A comprehensive node inertia evaluation method considering source-side synchronous inertia and bus-side dynamic support

Abstract

The application relates to the technical field of smart power grids, and discloses a comprehensive node inertia evaluation method considering source-side synchronous inertia and bus-side dynamic support, which comprises the following steps: obtaining power system operation data and equipment parameters; calculating source-side synchronous inertia node mapping based on synchronous machine swing equation, frequency distribution criteria and disturbance initial power sharing relationship; extracting effective inertia components based on frequency control channels of grid-following new energy units and motor load slip-torque dynamics, and constructing a bus-side dynamic inertia matrix; and finally, incorporating the bus-side dynamic inertia matrix into the source-side node inertia mapping relationship to obtain comprehensive node inertia considering source-side synchronous inertia, grid-following new energy units and motor load contribution. The method can distinguish the physical sources of source-side synchronous inertia and bus-side dynamic support, avoid directly equating equipment nominal inertia or control set values to node inertia, and thus accurately evaluate the inertia support capacity of different nodes in a power system.

Description

Technical Field

[0001] This invention relates to the field of smart grid technology, and in particular to power system frequency security analysis and inertia assessment technology. Specifically, it relates to a comprehensive nodal inertia assessment method that considers source-side synchronous inertia and bus-side dynamic support. Background Technology

[0002] With the large-scale integration of new energy power generation and power electronic interface equipment, the proportion of synchronous generators in the power system is gradually decreasing, and the system frequency response characteristics are showing features such as low inertia, strong time variation, and spatial non-uniformity. Traditional system inertia assessment methods usually take the equivalent inertia of the entire system or the inertial center frequency as the object, which can reflect the overall frequency support capability of the system, but it is difficult to describe the differences in the local frequency change rate of different nodes after disturbance.

[0003] In practical power systems, node frequency variations are not only affected by the inertia of synchronous generators and condensers, but are also closely related to network topology, disturbance location, electrical distance, and equipment dynamic response. Even if all synchronous generators have the same inertia, different nodes may exhibit different equivalent node inertia due to differences in frequency distribution characteristics and disturbance power sharing relationships.

[0004] Furthermore, grid-connected renewable energy units and motor loads also exhibit a certain dynamic support capability in the early stages of disturbances. Grid-connected renewable energy units can change their active power output through additional frequency control, virtual inertia control, or rapid frequency response; motor loads can dynamically release or absorb rotor kinetic energy through slip-torque. However, these devices are not source-side inertia sources in the form of potential nodes within synchronous machines; their port active power also includes components such as frequency deviation response, voltage-sensitive response, current-limiting response, and control transients. Directly including their nominal inertia or control setpoints in the node inertia can easily lead to an overestimation of inertia contribution or confusion of its physical meaning. Summary of the Invention

[0005] To address the issues of unclear mixing of source-side synchronous inertia and bus-side dynamic support in existing nodal inertia assessment methods, and the inconsistency between the virtual inertia set for grid-connected new energy units and the actual effective inertia, this invention aims to provide a comprehensive nodal inertia assessment method that considers both source-side synchronous inertia and bus-side dynamic support. Based on the nodal inertia formed by network mapping of source-side synchronous inertia, this method further extracts the effective inertia component in phase with the rate of frequency change from the active power at the load ports of grid-connected new energy units and motors, and incorporates it as bus-side dynamic inertia into the nodal inertia calculation framework. This allows for a more accurate evaluation of the inertia support capabilities of different nodes in new power systems.

[0006] According to a first aspect of the present invention, a comprehensive nodal inertia evaluation method considering both source-side synchronous inertia and bus-side dynamic support is proposed, comprising the following steps:

[0007] Step 1: Obtain power system network operation data and equipment parameters. In the power system network, synchronous generators and synchronous condensers are used as source-side synchronous inertia sources, and grid-connected new energy units and motor loads are used as dynamic support equipment. All of them are connected to the bus side and directly respond to changes in bus frequency.

[0008] Step 2: Based on the obtained power system network operation data and equipment parameters, combined with the swing equation of the synchronous generator after disturbance, the frequency allocation criterion, and the power sharing relationship in the early stage of disturbance, calculate the source-side node inertia of the synchronous generator and the synchronous condenser acting on each node after network coupling.

[0009] Step 3: Based on the frequency control channel and motor load slip-torque dynamics of the grid-connected new energy unit, extract the effective inertia component in phase with the frequency change rate in the active power at the bus-side equipment port.

[0010] Step 4: After reducing the effective inertia of grid-connected new energy generating units and the effective inertia of motor loads on the same busbar according to capacity, construct the dynamic inertia matrix on the input and output busbar sides; and

[0011] Step 5: Establish the source-side frequency change rate sensitivity matrix based on the source-side node inertia, and incorporate the bus-side dynamic inertia matrix into the source-side frequency change rate sensitivity matrix to form a comprehensive node inertia calculation relationship, thereby obtaining the comprehensive node inertia that takes into account the source-side synchronous inertia, the dynamic support of grid-connected new energy units, and the contribution of motor load inertia.

