Direct-current fault ride-through method and device based on switch assistance

Abstract

The invention discloses a direct-current fault ride-through method and device based on switch assistance, and the method comprises the steps: arranging an auxiliary switch at a wire outlet end of a transmitting-end flexible direct-current converter station or a wire outlet end of a receiving-end flexible direct-current converter station, and enabling the auxiliary switch to be connected with a direct-current bus between the transmitting end and the receiving end; a converter station connected with a fault point prevents reverse arcing of the fault point by controlling voltage and current reduction operation, actively injecting circulating current, forming small alternating current quantity on a direct current side, pulling an auxiliary switch open, forming physical fractures on two sides of the fault point, forcing arc quenching or isolation of the fault point, and controlling the auxiliary switch to be reclosed after free time is removed, so that the fault point is prevented from reverse arcing. And the current converter with the reduced voltage and the reduced current recovers normal operation, the fault clearing process is completed, and the technical problems that in the prior art, when a negative pressure clearing technology is adopted for achieving fault clearing of the current converter, reverse reignition of an arc at a fault point may be caused by output of negative pressure, even zero-crossing repeated reignition may be caused, the fault clearing time cannot be guaranteed, and the clearing effect is unstable are solved.

Description

Technical Field

[0001] The present invention relates to the technical field of power grid fault ride-through, and in particular to a switch-assisted direct current fault ride-through method and device. Background Art

[0002] DC line fault clearing is a key technology for flexible DC transmission projects. When a flexible DC line fails, the AC side continuously injects fault current into the DC side fault point through an anti-parallel diode, and the fault cannot be cleared automatically. If the AC incoming line switch of the converter station needs to be tripped, the fault recovery time is long, and the DC side fault will cause a three-phase short circuit on the AC side, expanding the scope of the fault.

[0003] In the prior art, a full-bridge + half-bridge hybrid structure is used in DC engineering, and the full-bridge characteristics are used to actively output negative DC voltage, discharge the line energy to the AC systems on both sides, and realize self-clearing of DC overhead line faults. However, when the DC engineering negative pressure clearing technology realizes fault clearing in the converter, the output negative pressure may cause the arc at the fault point to reignite in the reverse direction, or even reignite multiple times after crossing zero, so the fault clearing time cannot be guaranteed and the clearing effect is unstable. Summary of the invention

[0004] The present invention provides a switch-assisted DC fault ride-through method and device, which is used to solve the technical problem that when the negative pressure clearing technology is used in the prior art to realize fault clearing in the converter, the output negative pressure may cause the arc at the fault point to reignite in the reverse direction or even reignite multiple times after crossing zero, and the fault clearing time cannot be guaranteed, and the clearing effect is unstable.

[0005] In view of this, a first aspect of the present invention provides a DC fault ride-through method based on switch assistance, which is applied to a flexible multi-terminal DC transmission system. The flexible multi-terminal DC transmission system includes a sending-end flexible DC converter station and a receiving-end flexible DC converter station. A positive DC bus and a negative DC bus are connected between the sending-end flexible DC converter station and the receiving-end flexible DC converter station. The flexible multi-terminal DC transmission system also includes an auxiliary switch, which is installed at the outgoing terminal of the sending-end flexible DC converter station or the outgoing terminal of the receiving-end flexible DC converter station. The DC fault ride-through method based on switch assistance includes:

[0006] When a DC side fault occurs in the flexible multi-terminal DC power transmission system, the sending-end flexible DC converter station and the receiving-end flexible DC converter station respectively control the voltage or current on the DC side to decrease, so that the current flowing through the auxiliary switch is reduced to zero;

[0007] When the current flowing through the auxiliary switch is reduced to zero, the auxiliary switch is opened, and the DC bus current where the DC side fault occurs is controlled to be reduced and injected into the circulating current through the sending-end flexible DC converter station or the receiving-end flexible DC converter station that can inject energy into the fault point, so as to form an AC zero-crossing point on the auxiliary switch;

[0008] After the de-freeing time, the auxiliary switch is controlled to reclose, and the sending-end flexible DC converter station and the receiving-end flexible DC converter station are controlled to re-establish voltage and restore power.

[0009] Optionally, the auxiliary switch is a high-speed mechanical switch or an AC circuit breaker.

[0010] A second aspect of the present invention provides another switch-assisted DC fault ride-through method, which is applied to a flexible multi-terminal DC transmission system, wherein the flexible multi-terminal DC transmission system includes a sending-end flexible DC converter station and a receiving-end flexible DC converter station, wherein a positive DC bus and a negative DC bus are connected between the sending-end flexible DC converter station and the receiving-end flexible DC converter station, and the flexible multi-terminal DC transmission system further includes an auxiliary switch, wherein the auxiliary switch is installed at the outgoing terminal of the sending-end flexible DC converter station and the outgoing terminal of the receiving-end flexible DC converter station, and the switch-assisted DC fault ride-through method includes:

[0011] When a DC side fault occurs in the flexible multi-terminal DC power transmission system, the sending-end flexible DC converter station and the receiving-end flexible DC converter station control the voltage or current on the DC side to decrease, so that the current flowing through the auxiliary switch is reduced to zero;

[0012] Detecting whether the auxiliary switch of the sending-end flexible DC converter station and the auxiliary switch of the receiving-end flexible DC converter station are both opened;

[0013] If the auxiliary switch of the sending-end flexible DC converter station and the auxiliary switch of the receiving-end flexible DC converter station are both opened, then after the de-free time, the auxiliary switch of the sending-end flexible DC converter station and the auxiliary switch of the receiving-end flexible DC converter station are controlled to be reclosed, and the sending-end flexible DC converter station and the receiving-end flexible DC converter station are controlled to re-establish voltage and restore power;

[0014] If only one of the auxiliary switches of the sending-end flexible DC converter station and the receiving-end flexible DC converter station is opened, the DC bus current where the DC side fault occurs is controlled to be reduced and the circulating current is injected through the sending-end flexible DC converter station or the receiving-end flexible DC converter station which can inject energy into the fault point, so as to form an AC zero-crossing point on the opened auxiliary switch. After the de-free time, the opened auxiliary switch is controlled to reclose, and the sending-end flexible DC converter station and the receiving-end flexible DC converter station are controlled to re-establish voltage and restore power.

