A transient current calculation method and system suitable for a ring direct current distribution network

Abstract

The application relates to the technical field of direct-current power distribution networks, and discloses a transient current calculation method and system suitable for a ring-shaped direct-current power distribution network. The method considers the common feeding effect of different types of converter stations of the direct-current power distribution network on a fault point, constructs an equivalent circuit model of the ring-shaped direct-current power distribution network in the case of an inter-pole fault of a direct-current line, converts the equivalent circuit model to a complex frequency domain to obtain a short-circuit current complex frequency domain model, converts the short-circuit current complex frequency domain model to a time domain to obtain a short-circuit current time domain calculation model, solves the short-circuit current time domain calculation model to obtain a time domain solution of the transient current, and thus the accuracy of transient current calculation of the ring-shaped direct-current power distribution network is improved.

Description

Technical Field

[0001] This invention relates to the field of DC distribution network technology, and in particular to a transient current calculation method and system applicable to ring DC distribution networks. Background Technology

[0002] Compared to AC distribution networks, DC distribution networks enable efficient and flexible integration of distributed renewable energy sources, DC loads, and frequency converter loads, significantly improving the flexibility of distribution-side operation and control. Compared to AC grid faults, DC distribution networks experience lower damping and faster fault current rise. Furthermore, the absence of a natural zero-crossing point in DC networks places higher demands on protection technologies.

[0003] When a DC-side inter-pole fault occurs in a DC distribution network, the fault current mainly consists of capacitor discharge current and AC-side feed-in current. Regardless of whether it is a full-bridge submodule or a half-bridge submodule, capacitor discharge is the main cause of overcurrent in the bridge arm before the submodule is locked out.

[0004] Existing methods mainly study the transient process of a single converter station during a DC fault, neglecting the coupling effect of different converter stations and failing to consider the common feed current effect of different types of converter stations (AC / DC and DC / DC) on the fault point in the DC distribution network. This makes it difficult to characterize the coupling effect between different converter stations and to accurately calculate the transient current of a ring DC distribution network. Summary of the Invention

[0005] This invention provides a transient current calculation method and system suitable for ring DC distribution networks, which solves the technical problem of low accuracy in transient current calculation for ring DC distribution networks.

[0006] In view of this, the first aspect of the present invention provides a transient current calculation method applicable to a ring-shaped DC distribution network, comprising the following steps:

[0007] Obtain the circuit component parameters and topology of the ring DC distribution network under DC line inter-pole fault, and construct an equivalent circuit model under the capacitor discharge stage;

[0008] Based on Kirchhoff's current law, the equivalent circuit model is converted to the complex frequency domain to obtain the short-circuit current complex frequency domain model.

[0009] The short-circuit current complex frequency domain model is converted to the time domain to obtain the short-circuit current time domain calculation model. The short-circuit current time domain calculation model is solved to obtain the time domain solution of the transient current.

[0010] Preferably, the ring DC distribution network includes three distribution nodes, which are sequentially connected to form a ring DC distribution network structure. The first and second distribution nodes each include a converter, and the third distribution node includes a DCT transmission. A short-circuit node is provided on the connection line between any one of the first or second distribution nodes and the third distribution node. The equivalent circuit model includes: capacitors C1, C2, and C3; inductors L1 and L3; resistors R1, R2, R3, and R4; and a short-circuit branch. The capacitor C3 is connected in parallel with the short-circuit branch. The inductor L1, the resistor R1, and the resistor R2 are connected in series between the capacitor C1 and the capacitor R2. A branch is led out from the line between the inductor L1 and the resistor R1 and connected to the capacitor C3. The inductor L3 and the resistor R3 are connected in series on the branch led out from the line between the inductor L1 and the resistor R1. A branch is led out from the line between the inductor L3 and the resistor R3 and connected to the resistor R2 and the capacitor C2 respectively. The resistor R4 is connected in series on the branch led out from the line between the inductor L3 and the resistor R3.

