Receiving end power grid minimum inertia demand evaluation method considering different fault types

Abstract

The invention provides a receiving-end power grid minimum inertia demand evaluation method considering different fault types, and the method comprises the steps: S1, collecting the system data of a receiving-end power grid, and enabling the system data to comprise the data of a power generator and a line; constructing a first model according to the generator and the line data; the first model is a multi-machine frequency response model comprising multiple types of units of a receiving-end power grid and an alternating-current tie line; s2, discretizing the first model based on Laplace transform and a backward difference operator to obtain a second model; and S3, setting a first condition for the second model, and calculating the minimum inertia demand of the receiving-end power grid based on the first condition and the second model in combination with an improved Newton-Raphson algorithm. The method can ensure safe and stable operation of the receiving-end power grid, enhance the frequency stability of the power grid, and guarantee stable operation of the system in different scenes.

Description

Technical Field

[0001] The invention relates to the technical field of power system planning, and in particular to a method for evaluating minimum inertia demand of a power grid. Background Art

[0002] As the proportion of large-scale renewable energy such as wind power and photovoltaic power gradually increases, the power system presents the "double high" characteristics of high proportion of renewable energy access and high proportion of power electronic equipment application. The inertia provided by renewable energy connected to the power system using power electronic interfaces is called "virtual inertia", which cannot provide reliable primary frequency regulation support for the system like synchronous generators such as thermal power and hydropower; in addition, the system frequency change rate and the lowest frequency point deteriorate significantly under power disturbances, leading to extreme accidents such as large-scale power outages. In order to explore the safety boundary of the power system inertia and ensure the stable operation of the system in different scenarios, it is of great significance to accurately evaluate the system inertia demand.

[0003] In the context of a high proportion of new energy power systems, the continuous increase in the penetration rate of new energy over time will inevitably cause changes in system inertia and frequency modulation parameters. The changes in the inertia composition structure also make the system frequency response process more complex. In addition, the system inertia demand also varies in different spatial dimensions, so it is necessary to evaluate the system inertia demand for different scenarios. However, the existing system inertia demand evaluation method is mainly based on the frequency change rate and the frequency minimum point constraints. The analysis of the problem is not in-depth enough, the scenario setting is not flexible enough, and the considerations are not comprehensive enough.

[0004] The invention patent with the publication number CN 118868073A discloses a method and system for evaluating the minimum inertia requirement of a new energy power system, including obtaining source data and load data of the new energy power system; fitting and constructing the low-order transfer function of the synchronous unit, the transfer function of the new energy station and the low-order transfer function of the load; constructing a frequency response model of the power system, and establishing a set of equations including the time point corresponding to the maximum frequency deviation of the system, the maximum frequency deviation constraint and the minimum inertia time constant through open-loop processing; solving the set of equations to calculate the total equivalent kinetic energy of the system that meets the minimum inertia requirement of the system. This method realizes the evaluation of the minimum inertia requirement of the system considering the maximum frequency deviation constraint, but it is difficult to apply to receiving-end power grids with different new energy penetration rates and different fault types. Summary of the invention

[0005] In view of the technical problem that the existing inertia demand assessment method is difficult to apply to receiving power grids with different renewable energy penetration rates and different fault types, the present invention proposes a minimum inertia demand assessment method for receiving power grids taking into account different fault types. The minimum inertia demand of the receiving power grid under different fault conditions and different renewable energy penetration rates is calculated by combining a discretized multi-machine frequency response model with an improved Newton-Raphson algorithm. This can ensure the safe and stable operation of the receiving power grid, enhance the frequency stability of the power grid, and ensure the stable operation of the system in different scenarios.

[0006] In order to achieve the above object, the technical solution of the present invention is achieved as follows:

[0007] A method for evaluating the minimum inertia requirement of a receiving-end power grid considering different fault types comprises the following steps:

[0008] S1: Collecting receiving-end power grid system data, the system data including generator and line data; constructing a first model based on the generator and line data; the first model is a multi-machine frequency response model including multiple types of units and AC tie lines in the receiving-end power grid;

[0009] S2: discretizing the first model based on Laplace transform and backward difference operator to obtain a second model;

[0010] S3: Setting a first condition for the second model, and calculating the minimum inertia requirement of the receiving-end power grid based on the first condition and the second model combined with an improved Newton-Raphson algorithm; the setting of the first condition includes setting different preset fault types and different new energy penetrations.

[0011] The method for constructing the first model according to the generator and line data is:

[0012] The parameters of the frequency response control link are obtained according to the generator and line data, including the system equivalent inertia constant and the primary frequency regulation control coefficient. The regulation power model of multiple units and the regulation power model of AC interconnection lines are constructed according to the system equivalent inertia constant and the primary frequency regulation control coefficient. The first model is constructed by considering the new energy penetration rate and combining the regulation power model of multiple units, the regulation power model of AC interconnection lines and the rotor motion equation.

