CN115051335A - Primary loop configuration method and system for inhibiting fault current of direct-current power distribution network - Google Patents

Abstract

The invention provides a primary loop configuration method and a primary loop configuration system for inhibiting fault current of a direct current power distribution network, wherein the method comprises the steps of configuring current limiting reactors at a full-bridge MMC converter station node, a half-bridge MMC converter station node and a direct current transformer node in the direct current power distribution network, configuring a superconducting current limiter at the half-bridge MMC converter station node, and configuring a capacitance separation switch at the direct current transformer node; the method also comprises the steps that a direct current breaker is configured at a node of the half-bridge MMC converter station, and parameters of all equipment are determined by converter station parameters and line parameters; and obtaining the optimal short-circuit current level which meets the economic and safety requirements simultaneously according to the cost function of each device and the short-circuit current level, thereby determining the primary loop configuration of the direct-current power distribution network. According to the invention, corresponding current limiting equipment is configured at different nodes of the power distribution network, the differential requirements on various current limiting equipment are considered, and the configuration of primary loop equipment is optimized, so that the economy and the safety of construction and operation of the direct-current power distribution network are met.

Description

Primary loop configuration method and system for inhibiting fault current of direct-current power distribution network

Technical Field

The invention belongs to the technical field of direct-current power distribution networks, and particularly relates to a primary circuit configuration method and a primary circuit configuration system for inhibiting fault currents of a direct-current power distribution network.

Background

Compared with an alternating-current power distribution network, the direct-current power distribution network can realize efficient and flexible access of distributed new energy, direct-current loads and variable-frequency loads, and remarkably improves the flexibility of operation control of a power distribution side. Compared with the fault of the alternating current power grid, the direct current power distribution grid has small damping and high fault current rising speed, and the direct current has no natural zero crossing point, so that higher requirements are provided for the protection technology of the direct current power distribution grid.

In order to inhibit the rapid rise of the fault current of the direct-current power distribution network, ensure the safety of key equipment of the direct-current power distribution network, and increase the reactance value and the resistance value of a fault loop is a necessary means. At present, the primary loop configuration for fault current suppression of a direct-current power distribution network is mainly limited to the current limiting effect of a current limiting reactor and a superconducting current limiter, on one hand, the demand difference of a full-bridge MMC (modular multilevel converter), a half-bridge MMC and a direct-current transformer on current limiting primary equipment is not considered, and on the other hand, the cost integral optimization of the current limiting equipment and a direct-current circuit breaker is not considered.

Disclosure of Invention

In view of this, the present invention aims to solve the problems that the demand differences of full-bridge MMC (modular multilevel converter), half-bridge MMC and dc transformers for current-limiting primary devices are not considered in the current-limiting primary loop configuration for dc power distribution network fault current suppression at present, and the cost integral optimization of the current-limiting devices and the dc circuit breakers is not considered.

In order to solve the technical problems, the invention provides the following technical scheme:

in a first aspect, the present invention provides a primary loop configuration method for suppressing a fault current of a dc power distribution network, which is suitable for any multi-terminal dc power distribution network including a full-bridge MMC converter station, a half-bridge MMC converter station, and a dc transformer, and includes the following steps:

acquiring direct current distribution network topology, converter station parameters and line parameters;

performing primary loop equipment configuration on a direct current distribution network topology based on a configuration principle, wherein the configuration principle comprises that a first current-limiting reactor is configured at a node of a full-bridge MMC converter station, a second current-limiting reactor and a superconducting current limiter are configured at a node of a half-bridge MMC converter station, and a third current-limiting reactor and a capacitance separation switch are configured at a node of a direct current transformer; the method also comprises the steps that a direct current breaker is configured at nodes of the half-bridge MMC converter station, wherein the lower limit of the inductance value of a current-limiting reactor, the lower limit of the quench resistance value of a superconducting current limiter, the withstand voltage value of a capacitance separation switch and the withstand voltage value of the direct current breaker at each node are determined according to converter station parameters and line parameters;

determining a cost function according to the relation between various devices and the short-circuit current level, solving the optimal short-circuit current level which meets the economic and safety requirements simultaneously based on the cost function, and determining the primary loop configuration of the direct-current power distribution network according to the optimal short-circuit current level.