[0011] Preferably, the step of converting the equivalent circuit model to the complex frequency domain based on Kirchhoff's current law to obtain the short-circuit current complex frequency domain model specifically includes:

[0012] Converting the equivalent circuit model to the complex frequency domain, the voltage and current relationships for each distribution node are constructed based on the component parameters in the equivalent circuit model as follows:

[0013]

[0014] In Equation 1 above, U1 and I1 are the complex frequency domain variables corresponding to the voltage and current of the first distribution node, U2 and I2 are the complex frequency domain variables corresponding to the voltage and current of the second distribution node, U3 and I3 are the complex frequency domain variables corresponding to the voltage and current of the third distribution node, and s is the complex frequency.

[0015] Based on Kirchhoff's current law, the voltage and current relationship for each distribution node is constructed according to the component parameters in the equivalent circuit model as follows:

[0016]

[0017] Based on Kirchhoff's current law, the short-circuit current at the short-circuit node is calculated as i. f =-(i1+i2+i3), where i1 represents the current of the first distribution node, i2 represents the current of the second distribution node, and i3 represents the current of the third distribution node;

[0018] Combining Equations 1 and 2, the short-circuit current is converted to the complex frequency domain, resulting in the complex frequency domain model of the short-circuit current as follows:

[0019]

[0020] In Equation 3, K i These are the coefficients of the complex frequency domain equation.

[0021] Preferably, the steps of converting the short-circuit current complex frequency domain model to the time domain to obtain the short-circuit current time domain calculation model, and solving the short-circuit current time domain calculation model to obtain the time domain solution of the transient current specifically include:

[0022] Converting the short-circuit current complex frequency domain model to the time domain, we obtain the short-circuit current time domain calculation model as follows:

[0023]

[0024] Solve the time-domain calculation model of the short-circuit current to obtain the time-domain solution of the transient current.

[0025] Secondly, the present invention also provides a transient current calculation system suitable for ring-shaped DC distribution networks, comprising:

[0026] The acquisition module is used to acquire the circuit element parameters and topology of the ring DC distribution network when it is in the inter-pole fault of the DC line, and to construct the equivalent circuit model under the capacitor discharge stage.

[0027] The complex frequency domain conversion module is used to convert the equivalent circuit model to the complex frequency domain based on Kirchhoff's current law, so as to obtain the short-circuit current complex frequency domain model.

[0028] The time-domain conversion module is used to convert the short-circuit current complex frequency domain model to the time domain to obtain the short-circuit current time-domain calculation model, solve the short-circuit current time-domain calculation model, and obtain the time-domain solution of the transient current.

[0029] Preferably, the ring DC distribution network includes three distribution nodes, which are sequentially connected to form a ring DC distribution network structure. The first and second distribution nodes each include a converter, and the third distribution node includes a DCT transmission. A short-circuit node is provided on the connection line between any one of the first or second distribution nodes and the third distribution node. The equivalent circuit model includes: capacitors C1, C2, and C3; inductors L1 and L3; resistors R1, R2, R3, and R4; and a short-circuit branch. The capacitor C3 is connected in parallel with the short-circuit branch. The inductor L1, the resistor R1, and the resistor R2 are connected in series between the capacitor C1 and the capacitor R2. A branch is led out from the line between the inductor L1 and the resistor R1 and connected to the capacitor C3. The inductor L3 and the resistor R3 are connected in series on the branch led out from the line between the inductor L1 and the resistor R1. A branch is led out from the line between the inductor L3 and the resistor R3 and connected to the resistor R2 and the capacitor C2 respectively. The resistor R4 is connected in series on the branch led out from the line between the inductor L3 and the resistor R3.

