions of the thirteenth thyristor 400000 and the fourteenth thyristor 400001 are opposite; the eighth switch circuit 40001 includes a fifteenth thyristor 400010 and a sixteenth thyristor 400011 connected in parallel, and the current conduction directions of the fifteenth thyristor 400010 and the sixteenth thyristor 400011 are opposite;

[0127] The thirteenth thyristor 400000 and the fifteenth thyristor 400010 are connected in series, and the current conduction direction of the thirteenth thyristor 400000 and the fifteenth thyristor 400010 is the same; the fourteenth thyristor 400001 and the sixteenth thyristor 400011 are connected in series, and the current conduction direction of the fourteenth thyristor 400001 and the sixteenth thyristor 400011 is the same.

[0128] In an exemplary embodiment, see Figure 8 , the third full-bridge control circuit 3001 and the fourth full-bridge control circuit 4001 can be further defined, wherein: the third full-bridge control circuit 3001 includes a third control component 30010 and a third inductor 30011, one end of the third control component 30010 is connected to the common connection end of the fifth group of switch circuits 30000 and the sixth group of switch circuits 30001, the other end of the third control component 30010 is connected to one end of the third inductor 30011, and the other end of the third inductor 30011 is connected to the input end of the coupling circuit 30;

[0129] The fourth full-bridge control circuit 4001 includes a fourth inductor 40010 and a fourth control component 40011, one end of the fourth inductor 40010 is connected to the output end of the coupling circuit 30, the other end of the fourth inductor 40010 is connected to one end of the fourth control component 40011, the other end of the fourth control component 40011 is connected to the common connection end of the seventh group of switch circuits 40000 and the eighth group of switch circuits 40001, and the common connection end of the seventh group of switch circuits 40000 and the eighth group of switch circuits 40001 is connected to the second external power supply circuit 201.

[0130] In the embodiment of the present application, the conventional LCC-HVDC thyristor is improved, the original thyristor is still used to transmit normal power, and the added IGBT full bridge module (FB-CL) is used to actively control the on and off of the main thyristor bridge, and provide soft switching and forced commutation for the thyristor by applying a step conversion voltage with appropriate amplitude and polarity. Fig. 9 , the specific implementation plan is as follows:

[0131] The series thyristors SCR1 and SCR3 are used as the main current path, and the anti-parallel thyristors SCR2 and SCR4 are used as the current freewheeling path for the full power factor range. The commutation of the thyristor bridge is guaranteed by the actively controlled FB-CL, which can actively provide reverse voltage to force the thyristor to turn off and start the anti-parallel thyristor. The FB-CL is a string of full-bridge modules using self-commutated IGBTs, which are only effective during thyristor commutation. To ensure the orderly conduction and shutdown of the thyristors, one thyristor is triggered at each instance according to the voltage level command and current polarity. When the load current is lower than the thyristor latch current or any current sampling mismatch, the FB-CL acts as a freewheeling path. Fig. 9 In the example, if the forced commutation bridge DC bus voltage is Vdc at the neutral point O, the FB-CL should be designed with internal redundancy to allow the trajectory of its output voltage VFB to exceed the envelope of ±1 / 2Vdc. When |VFB| is higher than 1 / 2Vdc, the upper (lower) thyristor string SCR1 (SCR3) can be turned off if its gate signal is removed. On the other hand, when |VFB| is lower than 1 / 2Vdc, the turn-off of the anti-parallel device SCR2 (SCR4) can be achieved. In addition, the FB-CL provides step transition and zero voltage switching for the thyristors to be compatible with the system change rate dv / dt and di / dt to achieve safe operation of the equipment.

[0132] In this way, VSC properties are established for the forced commutation thyristor converter; therefore, active power and reactive power control can be decoupled. Compared with the traditional LCC, this scheme enables the thyristor to actively change the direction of the DC current and provide current reversal capability to achieve power flow reversal.

