Power grid strength dynamic identification method based on micro-increment model and related device

Abstract

The invention discloses a power grid strength dynamic identification method based on a micro-increment model and a related device, and relates to the field of power grid strength identification, and the method comprises the steps: determining a current power grid structure and an operation state, and constructing a whole-system micro-increment model; the whole-system micro-increment model comprises a micro-increment model of VSC type grid-connected equipment, a micro-increment model of LCC type grid-connected equipment and a micro-increment model of an alternating-current power grid; solving the micro-increment model of the whole system to obtain micro-increments of voltage and current of the equipment port of each piece of grid-connected equipment; further calculating the equivalent operation impedance of each piece of grid-connected equipment, and further determining a short-circuit ratio; and when the current operation state of the power grid does not change, identifying the power grid strength of the grid-connected equipment according to the short-circuit ratio. The method fully considers the influence of the VSC and the LCC on the receiving end power grid, adopts an operation impedance mode to be equivalent to power electronic equipment, considers the influence of the dynamic change of the power grid on the intensity, and enables the calculation of the power grid intensity to be more accurate.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of power grid strength identification, and particularly relates to a power grid strength dynamic identification method based on a micro-increment model and a related device. BACKGROUND

[0002] With the development of China's economy and the increase of renewable energy utilization, more and more electric energy needs to be transmitted from the western region to the central and eastern regions, and long-distance DC transmission projects play an important role in it. The central China, east China and other places have formed a multi-DC infeed receiving end grid pattern. The main receiving end grid areas among them are facing significant reactive power and voltage problems. First, the large power receiving of external DC has a great impact on the power flow, voltage and system stability of the power grid, especially the forced shutdown of DC bipolar may cause severe fluctuations of system voltage, frequency and line power flow, threatening the stable operation of the system. Second, the converter in the traditional DC transmission system (LCC-HVDC) consumes a large amount of reactive power (about half of the transmitted active power), resulting in a lack of system reactive power and increasing the difficulty of voltage control. In addition, the DC transmission control mode is not flexible, which easily leads to voltage instability accidents, further aggravating the voltage stability problem of the receiving end grid. The prerequisite for solving the above problems is to first determine the grid strength.

[0003] At present, the short-circuit ratio is usually used to measure the grid strength after the LCC-HVDC is fed into the receiving end grid, but at present there are a large number of new energy power sources such as photovoltaic / wind power connected to the receiving end grid. The interaction between the power electronic equipment in the new energy base and the grid is closely related to the strength of the grid. The description of the traditional grid strength based on short-circuit current calculation is no longer accurate. For example, the regulation effect of converter-type power sources, LCC-type DC and VSC-type DC on the grid voltage will all affect the grid strength. At the same time, the changes in the grid operation mode and system structure will also cause changes in the grid strength, affecting the stability of the LCC grid-connected system. SUMMARY

[0004] The purpose of the present application is to provide a grid strength dynamic identification method based on a micro-increment model and a related device, which can realize dynamic and accurate identification of the grid strength.

[0005] To achieve the above purpose, the present application provides the following solutions: In a first aspect, the present application provides a grid strength dynamic identification method based on a micro-increment model, comprising: determining the current grid structure and operation state; constructing a full-system micro-increment model according to the current grid structure and operation state; the full-system micro-increment model includes a micro-increment model of VSC-type grid-connected equipment, a micro-increment model of LCC-type grid-connected equipment and a micro-increment model of an AC grid; Solving the full-system micro-increment model, micro-increments of device port voltage and current of each grid-connected device are obtained; the grid-connected device includes a VSC type grid-connected device and an LCC type grid-connected device; According to the micro-increments of device port voltage and current of the grid-connected device, the equivalent operating impedance of each grid-connected device is obtained; According to the equivalent operating impedance of each grid-connected device, the short-circuit ratio of each grid-connected device is determined; When the current grid operating state does not change, the grid strength of the grid-connected device is identified according to the short-circuit ratio of each grid-connected device.

[0006] In a second aspect, the present application provides a computer device, comprising: a memory, a processor, and a computer program stored in the memory and executable on the processor, and the processor executes the computer program to implement the above-mentioned grid strength dynamic identification method based on the micro-increment model.

[0007] In a third aspect, the present application provides a computer readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the above-mentioned grid strength dynamic identification method based on the micro-increment model.

