CN110082643B - Sag domain identification method considering load sensitivity uncertainty - Google Patents

Abstract

The invention discloses a sag domain identification method considering uncertainty of load sensitivity, which comprises the following steps of: carrying out load flow calculation to obtain a voltage amplitude of a system node before a fault; calculating the impedance of each sequence; calculating fault residual voltage of each bus; obtaining the upper limit and the lower limit of the sensitive load uncertain interval according to the existing voltage tolerance curve to form a discrimination matrix; calculating a line critical point according to the discrimination matrix and the lower bound and the upper bound of the sensitive load uncertain interval; and traversing all the lines and all the uncertain spaces, and outputting two sag domain identification results corresponding to the upper limit and the lower limit of the sensitive load uncertain interval. The invention considers the uncertain interval of the load sensitivity, delineates the sag domains closer to the actual engineering, and overcomes the defects that the different tolerance capacities of the sensitive load to the voltage sag are not considered in the conventional sag domain identification method, the sag domains are fixed by a clear boundary line, and all the sag domain critical points cannot be considered.

Description

Sag domain identification method considering load sensitivity uncertainty

Technical Field

The invention relates to the technical field of voltage sag domain identification of a power system, in particular to a sag domain identification method considering load sensitivity uncertainty.

Background

The load sensitivity refers to the sensitivity of the load to the power quality problems such as voltage quality, when the power quality provided for the load is poor, the load can still work normally under interference, the lower the capability is, the higher the sensitivity is, and the load sensitivity is uncertain in the actual power system operation; the sag domain is a set of fault points, wherein when short-circuit faults occur in a power system, the voltage amplitude of a sensitive point is reduced to be below a certain voltage tolerance threshold value due to the faults, so that the sensitive load cannot normally work, and important guiding significance is provided for reducing the adverse effect of voltage sag on the sensitive load, realizing reliable and high-quality operation of a power grid and researching a method for identifying the voltage sag domain.

The sag area is not strictly a region in the strict sense, but is a set of points (substations) and lines (lines and cables), but the region enclosed by the envelope is more favorable for visualization of the concept, and whether the electrical elements fall into the sag area can be determined.

At present, various sag domain identification methods are proposed at home and abroad, and mainly comprise methods such as a fault point method, a critical distance method, an analytic method and the like, and the methods have more or less defects in sag domain identification and calculation, for example, when the fault point method is used for sag domain identification and calculation, the precision is difficult to guarantee and a large amount of fault point information is needed to improve the calculation precision, the method is used for solving the problems that the existing sag domain identification and calculation methods have more or less defects, such as iron sensitivity, and the voltage sag evaluation based on the improved fault point method is mentioned in the electric power automation equipment (2008,28(6)) published by Yang Hongkong; moreover, the existing sag domain calculation methods are all based on traditional short circuit calculation, influence factors considered by an algorithm are few, and the sag domain pre-evaluation result is greatly different from an actual result, on the other hand, the existing methods calculate an exact sag domain boundary, the range of the sag domain is mainly determined by the voltage sag tolerance capacity of equipment, although the voltage sag tolerance capacity of a sensitive load is considered to be a specific value under normal conditions, but the tolerance capability of the sensitive equipment may be different due to different operation modes and load conditions of the equipment, and in this case, the voltage sag tolerance characteristics of sensitive loads cannot be characterized by a fixed voltage sag tolerance curve, the position of the voltage sag tolerance curve has uncertainty, and the corresponding voltage critical point cannot be fully considered, so that the fixed sag domain boundary has certain limitation at this time.

Disclosure of Invention

The invention provides a sag domain identification method considering load sensitivity uncertainty based on the upper and lower boundaries of the variation range of a sensitive load voltage tolerance curve interval, aiming at overcoming the defects that the different tolerance capacities of sensitive loads to voltage sag are not considered in the conventional sag domain identification method, the sag domain is fixed by a definite boundary line, and all voltage critical points cannot be considered.

In order to achieve the technical effects, the technical scheme of the invention is as follows:

the method comprises the following steps:

s1: load flow calculation is carried out on the system, and the voltage amplitude U of each node of the system in normal operation before short circuit fault is obtained_pref；

S2: setting a short-circuit fault node K and a sensitive load access node m, and calculating zero sequence, positive sequence and negative sequence transfer impedances between the point K and the point m, input impedance of the point K and a voltage amplitude before fault;

s3: calculating residual voltage amplitude U of each bus according to voltage amplitude of each node of the system before the fault and input impedance of the fault point K_mag；

S4, obtaining an upper limit U of the uncertain interval of the voltage tolerance capacity curve through the change range of the uncertain interval of the known voltage tolerance capacity curve graph_maxAnd a lower bound limit U_minAnd combining the residual voltage amplitude U of each bus fault_magForming discrimination matrices BUS and L INE;

s5, making the voltage tolerance value U of the load on the node m_thTaking the lower limit value U of the uncertain interval_minAccording to the value of the discrimination matrix L INE, calculating the critical point of the line, and determining the inclusion condition of the line in the sag domain;

s6, judging whether all the lines of the system are traversed or not and whether all the uncertain spaces are traversed or not, and if so, outputting a sag domain identification result; if not, returning to step S4 to perform the next route identification calculation; if all the lines have been traversed but not all the uncertain space has been traversed, let U_thTaking the upper bound U of the uncertainty interval_maxReturning to step S4 to continue the calculation;

s7, counting twice to obtain U_minCorresponding sag fields 1 and U_maxAnd obtaining a final sag domain identification result by the corresponding sag domain 2.

