Impedance short-circuit ratio-based high-proportion new energy grid grid-connected power source site selection method

Abstract

The application discloses a high-proportion new energy grid-connected power source site selection method based on impedance short-circuit ratio, first defines impedance short-circuit ratio of an in-grid device, and after all grid-connected power sources outside the in-grid device are respectively equivalent to ground admittance, node impedance matrix and Thevenin equivalent impedance of the in-grid device are sequentially solved according to system topology and parameters, equivalent ground admittance value rules and the like; then, a change amount of impedance short-circuit ratio brought by full-load operation of the in-grid device when external grid-connected power sources are accessed or exited is solved; finally, a final power source site selection scheme is decided according to a decision weighted sum of impedance short-circuit ratios of all devices, the change amount and a minimum value of the changed impedance short-circuit ratio. The application realizes a breakthrough from single-point device evaluation to system global optimization for grid-connected power source planning, improves the scientificity of system planning and the safety of grid operation, and provides a system-level decision quantification tool for grid-connected power source site selection.

Description

Technical Field

[0001] This invention belongs to the field of power system transmission and distribution technology, and specifically relates to a method for selecting the location of grid-connected power sources for high-proportion new energy power grids based on impedance short-circuit ratio. Background Technology

[0002] A high proportion of renewable energy has become a key path to achieving energy transition. As of June 2025, my country's total installed renewable energy capacity exceeded 2.1 billion kilowatts, accounting for more than half of the country's cumulative installed power generation capacity. However, asynchronous power sources connected to the grid via power electronic equipment have different grid connection characteristics than synchronous power sources. Their large-scale integration significantly alters the dynamic characteristics of the system, and the grid connection location of different types of power sources will directly affect the system's intensity distribution and voltage support capacity. With the rapid penetration of renewable energy, the requirements for safe and stable operation and efficient renewable energy absorption capacity in high-proportion renewable energy power systems are gradually increasing, and the need for precise site selection of grid-connected power sources is becoming increasingly urgent.

[0003] Improper grid-connected power source location can lead to deterioration of local area safety and stability characteristics. Existing location methods [Wu Xi, Wang Yinhua, Si Jindong. Flexible interconnection location and capacity determination based on topology-power transmission relationship [J]. Automation of Electric Power Systems, 2025, 49(23):48-56] rarely consider the impact of asynchronous power source control methods on system dynamic characteristics, and it is difficult to quantitatively assess the coupling relationship between grid-connected power source location and grid strength, which restricts the accuracy and reliability of grid-connected planning for high-proportion new energy power systems. Therefore, there is an urgent need for a location method that can reflect the external characteristics of asynchronous power sources and accurately assess their impact on system strength, thereby accurately characterizing the contribution of different types of grid-connected power sources to system strength and their interaction with other equipment, providing a quantitative tool for system-level decision-making for grid-connected power source location, which is of great value for improving the scientific nature of system planning and the safety of grid operation.

[0004] To address these challenges, it is essential to introduce a site selection method that reflects the impact of the external characteristics of different types of grid-connected power sources on grid strength. In this context, the impedance-to-short-circuit ratio provides a reliable approach to quantifying the grid-connected strength of new energy sources. It comprehensively considers the interaction between different types of grid-connected power sources, the operating status of grid-connected equipment, and the grid structure, providing a theoretical foundation for a breakthrough in site selection methods from single-point assessment to system-level decision-making.

[0005] However, existing research still has shortcomings in grid-connected power source location methods based on impedance short-circuit ratio [Chen Yanmei, Xiong Guojiang, Huang Dong. Multi-objective location and capacity determination research of distributed generation and parallel capacitors [J / OL]. Modern Power, 1-9, 2026]. Therefore, this paper selects the impedance short-circuit ratio index, which takes into account the external characteristics of synchronous power sources and different asynchronous power sources, to construct a systematic framework for rapid quantitative assessment of grid strength. It proposes a quantitative method for grid-connected power source location effect considering stability boundary constraints and overall system strength optimization, so as to realize the progressive decision-making of grid-connected power source planning from single-point safety to global optimization. This method has great application potential in the field of grid-connected power source location based on impedance short-circuit ratio. Summary of the Invention

[0006] In view of the above, the present invention provides a method for selecting grid-connected power sources with a high proportion of new energy power grids based on impedance short-circuit ratio. This method is simple to implement, highly applicable, and has great value in engineering design.