Further, 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 Decay time constant of discharge current of MMC capacitor, U _dc Is a pre-fault DC voltage, C ₀ Is the sub-module capacitance value, n is the bridge arm sub-module number, L _bridge For bridge arm reactor inductance value, L _r Is the inductance of the current-limiting reactor, omega is the oscillation angular frequency of the discharge current, I ₀ For outputting direct current, I, to the MMC at the moment before the fault _{c_MMC} Short-circuit fault current before locking for full-bridge MMC converter station, I _max1 An upper limit is allowed for the fault current before latching.

Further, 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} Bridge arm current at the moment of locking of half-bridge MMC converter station, L _bridge Is bridge arm inductance, R _L Is a discharge loop resistance value, R _SR Being quench resistances of superconducting current limiters, I _{MMC_bridge} For bridge arm follow current, I, of half-bridge MMC converter station _max2 The maximum breaking current of the direct current breaker.

Further, 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 The discharge current of the DC transformer has a very short decay time, U _dc For pre-fault DC voltages, omega _d Oscillating angular frequency, L, of discharging current for capacitor of DC transformer _s Is an equivalent inductance value of the discharge circuit, L _r For current-limiting reactor inductance values, i _{c_DCT} For discharging current of DC transformer capacitor, t ₁ For the inverter blocking moment, I _max3 And (4) fault current allowable upper limit before current is blocked.

Further, 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 which meets the economic and safety requirements simultaneously is obtained based on the cost function, and the method specifically comprises the following steps:

separately establishing a cost function of the current limiting device and the DC breaker and the short-circuit current level, 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 breaker, I _k For short circuit current level, the current limiting device comprises a current limiting reactor and a superconducting current limiter;

finding I _k0 So that f' (I) _k0 )+g′(I _k0 ) 0, where f '(. cndot.) and g' (. cndot.) are derivatives of equipment cost versus short circuit current level, I _k0 To meet the optimum short circuit current level required for economy and safety at the same time.

In a second aspect, the present invention provides a primary loop configuration system for suppressing a fault current of a dc power distribution network, which is suitable for any multi-terminal dc power distribution network including a full-bridge MMC converter station, a half-bridge MMC converter station, and a dc transformer, and includes:

the parameter acquisition unit is used for acquiring the topology of the direct current power distribution network, the parameters of the converter station and the parameters of the line;

the device configuration unit is used for performing primary loop device configuration on the direct current distribution network topology based on a configuration principle, wherein the configuration principle comprises the steps that a first current-limiting reactor is configured at a node of a full-bridge MMC converter station, a second current-limiting reactor and a superconducting current limiter are configured at a node of a half-bridge MMC converter station, and a third current-limiting reactor and a capacitance separation switch are configured at a node of a direct current transformer; the method also comprises the steps that a direct-current breaker is configured at a node of the half-bridge MMC converter station, wherein the lower limit of the inductance value of a current-limiting reactor, the lower limit of the quench resistance value of a superconducting current limiter, the withstand voltage value of a capacitance separation switch and the withstand voltage value of the direct-current breaker at each node are determined according to converter station parameters and line parameters;

and the configuration optimization unit is used for determining a cost function according to the relation between various devices and the short-circuit current level, obtaining the optimal short-circuit current level which meets the economic and safety requirements simultaneously based on the cost function, and determining the primary loop configuration of the direct-current power distribution network according to the optimal short-circuit current level.

Further, 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 Decay time constant of discharge current of MMC capacitor, U _dc To a pre-fault DC voltage, C ₀ Is the capacitance of the sub-module, n is the number of the bridge arm sub-modules, L _bridge For bridge arm reactor inductance value, L _r Is the inductance of the current-limiting reactor, omega is the oscillation angular frequency of the discharge current, I ₀ For outputting direct current, I, to the MMC at the moment before the fault _{c_MMC} Short-circuit fault current before locking for full-bridge MMC converter station, I _max1 An upper limit is allowed for the fault current before latching.