[0015] Optionally, the auxiliary switch is a high-speed mechanical switch or an AC circuit breaker.

[0016] A third aspect of the present invention provides another switch-assisted DC fault ride-through method, which is applied to a flexible multi-terminal DC transmission system, wherein the flexible multi-terminal DC transmission system includes a sending-end flexible DC converter station and a receiving-end flexible DC converter station, wherein a double-circuit positive DC bus and a double-circuit negative DC bus are connected between the sending-end flexible DC converter station and the receiving-end flexible DC converter station, and the flexible multi-terminal DC transmission system further includes an auxiliary switch, wherein the auxiliary switch is installed at the outgoing line end of the sending-end flexible DC converter station and the outgoing line end of the receiving-end flexible DC converter station of the double-circuit positive DC bus and the double-circuit negative DC bus. The switch-assisted DC fault ride-through method includes:

[0017] When a DC side fault occurs in the flexible multi-terminal DC power transmission system, the sending-end flexible DC converter station and the receiving-end flexible DC converter station control the voltage or current on the DC side to decrease, so that the current flowing through the auxiliary switch on the DC bus where the DC side fault occurs is reduced to zero;

[0018] After the auxiliary switch on the DC bus passing through the DC side fault is opened, the sending-end flexible DC converter station and the receiving-end flexible DC converter station are controlled to re-establish voltage and restore power;

[0019] After the de-ionization time, the auxiliary switch that has been pulled open is controlled to be reclosed.

[0020] A fourth aspect of the present invention provides a switch-assisted DC fault ride-through device, which is applied to a flexible multi-terminal DC transmission system, wherein the flexible multi-terminal DC transmission system includes a sending-end flexible DC converter station and a receiving-end flexible DC converter station, wherein a positive DC bus and a negative DC bus are connected between the sending-end flexible DC converter station and the receiving-end flexible DC converter station, and the flexible multi-terminal DC transmission system further includes an auxiliary switch, wherein the auxiliary switch is installed at the outgoing terminal of the sending-end flexible DC converter station or the outgoing terminal of the receiving-end flexible DC converter station, and the switch-assisted DC fault ride-through device includes:

[0021] a first control unit, configured to, when a DC side fault occurs in the flexible multi-terminal DC power transmission system, control the DC side voltage or current of the sending-end flexible DC converter station and the receiving-end flexible DC converter station to be reduced respectively, so that the current flowing through the auxiliary switch is reduced to zero;

[0022] a second control unit, configured to, when the current flowing through the auxiliary switch is reduced to zero, open the auxiliary switch, control the DC bus current where the DC side fault occurs to be reduced and inject a circulating current through the sending-end flexible DC converter station or the receiving-end flexible DC converter station that can inject energy into the fault point, and form an AC zero-crossing point on the auxiliary switch;

[0023] The third control unit is used to control the auxiliary switch to reclose after the de-free time, and control the sending-end flexible DC converter station and the receiving-end flexible DC converter station to re-establish voltage and restore power.

[0024] Optionally, the auxiliary switch is a high-speed mechanical switch or an AC circuit breaker.

[0025] A fifth aspect of the present invention provides another switch-assisted DC fault ride-through device, which is applied to a flexible multi-terminal DC transmission system, wherein the flexible multi-terminal DC transmission system includes a sending-end flexible DC converter station and a receiving-end flexible DC converter station, wherein a positive DC bus and a negative DC bus are connected between the sending-end flexible DC converter station and the receiving-end flexible DC converter station, and the flexible multi-terminal DC transmission system further includes an auxiliary switch, wherein the auxiliary switch is installed at the outgoing terminal of the sending-end flexible DC converter station and the outgoing terminal of the receiving-end flexible DC converter station, and the switch-assisted DC fault ride-through device includes:

[0026] a fourth control unit, configured to, when a DC side fault occurs in the flexible multi-terminal DC power transmission system, control the DC side voltage or current of the sending-end flexible DC converter station and the receiving-end flexible DC converter station to decrease, so that the current flowing through the auxiliary switch is reduced to zero;

[0027] A detection unit, used for detecting whether the auxiliary switch of the sending-end flexible DC converter station and the auxiliary switch of the receiving-end flexible DC converter station are both opened;

[0028] a fifth control unit, for controlling the auxiliary switch of the sending-end flexible DC converter station and the auxiliary switch of the receiving-end flexible DC converter station to be reclosed after a de-free time if the auxiliary switch of the sending-end flexible DC converter station and the auxiliary switch of the receiving-end flexible DC converter station are both opened, and controlling the sending-end flexible DC converter station and the receiving-end flexible DC converter station to re-establish voltage and restore power;

[0029] The sixth control unit is used for controlling the DC bus current of the DC side fault to be reduced and injecting circulating current through the sending-end flexible DC converter station or the receiving-end flexible DC converter station which can inject energy into the fault point if only one of the auxiliary switches of the sending-end flexible DC converter station and the receiving-end flexible DC converter station is opened, thereby forming an AC zero-crossing point on the opened auxiliary switch, and controlling the opened auxiliary switch to reclose after the de-free time, and controlling the sending-end flexible DC converter station and the receiving-end flexible DC converter station to re-establish voltage and restore power.

[0030] Optionally, the auxiliary switch is a high-speed mechanical switch or an AC circuit breaker.

