A primary circuit configuration method and system for suppressing fault current in a DC distribution network

Abstract

The present invention provides a primary circuit configuration method and system for suppressing fault current of a DC distribution network, wherein the method of the present invention includes configuring a current limiting reactor at a full-bridge MMC converter station node, a half-bridge MMC converter station node and a DC transformer node in a DC distribution network, configuring a superconducting current limiter at a half-bridge MMC converter station node, and configuring a capacitor separation switch at a DC transformer node; also includes configuring a DC circuit breaker at a half-bridge MMC converter station node, and the parameters of each device are determined by the converter station parameters and the line parameters; according to the cost function of each device and the short-circuit current level, the optimal short-circuit current level that meets both the economic and safety requirements is obtained, thereby determining the primary circuit configuration of the DC distribution network. The present invention configures corresponding current limiting devices at different nodes of the distribution network, takes into account the differentiated needs for various current limiting devices and optimizes the configuration of the primary circuit equipment, so that it meets the economy and safety of the construction and operation of the DC distribution network.

Description

Technical Field

[0001] The present invention belongs to the technical field of direct current distribution networks, and in particular relates to a primary circuit configuration method and system for suppressing fault current in a direct current distribution network. Background Art

[0002] Compared with AC distribution network, DC distribution network can realize the efficient and flexible access of distributed new energy, DC load and variable frequency load, and significantly improve the flexibility of operation control on the distribution side. Compared with AC grid fault, DC distribution network has small damping and fast fault current rise speed. In addition, since DC has no natural zero crossing point, higher requirements are put forward for the protection technology of DC distribution network.

[0003] In order to suppress the rapid rise of fault current in DC distribution network and ensure the safety of key equipment in DC distribution network, it is necessary to increase the reactance and resistance of fault circuit. At present, the configuration of primary circuit for fault current suppression in DC distribution network is mainly limited to the current limiting effect of current limiting reactor and superconducting current limiter. On the one hand, the difference in the demand for current limiting primary equipment of full-bridge MMC (modular multilevel converter), half-bridge MMC and DC transformer is not considered. On the other hand, the overall cost optimization of current limiting equipment and DC circuit breaker is not considered. Summary of the invention

[0004] In view of this, the present invention aims to solve the problem that the current primary circuit configuration for fault current suppression in a DC distribution network does not take into account the differences in the requirements for current limiting primary devices among full-bridge MMC (modular multilevel converter), half-bridge MMC, and DC transformers, and does not take into account the overall cost optimization of current limiting devices and DC circuit breakers.

[0005] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0006] In a first aspect, the present invention provides a primary circuit configuration method for suppressing fault current in a DC distribution network, which is applicable to any multi-terminal DC distribution network including a full-bridge MMC converter station, a half-bridge MMC converter station and a DC transformer, and comprises the following steps:

[0007] Obtain DC distribution network topology, converter station parameters and line parameters;

[0008] The primary circuit equipment of the DC distribution network topology is configured based on the configuration principle, and the configuration principle includes configuring a first current limiting reactor at the full-bridge MMC converter station node, configuring a second current limiting reactor and a superconducting current limiter at the half-bridge MMC converter station node, and configuring a third current limiting reactor and a capacitor separation switch at the DC transformer node; and also includes configuring a DC circuit breaker at the half-bridge MMC converter station node, wherein the lower limit of the inductance value of the current limiting reactor, the lower limit of the quench resistance value of the superconducting current limiter, the withstand voltage value of the capacitor separation switch, and the withstand voltage value of the DC circuit breaker at each node are determined according to the converter station parameters and the line parameters;

[0009] The cost function is determined according to the relationship between various equipment and short-circuit current levels. The optimal short-circuit current level that meets both economic and safety requirements is obtained based on the cost function. The primary circuit configuration of the DC distribution network is determined according to the optimal short-circuit current level.