[0133] In the embodiment of the present application, a forced commutation strategy is specifically provided, and the forced commutation strategy of the converter bridge includes:

[0134] (1) During normal operation, the anti-parallel thyristors SCR2 and SCR4 are both turned off, FB-CL is turned off, and SCR1 and SCR3 are put into operation normally. At this time, the operation mode is the same as that of LCC-HVDC. SCR1 and SCR3 provide the current conduction path during normal operation;

[0135] (2) When the forced commutation strategy is activated, SCR2 is started, FB-CL is voltage controlled, and its voltage VFB is actively controlled to increase to 2 / 3Vdc. At this time, SCR1 is subjected to reverse voltage and is turned off. At this time, SCR1 is stopped, SCR2 is subjected to forward voltage and is turned on, and the upper bridge arm completes the bridge arm direction conversion;

[0136] (3) After SCR1 is shut down, FB-CL is converted to current control. When the conduction current iFB is controlled to 0, SCR3 is shut down at the same time and SCR4 is put into operation. At this time, SCR4 is not turned on due to the reverse voltage. Since the lower bridge arm has no conduction path, iL flows through thyristor SCR2 during this period, and SCR2 continues to conduct.

[0137] (4) After SCR3 stops operating, FB-CL switches to voltage control, iFB is no longer actively controlled, and VFB is controlled to decrease to -2 / 3Vdc in a step-by-step transition manner. During the voltage reduction process, when SCR2 is turned off due to reverse voltage, the upper and lower bridge arms are not turned on at this time, and the FB-CL current iFB is completely transferred to the load side, that is, iL=iFB;

[0138] (5) As the voltage of FB-CL continues to decrease to -2 / 3Vdc, SCR4 is turned on by the forward voltage, and the lower arm conduction bridge is switched from SCR3 to SCR4. When SCR4 is triggered, the submodule voltage unit of FB-CL is disabled, and the output current is transmitted from FB-CL to SCR4 in a zero voltage turn-on mode. The forced commutation ends, and the converter realizes reverse current operation.

[0139] In one embodiment, a method for achieving power flow reversal is also provided, including:

[0140] Step 1: In normal operation, S1 uses PS1_dc_ref as the reference value and controls the DC power by controlling the DC current, such as Fig.10 As shown, S2 controls the DC voltage with VS2_dc_ref as the reference value, and its voltage reference value VS2_dc_ref is determined by the external reactive outer loop to ensure the reactive power stability of the converter during the commutation process. Once the power flow reversal signal RS is triggered, as shown Fig.11 As shown, the DC power reference value of S1 will become PS1_dc_ref1. In order to stably achieve power flow reversal, PS1_dc_ref1 will gradually decrease according to the linear decline mode, thereby gradually reducing the DC current, the current flows in the opposite direction and approaches the reference value, and the active power gradually decreases from the initial value to zero, so as to achieve subsequent current reversal. Fig.12 As shown, the outer FB controller is determined by the external current of the converter station. When the DC current drops to a certain value, the start signal Start is generated by the current comparator to start the FB-CL controller. While the power is decreasing, at S2, the controller continuously stabilizes the voltage through DC voltage control. It can be seen that during the power flow conversion process, since Isi_dc_pu decreases with the slope of the reference value, the αSi_Vref of S2 under constant DC voltage control decreases accordingly.

[0141] Step 2: In the early stage of reversal, the system operates at a lower DC power level. In order to shorten the time of this stage, when the active power reaches the predetermined threshold value P_dcmin, the present invention will further increase the slope rate of the DC power decline. To further accelerate the speed of DC current reversal. In this process, the fixed reactive outer loop controls the reactive power at a certain value to support the DC voltage stability during the control period. At the same time, FB-CL executes the commutation strategy, and switches the control mode through the thyristor shutdown signal SW to realize the start-up of the anti-parallel thyristor and realize the direction conversion of the current.

[0142] Step 3: Once the anti-parallel thyristor is triggered, the DC current will start to flow in the opposite direction. Subsequently, S1 will control the DC power to increase in the opposite direction with a large slope. When the DC current flows in the opposite direction of the reference value and the DC power recovers to a certain value, the power change slope decreases (the whole process is symmetrical with the power change before the reversal). After the DC voltage polarity changes, the power flow command is converted from zero to the opposite sign value to establish a reverse power flow.

[0143] In an exemplary embodiment, see Fig.13 , the first external power supply circuit 101 and the second external power supply circuit 201 may also be defined, the first external power supply circuit 101 includes an input circuit 1010 and a first voltage conversion circuit 1011, and the second external power supply circuit 201 includes a second voltage conversion circuit 2010 and an output circuit 2011;

[0144] The output end of the input circuit 1010 is connected to the input end of the first switching module 100, the output end of the first switching module 100 is connected to the input end of the coupling circuit 30, the output end of the coupling circuit 30 is connected to the input end of the second switching module 200, the output end of the second switching module 200 is connected to the input end of the second transformer circuit 2010, and the output end of the second transformer circuit 2010 is connected to the output circuit 2011.