[0012] As an optional implementation, in step 2, for the i-th source-side synchronous inertia source, the dynamic rotational speed after disturbance is jointly determined by the change in rotor kinetic energy, the increment of mechanical power, the increment of electromagnetic power and the damping power, thereby determining the swing equation of the synchronous generator after disturbance.

[0013] As an optional implementation, in step 2, at the initial stage of the disturbance, the governor and prime mover mechanical power adjustment have not yet been activated, and the rotational speed, as a state variable, cannot change abruptly. Therefore, the initial conditions that the mechanical power increment and the initial speed deviation must satisfy are determined as follows:

[0014] Furthermore, by combining the above initial conditions into the oscillation equation, the damping term is zero at time 0+, thus obtaining the initial frequency change rate of the i-th synchronous inertia source, which represents the internal rotational speed response of the synchronous inertia source.

[0015] Furthermore, by introducing a frequency allocation criterion based on the frequency allocation matrix and the synchronous inertia source speed deviation vector, the internal speed response of the synchronous inertia source is applied to the network bus of the power grid system. The frequency allocation matrix is ​​used to describe the degree of participation of the synchronous inertia source speed change on the frequency change of each bus.

[0016] As an optional implementation, in step 2, when an active disturbance is applied to node j, the proportion of disturbance power borne by the i-th synchronous inertial source is the product of the disturbance power and the sharing coefficient of the i-th synchronous inertial source on the disturbance power of node j.

[0017] The sharing factor is obtained by normalizing the electrical coupling strength between the synchronous inertia source and the disturbance node.

[0018] As an optional implementation, in step 3, for the g-th grid-connected new energy unit connected to bus b, the effective inertia of the grid-connected new energy unit is determined by its frequency control channel combined with the time establishment process. When the disturbance time window is much smaller than the inertia control differential time constant, the effective inertia of the g-th grid-connected new energy unit is approximately expressed as:

[0019] ;

[0020] in, This is the proportional coefficient for inertia control.

[0021] As an optional implementation, in step 3, the effective inertia of the motor load is obtained by dynamic calculation of slip-torque. For the m-th motor load connected to bus b, the first-order following relationship between the motor rotor speed and the grid synchronization speed is obtained by combining the motor slip change equation and the motor rotor motion equation.

[0022] Within the initial time window of the disturbance, the rotor inertia of the motor is gradually coupled to the grid side through the above first-order following relationship, so as to obtain the effective inertia of the m-th motor load reflected on the bus side within time t.

[0023] As an optional implementation, in step 4, for bus b, the bus-side dynamic inertia matrix is ​​a diagonal matrix used to characterize the access location and capacity weight of the bus-side dynamic support equipment, and its off-diagonal elements are zero.

[0024] As an optional implementation, in step 5, a source-side frequency change rate sensitivity matrix is ​​first established based on the source-side node inertia. This source-side frequency change rate sensitivity matrix is ​​used to describe the sensitivity relationship between node disturbance power and node frequency change rate when only the source-side synchronous inertia is considered.

[0025] Then, the dynamic inertia matrix on the bus side is incorporated into the frequency change rate sensitivity matrix on the source side to form a comprehensive nodal inertia calculation relationship, thereby obtaining the comprehensive frequency change rate sensitivity matrix after taking into account the dynamic support on the bus side.

[0026] In a further embodiment, in step 5, based on the comprehensive frequency change rate sensitivity matrix after taking into account the dynamic support on the bus side, the comprehensive node inertia of node j is defined as the reciprocal norm of the j-th row of the comprehensive frequency change rate sensitivity matrix, thereby obtaining the comprehensive node inertia exhibited at node j after taking into account the combined effects of the source-side synchronous inertia, the dynamic support of the grid-connected new energy unit, and the motor load inertia.

[0027] As can be seen from the above technical solutions, the comprehensive node inertia assessment method for power systems proposed in this invention, which takes into account the combined effects of source-side synchronous inertia, grid-connected new energy unit dynamic support, and motor load inertia, can distinguish the physical sources of source-side synchronous inertia and bus-side dynamic support, avoiding the direct equation of equipment nominal inertia or control setpoints with node inertia. It can be used for identifying weak inertia areas in new power systems, frequency security assessment, and dynamic support resource allocation. Compared with existing technologies, its significant advantages are:

[0028] (1) The present invention calculates the source-side node inertia based on the oscillation equation of the synchronous machine, the frequency allocation formula and the disturbance power sharing relationship, which can reflect the spatial distribution difference of the inertia of the synchronous machine and the condenser at different nodes after network coupling;

[0029] (2) In this invention, the grid-connected new energy generator units and motor loads are treated as dynamic support equipment on the bus side. Only the effective component in phase with the frequency change rate in the active power at the port is extracted and included in the inertia, so as to avoid incorrectly including the control setpoint, droop response, voltage sensitive item or current limiting response in the inertia contribution.

