CN117810981A

CN117810981A - Minimum safe inertia assessment method and system for power systems based on quasi-steady-state modeling

Info

Publication number: CN117810981A
Application number: CN202311856283.5A
Authority: CN
Inventors: 戴博伟; 段超; 彭泽敏; 吴佳泽; 曹怡菲; 秦玉文
Original assignee: Xian Jiaotong University; State Grid Shanghai Electric Power Co Ltd
Current assignee: Xian Jiaotong University; State Grid Shanghai Electric Power Co Ltd
Priority date: 2023-12-29
Filing date: 2023-12-29
Publication date: 2024-04-02

Abstract

The invention discloses a method and system for evaluating the minimum safe inertia of a power system based on quasi-steady modeling. It establishes a quasi-steady model of each device based on the power system network topology and power flow results; selects fault i and generates a fault period based on the fault information. The power system node admittance matrix Y' is combined with the quasi-steady-state model to evaluate the DC and new energy operating status during the fault, and obtain the operating status of each equipment in the power system during the fault; the post-fault power system node admittance is generated based on the post-fault information of fault i Matrix Y", combined with the operating status of each equipment during the fault, calculates the quasi-steady operating status of each equipment under the power system network topology after the fault, and estimates the power imbalance of the entire system after experiencing fault i; traverse all the obtained power system The maximum fault imbalance amount is selected from the fault set, and the minimum safe inertia for frequency stability of the power system is calculated based on the system inertia center frequency change rate; it broadens the application scenarios of the power system inertia assessment problem.

Description

Power system minimum safety inertia assessment method and system based on quasi-steady state modeling

Technical Field

The invention belongs to the technical field of power systems, and particularly relates to a power system minimum safety inertia assessment method and system based on quasi-steady-state modeling.

Background

The new energy is interconnected with the power grid through the power electronic interface equipment, and the power electronic equipment has the advantages of flexible control and high response speed. When a fault such as a short circuit occurs in the ac system, the new energy unit typically enters a low voltage ride through control mode in order to provide voltage support during transients. At this time, the device outputs reactive power, and the active power is usually reduced rapidly and greatly, and the new energy power is gradually recovered after the fault is cleared and the voltage is recovered. In the process, the power flow and the voltage of the system can obviously fluctuate, and for a multi-DC feed-in receiving end power grid, direct current phase change failure can be caused during the period, and the direct current transmission power is rapidly changed and uncontrollable. Under severe conditions, the system can generate serious consequences such as low-voltage interlocking off-grid, direct-current continuous commutation failure even locking, large-range deviation of system frequency, third line defense action of a power grid, power failure accidents and the like.

With the new energy as the main body, the new energy ratio is further improved. For a receiving-end power grid with multiple direct current feeds, as a large number of synchronous generators are replaced, the dynamic reactive power supporting capability is reduced, the strength of an alternating current system is greatly reduced, the low-voltage ride-through range of a new energy source caused by a power grid short circuit fault can be further expanded, meanwhile, coupling with direct current commutation failure is possible, the recovery process can be further prolonged, the risk of the system bearing high-power impact disturbance is increased, and the impact quantity is difficult to quantitatively evaluate; on the other hand, because the short-term power disturbance caused by the failure of the new energy fault ride through and the failure of the direct current conversion is basically different from the permanent disturbance such as direct current blocking, the new energy off-grid and the like, the traditional stable control measures are difficult to adapt; meanwhile, the distribution range of the new energy station is relatively wide, the fault ride-through process is closely coupled with the direct current commutation recovery process, the nonlinearity degree of the power system is further deepened, the frequency stability characteristic of the power grid is closely coupled with the voltage stability, and the conventional stability control measures for coping with permanent power disturbance are difficult to adapt.

The existing method is mainly a minimum safety inertia assessment method based on power system frequency response model modeling, and the existing method is used for analyzing by establishing a system frequency response model of synchronous generators, loads, new energy and other equipment and a corresponding open loop transfer function, so that an expression relation between disturbance power and power system inertia center frequency is established, and further the current network topology level of the power system and the system inertia level and the adequacy thereof under the condition of specific small disturbance power disturbance are analyzed. The research method is effective for small-interference (power disturbance, small-range load switching) disturbance of the power system, when the power system suffers from large-disturbance faults (single-phase and three-phase short-circuit faults), new energy sources such as photovoltaics and wind power can possibly enter a low-voltage crossing state due to rapid voltage reduction of the power system, and direct-current inversion failure caused by voltage reduction of a direct-current inversion side can cause the equipment operation mode to be switched from a normal mode to a fault state. This makes the conventional inertia evaluation method based on the power system frequency response model ineffective; on the other hand, the current research on the inertia evaluation of the power system has not been developed on the research on the ac-dc hybrid grid.

At present, the power system relies on western electric east power transmission engineering to transmit western surplus power to eastern provinces through a direct current transmission line, and whether the direct current transmission line can be in a normal working mode greatly influences the frequency safety characteristics of the power system.

Disclosure of Invention

Aiming at the defects in the prior art, the invention provides a minimum safety inertia evaluation method and a minimum safety inertia evaluation system for an electric power system based on quasi-steady-state modeling, which are used for solving the technical problem that the existing minimum safety inertia evaluation method is difficult to apply to applicability of the transient stability problem.

The invention adopts the following technical scheme:

the power system minimum safety inertia assessment method based on quasi-steady state modeling comprises the following steps:

establishing a quasi-steady-state model of each device according to the network topology of the power system and the tide result;

selecting a fault i, generating a node admittance matrix Y 'of the power system during the fault according to fault information, and evaluating the running states of direct current and new energy sources during the fault by combining the established quasi-steady state model to obtain the running state p' of each device in the power system during the fault;

Generating a node admittance matrix Y 'of the power system after the fault according to the information after the fault i and the fault, simultaneously combining the obtained running states P' of the devices during the fault to calculate the quasi-steady running state of the devices under the network topology of the power system after the fault, and estimating the power unbalance amount Sigma delta P of the whole system of the power system after the power system is subjected to the fault i _i ；

And traversing all fault sets in the obtained power system, selecting the maximum fault unbalance amount, and calculating the frequency stable minimum safety inertia of the power system by combining the system inertia center frequency change rate.

Preferably, establishing a quasi-steady-state model of each device according to the network topology and the tide result of the power system is specifically as follows:

the quasi-steady-state model of each device comprises a quasi-steady-state model of a synchronous generator, a quasi-steady-state model of a load, a quasi-steady-state model of new energy and a quasi-steady-state model of a direct current system, an algebraic equation of the power system is constructed based on the quasi-steady-state model of each device, and the transmitting end system enablesUsing the frequency change rate as the system inertia adequacy criterion, and in the receiving end system, when two frequency correlation indexes are obtainedAnd when the frequency problem is larger than 0.8, calculating by adopting the maximum value of the system frequency change rate as a frequency problem index.

