An environmental state driven neutral point impedance robust configuration method and system for coastal low-voltage IT systems

Abstract

This invention relates to a robust configuration method and system for neutral point impedance in a coastal low-voltage IT system driven by environmental conditions, comprising the following steps: Step 1: Based on the environmental and operational data of the coastal low-voltage IT system, establish a coastal environmental grounding resistance model and an insulation resistance model, construct a hierarchical electrical model corresponding to the two resistance models, including unified calculation and analysis of normal operation and initial grounding fault conditions; construct a dual-factor environmental condition for protective grounding path and insulation, design a cross-state scanning and safety verification method for candidate neutral point impedance, and determine the feasibility of candidate neutral points based on safety thresholds; Step 3: Obtain the common robust feasible region of candidate neutral point impedances and record failure states and triggering constraints, design a safety margin balancing optimization method based on the Pareto-max-min criterion, realize failure tracing of candidate configurations, and obtain the optimal neutral point impedance configuration result. This invention considers practical engineering applications, not only solving the problems of traditional configuration methods being difficult to adapt to changes in the coastal environment and ensure long-term operational stability, but also realizing configuration failure tracing and cross-state safety margin balancing, providing parameter basis for equipment selection, engineering configuration, and operational verification.

Description

Technical Field

[0002] This invention belongs to the field of grounding protection technology for low-voltage power distribution systems, specifically relating to a robust configuration method and system for neutral point impedance in a coastal low-voltage IT system driven by environmental conditions. Background Technology

[0004] With the development of island renewable energy microgrids, coastal industrial power distribution, and other continuous power supply scenarios, low-voltage IT systems have good application value due to their relatively small initial ground fault current and ability to maintain a certain degree of power supply continuity in conjunction with insulation monitoring. However, coastal areas are subject to long-term effects such as humidity, salt spray, low temperature, freeze-thaw cycles, and aging, causing continuous changes in the protective grounding path status and the insulation status relative to ground. At the same time, the connection of renewable energy converters, multi-feeder loads, and filter capacitors can also alter the system's ground capacitance and the unbalanced injection of the neutral-to-ground network, resulting in significant operating condition correlations in safety indicators such as neutral point displacement, initial ground fault current, and contact voltage.

[0005] To address this, a fixed neutral point impedance branch can be set between the system neutral point and ground to adjust the characteristics of the neutral point-to-ground network and conduct operational and fault safety verification. However, traditional impedance configuration methods often determine parameters based on single indicators under nominal conditions, making it difficult to reflect the common constraints of different environmental conditions on the configuration boundary. Furthermore, even if multiple candidate configurations meet all safety constraints, their three safety margins are not the same, and over-optimization of any one indicator may make other indicators weak points.

[0006] Currently, there are three main problems:

[0007] (1) The traditional nominal operating impedance configuration method is difficult to adapt to changes in coastal environmental conditions:

[0008] Traditional neutral point impedance configurations typically select parameters based on a single typical operating condition, failing to adequately consider the continuous drift of protective grounding path resistance and ground insulation state caused by factors such as humid heat, salt spray, low-temperature freeze-thaw cycles, and operational aging in coastal areas. This type of configuration cannot reflect the changes in neutral point-to-ground network characteristics under the combined effects of grounding path degradation, insulation asymmetry, and disturbances from new energy operation. It can easily lead to problems such as increased neutral point displacement, excessive fault current, or insufficient contact voltage margin in fixed impedance branches under certain environmental conditions, making it difficult to guarantee long-term operational safety and stability.

[0009] (2) The existing configuration verification results lack cross-state failure tracing capabilities and are difficult to support engineering review and operation and maintenance decisions:

[0010] Existing neutral point impedance configuration methods typically only provide whether a certain parameter combination meets voltage and current limits under single or limited operating conditions. They lack a unified recording and interpretation mechanism for the failure causes of candidate configurations under different grounding path states, insulation asymmetry states, and composite environmental states. When the configuration does not meet the requirements, it is difficult to further identify its corresponding failure environment state and whether the dominant triggering constraint is neutral point displacement, first ground fault current, or contact voltage. This results in a static conclusion of "usable" or "unusable," failing to form a traceable correlation between "candidate configuration - failure environment state - triggering safety constraint," which is not conducive to equipment selection review, subsequent status monitoring, and targeted operation and maintenance.

[0011] (3) The problem of uneven distribution of safety margin when selecting impedance parameters using the traditional nominal operating condition impedance configuration method:

[0012] In configuration processes primarily based on target ground fault current, single-phase neutral point voltage limits, or empirical impedance ranges, parameter selection often focuses on meeting a single dominant metric, or simply determining whether a candidate configuration passes all thresholds. Even if multiple candidate configurations meet neutral point displacement, initial ground fault current, and contact voltage constraints, their safety margins may still differ significantly under different environmental conditions. When one metric is over-optimized, other metrics may approach their limits, creating new safety vulnerabilities. Therefore, relying solely on "feasibility" or single-metric optimization as the configuration criterion makes it difficult to obtain fixed neutral point impedance branches with high safety margins across states and constraints. Summary of the Invention

[0014] This invention addresses the problems of existing technologies by proposing a robust neutral point impedance configuration method and system for environmentally driven coastal low-voltage IT systems. This invention is achieved through the following technical solutions:

[0015] A robust configuration method and system for neutral point impedance in a coastal low-voltage IT system based on environment conditions, comprising the following steps:

[0016] Step 1: Based on the environmental and operational data of the coastal low-voltage IT system, establish a coastal environmental grounding resistance model and an insulation resistance model, and construct a hierarchical electrical model corresponding to the two resistance models, including unified calculation and analysis of normal operation and initial grounding fault conditions.

[0017] Step 2: Construct the protective grounding path-insulation dual-factor environmental state, design a cross-state scanning and safety verification method for candidate neutral point impedance, and determine the feasibility of candidate neutral points based on safety thresholds;

[0018] Step 3: Obtain the common robust feasible region of candidate neutral point impedances and record the failure state and triggering constraints. Design a safety margin equalization optimization method based on the Pareto-max-min criterion to realize the failure source of candidate configurations and obtain the optimal neutral point impedance configuration result.

[0019] Furthermore, in step one, the specific methods for establishing the coastal environmental grounding resistance model and insulation resistance model are as follows:

[0020] Considering the combined effects of actual factors such as temperature, humidity, salinity, operational aging, and historical environmental exposure, and combining relevant environmental parameter change data and electrical performance change patterns, an engineering equivalent model of protective grounding resistance and relative insulation resistance to ground is constructed for fitting and verification.

[0021] Regarding protective grounding resistance:

[0022]

[0023] In the formula, R g To protect the grounding resistance, R g0 For reference grounding resistance, t f D is the time when the fault occurs. hist For historical environmental exposure information, ρ env For the temperature T f θ f Salt state S f The obtained environmental equivalent resistivity, ρ ref For reference resistivity, F cor It is a corrosion or degradation correction factor.