[0010] Furthermore, the lower limit of the inductance value of the first current limiting reactor is determined according to the following formula:

[0011]

[0012] In the formula, τ 1 is the MMC capacitor discharge current decay time constant, U dc is the DC voltage before the fault, C 0 is the submodule capacitance value, n is the number of bridge arm submodules, L bridge is the inductance of the bridge arm reactor, L r is the inductance of the current limiting reactor, ω is the oscillation angular frequency of the discharge current, I 0 I is the DC current output by MMC immediately before the fault. c_MMC is the short-circuit fault current before the full-bridge MMC converter station is locked, I max1 It is the upper limit of the fault current allowed before locking.

[0013] Furthermore, the lower limit of the quench resistance value of the superconducting current limiter is determined according to the following formula:

[0014]

[0015] In the formula, I 0_MMC is the arm current of the half-bridge MMC converter station at the time of locking, L bridge is the bridge arm inductance, R L is the resistance value of the discharge circuit, R SR is the quench resistance of the superconducting current limiter, I MMC_bridge is the freewheeling current of the half-bridge MMC converter station bridge arm, I max2 It is the maximum breaking current of DC circuit breaker.

[0016] Furthermore, the lower limit of the inductance value of the third current limiting reactor is determined according to the following formula:

[0017]

[0018] In the formula, τ 2 is the DC transformer capacitor discharge current decay time constant, U dc is the DC voltage before the fault, ω d is the oscillation angular frequency of the DC transformer capacitor discharge current, L s is the equivalent inductance of the discharge circuit, L r is the inductance of the current limiting reactor, i c_DCT is the DC transformer capacitor discharge current, t 1 is the converter locking time, I max3 It is the upper limit of the fault current allowed before the current is blocked.

[0019] Furthermore, a cost function is determined according to the relationship between various devices and the short-circuit current level, and an optimal short-circuit current level that satisfies both economic and safety requirements is obtained based on the cost function, specifically including:

[0020] The cost functions of current limiting devices and DC circuit breakers and short-circuit current levels are established respectively, denoted as f(I k ) and g(I k ), where f(·) is the cost of the current limiting device, g(·) is the cost of the DC circuit breaker, and I k For the short-circuit current level, the current limiting devices include current limiting reactors and superconducting current limiters;

[0021] Find I k0 , so that f′(I k0 )+g′(I k0 )=0, where f′(·) and g′(·) are the derivatives of the equipment cost with respect to the short-circuit current level, I k0 It is the optimal short-circuit current level that meets both economic and safety requirements.

[0022] In a second aspect, the present invention provides a primary circuit configuration system for suppressing fault current in a DC distribution network, which is applicable to any multi-terminal DC distribution network including a full-bridge MMC converter station, a half-bridge MMC converter station and a DC transformer, including:

[0023] A parameter acquisition unit, used to acquire DC distribution network topology, converter station parameters and line parameters;

[0024] The equipment configuration unit is used to configure the primary circuit equipment of the DC distribution network topology based on the configuration principle, wherein the configuration principle includes configuring the first current limiting reactor at the full-bridge MMC converter station node, configuring the second current limiting reactor and the superconducting current limiter at the half-bridge MMC converter station node, and configuring the third current limiting reactor and the capacitor separation switch at the DC transformer node; and also includes configuring the DC circuit breaker at the half-bridge MMC converter station node, wherein the lower limit of the inductance value of the current limiting reactor at each node, the lower limit of the quench resistance value of the superconducting current limiter, the withstand voltage value of the capacitor separation switch, and the withstand voltage value of the DC circuit breaker are determined according to the converter station parameters and the line parameters;

[0025] The configuration optimization unit is used to determine the cost function according to the relationship between various devices and the short-circuit current level, obtain the optimal short-circuit current level that meets both economic and safety requirements based on the cost function, and determine the primary circuit configuration of the DC distribution network according to the optimal short-circuit current level.

[0026] Furthermore, the lower limit of the inductance value of the first current limiting reactor is determined according to the following formula:

[0027]

[0028] In the formula, τ 1 is the MMC capacitor discharge current decay time constant, U dc is the DC voltage before the fault, C 0 is the submodule capacitance value, n is the number of bridge arm submodules, L bridge is the inductance of the bridge arm reactor, L r is the inductance of the current limiting reactor, ω is the oscillation angular frequency of the discharge current, I 0 I is the DC current output by MMC immediately before the fault. c_MMC is the short-circuit fault current before the full-bridge MMC converter station is locked, I max1 It is the upper limit of the fault current allowed before locking.