Preferably, the transfer impedances between the fault node K and the sensitive load access node m in the step S2 in each order are:

Z_mK,0＝Z_mF,0+p(Z_mT,0-Z_mF,0)

Z_mK,1＝Z_mF,1+p(Z_mT,1-Z_mF,1)

Z_mK,2＝Z_mF,2+p(Z_mT,2-Z_mF,2)

wherein Z is_mK,0、Z_mK,1、Z_mK,2Transferring impedance for each sequence between a fault node K and a sensitive load access node m, wherein Z_mK,0For zero sequence transfer impedance, Z_mK,1For positive sequence transfer of impedance, Z_mK,2Negative sequence transfer impedance; z_mF,0、Z_mF,1、Z_mF,2Transferring impedance for each sequence between a head-end bus node F of a sensitive load node m and a load point m, wherein Z_mF,0For zero sequence transfer impedance, Z_mF,1For positive sequence transfer of impedance, Z_mF,2Negative sequence transfer impedance; z_mT,0、Z_mT,1、Z_mT,2Transferring impedance for each sequence between tail end bus node T of sensitive load node m and load point m, wherein Z_mT,0For zero sequence transfer impedance, Z_mT,1For positive sequence transfer of impedance, Z_mT,2Negative sequence transfer impedance; p is the per unit value representation of the distance from the fault point K to the bus head end node F;

the input impedance of the fault node K is:

Z_KK,0＝p²(Z_FF,0+Z_TT,0-2Z_FT,0-Z_C,0)+p[Z_C,0-2(Z_FF，0-Z_TT,0)]+Z_FF，0

Z_KK，1＝p²(Z_FF，1+Z_TT，1-2Z_FT，1-Z_C，1)+p[Z_C，1-2(Z_FF，1-Z_TT，1)]+Z_FF，1

Z_KK，2＝p²(Z_FF,2+Z_TT,2-2Z_FT,2-Z_C,2)+p[Z_C,2-2(Z_FF,2-Z_TT,2)]+Z_FF,2

in the formula, Z_KK,0、Z_KK,1、Z_KK,2Is the sequence input impedance of the fault node K, wherein Z_KK,0Is zero sequence impedance, Z_KK,1Is a positive sequence input impedance, Z_KK,2Is a negative sequence input impedance; z_FF,1、Z_FF,2Z_FF,0、Z_FF,1、 Z_FF,2Input impedance of head end bus node F as fault point k, where Z_FF,0Is a zero sequence input impedance, Z_FF,1Is a positive sequence input impedance, Z_FF,2Is a negative sequence input impedance; z_TT,0、Z_TT,1、Z_TT,2The input impedance for each sequence of tail bus node T, wherein Z_TT,0Is a zero sequence input impedance, Z_TT,1Is a positive sequence input impedance, Z_TT,2Is a negative sequence input impedance; z_C,0、Z_C,1、Z_C,2Is the sequence impedance on the line FT, where Z_C,0Is zero sequence impedance, Z_C,1Is a positive sequence impedance, Z_C,2Is a negative sequence impedance, p is as defined above;

the voltage amplitude before the short-circuit fault occurs at the node K is represented as:

U_K,pref＝U_F,pref+p(U_T,pref-U_F,pref)

wherein, U_K,prefRepresenting the voltage of the K node before short-circuit fault occurs; u shape_F,prefRepresenting the node voltage amplitude of the bus node F before the fault; u shape_T,prefRepresenting the node voltage amplitude of the bus node T before the fault; p and the preambleThe meanings are consistent.

Preferably, the bus fault residual voltage amplitude U in step S3_mag：

Wherein, U_magRepresenting the amplitude of the fault residual voltage of the bus;

the amplitude of each phase voltage of the bus m when the K point fails,

which represents the amplitude of the a-phase voltage,

representing the magnitude of the B-phase voltage,

representing the amplitude of the C-phase voltage; u shape_A,m,prefThe amplitude of the A phase voltage before m-point fault; a denotes a twiddle factor e^j120°；

And the voltage amplitude of the m point when the bus node K fails is shown.

Preferably, the upper limit and the lower limit of the uncertainty interval corresponding to the uncertainty curve of the voltage sag tolerance of the sensitive load described in step S4 are U respectively_maxAnd U_minThe decision matrices BUS and L INE are formed as follows:

wherein, U_thRepresents the voltage endurance of the load carried by the node m; delta U_mag,nRepresents the bus residual voltage amplitude U_magAnd voltage endurance U_thΔ U for i ∈ (1, …, n)_mag,iWhen the value of (B) is less than or equal to zero, BUS_iTaking 1 to indicate that the bus i is contained in the sag domain; delta U_mag,iWhen the value of (B) is greater than zero, BUS_iTaking 0 to indicate that the bus i is not contained in the sag domain, L INE value is a sag domain discrimination parameter of the line, L INE_iA value of 0, indicating that the bus i is not in the sag domain, L INE_iA value of 1 indicates that bus i contains a critical point, L INE_iThe value is 2, which indicates that there are two critical points on the bus i;

judging parameters for sag domains of the bus F at two ends of the line i;

when one of the sag domain discrimination parameters is 1, L INE is used_iIf 1 is taken to indicate that the line has a critical point, and if 0 is taken to indicate that the line has a critical point, L INE is used_iIf the value is 0, the line has no critical point, if both values are 1, L INE is added_iThe value of 2 indicates that the line has two critical points.

Preferably, the upper limit U of the uncertainty curve of the voltage sag withstand capability of the sensitive load_maxRepresenting a boundary between the immune region and the uncertain region; lower bound U_minIndicating an uncertainty regionThe boundary with the failure zone.

Preferably, the process of step S5 is:

s501, judging L INE_iIf L INE is equal to_iIf the value of (A) is 0, the bus i is positioned outside the sag domain, the next line judgment is carried out, and if L INE is adopted_iIf not, obtaining a voltage sag amplitude curve by utilizing a cubic spline interpolation method, and executing the step S502;

s502, judge L INE_iIf L INE is equal to_iValue of (1) to find the critical point, L INE_iIf not 1, go to step S503;

s503: calculating the maximum point p of the voltage sag amplitude value on the line by using a golden section search method_maxAnd | f (pmax) | of the residual voltage equation function f;

s504: finding p_maxRear judgment | f (p)_max) I and U_thIf | f (p)_max) | is less than U_thIf yes, the whole line is included in the sag domain, and the step S501 is returned to continue to be executed; if | f (p)_max) | is greater than U_thThen according to L INE_iThe critical point is obtained by a critical point obtaining method with a value of 1.