[0024] Regarding insulation resistance:

[0025]

[0026] In the formula, R ins,k R is the insulation resistance to ground of phase k. ins0 For reference insulation resistance, Φ ins,k F is the composite environmental insulation retention factor of phase k. T,k F H,k F S,k F age,k These represent temperature, humidity, salt pollution, and aging correction factor, respectively.

[0027] Furthermore, in step one, the method for establishing the hierarchical electrical model corresponding to the resistance model is as follows:

[0028] For normal operation, assuming any phase k∈{a,b,c}, the phase branch admittance of the normal admittance layer is:

[0029]

[0030] In the formula, Y ins,k For phase k, the relative ground insulation-capacitance admittance, C ph Y is the equivalent capacitance to ground for each phase. leak,total ω represents the total leakage admittance between the three phases and ground, j is the imaginary unit, and ω is the angular frequency.

[0031] Based on the above three-phase relative leakage total admittance Y leak,total The impedance, admittance, and normal IT system admittance to ground of the fixed series RL neutral point impedance branch are as follows:

[0032]

[0033] In the formula, Z n To fix the series resistance—the neutral point branch impedance of the reactor, R n For the neutral point resistance, L n For the reactor inductance, Y n For the neutral point branch admittance, Y IT This is the equivalent admittance of a normal IT system to ground.

[0034] When there is asymmetry in insulation condition, capacitance to ground, or external operating disturbance, an equivalent unbalanced injection will be formed. Further calculation of the neutral point displacement voltage caused by this unbalanced injection is required.

[0035]

[0036] In the formula, V n I is the neutral point displacement voltage. unb,total The total disturbance current injected into the neutral-ground equivalent network.

[0037] For the initial ground fault condition, let the faulty phase be p, and the other two phases be q and r. Define the phase-specific transfer admittance and the ground node driving point admittance as follows:

[0038]

[0039] In the formula, p represents the faulty phase, q and r represent the non-faulty phases, and Y tr,p Y is the transfer admittance corresponding to the fault phase p. dp,p U is the admittance of the ground node driving point corresponding to the fault phase p. p U q U r These are the phase voltage phasors for the corresponding phases, Y ins,q and Y ins,r These are the ground insulation-capacitance admittances of the non-faulty phases q and r, respectively.

[0040] The resistance of the grounding device and the resistance of the protective conductor are combined and defined as the comprehensive resistance R of the protective grounding.A :

[0041]

[0042] In the formula, R PE To protect the conductor's resistance.

[0043] Then the initial ground fault current and contact voltage corresponding to the faulty phase p are:

[0044]

[0045] In the formula, I d,p I is the fault current when the faulty phase p experiences its first ground fault. d U is the maximum initial ground fault current in the three phases. T This is the contact voltage.

[0046] Furthermore, in step two, the method for constructing the protective grounding path-insulation two-factor environmental state is as follows:

[0047] The environmental condition of the coastal low-voltage IT system is broken down into two combinable factors. The first factor is the protective grounding path condition G, where G0 represents the reference grounding path condition, corresponding to the reference grounding resistance R. g and protective conductor resistance R PE The lower R constituted A The range, G1, represents the R range constructed jointly by historical environmental data, operation and maintenance information, and environmental grounding resistance model. g Increase, thus making R A An increased scope of representation.

[0048] The second type of factor is the insulation state I, where I0 represents an approximately symmetrical three-phase insulation state, and I1 represents an asymmetrical state in which the insulation of at least one phase is significantly reduced. The difference between the symmetrical reference admittance and the actual admittance introduces an environmental unbalanced current I. env :

[0049]

[0050] In the formula, U a U b U c For three-phase phase voltage phasors, ΔY a ΔY b ΔY c For the three-phase relative admittance deviation, Y ref,k Let k be the symmetric reference admittance.

[0051] The total disturbance current is:

[0052]

[0053] In the formula, I unb,PV Inject the equivalent unbalanced current of the neutral point-to-ground network into new energy sources or operational disturbances.

[0054] The above two factors form four environmental states: E1 = (G0, I 0) E2 = (G0, I1), E3 = (G1,I0), E4 = (G1, I1), where E1 to E4 are four environmental states formed by the combination of the two factors G and I.

[0055] Furthermore, in step two, the design method for the candidate neutral point impedance transstate sweep and safety check is as follows:

[0056] Candidate neutral point impedance points x = (R) are generated within the preset neutral point resistance range and reactor inductance range. n ,L n );

[0057] For any candidate neutral point impedance point x, calculate its neutral point displacement voltage, first ground fault current and contact voltage under various environmental conditions based on the normal operation state and the first ground fault state.

[0058] Define three types of feasibility predicates: neutral point displacement, initial ground fault current, and touch voltage.

[0059]

[0060] In the formula, e represents the environmental state, x represents the candidate neutral point impedance, and p V (e,x), p I (e,x), p U (e,x) represent the feasibility predicates for neutral point displacement, initial ground fault current, and contact voltage under state e and candidate point x, respectively. lim I lim U lim These are the neutral point displacement operating threshold, the first ground fault current threshold, and the contact voltage threshold, respectively.

[0061] The comprehensive feasibility definition of candidate point x under each environmental state e is as follows:

[0062]

[0063] In the formula, Rec(e,x) is the comprehensive feasibility predicate of candidate point x under state e, and the symbol ∧ represents the logical "and".

[0064] Furthermore, in step three, the method for determining the common robust feasible region, failure states, and triggering constraints is as follows:

[0065] The common robust feasible region is obtained by intersecting the feasible regions of all states:

[0066]

[0067] For those not entering the public robust feasible region Ω robust The candidate neutral point impedance point is recorded, and the environmental state in which it does not meet the comprehensive feasibility judgment is recorded, and the safety constraint that triggers the failure to meet the judgment is also recorded.

[0068] The triggering safety constraints include at least one of neutral point displacement constraints, first ground fault current constraints, and contact voltage constraints.

[0069] Furthermore, in step three, the safety margin equilibrium optimization method based on the Pareto-max-min criterion is specifically as follows:

[0070] Within the common robust feasible region, the following normalization margin is adopted:

[0071]

[0072] In the formula, S V (x), S I (x), S U (x) represents the normalized margin of candidate point x under the constraints of neutral point displacement, first ground fault current and contact voltage. The maximum value operation in the equation represents taking the maximum value for all environmental states e.

[0073] The weakest margin of the candidate point is:

[0074]

[0075] In the formula, S min (x) represents the weakest normalization margin of candidate point x, and min{·} represents taking the minimum value among the three margins.

[0076] For any two candidate points x1 and x2 within the common robust feasible region, when S V (x1) ≥ S V (x2), S I (x1)≥ S I (x2), S U (x1) ≥ S U If x1 is Pareto-dominated by x2, and at least one of them is strictly greater than x2, then x1 is said to be Pareto-dominated by x2. The Pareto non-dominated candidate set P is composed of all candidate points that are not Pareto-dominated by other candidate points.

[0077] Within the Pareto non-dominated candidate set P, choose:

[0078]

[0079] In the formula, x* is the finally selected fixed series RL branch configuration point, R n * and L n *These represent the selected neutral point resistor and reactor inductance, respectively.