[0031] A sixth aspect of the present invention provides another switch-assisted DC fault ride-through device, which is applied to a flexible multi-terminal DC transmission system, wherein the flexible multi-terminal DC transmission system includes a sending-end flexible DC converter station and a receiving-end flexible DC converter station, wherein a double-circuit positive DC bus and a double-circuit negative DC bus are connected between the sending-end flexible DC converter station and the receiving-end flexible DC converter station, and the flexible multi-terminal DC transmission system further includes an auxiliary switch, wherein the auxiliary switch is installed at the outgoing line end of the sending-end flexible DC converter station and the outgoing line end of the receiving-end flexible DC converter station of the double-circuit positive DC bus and the double-circuit negative DC bus, and the switch-assisted DC fault ride-through device includes:

[0032] a seventh control unit, configured to, when a DC side fault occurs in the flexible multi-terminal DC power transmission system, control the DC side voltage or current to be reduced by the sending-end flexible DC converter station and the receiving-end flexible DC converter station, so that the current flowing through the auxiliary switch on the DC bus where the DC side fault occurs is reduced to zero;

[0033] an eighth control unit, configured to control the sending-end flexible DC converter station and the receiving-end flexible DC converter station to re-establish voltage and restore power after the auxiliary switch on the DC bus passing through the DC side fault is opened;

[0034] The ninth control unit is used to control the auxiliary switch that has been pulled open to reclose after the de-ionization time.

[0035] It can be seen from the above technical solutions that the longitudinal protection method for the transmission line of the new energy station provided by the present invention has the following advantages:

[0036] The switch-assisted DC fault riding method provided by the present invention sets an auxiliary switch at the outgoing line end of the sending-end flexible DC converter station or the outgoing line end of the receiving-end flexible DC converter station to connect the DC busbar between the sending and receiving ends. When a DC side fault is detected, the converter station connected to the fault point controls the voltage reduction and current reduction operation, and forms a small AC volume on the DC side by actively injecting circulating current. The auxiliary switch is pulled open, and a physical break is formed on both sides of the fault point, forcing the fault point to extinguish the arc or isolate it to prevent reverse arcing at the fault point. The arc extinguishing time is stable and reliable. After the de-ionization time, the auxiliary switch is controlled to reclose, and the converter with voltage reduction and current reduction resumes normal operation, and the fault clearing process is completed. The technical problem that in the prior art, when the negative pressure clearing technology is used to realize fault clearing in the converter, the output negative pressure may cause the arc at the fault point to reignite in the reverse direction, or even reignite multiple times after crossing zero, and the fault clearing time cannot be guaranteed, and the clearing effect is unstable is solved.

[0037] At the same time, the switch-assisted DC fault riding method provided by the present invention uses a high-speed mechanical switch or an AC circuit breaker instead of a DC switch as an auxiliary switch, does not require the auxiliary switch to have a DC breaking capability, has low requirements on switch performance, and reduces costs.

[0038] At the same time, the switch-assisted DC fault ride-through method provided by the present invention does not need to consider the fault point de-freezing time in the double-circuit line topology, which can greatly shorten the power interruption time. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0040] Figure 1 A schematic diagram of a flow chart of a switch-assisted DC fault ride-through method provided in the present invention;

[0041] Figure 2 It is a schematic diagram of the fault ride-through of the first flexible multi-terminal DC transmission system;

[0042] Figure 3 for Figure 2 Schematic diagram of reclosing after fault ride-through of the flexible multi-terminal DC transmission system;

[0043] Figure 4 A schematic flow chart of another switch-assisted DC fault ride-through method provided in the present invention;

[0044] Figure 5A topological structure diagram of a second flexible multi-terminal direct current power transmission system provided in the present invention when a direct current side fault occurs;

[0045] Figure 6 for Figure 5 The fault ride-through diagram of the flexible multi-terminal DC transmission system provided in;

[0046] Figure 7 for Figure 5 Schematic diagram of reclosing after fault ride-through of the flexible multi-terminal DC transmission system;

[0047] Figure 8 A schematic flow chart of another switch-assisted DC fault ride-through method provided in the present invention;

[0048] Fig. 9 A topological structure diagram of a third flexible multi-terminal direct current transmission system provided in the present invention;

[0049] Fig.10 A topological structure diagram of the third flexible multi-terminal direct current power transmission system provided in the present invention when a positive DC side fault occurs;

[0050] Fig.11 for Fig. 9 Fault ride-through diagram of the flexible multi-terminal DC transmission system;

[0051] Fig.12 for Fig. 9 Schematic diagram of reclosing after fault ride-through of the flexible multi-terminal DC transmission system;

[0052] Fig.13 This is a structural schematic diagram of a first switch-assisted DC fault ride-through device provided in the present invention;

[0053] Fig.14 This is a structural schematic diagram of a second switch-assisted DC fault ride-through device provided in the present invention;

[0054] Fig.15 This is a schematic structural diagram of a third switch-assisted DC fault ride-through device provided in the present invention. DETAILED DESCRIPTION

[0055] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0056] For easier understanding, see Figures 1 to 3 The present invention provides an embodiment of a DC fault ride-through method based on switch assistance, which is applied to a flexible multi-terminal DC transmission system. The flexible multi-terminal DC transmission system includes a sending-end flexible DC converter station and a receiving-end flexible DC converter station. A positive DC bus and a negative DC bus are connected between the sending-end flexible DC converter station and the receiving-end flexible DC converter station. The flexible multi-terminal DC transmission system also includes an auxiliary switch, which is installed at the outgoing line end of the sending-end flexible DC converter station or the outgoing line end of the receiving-end flexible DC converter station. The DC fault ride-through method based on switch assistance includes:

[0057] Step 101: When a DC side fault occurs in the flexible multi-terminal DC transmission system, the sending-end flexible DC converter station and the receiving-end flexible DC converter station respectively control the voltage or current on the DC side to decrease, so that the current flowing through the auxiliary switch is reduced to zero.

[0058] Step 102: When the current flowing through the auxiliary switch is reduced to zero, the auxiliary switch is opened, and the DC bus current where the DC side fault occurs is controlled to be reduced and injected into the circulating current through the sending-end flexible DC converter station or the receiving-end flexible DC converter station that can inject energy into the fault point, thereby forming an AC zero-crossing point on the auxiliary switch.