Preferably, in step S502, if L INE_iThe value of (1) is obtained by the following method:

s5021: spline interpolation is carried out by using three points of p-0, p-0.5 and p-1 to obtain a residual voltage equation function of

Definition of U_th＝f(p_i) In the formula, x₁、x₂、x₃As a coefficient of function, p_iArgument to function, p at this time_iRespectively take p_i＝0、p_i0.5 and p_i＝1；

S5022: calculating | f (0.5) |, sequentially corresponding the short-circuit voltage amplitude of the first node of the line, the short-circuit voltage amplitude of the tail node of the line and | f (0.5) | at the three points in the step S5021, and solving the equation function of the residual voltage that p is more than or equal to 0_icRoot p of less than or equal to 1_ic；

S5023: defining an initial iteration value using the roots of the residual voltage equation, determining two initial iteration values near a critical point, taking [ p ]_ic,p_ic+Δp]Or [ p ]_ic-Δp,p_ic]△ p is the initial point p of secant iteration 0.01_fromAnd p_endCalculating a critical point; the iterative process is as follows:

p_new＝p_end-[f(p_end)-U_th](p_end-p_from)/[|f(p_end)|-|f(p_from)|]

p_from＝p_end

p_end＝p_new

wherein p is_from、p_endTwo initial value points of iteration; p is a radical of_newNew iteration values for the critical points; f (p)_end) Represents a point p_endThe residual voltage amplitude of; f (p)_from) Represents a point p_fromThe residual voltage amplitude of; u shape_thRepresents the voltage endurance of the load carried by the node m;

the convergence conditions are as follows:

||f(p_new)|-U_th|＜tol

wherein tol is convergence accuracy; p is a radical of_new、U_thAre consistent with the meaning set forth above.

S5024: and (4) obtaining an accurate critical point accurate value by using a Newton method.

Preferably, the step S503 is executed to calculate the maximum point p of the voltage sag amplitude on the line_maxAnd the | f (pmax) | golden section searching method of the residual voltage equation function f comprises the following steps:

s5031: according to the golden section point

Two initial value points p are defined₁、p₂The expression of the two initial value points is:

s5032: computingp₁、p₂Corresponding residual pressure equation function value | f (p)₁) I and | f (p)₂)|；

S5033: judgment of | f (p)₁) Whether | is greater than or equal to | f (p)₂) If | f (p)₁)|≥|f(p₂) If, then the following iteration of assignment is performed:

if | f (p)₁)|＜|f(p₂) If, then the following iteration of assignment is performed:

s5033: judgment | p_b-p_aWhether the | is less than or equal to the established value or not represents the calculation setting precision; if p_b-p_aIf | is less than or equal to true, then use the current p₁、p₂Calculating a maximum point P_max:P_max＝(p_b+p_a) /2 and corresponding residual pressure equation function value | f (P)_max)|。

Preferably, step S504 is as described in L INE_iThe method for solving the critical point with the value of 1 comprises the following steps:

s5041: using p ═ 0, p ═ p_maxCarrying out spline interpolation on three points of p-1 to obtain a residual voltage equation function of

Definition of U_th＝f(p_i) In the formula, x₁、x₂、x₃As a coefficient of function, p_iArgument to function, p at this time_iRespectively take p_i＝0、p_i＝p_maxAnd p_i＝1；

S5042: calculate | f (p)_max) I, the three points in step S5042 sequentially correspond to the short-circuit voltage amplitude of the first node of the line, the short-circuit voltage amplitude of the tail node of the line, and | f (p)_max) I, obtaining the residual voltage equation function with p being more than or equal to 0_icRoot p of less than or equal to 1_ic；

S5043: defining an initial iteration value using the roots of the residual voltage equation, determining two initial iteration values near a critical point, taking [ p ]_ic,p_ic+Δp]Or [ p ]_ic-Δp,p_ic]△ p is the initial point p of secant iteration 0.01_fromAnd p_endCalculating a critical point; the iterative process is as follows:

p_new＝p_end-[f(p_end)-U_th](p_end-p_from)/[|f(p_end)|-|f(p_from)|]

p_from＝p_end

p_end＝p_new

wherein p is_from、p_endTwo initial value points of iteration; p is a radical of_newNew iteration values for the critical points; f (p)_end) Represents a point p_endThe residual voltage amplitude of; f (p)_from) Represents a point p_fromThe residual voltage amplitude of; u shape_thRepresents the voltage endurance of the load carried by the node m;

the convergence conditions are as follows:

||f(p_new)|-U_th|＜tol

where tol is convergence accuracy, p_new、U_thAre consistent with the meaning set forth above.

S5043: obtaining | f (p) by Newton's method_max) | is greater than U_thThe exact value of the time critical point.

Compared with the prior art, the technical scheme of the invention has the beneficial effects that: the method of the invention selects the upper limit and the lower limit of the uncertain interval to respectively obtain the critical points based on the uncertain interval of the existing voltage tolerance curve, and delineates the sag domains which are closer to the actual engineering, thereby overcoming the defects that the existing sag domain identification method does not consider the different tolerance capacities of sensitive loads to voltage sag, fixes the sag domains by a definite boundary and cannot consider all the sag domain critical points.

Drawings

Fig. 1 shows a flowchart of a sag domain identification method according to an embodiment of the present invention.

Fig. 2 shows an IEEE30 node system diagram.

Fig. 3 shows a schematic diagram of a line FT malfunctioning.