Further, 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} Bridge arm current at the moment of locking of half-bridge MMC converter station, L _bridge Is bridge arm inductance, R _L Is a discharge loop resistance value, R _SR Being the quench resistance of a superconducting current limiter, I _{MMC_bridge} For bridge arm follow current of half-bridge MMC converter station, I _max2 The maximum breaking current of the direct current breaker.

Further, the third current limiting reactor inductance lower limit is determined according to the following formula:

in the formula, τ ₂ The discharge current of the DC transformer has a very short decay time, U _dc For dc voltage before failure, omega _d Oscillating angular frequency, L, of discharging current for capacitor of DC transformer _s Is an equivalent inductance value of the discharge circuit, L _r For limiting inductance of reactors, i _{c_DCT} For discharging current of DC transformer capacitor, t ₁ For the inverter blocking moment, I _max3 And (4) fault current allowable upper limit before current is blocked.

Further, the configuration optimization unit determines a cost function according to the relationship between various devices and the short-circuit current level, and obtains an optimal short-circuit current level which meets the economic and safety requirements simultaneously based on the cost function, and specifically includes:

separately establishing a cost function of the current limiting device and the DC breaker and the short-circuit current level, denoted as f (I) _k ) And g (I) _k ) Where f (-) is the current limiting equipment cost, g (-) is the DC breaker cost, I _k For short circuit current level, the current limiting device comprises a current limiting reactor and a superconducting current limiter;

obtaining I _k0 So that f' (I) _k0 )+g′(I _k0 ) 0, where f '(. cndot.) and g' (. cndot.) are the equipment cost derivative to the short circuit current level, I _k0 To meet the optimum short circuit current level required for economy and safety at the same time.

In summary, the present invention provides a primary loop configuration method and system for suppressing fault current of a dc power distribution network, wherein the method of the present invention includes configuring current limiting reactors at nodes of a full-bridge MMC converter station, nodes of a half-bridge MMC converter station, and nodes of a dc transformer in the dc power distribution network, configuring a superconducting current limiter at the nodes of the half-bridge MMC converter station, and configuring a capacitance separation switch at the nodes of the dc transformer; the method also comprises the steps that a direct current breaker is configured at a node of the half-bridge MMC converter station, and parameters of each device are determined by converter station parameters and line parameters; and obtaining the optimal short-circuit current level which meets the economic and safety requirements simultaneously according to the cost function of each device and the short-circuit current level, thereby determining the primary loop configuration of the direct-current power distribution network. According to the invention, corresponding current limiting equipment is configured at different nodes of the power distribution network, the differential requirements on various current limiting equipment are considered, and the configuration of primary loop equipment is optimized, so that the economy and the safety of construction and operation of a direct current power distribution network are met.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without creative efforts.

Fig. 1 is a schematic flowchart of a primary circuit configuration method for suppressing fault current in a dc power distribution network according to an embodiment of the present invention;

fig. 2 is a schematic diagram of an exemplary dc distribution network according to an embodiment of the present invention;

fig. 3 is a simplified flowchart of a primary loop configuration method for suppressing a fault current in a dc power distribution network according to an embodiment of the present invention.

Detailed Description

In order to make the objects, features and advantages of the present invention more obvious and understandable, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention, and it is obvious that the embodiments described below are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Compared with an alternating-current power distribution network, the direct-current power distribution network can realize efficient and flexible access of distributed new energy, direct-current loads and variable-frequency loads, and remarkably improves the flexibility of operation control of a power distribution side. Compared with the fault of the alternating current power grid, the direct current power distribution grid has small damping and high fault current rising speed, and the direct current has no natural zero crossing point, so that higher requirements are provided for the protection technology of the direct current power distribution grid.

In order to inhibit the rapid rise of the fault current of the direct-current power distribution network, ensure the safety of key equipment of the direct-current power distribution network, and increase the reactance value and the resistance value of a fault loop is a necessary means. At present, the primary circuit configuration for suppressing the fault current of the direct-current power distribution network is mainly limited to the current limiting action of a current limiting reactor and a superconducting current limiter, on one hand, the demand difference of a full-bridge MMC (modular multilevel converter), a half-bridge MMC and a direct-current transformer on current limiting primary equipment is not considered, and on the other hand, the integral optimization of the cost of the current limiting equipment and a direct-current circuit breaker is not considered.