[0059] Step 103: After the de-ionization time, control the auxiliary switch to reclose, and control the sending-end flexible DC converter station and the receiving-end flexible DC converter station to re-establish voltage and restore power.

[0060] It should be noted that if Figure 2 As shown, the auxiliary switch action only on the sending end side is taken as an example (the scenario of the auxiliary switch action only on the receiving end can be obtained in the same way). When a metal grounding fault occurs on the DC positive busbar, the sending-end flexible DC converter station and the receiving-end flexible DC converter station respectively control the voltage or current on the DC side to decrease, so that the current flowing through the auxiliary switch is reduced to zero. The auxiliary switch is directly opened and is opened. At this time, the sending end cannot inject energy into the fault point through the converter station. The positive DC busbar is actively injected into the circulating current through the receiving-end positive converter station to form an AC zero-crossing point on the switch. Since the energy source of the fault point is only the receiving end, the auxiliary switch current crosses the zero point earlier, the arc extinguishing speed is faster, and the probability of reigniting the arc is reduced. After the arc is extinguished and the de-ionization time passes, the auxiliary switch in the opened state is reclosed, as shown in Figure 3 As shown, the sending-end flexible DC converter station and the receiving-end flexible DC converter station are controlled to re-establish voltage and restore power, and the fault clearing process ends. At the same time, the auxiliary switch in the embodiment of the present invention is not required to have DC breaking capability, and a high-speed mechanical switch or AC circuit breaker can be directly selected without relying on expensive DC switches.

[0061] The switch-assisted DC fault riding method provided by the present invention sets an auxiliary switch at the outgoing line end of the sending-end flexible DC converter station or the outgoing line end of the receiving-end flexible DC converter station to connect the DC busbar between the sending and receiving ends. When a DC fault is detected, the converter station connected to the fault point controls the voltage reduction and current reduction to operate, and forms a small AC volume on the DC side by actively injecting circulating current. The auxiliary switch is pulled open, and a physical break is formed on both sides of the fault point, forcing the fault point to extinguish the arc or isolate it to prevent reverse arcing at the fault point. The arc extinguishing time is stable and reliable. After the de-ionization time, the auxiliary switch is controlled to reclose, and the converter with voltage reduction and current reduction resumes normal operation, and the fault clearing process is completed. The technical problem that in the prior art, when the negative pressure clearing technology is used to realize fault clearing in the converter, the output negative pressure may cause the arc at the fault point to reignite in the reverse direction, or even reignite multiple times after crossing zero, and the fault clearing time cannot be guaranteed, and the clearing effect is unstable is solved.

[0062] At the same time, the switch-assisted DC fault riding method provided by the present invention has a short power recovery time for the flexible multi-terminal DC transmission system and has strong adaptability in flexible DC projects.

[0063] For easier understanding, see Figures 4 to 7 The present invention provides another embodiment of a DC fault ride-through method based on switch assistance, which is applied to a flexible multi-terminal DC transmission system. The flexible multi-terminal DC transmission system includes a sending-end flexible DC converter station and a receiving-end flexible DC converter station. A positive DC bus and a negative DC bus are connected between the sending-end flexible DC converter station and the receiving-end flexible DC converter station. The flexible multi-terminal DC transmission system also includes an auxiliary switch, which is installed at the outgoing line end of the sending-end flexible DC converter station and the outgoing line end of the receiving-end flexible DC converter station. The DC fault ride-through method based on switch assistance includes:

[0064] Step 201: When a DC side fault occurs in the flexible multi-terminal DC transmission system, the sending-end flexible DC converter station and the receiving-end flexible DC converter station control the voltage or current on the DC side to decrease, so that the current flowing through the auxiliary switch is reduced to zero.

[0065] Step 202: Detect whether the auxiliary switch of the sending-end flexible DC converter station and the auxiliary switch of the receiving-end flexible DC converter station are both opened;

[0066] Step 203: If the auxiliary switch of the sending-end flexible DC converter station and the auxiliary switch of the receiving-end flexible DC converter station are both opened, then after the de-ionization time, the auxiliary switch of the sending-end flexible DC converter station and the auxiliary switch of the receiving-end flexible DC converter station are controlled to be reclosed, and the sending-end flexible DC converter station and the receiving-end flexible DC converter station are controlled to re-establish voltage and restore power.

[0067] Step 204: If only one side of the auxiliary switch of the sending-end flexible DC converter station and the auxiliary switch of the receiving-end flexible DC converter station is opened, the DC bus current where the DC side fault occurs is controlled to be reduced and the circulating current is injected through the sending-end flexible DC converter station or the receiving-end flexible DC converter station which can inject energy into the fault point, so as to form an AC zero-crossing point on the opened auxiliary switch. After the de-free time, the opened auxiliary switch is controlled to reclose, and the sending-end flexible DC converter station and the receiving-end flexible DC converter station are controlled to re-establish voltage and restore power.

[0068] It should be noted that, in the embodiment of the present invention, the outgoing line end of the flexible DC converter station at the sending end and the outgoing line end of the flexible DC converter station at the receiving end are both provided with auxiliary switches connected to the DC bus. When a DC side fault occurs in the flexible multi-terminal DC transmission system in the embodiment of the present invention, the flexible DC converter station at the sending end and the flexible DC converter station at the receiving end control the voltage or current on the DC side to decrease, so that the current flowing through the auxiliary switch is reduced to zero. At this time, the fault pole converter stations on both sides of the sending and receiving sides actively inject commutation, the current amplitude of the DC bus is controlled, the converter station injects AC into the DC bus current, the DC bus has a zero crossing point, and the auxiliary switch has the conditions to be directly pulled open. The DC bus current AC zero crossing is cut off on the auxiliary switch and the insulation is restored, and a physical break is formed on both sides of the fault point, and the fault is isolated. The positive pole converter stations on both sides are in a zero power state, and the arc at the fault point is forced to extinguish and the insulation is restored due to the lack of energy input. At this time, the converter stations at both ends of the negative pole can still operate normally to transmit power. The auxiliary switch may fail to operate and open due to signal interruption and other reasons. Therefore, after the voltage or current on the DC side of the sending-end flexible DC converter station and the receiving-end flexible DC converter station is reduced by controlling the voltage or current so that the current flowing through the auxiliary switch is reduced to zero, it is necessary to detect whether the auxiliary switch of the sending-end flexible DC converter station and the auxiliary switch of the receiving-end flexible DC converter station have been opened.