[0008] According to the specific embodiments provided by the present application, the following technical effects are disclosed: The present application provides a grid strength dynamic identification method based on a micro-increment model and related devices, determines the current grid structure and operating state and constructs a full-system micro-increment model; the full-system micro-increment model includes a micro-increment model of a VSC type grid-connected device, a micro-increment model of an LCC type grid-connected device and a micro-increment model of an alternating current grid; solving the full-system micro-increment model, micro-increments of device port voltage and current of each grid-connected device are obtained; further calculating the equivalent operating impedance of each grid-connected device, and then determining the short-circuit ratio; when the current grid operating state does not change, the grid strength of the grid-connected device is identified according to the short-circuit ratio. The present application fully considers the influence of VSC and LCC on the receiving end grid, uses the operating impedance to equivalent power electronic device, considers the influence of the dynamic change of the grid on the strength, so that the calculation of the grid strength is more accurate. BRIEF DESCRIPTION OF DRAWINGS

[0009] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed in the embodiments will be briefly introduced as follows. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0010] Figure 1 It is an application environment diagram for a grid strength dynamic identification method based on a micro-increment model in an embodiment of the present application; Figure 2 A flowchart of a micro-increment model-based power grid strength dynamic identification method provided by an embodiment of the present application is shown in FIG. 1. Figure 3 A technical concept diagram of a micro-increment model-based power grid strength dynamic identification method provided by an embodiment of the present application is shown in FIG. 2. Figure 4 A schematic diagram of a hybrid multi-infeed receiving-end power grid provided by an embodiment of the present application is shown in FIG. 3. Figure 5 A schematic diagram of a VSC grid-connected structure provided by an embodiment of the present application is shown in FIG. 4. Figure 6 A schematic diagram of impedance equivalence provided by an embodiment of the present application is shown in FIG. 5. Figure 7 A structural schematic diagram of a computer device provided by an embodiment of the present application is shown in FIG. 6. DETAILED DESCRIPTION

[0011] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the scope of protection of the present application.

[0012] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the present application will be further described in detail below with reference to the drawings and specific embodiments.

[0013] The micro-increment model-based power grid strength dynamic identification method provided by the embodiments of the present application can be applied to, for example, Figure 1The application environment shown. Among them, the terminal communicates with the server through the network. The data storage system can store the data required by the server to process. The data storage system can be set up separately, or integrated on the server, or placed on the cloud or other servers. The terminal can send the current power grid structure and operating state to the server, and after the server receives the current power grid structure and operating state, the server constructs a full-system micro-incremental model according to the current power grid structure and operating state; The full-system micro-incremental model includes a micro-incremental model of a VSC-type grid-connected device, a micro-incremental model of an LCC-type grid-connected device, and a micro-incremental model of an alternating current power grid; The full-system micro-incremental model is solved to obtain the micro-incremental of the device port voltage and current of each grid-connected device; The grid-connected device includes a VSC-type grid-connected device and an LCC-type grid-connected device; The equivalent operating impedance of each grid-connected device is obtained according to the micro-incremental of the device port voltage and current of the grid-connected device; The short-circuit ratio of each grid-connected device is determined according to the equivalent operating impedance of each grid-connected device; When the current power grid operating state does not change, the grid strength of the grid-connected device is identified according to the short-circuit ratio of each grid-connected device. The server can feed back the identified grid strength of the grid-connected device to the terminal.

[0014] Among them, the terminal can be, but not limited to, various desktop computers, notebook computers, smart phones, tablet computers, Internet of Things devices and portable wearable devices, the server can be realized by an independent server or a server cluster composed of multiple servers, and can also be a cloud server.

[0015] In an exemplary embodiment, as shown in Figure 2 and Figure 3 A micro-incremental model-based power grid strength dynamic identification method is provided, which is executed by a computer device, specifically by a terminal or a server, or by both, in the embodiments of the present application, the method is applied to Figure 1 the server in , including the following steps 101 to 106.

[0016] Step 101, determine the current power grid structure and operating state.

[0017] Determining the power grid structure means determining the power electronic devices and line structure in the power grid, and determining the power grid operating state means confirming whether the power grid is currently in steady-state operation or fault fluctuation, transient state.

[0018] Step 102, construct a full-system micro-incremental model according to the current power grid structure and operating state; The full-system micro-incremental model includes a micro-incremental model of a VSC-type grid-connected device (a device that has accessed the power grid), a micro-incremental model of an LCC-type grid-connected device (a device that has accessed the power grid), and a micro-incremental model of an alternating current power grid.

[0019] Step 103: Solve the micro-incremental model of the entire system to obtain the micro-incremental voltage and current of each grid-connected device's port; the grid-connected devices include VSC type grid-connected devices and LCC type grid-connected devices.

[0020] Step 104: Calculate the equivalent operating impedance of each grid-connected device based on the minute increments of the device port voltage and current of the grid-connected device.

[0021] Step 105: Determine the short-circuit ratio of each grid-connected device based on its equivalent operating impedance.