[0030] Preferably, the complex frequency domain conversion module specifically includes:

[0031] The first calculation module is used to convert the equivalent circuit model to the complex frequency domain, and construct the voltage and current relationship of each distribution node based on the component parameters in the equivalent circuit model as follows:

[0032]

[0033] In Equation 1 above, U1 and I1 are the complex frequency domain variables corresponding to the voltage and current of the first distribution node, U2 and I2 are the complex frequency domain variables corresponding to the voltage and current of the second distribution node, U3 and I3 are the complex frequency domain variables corresponding to the voltage and current of the third distribution node, and s is the complex frequency.

[0034] The second calculation module is used to construct the voltage and current relationship of each distribution node based on Kirchhoff's current law and the component parameters in the equivalent circuit model:

[0035]

[0036] The third calculation module is used to calculate the short-circuit current i at the short-circuit node based on Kirchhoff's current law. f =-(i1+i2+i3), where i1 represents the current of the first distribution node, i2 represents the current of the second distribution node, and i3 represents the current of the third distribution node;

[0037] The conversion module combines Equations 1 and 2 to convert the short-circuit current to the complex frequency domain, resulting in the complex frequency domain model of the short-circuit current.

[0038]

[0039] In Equation 3, K i These are the coefficients of the complex frequency domain equation.

[0040] Preferably, the time-domain conversion module is specifically used to convert the short-circuit current complex frequency domain model to the time domain, resulting in the short-circuit current time-domain calculation model:

[0041]

[0042] It is also used to solve the time-domain calculation model of the short-circuit current to obtain the time-domain solution of the transient current.

[0043] As can be seen from the above technical solutions, the present invention has the following advantages:

[0044] This invention constructs an equivalent circuit model of a ring DC distribution network under inter-pole fault conditions by considering the common feed current effect of different types of converter stations on the fault point. The equivalent circuit model is converted to the complex frequency domain to obtain the short-circuit current complex frequency domain model. Then, the short-circuit current complex frequency domain model is converted to the time domain to obtain the short-circuit current time domain calculation model. Solving the short-circuit current time domain calculation model yields the time domain solution of the transient current, thereby improving the accuracy of transient current calculation for ring DC distribution networks. Attached Figure Description

[0045] Figure 1 A flowchart of a transient current calculation method applicable to a ring DC distribution network provided in an embodiment of the present invention;

[0046] Figure 2 This is a schematic diagram of the structure of a ring-shaped DC distribution network provided in an embodiment of the present invention;

[0047] Figure 3 This is a schematic diagram of the equivalent circuit model provided in an embodiment of the present invention;

[0048] Figure 4 This is a schematic diagram of another equivalent circuit model provided in an embodiment of the present invention;

[0049] Figure 5 This is a schematic diagram of a transient current calculation system suitable for a ring-shaped DC distribution network, provided as an embodiment of the present invention. Detailed Implementation

[0050] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0051] For easier understanding, please refer to Figure 1 The present invention provides a transient current calculation method applicable to ring DC distribution networks, comprising the following steps:

[0052] S1. Obtain the circuit element parameters and topology of the ring DC distribution network when it is in the DC line inter-pole fault, and construct the equivalent circuit model under the capacitor discharge stage.

[0053] Among them, such as Figure 2 As shown, the ring DC distribution network is a typical ring DC distribution network. The ring DC distribution network includes three distribution nodes, which are connected in sequence to form the ring DC distribution network structure. The first and second distribution nodes each contain a converter, and the third distribution node contains a DCT transmission. There is a short-circuit node on the connection line between any of the first and second distribution nodes and the third distribution node. The fault type of the short-circuit node is a DC line inter-pole fault.

[0054] When a DC line inter-pole fault occurs, both the converter and the DCT transmission short-circuit before the power module is locked. Specifically, the capacitors of the converters at the first and second distribution nodes discharge to the short-circuit point through the bridge arm reactors and line resistance, while the capacitors of the DCT transmission at the third distribution node discharge directly to the short-circuit point through the line resistance.