Based on the method, the invention provides a primary loop configuration method and a primary loop configuration system for inhibiting fault current of a direct-current power distribution network.

The method for configuring a primary circuit for suppressing a fault current in a dc power distribution network according to the present invention will be described in detail below.

Referring to fig. 1, the present embodiment provides a primary loop configuration method for suppressing a fault current of a dc power distribution network, and the method is applicable to any multi-terminal dc power distribution network including a full-bridge MMC converter station, a half-bridge MMC converter station, and a dc transformer. The method comprises the following steps:

s100: and acquiring the topology of the direct current power distribution network, the parameters of the converter station and the parameters of the line.

Firstly, basic conditions of a target direct-current power distribution network are obtained, wherein the basic conditions comprise a direct-current power distribution network topological structure, current conversion station parameters (full-bridge MMC/half-bridge MMC) and line parameters, and the parameters comprise rated direct-current voltage, the number of bridge arm sub-modules, capacitance values of the MMC sub-modules, inductance values of bridge arm reactors and inductance values of connecting transformers. Wherein, direct current distribution network topology parameter has represented half-bridge MMC, full-bridge MMC, direct current transformer's quantity and interconnection relation, is used for determining which website need carry out current limiting device configuration on the one hand, and on the other hand, instantaneous current I before the trouble ₀ (MMC outputs DC Current immediately before Fault) and I _{0_MMC} (bridge arm current at the locking moment of current changing station)To topological effects.

S200: performing primary loop equipment configuration on a direct current power distribution network topology based on a configuration principle, wherein the configuration principle comprises the steps of configuring a first current-limiting reactor at a node of a full-bridge MMC converter station, configuring a second current-limiting reactor and a superconducting current limiter at the node of the half-bridge MMC converter station, and configuring a third current-limiting reactor and a capacitance separation switch at the node of a direct current transformer; the method also comprises the step of configuring a direct current breaker at nodes of the half-bridge MMC converter station, 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 capacitance isolating switch and the withstand voltage value of the direct current breaker at each node are determined according to converter station parameters and line parameters.

Referring to fig. 2, a primary loop device configuration is illustrated by taking the exemplary dc distribution network topology shown in fig. 2 as an example. Wherein, node 1 is half-bridge MMC converter station node, and node 2 is the direct current transformer node, and node 3 is full-bridge MMC converter station node. The installed current limiting equipment comprises a current limiting reactor, a superconducting current limiter and a capacitance separation switch.

For a full-bridge MMC converter station, because the converter station can isolate direct-current faults after being locked, only a current-limiting reactor such as a node 3 in fig. 2 needs to be configured to reduce the rising rate of fault current before locking. The calculation formula of the short-circuit fault current before the locking of the full-bridge MMC converter station is as follows:

wherein tau is ₁ Is MMC capacitor discharge current decay time constant, U _dc Is a pre-fault DC voltage, C ₀ Is the capacitance of the sub-module, n is the number of the bridge arm sub-modules, L _bridge For bridge arm reactor inductance value, L _r For the inductance value of the current-limiting reactor, omega is the angular frequency of the discharge current oscillation, I ₀ And outputting direct current for the MMC at the moment before the fault.

To ensure the safety of the full-bridge MMC converter equipment, the fault current before locking is not allowed to exceed the safety allowable upper limit, so i is provided _{c_MMC} (t ₁ )＜I _max1 Wherein t is ₁ For converter blocking time，I _max1 An upper limit is allowed for the fault current before latching. The formula determines the lower limit L of the inductance value of the current-limiting reactor _{r_min} 。

For a half-bridge MMC converter station, the converter station still has alternating-current side feed-in current and bridge arm continuous-current after being locked, so that direct-current faults cannot be isolated, and therefore a current-limiting reactor and a superconducting current limiter need to be configured according to a node 1, the rising rate of short-circuit fault current before locking is reduced, and the fault overcurrent level after locking is also reduced. The method of configuring the current limiting reactor in this step is the same as that in S1. The superconductive current limiter mainly considers and limits the bridge arm follow current, and the calculation formula is as follows:

wherein I _{0_MMC} For the moment of locking of the converter station the bridge arm current,

L _bridge is bridge arm inductance, R _L Is a discharge loop resistance value, R _SR Is a superconducting current limiter quench resistor.