Fig. 4 shows a graph of voltage sag withstand capability for a sensitive load.

Fig. 5 is a schematic flow chart of the golden section searching method.

FIG. 6 is a diagram illustrating a read of a threshold dip field result.

FIG. 7 is a diagram illustrating the reading of two threshold dip domain results.

Fig. 8 is a diagram illustrating the result of identifying the sag domain of the IEEE30 node system.

Detailed Description

The drawings are for illustrative purposes only and are not to be construed as limiting the patent;

for the purpose of better illustrating the embodiments, certain features of the drawings may be omitted, enlarged or reduced, and do not represent the size of an actual product;

it will be understood by those skilled in the art that certain well-known structures in the drawings and descriptions thereof may be omitted.

The technical solution of the present invention is further described below with reference to the accompanying drawings and examples.

A flow chart of the implementation method of this embodiment is shown in fig. 1, taking the system of IEEE30 node shown in fig. 2 as an example, and assuming that the type of fault occurring in the system is a single-phase ground fault, as shown in fig. 1, the sag domain calculation process is as follows:

s1: performing load flow calculation according to the existing network parameters and operation data of the system shown in FIG. 2 to obtain the voltage amplitude U of each node of the system before short circuit fault during normal operation_pref；

S2: as shown in fig. 3, a short-circuit fault node K and a sensitive load access node m are arranged on a line FT, and zero sequence, positive sequence and negative sequence transfer impedances between the point K and the point m, input impedance of the point K, and a voltage amplitude before fault are calculated:

the transfer impedance between the fault node K and the sensitive load node m in each sequence is as follows:

Z_mK,0＝Z_mF,0+p(Z_mT,0-Z_mF,0)

Z_mK,1＝Z_mF,1+p(Z_mT,1-Z_mF,1)

Z_mK,2＝Z_mF,2+p(Z_mT,2-Z_mF,2)

wherein Z is_mK,0、Z_mK,1、Z_mK,2Transferring impedance for each sequence between a fault node K and a sensitive load access node m, wherein Z_mK,0For zero sequence transfer impedance, Z_mK,1For positive sequence transfer of impedance, Z_mK,2Negative sequence transfer impedance; z_mF,0、Z_mF,1、Z_mF,2Transferring impedance for each sequence between a head-end bus node F of a sensitive load node m and a load point m, wherein Z_mF,0For zero sequence transfer impedance, Z_mF,1For positive sequence transfer of impedance, Z_mF,2Negative sequence transfer impedance; z_mT,0、Z_mT,1、Z_mT,2Transferring impedance for each sequence between tail end bus node T of sensitive load node m and load point m, wherein Z_mT,0For zero sequence transfer impedance, Z_mT,1For positive sequence transfer of impedance, Z_mT,2Negative sequence transfer impedance; p is the per unit value representation of the distance from the fault point K to the bus head end node F;

the input impedance of the fault node K is:

Z_KK,0＝p²(Z_FF,0+Z_TT,0-2Z_FT,0-Z_C,0)+p[Z_C,0-2(Z_FF，0-Z_TT,0)]+Z_FF，0

Z_KK，1＝p²(Z_FF，1+Z_TT，1-2Z_FT，1-Z_C，1)+p[Z_C，1-2(Z_FF，1-Z_TT，1)]+Z_FF，1

Z_KK，2＝p²(Z_FF,2+Z_TT,2-2Z_FT,2-Z_C,2)+p[Z_C,2-2(Z_FF,2-Z_TT,2)]+Z_FF,2

in the formula, Z_KK,0、Z_KK,1、Z_KK,2Is the sequence input impedance of the fault node K, wherein Z_KK,0Is zero sequence impedance, Z_KK,1Is a positive sequence input impedance, Z_KK,2Is a negative sequence input impedance; z_FF,1、Z_FF,2Z_FF,0、Z_FF,1、 Z_FF,2Input impedance of head end bus node F as fault point k, where Z_FF,0Is a zero sequence input impedance, Z_FF,1Is a positive sequence input impedance, Z_FF,2Is a negative sequence input impedance; z_TT,0、Z_TT,1、Z_TT,2The input impedance for each sequence of tail bus node T, wherein Z_TT,0Is a zero sequence input impedance, Z_TT,1Is a positive sequence input impedance, Z_TT,2Is a negative sequence input impedance; z_C,0、Z_C,1、Z_C,2Is the sequence impedance on the line FT, where Z_C,0Is zero sequence impedance, Z_C,1Is a positive sequence impedance, Z_C,2Is a negative sequence impedance, p is as defined above;

the voltage amplitude before the short-circuit fault occurs at the node K is represented as:

U_K,pref＝U_F,pref+p(U_T,pref-U_F,pref)

wherein, U_K,prefRepresenting the voltage of the K node before short-circuit fault occurs; u shape_F,prefRepresenting the node voltage amplitude of the bus node F before the fault; u shape_T,prefRepresenting the node voltage amplitude of the bus node T before the fault; p is as defined above.

S3: calculating residual voltage amplitude U of each bus according to voltage amplitude of each node of the system before the fault and input impedance of the fault point K_mag。

U_magThe following is obtained:

wherein, U_magRepresenting the amplitude of the fault residual voltage of the bus;

the amplitude of each phase voltage of the bus m when the K point fails,

which represents the amplitude of the a-phase voltage,

representing the magnitude of the B-phase voltage,

representing the amplitude of the C-phase voltage; u shape_A,m,prefThe amplitude of the A phase voltage before m-point fault; a denotes a twiddle factor e^j120°；

And the voltage amplitude of the m point when the bus node K fails is shown.