[0080] The present invention also relates to an environment-state driven robust neutral point impedance configuration system for a coastal low-voltage IT system, comprising a computer module that utilizes an environment-state driven robust neutral point impedance configuration method for a coastal low-voltage IT system.

[0081] Beneficial effects

[0082] This invention considers the impact of coastal environmental changes, grounding path degradation, insulation asymmetry, and operational disturbances on the neutral-to-ground network of low-voltage IT systems. It proposes an environment-state-driven robust neutral-point impedance configuration method and system for coastal low-voltage IT systems to achieve cross-state safety configuration and margin optimization for fixed series RL branches. The main contents include:

[0083] (1) Based on the coastal environment exposure, grounding path degradation and insulation state change patterns, establish a coastal environment grounding and insulation resistance model and a low-voltage IT system hierarchical model.

[0084] Unlike traditional methods that treat protective grounding resistance and insulation resistance as fixed equivalent parameters, this invention maps factors such as temperature, humidity, salt contamination, and operational aging into equivalent parameters of protective grounding resistance and insulation resistance to ground. It also separates the calculation of normal neutral point displacement from the calculation of initial grounding fault safety, reflecting the characteristics of the neutral point-to-ground network under changing environmental conditions, and providing a basis for the robust configuration of fixed series RL branches.

[0085] (2) Unlike the traditional configuration method that only verifies based on a single nominal operating condition, a G / I two-factor environmental state and full-state candidate neutral point impedance scanning mechanism is constructed.

[0086] To address the problem that traditional configurations typically only verify single or limited typical operating conditions and are difficult to reveal the causes of cross-state failures, this invention constructs states E1 to E4 using protective grounding path state G and insulation state I, and sets a preset R... n -L n The neutral point displacement, initial ground fault current, and contact voltage are calculated point by point for each candidate branch within the range, forming a failure tracing result of "candidate configuration - environmental state - triggering constraint".

[0087] (3) Based on the common robust feasible region and the Pareto-max-min criterion, the parameters of the fixed series RL neutral point branch are further optimized, which effectively solves the problems of difficulty in adapting to changes in coastal environmental conditions and uneven distribution of safety margin.

[0088] This invention addresses the problem that while multiple candidate configurations may pass the safety threshold, their safety margins are uneven. First, the intersection of candidate points that satisfy the three constraints in states E1 to E4 is taken to obtain a common robust feasible region. Then, the normalized margins of the three indicators are compared, Pareto dominance points are eliminated, and the configuration with the weakest margin is selected, so that the fixed branch takes into account cross-state safety, margin balance, and engineering repeatability. Attached Figure Description

[0090] Figure 1 This is a schematic diagram of the hierarchical electrical model of a low-voltage IT system with a fixed series RL neutral point branch according to the present invention;

[0091] Figure 2 A matrix diagram of two-factor environmental conditions, namely the protective grounding path state and the insulation state, is constructed for this invention.

[0092] Figure 3 This is a flowchart of the environmental condition-driven method for robust neutral point impedance configuration in a coastal low-voltage IT system according to the present invention.

[0093] Figure 4 This is a diagram showing the common robust feasible region and dominant safety boundary distribution of the candidate neutral point impedances of this invention.

[0094] Figure 5 This is a diagram showing the normalized weakest margin distribution and Pareto-max-min preferred configuration location within the common robust feasible region of this invention.

[0095] Figure 6 This is a comparison diagram of the cross-state feasibility of the traditional baseline configuration and the fixed series RL configuration of the present invention. Detailed Implementation

[0097] The following is in conjunction with the appendix Figures 1 to 6 The present invention further details a method and system for robust neutral point impedance configuration in an environment-state driven coastal low-voltage IT system.

[0098] The present invention provides a robust neutral point impedance configuration method for an environment-state driven coastal low-voltage IT system, which mainly includes the following steps:

[0099] Step 1: Based on the environmental and operational data of the coastal low-voltage IT system, establish a coastal environmental grounding resistance model and an insulation resistance model, and construct a hierarchical electrical model corresponding to the two resistance models, including unified calculation and analysis of normal operation and initial grounding fault conditions.

[0100] The grounding resistance model and insulation resistance model are as follows:

[0101] Regarding protective grounding resistance:

[0102]

[0103] In the formula, R g To protect the grounding resistance, R g0 For reference grounding resistance, t f D is the time when the fault occurs. hist For historical environmental exposure information, ρ env For the temperature T f θ f Salt state S f The obtained environmental equivalent resistivity, ρ ref For reference resistivity, F cor It is a corrosion or degradation correction factor.

[0104] Among them, the environmental equivalent resistivity ρ env The resistivity is determined based on the temperature, moisture content or humidity, and salinity at the time of the fault. For discrete temperature-moisture content data, the natural logarithm of resistivity is linearly interpolated between adjacent data points, and the corresponding resistivity is obtained by exponential restoration. The effect of salinity is normalized by the resistivity response ratio of the target salinity state relative to the reference salinity state.

[0105] Regarding insulation resistance:

[0106]

[0107] In the formula, R ins,k R is the insulation resistance to ground of phase k. ins0 For reference insulation resistance, Φ ins,k F is the composite environmental insulation retention factor of phase k. T,k F H,k F S,k F age,k These represent temperature, humidity, salt pollution, and aging correction factor, respectively.

[0108] The temperature, humidity, salt contamination, and aging correction factors are determined based on relevant experimental data, electrical performance variation patterns, historical monitoring data, or fitting relationships. When the target environmental parameters are located between discrete data points, the corresponding correction factors are obtained through interpolation. Different phases can use different correction factors based on their local moisture, salt contamination, defects, and aging levels to obtain the relative insulation resistance to ground of each phase and characterize the symmetrical or asymmetrical state of the three-phase insulation.

[0109] The hierarchical electrical model corresponding to the two resistance models is:

[0110] For normal operation, assuming any phase k∈{a,b,c}, the phase branch admittance of the normal admittance layer is:

[0111]

[0112] In the formula, Y ins,k For phase k, the relative ground insulation-capacitance admittance, C ph Y is the equivalent capacitance to ground for each phase. leak,total ω represents the total leakage admittance between the three phases and ground, j is the imaginary unit, and ω is the angular frequency.

[0113] Based on the above three-phase relative leakage total admittance Y leak,total The impedance, admittance, and normal IT system admittance to ground of the fixed series RL neutral point impedance branch are as follows:

[0114]

[0115] In the formula, Z n To fix the series resistance—the neutral point branch impedance of the reactor, R n For the neutral point resistance, L n For the reactor inductance, Y n For the neutral point branch admittance, Y IT This is the equivalent admittance of a normal IT system to ground.

[0116] When there is asymmetry in insulation condition, capacitance to ground, or external operating disturbance, an equivalent unbalanced injection will be formed. Further calculation of the neutral point displacement voltage caused by this unbalanced injection is required.