More preferably, the quasi-steady state model of the synchronous generator is:

Wherein V is _d For rotating the direct-axis voltage of the coordinate system of the synchronous generator grid connection point, V _q For synchronous generator grid-connected point rotation coordinate system quadrature axis voltage, I _d For synchronizing the generator direct-axis current, I _q For synchronizing the generator cross-axis current, T' _d0 T 'is the transient time constant of the direct shaft of the synchronous generator' _q0 For synchronizing generator cross-axis transient time constant E' _d For the direct-axis transient electromotive force of the synchronous generator E' _q For synchronizing the generator cross-axis transient electromotive force E _fd To synchronize the excitation voltage of the generator, x _d For the direct-axis reactance of synchronous generator, x _q For synchronizing the generator quadrature reactance, x' _d For the direct-axis transient reactance of the synchronous generator, x' _q For the transient reactance of the synchronous generator cross shaft, T _j For inertia time constant of synchronous generator, ω is synchronous generator rotation speed, P _m To synchronize the mechanical power of the generator, P _e The electromagnetic power of the synchronous generator is D, the damping coefficient omega of the synchronous generator ₀ The synchronous rotation speed of the power grid is shown, and delta is the power angle of the synchronous generator;

the injection current of the synchronous generator to the node is expressed as:

wherein V is _x For the real part of the voltage of the synchronous generator grid-connected absolute coordinate system, V _y The voltage imaginary part of the grid-connected point absolute coordinate system of the synchronous generator;

the electromagnetic power estimation at the corresponding time of the synchronous generator is as follows:

Wherein I is _d 、I _q For d, q axis current, V _d 、V _q D, q axis voltages;

the quasi-steady state model of the load is:

therein, V, V ₀ Respectively representing the current voltage amplitude and the steady-state voltage amplitude of the load at the node; p (P) ₀ 、Q ₀ Representing the active and reactive power of the load at steady state; p (P) _L 、Q _L The actual active power and reactive power of the load at the current voltage level; p (P) ₁ 、P ₂ 、P ₃ And Q ₁ 、Q ₂ 、Q ₃ Constant impedance, constant current and constant power proportionality coefficient of active and reactive load respectively;

the current injected by the load to the node is:

wherein I is _Ld 、I _Lq Injecting real parts and imaginary parts of currents under d and q axes rotation coordinate systems to load slave nodes respectively;

the new energy is controlled by constant power in the normal working mode, and when the voltage of the grid-connected point is too high or too low, the new energy equipment works in the traversing mode, and the injection current of the power grid is expressed as:

wherein i is _d1 ,i _q1 ,i _d2 ,i _q2 The current is output by the d and q axes of the new energy normal control mode respectively, P _ref ,Q _ref Active and reactive control fixed value parameters, |U, of a normal control mode of the new energy equipment respectively _PCC I is the voltage amplitude value of the grid-connected point of the new energy equipment, and k is the voltage amplitude value of the grid-connected point of the new energy equipment _d1 ,k _d2 ,I _Pset The active control coefficient is traversed for the new energy equipment fault, _i ' _max the maximum limit value k of the fault ride-through current of the new energy equipment _q1 ,k _q2 ,I _Qset For new energy equipment fault ride-through reactive power control coefficient, U _Lin The threshold value of the new energy equipment fault crossing mode and the normal mode is located;

the quasi-steady state model of the direct current system is as follows:

wherein U is _dh 、U _dl Respectively controlling high voltage and low voltage of a threshold by low-voltage current limiting, I _dmin The minimum current limit is limited for low voltage.

Preferably, the power system node admittance matrix Y' during the fault is:

Y'[V]e ^jθ ＝[e ^jθ ](I _d (V,p')-jI _q (V,p'))+I _g (δ,x)

wherein, p' is the running state of each device in the power system during the fault period, V is the voltage amplitude of each node of the power grid, e ^jθ For each node voltage phase angle of the power grid, I _d (V,p')、I _q (V, p') is that each element except the synchronous generator injects d, q-axis current into the power grid, I _g (delta, x) is the injection of current into the grid by the synchronous generator.

Preferably, the power system is subjected to a fault i followed by a total system power imbalance ΣΔp _i The method comprises the following steps:

∑ΔP _i ＝∑(P _m -P _e (δ,x))

wherein P is _m For synchronizing the mechanical power of the generator，P _e And (delta, x) is synchronous generator electromagnetic power.

More preferably, the post-fault i-fault information generating post-fault power system node admittance matrix Y "is:

Y”[V]e ^jθ ＝[e ^jθ ](I _d (V,p',p”)-jI _q (V,p',p”))+I _g (δ,x)

wherein I is _d (V,p',p”)-jI _q (V, p') is that the power electronic devices will output current to the grid based on the operating state during the fault together with the estimated state at the moment of the fault.

Preferably, traversing all fault sets in the obtained power system, and selecting the maximum fault unbalance amount specifically comprises the following steps:

The inertia of the synchronous generator of the power system meets the following conditions:

minimum full system inertia M when power system frequency safety constraint is satisfied _sufficiency ≥∑T _ji When the inertia provided by the current synchronous generator is insufficient to maintain the stable frequency of the system, additional rotary spare capacity is required to be provided, and the supplementary inertia value is as follows: m is M _sufficiency -∑T _ji ；

When the frequency safety constraint of the power system is met, the minimum full system inertia is realized<∑T _ji When the synchronous generator of the current system has abundant inertia, the system frequency can be maintained stable.

More preferably, the maximum power imbalance ΔP selected for all incident sets is traversed _max The method comprises the following steps:

ΔP _max ＝-max(|∑ΔP _i |)

more preferably, the system inertial center frequency rate of change ROCOF is:

wherein T is _ji Is the inertia time constant of the ith synchronous generator, P _mi For the mechanical power of the i-th synchronous generator, P _ei And (delta, x) is electromagnetic power of the ith synchronous generator, and delta P is the unbalance of the power of the whole system.

In a second aspect, an embodiment of the present invention provides a power system minimum safe inertia evaluation system based on quasi-steady state modeling, which is characterized by comprising:

the construction module is used for establishing a quasi-steady-state model of each device according to the network topology and the tide result of the power system;

the state module is used for selecting a fault i, generating a node admittance matrix Y 'of the power system during the fault according to fault information, and evaluating the running states of direct current and new energy sources during the fault by combining a quasi-steady-state model established by the construction module to obtain the running state p' of each device in the power system during the fault;

The calculation module is used for generating a node admittance matrix Y 'of the power system after the fault according to the information after the fault i, calculating a quasi-steady state running state of each device under the network topology of the power system after the fault by combining the running state P' of each device obtained by the state module during the fault, and estimating the total system power unbalance amount Sigma delta P of the power system after the power system is subjected to the fault i _i ；

And the output module is used for traversing all fault sets in the power system obtained by the calculation module to select the maximum fault unbalance amount and calculating the frequency stable minimum safety inertia of the power system by combining the system inertia center frequency change rate.

Preferably, in the calculation module, the power system is subjected to a fault i, and then the total system power imbalance amount ΣΔp is calculated _i The method comprises the following steps:

∑ΔP _i ＝∑(P _m -P _e (δ,x))

wherein P is _m To synchronize the mechanical power of the generator, P _e (delta, x) is synchronous generator electromagnetic power;

the information after the fault i and the fault generates a node admittance matrix Y' of the power system after the fault as follows:

Y”[V]e ^jθ ＝[e ^jθ ](I _d (V,p',p”)-jI _q (V,p',p”))+I _g (δ,x)

Preferably, in the output module, traversing all fault sets in the obtained power system, and selecting the maximum fault unbalance amount specifically includes:

In a third aspect, a computer device includes a memory, a processor, and a computer program stored in the memory and executable on the processor, the processor implementing the steps of the quasi-steady state modeling based power system minimum safe inertia evaluation method described above when the computer program is executed.