[0022] Step 106: When the current power grid operating status has not changed, identify the power grid strength of the grid-connected equipment (equipment to be connected) based on the short-circuit ratio of each grid-connected equipment.

[0023] By implementing steps 101 to 106 above, the impact of VSC and LCC on the receiving-end power grid is fully considered. The operating impedance is used to represent the power electronic equipment, and the impact of the dynamic changes of the power grid on the strength is taken into account, making the calculation of the power grid strength more accurate.

[0024] In step 102, the establishment of the incremental model for the entire system is as follows: Figure 4 This illustrates a hybrid multi-feed receiving-end grid. If the grid load continues to increase, a new DC line needs to be connected to the receiving-end grid to meet the requirements, such as... Figure 4 LCC1 in the context of grid strength is closely related to the DC power input and the number of DC connections. To ensure that the connected DC power can operate reliably and transmit power, it is necessary to accurately calculate the grid strength.

[0025] Traditional grid strength is measured using the short-circuit ratio, but this ratio only considers the impact of short-circuit capacity. However, current receiving-end grids include various types of power electronic equipment such as LCCs and VSCs. To obtain grid strength that takes into account the grid-connected regulation effects of these power electronic devices, it is necessary to consider the voltage regulation effects of the converter's physical processes and control mechanisms. This can be achieved by incrementally representing the converter as an equivalent impedance, thus allowing for the calculation of grid strength that considers the converter and other power electronic equipment.

[0026] Under steady-state conditions, when voltage or power disturbances occur in the receiving-end power grid system, the grid-connected power electronic equipment will adjust the active and reactive current injected into the system according to different control methods. At this time, the current at the grid connection point will fluctuate; voltage changes cause current changes, resulting in overall impedance characteristics. Based on this, the equivalent operating impedance Z of the power electronic equipment can be defined. C : (1-1) In the formula, Δ u cd and Δ u cqare the micro-increments of the device port voltage in the dq coordinate system, respectively i cd and i cq are the micro-increments of the device port current in the dq coordinate system, respectively.

[0027] The operating impedance calculation method shown in formula (1-1) needs to calculate the micro-increments of the device port voltage and current first. When a disturbance occurs in the system, the voltage and current changes of the device port are not only affected by the device itself, but also affected by other devices in the receiving end power grid, including grid-connected VSC, LCC, and AC network architecture. In order to ensure that the micro-increments of voltage and current can be calculated through a given disturbance, it is necessary to establish a micro-increment model of VSC, LCC, and AC network, and solve the micro-increments of the voltage and current of the device to be connected to the grid under the given disturbance.

[0028] Among them, for the establishment of the micro-increment model of the VSC grid-connected device: as Figure 5 , the VSC grid-connected structure is shown, Figure 5 Among them, P and Q are the active power and reactive power absorbed by the converter from the AC network, is the voltage at the grid connection point of the converter station or new energy field station, is the equivalent impedance of the device between the converter and the grid connection point, including the converter transformer, filter device, etc. is the current injected by the grid to the VSC, is the voltage at the outlet of the converter, and δ is the corresponding phase angle.

[0029] According to the power transmission direction and the parameters of each part shown in Figure 5 , the active power and reactive power absorbed by the converter from the AC network can be expressed as: (1-2) The VSC grid-connected device usually adopts vector current control, therefore, it is necessary to convert the abc coordinate system to the dq coordinate system through coordinate transformation. In the dq synchronous rotating coordinate system, the active power P and the reactive power Q exchanged between the AC system and the voltage source converter are changed from formula (1-2) to: (1-3) In the formula, u vd , u vq , i vd and i vq are U v and Iv The results converted from the abc coordinate system to the dq coordinate system.

[0030] The formula (1-3) is linearized and expanded around the rated operating point, and the high order terms are eliminated, to obtain the micro-increment model of the flexible DC port: (1-4) In the formula, Δ u vd , Δ u vq , Δ i vd and Δ i vq are the corresponding micro-increments. u vd0 , u vq0 , i vd0 and i vq0 are the initial values of u vd , u vq , i vd and i vq , respectively. The initial value is the value at the steady state operation.

[0031] According to different VSC control modes, different constraint conditions need to be added. For the converter using constant power control, it can be approximately considered that the power injected by the converter into the system is constant zero, so the micro-increment model of the foregoing formula (1-4) can be added with the constraint: (1-5) When the control mode is: constant DC power and constant AC voltage amplitude on one side, and constant DC voltage and constant AC voltage amplitude on the other side, the micro-increment model of the foregoing formula (1-4) can be added with the constraint: (1-6) For the establishment of the micro-increment model of the LCC type grid-connected device: for the LCC type grid-connected device connected to the AC power grid, its operation can be represented by the model as shown below: (1-7) In the model, i ld and i lq are the d, q axis components of the AC current injected by the converter station into the power grid, U dcis the DC voltage of LCC system, n is the number of six-pulse converters, k is the transformer ratio of converter transformer, U l is the effective value of line voltage on AC side of converter station, u ld and u lq are the corresponding d, q-axis components, X L is the commutation reactance, δ is the phase angle of AC voltage, i dc is the DC current, α is the firing angle of converter, μ is the commutation overlap angle of converter.