[0029] Furthermore, the lower limit of the quench resistance value of the superconducting current limiter is determined according to the following formula:

[0030]

[0031] In the formula, I 0_MMC is the arm current of the half-bridge MMC converter station at the time of locking, L bridge is the bridge arm inductance, R L is the resistance value of the discharge circuit, R SR is the quench resistance of the superconducting current limiter, I MMC_bridge is the freewheeling current of the half-bridge MMC converter station bridge arm, I max2 It is the maximum breaking current of DC circuit breaker.

[0032] Furthermore, the lower limit of the inductance value of the third current limiting reactor is determined according to the following formula:

[0033]

[0034] In the formula, τ 2 is the DC transformer capacitor discharge current decay time constant, U dc is the DC voltage before the fault, ω d is the oscillation angular frequency of the DC transformer capacitor discharge current, L s is the equivalent inductance of the discharge circuit, L r is the inductance of the current limiting reactor, i c_DCT is the DC transformer capacitor discharge current, t 1 is the converter locking moment, I max3 It is the upper limit of the fault current allowed before the current is blocked.

[0035] Furthermore, the configuration optimization unit determines a cost function according to the relationship between various devices and the short-circuit current level, and obtains the optimal short-circuit current level that satisfies both economic and safety requirements based on the cost function, specifically including:

[0036] The cost functions of current limiting devices and DC circuit breakers and short-circuit current levels are established respectively, denoted as f(I k ) and g(I k ), where f(·) is the cost of the current limiting device, g(·) is the cost of the DC circuit breaker, and I k For the short-circuit current level, the current limiting devices include current limiting reactors and superconducting current limiters;

[0037] Find I k0 , so that f′(I k0 )+g′(I k0 )=0, where f′(·) and g′(·) are the derivatives of the equipment cost with respect to the short-circuit current level, I k0 It is the optimal short-circuit current level that meets both economic and safety requirements.

[0038] In summary, the present invention provides a primary circuit configuration method and system for suppressing fault current in a DC distribution network, wherein the method of the present invention includes configuring a current limiting reactor at a full-bridge MMC converter station node, a half-bridge MMC converter station node, and a DC transformer node in a DC distribution network, configuring a superconducting current limiter at a half-bridge MMC converter station node, and configuring a capacitor separation switch at a DC transformer node; and also includes configuring a DC circuit breaker at a half-bridge MMC converter station node, and the parameters of each device are determined by the converter station parameters and the line parameters; according to the cost function of each device and the short-circuit current level, the optimal short-circuit current level that meets both the economic and safety requirements is obtained, thereby determining the primary circuit configuration of the DC distribution network. The present invention configures corresponding current limiting devices at different nodes of the distribution network, takes into account the differentiated needs for various current limiting devices and optimizes the configuration of the primary circuit equipment, so that it meets the economy and safety of the construction and operation of the DC distribution network. 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 drawings can be obtained based on these drawings without paying creative labor.

[0040] Figure 1 A schematic flow chart of a primary circuit configuration method for suppressing fault current in a DC distribution network provided by an embodiment of the present invention;

[0041] Figure 2 A schematic diagram of a typical DC distribution network provided by an embodiment of the present invention;

[0042] Figure 3 A simplified flow chart of a primary circuit configuration method for suppressing fault current in a DC distribution network provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0043] In order to make the purpose, features and advantages of the present invention more obvious and easy to understand, the technical solutions 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 embodiments described below 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.

[0044] Compared with AC distribution network, DC distribution network can realize the efficient and flexible access of distributed new energy, DC load and variable frequency load, and significantly improve the flexibility of operation control on the distribution side. Compared with AC grid fault, DC distribution network has small damping and fast fault current rise speed. In addition, since DC has no natural zero crossing point, higher requirements are put forward for the protection technology of DC distribution network.