The superconducting current limiter has the function of ensuring that the fault current of the half-bridge MMC converter is less than the maximum cut-off current of the direct current breaker before the direct current breaker is cut off, so that I is provided _{0_MMC} ＜I _max2 ，I _max2 The maximum switching current of the direct current breaker is achieved. Therefore, the quench resistance value lower line R of the superconducting current limiter can be obtained _{SR_min} 。

For a direct current transformer, the capacitor discharge cannot be blocked by the converter latch, so that the capacitor discharge cannot be blocked by the capacitor separating switch, and the current-limiting reactor is required to reduce the current rising rate before the capacitor separating. The calculation formula of the capacitor discharge current of the direct current transformer is as follows:

wherein tau is ₂ The discharge current of the DC transformer capacitor has a very short decay time, U _dc For pre-fault DC voltages, omega _d Is a direct currentOscillating angular frequency, L, of capacitor discharge current of transformer _s Is an equivalent inductance value of the discharge circuit, L _r Is a current limiting reactor inductance value.

To ensure the safety of the full-bridge MMC converter equipment, the fault current before locking is not allowed to exceed the safety allowable upper limit, so i is provided _{c_DCT} (t ₁ )＜I _max3 Wherein t is ₁ For the inverter blocking moment, I _max3 And (4) fault current allowable upper limit before current is blocked. The formula determines the lower limit L of the inductance value of the current-limiting reactor _{r_min} 。

For a capacitive isolating switch, the withstand voltage current level should be greater than the maximum voltage and current before and after the capacitor is cut out of the circuit.

The above design is a principle of current limiting device configuration for the primary circuit of the dc power distribution network in this embodiment, and besides, the dc power distribution network is further provided with a protection device. Specifically, for the dc distribution network shown in fig. 2, since the full-bridge MMC and the dc transformer both have dc fault blocking capability, only a dc breaker (e.g., node 1 in fig. 2) needs to be installed at the half-bridge MMC access point, and the withstand voltage and current level of the dc breaker should be determined by combining the current manufacturing level and the short-circuit current level after current limiting.

S300: determining a cost function according to the relation between various devices and the short-circuit current level, solving the optimal short-circuit current level which meets the economic and safety requirements simultaneously based on the cost function, and determining the primary loop configuration of the direct-current power distribution network according to the optimal short-circuit current level.

According to the steps, the short-circuit current of the direct current distribution network can be effectively limited, the cost of the input current limiting equipment and the short-circuit current level are in a negative correlation relationship, and the cost function is expressed as f (I) _k ) Where f (-) is the current limiting equipment cost, I _k Is the short circuit current level. However, the equipment cost of the DC circuit breaker is in positive correlation with the short-circuit current level and is expressed as g (I) by a cost function _k ) Where g (-) is the DC breaker cost. Therefore, the configuration cost of the primary loop protection equipment for protecting the direct current distribution network is f (I) _k )+g(I _k ). Obtaining I _k0 So that f' (I) _k0 )+g′(I _k0 ) 0, where f '(. cndot.) and g' (. cndot.) are the equipment cost derivative to the short circuit current level. Therefore, the short-circuit current level which can simultaneously satisfy the economy and the safety can be obtained, and the configuration of the current-limiting reactor, the superconducting current limiter and the breaker can be further determined. I.e. according to the optimum short-circuit current level I _k0 And calculating the input cost of each current limiting device and each protection device, and carrying out specific configuration on the primary loop according to the input cost. It is understood that the cost function should be established according to the actual dc distribution network topology, and it should satisfy the correlation with the short-circuit current level, and the specific function form is not limited herein.

Based on the above steps, a primary loop configuration flow for suppressing the fault current of the dc distribution network is obtained as shown in fig. 3.