S4, obtaining the upper limit U of the uncertain interval through the variation range of the uncertain interval of the existing known voltage tolerance capacity curve_maxAnd a lower bound limit U_minAnd combining the residual voltage amplitude U of each bus fault_magForming discrimination matrices BUS and L INE;

as shown in the sensitive load voltage sag tolerance curve shown in fig. 4, the upper limit and the lower limit of the uncertainty interval corresponding to the sensitive load voltage sag tolerance uncertainty curve are U_maxAnd U_min，U_maxRepresenting a boundary between the immune region and the uncertain region; u shape_minThe demarcation lines representing the area of uncertainty region failure, the decision matrices BUS and L INE are formed as follows:

wherein, U_thRepresents the voltage endurance of the load carried by the node m; delta U_mag,nRepresents the bus residual voltage amplitude U_magAnd voltage endurance U_thΔ U for i ∈ (1, …, n)_mag,iWhen the value of (B) is less than or equal to zero, BUS_iTaking 1 to indicate that the bus i is contained in the sag domain; delta U_mag,iWhen the value of (B) is greater than zero, BUS_iTaking 0 to indicate that the bus i is not contained in the sag domain, L INE value is a sag domain discrimination parameter of the line, L INE_iA value of 0, indicating that the bus i is not in the sag domain, L INE_iA value of 1 indicates that bus i contains a critical point, L INE_iThe value is 2, which indicates that there are two critical points on the bus i;

judging parameters for sag domains of the bus F at two ends of the line i;

when one of the sag domain discrimination parameters is 1, L INE is used_iIf 1 is taken to indicate that the line has a critical point, and if 0 is taken to indicate that the line has a critical point, L INE is used_iIf the value is 0, the line has no critical point, if both values are 1, L INE is added_iThe value of 2 indicates that the line has two critical points.

S5, making the voltage tolerance value U of the load on the m point of the bus_thTaking the lower limit value U of the uncertain interval_minAccording to the value of the decision matrix L INE, the critical point of the line is calculated, and the inclusion condition of the line in the sag domain is determined, as shown in fig. 1, the process is as follows:

s501, judging L INE_iIf L INE is equal to_iIs 0, indicating that the bus i is outside the sag domain, the next bus is performedLine judgment, if L INE_iIf not, obtaining a voltage sag amplitude curve by utilizing a cubic spline interpolation method, and executing the step S502;

s502, judge L INE_iIf L INE is equal to_iValue of (1) to find the critical point, L INE_iIf not 1, go to step S503;

s503: calculating the maximum point p of the voltage sag amplitude value on the line by using a golden section search method_maxAnd | f (pmax) | of the residual voltage equation function f;

s504: finding p_maxRear judgment | f (p)_max) I and U_thIf | f (p)_max) | is less than U_thIf yes, the whole line is included in the sag domain, and the step S501 is returned to continue to be executed; if | f (p)_max) | is greater than U_thThen according to L INE_iThe critical point is obtained by a critical point obtaining method with a value of 1.

Referring to FIG. 1, in step S502, if L INE is present_iThe value of (1) and the step of finding the critical point is:

s5021: spline interpolation is carried out by using three points of p-0, p-0.5 and p-1 to obtain a residual voltage equation function of

Definition of U_th＝f(p_i) In the formula, x₁、x₂、x₃As a coefficient of function, p_iArgument to function, p at this time_iRespectively take p_i＝0、p_i0.5 and p_i＝1；

S5022: calculating | f (0.5) |, sequentially corresponding the short-circuit voltage amplitude of the first node of the line, the short-circuit voltage amplitude of the tail node of the line and | f (0.5) | at the three points in the step S5021, and solving the equation function of the residual voltage that p is more than or equal to 0_icRoot p of less than or equal to 1_ic；

S5023: defining an initial iteration value using the roots of the residual voltage equation, determining two initial iteration values near a critical point, taking [ p ]_ic,p_ic+Δp]Or [ p ]_ic-Δp,p_ic]△ p is the initial point p of secant iteration 0.01_fromAnd p_endCalculating a critical point; the iterative process is as follows:

p_new＝p_end-[f(p_end)-U_th](p_end-p_from)/[|f(p_end)|-|f(p_from)|]

p_from＝p_end

p_end＝p_new

wherein p is_from、p_endTwo initial value points of iteration; p is a radical of_newNew iteration values for the critical points; f (p)_end) Represents a point p_endThe residual voltage amplitude of; f (p)_from) Represents a point p_fromThe residual voltage amplitude of; u shape_thRepresents the voltage endurance of the load carried by the node m;

the convergence conditions are as follows:

||f(p_new)|-U_th|＜tol

wherein tol is convergence accuracy; p is a radical of_new、U_thAre consistent with the meaning set forth above.

S5024: and (4) obtaining an accurate critical point accurate value by using a Newton method.

Step S503, calculating the maximum value point p of the voltage sag amplitude on the line_maxAnd the steps of | f (pmax) | golden section search method of the residual voltage equation function f are as follows, and the flow chart is schematically shown in fig. 5:

s5031: according to the golden section point

Two initial value points p are defined₁、p₂The expression of the two initial value points is:

s5032: calculating p₁、p₂Corresponding residual pressure equation function value | f (p)₁) I and | f (p)₂)|；

S5033: judgment of | f (p)₁) Whether | is greater than or equal to | f (p)₂) If | f (p)₁)|≥|f(p₂) If, then the following iteration of assignment is performed:

if | f (p)₁)|＜|f(p₂) If, then the following iteration of assignment is performed:

s5033: judgment | p_b-p_aWhether the | is less than or equal to the established value or not represents the calculation setting precision; if p_b-p_aIf | is less than or equal to true, then use the current p₁、p₂Calculating a maximum point P_max:P_max＝(p_b+p_a) /2 and corresponding residual pressure equation function value | f (P)_max)|。

S6, judging whether all lines are traversed or not and whether all the uncertain spaces are traversed or not, and if so, outputting a sag domain identification result; if not, returning to step S4 to execute the next route calculation; if all the lines have been traversed but not all the uncertain space has been traversed, let U_thTaking the upper bound U of the uncertainty interval_maxReturning to step S4 to continue the calculation;

s7, counting twice to obtain U_minCorresponding sag fields 1 and U_maxAnd obtaining a final sag domain identification result by the corresponding sag domain 2.