[0117]

[0118] In the formula, V n I is the neutral point displacement voltage. unb,total The total disturbance current injected into the neutral-ground equivalent network.

[0119] For the initial ground fault condition, let the faulty phase be p, and the other two phases be q and r. Define the phase-specific transfer admittance and the ground node driving point admittance as follows:

[0120] ;

[0121] In the formula, p represents the faulty phase, q and r represent the non-faulty phases, and Y tr,p Y is the transfer admittance corresponding to the fault phase p. dp,p U is the admittance of the ground node driving point corresponding to the fault phase p. p U q U r These are the phase voltage phasors for the corresponding phases, Y ins,q and Y ins,r These are the ground insulation-capacitance admittances of the non-faulty phases q and r, respectively.

[0122] The resistance of the grounding device and the resistance of the protective conductor are combined and defined as the comprehensive resistance R of the protective grounding. A :

[0123] ;

[0124] In the formula, R PE To protect the conductor's resistance.

[0125] Then the initial ground fault current and contact voltage corresponding to the faulty phase p are:

[0126] ;

[0127] In the formula, I d,p I is the fault current when the faulty phase p experiences its first ground fault. d U is the maximum initial ground fault current in the three phases. T This is the contact voltage.

[0128] Step 2: Construct the protective grounding path-insulation dual-factor environmental state, design a cross-state scanning and safety verification method for candidate neutral point impedance, and determine the feasibility of candidate neutral points based on safety thresholds;

[0129] The method for constructing the protective grounding path-insulation two-factor environmental state is as follows:

[0130] The environmental condition of the coastal low-voltage IT system is broken down into two combinable factors. The first factor is the protective grounding path condition G, where G0 represents the reference grounding path condition, corresponding to the reference grounding resistance R. g and protective conductor resistance R PE The lower R constituted A The range, G1, represents the R range constructed jointly by historical environmental data, operation and maintenance information, and environmental grounding resistance model. g Increase, thus making R A An increased scope of representation.

[0131] The second type of factor is the insulation state I, where I0 represents an approximately symmetrical three-phase insulation state, and I1 represents an asymmetrical state in which the insulation of at least one phase is significantly reduced. The difference between the symmetrical reference admittance and the actual admittance introduces an environmental unbalanced current I. env :

[0132] ;

[0133] In the formula, U a U b U c For three-phase phase voltage phasors, ΔY a ΔY b ΔY c For the three-phase relative admittance deviation, Yref,k Let k be the symmetric reference admittance.

[0134] The total disturbance current is:

[0135] ;

[0136] In the formula, I unb,PV Inject the equivalent unbalanced current of the neutral point-to-ground network into new energy sources or operational disturbances.

[0137] The above two factors form four environmental states: E1 = (G0, I 0) E2 = (G0, I1), E3 = (G1,I0), E4 = (G1, I1), where E1 to E4 are four environmental states formed by the combination of the two factors G and I.

[0138] For any environmental state e, the corresponding protective grounding resistance R g , Protective conductor resistance R PE Three-phase to ground insulation resistance R ins,a R ins,b and R ins,c Three-phase ground capacitance C sum and total disturbance current I unb,total The state parameter set is formed and used as the state input for calculating the candidate neutral point impedance.

[0139] The method for cross-state scanning and safety verification of candidate neutral point impedance is as follows:

[0140] Within the preset neutral point resistance range and reactor inductance range, candidate neutral point impedance points x = (R) are discretized and generated according to equal spacing, logarithmic spacing, adaptive spacing, or combinations thereof. n ,L n );

[0141] For any candidate neutral point impedance point x, calculate its neutral point displacement voltage, first ground fault current and contact voltage under various environmental conditions based on the normal operation state and the first ground fault state.

[0142] Define three types of feasibility predicates: neutral point displacement, initial ground fault current, and touch voltage.

[0143] ;

[0144] In the formula, e represents the environmental state, x represents the candidate neutral point impedance, and p V (e,x), p I (e,x), p U(e,x) represent the feasibility predicates for neutral point displacement, initial ground fault current, and contact voltage under state e and candidate point x, respectively. lim I lim U lim These are the neutral point displacement operating threshold, the first ground fault current threshold, and the contact voltage threshold, respectively.

[0145] The same system rated voltage, frequency, candidate impedance range and safety threshold are used for all environmental conditions to ensure that the calculation results under different conditions adopt a unified evaluation caliber.

[0146] The comprehensive feasibility definition of candidate point x under each environmental state e is as follows:

[0147] ;

[0148] In the formula, Rec(e,x) is the comprehensive feasibility predicate of candidate point x under state e, and the symbol ∧ represents the logical "and".

[0149] Step 3: Obtain the common robust feasible region of candidate neutral point impedances and record the failure state and triggering constraints. Design a safety margin equalization optimization method based on the Pareto-max-min criterion to realize the failure source of candidate configurations and obtain the optimal neutral point impedance configuration result.

[0150] The method for determining the common robust feasible region, failure states, and triggering constraints is as follows:

[0151] The common robust feasible region is obtained by intersecting the feasible regions of all states:

[0152]

[0153] For those not entering the public robust feasible region Ω robust The candidate neutral point impedance point is recorded, and the environmental state in which it does not meet the comprehensive feasibility judgment is recorded, and the safety constraint that triggers the failure to meet the judgment is also recorded.

[0154] The triggering safety constraints include at least one of neutral point displacement constraints, first ground fault current constraints, and contact voltage constraints.

[0155] Within the common robust feasible region, the following normalization margin is adopted:

[0156]

[0157] In the formula, S V (x), S I (x), S U(x) represents the normalized margin of candidate point x under the constraints of neutral point displacement, first ground fault current and contact voltage. The maximum value operation in the equation represents taking the maximum value for all environmental states e.

[0158] The weakest margin of the candidate point is:

[0159]

[0160] In the formula, S min (x) represents the weakest normalization margin of candidate point x, and min{·} represents taking the minimum value among the three margins.

[0161] For any two candidate points x1 and x2 within the common robust feasible region, when S V (x1) ≥ S V (x2), S I (x1)≥ S I (x2), S U (x1) ≥ S U If x1 is Pareto-dominated by x2, and at least one of them is strictly greater than x2, then x1 is said to be Pareto-dominated by x2. The Pareto non-dominated candidate set P is composed of all candidate points that are not Pareto-dominated by other candidate points.

[0162] Finally, within the Pareto non-dominated candidate set P, the following is selected:

[0163]

[0164] In the formula, x* is the finally selected fixed series RL branch configuration point, R n * and L n *These represent the selected neutral point resistor and reactor inductance, respectively.

[0165] Example

[0166] 1. Calculation of environmental electrical parameters and input of hierarchical model

[0167] This embodiment uses historical environmental data from a coastal area during the cold season over many years, including surface soil temperature, water content or humidity, and salinity at the time of the fault. It combines this data with grounding device testing results, corrosion status, and maintenance records to determine the protective grounding path parameters. For temperature and humidity combinations not directly provided in the environmental data, the aforementioned logarithmic interpolation method is used to determine the corresponding environmental equivalent resistivity. For the influence of salinity, the resistivity response ratio of the target salinity state relative to the reference salinity state is used for correction.