[0045] In order to suppress the rapid rise of fault current in DC distribution network and ensure the safety of key equipment in DC distribution network, it is necessary to increase the reactance and resistance of fault circuit. At present, the configuration of primary circuit for fault current suppression in DC distribution network is mainly limited to the current limiting effect of current limiting reactor and superconducting current limiter. On the one hand, the difference in the demand for current limiting primary equipment of full-bridge MMC (modular multilevel converter), half-bridge MMC and DC transformer is not considered. On the other hand, the overall cost optimization of current limiting equipment and DC circuit breaker is not considered.

[0046] Based on this, the present invention provides a primary circuit configuration method and system for suppressing fault current in a DC distribution network.

[0047] A primary circuit configuration method for suppressing fault current in a DC power distribution network according to the present invention is described in detail below.

[0048] See also Figure 1 This embodiment provides a primary circuit configuration method for suppressing fault current in a DC distribution network. The method is applicable to any multi-terminal DC distribution network including a full-bridge MMC converter station, a half-bridge MMC converter station and a DC transformer. The method includes the following steps:

[0049] S100: Obtain DC distribution network topology, converter station parameters, and line parameters.

[0050] First, the basic situation of the target DC distribution network should be obtained, including the DC distribution network topology, converter station parameters (full-bridge MMC / half-bridge MMC), and line parameters. The parameters to be determined include the rated DC voltage, the number of bridge arm submodules, the MMC submodule capacitance, the bridge arm reactor inductance, and the connection transformer inductance. Among them, the DC distribution network topology parameters represent the number and interconnection relationship of half-bridge MMC, full-bridge MMC, and DC transformer. On the one hand, it is used to clarify which sites need to be configured with current limiting devices. On the other hand, the instantaneous current I before the fault 0 (MMC output DC current immediately before fault) and I 0_MMC (Bridge arm current at the time when the converter station is locked) is also affected by the topological structure.

[0051] S200: Perform primary circuit equipment configuration for the DC distribution network topology based on configuration principles, the configuration principles include configuring a first current limiting reactor at the full-bridge MMC converter station node, configuring a second current limiting reactor and a superconducting current limiter at the half-bridge MMC converter station node, and configuring a third current limiting reactor and a capacitor separation switch at the DC transformer node; and also include configuring a DC circuit breaker at the half-bridge MMC converter station node, wherein the lower limit of the inductance value of the current limiting reactor, the lower limit of the quench resistance value of the superconducting current limiter, the withstand voltage value of the capacitor separation switch, and the withstand voltage value of the DC circuit breaker at each node are determined according to the converter station parameters and the line parameters.

[0052] See also Figure 2 ,by Figure 2 The typical DC distribution network topology shown in the figure is used as an example to illustrate the configuration of the primary circuit equipment. Among them, node 1 is a half-bridge MMC converter station node, node 2 is a DC transformer node, and node 3 is a full-bridge MMC converter station node. The installed current limiting equipment includes current limiting reactors, superconducting current limiters, and capacitor separation switches.

[0053] For the full-bridge MMC converter station, since the DC fault can be isolated after the converter station is locked, it is only necessary to configure Figure 2 The current limiting reactor at the middle node 3 can reduce the rate of rise of the fault current before blocking. The calculation formula for the short-circuit fault current before blocking of the full-bridge MMC converter station is:

[0054] where τ 1 is the MMC capacitor discharge current decay time constant, U dc is the DC voltage before the fault, C 0 is the submodule capacitance value, n is the number of bridge arm submodules, L bridge is the inductance of the bridge arm reactor, L r is the inductance of the current limiting reactor, ω is the oscillation angular frequency of the discharge current, I 0 This is the DC current output by the MMC immediately before a fault occurs.

[0055] In order to ensure the safety of the full-bridge MMC converter equipment, the fault current is not allowed to exceed the upper limit of safety before blocking, so there is i c_MMC (t 1 )<I max1 , where t 1 is the converter locking moment, I max1 is the upper limit of the fault current allowed before blocking. This formula determines the lower limit of the inductance value of the current limiting reactor L r_min .