Calculating a voltage sag domain of an IEEE30 node system shown in FIG. 2 according to the method provided by the invention, selecting a bus 20 as a sensitive load access bus node, wherein the fault type is a single-phase earth fault, and the method comprises the voltage sag domain identification corresponding to other fault types except the single-phase earth fault, which is not repeated in the specific embodiment, and the upper limit U of the uncertain space of the sensitive load voltage tolerance curve is not repeated_maxTake 0.8, lower bound U_minTake 0.7 of U_minThe corresponding calculated value is a sag field 1, U_maxThe corresponding calculation value is sag field 2, and the calculation result is shown in table 1:

TABLE 1

As shown in table 1, the contents of the first column in table 1 indicate the head end number of the line, and the contents of the second column indicate the tail end number of the line; the contents of the third column indicate U_minThe number of corresponding calculated critical points, the content of the fourth column represents and U_maxCorrespondingly calculating the number of the obtained critical points, wherein 0 represents that the section of line is not contained in the sag domain; 1 indicates that the section of the line has a critical point; 2, the section of the circuit has two critical points; 3 indicates that the segment of the line is completely contained in the sag domain; the contents of the fifth column to the eighth column represent the inclusion conditions of the lines specified by the first column and the second column before the table in the sag field 1 and the sag field 2, if the number of the critical points is 0, namely the starting point and the end point values are both 0, the line is not included in the sag field; if the number of critical points is 1, the starting point and the end point are [0, x ]]Or [ x,1 ]]At this time, the reading result is shown in fig. 6, where x is the per unit value of the distance from the head end of the line to the critical point and the total length, the dotted line part represents the sag domain, and the starting point and ending point values are [0, x [ ]]When the line length is 0 to x, the part of the line length belongs to the sag domain; starting point and end point values of [ x,1]Then, the portion of the line length x to 1 belongs to the sag domain.

If the number of the critical points is 2, the starting point and ending point values are [ x1, x2], and the reading result is shown in fig. 7, where x1 is a per unit value of the distance from the head end of the line to the first critical point and the total length, x2 is a per unit value of the distance from the head end of the line to the second critical point and the total length, the imaginary line part represents the sag domain, and the starting point and ending point values are [ x1, x2], that is, when there are two critical points, the line lengths 0 to x1 and x2 to 1 belong to the sag domain.

If the number of the critical points is 3, the whole line is in the sag domain, the starting point value is 0, and the end point value is 1, that is, the whole line belongs to the sag domain.

FIG. 8 is a diagram illustrating the result of the sag domain of the IEEE30 node system considering the upper and lower limits of the uncertainty interval of the sensitive load tolerance capability, and referring to FIG. 8, the obtained sag domain is divided by an interval U_minCorresponding sag fields 1 and U_maxCorresponding to the composition of the sag field 2, and the solid line corresponding to the lower limit U of the tolerance capability_minThe calculated boundary of the sag domain 1 is a dotted line corresponding to an upper bound U of the tolerance capability_maxAnd at the boundary of the sag domain 2 obtained by calculation, the single-phase earth faults of the parts outside the dotted line can not cause the voltage sag event of the sensitive load connected to the bus 20, the single-phase earth faults of the parts inside the solid line can cause the voltage sag event of the bus 20, namely, the sag of the parts inside the boundary of the sag domain 1 can certainly influence the sensitive load, the sag of the parts outside the boundary of the sag domain 2 cannot certainly influence the sensitive load, and the parts between the two boundaries belong to an uncertainty region, namely, the uncertainty region can not necessarily influence the sensitive load.

The same or similar reference numerals correspond to the same or similar parts;

the positional relationships depicted in the drawings are for illustrative purposes only and are not to be construed as limiting the present patent;

it should be understood that the above-described embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. And are neither required nor exhaustive of all embodiments. Any modification, equivalent replacement, and improvement made within the spirit and principle of the present invention should be included in the protection scope of the claims of the present invention.

Claims (8)

1. A sag domain identification method considering load sensitivity uncertainty, the method comprising the steps of:

s1: load flow calculation is carried out on the system, and the voltage amplitude U of each node of the system in normal operation before short circuit fault is obtained_pref；

S2: setting a short-circuit fault node K and a sensitive load access node m, and calculating zero sequence, positive sequence and negative sequence transfer impedances between the point K and the point m, input impedance of the point K and a voltage amplitude before fault;

s3: calculating residual voltage amplitude U of each bus according to voltage amplitude of each node of the system before the fault and input impedance of the fault point K_mag；

S4: obtaining an upper limit U of the uncertain interval of the voltage tolerance capacity curve by knowing the variation range of the uncertain interval of the voltage tolerance capacity curve_maxAnd a lower bound limit U_minAnd combining the residual voltage amplitude U of each bus fault_magForming discrimination matrixes BUS and L INE and an upper limit U of a sensitive load voltage sag endurance uncertainty curve_maxRepresenting a boundary between the immune region and the uncertain region; lower bound U_minA boundary representing an uncertain region and a failed region;

s5: voltage tolerance value U for load on node m_thTaking the lower limit value U of the uncertain interval_minAccording to the value of the discrimination matrix L INE, calculating the critical point of the line, and determining the inclusion condition of the line in the sag domain;

s6: judging whether all lines of the system are traversed or not and whether all the uncertain spaces are traversed or not, and outputting a sag domain identification result if all the uncertain spaces are traversed; if not, returning to step S4 to perform the next route identification calculation; if all the lines have been traversed but not all the uncertain space has been traversed, let U_thTaking the upper bound U of the uncertainty interval_maxReturning to step S4 to continue the calculation;

s7: counting twice to obtain U_minCorresponding sag fields 1 and U_maxAnd obtaining a final sag domain identification result by the corresponding sag domain 2.