[0032] In the formula, M is a fixed coefficient generated in the calculation process: (1-8) Linearization of formula (1-7) can be obtained after expansion: (1-9) In the formula, k a - k l The expression is as follows: (1-10) In the formula, Δ i ld and Δ i lq are the corresponding micro-increments; i ld and i lq are the corresponding micro-increments; i ld and i lq are the d, q-axis components of AC current injected by LCC converter station into power grid; Δ u ld and Δ u lq are the corresponding micro-increments; u ld and u lq are the corresponding micro-increments; u ld and u lq are the d, q-axis components of DC voltage of LCC converter station U dc ; Δ i dc is the corresponding micro-increment idc corresponding micro-increments; i dc is the direct current; Δ α is α corresponding micro-increments; i dc0 is i dc corresponding initial values; X L is the commutation reactance; k is the transformer ratio of the converter transformer; U l0 is the initial value of the effective value of the line voltage on the AC side of the converter station; α 0 is the initial value of the firing angle of the converter; μ 0 is the initial value of the commutation overlap angle of the converter; δ 0 is the initial value of the phase angle of the AC voltage; n is the number of six-pulse converters; I dc0 is the initial value of the direct current.

[0033] The above model considers the LCC from the perspective of the rectifier side, but the receiving end power grid is usually an inverter station, so the relationship between the firing angle and the turn-off angle needs to be considered: (1-11) wherein, α is the firing angle of the rectifier station, β is the advanced firing angle of the inverter station, γ is the turn-off angle of the inverter station.

[0034] At the same time, the turn-off angle γ and the commutation overlap angle μ also satisfy the following relationship: (1-12) Generally, the control mode of the LCC-HVDC system is to set the current on the rectifier side, and the inverter side adopts a low-voltage current-limiting fixed turn-off angle control, so the turn-off angle is constant at steady state, at which time, according to formula (1-9) to formula (1-12), we can obtain: (1-13) In the formula, a, b, and c are values derived from each element of the matrix according to formula (1-9), as shown in formula (1-14): (1-14) At this time, the micro-increment model of the LCC grid-connected device can be unified with the VSC, and formula (1-9) can be simplified as: (1-15) wherein the elements of matrix A2, B2 are composed of elements shown in equation (1-10): (1-16) For the establishment of the incremental model of AC power grid: for any branch in the AC power grid system, the power flowing from node i to node j can be described as: (1-17) wherein, U i 、 U j Vi and Vj are the voltages of node i and node j, I ij I is the current of the branch, R ij 、 X ij R and X are the resistance and reactance of the branch, S ij P is the complex power flowing from node i to node j. Further, the active and reactive power expressions flowing from node i to node j can be obtained: (1-18) wherein, P ij P is the active power flowing through the branch, Q ij Q is the reactive power flowing through the branch.

[0035] Simultaneous equations (1-17) and (1-18) are converted into the dq coordinate system: (1-19) wherein, u id and u iq Vi and Vj are the dq-axis components of the voltages of node i and node j, u jd and u jq Vi and Vj are the dq-axis components of the voltages of node i and node j.

[0036] Linear expansion of equation (1-19) and elimination of high-order terms can obtain the relationship between the line transmission power and the line impedance and the voltages of the nodes at both ends of the line in the AC power grid system. Linear expansion and elimination of high-order terms can obtain the power incremental model of the AC branch: (1-20) wherein, ΔP ij and ΔQ ij are the active power and reactive power increments of the branch corresponding to node i and node j in the AC power grid, respectively; Δu id and Δ u iq are the d, q-axis components of the voltage at node i, respectively; Δ u id and u iq are the micro-increments of u id and u iq are the d, q-axis components of the voltage at node i, respectively; Δ u jd and Δ u jq are the d, q-axis components of the voltage at node i, respectively; Δ u jd and u jq are the micro-increments of u jd and u jq are the d, q-axis components of the voltage at node j, respectively.

[0037] M The elements in (1-1) are constants derived from (1-17) and the specific expressions are shown in (1-21): (1-21) where, u id0 , u iq0 , u jd0 and u jq0 are the initial values of u id , u iq , u jd and u jq .

[0038] For any node in the AC power grid system, the power micro-increment injected into the node can be described as: (1-22) where, Δ P i is the micro-increment of the power injected into the node, j is the node number connected to node i, and m is the number of nodes connected to node i.