[0030] (3) The present invention describes the access location and capacity weight of grid-connected new energy units and motor loads through the dynamic inertia matrix on the bus side, which can reflect the spatial distribution characteristics of dynamic support on the bus side.

[0031] (4) This invention incorporates the dynamic inertia matrix on the bus side into the frequency change rate sensitivity matrix on the source side to form a comprehensive node inertia calculation method, which is applicable to the identification of weak inertia areas, frequency security assessment and dynamic support resource allocation in high-proportion new energy power systems.

[0032] It should be understood that all combinations of the foregoing concepts and the additional concepts described in more detail below may be considered part of the inventive subject matter of this disclosure, provided that such concepts do not contradict each other. Furthermore, all combinations of the claimed subject matter are considered part of the inventive subject matter of this disclosure.

[0033] The foregoing and other aspects, embodiments, and features of the teachings of the present invention will be more fully understood from the following description in conjunction with the accompanying drawings. Other additional aspects of the invention, such as features and / or beneficial effects of exemplary embodiments, will become apparent from the following description or may be learned through practice of specific embodiments according to the teachings of the present invention. Attached Figure Description

[0034] The accompanying drawings are not intended to be drawn to scale. In the drawings, each identical or nearly identical component shown in the various figures may be denoted by the same reference numeral. For clarity, not every component is labeled in each figure. Embodiments of various aspects of the invention will now be described by way of example and with reference to the accompanying drawings.

[0035] Figure 1 This is a flowchart illustrating a comprehensive nodal inertia evaluation method that considers source-side synchronous inertia and bus-side dynamic support according to an embodiment of the present invention.

[0036] Figure 2 This is a schematic diagram of the calculation principle of the integrated nodal inertia considering the dynamic support on the busbar side according to an embodiment of the present invention.

[0037] Figure 3 This is a distribution diagram of the calculation results of the combined node inertia of different types of nodes according to an embodiment of the present invention. Detailed Implementation

[0038] To better understand the technical content of the present invention, specific embodiments are described below in conjunction with the accompanying drawings.

[0039] Various aspects of the invention are described in this disclosure with reference to the accompanying drawings, which illustrate numerous illustrative embodiments. The embodiments of this disclosure are not necessarily intended to encompass all aspects of the invention. It should be understood that the various concepts and embodiments described above, as well as those described in more detail below, can be implemented in any of many ways, because the concepts and embodiments disclosed herein are not limited to any particular implementation. Furthermore, some aspects of the invention disclosed may be used alone or in any suitable combination with other aspects of the invention disclosed.

[0040] Combined with appendix Figure 1 To be continued Figure 3 As shown, the integrated nodal inertia evaluation method considering source-side synchronous inertia and bus-side dynamic support according to an embodiment of the present invention includes the following steps:

[0041] Step 1: Obtain power system network operation data and equipment parameters. In the power system network, synchronous generators and synchronous condensers are used as source-side synchronous inertia sources, and grid-connected new energy units and motor loads are used as dynamic support equipment. All of them are connected to the bus side and directly respond to changes in bus frequency.

[0042] Step 2: Based on the obtained power system network operation data and equipment parameters, combined with the swing equation of the synchronous generator after disturbance, the frequency allocation criterion, and the power sharing relationship in the early stage of disturbance, calculate the source-side node inertia of the synchronous generator and the synchronous condenser acting on each node after network coupling.

[0043] Step 3: Based on the slip-torque dynamics of the frequency control channel and motor load of the grid-connected new energy unit, extract the effective inertia component in phase with the frequency change rate in the active power at the bus-side equipment port.

[0044] Step 4: After reducing the effective inertia of grid-connected new energy generating units and the effective inertia of motor loads on the same busbar according to capacity, construct the dynamic inertia matrix on the input and output busbar sides; and

[0045] Step 5: Establish the source-side frequency change rate sensitivity matrix based on the source-side node inertia, and incorporate the bus-side dynamic inertia matrix into the source-side frequency change rate sensitivity matrix to form a comprehensive node inertia calculation relationship, thereby obtaining the comprehensive node inertia that takes into account the source-side synchronous inertia, the dynamic support of grid-connected new energy units, and the contribution of motor load inertia.

[0046] In step 1, the following parameters are obtained: power system network admittance matrix, power flow operating point, node voltage, node phase angle, synchronous generator parameters, synchronous condenser parameters, frequency control parameters of grid-connected new energy units, motor load parameters, equipment capacity, and system unified reference capacity.

[0047] Synchronous generators and synchronous condensers serve as source-side synchronous inertia sources, while grid-connected new energy units and motor loads serve as bus-side dynamic support equipment. The capacity of all equipment is calculated according to the unified system benchmark capacity S_B, thereby ensuring that the source-side inertia sources, bus-side dynamic support equipment, and nodal inertia calculations have a consistent capacity caliber.