2. The method for identifying a sag domain with consideration of load sensitivity uncertainty according to claim 1, wherein the sequence transfer impedances between the fault node K and the sensitive load access node m in step S2 are:

Z_mK，0＝Z_mF，0+p(Z_mT，0-Z_mF，0)

Z_mK，1＝Z_mF，1+p(Z_mT，1-Z_mF，1)

Z_mK，2＝Z_mF，2+p(Z_mT，2-Z_mF，2)

wherein Z is_mK，0、Z_mK，1、Z_mK，2Transferring impedance for each sequence between a fault node K and a sensitive load access node m, wherein Z_mK，0For zero sequence transfer impedance, Z_mK，1For positive sequence transfer of impedance, Z_mK，2Negative sequence transfer impedance; z_mF，0、Z_mF，1、Z_mF，2Transferring impedance for each sequence between a head-end bus node F of a sensitive load node m and a load point m, wherein Z_mF，0For zero sequence transfer impedance, Z_mF，1For positive sequence transfer of impedance, Z_mF，2Negative sequence transfer impedance; z_mT，0、Z_mT，1、Z_mT，2Transferring impedance for each sequence between tail end bus node T of sensitive load node m and load point m, wherein Z_mT，0For zero sequence transfer impedance, Z_mT，1For positive sequence transfer of impedance, Z_mT，2Negative sequence transfer impedance; p is the per unit value representation of the distance from the fault point K to the bus head end node F;

the input impedance of the fault node K is:

Z_KK，0＝p²(Z_FF，0+Z_TT，0-2Z_FT，0-Z_C，0)+p[Z_C，0-2(Z_FF，0-Z_TT，0)]+Z_FF，0

Z_KK，1＝p²(Z_FF，1+Z_TT，1-2Z_FT，1-Z_C，1)+p[Z_C，1-2(Z_FF，1-Z_TT，1)]+Z_FF，1

Z_KK，2＝p²(Z_FF，2+Z_TT，2-2Z_FT，2-Z_C，2)+p[Z_C，2-2(Z_FF，2-Z_TT，2)]+Z_FF，2

in the formula, Z_KK，0、Z_KK，1、Z_KK，2For each sequence input of a faulty node KImpedance of, wherein, Z_KK，0Is zero sequence impedance, Z_KK，1Is a positive sequence input impedance, Z_KK，2Is a negative sequence input impedance; z_FF，1、Z_FF，2Z_FF，0、Z_FF，1、Z_FF，2Input impedance of head end bus node F as fault point k, where Z_FF，0Is a zero sequence input impedance, Z_FF，1Is a positive sequence input impedance, Z_FF，2Is a negative sequence input impedance; z_TT，0、Z_TT，1、Z_TT，2The input impedance for each sequence of tail bus node T, wherein Z_TT，0Is a zero sequence input impedance, Z_TT，1Is a positive sequence input impedance, Z_TT，2Is a negative sequence input impedance; z_C，0、Z_C，1、Z_C，2Is the sequence impedance on the line FT, where Z_C，0Is zero sequence impedance, Z_C，1Is a positive sequence impedance, Z_C，2P is the per unit value representation of the distance from the fault point K to the bus head end node F;

the voltage amplitude before the short-circuit fault occurs at the node K is represented as:

U_K，pref＝U_F，pref+p(U_T，pref-U_F，pref)

wherein, U_K，prefRepresenting the voltage of the K node before short-circuit fault occurs; u shape_F，prefRepresenting the node voltage amplitude of the bus node F before the fault; u shape_T，prefRepresenting the node voltage amplitude of the bus node T before the fault; p is as defined above.

3. The method for identifying sag domain with consideration of load sensitivity uncertainty as claimed in claim 1, wherein the bus fault residual voltage amplitude U of step S3_mag：

Wherein, U_magRepresenting the amplitude of the fault residual voltage of the bus;

the amplitude of each phase voltage of the bus m when the K point fails,

which represents the amplitude of the a-phase voltage,

representing the magnitude of the B-phase voltage,

representing the amplitude of the C-phase voltage; u shape_A，m，prefThe amplitude of the A phase voltage before m-point fault; a denotes a twiddle factor e^j120°；

And the voltage amplitude of the m point when the bus node K fails is shown.

4. The method as claimed in claim 1, wherein the upper limit and the lower limit of the uncertainty interval corresponding to the uncertainty curve of the voltage sag tolerance of the sensitive load in step S4 are respectively U_maxAnd U_minThe decision matrices BUS and L INE are formed as follows:

wherein, U_thRepresents the voltage endurance of the load carried by the node m; delta U_mag，nRepresents the bus residual voltage amplitude U_magAnd voltage endurance U_thΔ U for i ∈ (1, …, n)_mag，iWhen the value of (B) is less than or equal to zero, BUS_iTaking 1 to indicate that the bus i is contained in the sag domain; delta U_mag，iWhen the value of (B) is greater than zero, BUS_iTaking 0 to indicate that the bus i is not contained in the sag domain, L INE value is a sag domain discrimination parameter of the line, L INE_iA value of 0, indicating that the bus i is not in the sag domain, L INE_iA value of 1 indicates that bus i contains a critical point, L INE_iThe value is 2, which indicates that there are two critical points on the bus i;

judging parameters for sag domains of the bus F at two ends of the line i;

when one of the sag domain discrimination parameters is 1, L INE is used_iIf 1 is taken to indicate that the line has a critical point, and if 0 is taken to indicate that the line has a critical point, L INE is used_iIf the value is 0, the line has no critical point, if both values are 1, L INE is added_iThe value of 2 indicates that the line has two critical points.