[0039] For the formation of the micro-increment model of the whole system, if a node contains a VSC or LCC feed-in, the micro-increment expressions of the node and branch power and the system structure can be combined to obtain the micro-increment model of the whole system on the AC side: (1-23) in, ΔP, ΔQ The incremental power injected into the node is related to Δ in equation (1-20). P ij and Δ Q ij The meanings are different, Δ u d Δ u q This is a column vector of node voltage increments. M Δ For the corresponding coefficient matrix, the matrix in equation (1-20) M It comes from increased dimensions. ΔP is shown in equation (1-22), the rest... ΔQ, Δ u d Δ u The same applies to parameters.

[0040] In steps 103 to 105, the aforementioned incremental model describes the relationship between the incremental active and reactive power of the VSC, LCC, and AC network and the incremental voltage and current of each node. Since both the VSC and LCC are directly connected to the AC network, the voltage and current at the grid-connected nodes of both types of equipment satisfy both the incremental model relationship of the grid-connected equipment and the incremental model of the AC network. By analyzing the electrical connections of the actual network, the three incremental models of the VSC, LCC, and AC network can be mathematically combined. For ease of calculation, when solving this combined model, the VSC and LCC need to be considered as injecting power into the AC network. The incremental power injected by the VSC and LCC into the AC system can be described as: (2-1) Among them, VSC satisfies both equations (2-1) and (1-4), and LCC satisfies both equations (2-1) and (1-15). By simultaneously solving equations (2-1), (1-23), (1-15), and (1-4), the infinitesimal increments of the port voltage and current of a certain device in the dq coordinate system can be obtained. Substituting these into equation (1-1), the operating impedance Z of any VSC or LCC converter can be solved. C Z C It is Z VSCi The higher-level concept, depending on the different converters or AC systems, is the operating impedance Z. C It can be named Zvsci\Zlccm\....

[0041] After calculating the converter's operating impedance Zc according to the process described above, the receiving-end system structure is as follows: Figure 6 As shown. Figure 6 In (1), Z VSCi ZVSCj are the operating impedances equivalent to the VSCs incorporated into node i and node j, respectively LCCe , Z LCCg are the operating impedances equivalent to the LCCs incorporated into node e and node g, respectively. In order to calculate the grid strength, the receiving end system and the converter node can be taken as a Thevenin equivalent port, and the entire receiving end system is equivalent to a voltage source + equivalent impedance in series, as shown in the structure of (2) in Figure 6 , Z Figure 6 in (2) in p.u. , which is the equivalent receiving end system impedance obtained in series with the receiving end links such as converter transformer impedance. At this time, the grid strength of a certain device can be calculated by formula (2-2): (2-2) In the formula, SCR is the short-circuit ratio of the grid-connected device, which is used to represent the strength. Z p.u. is equivalent to the operating impedance of other devices and the grid impedance except for the device. By solving the equivalent operating impedance of different devices, the identified grid strength of the entire system is further solved. For Figure 6 , when calculating the grid strength of LCC1, Z p.u. is equivalent to the operating impedance of other devices and the grid impedance except for the device. By solving the equivalent operating impedance of different devices, the identified grid strength of the entire system is further solved. For Figure 6 , when calculating the grid strength of LCC1, Z VSCi \Z VSCj \Z LCCei \Z LCCg and the grid impedance.

[0042] Based on the above, in step 104, the full system incremental model is solved to obtain the incremental voltage and current of each grid-connected device, which specifically includes: (1) The VSC-type power supply and the LCC-type power supply are regarded as injecting power into the AC grid, and the incremental power injection model of the VSC-type power supply and the LCC-type power supply into the AC grid is defined, denoted as The incremental power injection model is defined.

[0043] (2) According to the defined incremental power injection model, the incremental model of the VSC-type grid-connected device, and the full system incremental model, the incremental voltage and current of each VSC-type grid-connected device are calculated.

[0044] (3) According to the defined incremental power injection model, the incremental model of the LCC-type grid-connected device, and the full system incremental model, the incremental voltage and current of each LCC-type grid-connected device are calculated.

[0045] In step 104, the equivalent operating impedance of each grid-connected device is obtained according to the incremental voltage and current of the device port of the grid-connected device, which specifically includes: (1) According to the micro-increments of the device port voltage and current of the VSC type grid-connected device, the equivalent operating impedance of the VSC type grid-connected device is determined.

[0046] (2) According to the micro-increments of the device port voltage and current of the LCC type grid-connected device, the equivalent operating impedance of the LCC type grid-connected device is determined.