[0055] according to Figure 2 The circuit component parameters and topology of the ring DC distribution network in the diagram can be obtained. Figure 3The equivalent circuit model shown is for the capacitor discharge stage. The equivalent circuit model includes: capacitors C1, C2, and C3; inductors L1 and L3; resistors R1, R2, R3, and R4; and a short-circuit branch. Capacitors C1, C2, and C3, along with the short-circuit branch, are connected in parallel. Inductor L1, resistor R1, and resistor R2 are connected in series between capacitors C1 and R2. A branch is drawn from the line between inductor L1 and resistor R1, connecting to capacitor C3. Inductor L3 and resistor R3 are connected in series on the branch drawn from the line between inductor L1 and resistor R1. A branch is drawn from the line between inductor L3 and resistor R3, connecting to resistor R2 and capacitor C2 respectively. Resistor R4 is connected in series on the branch drawn from the line between inductor L3 and resistor R3.

[0056] Among them, capacitors C1 and C2 are the equivalent module capacitors of the MMC converter at the first power distribution node and the equivalent module capacitors of the DCT transmission at the third power distribution node, respectively; inductors L1 and L3 are the equivalent bridge arm inductors of the MMC converters at the first and second power distribution nodes, respectively; resistors R1 and R2 are the line resistances from the first and second power distribution nodes to the third power distribution node, respectively; R3 is the line resistance from the first power distribution node to the second power distribution node; and R4 is the line resistance from the third power distribution node to the first power distribution node.

[0057] S2. Based on Kirchhoff's current law, the equivalent circuit model is converted to the complex frequency domain to obtain the complex frequency domain model of the short-circuit current.

[0058] S3. Convert the short-circuit current complex frequency domain model to the time domain to obtain the short-circuit current time domain calculation model. Solve the short-circuit current time domain calculation model to obtain the time domain solution of the transient current.

[0059] This invention provides a transient current calculation method applicable to ring-shaped DC distribution networks. By considering the common feed current effect of different types of converter stations on the fault point in the DC distribution network, an equivalent circuit model of the ring-shaped DC distribution network under inter-pole fault of the DC line is constructed. The equivalent circuit model is converted to the complex frequency domain to obtain the short-circuit current complex frequency domain model. Then, the short-circuit current complex frequency domain model is converted to the time domain to obtain the short-circuit current time domain calculation model. Solving the short-circuit current time domain calculation model yields the time domain solution of the transient current, thereby improving the accuracy of transient current calculation for ring-shaped DC distribution networks.

[0060] In one specific embodiment, step S2 specifically includes:

[0061] S201. Convert the equivalent circuit model to the complex frequency domain, and construct the voltage and current relationship for each distribution node based on the component parameters in the equivalent circuit model:

[0062]

[0063] In Equation 1 above, U1 and I1 are the complex frequency domain variables corresponding to the voltage and current of the first distribution node, U2 and I2 are the complex frequency domain variables corresponding to the voltage and current of the second distribution node, U3 and I3 are the complex frequency domain variables corresponding to the voltage and current of the third distribution node, and s is the complex frequency.

[0064] S202. Based on Kirchhoff's Current Law, the voltage and current relationship of each distribution node is constructed according to the component parameters in the equivalent circuit model as follows:

[0065]

[0066] S203. Based on Kirchhoff's current law, calculate the short-circuit current at the short-circuit node as i. f =-(i1+i2+i3), where i1 represents the current of the first distribution node, i2 represents the current of the second distribution node, and i3 represents the current of the third distribution node;

[0067] S204. Combining Equations 1 and 2, the short-circuit current is converted to the complex frequency domain, resulting in the complex frequency domain model of the short-circuit current.

[0068]

[0069] In Equation 3, K i These are the coefficients of the complex frequency domain equation.

[0070] It is understandable that the equivalent circuit contains 5 independent energy storage elements, that is, the circuit is a 5th-order circuit, which yields Equation 3. The coefficients of the complex frequency domain equations differ for different circuit topologies and circuits of different orders, but since the circuit is a 5th-order circuit, the corresponding complex frequency domain equation coefficients can be obtained.