[0048] In step 2, the source-side synchronous inertia is mapped to the network nodes through the calculation of the synchronous generator and the synchronous condenser via network coupling, and the source-side node inertia acting on each node is determined.

[0049] For the i-th source-side synchronous inertia source, the dynamic rotational speed after disturbance is jointly determined by the change in rotor kinetic energy, the increment of mechanical power, the increment of electromagnetic power, and the damping power. Therefore, the oscillation equation of the synchronous generator after disturbance is determined as follows:

[0050] ;

[0051] in, Let be the inertial time constant of the i-th synchronous inertial source. For speed deviation, For mechanical power increment, For electromagnetic power increment, is the damping coefficient.

[0052] As can be seen from the oscillation equation after the synchronous generator is disturbed, when the electromagnetic power changes abruptly, the synchronous inertia source suppresses the rapid change in rotational speed by changing the rotor kinetic energy.

[0053] In the initial stage of the disturbance, the governor and prime mover mechanical power regulation have not yet been activated, and the rotational speed, as a state variable, cannot change abruptly. Therefore, the initial conditions for the mechanical power increment and the initial speed deviation to satisfy the following are determined:

[0054] ;

[0055] ;

[0056] Furthermore, by incorporating the aforementioned initial conditions into the oscillation equation, where the damping term is zero at time 0+, the initial frequency change rate of the i-th synchronous inertial source can be obtained, which represents the internal rotational speed response of the synchronous inertial source, as follows:

[0057] ;

[0058] The initial frequency change rate of the synchronous inertial source is determined by the inertial time constant. and the increase in electromagnetic power borne by the disturbance instantaneously A joint decision.

[0059] Furthermore, by introducing a frequency allocation criterion, the internal rotational speed response of the synchronous inertia source is applied to the power grid network bus. The frequency allocation criterion is as follows:

[0060] ;

[0061] in, This is the bus frequency deviation vector. The rotational speed deviation vector of the synchronous inertia source. A frequency allocation matrix is ​​used to describe the degree to which the rotational speed change of the synchronous inertia source affects the frequency change of each bus.

[0062] Furthermore, by differentiating both sides of the frequency allocation criterion, we obtain:

[0063] ;

[0064] Therefore, the initial frequency change rate of node j is not determined by a single synchronous inertial source, but is formed by the weighted sum of the initial frequency change rates of each synchronous inertial source after the j-th row of Φ.

[0065] When an active disturbance is applied to node j, the proportion of disturbance power borne by the i-th synchronous inertial source is:

[0066] ;

[0067] The disturbance power is , Let be the power sharing factor of the i-th synchronous inertial source to node j, which is obtained by normalization based on the electrical coupling strength between the synchronous inertial source and the disturbing node:

[0068] ;

[0069] Where G is the set of synchronous inertia sources. Let be the synchronization power coefficient between the i-th synchronous inertia source and node j.

[0070] To illustrate its physical meaning, without delving into the details of network reduction, the aforementioned synchronization power coefficient... It can be expressed in the following approximate form:

[0071] ;

[0072] in, To synchronize the potential amplitude within the inertial source, Let j be the voltage amplitude at node j. The equivalent transfer susceptance between the two, and These are the phase angles of the internal potential of the synchronous inertia source and the phase angles of the node voltage, respectively. The larger the value, the stronger the electrical coupling between the synchronous inertial source and node j at the initial moment of the disturbance, and the higher the proportion of disturbance power it bears.

[0073] Substituting the disturbance power sharing relationship into the expression for the initial frequency change rate of the synchronous inertial source, and mapping it to node j via the frequency allocation matrix, we can obtain the initial frequency change rate of node j:

[0074] ;

[0075] On the other hand, according to the equivalent definition of nodal inertia, if the disturbance power of node j The resulting rate of change of initial frequency is caused by the source-side equivalent inertia. The representation is as follows:

[0076] ;

[0077] By comparing the two expressions above regarding the rate of change of the initial frequency of node j, the source-side node inertia of node j can be derived as follows:

[0078] (33)

[0079] in, Let be the source node inertia of node j. Assigning a frequency matrix The element in the j-th row and i-th column. This expression shows that, It is not the inertia of a particular neighboring synchronous machine, but rather the equivalent inertia exhibited at node j after the synchronous generator and synchronous condenser work together through network frequency allocation and disturbance power sharing.

[0080] Furthermore, combined Figure 2 As shown, both the grid-connected new energy generating units and motor loads are connected to the bus side and directly respond to changes in bus frequency. In step 3, to avoid directly equating the nominal inertia of the equipment, control setpoint, frequency deviation response, voltage sensitivity, or current limiting term with inertia, this invention only converts the short-time component of the active power at the port that is in phase with the rate of frequency change into an equivalent effective inertia.

[0081] First, define the frequency change rate in the decreasing direction of bus b as:

[0082] ;

[0083] in, This is the per-unit value of the frequency deviation of bus b.

[0084] When the system frequency decreases .