[0013] The regulating power model of the multi-units is:

[0014] ΔP G =(1-K X )(GJGATBΔf+GSTBΔf+GSTAΔf+GHΔf);

[0015] Among them, ΔP G Indicates the total regulating power of the unit; K Xrepresents the penetration rate of renewable energy; Δf represents the system frequency deviation; GJGATB, GSTB, GSTA, and GH all represent the primary frequency regulation coefficient of the unit;

[0016] The regulation power model of the AC tie line is:

[0017] ΔP J =K J Δf;

[0018] Among them, ΔP J Indicates the regulation power of the system AC tie line; K J Indicates the primary frequency modulation control coefficient of the system AC tie line;

[0019] The first model is:

[0020]

[0021] Among them, H sys Indicates the system equivalent inertia constant; ΔP d is the disturbance power; D sys Represents the system damping coefficient.

[0022] The method for obtaining the second model is: based on Laplace transform, using a backward difference operator to convert the differential part of the first-order derivative in the time domain differential expression corresponding to the transfer function in the frequency response control link into a differential part, completing the discretization processing of the frequency response control, and obtaining a discretized time domain expression of the frequency response control link; using a backward difference operator to discretize the first model to obtain the second model.

[0023] The backward difference operator expression is:

[0024]

[0025] Where i represents the discrete time domain time period number, and Δt represents the time interval of each discrete time domain;

[0026] The discrete time domain expression of the frequency response control link includes the discrete time domain expression of the inertial response link, the discrete time domain expression of the proportional link, the discrete time domain expression of the differential link and the discrete time domain expression of the integral link.

[0027] The second model is:

[0028]

[0029] Among them, Δf(i) represents the system frequency deviation of the i-th discrete time domain; Δf(i-1) represents the system frequency deviation of the i-1-th discrete time domain; Δt represents the time interval of each discrete time domain.

[0030] The different preset fault types include two DC bipolar locking fault step fault, two DC simultaneous commutation failure fault, two DC continuous commutation failure non-step fault and large-scale new energy low-throughput short-term power impact fault; different preset fault types are determined by disturbance power ΔP d Set up; disturbance power ΔP d The setting formulas are:

[0031] ΔP d =P d ;

[0032]

[0033] Where P d is the disturbance power of two DC bipolar blocking faults; P d1 P is the disturbance power caused by the failure of commutation of two DC circuits at the same time; d2 and P d3 is the disturbance power of two DC continuous commutation failures; P d4 is the disturbance power of short-term power shock fault caused by large-scale new energy low penetration; t1, t2 and t3 are the preset times for different fault types.

[0034] The method for calculating the minimum inertia requirement of the receiving-end power grid by combining the improved Newton-Raphson algorithm is as follows:

[0035] A1: Initialize the system equivalent inertia constant H sys =H0, based on the disturbance power ΔP d The setting formula setting failure; set the new energy penetration rate K according to demand X ; Preset the maximum system frequency deviation constraint value and the maximum frequency change rate constraint value;

[0036] A2: According to the inertia requirement value H k-1 Combined with the second model, simulation iterative calculation is performed to obtain the corresponding system frequency deviation and frequency change rate, H k-1 The inertia demand value calculated for the previous iteration simulation;

[0037] A3: Determine whether the system frequency deviation and frequency change rate meet the constraint critical conditions; if so, enter A4; if not, correct the inertia demand value through the Newton-Raphson algorithm and enter A2;

[0038] A4: Set the inertia requirement value H k-1 Output is the minimum inertia requirement.

[0039] The frequency change rate calculation formula is:

[0040]

[0041] Among them, ROCOF(i k ) represents the frequency change rate of the i-th discrete time domain in the k-th simulation iteration calculation; f(i k ) represents the system frequency of the i-th discrete time domain in the k-th simulation iteration calculation; f(i k ) represents the system frequency of the i-1th discrete time domain in the kth simulation iteration calculation;

[0042] The constraint critical conditions are: the maximum system frequency deviation value ≤ the maximum system frequency deviation constraint value and the frequency change rate ≤ the maximum frequency change rate constraint value.

[0043] The method for correcting the inertia requirement value by using the Newton-Raphson algorithm is:

[0044] Set the objective function for inertia correction:

[0045] Δf m (k)-Δf max =0;

[0046] Where Δf m (k) represents the maximum frequency deviation of the kth simulation calculation; Δf max Indicates the maximum frequency deviation constraint value;

[0047] Calculate the correction amount and calculate the approximate solution H based on the correction amount k ;

[0048]

[0049] H k =H k-1 +H X ;

[0050] Among them, Δf′(H k ) indicates that the objective function is in the approximate solution H k The first derivative of X is the correction amount.

[0051] The beneficial effects of the present invention are:

[0052] The minimum inertia requirement assessment method for a receiving power grid considering different fault types of the present invention provides data support for the power system planning of the receiving power grid, facilitates the receiving system to carry out energy storage planning and new energy flexibility transformation, can improve the flexibility of inertia resources, can ensure the safe and stable operation of the receiving power grid, enhance the frequency stability of the power grid, and ensure the stable operation of the system in different scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0054] The drawings constituting a part of this application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0055] Figure 1 It is a flow chart of the preferred embodiment 1 of the present invention.