In a fourth aspect, an embodiment of the present invention provides a computer readable storage medium, including a computer program, which when executed by a processor, implements the steps of the above-described power system minimum safe inertia assessment method based on quasi-steady state modeling.

Compared with the prior art, the invention has at least the following beneficial effects:

the minimum safety inertia evaluation method of the electric power system based on the quasi-steady modeling considers the influence of the new energy-containing and direct current equipment on the inertia evaluation problem of the electric power system, and is suitable for the AC/DC series-parallel electric power system containing the new energy-containing and direct current equipment; on the other hand, the quasi-steady state modeling method of the new energy and the direct current equipment takes the operation characteristics of the control strategy according to the voltage change of the grid-connected point into account, so that the inertia evaluation method can be applied to a large-interference stable operation scene considering short circuit faults.

Furthermore, for the power grid system at the receiving end, the correlation between the ROCOFmax and the fnadir index of the researched system is firstly verified, the correlation coefficient is verified to prove that the ROCOFmax and the fnadi frequency index have strong correlation, the ROCOFmax index can be utilized to reflect the characteristic of the fnadir index, and the evaluation method for evaluating the minimum frequency safety inertia of the researched power system by utilizing the ROCOFmax frequency index in the subsequent step of the invention is reasonable.

Furthermore, the invention calculates two calculation scenes of the power system quasi-stable state in fault and after fault based on the quasi-stable state modeling of each element, and compared with the calculation scene of calculating and simulating each calculation scene of each time step power system running state total required to calculate and simulate the simulation market/simulation step by the time step simulation method, the calculation complexity is greatly reduced, and the power system simulation efficiency is improved.

Further, in step S3, the operation of the new energy source and the dc device of each node after the failure is continuously estimated according to the operation state of the new energy source and the dc device obtained from the calculation scene in the preamble failure, which has the time sequence characteristic, inherits the simulation continuity characteristic of the traditional time domain simulation method, and improves the accuracy of the estimation.

Furthermore, the maximum power unbalance finally calculated by traversing all possible fault sets of the system represents the maximum possible system power disturbance quantity in the system, and compared with the previous method for setting the quantitative power disturbance quantity at a certain node by people, the method has robustness, so that the minimum inertia required by the system frequency safety finally calculated can be suitable for all disturbance, and the effectiveness and the robustness of a calculation result are improved.

It will be appreciated that the advantages of the second aspect may be found in the relevant description of the first aspect, and will not be described in detail herein.

In summary, the invention has the following characteristics:

1) The invention considers the synchronous generator, load, new energy and direct current system contained in the novel power system, so that the invention can be suitable for the inertia evaluation of the AC/DC series-parallel power system containing new energy and direct current, and expands the application range of the minimum inertia evaluation method of the original power system.

2) According to the quasi-steady-state model established by the invention, the element differential equation is converted into the algebraic equation, so that the calculation complexity and iteration times are reduced while the solving precision of the whole system model is maintained, and the convenience of the evaluation method is improved compared with the traditional time domain simulation method.

3) Compared with the original evaluation method, the power unbalance amount obtained by traversing all fault sets of the system is more robust, and finally the minimum safety inertia of the system frequency obtained by calculation is compared with the inertia contained in the current system synchronous machine, so that a conclusion can be obtained by comparing two values only to determine whether the system inertia level is abundant, the calculation method has intuitiveness and convenience, and actual production operators can intuitively judge whether the current system frequency is stable or not.

The technical scheme of the invention is further described in detail through the drawings and the embodiments.

Drawings

FIG. 1 is a flow chart of a power system minimum safety inertia evaluation method calculation based on quasi-steady state modeling;

fig. 2 is a time domain simulation graph of frequency and frequency change rate (rocf) of an electric power system including new energy and dc devices according to an exemplary embodiment of the present invention;

FIG. 3 is a ROCOF of traversing critical incidents of DC devices with new energy provided in an exemplary embodiment of the invention _max Fitting a graph with the relationship between the lowest frequency point and the graph;

FIG. 4 is a topology diagram of a typical test system for CSEE-VS China sender provided by an exemplary embodiment of the present invention;

FIG. 5 is a schematic diagram of a computer device according to an embodiment of the present invention;

Fig. 6 is a block diagram of a chip according to an embodiment of the present invention.

Detailed Description

The following description of the embodiments of the present invention will be made clearly and fully with reference to the accompanying drawings, in which it is evident that the embodiments described are some, but not all embodiments of the invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.

In the description of the present invention, it will be understood that the terms "comprises" and "comprising," when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

It is also to be understood that the terminology used in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used in this specification and the appended claims, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

It should be further understood that the term "and/or" as used in the present specification and the appended claims refers to any and all possible combinations of one or more of the associated listed items, and includes such combinations, e.g., a and/or B, may represent: a exists alone, A and B exist together, and B exists alone. In the present invention, the character "/" generally indicates that the front and rear related objects are an or relationship.

It should be understood that although the terms first, second, third, etc. may be used to describe the preset ranges, etc. in the embodiments of the present invention, these preset ranges should not be limited to these terms. These terms are only used to distinguish one preset range from another. For example, a first preset range may also be referred to as a second preset range, and similarly, a second preset range may also be referred to as a first preset range without departing from the scope of embodiments of the present invention.

Depending on the context, the word "if" as used herein may be interpreted as "at … …" or "at … …" or "in response to a determination" or "in response to detection". Similarly, the phrase "if determined" or "if detected (stated condition or event)" may be interpreted as "when determined" or "in response to determination" or "when detected (stated condition or event)" or "in response to detection (stated condition or event), depending on the context.

Various structural schematic diagrams according to the disclosed embodiments of the present invention are shown in the accompanying drawings. The figures are not drawn to scale, wherein certain details are exaggerated for clarity of presentation and may have been omitted. The shapes of the various regions, layers and their relative sizes, positional relationships shown in the drawings are merely exemplary, may in practice deviate due to manufacturing tolerances or technical limitations, and one skilled in the art may additionally design regions/layers having different shapes, sizes, relative positions as actually required.

Referring to fig. 1, the method for evaluating minimum safety inertia of an electric power system based on quasi-steady modeling of the invention comprises the following steps:

s1, establishing a quasi-steady state model of each device according to a current researched network topology structure of the power system and according to a tide result and dynamic parameters of each device in the power system;

wherein the equipment includes: synchronous generator, load, photovoltaic, new energy, direct current equipment, generally speaking, describing the dynamic process of the power system requires that algebraic equation describing the network topology of the power system and differential equation describing the dynamic characteristics of the equipment are combined to form a differential algebraic equation set (DAE), and the DAE equation is solved or simulated to obtain the dynamic response characteristic curve of the equipment or the result of whether the power system is stable, wherein the generalized abstract form of the DAE equation set is as follows:

In the formula (1), x ₁ Is a state variable of electromechanical transient time scale, such as a control variable of synchronous generator rotor angle, a speed regulator, an exciter and the like, and x is a control variable of synchronous generator rotor angle, a speed regulator, an exciter and the like ₂ The system is characterized in that the system is an electromagnetic transient time scale state variable, such as a control variable of photovoltaic, new energy and direct current converter equipment, y is an algebraic variable describing a network equation of a power system, such as node voltage, current and the like, and the action time scale of power electronic devices such as the converter equipment and the like is far smaller than the electromechanical transient time scale, so that the power electronic devices are approximately considered to be controlled to a target value to reach a relative steady state in the electromechanical time scale; it is therefore considered that the left differential equation of the second equation in equation (1) is simplified to an algebraic equation, where equation (1) is expressed as:

further; for the state variables of the electromechanical transient time scale, the motor power angle and the rotating speed state quantity of the synchronous generator at each moment directly affect the current injected into the nodes of the power system, and the formula (2) at a specific moment is specifically expressed as follows:

delta in the formula (3) is the power angle of the synchronous generator; omega is the rotor speed of the synchronous generator; m, P _m 、P _e Inertia, mechanical power and electromagnetic power of the synchronous generator, respectively. Y, V, I the node admittance matrix, node voltage and node current of the power system, the injection current of each device to the node is determined by the voltage and phase of the node, the equation (3) can be completely converted into algebraic equation at a specific time, and the algebraic equation system can be solved for quantification Analyzing the stability of the current power system and optimizing the topology structure of the power system and the combination configuration strategy and control parameters of the unit based on the sensitivity information of the current power system; compared with the original DAE time domain simulation solution, the method can effectively reduce the simulation iteration times on the premise of ensuring the solution precision.

The quasi-steady state modeling steps of each device depending on the grid-connected node voltage are as follows:

s101, establishing a quasi-steady-state model of the synchronous generator, and describing a dynamic response process of the synchronous generator by using a six-order differential equation comprising stator and rotor differential equations for the synchronous generator in an electric power system, wherein the equation is as follows:

wherein V is _d ,V _q The grid-connected point d and the q-axis voltage of the synchronous generator are respectively; e' _d ,E″ _q ,E′ _d ,E′ _q The synchronous generator set d and q axis secondary transient electromotive forces and the transient electromotive forces are respectively adopted; x' _d ,x″ _q ,x′ _d ,x′ _q ,x _d ,x _q Respectively representing the sub-transient state, the transient state and the synchronous reactance of the synchronous generator set; i _d ,I _q D, injecting d and q-axis currents into the power grid for the synchronous generators respectively; t' _d0 ,T″ _q0 ,T′ _d0 ,T′ _q0 Respectively synchronizing transient potential and sub-transient time constant of the generator set; e (E) _fd Exciting voltage for synchronous generator; omega, omega ₀ Respectively the current time rotating speed and the synchronous rotating speed of the synchronous generator, delta is the power angle of the synchronous generator, T _j For synchronizing generator inertia time constant, P _m ,P _m D is the mechanical power, electromagnetic power and damping coefficient of the synchronous generator respectively.

Further; the synchronous generator sub-transient process is approximately considered to have ended within the electromechanical time scale, so the equation (4) is reduced to a biaxial model:

further, δ and ω of the synchronous generator are determined at a specific moment, the exciter is set to maintain constant d, q-axis excitation voltages, the action of the controller of the other parts of the synchronous generator is represented in a damped form, and the injection current of the synchronous generator to the node is expressed as:

meanwhile, the electromagnetic power of the synchronous generator at the moment can be estimated by d and q axis voltage and current as follows:

the above is the specific moment corresponding to E' _d 、E' _q A quasi-steady state model of the synchronous generator in delta state, a corresponding current injected into the power system and an electromagnetic power magnitude of the synchronous generator itself.

S102, establishing a quasi-steady state model of the load, taking a common model of the load of the power system as a ZIP load model as an example, wherein the expression is as follows:

v, V in the formula (8) ₀ Respectively representing the current voltage amplitude and the steady-state voltage amplitude of the load at the node; p (P) ₀ 、Q ₀ Representing the active and reactive power of the load at steady state; PL, QL are the actual active and reactive power of the load at the current voltage level; p (P) ₁ 、P ₂ 、P ₃ And Q ₁ 、Q ₂ 、Q ₃ Constant impedance, constant current and constant power ratio coefficients of active and reactive loads respectively, the coefficients are required to meet P ₁ +P ₂ +P ₃ ＝1；Q ₁ +Q ₂ +Q ₃ =1; because the expression (9) is an algebraic equation, the electromechanical transient model of the ZIP load is a corresponding quasi-steady state model.

Further; the current injected by the load to the node can be expressed as:

in the formula (9), I _Ld 、I _Lq The real part and the imaginary part of the current under the d and q axis rotation coordinate system are respectively injected into the load slave nodes.

S103, establishing a quasi-steady-state model of new energy, wherein the new energy equipment generally comprises a photovoltaic, a direct-driven fan, a doubly-fed fan and the like, the new energy equipment is connected with a power grid through a grid-connected converter, the current of the current source is modeled in the form of a current source when the power system actually operates, and the current of the direct-current side of the new energy is tradition to the grid side through a direct-current capacitor of the converter, and the expression is as follows:

in the formula (10), C is a direct-current capacitance value; udc is the direct current capacitor voltage as a state variable; pg and Pr are the direct current side power and the alternating current side power of the new energy respectively, and because the direct current capacitor voltage acts faster, the dynamic process is ignored, and because the new energy is in constant power control, namely Pg=Pr, in the normal working mode, when the voltage of a grid-connected point is too high or too low, the new energy equipment works in the traversing mode, and therefore, the injection current of the new energy equipment to the power grid is expressed as:

In the formula (11), i _d1 ,i _q1 ,i _d2 ,i _q2 The current is output by the d and q axes of the new energy normal control mode respectively, P _ref ,Q _ref Active and reactive power of the new energy equipment in the normal control mode respectivelyThe fixed value parameters are controlled, and pref=pg=pr, |U is combined with a direct-current capacitor voltage state equation _PCC I is the voltage amplitude value of the grid-connected point of the new energy equipment, and k is the voltage amplitude value of the grid-connected point of the new energy equipment _d1 ,k _d2 ,I _Pset The active control coefficient is i 'for the fault ride-through of new energy equipment' _max The maximum limit value k of the fault ride-through current of the new energy equipment _q1 ,k _q2 ,I _Qset For new energy equipment fault ride-through reactive power control coefficient, U _Lin The threshold value of the new energy equipment fault crossing mode and the normal mode is located.