[0168] Substitute the above data into the aforementioned protective grounding resistance model. For the baseline protective grounding path state G0, the range of protective grounding resistance under moderate environmental exposure conditions is taken as: Rg =1.24~1.38 Ω.

[0169] For the protective grounding path degradation state G1, based on the aforementioned cold season environmental data and soil condition conversion results, the representative value of the protective grounding resistance at the time of the fault occurrence is: R g = 5.02 Ω. Based on this, considering the corrosion of the grounding device and the degradation of the grounding path caused by long-term action in a wet saline environment, a corrosion or degradation correction factor is taken: F cor =1.280, therefore the upper limit of the grounding resistance in the degraded state of the protective grounding path is: R g =5.02×1.280≈6.43 Ω.

[0170] Therefore, in this embodiment, the protective grounding resistance range for state G1 is taken as 5.02–6.43 Ω. This range is used to characterize the unfavorable engineering envelope of the protective grounding path under the combined effects of soil conditions and historical wet salt corrosion at the time of the fault.

[0171] For the phase-to-ground insulation state, this embodiment uses 1 MΩ as the reference value for the three-phase phase-to-ground insulation resistance. Under the insulation symmetry state I0, the insulation retention factor of each phase composite environment is taken as 1, resulting in: R ins,a =R ins,b =R ins,c =1 MΩ.

[0172] Insulation asymmetry state I1 is used to characterize severe single-phase insulation degradation caused by localized moisture, salt contamination, insulation defects, or operational aging. Under this state, the composite environmental insulation retention factor for phase A is taken as: Φ ins,a =0.036, the composite environmental insulation retention factor of phase B and phase C remains at 1.

[0173] Based on the difference between the actual three-phase-to-ground admittance under state I1 and the symmetrical reference admittance under state I0, the environmental unbalanced current generated by insulation asymmetry is obtained according to the aforementioned method for calculating environmental unbalanced current: I env =6.159 mA.

[0174] After completing the above calculations of environmental electrical parameters, input the protective grounding resistance, protective conductor resistance, three-phase-to-ground insulation resistance, three-phase-to-ground capacitance, and total disturbance current. Figure 1 The layered electrical model shown.

[0175] Under normal operating conditions, the three-phase phase-to-ground insulation resistance and the corresponding phase-to-ground capacitance form a three-phase phase-to-ground insulation-capacitor branch; the three-phase branch admittance and the candidate fixed series RL neutral point branch admittance together constitute the normal to-ground admittance layer.

[0176] The protective grounding resistance is not included in the neutral point-to-ground admittance calculation under normal operating conditions. When the first ground fault occurs in phase A, phase B, or phase C, the protective grounding resistance and the protective conductor resistance together constitute the comprehensive protective grounding resistance and participate in the calculation of the first ground fault loop.

[0177] 2. Environmental condition construction, candidate neutral point impedance scanning and feasibility assessment

[0178] Based on the aforementioned calculation results of environmental electrical parameters, this embodiment combines the protective grounding path states G0 and G1 with the insulation states I0 and I1 to form four environmental states, E1 to E4, as follows: Figure 2 As shown.

[0179] Among them, E1 is the benchmark operating state formed by the symmetrical combination of the benchmark protective grounding path and the three-phase insulation; E2 is the insulation asymmetric influence state formed by the combination of the benchmark protective grounding path and the significant decrease in single-phase insulation; E3 is the grounding path degradation influence state formed by the combination of protective grounding path degradation and the symmetrical combination of three-phase insulation; and E4 is the combined engineering envelope state formed by the combined effect of protective grounding path degradation and the significant decrease in single-phase insulation.

[0180] The protective conductor resistance R in this embodiment PE Take 0.1 Ω. Adjust the protective grounding resistor R... g With the resistance R of the protective conductor PE By adding them together, we can obtain the range of comprehensive protective grounding resistance under different protective grounding path conditions.

[0181] Under E1 and E3 conditions, the insulation resistance between the three phases and ground is the same, the environmental unbalanced current is zero, and the total disturbance current is equal to the unbalanced current caused by the operation of new energy sources or other operational disturbances. Therefore, I unb,total Take 5~20 mA.

[0182] Under conditions E2 and E4, the insulation resistance of phase A to ground decreases to 0.036 MΩ, while the insulation resistance of phases B and C to ground remains at 1 MΩ. Following the aforementioned method for calculating environmental unbalanced current, I is obtained. env =6.159 mA, and this is added to the disturbance current of the new energy source operation to obtain I. unb,total =11.159~26.159 mA.

[0183] In this embodiment, the neutral point displacement operating threshold V is taken. lim =100 V, first ground fault current threshold I lim =1 A, Contact voltage threshold U lim =50 V. E1 to E4 use the same system rated parameters, ground capacitance values, candidate impedance ranges, and safety thresholds to ensure that the calculation results for each environmental condition are judged using a unified standard.

[0184] In R n =100~10000 Ω, L n Candidate points for the neutral point impedance of a fixed series RL circuit are generated within the range of 0 to 15 H, x = (R n L n ), where R n 121 sampling points were set using a logarithmic interval, L n Using a linear interval, 121 sampling points were set, resulting in a total of 121 × 121 = 14641 candidate points.

[0185] For any candidate neutral point impedance point x, substitute it into the four environmental states from E1 to E4 in sequence, and perform calculations according to the aforementioned hierarchical electrical model.

[0186] Under normal operating conditions, based on the candidate neutral point resistance R n Reactor Inductance L n Calculate the neutral point displacement voltage V under the corresponding environmental conditions, considering the three-phase phase-to-ground insulation-capacitor branch and the total disturbance current. n .

[0187] Under the initial ground fault condition, phases a, b, and c are set as fault phases respectively. The initial ground fault current and contact voltage corresponding to each fault are calculated, and the maximum value among the calculation results of the three fault phases is taken as the initial ground fault current I of the candidate point under the corresponding environmental condition. d and contact voltage U T .

[0188] For environmental state parameters given in the form of a range, calculations are performed according to the preset range of state parameters in this embodiment, and the most unfavorable calculation results under the corresponding environmental state are retained.

[0189] Subsequently, the neutral point displacement voltage, initial ground fault current, and contact voltage of each candidate point under each environmental condition are compared with three safety thresholds. If all three thresholds are less than the candidate point's value, the point is deemed feasible under the current environmental condition. If a candidate point fails to meet one or more of the above safety requirements, the corresponding environmental condition and triggering constraints are recorded. The neutral point displacement exceeding the limit is denoted as m. V The first ground fault current exceeding the limit is recorded as m. I The contact voltage exceeding the limit is recorded as m. U .

[0190] After the scan is completed, feasible candidate point sets are obtained under four environmental conditions, forming a candidate R set. n L nThe failure record includes the failure environment state, triggering constraints, and corresponding calculated values. The set of feasible candidate points for each state and the failure record serve as inputs for the next step of obtaining the common robust feasible region and optimizing the safety margin.