[0056] Figure 2 It is a comparison diagram of the simulation frequency curve of the multi-machine frequency response model in the single-loop DC bipolar blocking scenario of the preferred embodiment 2 of the present invention and the frequency curve of the PSD-BPA (Power System Dynamics-Basic Power Analysis) software.

[0057] Figure 3 It is a comparison diagram of the simulation frequency curve of the multi-machine frequency response model in the two-circuit DC bipolar locking scenario of the preferred embodiment 2 of the present invention and the PSD-BPA software frequency curve.

[0058] Figure 4 It is a comparison diagram of the power disturbance curves of each unit in the second preferred embodiment of the present invention.

[0059] Figure 5 It is a comparison diagram of the isovalue curve and the discretization curve in the two-circuit DC bipolar locking scenario of the preferred embodiment 2 of the present invention.

[0060] Figure 6 It is a comparison diagram of the isovalue curve and the discretization curve in the scenario of two DC circuits simultaneously commutating failure in the preferred embodiment 2 of the present invention.

[0061] Figure 7 It is a comparison diagram of the isovalue curve and the discretization curve in the multi-circuit DC continuous commutation failure scenario of the second preferred embodiment of the present invention.

[0062] Figure 8 This is a fault disturbance curve under a two-circuit DC bipolar locking fault scenario of the second preferred embodiment of the present invention.

[0063] Fig. 9 This is a fault disturbance curve in the scenario of simultaneous commutation failure of two DC circuits according to the second preferred embodiment of the present invention.

[0064] Fig.10This is a fault disturbance curve in a two-circuit DC continuous commutation failure scenario of the second preferred embodiment of the present invention.

[0065] Fig.11 It is a fault disturbance curve under the scenario of large-scale new energy low-penetration short-term power impact in the preferred embodiment 2 of the present invention.

[0066] Fig.12 This is a frequency change rate curve in a two-circuit DC bipolar locking scenario of the second preferred embodiment of the present invention.

[0067] Fig.13 This is a frequency change rate curve in the scenario of two DC circuits failing to commutate simultaneously according to the second preferred embodiment of the present invention.

[0068] Fig.14 This is a frequency change rate curve in a two-circuit DC continuous commutation failure scenario of the second preferred embodiment of the present invention.

[0069] Fig.15 It is the frequency change rate curve of the second preferred embodiment of the present invention under the scenario of large-scale new energy low-penetration short-term power impact.

[0070] Fig.16 This is a frequency response curve of the receiving-end power grid in a two-circuit DC bipolar blocking scenario of the second preferred embodiment of the present invention.

[0071] Fig.17 This is the minimum inertia requirement evolution curve of the receiving-end power grid in the two-circuit DC bipolar blocking scenario of the second preferred embodiment of the present invention.

[0072] Fig.18 This is a frequency response curve of the receiving-end power grid in the scenario of simultaneous commutation failure of two DC loops according to the second preferred embodiment of the present invention.

[0073] Fig.19 This is the minimum inertia requirement evolution curve of the receiving-end power grid in the scenario of simultaneous commutation failure of two DC loops in the second preferred embodiment of the present invention. DETAILED DESCRIPTION

[0074] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0075] The grid frequency regulation process can be mainly divided into: inertia response link, primary frequency regulation and secondary frequency regulation. That is to say, in the inertia response stage, in the grid, when the external load fluctuates, there will be an imbalance between the power generation power and the load power in the grid, and the rotor speed will change. The synchronous generator set will first use the rotational inertia in the rotor to suppress the frequency deviation, quickly release or absorb the rotor kinetic energy to provide active power support for the grid, and slow down the rate of frequency change; in the primary frequency regulation stage (including proportional, differential, and integral), since the rotor rotational inertia cannot instantly and completely make up for the power shortage in the grid, the grid frequency will still deviate. At this time, the speed regulator of the generator set needs to play a regulating role, adjust the output of the prime mover and then change the active power output of each unit to balance it with the external load power, minimize the total grid frequency deviation as much as possible, and realize differential regulation; and the secondary frequency regulation is based on the previous one, the frequency regulator acts to adjust the grid to change the output power so that the frequency gradually returns to the rated value, and realizes non-differential regulation.

[0076] Example 1

[0077] A method for evaluating the minimum inertia requirement of the receiving-end power grid considering different fault types, such as Figure 1 As shown, the steps include:

[0078] S1: Collecting receiving-end power grid system data, the system data including generator and line data; constructing a first model based on the generator and line data, the first model reflecting the multi-machine frequency response of various types of units and AC interconnection lines in the receiving-end power grid.

[0079] Taking into account that the types of generator sets in the receiving power grid are mainly composed of hydropower units and thermal power units, the hydropower units include turbines and generators, and the thermal power units include boilers, steam turbine units and generators, and the power input of the receiving power grid through the AC interconnection line is relatively high, so its frequency regulation effect is taken into account in the multi-machine equivalent frequency response model, and a multi-machine frequency response model including various types of units and AC interconnection lines of the receiving power grid is constructed, that is, the first model of the present invention.