[0056] For the half-bridge MMC converter station, after the converter station is locked, there will still be AC ​​side feed-in current and bridge arm freewheeling current, which will cause the DC fault to be unable to be isolated. Therefore, it is necessary to configure the current limiting reactor and superconducting current limiter as shown in node 1, which can reduce the short-circuit fault current rise rate before the lockout and the fault overcurrent level after the lockout. The configuration method of the current limiting reactor in this step is the same as that in S1. The superconducting current limiter mainly considers limiting the bridge arm freewheeling current, and its calculation formula is:

[0057] Among them I 0_MMC is the bridge arm current at the converter station locking moment, L bridge is the bridge arm inductance, R L is the resistance value of the discharge circuit, R SR It is the superconducting current limiter quenching resistance.

[0058] The function of the superconducting current limiter is to ensure that the fault current of the half-bridge MMC converter is less than the maximum breaking current of the DC circuit breaker before the DC circuit breaker is disconnected. 0_MMC <I max2 , I max2 is the maximum breaking current of the DC circuit breaker. Therefore, the lower limit of the quench resistance value R of the superconducting current limiter can be calculated. SR_min .

[0059] For DC transformers, converter lockout cannot block capacitor discharge, so it is necessary to install a capacitor separation switch to block capacitor discharge, and install a current limiting reactor to reduce the current rise rate before capacitor separation. The DC transformer capacitor discharge current calculation formula is:

[0060] where τ 2 is the DC transformer capacitor discharge current decay time constant, U dc is the DC voltage before the fault, ω d is the oscillation angular frequency of the DC transformer capacitor discharge current, L s is the equivalent inductance of the discharge circuit, L r is the inductance value of the current limiting reactor.

[0061] In order to ensure the safety of the full-bridge MMC converter equipment, the fault current is not allowed to exceed the upper limit of safety before blocking, so there is i c_DCT (t 1 )<I max3 , where t 1 is the converter locking time, I max3 The upper limit of the fault current allowed before the current is blocked. This formula determines the lower limit of the inductance value of the current limiting reactor L r_min .

[0062] For capacitor separation switches, their withstand voltage and current levels should be greater than the maximum voltage and maximum current before and after the capacitor is removed from the circuit.

[0063] The above design is the configuration principle of the current limiting device for the primary circuit of the DC distribution network in this embodiment. In addition, the DC distribution network is also equipped with protection devices. Figure 2 In the DC distribution network shown in FIG. 1 , since both the full-bridge MMC and the DC transformer have the capability of blocking DC faults, it is only necessary to install a DC circuit breaker at the half-bridge MMC access point (e.g. Figure 2 At the middle node 1), the withstand voltage and current level of the DC circuit breaker should be determined in combination with the current manufacturing level and the short-circuit current level after current limiting.

[0064] S300: Determine a cost function according to the relationship between various devices and short-circuit current levels, obtain an optimal short-circuit current level that satisfies both economic and safety requirements based on the cost function, and determine a primary circuit configuration of the DC distribution network according to the optimal short-circuit current level.

[0065] According to the above steps, the short-circuit current of the DC distribution network can be effectively limited. The cost of the current limiting equipment is negatively correlated with the short-circuit current level, which can be expressed as f(I k ), where f(·) is the cost of the current limiting device, I k is the short-circuit current level. However, the equipment cost of the DC circuit breaker is positively correlated with the short-circuit current level, which can be expressed as g(I k ), where g(·) is the cost of the DC circuit breaker. Therefore, the configuration cost of the DC distribution network protection primary circuit protection equipment is f(I k )+g(I k ). Find I k0 , so that f′(I k0 )+g′(I k0 )=0, where f′(·) and g′(·) are the derivatives of the equipment cost with respect to the short-circuit current level. Therefore, the short-circuit current level that satisfies both economy and safety can be obtained, and then the configuration of the current limiting reactor, superconducting current limiter, and circuit breaker can be determined. That is, according to the optimal short-circuit current level I k0 The investment cost of each current limiting device and protection device is calculated, and the specific configuration of the primary circuit is performed according to the investment cost. It can be understood that the establishment of the cost function should be based on the actual DC distribution network topology, and it should satisfy the correlation with the short-circuit current level. The specific function form is not limited here.

[0066] Based on the above steps, the primary circuit configuration process for suppressing fault current in DC distribution network is obtained as follows: Figure 3 shown.