[0069] If the auxiliary switch of the sending-end flexible DC converter station and the auxiliary switch of the receiving-end flexible DC converter station are both opened, then after the de-isolation time, the auxiliary switch of the sending-end flexible DC converter station and the auxiliary switch of the receiving-end flexible DC converter station are controlled to be reclosed, and the sending-end flexible DC converter station and the receiving-end flexible DC converter station are controlled to re-establish the voltage and restore the power, and the fault clearing process ends. As another improved embodiment, if the auxiliary switch of the sending-end flexible DC converter station and the auxiliary switch of the receiving-end flexible DC converter station are both opened, the sending-end flexible DC converter station and the receiving-end flexible DC converter station immediately restore the rated voltage, and after the de-isolation time, the auxiliary switch of the sending-end flexible DC converter station and the auxiliary switch of the receiving-end flexible DC converter station are controlled to re-close with voltage and re-establish the voltage and restore the power. In this way, the de-isolation time can be further compressed, and the voltage recovery time in the original power interruption time can be saved.

[0070] If only one of the auxiliary switches of the sending-end flexible DC converter station and the receiving-end flexible DC converter station is opened, the DC bus current where the DC side fault occurs is controlled to be reduced and injected into the circulating current through the sending-end flexible DC converter station or the receiving-end flexible DC converter station which can inject energy into the fault point, forming an AC zero-crossing point on the auxiliary switch. After the de-ionization time, the opened auxiliary switch is controlled to reclose, and the sending-end flexible DC converter station and the receiving-end flexible DC converter station are controlled to re-establish voltage and restore power, and the fault clearing process ends.

[0071] At the same time, the auxiliary switch in the embodiment of the present invention is not required to have a DC breaking capability, and a high-speed mechanical switch or an AC circuit breaker can be directly selected without relying on an expensive DC switch.

[0072] The switch-assisted DC fault riding method provided by the present invention sets auxiliary switches at the outgoing line end of the sending-end flexible DC converter station and the outgoing line end of the receiving-end flexible DC converter station to connect the DC busbars between the sending and receiving ends. When a DC side fault is detected, the converter station connected to the fault point operates by controlling the voltage reduction and current reduction, and forms a small AC volume on the DC side by actively injecting circulating current. The auxiliary switch is pulled open, and a physical break is formed on both sides of the fault point, forcing the fault point to extinguish the arc or isolate it to prevent reverse arcing at the fault point. The arc extinguishing time is stable and reliable. After the de-ionization time, the auxiliary switch is controlled to reclose, and the converter with voltage reduction and current reduction resumes normal operation, and the fault clearing process is completed. The technical problem that in the prior art, when the negative pressure clearing technology is used to realize fault clearing in the converter, the output negative pressure may cause the arc at the fault point to reignite in the reverse direction, or even reignite multiple times after crossing zero, and the fault clearing time cannot be guaranteed, and the clearing effect is unstable is solved.

[0073] For easier understanding, see Figures 8 to 12 The present invention provides another embodiment of a DC fault ride-through method based on switch assistance, which is applied to a flexible multi-terminal DC transmission system. The flexible multi-terminal DC transmission system includes a sending-end flexible DC converter station and a receiving-end flexible DC converter station. A double-circuit positive DC bus and a double-circuit negative DC bus are connected between the sending-end flexible DC converter station and the receiving-end flexible DC converter station. The flexible multi-terminal DC transmission system also includes an auxiliary switch, which is installed at the outgoing line end of the sending-end flexible DC converter station and the outgoing line end of the receiving-end flexible DC converter station of the double-circuit positive DC bus and the double-circuit negative DC bus. The DC fault ride-through method based on switch assistance includes:

[0074] Step 301: When a DC side fault occurs in the flexible multi-terminal DC transmission system, the sending-end flexible DC converter station and the receiving-end flexible DC converter station control the voltage or current on the DC side to decrease, so that the current flowing through the auxiliary switch on the DC bus where the DC side fault occurs is reduced to zero.

[0075] Step 302: After the auxiliary switch on the DC bus passing through the DC side fault is opened, the sending-end flexible DC converter station and the receiving-end flexible DC converter station are controlled to re-establish voltage and restore power.

[0076] Step 303: After the de-ionization time, control the opened auxiliary switch to reclose.

[0077] It should be noted that in the embodiment of the present invention, the flexible multi-terminal direct current transmission system is a symmetrical bipolar two-terminal flexible direct current topology structure, the positive and negative DC busbars are both double-circuit lines and each section of the DC busbar is connected to the busbar through a converter station. Fig.10 As shown in the figure, taking a DC side fault on a positive DC bus as an example, when a DC side fault occurs in the flexible multi-terminal DC transmission system, the sending-end flexible DC converter station and the receiving-end flexible DC converter station control the voltage or current on the DC side to decrease, so that the current flowing through the auxiliary switch on the DC bus where the DC side fault occurs is reduced to zero. When the DC bus voltage or current drops to near zero, the auxiliary switches at both ends of the faulty line are pulled apart to form a physical break, and the fault point is isolated, as shown in the figure. Fig.11 As shown. After the auxiliary switch is actuated, there is no need to wait for the de-ionization time. The converter stations on both sides of the transmission and reception can directly re-establish the bus voltage and restore power. The power interruption time is only the time between the converter station controlling the voltage reduction and current reduction and the switch opening, which can be controlled within 100ms at the shortest. In the past, the de-ionization time for fault clearing in engineering projects was greater than 500ms. The power interruption time is greatly reduced. After the auxiliary switch is opened and the de-ionization time has passed, the fault point is cleared, and the switches on both sides of the fault point are reclosed with power. The process is as follows Fig.12 At the same time, the auxiliary switch in the embodiment of the present invention is not required to have a DC breaking capability, and a high-speed mechanical switch or an AC circuit breaker can be directly selected without relying on an expensive DC switch.