[0071] In one specific embodiment, step S3 specifically includes:

[0072] S301. Convert the short-circuit current complex frequency domain model to the time domain to obtain the short-circuit current time domain calculation model as follows:

[0073]

[0074] S302. Solve the time-domain calculation model of the short-circuit current to obtain the time-domain solution of the transient current.

[0075] It should be noted that the initial conditions of the short-circuit current time-domain calculation model are the initial voltage of each capacitor and the initial current of the inductor. Equation 4 can be solved according to the fifth-order homogeneous differential equation with constant coefficients to obtain the time-domain solution of the transient current during the discharge stage.

[0076] Furthermore, this invention can also be conveniently extended to a ring-shaped DC distribution network with n nodes (where m are MMC converter station nodes and nm are DC transformer nodes). Based on the circuit topology and short-circuit fault conditions, a network can be constructed as follows: Figure 4 The equivalent circuit model shown has a circuit order of m+n, and its short-circuit current calculation model during the capacitor discharge stage is as follows:

[0077]

[0078] The above is a detailed description of an embodiment of a transient current calculation method for a ring DC distribution network provided by the present invention. The following is a detailed description of an embodiment of a transient current calculation system for a ring DC distribution network provided by the present invention.

[0079] For easier understanding, please refer to Figure 5 This invention provides a transient current calculation system suitable for ring-shaped DC distribution networks, comprising:

[0080] The acquisition module 100 is used to acquire the circuit element parameters and topology of the ring DC distribution network when it is in the DC line inter-pole fault, and to construct the equivalent circuit model under the capacitor discharge stage.

[0081] The complex frequency domain conversion module 200 is used to convert the equivalent circuit model to the complex frequency domain based on Kirchhoff's current law, so as to obtain the short-circuit current complex frequency domain model.

[0082] The time-domain conversion module 300 is used to convert the complex frequency domain model of the short-circuit current to the time domain, obtain the time-domain calculation model of the short-circuit current, solve the time-domain calculation model of the short-circuit current, and obtain the time-domain solution of the transient current.

[0083] In one specific embodiment, such as Figure 2 As shown, the ring DC distribution network includes three distribution nodes, which are connected in sequence to form the ring DC distribution network structure. The first and second distribution nodes each contain a converter, and the third distribution node contains a DCT transmission. A short-circuit node is provided on the connection line between any one of the first and second distribution nodes and the third distribution node.

[0084] like Figure 3As shown, the equivalent circuit model includes: capacitors C1, C2, and C3; inductors L1 and L3; resistors R1, R2, R3, and R4; and a short-circuit branch. Capacitors C1, C2, and C3, along with the short-circuit branch, are connected in parallel. Inductor L1, resistor R1, and resistor R2 are connected in series between capacitors C1 and R2. A branch is drawn from the line between inductor L1 and resistor R1 and connected to capacitor C3. Inductor L3 and resistor R3 are connected in series on the branch drawn from the line between inductor L1 and resistor R1. A branch is drawn from the line between inductor L3 and resistor R3 and connected to resistor R2 and capacitor C2 respectively. Resistor R4 is connected in series on the branch drawn from the line between inductor L3 and resistor R3.

[0085] In one specific embodiment, the complex frequency domain conversion module specifically includes:

[0086] The first calculation module is used to convert the equivalent circuit model to the complex frequency domain, and constructs the voltage and current relationship of each distribution node based on the component parameters in the equivalent circuit model as follows:

[0087]

[0088] In Equation 1 above, U1 and I1 are the complex frequency domain variables corresponding to the voltage and current of the first distribution node, U2 and I2 are the complex frequency domain variables corresponding to the voltage and current of the second distribution node, U3 and I3 are the complex frequency domain variables corresponding to the voltage and current of the third distribution node, and s is the complex frequency.