The embodiment provides a primary loop configuration method for inhibiting fault current of a direct current power distribution network, which comprises the steps of configuring current-limiting reactors at nodes of a full-bridge MMC converter station, nodes of a half-bridge MMC converter station and nodes of a direct current transformer in the direct current power distribution network, configuring superconducting current limiters at the nodes of the half-bridge MMC converter station, and configuring capacitance separation switches at the nodes of the direct current transformer; the method also comprises the steps that a direct current breaker is configured at a node of the half-bridge MMC converter station, and parameters of each device are determined by converter station parameters and line parameters; and solving the optimal short-circuit current level which meets the economic and safety requirements simultaneously according to the cost functions of each device and the short-circuit current level, thereby determining the primary loop configuration of the direct-current power distribution network. In the embodiment, corresponding current limiting equipment is configured at different nodes of the power distribution network, the differential requirements on various current limiting equipment are considered, and the configuration of primary loop equipment is optimized, so that the economy and the safety of construction and operation of the direct-current power distribution network are met.

The above is a detailed description of an embodiment of the primary circuit configuration method for suppressing fault current of the dc power distribution network according to the present invention, and the following is a detailed description of an embodiment of the primary circuit configuration system for suppressing fault current of the dc power distribution network according to the present invention.

This embodiment provides a primary circuit configuration system of suppression direct current distribution network fault current, is applicable to the arbitrary multi-terminal direct current distribution network who contains full-bridge MMC converter station, half-bridge MMC converter station and direct current transformer, includes: the device comprises a parameter acquisition unit, a device configuration unit and a configuration optimization unit.

In this embodiment, the parameter obtaining unit is configured to obtain a topology of a dc power distribution network, a parameter of a converter station, and a parameter of a line.

In this embodiment, the device configuration unit is configured to perform primary loop device configuration on a dc distribution network topology based on a configuration principle, where the configuration principle includes configuring a first current-limiting reactor at a node of a full-bridge MMC converter station, configuring a second current-limiting reactor and a superconducting current limiter at a node of a half-bridge MMC converter station, and configuring a third current-limiting reactor and a capacitor disconnect switch at a node of a dc transformer; the method also comprises the step of configuring a direct current breaker at nodes of the half-bridge MMC converter station, 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 capacitance separation switch and the withstand voltage value of the direct current breaker at each node are determined according to converter station parameters and line parameters.

Wherein, 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 Decay time constant of discharge current of MMC capacitor, U _dc Is a pre-fault DC voltage, C ₀ Is the capacitance of the sub-module, n is the number of the bridge arm sub-modules, L _bridge For bridge arm reactor inductance value, L _r Is the inductance of the current-limiting reactor, omega is the oscillation angular frequency of the discharge current, I ₀ For outputting direct current, I, to the MMC at the moment before the fault _{c_MMC} Short-circuit fault current before locking for full-bridge MMC converter station, I _max1 An upper limit is allowed for the fault current before latching.

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} Bridge arm current at the moment of locking of half-bridge MMC converter station, L _bridge Is bridge arm inductance, R _L Is a discharge loop resistance value, R _SR Being quench resistances of superconducting current limiters, I _{MMC_bridge} For bridge arm follow current of half-bridge MMC converter station, I _max2 The maximum breaking current of the direct current 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 The discharge current of the DC transformer capacitor has a very short decay time, U _dc For pre-fault DC voltages, omega _d Oscillating angular frequency, L, of discharging current for capacitor of DC transformer _s Is an equivalent inductance value of the discharge circuit, L _r For current-limiting reactor inductance values, i _{c_DCT} For discharging current of DC transformer capacitor, t ₁ For the inverter blocking moment, I _max3 And (4) fault current allowable upper limit before current is blocked.

In this embodiment, the configuration optimization unit is configured to determine a cost function according to a relationship between various devices and a short-circuit current level, obtain an optimal short-circuit current level that meets economic and safety requirements at the same time based on the cost function, and determine a primary loop configuration of the dc power distribution network according to the optimal short-circuit current level.

Specifically, the configuration optimization unit determines a cost function according to the relationship between various devices and the short-circuit current level, and finds an optimal short-circuit current level that meets both economic and safety requirements based on the cost function, and specifically includes:

separately establishing a cost function of the current limiting device and the DC breaker and the short-circuit current level, denoted as f (I) _k ) And g (I) _k ) Where f (-) is the current limiting equipment cost, g (-) is the DC breaker cost, I _k For short circuit current level, the current limiting device comprises a current limiting reactor and a superconducting current limitingA machine;

finding I _k0 So that f' (I) _k0 )+g′(I _k0 ) 0, where f '(. cndot.) and g' (. cndot.) are the equipment cost derivative to the short circuit current level, I _k0 To meet the optimum short circuit current level required for economy and safety at the same time.