[0145] In an exemplary embodiment, see Fig.14 , the coupling circuit 30 can also be described, the coupling circuit 30 includes a fifth inductor 600, a first resistor 601, a second resistor 602, a sixth inductor 603 and a capacitor 604;

[0146] The first end of the fifth inductor 600 is connected to the output end of the first switching module 100 and the output end of the third switching module 300, the second end of the fifth inductor 600 is connected to the first end of the first resistor 601, the second end of the first resistor 601 is connected to the first end of the second resistor 602 and the first end of the capacitor 604, the second end of the capacitor 604 is grounded, the second end of the second resistor 602 is connected to the first end of the sixth inductor 603, and the second end of the sixth inductor 603 is connected to the input end of the second switching module 200.

[0147] In one embodiment, see Fig.15 It also provides a complete current commutation system for the power grid, aiming to retain the advantages of the LCC-HVDC direct current transmission system such as large capacity and low loss. By introducing a forced commutation bridge, the LCC has the characteristics of a VSC, achieving low conversion loss, enhanced voltage scalability and operability of bipolar direct current, solving the problems caused by the reverse voltage when the current of the existing conventional direct current system is reversed, and enabling the LCC-HVDC system to be more flexibly connected to the large power grid or multi-terminal direct current system, helping to achieve the complementarity and optimal configuration of multi-regional energy, and improving the flexibility and reliability of power grid interconnection.

[0148] In an exemplary embodiment, see Fig.16 , a commutation method of a current commutation system of a power grid is also provided, which is applied to the current commutation system of the power grid as described in each of the above embodiments, and the commutation method includes:

[0149] S201. Control a first full-bridge control circuit in a current commutation system to conduct current in a first direction in a first switch branch in the current commutation system, so that a first converter station performs current commutation in a second direction.

[0150] The first direction and the second direction are opposite directions.

[0151] S202, controlling the second full-bridge control circuit in the current commutation system to conduct current in the second direction in the second switch branch of the current commutation system, so that the second converter station performs current commutation in the first direction.

[0152] In an exemplary embodiment, the process of controlling the first full-bridge control circuit to conduct current in the first direction of the first switch branch in the current commutation system may also be described in detail. The above S201 “controlling the first full-bridge control circuit to conduct current in the first direction of the first switch branch in the current commutation system” includes:

[0153] A first voltage is determined according to a first direction, and each first full-bridge control circuit is controlled to output the first voltage to the first common terminal of the corresponding first switch branch, so that the voltage at the first common terminal is greater than the voltage at the first output terminal of the first switch branch, and the voltage at the first common terminal is less than the voltage at the second output terminal of the first switch branch.

[0154] Correspondingly, the above-mentioned controlling the second full-bridge control circuit to conduct current in the second direction in the second switch branch of the current commutation system includes:

[0155] The second voltage is determined according to the second direction, and each second full-bridge control circuit is controlled to output the second voltage to the first common terminal of the corresponding second switch branch, so that the voltage at the second common terminal is less than the voltage at the first output terminal of the second switch branch, and the voltage at the second common terminal is greater than the voltage at the second output terminal of the second switch branch.

[0156] In order to verify the effectiveness of the control method proposed in the present invention, the present invention is described in detail below with examples and simulation diagrams. Fig.15 The LCC-HVDC transmission system with forced reversing valve based on CIGRE HVDC benchmark is shown. Before the power flow is reversed, the LCC-HVDC system transmits 1000 MW of active power from S1 to S2, with a rated DC voltage Udc=500 kV and a rated DC voltage Idc=2 kA. The purpose of the invention is to use a forced commutation bridge to control the current direction to achieve the bidirectional power flow capability of the system, that is, to transmit 1000 MW of active power from S2 to S1. And S1 is a constant DC power control, and S2 is a constant DC voltage control.