[0089] The second calculation module is used to construct the voltage and current relationship for each distribution node based on Kirchhoff's current law and the component parameters in the equivalent circuit model:

[0090]

[0091] The third calculation module is used to calculate the short-circuit current i at the short-circuit node based on Kirchhoff's current law. f =-(i1+i2+i3), where i1 represents the current of the first distribution node, i2 represents the current of the second distribution node, and i3 represents the current of the third distribution node;

[0092] The conversion module combines Equations 1 and 2 to convert the short-circuit current to the complex frequency domain, resulting in the complex frequency domain model of the short-circuit current.

[0093]

[0094] In Equation 3, K i These are the coefficients of the complex frequency domain equation.

[0095] In one specific embodiment, the time-domain conversion module is specifically used to convert the complex frequency domain model of the short-circuit current to the time domain, resulting in the following time-domain calculation model of the short-circuit current:

[0096]

[0097] It is also used to solve the time-domain calculation model of short-circuit current to obtain the time-domain solution of transient current.

[0098] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working processes of the systems, devices, and units described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here.

[0099] In the several embodiments provided by this invention, it should be understood that the disclosed apparatus and methods can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative; for instance, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces; the indirect coupling or communication connection between apparatuses or units may be electrical, mechanical, or other forms.

[0100] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0101] Furthermore, the functional units in the various embodiments of the present invention can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0102] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for transient current calculation suitable for a ring-type DC power distribution network, characterized in that, Includes the following steps: Obtain the circuit component parameters and topology of the ring DC distribution network under DC line inter-pole fault, and construct an equivalent circuit model under the capacitor discharge stage; The ring-shaped DC distribution network includes three distribution nodes, which are sequentially connected to form the ring-shaped DC distribution network structure. The first and second distribution nodes each include a converter, and the third distribution node includes a DCT transmission. A short-circuit node is provided on the connection line between any one of the first or second distribution nodes and the third distribution node. The equivalent circuit model includes: capacitors C1, C2, and C3; inductors L1 and L3; resistors R1, R2, R3, and R4; and a short-circuit branch. The capacitor C3 and the short-circuit branch are connected in parallel. The inductor L1, the resistor R1 and the resistor R2 are connected in series in sequence between the capacitor C1 and the capacitor R2. A branch is led out from the line between the inductor L1 and the resistor R1 and connected to the capacitor C3. The inductor L3 and the resistor R3 are connected in series on the branch led out from the line between the inductor L1 and the resistor R1. A branch is led out from the line between the inductor L3 and the resistor R3 and connected to the resistor R2 and the capacitor C2 respectively. The resistor R4 is connected in series on the branch led out from the line between the inductor L3 and the resistor R3. Based on Kirchhoff's current law, the equivalent circuit model is transformed into the complex frequency domain to obtain the short-circuit current complex frequency domain model, including: Converting the equivalent circuit model to the complex frequency domain, the voltage and current relationships for each distribution node are constructed based on the component parameters in the equivalent circuit model as follows: Formula 1 In the above equation 1, , are the complex frequency domain variables corresponding to the voltage and current of the first distribution node, respectively, , are the complex frequency domain variables corresponding to the voltage and current of the second power distribution node, respectively, , are the complex frequency domain variables corresponding to the voltage and current of the third power distribution node, respectively, is the complex frequency. Based on Kirchhoff's current law, the voltage and current relationship for each distribution node is constructed according to the component parameters in the equivalent circuit model as follows: Formula 2 Based on the Kirchhoff's current law, the short-circuit current of the short-circuit node is calculated as wherein i1 represents the current of the first distribution node, i2 represents the current of the second distribution node, and i3 represents the current of the third distribution node. Combining Equations 1 and 2, the short-circuit current is converted to the complex frequency domain, resulting in the complex frequency domain model of the short-circuit current as follows: Formula 3 In formula 3, are complex frequency domain equation coefficients; The short-circuit current complex frequency domain model is converted to the time domain to obtain the short-circuit current time domain calculation model. The short-circuit current time domain calculation model is solved to obtain the time domain solution of the transient current.