[0191] 3. Robust feasible region, failure state set, and Pareto-max-min selection

[0192] Since the fixed series RL neutral point branch in practical applications is not replaced or retuned online when the environmental state changes, this embodiment takes the intersection of the feasible candidate point sets under environmental states E1 to E4 according to the aforementioned common robust feasible region acquisition method to obtain a common robust feasible region that can simultaneously meet the safety requirements of all environmental states.

[0193] For candidate points that do not enter the common robust feasible region, record their corresponding neutral point resistance R. n Reactor Inductance L n The environmental conditions that fail the safety assessment and the triggered safety constraints. The triggered constraints include at least one of the following: neutral point displacement constraint, first ground fault current constraint, and contact voltage constraint.

[0194] When the same candidate point fails to meet the requirements under multiple environmental conditions, the corresponding environmental conditions are collectively recorded as the failure state set of the candidate point. When the same candidate point triggers multiple safety constraints simultaneously, each triggering constraint is recorded separately. This establishes a correspondence between the candidate neutral point impedance point, the failure environmental state, and the triggering safety constraints.

[0195] For candidate points within the common robust feasible region, the normalized margins for neutral point displacement, initial ground fault current, and contact voltage are calculated using the aforementioned normalized margin calculation method. Each normalized margin is determined using the most unfavorable response value of the candidate point under all environmental conditions from E1 to E4.

[0196] Subsequently, candidate points within the common robust feasible region are screened according to the aforementioned Pareto dominance relation, and candidate points that are dominated by other candidate points in the three normalization margins are eliminated to obtain the Pareto non-dominated candidate set.

[0197] For each candidate point in the Pareto non-dominated candidate set, the minimum of the three normalization margins is taken as the weakest normalization margin of the candidate point, and the candidate point with the largest weakest normalization margin is selected as the preferred configuration of the fixed series RL neutral point branch.

[0198] After the above processing, the preferred neutral point impedance parameter obtained in this embodiment is: R n * = 962.351 Ω, L n* =0.25 H.

[0199] The computer module outputs the preferred parameters and simultaneously outputs the common robust feasible region, the failure state set of each candidate point, triggering constraints, three normalization margins, the weakest normalization margin, and the dominant environmental state and dominant constraints, which are used for subsequent equipment selection, engineering configuration and operation verification.

[0200] When the standard parameters of the actual equipment cannot be completely consistent with the preferred parameters, the engineering standard parameters adjacent to the preferred point are selected in the common robust feasible domain, and the safety verification of all states from E1 to E4 is carried out again in accordance with the aforementioned method.

[0201] This embodiment presents a complete process from environmental electrical parameter calculation, environmental state construction, candidate neutral point impedance scanning, state-by-state feasibility assessment, common robust feasible region determination, failure tracing to parameter optimization, as follows: Figure 3 As shown.

[0202] Effect verification

[0203] This embodiment uses a three-phase 400 V line voltage, 230 V phase voltage, 50 Hz coastal low-voltage IT system as the calculation object; the total three-phase capacitance to ground is taken as C. sum = 0.3 μF, capacitor per phase according to C ph = C sum / 3 enters the phase branch. The range of the new energy disturbance current is taken as I. unb,PV = 5-20 mA, R PE Take 0.1 Ω.

[0204] In addition, this embodiment is based on the historical environmental data of a coastal area during the cold season over many years. Combined with the regional temperature and humidity conditions, the impact of salt pollution, and the historical degradation information of grounding path and insulation asymmetry, various environmental states are constructed. Table 1 shows the parameter table for each environmental state.

[0205] Table 1 Environmental Status Parameters for E1-E4

[0206] <![CDATA[E1]]> <![CDATA[G0,I0]]> 1.24-1.38 1 / 1 / 1 0 5-20 Baseline operating status <![CDATA[E2]]> <![CDATA[G0,I1]]> 1.24-1.38 0.036 / 1 / 1 6.159 11.159-26.159 Insulation Asymmetric Effect State <![CDATA[E3]]> <![CDATA[G1,I0]]> 5.02-6.43 1 / 1 / 1 0 5-20 Grounding path degradation affects status <![CDATA[E4]]> <![CDATA[G1,I1]]> 5.02-6.43 0.036 / 1 / 1 6.159 11.159-26.159 Combined engineering envelope state

[0207] In this embodiment, V is taken. lim =100 V、I lim =1 A、U lim =50 V. Where 100 V is the neutral point displacement operating threshold in this embodiment, 1 A is the upper limit of the fixed neutral point branch design and the nominal comparison target in this embodiment, and 50 V is the contact voltage threshold in this embodiment. Furthermore, for ease of explanation, m V m I and m UThese represent neutral point displacement constraint, initial ground fault current constraint, and contact voltage constraint, respectively.

[0208] Under the aforementioned state parameters and safety thresholds, for R n = 100–10000 Ω, L n A full-state scan is performed on a candidate grid of 0–15 H. The candidate parameters can be discretized using equal spacing, logarithmic spacing, adaptive spacing, or a combination thereof. In this embodiment, R n Using 121 sampling points with logarithmic intervals, L n 121 sampling points with linear spacing were used. The common robust feasible region contains 6630 candidate points, accounting for 45.284% of the total 14641 candidate points.

[0209] To reveal the dominant security boundary of candidate configurations, Figure 4 Furthermore, the dominant failure states and constraint partitions of the common robust feasible region and its external candidate points are given.

[0210] Figure 4 This indicates that, under the engineering parameter envelope of this embodiment, the insulation asymmetry state E2 constitutes the dominant limiting state for candidate neutral point impedance configuration by increasing the unbalanced injection of the neutral-to-ground network, and the neutral point displacement constraint determines the main boundary of the common robust feasible region; only in the low impedance, low inductance region does the first ground fault current constraint form a supplementary boundary. In contrast, the protective grounding path degradation has a relatively small impact on the feasible region boundary and area, but it will increase the contact voltage under the first ground fault and reduce its safety margin.

[0211] Therefore, the present invention sets up protective grounding path state and insulation state respectively, which can identify the key states and key constraints that determine the configuration boundary, and reflect the degradation factors that affect the safety margin within the feasible domain, thus avoiding the omission of the limiting effects of different environmental factors when using a single comprehensive harsh operating condition.

[0212] Based on this, Figure 4 The common robust feasible region shown is further optimized using the Pareto-max-min criterion, and the results are as follows: Figure 5 As shown.

[0213] Based on the Pareto-max-min criterion, the neutral point branch parameter of the fixed series resistor-reactor obtained in this embodiment is R. n * = 962.351 Ω, L n *= 0.25 H. The selected configuration in this embodiment meets the constraints in all four states from E1 to E4; the maximum neutral point displacement voltage is 24.6301 V, the maximum first ground fault current is 0.247076 A, the maximum contact voltage is 1.605091 V, the normalized weakest margin is 0.752924, and the dominant constraint is the first ground fault current constraint in state E2.