S104, establishing a quasi-steady-state model of a direct current system, wherein the direct current transmission equipment consists of a rectifying side and an inverting side, the rectifying side and the inverting side are jointly controlled by two side controllers to maintain the transmission power of a direct current line to be near a set value, and the primary side is described as follows:

in formula (12), U _dr ,U _di The direct current system rectifying side and the inversion side direct current voltage are respectively adopted; u (U) _cr ,U _ci The alternating current voltages are respectively the alternating current voltages at the rectifying side and the inverting side of the direct current system; x is X _cr ,X _ci, ,T _r ,T _i The direct current system rectifying side and the inversion side are respectively provided with a commutation reactance and a transformer transformation ratio, and alpha is a triggering delay angle of the direct current system rectifying side; beta, gamma is the inversion side trigger delay angle and the off angle of the direct current system; i _recd 、I _recq 、I _invd 、I _invq D and q axis currents which are respectively injected into the power grid at nodes on two sides of the rectifying side and the inverting side of the direct current system. When the capacitance of the direct current system is ignored, the rectification side current I of the direct current system is approximately considered _dr Inverter side current I _dr Approximately equal. Therefore, when the voltage across the DC system is known, the operating state will also be determined, and the fifth expression will be caused when the AC voltage on the inversion side of the DC system is loweredThe sharp decrease of the turn-off angle on the left side causes the possibility of commutation failure of the DC system, due toIt is extremely important to evaluate whether the direct current commutation fails at the moment of failure in an alternating current-direct current series-parallel system, and the direct current control system is fixed to gamma when the voltage is maintained at a normal level ₀ Control, gamma ₀ The inversion side arc extinguishing angle of the direct current system is at a steady state; when the direct current is lower than a certain value, a low-voltage current limiting (VDCOL) control mode is entered; when the fault is serious and the voltage drops rapidly at the moment of the fault, the direct current will be failed in commutation, and at this moment, in order to protect the power electronic equipment such as the thyristor, the direct current will be blocked to make the current transmitted by the direct current system be 0, and the quasi-steady state model of the direct current system and the controller strategy is as follows:

in the formula (13), U _dh 、U _dl Respectively controlling high voltage and low voltage of a threshold by low-voltage current limiting, I _dmin A low voltage current limiting minimum current limit; when the direct current voltage is larger than a threshold value, the voltage direct current system is in a normal control mode, when the direct current voltage is between VDCOL limiting threshold values, the direct current control is a current control instruction value under the voltage corresponding to the VDCOL, and a VDCOL control characteristic curve is set according to the type of the direct current control system and the topology of the direct current system and the actual requirements of an engineering site; beta ₀ The control command value of the lead angle is triggered by the inversion side before the fault of the direct current system, and when the fault occurs, beta is ₀ The arc extinguishing angle is not changed yet because of the inversion side U of the DC system _ci The AC voltage suddenly drops to cause the corresponding arc extinction angle gamma to suddenly change as shown in a formula (13), when gamma is smaller than gamma _min And when the limit value is met, the direct current is determined to have commutation failure.

S105, constructing an algebraic equation of the power system based on the quasi-steady state models of the devices in the steps S101 to S104:

Y[V]e ^jθ ＝[e ^jθ ](I _d (V,p)-jI _q (V,p))+I _g (δ,x) (14)

in the formula (14), Y is an admittance matrix of a power system node, [ V ]],e ^jθ Respectively amplitude and phase angle of all nodes of the power system, I _d (V,p)-jI _q (V, p) is that the power electronic equipment, namely the load, injects current into the power grid, which shows that the power electronic equipment is influenced by the voltage V of the grid-connected point, namely the current control state p, I _g And (delta, x) is that the synchronous generator injects current into the power grid, which shows that the synchronous generator is related to the power angle delta at the current moment and the transient electromotive force of the state variables, and the quasi-steady state of each device at the corresponding moment can be solved by changing the node admittance matrix Y and the state variables of each device.

S106, for a transmitting end system, generally using a frequency change Rate (ROCOF) as a system inertia adequacy criterion is feasible, for a receiving end system, firstly, verifying the correlation between the maximum value ROCOFmax of the system frequency change rate and the lowest frequency point (fnadir), as shown in fig. 2, collecting ROCOFmax and fnadir indexes in a system time domain simulation result of the electric power system under a certain fault, extracting corresponding frequency index results after multiple times of selection of different faults for simulation, and carrying out correlation analysis on the two indexes, as shown in fig. 5, wherein the two correlation indexes are calculated as follows:

In (15)For two frequency-dependent indicators, f _nadir,i 、f _ROCOF,max,i Corresponding frequency indexes under the fault i are respectively +.>For the average value of the corresponding frequency indexes under all selected faults, according to statistics, whenWhen the frequency problem is larger than 0.8, the two indexes are considered to be extremely strongly correlated, ROCOFmax can be used as a frequency problem index in a corresponding transmitting end system for calculation, and the ROCOFmax can be used as an index to reflect the characteristic of fnadir to a great extent.

S2, selecting a fault i, generating a node admittance matrix Y' of the power system during the fault according to fault information, and evaluating the running states of direct current and new energy sources during the fault by combining the quasi-steady-state model established in the step S1;

the required solution expression is:

Y'[V]e ^jθ ＝[e ^jθ ](I _d (V,p')-jI _q (V,p'))+I _g (δ,x) (16)

in the formula (16), Y 'is an admittance matrix of a node of the power system during the fault period, p' is the running state of each device in the power system during the fault period, and running state information is provided for calculating the power unbalance amount and evaluating the inertia after the fault by acquiring the state of each device during the fault period.

S3, generating a node admittance matrix Y 'of the power system after the fault according to the fault i after the fault, and simultaneously further calculating a quasi-steady state operation state of each device under the power system network topology after the fault by combining the p' state of each device obtained in the step S2, wherein the required solution expression is as follows:

Y”[V]e ^jθ ＝[e ^jθ ](I _d (V,p',p”)-jI _q (V,p',p”))+I _g (δ,x) (17)

In the formula (17), I _d (V,p',p”)-jI _q The output current of each power electronic device (V, p') to the power grid is determined based on the running state during the fault period and the instantaneous estimated state after the fault, if the new energy device enters the low voltage crossing state during the fault period and exits the low voltage state after the fault, the d-axis current is still output according to the instruction value during the fault period, namely the initial moment that the new energy enters the recovery mode, and on the other hand, the q-axis current of the new energy enters the normal state; for the direct current system, if the direct current enters a commutation failure state during the fault period, the direct current system still keeps the injection current to the power grid to be 0 at the moment after the fault, namely, the initial moment restarted by the commutation failure, and the power unbalance amount is the maximum in the above state.

The power system fault is generally removed through 100ms, at this time, the control devices such as the speed regulator of each synchronous generator are not operated, and the mechanical power of each synchronous generator can be approximately considered to be unchanged, so that the power unbalance amount of the whole system after the power system experiences the fault i can be estimated as follows:

∑ΔP _i ＝∑(P _m -P _e (δ,x)) (18)

s4, traversing all fault sets in the power system to select the maximum fault unbalance amount:

ΔP _max ＝-max(|∑ΔP _i |) (19)

in formula 19, ΔP _max And (5) traversing the maximum power unbalance amount selected by all accident sets, and taking the maximum power unbalance amount as a reference value to carry out minimum safety inertia evaluation comparison and calculation.

Further, when the power unbalance amount is calculated as ΔP _max The system inertia center frequency change rate is expressed as:

in the formula (20), M _i 、T _ji 、The inertia, the inertia time constant and the angular velocity variation of the ith synchronous generator are respectively calculated by combining the expression of the equation of motion of the rotor in the expression (5), and the neglected synchronous generator damping expression (20) is further expressed as follows:

in order to ensure that the frequency of the power system is safe and stable, ROCOF should be smaller than a limit value, otherwise, the lowest point of the system frequency is possibly lower than the lower limit value of the system frequency safety, thereby causing low-frequency load shedding and load shedding to influence the household electricity life, and therefore DeltaP is selected _max As the maximum power unbalance, the constraint ROCOF should be smaller than the limit value ζ, and the inertia of the corresponding power system synchronous generator should satisfy:

in the formula (22), M _sufficiency To meet the frequency safety constraint of the power system and minimum total system inertia, let M _sufficiency And Sigma T _ji In comparison, when M _sufficiency ≥∑T _ji The inertia that the synchronous generator of the current system can provide is insufficient to maintain the stable system frequency, and the additional rotary spare capacity needs to be provided, and the supplementary inertia value needs to be: m is M _sufficiency -∑T _ji ；M _sufficiency <∑T _ji The system frequency stability can be maintained by indicating that the inertia of the synchronous generator of the current system is abundant.