[0047] As shown in Figure 3 , whether the grid operation changes refers to whether the grid line changes and whether the power electronic device changes. The grid strength dynamic identification method based on the micro-increment model further comprises: when the current grid operation state changes, returning to the step of "determining the current grid structure and operation state", and updating the full-system micro-increment model. The influence of the dynamic change of the grid structure on the micro-increment model is introduced below.

[0048] With the vigorous development and application of new energy, and the operation of long-distance DC power transmission, more and more power electronic devices are connected to the receiving end grid. The power electronic device has controllability, therefore, for the needs of grid operation, the operating state of these power electronic devices will change frequently. If the grid strength is calculated according to a certain state, there will be certain errors, which may mislead the grid-connected operation of loads and DC devices, therefore, the influence of the dynamic change of the grid structure on the grid strength needs to be considered.

[0049] The change of the grid structure can be roughly divided into two categories, one is the change caused by the disconnection of the grid line and the switching of the load, and the other is the change caused by the switching and operating state change of the power electronic device.

[0050] (1) Line-induced change As shown in formula (1-21), the power micro-increment injected into a node is equal to the sum of the power micro-increment flowing from the node to other nodes, and when the node is disconnected or connected with other nodes, the micro-increment at the corresponding position needs to be increased or decreased.

[0051] (3-1) In the formula, is the power injection micro-increment of the node after the line change, Δ P ie and Δ P ig is the power micro-increment of the line between node i and node e, g.

[0052] Correspondingly, the micro-increment model composed of formula (1-23) needs to be adjusted at the corresponding position: (3-2) Wherein, This is the coefficient matrix of the incremental model after the line is interrupted. M 1 represents the sparse matrix change caused by line interruption. Taking the example of adding a new line between node i and node e, and breaking a line between node i and node g,... M 1 can be written as: (3-3) In the formula, M Ped , M Peq , M Pgd , M Pgq In the formula (1-21) M Pid , M Piq The result is obtained by replacing "i" with "e" and "g".

[0053] The result M Substituting 1 into equation (3-2), we get The adjusted whole-system incremental model is formed according to Equation (1-23). ​​Based on this, the equivalent operating impedance is solved to further identify the grid strength.

[0054] (2) Changes caused by power electronic devices (VSC and LCC) The dynamic changes of power electronic equipment can be broadly classified into two categories: one is the change in operating status, such as changes in transmission power; the other is the change in switching, such as the connection of new equipment to the grid or the disconnection of existing equipment. Both situations will cause changes in the voltage and power of each node in the receiving-end power grid system. Therefore, it is necessary to re-establish the incremental model, solve for the equivalent operating impedance, and further identify the grid strength.

[0055] This application focuses on calculating the grid strength of power electronic equipment connected to the grid, considering the dynamic changes in grid structure and grid-connected equipment. First, based on the operating principle of the Voltage Grid Concentrator (VSC), a steady-state mathematical model of the VSC is given, followed by a linear expansion to obtain a micro-incremental model of the VSC. Second, starting from the operating principle of the Voltage Grid Concentrator (LCC), considering the relationship between DC current, DC voltage, AC voltage, and AC current, a micro-incremental model of the LCC is obtained. Finally, combining the relationship between the power flowing on the AC line and the voltage at both ends of the line, a micro-incremental model of the entire system is formed. Using the micro-incremental model, the VSC and LCC equipment can be equivalently represented as impedances, and the grid strength of the receiving-end system containing power electronic equipment can be calculated using the equivalent operating impedance. If the grid structure changes, such as line interruption, equipment commissioning or decommissioning, the aforementioned micro-incremental model can be modified accordingly, and the grid strength can be recalculated.

[0056] In summary, the method adopted in the application fully considers the influence of VSC and LCC on the receiving end power grid, equivalently uses the operating impedance to the power electronic equipment, considers the influence of the dynamic change of the power grid on the strength, and makes the calculation of the power grid strength more accurate.

[0057] The application further provides an application scenario of the power grid strength dynamic identification method based on the micro-increment model. Specifically, the power grid strength dynamic identification method based on the micro-increment model can be applied in the power grid strength identification scenario of the receiving end power grid. The scenario includes a dynamic change acquisition link and an identification link. The dynamic change acquisition link is configured to acquire the change of the line and the dynamic change of the grid-connected equipment in the power grid. The identification link is configured to identify the power grid strength according to the data acquired by the dynamic change acquisition link. The power grid strength dynamic identification method based on the micro-increment model belongs to the identification link.