[0085] If the busbar side equipment provides For active power supports in phase, the power of the support can be expressed according to the ideal inertia support relationship as follows:

[0086] ;

[0087] in, This refers to the supporting power exhibited by the bus-side equipment to the system. This represents the effective inertia of the device at the current time scale.

[0088] Therefore, this definition provides a unified approach to extracting effective inertia from port active power support.

[0089] Combination Figure 1 , Figure 2 As shown, the effective inertia component in phase with the frequency change rate in the active power at the bus-side equipment port consists of the effective inertia of the grid-connected new energy generating unit and the effective inertia of the motor load.

[0090] As an optional implementation, the effective inertia of the grid-connected renewable energy unit is determined by its frequency control channel in conjunction with the time establishment process. Specifically, for the g-th grid-connected renewable energy unit connected to bus b, the inertia control channel can be equivalently represented in the initial disturbance analysis as follows:

[0091] ;

[0092] in, The active power increment generated by the inertia control channel for the g-th grid-connected new energy unit. This is the proportional coefficient for inertia control. The differential time constant for inertia control. Establish the time constant for the inertia control channel. For frequency measurement or filtering time constant, This is the Laplace transform of the rate of change of frequency in the direction of frequency decrease of bus b.

[0093] At the low-frequency limit, the dynamic link gain of the frequency measurement and control channels approaches 1. Comparing the WAI channel output with the ideal inertia support power, the ideal inertia support can be expressed as:

[0094] ;

[0095] Based on the relationship between the low-frequency gain of the WAI channel and the ideal inertia support, the set virtual inertia of the g-th grid-connected new energy unit can be obtained:

[0096] ;

[0097] in, This only represents the low-frequency setpoint corresponding to the control parameters and does not represent the inertia that has actually been released by the active power at the port during the initial stage of the disturbance.

[0098] Considering the process from disturbance occurrence to active power support establishment in the inertia control channel, a time establishment factor is further introduced:

[0099] ;

[0100] in, This characterizes the proportion of the inertia control channel that establishes itself to the low-frequency setpoint within time t. From this, we obtain the effective inertia actually exhibited by the g-th grid-connected new energy unit within time t:

[0101] ;

[0102] in, This represents the effective inertia actually established by the g-th grid-connected new energy unit within the disturbance time window. This indicates the low-frequency setpoint corresponding to the control parameter. The proportion of the low-frequency setpoint established by the inertia control channel within time t;

[0103] ;

[0104]

[0105] When the disturbance time window satisfies When the time-establishing factor is expanded using a first-order exponential function, we get:

[0106] ;

[0107] based on = Equivalent caliber, then:

[0108] ;

[0109] Therefore, it can be seen that the calculation of integrated nodal inertia... It refers to the effective inertia actually established within the disturbance time window, not the virtual inertia set by the controller itself. Only the positive component in the active power at the port that is in phase with RoCoF is converted into effective inertia; droop, frequency deviation, voltage sensitivity, and current limiting terms are not directly included in the inertia term.

[0110] As an optional implementation method, combined with Figure 2 As shown, in step 3, the effective inertia of the motor load is obtained by slip-torque dynamic calculation. For the m-th motor load connected to bus b, its active power is the absorbed power. For the system, the equivalent supporting power of the motor load is defined as the negative of its absorbed active power change, expressed as:

[0111] ;

[0112] in, Let be the change in active power absorbed by the m-th motor load. This represents the equivalent supporting power of the motor load on the system; when the system frequency decreases and the active power absorbed by the motor decreases... , making The motor load provides positive dynamic support to the system.

[0113] Near the steady-state operating point, the change in motor slip can be approximated as the difference between the grid synchronization angular velocity deviation and the rotor angular velocity deviation:

[0114] ;

[0115] The increase in electromagnetic torque is approximately proportional to the change in slip within a small disturbance range; therefore:

[0116] ;

[0117] in, For torque-slip stiffness, This represents the electromagnetic torque increment. The mechanical load torque increment can be linearized near the operating point as:

[0118] ;

[0119] in, This is the mechanical load damping coefficient. This represents the increment of the mechanical load torque. The rotor motion equation of the electric motor is:

[0120] ;

[0121] in, Let be the rotor inertia time constant of the m-th motor load. Substituting the linearized expressions for the electromagnetic torque and mechanical load torque into the rotor motion equation, we get:

[0122] ;

[0123] Performing a Laplace transform on the above equation yields the first-order following relationship between the motor rotor speed and the grid synchronization speed:

[0124] ;

[0125] in, For rotor angular velocity deviation, The synchronous angular velocity deviation of bus b, Let m be the rotor inertia time constant of the m-th motor load. For torque-slip stiffness, This is the mechanical load damping coefficient.