In still another embodiment of the present invention, a system for estimating minimum safe inertia of a power system based on a quasi-steady-state modeling is provided, where the system can be used to implement the method for estimating minimum safe inertia of a power system based on a quasi-steady-state modeling.

The construction module is used for establishing a quasi-steady-state model of each device according to the network topology of the power system and the tide result;

Total system power imbalance ΣΔp after power system experiences fault i _i The method comprises the following steps:

∑ΔP _i ＝∑(P _m -P _e (δ,x))

Y”[V]e ^jθ ＝[e ^jθ ](I _d (V,p',p”)-jI _q (V,p',p”))+I _g (δ,x)

Traversing all fault sets in the obtained power system, and selecting the maximum fault unbalance amount specifically as follows:

In yet another embodiment of the present invention, a terminal device is provided, the terminal device including a processor and a memory, the memory for storing a computer program, the computer program including program instructions, the processor for executing the program instructions stored by the computer storage medium. The processor may be a central processing unit (Central Processing Unit, CPU), but may also be other general purpose processor, digital signal processor (Digital Signal Processor, DSP), application specific integrated circuit (Application Specific Integrated Circuit, ASIC), off-the-shelf programmable gate array (Field-Programmable Gate Array, FPGA) or other programmable logic device, discrete gate or transistor logic device, discrete hardware components, etc., which are the computational core and control core of the terminal adapted to implement one or more instructions, in particular to load and execute one or more instructions to implement the corresponding method flow or corresponding functions; the processor according to the embodiment of the invention can be used for the operation of a power system minimum safety inertia assessment method based on quasi-steady state modeling, and comprises the following steps:

establishing a quasi-steady-state model of each device according to the network topology of the power system and the tide result; selecting a fault i, generating a node admittance matrix Y 'of the power system during the fault according to fault information, and evaluating the running state of direct current and new energy sources during the fault by combining a quasi-steady-state model to obtain the running state p' of each device in the power system during the fault; generating a node admittance matrix Y 'of the power system after the fault according to the fault i after the fault, simultaneously calculating a quasi-steady state running state of each device under the network topology of the power system after the fault by combining the running state P' of each device during the fault, and estimating the total system power unbalance amount Sigma delta P of the power system after the power system experiences the fault i _i The method comprises the steps of carrying out a first treatment on the surface of the And (5) selecting the maximum fault unbalance amount from all fault sets in the power system obtained through traversing, and calculating the frequency stable minimum safety inertia of the power system by combining the system inertia center frequency change rate.

Referring to fig. 5, the terminal device is a computer device, and the computer device 60 of this embodiment includes: a processor 61, a memory 62, and a computer program 63 stored in the memory 62 and executable on the processor 61, the computer program 63 when executed by the processor 61 implements the reservoir inversion wellbore fluid composition calculation method of the embodiment, and is not described in detail herein to avoid repetition. Alternatively, the computer program 63, when executed by the processor 61, implements the functions of each model/unit in the power system minimum safe inertia evaluation system based on quasi-steady state modeling, and is not described herein in detail to avoid repetition.

The computer device 60 may be a desktop computer, a notebook computer, a palm top computer, a cloud server, or the like. Computer device 60 may include, but is not limited to, a processor 61, a memory 62. It will be appreciated by those skilled in the art that fig. 5 is merely an example of a computer device 60 and is not intended to limit the computer device 60, and may include more or fewer components than shown, or may combine certain components, or different components, e.g., a computer device may also include an input-output device, a network access device, a bus, etc.

The processor 61 may be a central processing unit (Central Processing Unit, CPU), but may also be other general purpose processors, digital signal processors (Digital Signal Processor, DSP), application specific integrated circuits (Application Specific Integrated Circuit, ASIC), field programmable gate arrays (Field-Programmable Gate Array, FPGA) or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, or the like. A general purpose processor may be a microprocessor or the processor may be any conventional processor or the like.

The memory 62 may be an internal storage unit of the computer device 60, such as a hard disk or memory of the computer device 60. The memory 62 may also be an external storage device of the computer device 60, such as a plug-in hard disk provided on the computer device 60, a Smart Media Card (SMC), a Secure Digital (SD) Card, a Flash memory Card (Flash Card), or the like.

Further, the memory 62 may also include both internal storage units and external storage devices of the computer device 60. The memory 62 is used to store computer programs and other programs and data required by the computer device. The memory 62 may also be used to temporarily store data that has been output or is to be output.

Referring to fig. 6, the terminal device is a chip, and the chip 600 of this embodiment includes a processor 622, which may be one or more in number, and a memory 632 for storing a computer program executable by the processor 622. The computer program stored in memory 632 may include one or more modules each corresponding to a set of instructions. Further, the processor 622 may be configured to execute the computer program to perform the power system minimum safe inertia assessment method based on quasi-steady state modeling described above.

In addition, chip 600 may further include a power supply component 626 and a communication component 650, where power supply component 626 may be configured to perform power management of chip 600, and communication component 650 may be configured to enable communication of chip 600, e.g., wired or wireless communication. In addition, the chip 600 may also include an input/output (I/O) interface 658. Chip 600 may operate based on an operating system stored in memory 632.

In a further embodiment of the present invention, the present invention also provides a storage medium, in particular, a computer readable storage medium (Memory), which is a Memory device in a terminal device, for storing programs and data. It will be appreciated that the computer readable storage medium herein may include both a built-in storage medium in the terminal device and an extended storage medium supported by the terminal device. The computer-readable storage medium provides a storage space storing an operating system of the terminal. Also stored in the memory space are one or more instructions, which may be one or more computer programs (including program code), adapted to be loaded and executed by the processor. The computer readable storage medium may be a high-speed RAM Memory or a Non-Volatile Memory (Non-Volatile Memory), such as at least one magnetic disk Memory.

One or more instructions stored in a computer-readable storage medium may be loaded and executed by a processor to implement the respective steps of the above-described embodiments with respect to a quasi-steady state modeling-based method of estimating minimum safe inertia of an electrical power system; one or more instructions in a computer-readable storage medium are loaded by a processor and perform the steps of:

building according to network topology and tide results of power systemEstablishing a quasi-steady state model of each device; selecting a fault i, generating a node admittance matrix Y 'of the power system during the fault according to fault information, and evaluating the running state of direct current and new energy sources during the fault by combining a quasi-steady-state model to obtain the running state p' of each device in the power system during the fault; generating a node admittance matrix Y 'of the power system after the fault according to the fault i after the fault, simultaneously calculating a quasi-steady state running state of each device under the network topology of the power system after the fault by combining the running state P' of each device during the fault, and estimating the total system power unbalance amount Sigma delta P of the power system after the power system experiences the fault i _i The method comprises the steps of carrying out a first treatment on the surface of the And (5) selecting the maximum fault unbalance amount from all fault sets in the power system obtained through traversing, and calculating the frequency stable minimum safety inertia of the power system by combining the system inertia center frequency change rate.