[0080] The generator and line data of Henan power grid are collected; the parameters of the frequency response control link are obtained according to the generator and line data, including the system equivalent inertia constant and the primary frequency regulation control coefficient; the regulation power model of multiple units and the regulation power model of AC interconnection lines are constructed according to the system equivalent inertia constant and the primary frequency regulation control coefficient; the first model is constructed by considering the new energy penetration rate and combining the regulation power model of multiple units, the regulation power model of AC interconnection lines and the rotor motion equation.

[0081] The specific process of building the first model is as follows:

[0082] After the power system is disturbed, the system frequency of the receiving power grid will shift. At this time, the regulation power model of each type of unit is:

[0083] ΔP G =(1-K X )(GJGATBΔf+GSTBΔf+GSTAΔf+GHΔf);

[0084] Among them, ΔP G Indicates the total regulating power of each type of unit; K X represents the penetration rate of new energy; Δf represents the system frequency deviation; GJGATB, GSTB, GSTA and GH represent the primary frequency regulation control coefficients of each type of units respectively.

[0085] The regulation power model of the AC tie line is:

[0086] ΔP J =K J Δf;

[0087] Among them, ΔP J Indicates the regulation power of the system AC tie line; K J Represents the primary frequency modulation control coefficient of the system AC tie line.

[0088] After a disturbance occurs in the power system, in order to maintain the frequency stability of the system, active frequency regulation is required, including the inertial response link and the primary frequency regulation link. The regulation process can be expressed by the rotor motion equation:

[0089]

[0090] Among them, H sys represents the system equivalent inertia constant; Δf represents the system frequency deviation; ΔP m and ΔP d They represent the primary frequency modulation power adjustment and disturbance power respectively; D sys Represents the system damping coefficient.

[0091] The total regulating power of each type of unit ΔP G and the regulated power ΔP of the system AC tie line J Substitute into the rotor motion equation and consider the new energy permeability coefficient (1-K X ), we get the first model expression:

[0092]

[0093] The Simulink model is built based on the multi-machine frequency response equivalent model framework, in which the dynamic characteristics of the prime mover and speed control system of each generator set are equivalent to a single machine.

[0094] The steam turbine speed control system in the prime mover adopts the "GJ+GA+TB", "GS+TB" and "GS+TA" card models built into the PSD-BPA software, and the water turbine speed control system adopts the "GH" card model built into the software, and adds a frequency response module for the AC interconnection line.

[0095] After building the first model, based on the PSD-BPA software, set the fault disturbance in the software, output the frequency change curve, and compare it with the frequency change curve of the first model under the same disturbance to verify the validity of the first model and ensure its usability.

[0096] S2: discretize the first model based on Laplace transform and backward difference operator to obtain the second model.

[0097] The second model is used to complete the frequency response process simulation calculation when the receiving-end power grid encounters disturbance from the perspective of time domain simulation, and obtain the frequency response curve and output curves of various types of units.

[0098] Based on Laplace transform, the backward difference operator is used to convert the differential part of the first-order derivative in the time domain differential expression corresponding to the transfer function of each frequency response control link into the differential part, and the discretization processing of each frequency response control link is completed to obtain the discretized time domain expression. The backward difference expression is:

[0099]

[0100] Wherein, i represents the discrete time domain time period number, and Δt represents the time interval of each discrete time domain segment.

[0101] The method for discretizing the frequency response control link of each generator in the first model is:

[0102] For the proportional link, the transfer function is:

[0103] Y(s)=K p ·X(s);

[0104] Where Y(s) is the Laplace transform of the transfer function output signal, X(s) is the Laplace transform of the transfer function input signal, and K p is the proportionality coefficient and s is a complex variable in the frequency domain.

[0105] The time domain differential expression is:

[0106] y(t)=K p x(t);

[0107] Among them, y(t) is the output signal of the time domain differential expression, and x(t) is the input signal of the time domain differential expression. The discretized time domain expression is:

[0108] y(i)=K p x(i);

[0109] Among them, y(i) is the output signal of the discretized time domain expression, and x(i) is the input signal of the discretized time domain expression.

[0110] For the differential link, the transfer function is:

[0111] Y(s)=K d s·X(s);

[0112] Among them, K d is the differential coefficient.

[0113] The time domain differential expression is:

[0114]

[0115] Using the backward difference operator, the discretized time domain expression is obtained:

[0116]

[0117] For the integral link, the transfer function is:

[0118]

[0119] Among them, K i is the integration coefficient.

[0120] The time domain differential expression is:

[0121]

[0122] Using the backward difference operator, the discretized time domain expression is obtained:

[0123] y(i)=y(i-1)+K i ·Δt·x(i);

[0124] For the inertial response link, the transfer function and the corresponding time domain differential expression can be expressed as:

[0125]

[0126] Among them, K g is the gain coefficient of the inertial response link, and T is the time constant.

[0127] Using the backward difference operator, the discretized time domain expression is obtained:

[0128]

[0129] For the inertial response link, proportional link, differential link and integral link, where x(i) corresponds to the system frequency deviation in the second model expression, y(i) corresponds to the adjustment power, the adjustment power is adjusted by inputting the system frequency deviation.