[0126] Within the initial time window of the disturbance, the rotor inertia of the motor is gradually coupled to the grid side through the above-mentioned first-order following relationship (i.e., the first-order slip-torque path), and the effective inertia of the m-th motor load is expressed as:

[0127] ;

[0128] in, , These are the time constant and low-frequency participation factor for the m-th motor load, respectively:

[0129] ;

[0130] ;

[0131] in, This represents the effective inertia of the m-th motor load reflected on the bus side within time t.

[0132] Therefore, although the motor load has a real rotor inertia, this inertia needs to be gradually coupled to the grid side through the slip-torque channel. In the early stage of the disturbance, its nominal rotor inertia should not be directly taken.

[0133] Furthermore, combined Figure 2 As shown, the effective inertia of grid-connected new energy generating units and the effective inertia of motor loads on the same bus are reduced according to capacity, and a dynamic inertia matrix is ​​constructed on the input and output bus sides.

[0134] For bus b, the dynamic inertia matrix on the bus side It is a diagonal matrix used to represent the access location and capacity weight of dynamic support equipment on the bus side, and its off-diagonal elements are zero.

[0135] dynamic inertia matrix on the bus side The diagonal elements are:

[0136] ;

[0137] in, The dynamic inertia matrix on the bus side. This is a collection of grid-connected new energy generating units that are connected to bus b. For the set of motor loads connected to bus b, For the capacity of the g-th grid-connected new energy unit, Let m be the load capacity of the m-th motor. To establish a unified baseline capacity for the system.

[0138] As an optional implementation method, combined with Figure 2 As shown, in step 5, the source-side node inertia is first determined... Establish the source-side frequency change rate sensitivity matrix The source-side frequency change rate sensitivity matrix This describes the sensitivity relationship between node disturbance power and node frequency change rate when only source-side synchronous inertia is considered. Bus-side dynamic inertia is equivalent to providing RoCoF in-phase reverse support at the corresponding bus, thus correcting the node frequency change rate sensitivity.

[0139] As an example, the aforementioned source-side frequency change rate sensitivity matrix Specifically, it is expressed as:

[0140] ;

[0141] ;

[0142] in, It is a diagonal matrix composed of the inertial time constants of each synchronous generator and synchronous condenser. For the disturbance power sharing matrix, Assign a frequency matrix.

[0143] matrix The element in the k-th row and j-th column , indicating the degree of influence of the active disturbance of node j on the initial frequency change rate of node k after being shared by the synchronous inertia sources on each source side and allocated by the network frequency. Assigning a frequency matrix The element in the k-th row and i-th column, For the first A synchronous inertial source for the node The disturbance power sharing factor of active disturbance. Let be the inertial time constant of the i-th synchronous inertial source.

[0144] Then, the dynamic inertia matrix on the bus side... Incorporating the source-side frequency change rate sensitivity matrix This establishes the relationship for calculating the overall nodal inertia, as follows:

[0145] ;

[0146] Where I is the identity matrix, The sensitivity matrix for the overall frequency change rate after taking into account the dynamic support on the busbar side.

[0147] Therefore, the dynamic support on the busbar side is not directly added as a fixed inertia, but rather the sensitivity of the frequency change rate of each node after disturbance is corrected by the connection location and capacity weight.

[0148] Furthermore, in step 5, based on the comprehensive frequency change rate sensitivity matrix considering the dynamic support on the busbar side, the comprehensive nodal inertia of node j is defined as the reciprocal norm of the j-th row of the comprehensive frequency change rate sensitivity matrix, specifically expressed as:

[0149] ;

[0150] in, The comprehensive frequency change rate sensitivity matrix The j-th row, It is the sum of the absolute values ​​of the elements of the row vector. This represents the combined nodal inertia exhibited at node j after taking into account the synchronous inertia of the source side, the dynamic support of the grid-connected new energy unit, and the load inertia of the motor.

[0151] Furthermore, in this example, combining Figure 2 , Figure 3 The standard CSEE case study is used as an example to verify the evaluation process and results of the comprehensive node inertia of the above examples.

[0152] In this configuration, the system maintains a total active load of 4905 MW and a reactive load of 1647 Mvar. Actual operating conditions are parameterized by a total thermal power output of 1553 MW and renewable energy generation (wind and solar), resulting in a renewable energy penetration rate of 53.7%. The active load is relatively evenly distributed across the grid, while the DC interconnect transmission lines handle 1600 MW of power.

[0153] To verify the applicability of the nodal inertia calculation method, sections B01–B13, sections B34–B56 with motor loads, and GFL nodes WT01-0 and WT19-0 in the main power grid of the CSEE test case were selected as research objects, and the inertia value of each node was calculated at a given operating point.

[0154] First, the frequency allocation matrix and disturbance power sharing coefficient are calculated based on power flow and network parameters to obtain the inertia of each source-side node. Then, based on the inertia control parameters of the grid-connected new energy units and the motor load parameters, the following calculations are performed: , as well as Finally, the integrated nodal inertia is calculated based on the integrated frequency change rate sensitivity matrix, and the calculation results are shown in Table 1.