[0007] A method for selecting grid-connected power sources with a high proportion of new energy power grids based on impedance short-circuit ratio includes the following steps: (1) In a high proportion of new energy power system, determine the equivalent external characteristic models of asynchronous power sources with different control types under normal and fault conditions; (2) Based on the impedance short-circuit ratio expression of the grid-connected equipment and the power supply equivalent model, construct the node admittance matrix of the Thevenin equivalent impedance of the grid-connected equipment. After matrix inversion and self-impedance extraction, the Thevenin equivalent impedance of the grid-connected equipment is obtained. (3) When an external grid-connected power supply is connected to or disconnected from the system, the power supply is equivalent to the new admittance between its connection node and the reference zero potential point, and then the new admittance is used to solve the change in the Thevenin equivalent impedance. (4) For a single network access device, traverse all power access locations and calculate the impedance short-circuit ratio of the network access device at each access location; then perform a decision weighted summation of the impedance short-circuit ratios of all network access devices to screen effective location schemes and determine the final power supply location scheme.

[0008] Furthermore, in step (1), the asynchronous power supply represented by VSC (voltage source converter) is divided into normal state and fault state according to whether the inner loop current controller enters the limiting state due to a significant drop in PCC (point of common coupling) voltage. Under normal conditions, adopt V / fThe asynchronous power supply in (voltage-frequency ratio) control mode, PLL (phase-locked loop) synchronous constant DC voltage and AC voltage control mode, PLL synchronous constant active power and AC voltage control mode, PSL (power synchronization loop) synchronous constant active power and AC voltage control mode, or PSL synchronous constant active power and reactive power control mode is equivalent to a constant voltage source; the asynchronous power supply using PLL synchronous constant DC voltage and reactive power control mode or PLL synchronous constant active power and reactive power control mode is equivalent to a constant current source; under fault conditions, the asynchronous power supply is equivalent to a constant current source.

[0009] Furthermore, the expression for the impedance short-circuit ratio of the network-connected equipment in step (2) is as follows:

[0010] in: r SCR The impedance short-circuit ratio of the connected equipment. Z con The impedance modulus of the network-connected equipment. Z eq The modulus of the Thevenin equivalent impedance of the connected equipment; the external grid-connected power supply system only applies to... Z eq influential.

[0011] Furthermore, the specific implementation of step (2) is as follows: First, construct the original node admittance matrix Y based on the system topology and parameters. sys,ori Then, based on the rules for determining the equivalent ground admittance of the connected power supply, a general node admittance matrix Y is constructed. sys,gen Then use Y sys,gen Solve for the nodal admittance matrix Y of the Thevenin equivalent impedance of the connected device. sys,i Finally, regarding Y sys,i Inverse the matrix to obtain the corresponding nodal impedance matrix Z sys,i Extract Z sys,i The first in i The diagonal element is the Thevenin equivalent impedance of the network-connected device. Z eq,i , i This is the index number of the access node for the network-connected device.

[0012] Furthermore, the node admittance matrix Y sys,i The expression is as follows: ,

[0013] in: y gi For nodes i Equivalent earth admittance ygj For nodes j Equivalent earth admittance j =1,2,…, n , n This represents the number of nodes in the system.

[0014] Furthermore, the equivalent ground admittance y gj The rule for determining the value is: when the node j If no power supply is connected or an asynchronous machine power supply with an equivalent model of a constant current source is connected, then y gj Take 0; when node j If the asynchronous machine power supply with a constant voltage source as its equivalent model is connected, then y gj Take ∞; when node j If the equivalent model is a synchronous machine power supply with an impedance voltage source, then y gj equals 1 / Z Gk , Z Gk This is the connection impedance of the voltage source with impedance.