[0130] The method of discretizing the first model is:

[0131] The first model is discretized using a backward difference operator to obtain a second model; specifically, the backward difference expression is substituted into the first model expression to obtain a system frequency deviation expression, namely, the second model.

[0132]

[0133] Among them, H sys represents the system equivalent inertia constant; Δf(i) represents the system frequency deviation in the i-th discrete time domain; Δf(i-1) represents the system frequency deviation in the i-1th discrete time domain; ΔP G Indicates the total regulating power of each type of unit; ΔP J Indicates the regulation power of the system AC tie line; ΔP d represents the disturbance power; D sys represents the system damping coefficient; Δt represents the time interval of each discrete time domain.

[0134] In a preferred embodiment of the present invention, the backward difference expression is applied to the time domain differential expression, and the time domain expression of each commonly used control link in a specified time period can be derived. The module is discretized according to the multi-machine equivalent frequency response model constructed by Simulink, and it is converted from a frequency domain model to a multi-machine frequency response model in a discrete time domain. By completing the simulation calculation of the frequency response process when the receiving power grid encounters a disturbance from the perspective of time domain simulation, the frequency response curve and the output curve of each type of unit are obtained, bypassing the problem that the frequency response curve is difficult to analyze and describe, providing a calculation tool for building a minimum inertia demand assessment system, and providing conditions for solving the minimum inertia value. Discretizing the first model to obtain the second model is not only convenient for calculation, but also convenient for setting different fault types, and the frequency change at any moment of each simulation iteration can also be clearly obtained.

[0135] S3: Setting a first condition for the second model, and calculating the minimum inertia requirement of the receiving-end power grid based on the first condition and the second model in combination with an improved Newton-Raphson algorithm.

[0136] The first condition includes setting different preset fault types and different new energy penetration rates for the second model.

[0137] The new energy penetration rate is expressed by the variable K X To achieve this, we need to set up the new energy penetration rate KX The change will further change the system's own inertia and the frequency regulation capability of the synchronous unit. By changing the penetration rate of new energy, the equivalent inertia of the system will be changed. The inertia can provide energy support for electromagnetic power, maintain the active balance of the system, slow down the change of frequency, reduce the frequency change rate, and provide preparation time for the primary frequency regulation of the system.

[0138] The various preset fault types are determined by the disturbance power ΔP d Set up; the various preset fault types include two-circuit DC bipolar lockout fault step fault, two-circuit DC simultaneous commutation failure fault, two-circuit DC continuous commutation failure non-step fault and large-scale new energy low-power short-term power impact fault.

[0139] Disturbance power ΔP d The setting formulas are:

[0140] ΔP d =P d ;

[0141]

[0142]

[0143] Where: P d is the disturbance power of two DC bipolar blocking faults; P d1 P is the disturbance power caused by the failure of commutation of two DC circuits at the same time; d2 and P d3 is the disturbance power of two DC continuous commutation failures; P d4 is the disturbance power of short-term power shock fault caused by large-scale new energy low penetration; t1, t2 and t3 are the preset times for different fault types.

[0144] The above different disturbance powers ΔP d The setting formula and different new energy penetration rates K X Combine to form the first condition.

[0145] The method for calculating the minimum inertia requirement of the receiving-end power grid based on the first condition and the second model combined with the improved Newton-Raphson algorithm is:

[0146] A1: Initialize the system equivalent inertia constant H sys =H0, based on the disturbance power ΔP d The setting formula setting failure; set the new energy penetration rate K according to demand X ; Preset the maximum system frequency deviation constraint value and the maximum frequency change rate constraint value.

[0147] A2: According to the inertia requirement value H k-1Combined with the second model, simulation iterative calculation is performed to obtain the corresponding system frequency deviation and frequency change rate, H k-1 The inertia demand value calculated for the previous simulation iteration.

[0148] The calculation formula of system frequency deviation is:

[0149]

[0150] where i k represents the discrete time domain time period number in the kth simulation iteration calculation; Δf(i k ) represents the system frequency deviation of the i-th discrete time domain in the k-th simulation iteration calculation; Δf(i k -1) represents the system frequency deviation of the i-1th discrete time domain in the kth simulation iteration calculation.

[0151] According to the second model, the system frequency of each discrete time domain node under different fault type disturbances is calculated, and the frequency change rate can be expressed by the following relationship:

[0152]

[0153] Among them, ROCOF(i k ) represents the frequency change rate of the i-th discrete time domain in the k-th simulation iteration calculation; f(i k ) represents the system frequency of the i-th discrete time domain in the k-th simulation iteration calculation; f(i k ) represents the system frequency of the i-1th discrete time domain in the kth simulation iteration calculation; Δt represents the time interval of each discrete time domain.

[0154] Finally, the frequency deviation and frequency change rate of the discrete time domain system in the kth simulation iteration calculation are obtained.

[0155] A3: Determine whether the system frequency deviation and frequency change rate meet the critical constraint conditions; if so, enter A4; if not, correct the inertia demand value through the Newton-Raphson algorithm and enter A2.