[0155] Table 1 - Results of Composite Nodal Inertia Calculation

[0156] B01 30.86 32.0046 B02 30.83 31.9637 B03 30.78 31.9035 B04 30.88 32.0403 B05 30.49 31.4919 B06 30.09 30.9954 B07 31.78 33.2777 B08 30.51 31.5033 B09 30.57 31.5063 B10 31.57 32.9555 B11 31.08 32.2746 B12 31.55 32.9316 B13 30.49 31.4944 B34 30.28 31.9230 B36 30.24 31.8695 B38 30.21 31.8258 B40 30.29 31.9349 B42 29.88 29.3763 B44 29.49 29.8880 B46 31.18 31.1657 B48 29.91 30.3954 B50 29.98 30.4150 B52 30.96 30.8311 B54 30.49 29.1737 B56 31.03 31.9057 WT01-01 29.07 30.13 WT19-01 29.34 28.99

[0157] It should be noted that the reason why the calculated value is around 30s is that the power base value PB is taken as 100MVA when calculating the nodal inertia.

[0158] As can be seen from the calculation results in Table 1, the results of the nodal inertia assessment method provided by this invention show good consistency with the simulation verification results in terms of overall numerical level and variation trend among nodes. Except for B34, B36, B38, and B40, whose errors slightly exceed 5%, the errors of the remaining nodes are all below 5%, and the overall average absolute deviation percentage is 3.16%. The inertia of each node in the CSEE system is accurately calculated, which has good applicability and provides scientific and accurate support for the identification of weak inertia areas, frequency security assessment, and dynamic support resource allocation in new power systems.

[0159] While the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the invention. Those skilled in the art can make various modifications and refinements without departing from the spirit and scope of the invention. Therefore, the scope of protection of the present invention shall be determined by the claims.

Claims

1. A comprehensive nodal inertia evaluation method considering both source-side synchronous inertia and bus-side dynamic support, characterized in that, Includes the following steps: Step 1: Obtain power system network operation data and equipment parameters. In the power system network, synchronous generators and synchronous condensers are used as source-side synchronous inertia sources, and grid-connected new energy units and motor loads are used as dynamic support equipment. All of them are connected to the bus side and directly respond to changes in bus frequency. Step 2: Based on the obtained power system network operation data and equipment parameters, combined with the swing equation of the synchronous generator after disturbance, the frequency allocation criterion, and the power sharing relationship in the early stage of disturbance, calculate the source-side node inertia of the synchronous generator and the synchronous condenser acting on each node after network coupling. Step 3: Based on the slip-torque dynamics of the frequency control channel and motor load of the grid-connected new energy unit, extract the effective inertia component in phase with the frequency change rate in the active power at the bus-side equipment port. Step 4: After reducing the effective inertia of grid-connected new energy generating units and the effective inertia of motor loads on the same busbar according to capacity, construct the dynamic inertia matrix on the input and output busbar sides. as well as Step 5: Establish the source-side frequency change rate sensitivity matrix based on the source-side node inertia, and incorporate the bus-side dynamic inertia matrix into the source-side frequency change rate sensitivity matrix to form a comprehensive node inertia calculation relationship, thereby obtaining the comprehensive node inertia that takes into account the source-side synchronous inertia, the dynamic support of grid-connected new energy units, and the contribution of motor load inertia.

2. The comprehensive nodal inertia evaluation method considering source-side synchronous inertia and bus-side dynamic support according to claim 1, characterized in that, In step 2, for the i-th source-side synchronous inertia source, the dynamic rotational speed after disturbance is jointly determined by the change in rotor kinetic energy, the increment of mechanical power, the increment of electromagnetic power, and the damping power. Therefore, the oscillation equation of the synchronous generator after disturbance is determined as follows: ； in, Let be the inertial time constant of the i-th synchronous inertial source. For speed deviation, For mechanical power increment, For electromagnetic power increment, is the damping coefficient.

3. The comprehensive nodal inertia evaluation method considering source-side synchronous inertia and bus-side dynamic support according to claim 2, characterized in that, In step 2, at the initial stage of the disturbance, the mechanical power adjustment has not yet been activated and the speed cannot change abruptly. Therefore, the mechanical power increment and the initial speed deviation satisfy the initial condition as follows: ； ； Furthermore, by incorporating the aforementioned initial conditions into the oscillation equation, where the damping term is zero at time 0+, we obtain the initial frequency change rate of the i-th synchronous inertial source, which represents the internal rotational speed response of the synchronous inertial source, as follows: ; Furthermore, by introducing a frequency allocation criterion, the internal rotational speed response of the synchronous inertia source is applied to the power grid network bus. The frequency allocation criterion is as follows: ； in, This is the bus frequency deviation vector. The rotational speed deviation vector of the synchronous inertia source. A frequency allocation matrix is ​​used to describe the degree to which the rotational speed change of the synchronous inertia source affects the frequency change of each bus.