[0015] Furthermore, the expression for the change in admittance caused by the Thevenin equivalent impedance in step (3) is as follows:

[0016] Where: Δ Z eq,i Δ is the change in Thevenin equivalent impedance. y k For the addition of admittance, Z ik,i The node impedance matrix Z sys,i The Middle k Liede i row element, Z kk,i The node impedance matrix Z sys,i The Middle k Liede k row element, k This is the index number of the external grid-connected power supply node.

[0017] Furthermore, in step (4), for any network access device i When an external grid-connected power source is connected to a node, the connected equipment... i impedance short-circuit ratio r SCR-new,i The calculation expression is as follows:

[0018] Then, the impedance short-circuit ratio of all network-connected devices is weighted and summed according to the following formula:

[0019]

[0020] in: U N,i and S N,i Network access devices i Rated voltage and rated capacity, Z eq,i and Δ Z eq,i Network access devices i Thevenin equivalent impedance and its variation. r sys-new The weighted summation result for the decision, S sel,i Let be the decision function. k sel,i The weights considered for the impedance short-circuit ratio.

[0021] Furthermore, in step (4), when an external grid-connected power source is connected to a node, if the impedance short-circuit ratio of all connected devices is greater than the minimum impedance short-circuit ratio requirement they must meet, then the location scheme corresponding to the connected node is recorded as a valid location scheme; all power source connection locations are traversed, valid location schemes are selected, and the location schemes corresponding to all valid location schemes are... r sys-new Sort and retrieve r sys-new The effective addressing scheme corresponding to the maximum value is used as the final power supply addressing scheme.

[0022] A computer device includes a memory and a processor, wherein the memory stores a computer program, and the processor executes the computer program to implement the above-described method for selecting high-proportion renewable energy grid-connected power sources based on impedance short-circuit ratio.

[0023] A computer-readable storage medium storing a computer program, which, when executed by a processor, implements the above-described method for selecting grid-connected power sources for high-proportion renewable energy grids based on impedance short-circuit ratio.

[0024] Based on the above technical solution, the present invention has the following beneficial technical effects: 1. Regarding the grid-connected power source location method, this invention fills the current research gap in the field of impedance short-circuit ratio in the grid-connected power source location method, and can provide a certain reference for the planning and development of future high-proportion new energy power systems.

[0025] 2. This invention has strong versatility and a clear selection method, and is theoretically applicable to high-proportion renewable energy power systems under any power source grid connection conditions.

[0026] 3. This invention achieves a breakthrough in grid-connected power source planning, moving from single-point equipment evaluation to system-wide optimization, thereby improving the scientific nature of system planning and the safety of grid operation, and providing a quantitative tool for system-level decision-making in grid-connected power source site selection. Attached Figure Description

[0027] Figure 1 This is a flowchart illustrating the classification process of asynchronous machine power controllers.

[0028] Figure 2 A schematic diagram of the power supply equivalence for asynchronous machines when obtaining the Thevenin equivalent impedance.

[0029] Figure 3 This is a schematic diagram of the simulation topology for a high-proportion renewable energy power system. Detailed Implementation

[0030] To describe the present invention in more detail, the technical solution of the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0031] This embodiment provides a method for selecting grid-connected power sources with a high proportion of new energy power grids based on impedance short-circuit ratio, including the following steps: (1) The equivalent external characteristics of asynchronous power supplies represented by VSC are determined by the control method adopted by itself and the limiting state of the inner loop current controller. Based on whether the inner loop current controller enters the limiting state due to a significant drop in the voltage of the common coupling point PCC, the operating conditions of asynchronous power supplies are divided into normal state and fault state. Then, the equivalent external characteristic models of asynchronous power supplies with different control types under the above two operating conditions are determined: Under normal state, asynchronous power supplies are equivalent to constant voltage source or constant current source due to different control methods; Under fault state, all types of asynchronous power supplies are uniformly equivalent to constant current source due to entering the current saturation mode.