[0156] After the system frequency deviation and the frequency change rate are calculated, the maximum value of the system frequency deviation and the maximum value of the frequency change rate in multiple discrete time domains are obtained.

[0157] The critical constraint conditions are: the maximum system frequency deviation ≤ the maximum system frequency deviation constraint value and the frequency change rate ≤ the maximum frequency change rate constraint value.

[0158] The method of correcting the inertia demand value by the Newton-Raphson algorithm is: to obtain the inertia value that makes the frequency response curve located at the critical position of the constraint by numerical correction; the specific method is to set the objective function of the inertia correction:

[0159] Δf m (k)-Δf max =0;

[0160] Where Δf m (k) represents the maximum frequency deviation of the kth simulation calculation; Δf max Indicates the maximum frequency deviation constraint value.

[0161] According to the calculation formula of system frequency deviation, when other parameters are known, the calculation formula of system frequency deviation can be regarded as a function of the inertia demand value, that is, Δf m (k)-Δf max =Δf(H k )=0; In the improved Newton-Raphson algorithm, the numerator of the correction quantity represents the approximate solution H k The function value Δf(H k ), the constraint gap Δf calculated by the k-th simulation m (k)-Δf max Instead; the denominator of the correction amount represents the objective function in the approximate solution H k The first derivative of :

[0162]

[0163] H k =H k-1 +H X ;

[0164] A4: Set the inertia requirement value H k-1 The output is the minimum inertia requirement.

[0165] Example 2

[0166] A method for evaluating the minimum inertia requirement of the receiving-end power grid considering different fault types is as follows:

[0167] In a preferred embodiment of the present invention, the solution of the present invention is applied to the receiving power grid in Province Q, and the minimum inertia requirement of the receiving power grid in the 2025 planning scenario (new energy output accounts for 15%, Xiada mode) is evaluated.

[0168] 1. Verification of multi-machine equivalent frequency response model and discretization accuracy.

[0169] A multi-machine frequency response model is constructed based on the solution of the present invention, and the simulated frequency curves of the multi-machine frequency response model constructed based on the solution of the present invention in two scenarios of single-circuit DC bipolar blocking and two-circuit DC bipolar blocking are compared with the PSD-BPA frequency curves. See the comparison diagram for details. Figures 2 to 3 ,The specific extreme value frequency and extreme value time are shown in Table 1.

[0170] Table 1 Extreme frequency and extreme time of simulation frequency curve and PSD-BPA frequency curve

[0171]

[0172] Since the PSD-BPA model has stronger interactive ability, the model has a smaller steady-state frequency deviation in the later stage of the frequency response steady state, and there is a certain error with the steady-state frequency deviation of the simulation frequency curve. However, in the early stage of the disturbance, the frequency dynamic characteristics of the two models are basically the same, and the errors of the extreme frequency and extreme time of the single-loop DC bipolar lockout are 0.0042Hz and 0.29s, and the errors of the extreme frequency and extreme time of the two-loop DC bipolar lockout are 0.0087Hz and 0.56s. In these two fault conditions, the frequency prediction error is extremely small, and the impact on the evaluation of the minimum inertia requirement is extremely small, which can verify the accuracy of the multi-machine frequency response model.

[0173] Discretize the multi-machine frequency response model and compare the power disturbance curves of each unit. See the comparison chart for details. Figure 4 , and compare the discretized frequency response curve with the equivalent frequency response curve under different fault types (two DC bipolar blocking, two DC simultaneous commutation failure and multiple DC continuous commutation failure). See the comparison chart for details. Figures 5 to 7 .

[0174] The power dynamic characteristics of the power disturbance curve of each unit after discretization are basically consistent with the power disturbance curve of the equivalent frequency response model. The frequency dynamic characteristics of the discretized frequency response curve and the equivalent frequency response curve under different fault conditions are basically consistent. The errors in the time and size of the extreme frequency are both within a very small range. It can be verified that the multi-machine equivalent frequency response model in the discrete time domain has high accuracy and is applicable in the minimum inertia requirement assessment.

[0175] 2. Assessment of minimum inertia requirement and accuracy verification of the receiving power grid in Province Q.

[0176] (1) Evaluation of the minimum inertia requirement of the receiving power grid under different anticipated fault conditions.

[0177] Set different fault types as two-way DC bipolar blocking, two-way DC simultaneous commutation failure, two-way DC continuous commutation failure and large-scale new energy low-throughput short-term power impact. The fault disturbance curves are shown in Figures 8 to 11 As shown. The frequency constraint condition is that the frequency change rate is no more than 2Hz / s, and the maximum frequency deviation is within the range of 0.5±0.0005Hz. Under these four scenarios, the minimum inertia requirement of the receiving power grid considering the 2025 planning scenario (new energy output accounts for 15%, Xiada mode) is solved.