2. The method for transient current calculation suitable for a ring-type DC distribution network according to claim 1, characterized by, The steps of converting the short-circuit current complex frequency domain model to the time domain to obtain the short-circuit current time domain calculation model, and solving the short-circuit current time domain calculation model to obtain the time domain solution of the transient current specifically include: Converting the short-circuit current complex frequency domain model to the time domain, we obtain the short-circuit current time domain calculation model as follows: Formula 4 Solve the time-domain calculation model of the short-circuit current to obtain the time-domain solution of the transient current.

3. A transient current calculation system for a ring-type DC power distribution network, characterized by, include: The acquisition module is used to acquire the circuit element parameters and topology of the ring DC distribution network when it is in the inter-pole fault of the DC line, and to construct the equivalent circuit model under the capacitor discharge stage. The ring-shaped DC distribution network includes three distribution nodes, which are sequentially connected to form the ring-shaped DC distribution network structure. The first and second distribution nodes each include a converter, and the third distribution node includes a DCT transmission. A short-circuit node is provided on the connection line between any one of the first or second distribution nodes and the third distribution node. The equivalent circuit model includes: capacitors C1, C2, and C3; inductors L1 and L3; resistors R1, R2, R3, and R4; and a short-circuit branch. The capacitor C3 and the short-circuit branch are connected in parallel. The inductor L1, the resistor R1 and the resistor R2 are connected in series in sequence between the capacitor C1 and the capacitor R2. A branch is led out from the line between the inductor L1 and the resistor R1 and connected to the capacitor C3. The inductor L3 and the resistor R3 are connected in series on the branch led out from the line between the inductor L1 and the resistor R1. A branch is led out from the line between the inductor L3 and the resistor R3 and connected to the resistor R2 and the capacitor C2 respectively. The resistor R4 is connected in series on the branch led out from the line between the inductor L3 and the resistor R3. The complex frequency domain conversion module is used to convert the equivalent circuit model to the complex frequency domain based on Kirchhoff's current law, so as to obtain the short-circuit current complex frequency domain model. The complex frequency domain conversion module specifically includes: The first calculation module is used to convert the equivalent circuit model to the complex frequency domain, and construct the voltage and current relationship of each distribution node based on the component parameters in the equivalent circuit model as follows: Formula 1 In the above equation 1, , are the complex frequency domain variables corresponding to the voltage and current of the first distribution node, respectively, , are the complex frequency domain variables corresponding to the voltage and current of the second power distribution node, respectively, , are the complex frequency domain variables corresponding to the voltage and current of the third power distribution node, respectively, is the complex frequency. The second calculation module is used to construct the voltage and current relationship of each distribution node based on Kirchhoff's current law and the component parameters in the equivalent circuit model: Formula 2 The third calculation module is configured to calculate, based on the Kirchhoff's current law, the short-circuit current of the short-circuit node as wherein i1 represents the current of the first power distribution node, i2 represents the current of the second power distribution node, and i3 represents the current of the third power distribution node. The conversion module combines Equations 1 and 2 to convert the short-circuit current to the complex frequency domain, resulting in the complex frequency domain model of the short-circuit current. Formula 3 In formula 3, are complex frequency domain equation coefficients; The time-domain conversion module is used to convert the short-circuit current complex frequency domain model to the time domain to obtain the short-circuit current time-domain calculation model, solve the short-circuit current time-domain calculation model, and obtain the time-domain solution of the transient current.

4. The system for transient current calculation suitable for a ring-type DC distribution network according to claim 3, characterized by, The time-domain conversion module is specifically used to convert the short-circuit current complex frequency domain model to the time domain, resulting in the short-circuit current time-domain calculation model: Formula 4 It is also used to solve the time-domain calculation model of the short-circuit current to obtain the time-domain solution of the transient current.

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