[0032] In new power systems, asynchronous machine power sources are increasingly accounting for a larger proportion of power supply capacity. Asynchronous machine power sources, represented by VSC, are classified as follows: Figure 1 As shown, its synchronization methods mainly include phase-locked loop (PLL) synchronization control, power synchronization control using PSL synchronization, and constant frequency control (denoted as constant frequency control). f Control), its active power control objectives include constant DC voltage control (denoted as constant). U dc Control), constant active power control (denoted as constant) P pcc Control), its reactive power control objectives include constant AC voltage amplitude control (denoted as constant).U pccm (Control), constant reactive power control (denoted as constant) Q pcc (Control). In addition to adopting V / f Besides VSC control mode, the actual control objectives of the other 6 VSC controllers are achieved through conventional inner and outer loop controllers, and the final control loop uses an inner loop current controller with direct current control.

[0033] Because the d-axis and q-axis current command values ​​of the inner loop current controller and It is limited in amplitude. Once it enters the limited-amplitude operation state, the output of the inner-loop current controller can no longer achieve the predetermined control target of the outer-loop controller. Therefore, whether the inner-loop current controller operates in the limited-amplitude state has a decisive impact on the external characteristics of the VSC. The fundamental reason for the inner-loop current controller to switch to the limited-amplitude operation state is the drop in the PCC voltage of the VSC. Based on the magnitude of the PCC voltage drop, the operating conditions of the asynchronous power supply can be divided into normal and fault states. Under normal operating conditions, the PCC voltage is near its rated value, and the d-axis and q-axis current command values ​​of the inner-loop current controller are... and Neither will fall within the current limit value, and the asynchronous power supply can achieve the predetermined control objective; however, under fault conditions, the PCC voltage drops significantly, forcing the d-axis and q-axis current command values ​​of the inner loop current controller to... and This equals the current limit value, meaning the asynchronous power supply has entered current saturation and can no longer achieve the predetermined control objective.

[0034] The equivalent external characteristic circuits for the above seven types of asynchronous power supplies under normal and fault conditions are as follows: ① Normal operating conditions: For V / f PSL / P pcc - U pccm PSL / P pcc - Q pcc PLL / U dc - U pccm PLL / P pcc - U pccmIn normal operating conditions, when viewed from the AC system, an asynchronous power supply can be equivalent to a voltage source with constant amplitude and constant phase angle connected to the PCC; for PLL / U dc - Q pcc PLL / P pcc - Q pcc An asynchronous power supply, under normal operating conditions, has an external characteristic equivalent circuit that is a current source with constant amplitude and constant phase angle.

[0035] ② Fault-state operating conditions: d-axis and q-axis current command values ​​of the inner loop current controller for 7 types of VSCs and When the current limit is equal to the current limit, the asynchronous power supply enters the current saturation state. From the perspective of the AC system to the asynchronous power supply, its external characteristics are equivalent to a current source with constant amplitude and constant phase angle.

[0036] (2) For the network-connected equipment under investigation, its impedance short-circuit ratio is defined as the impedance magnitude of the equipment itself. Z con Its Thevenin equivalent impedance modulus Z eq The ratio is such that the connection of the external synchronous power supply and the asynchronous power supply only affects... Z eq Therefore, only the power supply connection situation is considered. Z eq The impact. Calculation. Z eq First, the original node admittance matrix Y of the system is constructed based on the system topology and parameters. sys,ori (Matrix is ​​represented by bold regular letters), and then all synchronous and asynchronous power supplies are equivalent to the ground admittance of their respective PCC points. y gk And based on the rules for determining the equivalent impedance of the access equipment, a solution is constructed to calculate the Thevenin impedance of each network access equipment. Z eq The general node admittance matrix Y sys,gen Subsequently based on Y sys,gen Construct a solution for network access devices i Thevenin impedance Z eq,i The nodal admittance matrix Y sys,i And solve for its corresponding nodal impedance matrix Z. sys,i The obtained Z sys,i Nodes in the diagonal elements i Corresponding self-impedance Z ii,i That is, network access equipmenti Thevenin equivalent impedance Z eq,i .