[0214] To further verify the cross-state robustness of the selected configuration and its engineering advantages relative to different configurations, the fixed series RL configuration of the present invention is compared with the traditional nominal tuning benchmark tuned according to the pure IT reference and the three safety thresholds and evaluation criteria under the same E1 to E4 environmental conditions, three safety thresholds and evaluation criteria. Figure 6 From the perspectives of full-state feasibility coverage and weakest normalization margin, this study examines the comprehensive adaptability of different configurations to neutral point displacement, first ground fault current, and contact voltage constraints, and further reveals the configuration effect of the transformation from "feasible under a single nominal condition" to "safe and available across states".

[0215] Figure 6 This indicates that while the pure IT reference has a smaller first-ground fault current, it is limited by neutral point displacement constraints under asymmetrical insulation conditions, making it impossible to form a feasible cross-state configuration. The fact that a fixed resistor set to a nominal 1 A target triggers the first-ground fault current constraint under E2 state demonstrates that selection based solely on the baseline state is insufficient to cover the limitations caused by insulation degradation. In contrast, this invention, through full-state screening from E1 to E4, failure constraint tracing, and Pareto-max-min margin optimization, outputs a fixed series RL configuration that satisfies all three safety constraints under all four states, achieving a shift from selection based on a single nominal operating condition to a robust cross-state configuration.

[0216] To Figure 6 The cross-state feasibility coverage and margin differences shown in the table are quantitatively audited. Table 2 further summarizes the worst values ​​of the number of passing states, neutral point displacement voltage, first ground fault current, and contact voltage for each configuration in all states from E1 to E4, as well as the weakest normalized margin and the corresponding dominant state / constraint. Among them, the number of states characterizes the cross-state safety coverage capability of the configuration, the worst values ​​of the three indicators reflect the most unfavorable safety performance under the full-state engineering envelope, and the weakest normalized margin and dominant state / constraint are used to locate the safety shortcomings of the configuration.

[0217] Table 2. Full-state security audit results of traditional baseline configuration and the configuration of this invention.

[0218] Pure IT Reference 0 / 4 264.6587 V 0.028776 A 0.187915 V -1.646587 <![CDATA[E2+E4 / m V ]]> Nominal 1 A fixed resistor 3 / 4 5.9416 V 1.009264 A 6.449148 V -0.009264 <![CDATA[E2 / m I <!-- 13 -->]]> This invention has a fixed RL configuration. 4 / 4 24.6301 V 0.247076 A 1.605091 V 0.752924 <![CDATA[E2 / m I ]]>

[0219] As shown in the quantitative audit results in Table 2, although the pure IT reference has a smaller first-ground fault current, its worst-case neutral point displacement exceeds the operating threshold of this embodiment, failing to meet the requirements for cross-state operation. The traditional nominal condition 1A current setting resistor configuration triggers the first-ground fault current constraint under the E2 insulation asymmetry state, indicating that impedance setting based solely on a single nominal condition is insufficient to cover the safety boundary formed by actual environmental degradation. In contrast, the fixed series RL configuration of this invention achieves cross-state safety coverage and balanced margin configuration by passing neutral point displacement, first-ground fault current, and contact voltage constraints under all four conditions from E1 to E4, with a weakest normalized margin of 0.752924.

[0220] In addition, to test the adaptability of the selected fixed configuration to deviations in the main input parameters, while maintaining R... n * = 962.351Ω, L n * With H constant at 0.25, and without rescanning the feasible region or re-optimizing parameters, single-factor ±10% perturbations were applied to the disturbance current of new energy operation, A-phase insulation resistance, three-phase total ground capacitance, degradation state grounding resistance, and protective conductor resistance. The results show that all four states (E1 to E4) still satisfy the neutral point displacement, first ground fault current, and contact voltage constraints under each perturbation direction. The weakest normalized margin is the lowest at 0.734868, maintaining a positive margin. Among these, the increase in disturbance current has the greatest impact on the weakest margin, while changes in grounding resistance and protective conductor resistance mainly affect the contact voltage. Therefore, the selected fixed series RL configuration does not require retuning within the investigated parameter deviation range and remains feasible across states.

[0221] Therefore, the output of this invention is not merely an impedance value applicable to a single nominal operating condition, but rather a configuration result for the neutral point branch of a fixed series resistor-reactor system, supported by environmental state boundaries, constraint triggering information, and safety margins. This result can provide quantifiable and traceable parameter basis for equipment selection, engineering construction configuration, condition verification, and subsequent targeted operation and maintenance of coastal low-voltage IT systems, improving the engineering applicability and long-term operational reliability of fixed neutral point impedance configuration under complex environmental change conditions.

[0222] The above description of the present invention is only a preferred embodiment of the present invention and is not intended to limit the implementation of the present invention. Those skilled in the art can easily make corresponding modifications or alterations based on the main concept and spirit of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of protection claimed in the claims.

Claims

1. A robust configuration method for neutral point impedance in an environment-state driven coastal low-voltage IT system, characterized in that, Includes the following steps: Step 1: Based on the environmental and operational data of the coastal low-voltage IT system, establish a coastal environmental grounding resistance model and an insulation resistance model, and construct a hierarchical electrical model corresponding to the two resistance models, including unified calculation and analysis of normal operation and initial grounding fault conditions. Step 2: Construct the protective grounding path-insulation dual-factor environmental state, design a cross-state scanning and safety verification method for candidate neutral point impedance, and determine the feasibility of candidate neutral points based on safety thresholds; Step 3: Obtain the common robust feasible region of candidate neutral point impedances and record the failure state and triggering constraints. Design a safety margin equalization optimization method based on the Pareto-max-min criterion to realize the failure source of candidate configurations and obtain the optimal neutral point impedance configuration result.

2. The method for robust neutral point impedance configuration in an environment-state driven coastal low-voltage IT system according to claim 1, characterized in that, In step one, the specific method for establishing the coastal environmental grounding resistance model and insulation resistance model is as follows: Considering the comprehensive impact of actual factors, and combining relevant environmental parameter change data and electrical performance change patterns for fitting and verification, an engineering equivalent model of protective grounding resistance and relative insulation resistance to ground is constructed. Regarding protective grounding resistance: ； In the formula, R g To protect the grounding resistance, R g0 For reference grounding resistance, t f D is the time when the fault occurs. hist For historical environmental exposure information, ρ env For the temperature T f θ f Salt state S f The obtained environmental equivalent resistivity, ρ ref For reference resistivity, F cor It is a corrosion or degradation correction factor; Regarding insulation resistance: ； In the formula, R ins,k R is the insulation resistance to ground of phase k. ins0 For reference insulation resistance, F is the composite environmental insulation retention factor of phase k. T,k F H,k F S,k F age,k These represent temperature, humidity, salt pollution, and aging correction factor, respectively.