For the purpose of making the objects, technical solutions and advantages of the embodiments of the present invention more apparent, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention, and it is apparent that the described embodiments are some embodiments of the present invention, but not all embodiments of the present invention. The components of the embodiments of the present invention generally described and illustrated in the figures herein may be arranged and designed in a wide variety of different configurations. Thus, the following detailed description of the embodiments of the invention, as presented in the figures, is not intended to limit the scope of the invention, as claimed, but is merely representative of selected embodiments of the invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.

In order to verify the effectiveness of the method for evaluating the minimum safety inertia of the power system, the invention takes a high-proportion new energy AC/DC hybrid power grid test example CSEE-VS test system shown in fig. 4 as an embodiment, the final calculation result is compared with PSD-BPA power system analysis software, the test system comprises 4 synchronous generator sets, 3 new energy clusters and a bipolar DC power line, the system has stronger homology, and the verified system ROCOFmax is strongly related to fnadir. The parameters of the synchronous generator are shown in table 1, 600MW active power is generated by three new energy plant stations of PV-18, WT-01 and WT-19 respectively, 800MW active power is transmitted by a single pole of a direct current circuit and is transmitted to 1600MW active power in total, the total active load 4905MW and the reactive load 1647Mvar of the whole system are distributed relatively uniformly in the whole network, no obvious load center exists, in order to ensure the convergence of simulation, the load is set as a constant current load of 20% of constant impedance loads of ZIP loads, and a load switching logic strategy for switching load voltage below a certain threshold value into constant impedance loads is not set; because the load distribution is uniform, the accident set is selected, and the B02-B01, B06-B09, B11-B08 new energy main network grid-connected nodes are grounded for 100ms, then fault lines are cut off, the B13 direct current line connecting nodes are grounded for 100ms and then restored, and the B03-B05 SanYong N-1 is used as a key accident set.

TABLE 1CSEE-VS test System synchronous Generator parameters

The maximum unbalance of the power in the whole simulation time is obtained by respectively calculating 5 different faults and performing time domain simulation, and the calculation result of the method is shown in the table 2:

table 2CSEE-VS full time domain power maximum imbalance for different faults and the calculation results of the present invention:

as can be seen from Table 2, the calculated result of the method is relatively close to the calculated result of the time domain simulation result, and the absolute value is larger than the corresponding fault simulation value, which indicates that the accuracy and the robustness of the method can be better applied to the estimation of the power unbalance of the transient stability problem.

Further setting a system frequency security rocofLimit value ζ=5 Hz/s and selecting ΔP _max Checking the= -1322.14, and calculating M _sufficiency = 264.428, the current total inertial time constant of the whole system is: sigma T _ji = 173.712 due to M _sufficiency Greater than sigma T _ji Therefore, the system has potential frequency safety hazards under the current situation, the system can be unstable under serious faults, and the network frame operation topology of the system and the starting mode of the synchronous generator need to be planned again to increase the safety and stability margin of the system frequency.

In summary, according to the power system minimum safety inertia evaluation method and system based on the quasi-steady state modeling, the quasi-steady state model established for the common synchronous machine, the load, the new energy and the direct current transmission element contained in the novel power system at present is calculated and evaluated by the power system based on the quasi-steady state model, and compared with the traditional time domain simulation method, the iteration times are effectively reduced while the ROCOFmax calculation accuracy is ensured to be solved; according to the method, the influence of the direct current system on the system frequency in the operation of the power system is considered, and the direct current mathematical model is analyzed and established, so that the power system inertia evaluation method can be used in the traditional alternating current system field and can be applied to an alternating current-direct current hybrid system, and the application scene of the power system inertia evaluation problem is widened; the method considers the influence of new energy and the switching of the running control state of the direct current system on the frequency inertia evaluation of the power system, and can be used for evaluating the minimum inertia required by the frequency safety stability of the novel power system, so that the minimum safety inertia evaluation technology is not limited to the small-interference stability problem range, but is also applicable to the transient stability problem range.

The above is only for illustrating the technical idea of the present invention, and the protection scope of the present invention is not limited by this, and any modification made on the basis of the technical scheme according to the technical idea of the present invention falls within the protection scope of the claims of the present invention.

Claims

1. A method for evaluating the minimum safe inertia of a power system based on quasi-steady-state modeling, characterized in that it comprises the following steps:

Establish a quasi-steady-state model of each device based on the power system network topology and power flow results;

Select fault i, generate the power system node admittance matrix Y' during the fault based on the fault information, evaluate the DC and new energy operating status during the fault based on the established quasi-steady-state model, and obtain the operating status p' of each equipment in the power system during the fault;

The post-fault power system node admittance matrix Y" is generated based on the post-fault information of fault i. At the same time, combined with the obtained operating status p' of each device during the fault, the quasi-steady state operating status of each device under the post-fault power system network topology is calculated, and the power is estimated The whole system power imbalance amount ∑ΔP _i after the system experiences fault i;

All fault sets in the obtained power system are traversed, the maximum fault imbalance is selected, and the minimum safe inertia for frequency stability of the power system is calculated based on the system inertia center frequency change rate.

2. The minimum safe inertia evaluation method of the power system based on quasi-steady modeling according to claim 1, characterized in that establishing the quasi-steady state model of each device based on the power system network topology and power flow results is specifically:

The quasi-steady-state model of each equipment includes the quasi-steady-state model of the synchronous generator, the quasi-steady-state model of the load, the quasi-steady-state model of the new energy source, and the quasi-steady-state model of the DC system. The power system is constructed based on the quasi-steady-state model of each equipment. Algebraic equation, the sending end system uses the frequency change rate as the system inertia margin criterion. In the receiving end system, when two frequency correlation indicators When it is greater than 0.8, the maximum value of the system frequency change rate is used as the frequency problem indicator for calculation.

3. The minimum safe inertia evaluation method of the power system based on quasi-steady modeling according to claim 2, characterized in that the quasi-steady state model of the synchronous generator is:

Among them, V _d is the direct axis voltage of the rotating coordinate system of the synchronous generator grid connection point, V _q is the quadrature axis voltage of the synchronous generator grid connected point rotating coordinate system, I _d is the direct axis current of the synchronous generator, and I _q is the quadrature axis of the synchronous generator Current, T′ _d0 is the direct axis transient time constant of the synchronous generator, T′ _q0 is the quadrature axis transient time constant of the synchronous generator E′ _d is the direct axis transient electromotive force of the synchronous generator, E′ _q is the alternating current of the synchronous generator Shaft transient electromotive force, E _fd is the excitation voltage of the synchronous generator, x _d is the direct axis reactance of the synchronous generator, x _q is the quadrature axis reactance of the synchronous generator, x′ _d is the direct axis transient reactance of the synchronous generator, x′ _q is the quadrature axis transient reactance of the synchronous generator, T _j is the inertia time constant of the synchronous generator, ω is the rotation speed of the synchronous generator, P _m is the mechanical power of the synchronous generator, P _e is the electromagnetic power of the synchronous generator, and D is the synchronous generator Damping coefficient, ω ₀ is the synchronous speed of the power grid, δ is the power angle of the synchronous generator;

The injection current of the node from the synchronous generator is expressed as:

Among them, V _x is the real part of the absolute coordinate system voltage of the synchronous generator grid connection point, and V _y is the imaginary part of the absolute coordinate system voltage of the synchronous generator grid connection point;

The electromagnetic power of the synchronous generator at the corresponding time is estimated as:

Among them, I _d and I _q are the d and q axis currents, V _d and V _q are the d and q axis voltages;

The quasi-steady-state model of the load is:

Among them, V and V ₀ respectively represent the current voltage amplitude and steady-state voltage amplitude of the load at the node; P ₀ and Q ₀ represent the active power and reactive power of the load at steady state; P _L and Q _L represent the load at the node. The actual active power and reactive power at the current voltage level; P ₁ , P ₂ , P ₃ and Q ₁ , Q ₂ , Q ₃ are the constant impedance, constant current, and constant power proportional coefficients of the load's active and reactive power respectively;

The current injected by the load to the node is:

Wherein, I _Ld and I _Lq are the real and imaginary parts of the load injected current from the node in the d-axis and q-axis rotating coordinate systems respectively;

New energy is under constant power control in normal working mode. When the voltage at the grid connection point is too high or too low, the new energy equipment works in ride-through mode, and the current injected into the grid is expressed as:

Among them, i _d1 , i _q1 , i _d2 , and i _q2 are the d and q-axis output currents of the new energy normal control mode respectively, P _ref and Q _ref are the active and reactive power control fixed value parameters of the new energy equipment normal control mode respectively, | U _PCC | is the voltage amplitude of the grid-connected point of new energy equipment, k _d1 ,k _d2 , I _Pset is the fault ride-through active power control coefficient of new energy equipment, i' _max is the maximum limit value of fault ride-through current of new energy equipment, k _q1 ,k _q2 , I _Qset is the fault ride-through reactive power control coefficient of new energy equipment, U _Lin is the threshold between fault ride-through mode and normal mode of new energy equipment;

The quasi-steady-state model of the DC system is:

Among them, U _dh and U _dl are the low voltage and low voltage of the low voltage current limit control threshold respectively, and I _dmin is the minimum current limit value of the low voltage current limit.

4. The minimum safe inertia evaluation method of the power system based on quasi-steady modeling according to claim 1, characterized in that the power system node admittance matrix Y' during the fault is:

Y'[V]e ^jθ =[e ^jθ ](I _d (V,p')-jI _q (V,p'))+I _g (δ,x)

Among them, p' is the operating status of each equipment in the power system during the fault, V is the voltage amplitude of each node in the power grid, e ^jθ is the voltage phase angle of each node in the power grid, I _d (V,p'), I _q (V,p ') is the d and q-axis current injected into the grid by each component except the synchronous generator, and I _g (δ,x) is the current injected into the grid by the synchronous generator.

5. The minimum safe inertia evaluation method of the power system based on quasi-steady-state modeling according to claim 1, characterized in that after the power system experiences fault i, the total system power imbalance ΣΔP _i is:

∑ΔP _i =∑(P _m -P _e (δ,x))

Among them, P _m is the mechanical power of the synchronous generator, and P _e (δ,x) is the electromagnetic power of the synchronous generator.

6. The minimum safe inertia evaluation method of the power system based on quasi-steady-state modeling according to claim 5, characterized in that the post-fault information generated by the fault i is the post-fault power system node admittance matrix Y":

Y”[V]e ^jθ =[e ^jθ ](I _d (V,p’,p”)-jI _q (V,p’,p”))+I _g (δ,x)

Among them, I _d (V,p',p")-jI _q (V,p',p") is the output current of each power electronic device to the grid, which will be determined based on the operating state during the fault and the estimated state immediately after the fault.

7. The minimum safe inertia evaluation method of the power system based on quasi-steady-state modeling according to claim 1, characterized in that, by traversing all the fault sets in the obtained power system, the maximum fault imbalance amount is selected as follows:

The inertia of the synchronous generator in the power system satisfies the following conditions:

When the minimum system-wide inertia M _sufficiency ≥∑T _ji meets the frequency safety constraints of the power system, the inertia provided by the current system synchronous generator is not enough to maintain system frequency stability, and additional rotating reserve capacity needs to be provided. The inertia value that needs to be supplemented is: M _sufficiency _-∑Tji ;

When the minimum system-wide inertia <∑T _ji meets the frequency safety constraints of the power system, the current system synchronous generator has sufficient inertia and can maintain system frequency stability.

8. The power system minimum safety inertia evaluation method based on quasi-steady-state modeling according to claim 7, characterized in that the maximum power imbalance ΔP _max selected by traversing all accident sets is:

ΔP _max =-max(|∑ΔP _i |).

9. The minimum safe inertia evaluation method of the power system based on quasi-steady modeling according to claim 7, characterized in that the system inertia center frequency change rate ROCOF is:

Among them, T _ji is the inertia time constant of the i-th synchronous generator, P _mi is the mechanical power of the i-th synchronous generator, _Pei (δ,x) is the electromagnetic power of the i-th synchronous generator, and ΔP is the power imbalance of the whole system.

10. A power system minimum safe inertia assessment system based on quasi-steady-state modeling, characterized by comprising:

Build a module to establish a quasi-steady-state model of each device based on the power system network topology and power flow results;

The state module selects fault i, generates the power system node admittance matrix Y' during the fault based on the fault information, and evaluates the DC and new energy operating status during the fault based on the quasi-steady-state model established by the building module, and obtains the operating status of each equipment in the power system during the fault. Running status p';

The calculation module generates the post-fault power system node admittance matrix Y" based on the post-fault information of fault i. At the same time, it combines the operating status p' of each device during the fault obtained by the status module to calculate the quasi-steady state of each device under the post-fault power system network topology. Operating status, estimate the power imbalance amount ∑ΔP _i of the whole system after the power system experiences fault i;

The output module traverses all the fault sets in the power system obtained by the calculation module to select the maximum fault imbalance, and calculates the minimum safe inertia for frequency stability of the power system based on the system inertia center frequency change rate.

11. The minimum safe inertia evaluation system of the power system based on quasi-steady-state modeling according to claim 10, characterized in that in the calculation module, the power imbalance amount ΣΔP _i of the whole system after the power system experiences fault i is:

∑ΔP _i =∑(P _m -P _e (δ,x))

Where, P _m is the mechanical power of the synchronous generator, and P _e (δ,x) is the electromagnetic power of the synchronous generator;

The post-fault information of fault i generates the post-fault power system node admittance matrix Y'':

Y”[V]e ^jθ =[e ^jθ ](I _d (V,p’,p”)-jI _q (V,p’,p”))+I _g (δ,x)

12. The minimum safe inertia evaluation system for power systems based on quasi-steady-state modeling according to claim 10, characterized in that in the output module, all fault sets in the obtained power system are traversed, and the maximum fault imbalance amount is selected as :

When the power system frequency security constraint minimum total system inertia <∑T _ji is met, the current system synchronous generator inertia is sufficient to maintain system frequency stability.

13. A computer-readable storage medium storing one or more programs, characterized in that the one or more programs include instructions that, when executed by a computing device, cause the computing device to perform claim 1 to any of the methods described in 9.

14. A computing device, characterized by:

One or more processors, memories, and one or more programs, wherein one or more programs are stored in the memory and configured for execution by the one or more processors, the one or more programs include In performing the steps in the method of any one of claims 1 to 9.