[0058] In an exemplary embodiment, a computer device is provided, which can be a server or a terminal. An internal structure diagram of the computer device can be as shown in Figure 7 The computer device includes a processor, a memory, an input / output interface (I / O) and a communication interface. The processor, the memory and the input / output interface are connected through a system bus, and the communication interface is connected to the system bus through the input / output interface. The processor of the computer device is configured to provide computing and control capabilities. The memory of the computer device includes a non-volatile storage medium and an internal memory. The non-volatile storage medium stores an operating system, a computer program and a database. The internal memory provides an environment for the operating system and the computer program in the non-volatile storage medium to run. The database of the computer device is configured to store power grid strength dynamic identification data based on the micro-increment model. The input / output interface of the computer device is configured to exchange information between the processor and external devices. The communication interface of the computer device is configured to communicate with external terminals through network connection. The computer program is executed by the processor to implement a power grid strength dynamic identification method based on the micro-increment model.

[0059] Those skilled in the art can understand that Figure 7 The structure shown in the figure is only a block diagram of part of the structure related to the scheme of the application, and does not constitute a limitation on the computer device to which the scheme of the application is applied. The specific computer device can include more or fewer components than those shown in the figure, or combine certain components, or have a different arrangement of components. In an exemplary embodiment, a computer device is provided, which includes a memory and a processor. The memory stores a computer program, and the processor executes the computer program to implement the steps in the above method embodiments.

[0060] In an example embodiment, a computer readable storage medium is provided, which stores a computer program. The computer program is executed by a processor to implement the steps in the above method embodiments.

[0061] It should be noted that the user information (including but not limited to user equipment information, user personal information, etc.) and data (including but not limited to data for analysis, stored data, displayed data, etc.) involved in the present application are all information and data authorized by the user or authorized by all parties, and the collection, use and processing of related data need to comply with relevant regulations.

[0062] It can be understood by those skilled in the art that all or part of the processes in the above embodiments can be completed by a computer program instructing related hardware. The computer program can be stored in a non-volatile computer readable storage medium. When the computer program is executed, it can include the processes of the above embodiments. Any reference to memory, database or other medium used in the embodiments provided by the present application can include at least one of non-volatile and volatile memory. Non-volatile memory can include read-only memory (ROM), magnetic tape, floppy disk, flash memory, optical storage, high-density embedded non-volatile memory, resistive memory (ReRAM), magnetoresistive random access memory (MRAM), ferroelectric memory (FRAM), phase change memory (PCM), graphene memory, etc. Volatile memory can include random access memory (RAM) or external cache memory, etc. As an illustration but not limitation, RAM can be in various forms, such as static random access memory (SRAM) or dynamic random access memory (DRAM), etc.

[0063] The database involved in the embodiments provided by the present application can include at least one of a relational database and a non-relational database. The non-relational database can include a distributed database based on blockchain, etc., without being limited thereto. The processor involved in the embodiments provided by the present application can be a general processor, a central processing unit, a graphics processing unit, a digital signal processor, a programmable logic device, a data processing logic device based on quantum computing, etc., without being limited thereto.

[0064] Any technical features in the above embodiments can be combined, and for the sake of brevity, not all possible combinations are described above, however, it should be understood that the application encompasses all possible combinations of the technical features unless such a combination is not technically possible.

[0065] The principles and implementation manners of the present application are described herein by using specific examples, and the above embodiments are only used to help understand the method of the present application and its core idea; meanwhile, according to the idea of the present application, a person skilled in the art can make changes in specific implementation manners and application scopes. In conclusion, the content of the present specification should not be understood as a limitation of the present application.

Claims

1. A method for dynamic identification of power grid strength based on micro-incremental model, characterized in that, The method comprises the following steps: determining a current power grid structure and operation state; constructing a full-system micro-increment model according to the current power grid structure and operation state; the full-system micro-increment model comprises a micro-increment model of a VSC grid-connected device, a micro-increment model of an LCC grid-connected device and a micro-increment model of an alternating current power grid; solving the full-system micro-increment model to obtain micro-increments of device port voltage and current of each grid-connected device; the grid-connected device comprises a VSC grid-connected device and an LCC grid-connected device; obtaining equivalent operating impedances of each grid-connected device according to the micro-increments of device port voltage and current of the grid-connected device; determining short-circuit ratios of each grid-connected device according to the equivalent operating impedances of each grid-connected device; when the current power grid operation state does not change, identifying the power grid strength of the grid-connected device according to the short-circuit ratios of each grid-connected device.

2. The microincremental model based power grid strength dynamic identification method according to claim 1, characterized in that, The micro-increment model-based power grid strength dynamic identification method further comprises: when the current power grid operation state changes, returning to the step of "determining a current power grid structure and operation state".