3. The robust configuration method for neutral point impedance in an environment-state driven coastal low-voltage IT system according to claim 1, characterized in that, In step one, the method for establishing the hierarchical electrical model corresponding to the resistance model is as follows: For normal operation, assuming any phase k∈{a,b,c}, the phase branch admittance of the normal admittance layer is: ； In the formula, k is the phase index, Y ins,k For phase k, the relative ground insulation-capacitance admittance, C ph The equivalent capacitance to ground for each phase, j is the imaginary unit, ω is the angular frequency, and Y... leak,total This is the total admittance for three-phase relative ground leakage; Based on the above three-phase relative leakage total admittance Y leak,total The impedance, admittance, and normal IT system admittance to ground of the fixed series RL neutral point impedance branch are as follows: ； In the formula, Z n To fix the series resistance—the neutral point branch impedance of the reactor, R n L is the neutral point resistance. n For the inductance of the reactor, Y n For the neutral point branch admittance, Y IT This represents the equivalent admittance to ground for a normal IT system. When there is asymmetry in insulation condition, capacitance to ground, or external operating disturbance, an equivalent unbalanced injection will be formed. Further calculation of the neutral point displacement voltage caused by this unbalanced injection is required. ； In the formula, V n I is the neutral point displacement voltage. unb,total The total disturbance current injected into the neutral-ground equivalent network.

4. A robust neutral point impedance configuration method for an environment-state-driven coastal low-voltage IT system according to claim 3, characterized in that, The method for establishing the hierarchical electrical model also includes: For the initial ground fault condition, let the faulty phase be p, and the other two phases be q and r. Define the phase-specific transfer admittance and the ground node driving point admittance as follows: ； In the formula, p represents the faulty phase, q and r represent the non-faulty phases, and Y tr,p Y is the transfer admittance corresponding to the fault phase p. dp,p U is the admittance of the ground node driving point corresponding to the fault phase p. p U q U r These are the phase voltage phasors for the corresponding phases, Y ins,q and Y ins,r These are the ground insulation-capacitance admittances of the non-faulty phases q and r, respectively; The resistance of the grounding device and the resistance of the protective conductor are combined and defined as the comprehensive resistance R of the protective grounding. A : In the formula, R PE To protect the conductor's resistance; Then the initial ground fault current and contact voltage corresponding to the faulty phase p are: ； In the formula, I d,p I is the fault current when the faulty phase p experiences its first ground fault. d U is the maximum initial ground fault current in the three phases. T This is the contact voltage.

5. A robust configuration method for neutral point impedance in an environment-state driven coastal low-voltage IT system according to claim 1, characterized in that, In step two, the method for constructing the protective grounding path-insulation two-factor environmental state is as follows: The environmental conditions of the coastal low-voltage IT system are divided into two combinable factors; the first factor is the protective grounding path state G, where G0 represents the reference grounding path state, corresponding to the reference grounding resistance R. g and protective conductor resistance R PE The lower R constituted A The range, G1, represents the R range constructed jointly by historical environmental data, operation and maintenance information, and environmental grounding resistance model. g Increase, thus making R A An increased scope of representation; The second type of factor is the insulation state I, where I0 represents an approximately symmetrical three-phase insulation state, and I1 represents an asymmetrical state in which the insulation of at least one phase is significantly reduced. The difference between the symmetrical reference admittance and the actual admittance introduces an environmental unbalanced current I. env : ； In the formula, U a U b U c For three-phase phase voltage phasors, ΔY a ΔY b ΔY c For the three-phase relative admittance bias, Y ref,k For phase k, the symmetric reference admittance; The total disturbance current is: In the formula, I unb,PV Injecting equivalent unbalanced current into the neutral-to-ground network for new energy sources or operational disturbances; The above two factors form four environmental states: E1 = (G0, I0), E2 = (G0, I1), E3 = (G1, I0), E4 = (G1, I1). E1 to E4 are four environmental states formed by the combination of the G / I two factors.

6. A robust neutral point impedance configuration method for an environment-state-driven coastal low-voltage IT system according to claim 1, characterized in that, In step two, the method for transstate scanning and safety verification of candidate neutral point impedance is as follows: Candidate neutral point impedance points x = (R) are generated within the preset neutral point resistance range and reactor inductance range. n ,L n ); For any candidate neutral point impedance point x, based on the normal operation state and the first ground fault state, calculate its neutral point displacement voltage, first ground fault current and contact voltage under various environmental conditions. Define three types of feasibility predicates: neutral point displacement, initial ground fault current, and touch voltage. ； In the formula, e represents the environmental state, x represents the candidate neutral point impedance, and p V (e,x), p I (e,x), p U (e,x) represent the feasibility predicates for neutral point displacement, initial ground fault current, and contact voltage under state e and candidate point x, respectively. lim I lim U lim These are the neutral point displacement operating threshold, the first ground fault current threshold, and the contact voltage threshold, respectively. The comprehensive feasibility definition of candidate point x under each environmental state e is as follows: ； In the formula, Rec(e,x) is the comprehensive feasibility predicate of candidate point x under state e, and the symbol ∧ represents the logical "and".

7. A robust neutral point impedance configuration method for an environment-state-driven coastal low-voltage IT system according to claim 1, characterized in that, In step three, the specific method for determining the common robust feasible region, failure state, and triggering constraints is as follows: The common robust feasible region is obtained by intersecting the feasible regions of all states: ； For those not entering the public robust feasible region Ω robust The candidate neutral point impedance point is recorded, and the environmental state in which it does not meet the comprehensive feasibility judgment is recorded, and the safety constraint that triggers the failure to meet the judgment is also recorded. The triggering safety constraints include at least one of neutral point displacement constraints, first ground fault current constraints, and contact voltage constraints.

8. A robust neutral point impedance configuration method for an environment-state-driven coastal low-voltage IT system according to claim 1, characterized in that, In step three, the safety margin equilibrium optimization method based on the Pareto-max-min criterion is specifically as follows: Within the common robust feasible region, the following normalization margin is adopted: ； In the formula, S V (x), S I (x), S U (x) represents the normalized margin of candidate point x under the constraints of neutral point displacement, first ground fault current and contact voltage. The maximum value operation in the equation represents taking the maximum value for all environmental states e. The weakest margin of the candidate point is: In the formula, S min (x) represents the weakest normalization margin of candidate point x, and min{·} represents taking the minimum value among the three margins; For any two candidate points x1 and x2 within the common robust feasible region, when S V (x1) ≥ S V (x2), S I (x1) ≥ S I (x2), S U (x1) ≥ S U If x1 is Pareto-dominated by x2, and at least one of them is strictly greater than x2, then x1 is said to be Pareto-dominated by x2. The Pareto non-dominated candidate set P is composed of all candidate points that are not Pareto-dominated by other candidate points. Within the Pareto non-dominated candidate set P, choose: ； In the formula, x* is the finally selected fixed series RL branch configuration point, R n * and L n *These represent the selected neutral point resistor and reactor inductance, respectively.

9. A robust neutral point impedance configuration system for an environment-state driven coastal low-voltage IT system, characterized in that, The system includes a computer module that utilizes an environment-state-driven method for robust neutral point impedance configuration in a coastal low-voltage IT system as described in any one of claims 1 to 8.

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