[0078] The switch-assisted DC fault riding method provided by the present invention sets auxiliary switches at the outgoing line end of the sending-end flexible DC converter station and the outgoing line end of the receiving-end flexible DC converter station to connect the DC busbars between the sending and receiving ends. When a DC side fault is detected, the converter station connected to the fault point operates by controlling the voltage reduction and current reduction, and forms a small AC volume on the DC side by actively injecting circulating current. The auxiliary switch is pulled open, and a physical break is formed on both sides of the fault point, forcing the fault point to extinguish the arc or isolate it to prevent reverse arcing at the fault point. The arc extinguishing time is stable and reliable. After the de-ionization time, the auxiliary switch is controlled to reclose, and the converter with voltage reduction and current reduction resumes normal operation, and the fault clearing process is completed. The technical problem that in the prior art, when the negative pressure clearing technology is used to realize fault clearing in the converter, the output negative pressure may cause the arc at the fault point to reignite in the reverse direction, or even reignite multiple times after crossing zero, and the fault clearing time cannot be guaranteed, and the clearing effect is unstable is solved.

[0079] For easier understanding, see Fig.13 , Figure 2 and Figure 3 The present invention provides an embodiment of a DC fault ride-through device based on switch assistance, which is applied to a flexible multi-terminal DC transmission system. The flexible multi-terminal DC transmission system includes a sending-end flexible DC converter station and a receiving-end flexible DC converter station. A positive DC bus and a negative DC bus are connected between the sending-end flexible DC converter station and the receiving-end flexible DC converter station. The flexible multi-terminal DC transmission system also includes an auxiliary switch, which is installed at the outgoing line end of the sending-end flexible DC converter station or the outgoing line end of the receiving-end flexible DC converter station. The DC fault ride-through device based on switch assistance includes:

[0080] The first control unit is used for, when a DC side fault occurs in the flexible multi-terminal DC transmission system, the sending-end flexible DC converter station and the receiving-end flexible DC converter station to respectively control the voltage or current on the DC side to be reduced, so that the current flowing through the auxiliary switch is reduced to zero;

[0081] The second control unit is used for, when the current flowing through the auxiliary switch is reduced to zero, the auxiliary switch is opened, and the DC bus current where the DC side fault occurs is controlled to be reduced and injected into the circulating current through the sending-end flexible DC converter station or the receiving-end flexible DC converter station that can inject energy into the fault point, so as to form an AC zero-crossing point on the auxiliary switch;

[0082] The third control unit is used to control the auxiliary switch to reclose after the de-free time, and control the sending-end flexible DC converter station and the receiving-end flexible DC converter station to re-establish voltage and restore power.

[0083] The auxiliary switch is a high-speed mechanical switch or an AC circuit breaker.

[0084] For easier understanding, see Fig.14 , Figures 5 to 7 The present invention provides another embodiment of a DC fault ride-through device based on switch assistance, which is applied to a flexible multi-terminal DC power transmission system. The flexible multi-terminal DC power transmission system includes a sending-end flexible DC converter station and a receiving-end flexible DC converter station. A positive DC bus and a negative DC bus are connected between the sending-end flexible DC converter station and the receiving-end flexible DC converter station. The flexible multi-terminal DC power transmission system also includes an auxiliary switch, which is installed at the outgoing line end of the sending-end flexible DC converter station and the outgoing line end of the receiving-end flexible DC converter station. The DC fault ride-through device based on switch assistance includes:

[0085] a fourth control unit, configured to control the voltage or current on the DC side of the sending-end flexible DC converter station and the receiving-end flexible DC converter station to decrease when a DC side fault occurs in the flexible multi-terminal DC transmission system, so that the current flowing through the auxiliary switch is reduced to zero;

[0086] A detection unit, used to detect whether the auxiliary switch of the sending-end flexible DC converter station and the auxiliary switch of the receiving-end flexible DC converter station are both opened;

[0087] a fifth control unit, for controlling the auxiliary switches of the sending-end flexible DC converter station and the receiving-end flexible DC converter station to be reclosed after the de-free time if the auxiliary switches of the sending-end flexible DC converter station and the receiving-end flexible DC converter station are both opened, so as to control the sending-end flexible DC converter station and the receiving-end flexible DC converter station to re-establish voltage and restore power;

[0088] The sixth control unit is used for controlling the DC bus current of the DC side fault to be reduced and injecting the circulating current through the sending-end flexible DC converter station or the receiving-end flexible DC converter station which can inject energy into the fault point if only one side of the auxiliary switch of the sending-end flexible DC converter station and the auxiliary switch of the receiving-end flexible DC converter station is opened, so as to form an AC zero-crossing point on the opened auxiliary switch, and control the opened auxiliary switch to reclose after the de-free time, so as to control the sending-end flexible DC converter station and the receiving-end flexible DC converter station to re-establish the voltage and restore the power.

[0089] The auxiliary switch is a high-speed mechanical switch or an AC circuit breaker.