[0037] Impedance-to-short-circuit ratio r SCR Defined as the impedance of the network access device Z con Modulus Z con Its Thevenin equivalent impedance Z eq Modulus Z eq The ratio:

[0038] Including n In a network of nodes, the original node admittance matrix Y is constructed based on the system topology and parameters. sys,ori :

[0039] in: y pq For nodes p With nodes q Admittance between ( p =1,2,…, n ; q =1,2,…, n ; p = q hour, y pq (This represents the self-admittance of the corresponding node).

[0040] like Figure 2 As shown, for each network access device r SCR During the calculation, all synchronous and asynchronous machine power supplies are denoted as power supplies. k (Indicates that the access point is a node) k ), and equivalently represent it as a node. k Earth-to-ground admittance y gk Therefore, for network access devices i (Indicates that the access point is a node) i In other words, if we consider it Z eq Recorded as Z eq,i Then the external power supply y gk Only affect its Z eq,i Therefore, when selecting a site, only the power supply location and the type of asynchronous power supply are considered. Z eq,iModulus Z eq,i The impact.

[0041] In determining y gk In terms of value selection, it is equivalent to a synchronous machine power supply with an impedance voltage source. k corresponding y gk Take its connection impedance Z Gk The reciprocal of 1 / Z Gk Asynchronous machine power supply, equivalent to a voltage source k corresponding y gk Take ∞; asynchronous machine power supply equivalent to a current source k corresponding y gk Set to 0; when completing the above steps, first for each node j A parallel ground admittance y gj The rules for its value are as follows:

[0042] All power supplies are equivalent to y gk Equivalent to Y sys,ori In y kk Plus y gk Based on the above value selection rules, a set of calculation methods can be generated for each network-connected device. r SCR The general node admittance matrix Y sys,gen :

[0043] For network access devices i In other words, to solve Z eq,i At that time, its self-guided absorption y ii It contains neither y gi It also does not contain its own grid connection impedance. Z con,i corresponding admittance y con,i Therefore, regarding network access devices i Based on Y sys,gen Construct a solution to it Z eq,i The nodal admittance matrix Y sys,i :

[0044] Find Y sys,i The corresponding node impedance matrix Z sys,i :

[0045] Network access devices i The corresponding port typically contains a zero-potential reference ground node, therefore the obtained Z sys,i The i Self-impedance corresponding to each diagonal element Z ii,i That is Z eq,i Z obtained from the original network sys,i , Z eq,i Let them be denoted as Z sys0,i , Z eq0,i .

[0046] (3) Network access equipment i External grid-connected power supply k Accessing or exiting the system during runtime is equivalent to being on a node. k The additional admittance Δ between the reference zero potential point and the reference zero potential point y k , through Δ y k It can then be solved as Z eq0,i The resulting change Δ Z eq,i .

[0047] Network access devices i External grid-connected power supply k Accessing or exiting the system during runtime is equivalent to being on a node. k The additional admittance Δ between the reference zero potential point and the reference zero potential point y k Its absolute value represents the external grid-connected power supply that is connected to or disconnected from the system operation. k The equivalent admittance, with its positive and negative values ​​corresponding to the connection and disconnection of the power source, respectively. Adding a new branch does not add a new node; the node impedance matrix Z after its connection is... sys-new,i for:

[0048] Z .k,i It is Z sys0,i The k List:

[0049] Z sys-new,i The first in i diagonal elements Zii-new,i For network access devices i Thevenin equivalent impedance in the new network Z eq-new,i Therefore:

[0050] Then the network access device i of Z eq0,i The change is Δ Z eq,i ,Right now:

[0051] (4) Calculate the network access devices in the original network. i Impedance-to-short-circuit ratio under full power output conditions r SCR0,i And through the decision function S sel,i Select the devices to be considered, and then solve for the network access devices to be considered. r SCR0,i Decision weighting r sys0 To assess the overall impact of new grid-connected power sources on system strength. During site selection, all candidate access points are traversed, based on Δ... Z eq,i Calculate the impedance-to-short-circuit ratio after grid-connected power supply is connected. r SCR-new,i and r SCR-new,i Decision weighting r sys-new Filter out those that meet all r SCR-new,i All of these are effective location schemes that exceed their respective minimum impedance short-circuit ratio requirements, and will r sys-new The largest effective location scheme is used as the final power supply location scheme.

[0052] Access devices in the original network i Impedance-short-circuit ratio under full power supply conditions of the system r SCR0,i for:

[0053] in: Z con,i for Z con,i The modulus, U N,i and S N,i Network access devices i The rated voltage and rated capacity.

[0054] For all network-connected devices in the system whose impedance short-circuit ratio needs to be considered, when selecting the location of the power supply for a newly connected system, the overall impact of the power supply connection on these network-connected devices must be considered. The following processing is performed based on the impedance short-circuit ratio calculation method for a single network-connected device: using a decision function... S sel,i Indicates network access device i of r SCR0,i Should we consider using k sel,i express r SCR0,i The weighting of power supply access and its overall impact on the original system are considered through all necessary factors. r SCR0,i Decision weighting and r sys0 To indicate:

[0055]

[0056] Iterate through all candidate power access locations and solve for the network access devices at each access location. i impedance short-circuit ratio r SCR-new,i :

[0057] and the newly obtained r SCR-new,i The decision weighted sum is recorded as r sys-new :

[0058] When the power supply is connected to a certain location, if all r SCR-new,i All are greater than their respective minimum impedance short-circuit ratio requirements. r SCR,i-min If the access location is selected, the corresponding location scheme is recorded as a valid location scheme, and all valid location schemes are considered... r sys-new Sort by size, corresponding to the largest r sys-new The effective location scheme is the final power supply location scheme.

[0059] The test system topology studied in the following embodiments is as follows: Figure 3As shown, to verify the effectiveness of the method of the present invention, PSCAD (Power System Computer-Aided Design) is used as the simulation module of the digital twin. The test system is established in PSCAD for time-domain simulation analysis. The high-proportion renewable energy power system in the test example consists of 10 nodes, and the rated AC voltage of the system is 220kV. Power sources A, B, C, D, and E are connected to nodes 1, 4, 5, 7, and 10, respectively. Power sources B and D, with a rated capacity of 400MVA, are two renewable energy power stations, both of which are asynchronous power sources without voltage support capability. The impedance between each node is shown in Table 1. Table 1

[0060] In the high-proportion renewable energy power system shown in this example, the AC voltage amplitudes at the PCC points of renewable energy power stations B and D are 199.41kV and 196.93kV, respectively, far lower than the rated voltage of the AC system at 220kV. To improve the grid connection point voltage of renewable energy power stations B and D, it is now considered to install a grid-connected power source with voltage support capability at one of the nodes 2, 6, and 8. Under the grid-connected power source location method of this invention, renewable energy power stations B and D are of equal importance. Under this premise, Table 2 lists the minimum impedance short-circuit ratio that each renewable energy power station must meet. r SCR,i-min The impedance-to-short-circuit ratio of each new energy power station before grid connection. r SCR0,i The impedance-to-short-circuit ratio of each new energy power station after grid connection. r SCR-new,i , r SCR-new,i Compared to r SCR0,i The increase value Δ r i Impedance-short-circuit ratio decision weighted sum before grid-connected power supply r sys0 Impedance-short-circuit ratio decision weighted sum after grid-connected power supply r sys-new , r sys-new Compared to r sys0 The increase value Δ r .