[0178] Table 2 Minimum inertia requirements of the receiving power grid under different fault scenarios

[0179]

[0180] Table 2 shows the minimum inertia requirement of the receiving power grid under different fault scenarios. The minimum inertia requirements in the four scenarios of two DC bipolar blocking, two DC simultaneous commutation failure, two DC continuous commutation failure and large-scale renewable energy low-through short-term power shock are 2.3356s, 2.3316s and 1.8148s respectively. It can be seen that the minimum inertia requirement of two DC continuous commutation failure is lower than that of two DC simultaneous commutation failure and two DC bipolar blocking, indicating that the harm of two DC continuous commutation failure to the frequency stability of the power grid is lower than that of two DC simultaneous commutation failure and two DC bipolar blocking. The continuous shock of two DC simultaneous commutation failure is more harmful to the power grid. In addition to inducing subsequent DC commutation failure by affecting the voltage and dynamic reactive support of the DC converter station through the coupling voltage, the power shock may even affect the synchronous stability of the AC system through the superposition of multiple DC power shocks. The large-scale and periodic oscillation changes of the state quantities such as the power angle, voltage, current and power of the synchronous power grid units in turn affect the subsequent commutation safety of the DC system.

[0181] (2) Verification of the effectiveness and accuracy of the minimum inertia requirement assessment of the receiving power grid under different anticipated fault conditions.

[0182] Substituting the calculated minimum inertia requirement into the second model, the system frequency deviation and frequency change rate can be obtained and analyzed. The maximum system frequency deviation under these four fault forms is shown in Table 3.

[0183] Table 3 Maximum frequency deviation of the receiving power grid under different fault scenarios

[0184]

[0185] From Table 3, it can be concluded that under different fault scenarios, when solving the minimum inertia requirement of the receiving-end power grid, the maximum frequency deviation reaches 0.4995 Hz, which meets the maximum frequency deviation constraint.

[0186] Figures 12 to 15 The frequency change rate curves under four fault forms. Figures 12 to 15 It can be found that at different fault occurrence times, the frequency change rate did not reach the maximum value. After a short period of fault continuation, the frequency change rate reached the maximum value. Table 4 shows the maximum frequency change rate of the receiving power grid under different fault scenarios. The frequency change rate did not exceed 2Hz / s, satisfying the maximum frequency change rate constraint.

[0187] Table 4 Maximum frequency change rate of the receiving power grid under different fault scenarios

[0188]

[0189] By substituting the calculated minimum inertia requirement into the second model, it is analyzed that both the system frequency deviation and the frequency change rate meet the set constraints. The effectiveness and accuracy of the minimum inertia requirement evaluated by this method are verified.

[0190] 3. Evaluation of the minimum inertia requirement of the receiving power grid under different renewable energy penetration rates.

[0191] Under two anticipated fault forms (two DC bipolar blocking and two DC simultaneous commutation failures), the renewable energy penetration rate is set to increase from 0 to 50%, and the minimum inertia requirements of the receiving power grid in 2025 are solved respectively. Figures 16 to 19 They are respectively the frequency response curve of the receiving power grid under different new energy penetration rates and the evolution trend of the minimum inertia requirement of the receiving power grid.

[0192] From the frequency response curves of the receiving power grid under different renewable energy penetration rates, it can be seen that as the renewable energy penetration rate gradually increases, its transient extreme frequency and quasi-steady-state extreme frequency are gradually decreasing. Figures 16 to 19 It can be seen from the figure that with the increase in the penetration rate of new energy, the minimum inertia requirement of the receiving power grid is gradually increasing. The gradual increase in the penetration rate of new energy has caused the system's frequency response capability to decline, the maximum frequency deviation to increase, and significantly affected the system's frequency stability; in the power balance, the effective capacity is far lower than that of conventional power sources, the supply guarantee capability is low, and the load support capability is weak.

[0193] Other methods and principles are the same as those in Example 1.

[0194] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for evaluating the minimum inertia requirement of a receiving-end power grid considering different fault types, characterized in that: Includes steps: S1: Collecting receiving-end power grid system data, the system data including generator and line data; constructing a first model based on the generator and line data; the first model is a multi-machine frequency response model including multiple types of units and AC tie lines in the receiving-end power grid; S2: discretizing the first model based on Laplace transform and backward difference operator to obtain a second model; S3: Setting a first condition for the second model, and calculating the minimum inertia requirement of the receiving-end power grid based on the first condition and the second model combined with an improved Newton-Raphson algorithm; the setting of the first condition includes setting different preset fault types and different new energy penetrations.

2. The method for evaluating the minimum inertia requirement of a receiving-end power grid considering different fault types according to claim 1 is characterized in that: The method for constructing the first model according to the generator and line data is: The parameters of the frequency response control link are obtained according to the generator and line data, including the system equivalent inertia constant and the primary frequency regulation control coefficient. The regulation power model of multiple units and the regulation power model of AC interconnection lines are constructed according to the system equivalent inertia constant and the primary frequency regulation control coefficient. The first model is constructed by considering the new energy penetration rate and combining the regulation power model of multiple units, the regulation power model of AC interconnection lines and the rotor motion equation.