It should be noted that, the primary loop configuration system provided in this embodiment is used to implement the primary loop configuration method of the foregoing embodiment, and the specific settings of each unit are subject to complete implementation of the method, which is not described herein again.

The above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it should be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.

Claims (10)

1. A primary loop configuration method for inhibiting fault current of a direct current power distribution network is characterized by being suitable for any multi-end direct current power distribution network comprising a full-bridge MMC converter station, a half-bridge MMC converter station and a direct current transformer, and comprising the following steps of:

acquiring direct current distribution network topology, converter station parameters and line parameters;

performing primary loop equipment configuration on the direct current power distribution network topology based on a configuration principle, wherein the configuration principle comprises that a first current-limiting reactor is configured at a node of the full-bridge MMC converter station, a second current-limiting reactor and a superconducting current limiter are configured at the node of the half-bridge MMC converter station, and a third current-limiting reactor and a capacitance separation switch are configured at the node of the direct current transformer; configuring a direct current breaker at nodes of the half-bridge MMC converter station, wherein the lower limit of the inductance value of a current-limiting reactor, the lower limit of the quench resistance value of the superconducting current limiter, the withstand voltage value of the capacitance separation switch and the withstand voltage value of the direct current breaker at each node are determined according to the converter station parameters and the line parameters;

determining a cost function according to the relation between various devices and the short-circuit current level, obtaining the optimal short-circuit current level which meets the economic and safety requirements simultaneously based on the cost function, and determining the primary loop configuration of the direct-current power distribution network according to the optimal short-circuit current level.

2. The method for configuring the primary circuit for suppressing the fault current of the direct-current power distribution network according to claim 1, wherein 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 Decay time constant of discharge current of MMC capacitor, U _dc Is a pre-fault DC voltage, C ₀ Is the capacitance of the sub-module, n is the number of the bridge arm sub-modules, L _bridge For bridge arm reactor inductance value, L _r For the inductance value of the current-limiting reactor, omega is the angular frequency of the discharge current oscillation, I ₀ For outputting direct current, I, to the MMC at the moment before the fault _{c_MMC} Short-circuit fault current before locking for full-bridge MMC converter station, I _max1 An upper limit is allowed for the fault current before latching.

3. The primary circuit configuration method for suppressing the fault current of the direct-current power distribution network according to claim 1, wherein 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} Bridge arm current, L, for the locking time of half-bridge MMC converter station _bridge Is bridge arm inductance, R _L Is a discharge loop resistance value, R _SR Being the quench resistance of a superconducting current limiter, I _{MMC_bridge} Bridge arm of MMC converter station of half-bridgeAfterflow current, I _max2 The maximum breaking current of the direct current breaker.

4. The method for configuring the primary circuit for suppressing the fault current of the direct-current power distribution network according to claim 1, wherein 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 The discharge current of the DC transformer has a very short decay time, U _dc For pre-fault DC voltages, omega _d Oscillating angular frequency, L, of the discharge current of the capacitor of the DC transformer _s Is an equivalent inductance value of the discharge circuit, L _r For current-limiting reactor inductance values, i _{c_DCT} For discharging current of DC transformer capacitor, t ₁ For the inverter blocking moment, I _max3 And (4) fault current allowable upper limit before current is blocked.

5. The primary loop configuration method for suppressing fault current of a direct-current power distribution network according to claim 1, wherein a cost function is determined according to a relation between various devices and a short-circuit current level, and an optimal short-circuit current level that meets economic and safety requirements at the same time is obtained based on the cost function, specifically comprising:

establishing a cost function of the current limiting device and the DC breaker and the short circuit current level, respectively, denoted as f (I) _k ) And g (I) _k ) Where f (-) is the current limiting equipment cost, g (-) is the DC breaker cost, I _k For short circuit current level, the current limiting device comprises a current limiting reactor and a superconducting current limiter;

finding I _k0 So that f' (I) _k0 )+g′(I _k0 ) 0, where f '(. cndot.) and g' (. cndot.) are derivatives of equipment cost versus short circuit current level, said I _k0 To meet the optimum short circuit current level for both economy and safety requirements.