[0061] Table 2

[0062] In the simulation system built based on the above example, grid-connected power sources with voltage support capabilities are connected to nodes 2, 6, and 8, respectively; correspondingly, the voltage amplitudes of the grid-connected power sources when connected to different nodes are shown in Table 3: Table 3

[0063] Simulation results show that when grid-connected power sources with voltage support capabilities are connected to different nodes, the voltage increase at the port of power source B, from largest to smallest, corresponds to the connection to nodes 8, 6, and 2, respectively. Similarly, the voltage increase at the port of power source D, from largest to smallest, corresponds to the connection to nodes 8, 6, and 2, respectively. These simulation results are consistent with the evaluation results of the site selection method of this invention. Furthermore, under the same conditions such as rated capacity, the relative magnitudes of the voltage increases at the ports of power sources B and D are consistent with the relative magnitudes of the weighted sum of impedance short-circuit ratio decisions. The simulation results demonstrate that the site selection method of this invention can evaluate the effectiveness of different grid-connected power source site selection schemes. Connecting grid-connected power sources according to the site selection results of this invention is beneficial for optimizing the grid strength of the system. These simulation results verify the effectiveness of the grid-connected power source site selection method for high-proportion renewable energy power systems of this invention, indicating that it achieves a breakthrough in grid-connected power source planning from single-point equipment evaluation to system-wide optimization, improving the scientific nature of system planning and the safety of grid operation, and providing a quantitative tool for system-level decision-making in grid-connected power source site selection.

[0064] The above description of the embodiments is provided to enable those skilled in the art to understand and apply the present invention. Those skilled in the art can readily make various modifications to the above embodiments and apply the general principles described herein to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made to the present invention by those skilled in the art based on the disclosure thereof should be within the scope of protection of the present invention.

Claims

1. A method for selecting grid-connected power sources with a high proportion of new energy power grids based on impedance short-circuit ratio, characterized in that, Includes the following steps: (1) In a high proportion of new energy power system, determine the equivalent external characteristic models of asynchronous power sources with different control types under normal and fault conditions; (2) Based on the impedance short-circuit ratio expression of the grid-connected equipment and the power supply equivalent model, construct the node admittance matrix of the Thevenin equivalent impedance of the grid-connected equipment. After matrix inversion and self-impedance extraction, the Thevenin equivalent impedance of the grid-connected equipment is obtained. (3) When an external grid-connected power supply is connected to or disconnected from the system, the power supply is equivalent to the new admittance between its connection node and the reference zero potential point, and then the new admittance is used to solve the change in the Thevenin equivalent impedance. (4) For a single network access device, traverse all power access locations and calculate the impedance short-circuit ratio of the network access device at each access location; then perform a decision weighted summation of the impedance short-circuit ratios of all network access devices to screen effective location schemes and determine the final power supply location scheme.

2. The method for selecting grid-connected power sources with a high proportion of new energy power grids based on impedance short-circuit ratio according to claim 1, characterized in that: In step (1), the asynchronous power supply represented by VSC is divided into normal state and fault state according to whether the inner loop current controller enters the limiting state due to a significant drop in PCC voltage. Under normal conditions, adopt V / f The asynchronous power supply in control mode, PLL synchronous constant DC voltage and AC voltage control mode, PLL synchronous constant active power and AC voltage control mode, PSL synchronous constant active power and AC voltage control mode, or PSL synchronous constant active power and reactive power control mode is equivalent to a constant voltage source; the asynchronous power supply in control mode, PLL synchronous constant DC voltage and reactive power control mode, or PLL synchronous constant active power and reactive power control mode is equivalent to a constant current source; under fault conditions, the asynchronous power supply is equivalent to a constant current source.