[0157] Figure 17-Figure 23 The simulation results for Case 1 are shown. Before the power reversal starts, power flows from S1 to S2, where S1 controls the DC current and S2 controls the DC voltage. The power reversal starts at 0.2 seconds. Fig.17 It can be seen that during the entire power reversal period, the DC current accurately follows the current reference value calculated by the active outer loop, first gradually decreasing to zero, and then gradually increasing in the opposite direction. The forced commutation bridge conducts most of its output current through a pair of fixed thyristors in either power flow direction. The reduction in DC current is caused by the increase in the firing angle at S1, such as Fig.18 At the same time, the reactive power at S2 can be controlled at a normal value by the reactive outer loop control through pure reactive power exchange, as shown in Fig.19 As shown, this is achieved by reducing the firing angle at S2, as Fig.19 The decrease in firing angle at S1 results in a decrease in DC voltage, as shown in Alpha_S2_Qcontrol in Figure 1. Fig. 20 At 1.7 seconds, when the DC power reaches the threshold value of Pdcmin (selected as 0.3 p.u. in this case study), the change in the slope of the DC power reference value causes the rate of rise of the DC current to increase, as shown in Fig.21 shown. Fig. 22 It shows that the reactive power consumption at S1 increases slightly. This is because the phenomenon that the reactive power consumption decreases due to the decrease of DC current at S1 is masked by the phenomenon that the reactive power consumption increases due to the increase of firing angle.

[0158] At approximately 2 seconds, the forward-conducting valves of S1 and S2 are blocked by FB-CL, and the main current is transferred to the reverse-parallel valves activated by FB-CL. The DC voltage is maintained at a certain level, such as Fig.23 As shown. In order to minimize the DC transient caused by the mismatch of the firing angles of S1 and S2, the reverse parallel valve of S1 is activated at about 117° and the reverse parallel valve of S2 is activated at about 60°. Then, the DC current gradually increases following the current reference value with a similar trajectory. During this process, the receiving end S1 controls the reactive power consumption at S1. It can be clearly seen from the above simulation results that in the proposed LCC-HVDC system, power reversal can be achieved without reversing the polarity of the DC voltage.

[0159] A person of ordinary skill in the art can understand that all or part of the processes in the above-mentioned embodiment method can be completed by instructing the relevant hardware through a computer program, and the computer program can be stored in a non-volatile computer-readable storage medium. When the computer program is executed, it can include the processes of the embodiments of the above-mentioned methods. Among them, any reference to the memory, database or other medium used in the embodiments provided in the present application can include at least one of non-volatile memory 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 (ReRAM), magnetic random access memory (MRAM), ferroelectric random access memory (FRAM), phase change memory (PCM), graphene memory, etc. Volatile memory can include random access memory (RAM) or external cache memory, etc. As an illustration and not limitation, RAM can be in various forms, such as static random access memory (SRAM) or dynamic random access memory (DRAM). The database involved in each embodiment provided in this application may include at least one of a relational database and a non-relational database. Non-relational databases may include distributed databases based on blockchains, etc., but are not limited to this. The processor involved in each embodiment provided in this application may be a general-purpose processor, a central processing unit, a graphics processor, a digital signal processor, a programmable logic device, a data processing logic device based on quantum computing, an artificial intelligence (AI) processor, etc., but are not limited to this.

[0160] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this application.

[0161] The above-described embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be construed as limiting the scope of the present application. It should be noted that, for a person of ordinary skill in the art, several modifications and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the attached claims.

Claims

1. A current commutation system for a power grid, characterized in that: The current commutation system comprises: a first converter station, a second converter station and a coupling circuit; The first converter station includes a first switching module and a first external power supply circuit; the first switching module includes at least three first switch branches connected in parallel and at least three first full-bridge control circuits connected in parallel; the second converter station includes a second switching module and a second external power supply circuit; the second switching module includes at least three second switch branches connected in parallel and at least three second full-bridge control circuits connected in parallel; one end of the first full-bridge control circuit is connected to the first switch branch, and the other end of the first full-bridge control circuit is connected to the input end of the coupling circuit; one end of the second full-bridge control circuit is connected to the second switch branch, and the other end of the second full-bridge control circuit is connected to the output end of the coupling circuit; The input end of the first switching module is connected to the first external power supply circuit, the output end of the first switching module is connected to the input end of the coupling circuit, the output end of the coupling circuit is connected to the input end of the second switching module, and the output end of the second switching module is connected to the second external power supply circuit; The first full-bridge control circuit is used to control the first switch branch to conduct current in a first direction, so that the first converter station performs current commutation in a second direction; the first direction and the second direction are opposite directions; The second full-bridge control circuit is used to control the second switch branch to conduct current in a second direction, so that the second converter station performs current commutation from the first direction.