3. The method for evaluating the minimum inertia requirement of a receiving-end power grid considering different fault types according to claim 2 is characterized in that: The regulating power model of the multi-units is: ΔP G =(1-K X )(GJGATBΔf+GSTBΔf+GSTAΔf+GHΔf); Among them, ΔP G Indicates the total regulating power of the unit; K X represents the penetration rate of renewable energy; Δf represents the system frequency deviation; GJGATB, GSTB, GSTA, and GH all represent the primary frequency regulation coefficient of the unit; The regulation power model of the AC tie line is: ΔP J =K J Δf; Among them, ΔP J Indicates the regulation power of the system AC tie line; K J Indicates the primary frequency modulation control coefficient of the system AC tie line; The first model is: Among them, H sys Indicates the system equivalent inertia constant; ΔP d is the disturbance power; D sys Represents the system damping coefficient.

4. The method for evaluating the minimum inertia requirement of a receiving-end power grid considering different fault types according to claim 3 is characterized in that: The method for obtaining the second model is: based on Laplace transform, using a backward difference operator to convert the differential part of the first-order derivative in the time domain differential expression corresponding to the transfer function in the frequency response control link into a differential part, completing the discretization processing of the frequency response control, and obtaining a discretized time domain expression of the frequency response control link; using a backward difference operator to discretize the first model to obtain the second model.

5. The method for evaluating the minimum inertia requirement of a receiving-end power grid considering different fault types according to claim 4 is characterized in that: The backward difference operator expression is: Where i represents the discrete time domain time period number, and Δt represents the time interval of each discrete time domain; The discrete time domain expression of the frequency response control link includes the discrete time domain expression of the inertial response link, the discrete time domain expression of the proportional link, the discrete time domain expression of the differential link and the discrete time domain expression of the integral link.

6. The method for evaluating the minimum inertia requirement of a receiving-end power grid considering different fault types according to claim 5 is characterized in that: The second model is: Among them, Δf(i) represents the system frequency deviation of the i-th discrete time domain; Δf(i-1) represents the system frequency deviation of the i-1-th discrete time domain; Δt represents the time interval of each discrete time domain.

7. The method for evaluating the minimum inertia requirement of a receiving-end power grid considering different fault types according to any one of claims 3 to 6, characterized in that: The different preset fault types include two DC bipolar locking fault step fault, two DC simultaneous commutation failure fault, two DC continuous commutation failure non-step fault and large-scale new energy low-throughput short-term power impact fault; different preset fault types are determined by disturbance power ΔP d Set up; disturbance power ΔP d The setting formulas are: ΔP d =P d ; Where: P d is the disturbance power of two DC bipolar blocking faults; P d1 P is the disturbance power caused by the failure of commutation of two DC circuits at the same time; d2 and P d3 is the disturbance power of two DC continuous commutation failures; P d4 is the disturbance power of short-term power shock fault caused by large-scale new energy low penetration; t1, t2 and t3 are the preset times for different fault types.

8. The method for evaluating the minimum inertia requirement of a receiving-end power grid considering different fault types according to claim 7 is characterized in that: The method for calculating the minimum inertia requirement of the receiving-end power grid by combining the improved Newton-Raphson algorithm is as follows: A1: Initialize the system equivalent inertia constant H sys =H0, based on the disturbance power ΔP d The setting formula setting failure; set the new energy penetration rate K according to demand X ; Preset the maximum system frequency deviation constraint value and the maximum frequency change rate constraint value; A2: According to the inertia requirement value H k-1 Combined with the second model, simulation iterative calculation is performed to obtain the corresponding system frequency deviation and frequency change rate, H k-1 The inertia demand value calculated for the previous iteration simulation; A3: Determine whether the system frequency deviation and frequency change rate meet the constraint critical conditions; if so, enter A4; if not, correct the inertia demand value through the Newton-Raphson algorithm and enter A2; A4: Set the inertia requirement value H k-1 Output is the minimum inertia requirement.

9. The method for evaluating the minimum inertia requirement of a receiving-end power grid considering different fault types according to claim 8, characterized in that: The frequency change rate calculation formula is: Among them, ROCOF(i k ) represents the frequency change rate of the i-th discrete time domain in the k-th simulation iteration calculation; f(i k ) represents the system frequency of the i-th discrete time domain in the k-th simulation iteration calculation; f(i k ) represents the system frequency of the i-1th discrete time domain in the kth simulation iteration calculation; The constraint critical conditions are: the maximum system frequency deviation value ≤ the maximum system frequency deviation constraint value and the frequency change rate ≤ the maximum frequency change rate constraint value.

10. The method for evaluating the minimum inertia requirement of a receiving-end power grid considering different fault types according to claim 9, characterized in that: The method for correcting the inertia requirement value by using the Newton-Raphson algorithm is: Set the objective function for inertia correction: Δf m (k)-Δf max =0; Where Δf m (k) represents the maximum frequency deviation of the kth simulation calculation; Δf max Indicates the maximum frequency deviation constraint value; Calculate the correction amount and calculate the approximate solution H based on the correction amount k ; H k =H k-1 +H X ; Among them, Δf′(H k ) indicates that the objective function is in the approximate solution H k The first derivative of X is the correction amount.

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