6. The utility model provides an restrain direct current distribution network fault current's primary circuit configuration system which characterized in that is applicable to the arbitrary multi-terminal direct current distribution network that contains full-bridge MMC converter station, half-bridge MMC converter station and direct current transformer, includes:

the parameter acquisition unit is used for acquiring the topology of the direct current power distribution network, the parameters of the converter station and the parameters of the line;

the device configuration unit is used for performing primary loop device configuration on the direct current power distribution network topology based on a configuration principle, wherein the configuration principle comprises that a first current-limiting reactor is configured at a node of the full-bridge MMC converter station, a second current-limiting reactor and a superconducting current limiter are configured at the node of the half-bridge MMC converter station, and a third current-limiting reactor and a capacitance separation switch are configured at the node of the direct current transformer; the method also comprises the step of configuring a direct current breaker at nodes of the half-bridge MMC converter station, wherein the lower limit of the inductance value of a current-limiting reactor, the lower limit of the quench resistance value of the superconducting current limiter, the withstand voltage value of the capacitance separation switch and the withstand voltage value of the direct current breaker at each node are determined according to converter station parameters and line parameters;

and the configuration optimization unit is used for determining a cost function according to the relation between various devices and the short-circuit current level, solving the optimal short-circuit current level which meets the economic and safety requirements simultaneously based on the cost function, and determining the primary circuit configuration of the direct-current power distribution network according to the optimal short-circuit current level.

7. The primary loop configuration system for suppressing fault currents in a direct current distribution network of claim 6, wherein 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 Decay time constant of discharge current of MMC capacitor, U _dc Is a pre-fault DC voltage, C ₀ Is the sub-module capacitance value, n is the bridge armNumber of modules, L _bridge For bridge arm reactor inductance value, L _r For the inductance value of the current-limiting reactor, omega is the angular frequency of the discharge current oscillation, I ₀ For outputting direct current, I, to the MMC at the moment before the fault _{c_MMC} Short-circuit fault current before locking for full-bridge MMC converter station, I _max1 An upper limit is allowed for the fault current before latching.

8. The primary loop configuration system for suppressing fault currents in a direct current distribution network according to claim 6, wherein 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} Bridge arm current at the moment of locking of half-bridge MMC converter station, L _bridge Is bridge arm inductance, R _L Is a discharge loop resistance value, R _SR Being the quench resistance of a superconducting current limiter, I _{MMC_bridge} For bridge arm follow current of half-bridge MMC converter station, I _max2 The maximum breaking current of the direct current breaker.

9. The primary loop configuration system for suppressing fault currents in a direct current distribution network of claim 6, wherein 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 The discharge current of the DC transformer capacitor has a very short decay time, U _dc For pre-fault DC voltages, omega _d Oscillating angular frequency, L, of discharging current for capacitor of DC transformer _s Is an equivalent inductance value of the discharge circuit, L _r For current-limiting reactor inductance values, i _{c_DCT} For discharging current of DC transformer capacitor, t ₁ For the inverter blocking moment, I _max3 To blockThe allowable upper limit of the fault current before the current.

10. The primary loop configuration system for suppressing fault current of a direct-current power distribution network according to claim 6, wherein the configuration optimization unit determines a cost function according to a relation between various devices and a short-circuit current level, and finds an optimal short-circuit current level that satisfies both economic and safety requirements based on the cost function, specifically comprising:

establishing a cost function of the current limiting device and the DC breaker and the short circuit current level, respectively, denoted as f (I) _k ) And g (I) _k ) Where f (-) is the current limiting equipment cost, g (-) is the DC breaker cost, I _k For short circuit current level, the current limiting device comprises a current limiting reactor and a superconducting current limiter;

finding I _k0 So that f' (I) _k0 )+g′(I _k0 ) 0, where f '(. cndot.) and g' (. cndot.) are the equipment cost derivative to the short-circuit current level, and I _k0 To meet the optimum short circuit current level required for economy and safety at the same time.

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