[0067] The present embodiment provides a primary circuit configuration method for suppressing fault current in a DC distribution network, including configuring current limiting reactors at full-bridge MMC converter station nodes, half-bridge MMC converter station nodes, and DC transformer nodes in the DC distribution network, configuring superconducting current limiters at half-bridge MMC converter station nodes, and configuring capacitor separation switches at DC transformer nodes; also including configuring DC circuit breakers at half-bridge MMC converter station nodes, and the parameters of each device are determined by converter station parameters and line parameters; according to the cost function of each device and short-circuit current level, the optimal short-circuit current level that meets both economic and safety requirements is obtained, thereby determining the primary circuit configuration of the DC distribution network. By configuring corresponding current limiting devices at different nodes of the distribution network, the present embodiment takes into account the differentiated needs for various current limiting devices and optimizes the configuration of the primary circuit equipment, so that it meets the economy and safety of the construction and operation of the DC distribution network.

[0068] The above is a detailed introduction to an embodiment of a primary circuit configuration method for suppressing fault current in a DC distribution network of the present invention. The following is a detailed introduction to an embodiment of a primary circuit configuration system for suppressing fault current in a DC distribution network of the present invention.

[0069] This embodiment provides a primary circuit configuration system for suppressing fault current in a DC distribution network, which is applicable to any multi-terminal DC distribution network including a full-bridge MMC converter station, a half-bridge MMC converter station and a DC transformer, and includes: a parameter acquisition unit, a device configuration unit and a configuration optimization unit.

[0070] In this embodiment, the parameter acquisition unit is used to acquire the DC distribution network topology, converter station parameters and line parameters.

[0071] In this embodiment, the equipment configuration unit is used to perform primary circuit equipment configuration on the DC distribution network topology based on the configuration principle, and the configuration principle includes configuring a first current limiting reactor at the full-bridge MMC converter station node, configuring a second current limiting reactor and a superconducting current limiter at the half-bridge MMC converter station node, and configuring a third current limiting reactor and a capacitor separation switch at the DC transformer node; and also includes configuring a DC circuit breaker at the half-bridge MMC converter station node, wherein the lower limit of the inductance value of the current limiting reactor, the lower limit of the quench resistance value of the superconducting current limiter, the withstand voltage value of the capacitor separation switch, and the withstand voltage value of the DC circuit breaker at each node are determined according to the converter station parameters and the line parameters.

[0072] The lower limit of the inductance value of the first current limiting reactor is determined according to the following formula:

[0073]

[0074] i c_MMC <I max1

[0075] In the formula, τ1 is the MMC capacitor discharge current decay time constant, U dc is the DC voltage before the fault, C 0 is the submodule capacitance value, n is the number of bridge arm submodules, L bridge is the inductance of the bridge arm reactor, L r is the inductance of the current limiting reactor, ω is the oscillation angular frequency of the discharge current, I 0 I is the DC current output by MMC immediately before the fault. c_MMC is the short-circuit fault current before the full-bridge MMC converter station is locked, I max1 It is the upper limit of the fault current allowed before locking.

[0076] The lower limit of the quench resistance value of the superconducting current limiter is determined according to the following formula:

[0077]

[0078]

[0079] I 0_MMC <I max2

[0080] In the formula, I 0_MMC is the arm current of the half-bridge MMC converter station at the time of locking, L bridge is the bridge arm inductance, R L is the resistance value of the discharge circuit, R SR is the quench resistance of the superconducting current limiter, I MMC_bridge is the freewheeling current of the half-bridge MMC converter station bridge arm, I max2 It is the maximum breaking current of DC circuit breaker.

[0081] The lower limit of the inductance value of the third current limiting reactor is determined according to the following formula:

[0082]

[0083] In the formula, τ 2 is the DC transformer capacitor discharge current decay time constant, U dc is the DC voltage before the fault, ω d is the oscillation angular frequency of the DC transformer capacitor discharge current, L s is the equivalent inductance of the discharge circuit, L r is the inductance of the current limiting reactor, i c_DCT is the DC transformer capacitor discharge current, t 1 is the converter locking moment, I max3 It is the upper limit of the fault current allowed before the current is blocked.