2. The current commutation system according to claim 1, characterized in that: The first switch branch includes a first group of switch circuits and a second group of switch circuits; The first switch circuit comprises a first thyristor and a second thyristor connected in parallel, and the current conduction directions of the first thyristor and the second thyristor are opposite; the second switch circuit comprises a third thyristor and a fourth thyristor connected in parallel, and the current conduction directions of the third thyristor and the fourth thyristor are opposite; The first thyristor and the third thyristor are connected in series, and the current conduction direction of the first thyristor and the third thyristor is the same; the second thyristor and the fourth thyristor are connected in series, and the current conduction direction of the second thyristor and the fourth thyristor is the same; The second switch branch includes a third switch circuit group and a fourth switch circuit group; The third switch circuit group includes a fifth thyristor and a sixth thyristor connected in parallel, and the current conduction directions of the fifth thyristor and the sixth thyristor are opposite; the fourth switch circuit group includes a seventh thyristor and an eighth thyristor connected in parallel, and the current conduction directions of the seventh thyristor and the eighth thyristor are opposite; The fifth thyristor and the seventh thyristor are connected in series, and the current conduction direction of the fifth thyristor and the seventh thyristor is the same; the sixth thyristor and the eighth thyristor are connected in series, and the current conduction direction of the sixth thyristor and the eighth thyristor is the same.

3. The current commutation system according to claim 2, characterized in that: The first full-bridge control circuit includes a first control component and a first inductor, one end of the first control component is connected to a common connection end of the first group of switch circuits and the second group of switch circuits, the other end of the first control component is connected to one end of the first inductor, and the other end of the first inductor is connected to an input end of the coupling circuit; The second full-bridge control circuit includes a second inductor and a second control component, one end of the second inductor is connected to the output end of the coupling circuit, the other end of the second inductor is connected to one end of the second control component, the other end of the second control component is connected to the common connection end of the third group of switch circuits and the fourth group of switch circuits, and the common connection end of the third group of switch circuits and the fourth group of switch circuits is connected to the second external power supply circuit.

4. The current commutation system according to claim 1, characterized in that: The first converter station further includes a third commutation module, and the second converter station further includes a fourth commutation module; the third commutation module and the first commutation module are connected in parallel between the input end of the coupling circuit and the first external power supply circuit; the second commutation module and the fourth commutation module are connected in parallel between the output end of the coupling circuit and the second external power supply circuit; The third switching module includes at least three third switch branches connected in parallel and at least three third full-bridge control circuits connected in parallel; the fourth switching module includes at least three fourth switch branches connected in parallel and at least three fourth full-bridge control circuits connected in parallel; one end of the third full-bridge control circuit is connected to the third switch branch, and the other end of the third full-bridge control circuit is connected to the input end of the coupling circuit; one end of the fourth full-bridge control circuit is connected to the fourth switch branch, and the other end of the fourth full-bridge control circuit is connected to the output end of the coupling circuit; The input end of the third switching module is connected to the first external power supply circuit, the output end of the third switching module is connected to the input end of the coupling circuit, the output end of the coupling circuit is connected to the input end of the fourth switching module, and the output end of the fourth switching module is connected to the second external power supply circuit; The third full-bridge control circuit is used to control the third switch branch to conduct current in the first direction, so that the third commutation module performs current commutation in the second direction; The fourth full-bridge control circuit is used to control the fourth switch branch to conduct current in the second direction, so that the fourth commutation module performs current commutation in the first direction.