3. The microincremental model based power system strength dynamic identification method according to claim 1, characterized in that, an expression of the micro-increment model of the VSC grid-connected device is as follows: wherein ΔP and ΔQ are micro-increments of active power and reactive power of the VSC grid-connected device respectively; Δ u vd 、Δ u vq 、Δ i vd and Δ i vq respectively u vd , u vq , i vd and i vq corresponding micro increments; u vd and u vq is the voltage dq component of the voltage of the VSC type converter station or new energy station grid connection point converted from the abc coordinate system to the dq coordinate system; i vd and i vq is the current dq component of the current injected by the power grid to the VSC converted from the abc coordinate system to the dq coordinate system; u vd0 , u vq0 , i vd0 and i vq0 is the initial value of u vd , u vq , i vd and i vq .

4. The microincremental model based power system strength dynamic identification method according to claim 1, characterized in that, an expression of the micro-increment model of the LCC grid-connected device is as follows: wherein ; ; ； ； where Δ i ld and Δ i lq are respectively i ld and i lq corresponding micro-increments; i ld and i lq are d, q-axis components of AC current injected by LCC converter station into power grid; Δ u ld and Δ u lq are respectively u ld and u lq corresponding micro-increments; u ld and u lq are d, q-axis components of DC voltage of LCC converter station U dc corresponding d, q-axis components; Δ i dc is i dc corresponding micro-increments; i dc is DC current; i dc0 is i dc corresponding initial value; X L is commutation reactance; k is transformer ratio of converter transformer; U l0 is initial value of effective value of line voltage on AC side of converter station; α 0 is initial value of firing angle of converter; μ 0 is initial value of commutation overlap angle of converter; δ 0 is initial value of phase angle of AC voltage; n is number of six-pulse converters; I dc0 is initial value of DC current.

5. The microincremental model based power system strength dynamic identification method according to claim 1, characterized in that, an expression of the micro-increment model of the alternating current power grid is as follows: wherein ; where ΔP ij and ΔQ ij are the incremental active power and reactive power of the branch corresponding to node i and node j in the alternating current power grid, respectively; Δ u id and Δ u iq are the incremental active power and reactive power of the branch corresponding to node i and node j in the alternating current power grid, respectively; Δ u id and u iq are the incremental active power and reactive power of the branch corresponding to node i and node j in the alternating current power grid, respectively; Δ u id and u iq are the d-axis and q-axis components of the voltage of node i, respectively; Δ u jd and Δ u jq are the incremental d-axis and q-axis components of the voltage of node i, respectively; Δ u jd and u jq are the incremental d-axis and q-axis components of the voltage of node i, respectively; Δ u jd and u jq are the d-axis and q-axis components of the voltage of node j, respectively; Δ u id0 , u iq0 , u jd0 and u jq0 are the initial values of u id , u iq , u jd and u jq , respectively; Δ R ij , X ij are the resistance and reactance of the branch corresponding to node i and node j.

6. The micro-delta model based power system strength dynamic identification method according to claim 1, characterized in that, solving the full-system micro-increment model to obtain micro-increments of device port voltage and current of each grid-connected device, specifically comprising: defining a power micro-increment model of the VSC grid-connected device and the LCC grid-connected device as power injected into the alternating current power grid, denoted as defining the power micro-increment model; calculating the micro-increments of device port voltage and current of each VSC grid-connected device according to the defined power micro-increment model, the micro-increment model of the VSC grid-connected device and the full-system micro-increment model; calculating the micro-increments of device port voltage and current of each LCC grid-connected device according to the defined power micro-increment model, the micro-increment model of the LCC grid-connected device and the full-system micro-increment model.

7. The microincremental model based power system strength dynamic identification method according to claim 6, characterized in that, obtaining equivalent operating impedances of each grid-connected device according to the micro-increments of device port voltage and current of the grid-connected device, specifically comprising: determining the equivalent operating impedance of the VSC grid-connected device according to the micro-increments of device port voltage and current of the VSC grid-connected device; determining the equivalent operating impedance of the LCC grid-connected device according to the micro-increments of device port voltage and current of the LCC grid-connected device.

8. The microincremental model based power system strength dynamic identification method according to claim 7, characterized in that, an expression of the equivalent operating impedance is as follows: wherein Zc is the equivalent operating impedance; Δ u cd and Δ u cq are the micro-increments of the device port voltage of the grid-connected device in the dq coordinate system, respectively; Δ i cd and Δ i cq are the micro-increments of the device port current of the grid-connected device in the dq coordinate system, respectively; j represents an imaginary part.

9. A computer device comprising: A memory, a processor and a computer program stored in the memory and executable on the processor, characterized in that the processor executes the computer program to implement the micro-increment model-based power grid strength dynamic identification method in any one of claims 1-8.

10. A computer-readable storage medium having stored thereon a computer program, characterized in that, The computer program is executed by the processor to implement the micro-increment model-based power grid strength dynamic identification method in any one of claims 1-8.

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