[0084] In this embodiment, the configuration optimization unit is used to determine the cost function according to the relationship between various devices and the short-circuit current level, obtain the optimal short-circuit current level that meets both economic and safety requirements based on the cost function, and determine the primary circuit configuration of the DC distribution network according to the optimal short-circuit current level.

[0085] Specifically, the configuration optimization unit determines a cost function according to the relationship between various devices and the short-circuit current level, and obtains the optimal short-circuit current level that satisfies both economic and safety requirements based on the cost function, specifically including:

[0086] The cost functions of current limiting devices and DC circuit breakers and short-circuit current levels are established respectively, denoted as f(I k ) and g(I k ), where f(·) is the cost of the current limiting device, g(·) is the cost of the DC circuit breaker, and I k For the short-circuit current level, the current limiting devices include current limiting reactors and superconducting current limiters;

[0087] Find I k0 , so that f′(I k0 )+g′(I k0 )=0, where f′(·) and g′(·) are the derivatives of the equipment cost with respect to the short-circuit current level, I k0 It is the optimal short-circuit current level that meets both economic and safety requirements.

[0088] It should be noted that the primary circuit configuration system provided in this embodiment is used to implement the primary circuit configuration method of the aforementioned embodiment, and the specific settings of each unit are subject to the complete implementation of the method, which will not be repeated here.

[0089] 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 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 primary circuit configuration method for suppressing fault current in a DC distribution network. It is characterized in that The method is applicable to any multi-terminal DC distribution network including a full-bridge MMC converter station, a half-bridge MMC converter station and a DC transformer, and includes the following steps: Obtain DC distribution network topology, converter station parameters and line parameters; The primary circuit equipment of the DC distribution network topology is configured based on the configuration principle, wherein the configuration principle includes configuring a first current limiting reactor at the full-bridge MMC converter station node, configuring a second current limiting reactor and a superconducting current limiter at the half-bridge MMC converter station node, configuring a third current limiting reactor and a capacitor separation switch at the DC transformer node; and also includes configuring a DC circuit breaker at the half-bridge MMC converter station node; Determine a cost function according to the relationship between various devices and short-circuit current levels, obtain an optimal short-circuit current level that satisfies both economic and safety requirements based on the cost function, and determine a primary circuit configuration of the DC distribution network according to the optimal short-circuit current level; The lower limit of the inductance value of the first current limiting reactor is determined according to the following formula: In the formula, τ 1 is the MMC capacitor discharge current decay time constant, U dc is the DC voltage before the fault, C 0 is the submodule capacitance value, n is the number of bridge arm submodules, L bridge is the inductance of the bridge arm reactor, L r is the inductance of the current limiting reactor, ω is the oscillation angular frequency of the discharge current, I 0 I is the DC current output by MMC immediately before the fault. c_MMC is the short-circuit fault current before the full-bridge MMC converter station is locked, I max1 It is the upper limit of the fault current allowed before blocking; The lower limit of the quench resistance value of the superconducting current limiter is determined according to the following formula: In the formula, I 0_MMC is the arm current of the half-bridge MMC converter station at the time of locking, L bridge is the bridge arm inductance, R L is the resistance value of the discharge circuit, R SR is the quench resistance of the superconducting current limiter, I MMC_bridge is the freewheeling current of the half-bridge MMC converter station bridge arm, I max2 is the maximum breaking current of the DC circuit breaker; The lower limit of the inductance value of the third current limiting reactor is determined according to the following formula: In the formula, τ 2 is the DC transformer capacitor discharge current decay time constant, U dc is the DC voltage before the fault, ω d is the oscillation angular frequency of the DC transformer capacitor discharge current, L s is the equivalent inductance of the discharge circuit, L r is the inductance of the current limiting reactor, i c_DCT is the DC transformer capacitor discharge current, t 1 is the converter locking time, I max3 It is the upper limit of the fault current allowed before the current is blocked.