5. The sag domain identification method considering load sensitivity uncertainty according to claim 1, wherein the process of step S5 is as follows:

s501, judging L INE_iIf L INE is equal to_iIs 0, indicating that the bus i is outside the sag domain, the next line is performedJudging if L INE_iIf not, obtaining a voltage sag amplitude curve by utilizing a cubic spline interpolation method, and executing the step S502;

s502, judge L INE_iIf L INE is equal to_iValue of (1) to find the critical point, L INE_iIf not 1, go to step S503;

s503: calculating the maximum point p of the voltage sag amplitude value on the line by using a golden section search method_maxAnd | f (pmax) | of the residual voltage equation function f;

s504: finding p_maxRear judgment | f (p)_max) I and U_thIf | f (p)_max) | is less than U_thIf yes, the whole line is included in the sag domain, and the step S501 is returned to continue to be executed; if | f (p)_max) | is greater than U_thThen according to L INE_iThe critical point is obtained by a critical point obtaining method with a value of 1.

6. The method for identifying sag domain with consideration of load sensitivity uncertainty as claimed in claim 5, wherein in step S502, if L INE_iThe value of (1) is obtained by the following method:

s5021: spline interpolation is carried out by using three points of p-0, p-0.5 and p-1 to obtain a residual voltage equation function of

Definition of U_th＝f(p_i) In the formula, x₁、x₂、x₃As a coefficient of function, p_iArgument to function, p at this time_iRespectively take p_i＝0、p_i0.5 and p_i＝1；

S5022: calculating | f (0.5) |, sequentially corresponding the short-circuit voltage amplitude of the first node of the line, the short-circuit voltage amplitude of the tail node of the line and | f (0.5) | at the three points in the step S5021, and solving the equation function of the residual voltage that p is more than or equal to 0_icRoot p of less than or equal to 1_ic；

S5023: defining an iteration initial value using the root of the residual voltage equation, determining two iteration initial values in the vicinity of the critical point, and takingp_ic，p_ic+Δp]Or [ p ]_ic-Δp，p_ic]Δ p is 0.01, which is the initial point p of secant iteration_fromAnd p_endCalculating a critical point; the iterative process is as follows:

p_new＝p_end-[f(p_end)-U_th](p_end-p_from)/[|f(p_end)|-|f(p_from)|]

p_from＝p_end

p_end＝p_new

wherein p is_from、p_endTwo initial value points of iteration; p is a radical of_newNew iteration values for the critical points; f (p)_end) Represents a point p_endThe residual voltage amplitude of; f (p)_from) Represents a point p_fromThe residual voltage amplitude of; u shape_thRepresents the voltage endurance of the load carried by the node m;

the convergence conditions are as follows:

||f(p_new)|-U_th|＜tol

wherein tol is convergence accuracy; p is a radical of_newNew iteration values for the critical points; u shape_thRepresents the voltage endurance of the load carried by the node m;

s5024: and (4) obtaining an accurate critical point accurate value by using a Newton method.

7. The method according to claim 5, wherein the step S503 is executed to calculate the maximum value p of the voltage sag amplitude on the line_maxAnd the | f (pmax) | golden section searching method of the residual voltage equation function f comprises the following steps:

s5031: according to the golden section point

Two initial value points p are defined₁、p₂The expression of the two initial value points is:

s5032: calculating p₁、p₂Corresponding residual pressure equation function value | f (p)₁) I and | f (p)₂)|；

S5033: judgment of | f (p)₁) Whether | is greater than or equal to | f (p)₂) If | f (p)₁)|≥|f(p₂) If, then the following iteration of assignment is performed:

if | f (p)₁)|＜|f(p₂) If, then the following iteration of assignment is performed:

s5033: judgment | p_b-p_aWhether the | is less than or equal to the established value or not represents the calculation setting precision; if p_b-p_aIf | is less than or equal to true, then use the current p₁、p₂Calculating a maximum point P_max：P_max＝(p_b+p_a) /2 and corresponding residual pressure equation function value | f (P)_max)|。

8. The method for identifying a sag domain with consideration of load sensitivity uncertainty as claimed in claim 5, wherein the step S504 is performed according to L INE_iThe method for solving the critical point with the value of 1 comprises the following steps:

s5041: using p ═ 0, p ═ p_maxCarrying out spline interpolation on three points of p-1 to obtain a residual voltage equation function of

Definition of U_th＝f(p_i) In the formula, x₁、x₂、x₃As a coefficient of function, p_iArgument to function, p at this time_iRespectively take p_i＝0、p_i＝p_maxAnd p_i＝1；

S5042: calculate | f (p)_max) I, the three points in step S5042 sequentially correspond to the short-circuit voltage amplitude of the first node of the line, the short-circuit voltage amplitude of the tail node of the line, and | f (p)_max) I, obtaining the residual voltage equation function with p being more than or equal to 0_icRoot p of less than or equal to 1_ic；

S5043: defining an initial iteration value using the roots of the residual voltage equation, determining two initial iteration values near a critical point, taking [ p ]_ic，p_ic+Δp]Or [ p ]_ic-Δp，p_ic]Δ p is 0.01, which is the initial point p of secant iteration_fromAnd p_endCalculating a critical point; the iterative process is as follows:

p_new＝p_end-[f(p_end)-U_th](p_end-p_from)/[|f(p_end)|-|f(p_from)|]

p_from＝p_end

p_end＝p_new

wherein p is_from、p_endTwo initial value points of iteration; p is a radical of_newNew iteration values for the critical points; f (p)_end) Represents a point p_endThe residual voltage amplitude of; f (p)_from) Represents a point p_fromThe residual voltage amplitude of; u shape_thRepresents the voltage endurance of the load carried by the node m;

the convergence conditions are as follows:

||f(p_new)|-U_th|＜tol

where tol is convergence accuracy, p_newIs a new iteration value of the critical point, U_thRepresents the voltage endurance of the load carried by the node m;

s5043: obtaining | f (p) by Newton's method_max) | is greater than U_thThe exact value of the time critical point.

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