[0090] For easier understanding, see Fig.15 , Figures 9 to 12 The present invention provides another embodiment of a DC fault ride-through device based on switch assistance, which is applied to a flexible multi-terminal DC transmission system. The flexible multi-terminal DC transmission system includes a sending-end flexible DC converter station and a receiving-end flexible DC converter station. A double-circuit positive DC bus and a double-circuit negative DC bus are connected between the sending-end flexible DC converter station and the receiving-end flexible DC converter station. The flexible multi-terminal DC transmission system also includes an auxiliary switch, which is installed at the outgoing line end of the sending-end flexible DC converter station and the outgoing line end of the receiving-end flexible DC converter station of the double-circuit positive DC bus and the double-circuit negative DC bus. The DC fault ride-through device based on switch assistance includes:

[0091] a seventh control unit, configured to control the voltage or current on the DC side of the sending-end flexible DC converter station and the receiving-end flexible DC converter station to decrease when a DC side fault occurs in the flexible multi-terminal DC transmission system, so that the current flowing through the auxiliary switch on the DC bus where the DC side fault occurs is reduced to zero;

[0092] an eighth control unit, configured to control the sending-end flexible DC converter station and the receiving-end flexible DC converter station to re-establish voltage and restore power after the auxiliary switch on the DC bus passing through the DC side fault is opened;

[0093] The ninth control unit is used to control the auxiliary switch that has been pulled open to reclose after the de-ionization time.

[0094] The auxiliary switch is a high-speed mechanical switch or an AC circuit breaker.

[0095] The switch-assisted DC fault ride-through device provided in the present invention is used to execute the switch-assisted DC fault ride-through method provided in the present invention. Its principle and technical effects achieved are similar to those of the switch-assisted DC fault ride-through method provided in the present invention, and will not be repeated here.

[0096] Those skilled in the art can clearly understand that, for the convenience and brevity of description, the specific working process of the device described above can refer to the corresponding process in the aforementioned method embodiment, and will not be repeated here.

[0097] The terms "first", "second", "third", "fourth", etc. in the specification of the present invention are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchangeable where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein, for example. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0098] As described above, the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features thereof may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A DC fault ride-through method based on switch assistance, characterized in that: Applied to a flexible multi-terminal direct current transmission system, the flexible multi-terminal direct current transmission system includes a sending-end flexible direct current converter station and a receiving-end flexible direct current converter station, a positive direct current bus and a negative direct current bus are connected between the sending-end flexible direct current converter station and the receiving-end flexible direct current converter station, the flexible multi-terminal direct current transmission system also includes an auxiliary switch, the auxiliary switch is installed at the outgoing line terminal of the sending-end flexible direct current converter station or the outgoing line terminal of the receiving-end flexible direct current converter station, and the DC fault ride-through method based on the switch assistance includes: When a DC side fault occurs in the flexible multi-terminal DC power transmission system, the sending-end flexible DC converter station and the receiving-end flexible DC converter station respectively control the voltage or current on the DC side to decrease, so that the current flowing through the auxiliary switch is reduced to zero; When the current flowing through the auxiliary switch is reduced to zero, the auxiliary switch is opened, and the DC bus current where the DC side fault occurs is controlled to be reduced and injected into the circulating current through the sending-end flexible DC converter station or the receiving-end flexible DC converter station that can inject energy into the fault point, so as to form an AC zero-crossing point on the auxiliary switch; After the de-freeing time, the auxiliary switch is controlled to reclose, and the sending-end flexible DC converter station and the receiving-end flexible DC converter station are controlled to re-establish voltage and restore power.

2. The switch-assisted DC fault ride-through method according to claim 1, characterized in that: The auxiliary switch is a high-speed mechanical switch or an AC circuit breaker.

3. A DC fault ride-through method based on switch assistance, characterized in that: Applied to a flexible multi-terminal direct current transmission system, the flexible multi-terminal direct current transmission system includes a sending-end flexible direct current converter station and a receiving-end flexible direct current converter station, a positive direct current bus and a negative direct current bus are connected between the sending-end flexible direct current converter station and the receiving-end flexible direct current converter station, the flexible multi-terminal direct current transmission system also includes an auxiliary switch, the auxiliary switch is installed at the outgoing line end of the sending-end flexible direct current converter station and the outgoing line end of the receiving-end flexible direct current converter station, and the DC fault ride-through method based on the switch assistance includes: When a DC side fault occurs in the flexible multi-terminal DC power transmission system, the sending-end flexible DC converter station and the receiving-end flexible DC converter station control the voltage or current on the DC side to decrease, so that the current flowing through the auxiliary switch is reduced to zero; Detecting whether the auxiliary switch of the sending-end flexible DC converter station and the auxiliary switch of the receiving-end flexible DC converter station are both opened; If the auxiliary switch of the sending-end flexible DC converter station and the auxiliary switch of the receiving-end flexible DC converter station are both opened, then after the de-free time, the auxiliary switch of the sending-end flexible DC converter station and the auxiliary switch of the receiving-end flexible DC converter station are controlled to be reclosed, and the sending-end flexible DC converter station and the receiving-end flexible DC converter station are controlled to re-establish voltage and restore power; If only one of the auxiliary switches of the sending-end flexible DC converter station and the receiving-end flexible DC converter station is opened, the DC bus current where the DC side fault occurs is controlled to be reduced and the circulating current is injected through the sending-end flexible DC converter station or the receiving-end flexible DC converter station which can inject energy into the fault point, so as to form an AC zero-crossing point on the opened auxiliary switch. After the de-free time, the opened auxiliary switch is controlled to reclose, and the sending-end flexible DC converter station and the receiving-end flexible DC converter station are controlled to re-establish voltage and restore power.

4. The switch-assisted DC fault ride-through method according to claim 3, characterized in that: The auxiliary switch is a high-speed mechanical switch or an AC circuit breaker.