2. The primary circuit configuration method for suppressing fault current in a DC distribution network according to claim 1, It is characterized in that Determining a cost function according to the relationship between various devices and short-circuit current levels, and obtaining an optimal short-circuit current level that satisfies both economic and safety requirements based on the cost function, specifically includes: The cost functions of the current limiting device and the DC circuit breaker and the short-circuit current level are established respectively, denoted as f(I k ) and g(I k ), where f(·) is the cost of the current limiting device, g(·) is the cost of the DC circuit breaker, I k is a short-circuit current level, the current limiting device includes a current limiting reactor and a superconducting current limiter; Find I k0 , so that f′(I k0 )+g′(I k0 )=0, where f′(·) and g′(·) are the derivatives of the equipment cost with respect to the short-circuit current level, and the I k0 It is the optimal short-circuit current level that meets both economic and safety requirements.

3. A primary circuit configuration system for suppressing fault current in a DC distribution network, It is characterized in that Applicable to any multi-terminal DC distribution network including full-bridge MMC converter station, half-bridge MMC converter station and DC transformer, including: A parameter acquisition unit, used to acquire DC distribution network topology, converter station parameters and line parameters; A device configuration unit, configured to perform primary circuit device configuration on the DC distribution network topology based on a configuration principle, wherein the configuration principle includes configuring a first current limiting reactor at the full-bridge MMC converter station node, configuring a second current limiting reactor and a superconducting current limiter at the half-bridge MMC converter station node, and configuring a third current limiting reactor and a capacitor separation switch at the DC transformer node; and also includes configuring a DC circuit breaker at the half-bridge MMC converter station node; A configuration optimization unit is used to determine a cost function according to the relationship between various devices and short-circuit current levels, obtain an optimal short-circuit current level that satisfies both economic and safety requirements based on the cost function, and determine a primary circuit configuration of the DC distribution network according to the optimal short-circuit current level; The lower limit of the inductance value of the first current limiting reactor is determined according to the following formula: In the formula, τ 1 is the MMC capacitor discharge current decay time constant, U dc is the DC voltage before the fault, C 0 is the submodule capacitance value, n is the number of bridge arm submodules, L bridge is the inductance of the bridge arm reactor, L r is the inductance of the current limiting reactor, ω is the oscillation angular frequency of the discharge current, I 0 I is the DC current output by MMC immediately before the fault. c_MMC is the short-circuit fault current before the full-bridge MMC converter station is locked, I max1 It is the upper limit of the fault current allowed before blocking; The lower limit of the quench resistance value of the superconducting current limiter is determined according to the following formula: In the formula, I 0_MMC is the arm current of the half-bridge MMC converter station at the time of locking, L bridge is the bridge arm inductance, R L is the resistance value of the discharge circuit, R SR is the quench resistance of the superconducting current limiter, I MMC_bridge is the freewheeling current of the half-bridge MMC converter station bridge arm, I max2 is the maximum breaking current of the DC circuit breaker; The lower limit of the inductance value of the third current limiting reactor is determined according to the following formula: In the formula, τ 2 is the DC transformer capacitor discharge current decay time constant, U dc is the DC voltage before the fault, ω d is the oscillation angular frequency of the DC transformer capacitor discharge current, L s is the equivalent inductance of the discharge circuit, L r is the inductance of the current limiting reactor, i c_DCT is the DC transformer capacitor discharge current, t 1 is the converter locking time, I max3 It is the upper limit of the fault current allowed before the current is blocked.

4. The primary circuit configuration system for suppressing fault current in a DC distribution network according to claim 3, It is characterized in that The configuration optimization unit determines a cost function according to the relationship between various devices and short-circuit current levels, and obtains an optimal short-circuit current level that satisfies both economic and safety requirements based on the cost function, specifically including: The cost functions of the current limiting device and the DC circuit breaker and the short-circuit current level are established respectively, denoted as f(I k ) and g(I k ), where f(·) is the cost of the current limiting device, g(·) is the cost of the DC circuit breaker, I k is a short-circuit current level, the current limiting device includes a current limiting reactor and a superconducting current limiter; Find I k0 , so that f′(I k0 )+g′(I k0 )=0, where f′(·) and g′(·) are the derivatives of the equipment cost with respect to the short-circuit current level, and the I k0 It is the optimal short-circuit current level that meets both economic and safety requirements.

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