5. The current commutation system according to claim 4, characterized in that: The third switch branch includes a fifth switch circuit group and a sixth switch circuit group; The fifth switch circuit group includes a ninth thyristor and a tenth thyristor connected in parallel, and the current conduction directions of the ninth thyristor and the tenth thyristor are opposite; the sixth switch circuit group includes an eleventh thyristor and a twelfth thyristor connected in parallel, and the current conduction directions of the eleventh thyristor and the twelfth thyristor are opposite; The ninth thyristor and the eleventh thyristor are connected in series, and the current conduction directions of the ninth thyristor and the eleventh thyristor are the same; the tenth thyristor and the twelfth thyristor are connected in series, and the current conduction directions of the tenth thyristor and the twelfth thyristor are the same; The fourth switch branch includes a seventh switch circuit group and an eighth switch circuit group; The seventh switch circuit group includes a thirteenth thyristor and a fourteenth thyristor connected in parallel, and the current conduction directions of the thirteenth thyristor and the fourteenth thyristor are opposite; the eighth switch circuit group includes a fifteenth thyristor and a sixteenth thyristor connected in parallel, and the current conduction directions of the fifteenth thyristor and the sixteenth thyristor are opposite; The thirteenth thyristor and the fifteenth thyristor are connected in series, and the current conduction direction of the thirteenth thyristor and the fifteenth thyristor is the same; the fourteenth thyristor and the sixteenth thyristor are connected in series, and the current conduction direction of the fourteenth thyristor and the sixteenth thyristor is the same.

6. The current commutation system according to claim 5, characterized in that: The third full-bridge control circuit includes a third control component and a third inductor, one end of the third control component is connected to the common connection end of the fifth group of switch circuits and the sixth group of switch circuits, the other end of the third control component is connected to one end of the third inductor, and the other end of the third inductor is connected to the input end of the coupling circuit; The fourth full-bridge control circuit includes a fourth inductor and a fourth control component, one end of the fourth inductor is connected to the output end of the coupling circuit, the other end of the fourth inductor is connected to one end of the fourth control component, the other end of the fourth control component is connected to the common connection end of the seventh group of switch circuits and the eighth group of switch circuits, and the common connection end of the seventh group of switch circuits and the eighth group of switch circuits is connected to the second external power supply circuit.

7. The current commutation system according to claim 1, characterized in that: The first external power supply circuit includes an input circuit and a first voltage conversion circuit, and the second external power supply circuit includes a second voltage conversion circuit and an output circuit; The output end of the input circuit is connected to the input end of the first switching module, the output end of the first switching module is connected to the input end of the coupling circuit, the output end of the coupling circuit is connected to the input end of the second switching module, the output end of the second switching module is connected to the input end of the second transformer circuit, and the output end of the second transformer circuit is connected to the output circuit.

8. The current commutation system according to claim 4, characterized in that: The coupling circuit includes a fifth inductor, a first resistor, a second resistor, a sixth inductor and a capacitor; The first end of the fifth inductor is connected to the output end of the first switching module and the output end of the third switching module, the second end of the fifth inductor is connected to the first end of the first resistor, the second end of the first resistor is connected to the first end of the second resistor and the first end of the capacitor, the second end of the capacitor is grounded, the second end of the second resistor is connected to the first end of the sixth inductor, and the second end of the sixth inductor is connected to the input end of the second switching module.

9. A commutation method for a current commutation system of a power grid, characterized in that: The method is applied to a current commutation system of a power grid according to any one of claims 1 to 8, and the commutation method comprises: Controlling the first full-bridge control circuit in the current commutation system to conduct current in the first direction of the first switch branch in the current commutation system, so that the first converter station performs current commutation in a second direction; the first direction and the second direction are opposite directions; The second full-bridge control circuit in the current commutation system is controlled to conduct current in the second direction in the second switch branch of the current commutation system, so that the second converter station performs current commutation from the first direction.

10. The commutation method according to claim 9, characterized in that: The controlling the first full-bridge control circuit to conduct current in a first direction in a first switch branch of the current commutation system includes: Determine a first voltage according to the first direction, and control each of the first full-bridge control circuits to output the first voltage to a first common terminal of a corresponding first switch branch, so that the voltage at the first common terminal is greater than the voltage at the first output terminal of the first switch branch, and the voltage at the first common terminal is less than the voltage at the second output terminal of the first switch branch; Correspondingly, controlling the second full-bridge control circuit to conduct current in the second direction in the second switch branch of the current commutation system includes: A second voltage is determined according to the second direction, and each of the second full-bridge control circuits is controlled to output the second voltage to the first common terminal of the corresponding second switch branch, so that the voltage at the second common terminal is less than the voltage at the first output terminal of the second switch branch, and the voltage at the second common terminal is greater than the voltage at the second output terminal of the second switch branch.

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