5. A DC fault ride-through method based on switch assistance, characterized in that: Applied to a flexible multi-terminal direct current transmission system, the flexible multi-terminal direct current transmission system includes a sending-end flexible direct current converter station and a receiving-end flexible direct current converter station, a double-circuit positive direct current bus and a double-circuit negative direct current bus are connected between the sending-end flexible direct current converter station and the receiving-end flexible direct current converter station, the flexible multi-terminal direct current transmission system also includes an auxiliary switch, the auxiliary switch is installed at the outgoing end of the sending-end flexible direct current converter station and the outgoing end of the receiving-end flexible direct current converter station of the double-circuit positive direct current bus and the double-circuit negative direct current bus, the DC fault ride-through method based on the switch assistance includes: When a DC side fault occurs in the flexible multi-terminal DC power transmission system, the sending-end flexible DC converter station and the receiving-end flexible DC converter station control the voltage or current on the DC side to decrease, so that the current flowing through the auxiliary switch on the DC bus where the DC side fault occurs is reduced to zero; After the auxiliary switch on the DC bus passing through the DC side fault is opened, the sending-end flexible DC converter station and the receiving-end flexible DC converter station are controlled to re-establish voltage and restore power; After the de-ionization time, the auxiliary switch that has been pulled open is controlled to be reclosed.

6. A DC fault ride-through device based on switch assistance, characterized in that: Applied to a flexible multi-terminal DC power transmission system, the flexible multi-terminal DC power transmission system includes a sending-end flexible DC converter station and a receiving-end flexible DC converter station, a positive DC bus and a negative DC bus are connected between the sending-end flexible DC converter station and the receiving-end flexible DC converter station, the flexible multi-terminal DC power transmission system also includes an auxiliary switch, the auxiliary switch is installed at the outgoing terminal of the sending-end flexible DC converter station or the outgoing terminal of the receiving-end flexible DC converter station, and the DC fault ride-through device based on the switch assistance includes: a first control unit, configured to, when a DC side fault occurs in the flexible multi-terminal DC power transmission system, control the DC side voltage or current of the sending-end flexible DC converter station and the receiving-end flexible DC converter station to be reduced respectively, so that the current flowing through the auxiliary switch is reduced to zero; a second control unit, configured to, when the current flowing through the auxiliary switch is reduced to zero, open the auxiliary switch, control the DC bus current where the DC side fault occurs to be reduced and inject a circulating current through the sending-end flexible DC converter station or the receiving-end flexible DC converter station that can inject energy into the fault point, and form an AC zero-crossing point on the auxiliary switch; The third control unit is used to control the auxiliary switch to reclose after the de-free time, and control the sending-end flexible DC converter station and the receiving-end flexible DC converter station to re-establish voltage and restore power.

7. The switch-assisted DC fault ride-through device according to claim 6, characterized in that: The auxiliary switch is a high-speed mechanical switch or an AC circuit breaker.

8. A DC fault ride-through device based on switch assistance, characterized in that: Applied to a flexible multi-terminal DC power transmission system, the flexible multi-terminal DC power transmission system includes a sending-end flexible DC converter station and a receiving-end flexible DC converter station, a positive DC bus and a negative DC bus are connected between the sending-end flexible DC converter station and the receiving-end flexible DC converter station, the flexible multi-terminal DC power transmission system also includes an auxiliary switch, the auxiliary switch is installed at the outgoing terminal of the sending-end flexible DC converter station and the outgoing terminal of the receiving-end flexible DC converter station, and the DC fault ride-through device based on the switch assistance includes: a fourth control unit, configured to, when a DC side fault occurs in the flexible multi-terminal DC power transmission system, control the DC side voltage or current of the sending-end flexible DC converter station and the receiving-end flexible DC converter station to decrease, so that the current flowing through the auxiliary switch is reduced to zero; A detection unit, used for detecting whether the auxiliary switch of the sending-end flexible DC converter station and the auxiliary switch of the receiving-end flexible DC converter station are both opened; a fifth control unit, for controlling the auxiliary switch of the sending-end flexible DC converter station and the auxiliary switch of the receiving-end flexible DC converter station to be reclosed after a de-free time if the auxiliary switch of the sending-end flexible DC converter station and the auxiliary switch of the receiving-end flexible DC converter station are both opened, and controlling the sending-end flexible DC converter station and the receiving-end flexible DC converter station to re-establish voltage and restore power; The sixth control unit is used for controlling the DC bus current of the DC side fault to be reduced and injecting circulating current through the sending-end flexible DC converter station or the receiving-end flexible DC converter station which can inject energy into the fault point if only one of the auxiliary switches of the sending-end flexible DC converter station and the receiving-end flexible DC converter station is opened, thereby forming an AC zero-crossing point on the opened auxiliary switch, and controlling the opened auxiliary switch to reclose after the de-free time, and controlling the sending-end flexible DC converter station and the receiving-end flexible DC converter station to re-establish voltage and restore power.

9. The switch-assisted DC fault ride-through device according to claim 8, characterized in that: The auxiliary switch is a high-speed mechanical switch or an AC circuit breaker.

10. A DC fault ride-through device based on switch assistance, characterized in that: Applied to a flexible multi-terminal direct current transmission system, the flexible multi-terminal direct current transmission system includes a sending-end flexible direct current converter station and a receiving-end flexible direct current converter station, a double-circuit positive direct current bus and a double-circuit negative direct current bus are connected between the sending-end flexible direct current converter station and the receiving-end flexible direct current converter station, the flexible multi-terminal direct current transmission system also includes an auxiliary switch, the auxiliary switch is installed at the outgoing line end of the sending-end flexible direct current converter station and the outgoing line end of the receiving-end flexible direct current converter station of the double-circuit positive direct current bus and the double-circuit negative direct current bus, the switch-assisted direct current fault ride-through device includes: a seventh control unit, configured to, when a DC side fault occurs in the flexible multi-terminal DC power transmission system, control the DC side voltage or current to be reduced by the sending-end flexible DC converter station and the receiving-end flexible DC converter station, so that the current flowing through the auxiliary switch on the DC bus where the DC side fault occurs is reduced to zero; an eighth control unit, configured to control the sending-end flexible DC converter station and the receiving-end flexible DC converter station to re-establish voltage and restore power after the auxiliary switch on the DC bus passing through the DC side fault is opened; The ninth control unit is used to control the auxiliary switch that has been pulled open to reclose after the de-ionization time.

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