3. The method for selecting high-proportion renewable energy grid-connected power sources based on impedance short-circuit ratio according to claim 1, characterized in that, The expression for the impedance short-circuit ratio of the network-connected equipment in step (2) is as follows: in: ρ SCR The impedance short-circuit ratio of the connected equipment. Z con The impedance modulus of the network-connected equipment. Z eq The modulus of the Thevenin equivalent impedance of the connected equipment; the external grid-connected power supply system only applies to... Z eq influential.

4. The method for selecting high-proportion renewable energy grid-connected power sources based on impedance short-circuit ratio according to claim 1, characterized in that, The specific implementation method of step (2) is as follows: First, construct the original node admittance matrix Y based on the system topology and parameters. sys,ori Then, based on the rules for determining the equivalent ground admittance of the connected power supply, a general node admittance matrix Y is constructed. sys,gen Then use Y sys,gen Solve for the nodal admittance matrix Y of the Thevenin equivalent impedance of the connected device. sys,i Finally, regarding Y sys,i Inverse the matrix to obtain the corresponding nodal impedance matrix Z sys,i Extract Z sys,i The first in i The diagonal element is the Thevenin equivalent impedance of the network-connected device. Z eq,i , i This is the index number of the access node for the network-connected device.

5. The method for selecting high-proportion renewable energy grid-connected power sources based on impedance short-circuit ratio according to claim 4, characterized in that, The node admittance matrix Y sys,i The expression is as follows: ， in: y gi For nodes i Equivalent earth admittance y gj For nodes j Equivalent earth admittance j =1,2,…, n , n This represents the number of nodes in the system.

6. The method for selecting high-proportion renewable energy grid-connected power sources based on impedance short-circuit ratio according to claim 5, characterized in that, The equivalent ground admittance y gj The rule for determining the value is: when the node j If no power supply is connected or an asynchronous machine power supply with an equivalent model of a constant current source is connected, then y gj Take 0; when node j If the asynchronous machine power supply with a constant voltage source as its equivalent model is connected, then y gj Take ∞; when node j If the equivalent model is a synchronous machine power supply with an impedance voltage source, then y gj equals 1 / Z Gk , Z Gk The impedance is the connection impedance of the voltage source with impedance.

7. The method for selecting high-proportion renewable energy grid-connected power sources based on impedance short-circuit ratio according to claim 4, characterized in that, The expression for the change in admittance caused by the Thevenin equivalent impedance in step (3) is as follows: Where: Δ Z eq,i Δ is the change in Thevenin equivalent impedance. y k For the addition of admittance, Z ik,i The node impedance matrix Z sys,i The Middle k Liede i row element, Z kk,i The node impedance matrix Z sys,i The Middle k Liede k row element, k This is the index number of the external grid-connected power supply node.

8. The method for selecting grid-connected power sources with a high proportion of new energy power grids based on impedance short-circuit ratio according to claim 1, characterized in that, In step (4), for any network access device i When an external grid-connected power source is connected to a node, the connected equipment... i impedance short-circuit ratio ρ SCR-new,i The calculation expression is as follows: Then, the impedance short-circuit ratio of all network-connected devices is weighted and summed according to the following formula: in: U N,i and S N,i Network access devices i Rated voltage and rated capacity, Z eq,i and Δ Z eq,i Network access devices i Thevenin equivalent impedance and its variation. ρ sys-new The weighted summation result for the decision, S sel,i Let be the decision function. k sel,i The weights considered for the impedance short-circuit ratio.

9. The method for selecting grid-connected power sources with a high proportion of new energy power grids based on impedance short-circuit ratio according to claim 8, characterized in that, In step (4), when an external grid-connected power source is connected to a node, if the impedance short-circuit ratio of all connected devices is greater than the minimum impedance short-circuit ratio requirement they must meet, then the location scheme corresponding to that connected node is recorded as a valid location scheme; all power source connection locations are traversed, and valid location schemes are selected, and the location schemes corresponding to all valid location schemes are... ρ sys-new Sort and retrieve ρ sys-new The effective addressing scheme corresponding to the maximum value is used as the final power supply addressing scheme.

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