4. The comprehensive nodal inertia evaluation method considering source-side synchronous inertia and bus-side dynamic support according to claim 1, characterized in that, In step 2, when an active disturbance is applied to node j, the proportion of disturbance power borne by the i-th synchronous inertial source is: ; in, Let be the sharing factor of the disturbance power of the i-th synchronous inertia source to node j, and let the disturbance power be . ; The sharing coefficient The electrical coupling strength between the synchronous inertia source and the disturbed node is obtained after normalization: ； Where G is the set of synchronous inertia sources. Let be the synchronization power coefficient between the i-th synchronous inertia source and node j.

5. The comprehensive nodal inertia evaluation method considering source-side synchronous inertia and bus-side dynamic support according to claim 1, characterized in that, The calculated source-side node inertia of the synchronous generator and synchronous condenser acting on node j after network coupling is expressed as: ； in, Let be the source node inertia of node j. Assigning a frequency matrix The element in the j-th row and i-th column.

6. The comprehensive nodal inertia evaluation method considering source-side synchronous inertia and bus-side dynamic support according to claim 1, characterized in that, In step 3, the effective inertia of the grid-connected renewable energy unit is determined by its frequency control channel combined with the time establishment process. Specifically, for the g-th grid-connected renewable energy unit connected to bus b, its effective inertia is expressed as: ； in, This represents the effective inertia actually established by the g-th grid-connected new energy unit within the disturbance time window. This indicates the low-frequency setpoint corresponding to the control parameter. The proportion of the low-frequency setpoint established by the inertia control channel within time t; ； ； When the disturbance time window satisfies At that time, the effective inertia of the g-th grid-connected new energy unit is approximately expressed as: ； in, This is the proportional coefficient for inertia control. The differential time constant for inertia control. Establish the time constant for the inertia control channel. = .

7. The comprehensive nodal inertia evaluation method considering source-side synchronous inertia and bus-side dynamic support according to claim 1, characterized in that, In step 3, the effective inertia of the motor load is obtained by slip-torque dynamic calculation. For the m-th motor load connected to bus b, the first-order following relationship between the motor rotor speed and the grid synchronization speed is obtained by combining the motor slip change equation and the motor rotor motion equation. ； in, For rotor angular velocity deviation, The synchronous angular velocity deviation of bus b Let m be the rotor inertia time constant of the m-th motor load. For torque-slip stiffness, This is the mechanical load damping coefficient; Within the initial time window of the disturbance, the rotor inertia of the motor is gradually coupled to the grid side through the above first-order following relationship, and the effective inertia of the m-th motor load is expressed as: ； in, , These are the time constant and low-frequency participation factor for the m-th motor load, respectively: ; ; in, This represents the effective inertia of the m-th motor load reflected on the bus side within time t.

8. The comprehensive nodal inertia evaluation method considering source-side synchronous inertia and bus-side dynamic support according to claim 6 or 7, characterized in that, In step 4, for bus b, the diagonal elements of the dynamic inertia matrix on the bus side are: ； in, The dynamic inertia matrix on the bus side. This is a collection of grid-connected new energy generating units that are connected to bus b. For the set of motor loads connected to bus b, For the capacity of the g-th grid-connected new energy unit, Let m be the load capacity of the m-th motor. To establish a unified baseline capacity for the system; Furthermore, the dynamic inertia matrix on the bus side It is a diagonal matrix used to represent the access location and capacity weight of dynamic support equipment on the bus side, and its off-diagonal elements are zero.

9. The comprehensive nodal inertia evaluation method considering source-side synchronous inertia and bus-side dynamic support according to claim 1, characterized in that, In step 5, a source-side frequency change rate sensitivity matrix is ​​first established based on the source-side node inertia. This source-side frequency change rate sensitivity matrix is ​​used to describe the sensitivity relationship between node disturbance power and node frequency change rate when only the source-side synchronous inertia is considered. Then, the dynamic inertia matrix on the bus side is incorporated into the frequency change rate sensitivity matrix on the source side to form the comprehensive nodal inertia calculation relationship, as follows: ； Where I is the identity matrix, To take into account the comprehensive frequency change rate sensitivity matrix after dynamic support on the busbar side, Indicates the source-side node inertia. This represents the source-side frequency change rate sensitivity matrix. This represents the dynamic inertia matrix on the bus side.

10. The comprehensive nodal inertia evaluation method considering source-side synchronous inertia and bus-side dynamic support according to claim 9, characterized in that, In step 5, based on the comprehensive frequency change rate sensitivity matrix considering the dynamic support on the busbar side, the comprehensive nodal inertia of node j is defined as the reciprocal norm of the j-th row of the comprehensive frequency change rate sensitivity matrix, specifically expressed as: ； in, The comprehensive frequency change rate sensitivity matrix The j-th row, It is the sum of the absolute values ​​of the elements of the row vector. This represents the combined nodal inertia exhibited at node j after taking into account the synchronous inertia of the source side, the dynamic support of the grid-connected new energy unit, and the load inertia of the motor.

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