Optimal power flow method considering subsynchronous frequency band stability boundary of grid-connected converter

Abstract

This application belongs to the field of power system optimization operation, specifically disclosing an optimal power flow method considering the stability boundary of the sub-synchronous frequency band of grid-connected converters. This application utilizes a d-q admittance model for grid-connected converters, quantifies the grid-connectable admittance margin, constructs stability constraints for the sub-synchronous frequency band of grid-connected converters, and embeds these constraints into the optimal power flow model for solution. This method can accurately characterize the output power boundary of grid-connected converters during stable operation. Through the above approach, this application can effectively ensure the grid-connected stability of each converter, thereby guaranteeing the stability of the power system and providing strong technical support for the safe and stable operation of the power system. This method is adaptable to system optimization under multiple operating conditions, not limited to a single operating scenario, and has strong practicality.

Description

Technical Field

[0001] This application belongs to the field of power system optimization operation, and more specifically, relates to the optimal power flow method considering the stability boundary of the subsynchronous frequency band of grid-connected converters. Background Technology

[0002] Compared to traditional thermal power units, renewable energy cannot provide inertia and voltage support for the power system, and the introduction of power electronic devices such as converters at the grid connection point poses a significant challenge to the safe and stable operation of the power system. Therefore, to ensure the stable operation of the power system while further increasing the penetration rate of renewable energy, the stability issues brought about by the grid connection of renewable energy must be considered.

[0003] In recent years, domestic and international scholars studying power system optimization have increasingly emphasized the stability issues brought about by the grid connection of renewable energy, and have proposed a considerable number of optimization methods. The core of these methods is to transform complex stability criteria into quantifiable mathematical constraints. Currently, power system optimization methods considering the stability of renewable energy grid connection mainly focus on voltage stability constraint modeling, frequency stability constraint modeling, transient stability constraint modeling, and dynamic stability constraint modeling. Among these, voltage stability constraint modeling and frequency stability constraint modeling focus on voltage fluctuations and frequency changes, respectively; transient stability constraint modeling focuses on system power angle stability; and dynamic stability constraint modeling emphasizes the system oscillation problem caused by the grid connection of high-proportion power electronic equipment.

[0004] To address this issue, most existing methods propose optimal power flow approaches that consider stability constraints from a system-wide perspective. However, these methods only consider the overall stability of the system. In this case, even if the power system guarantees stability, the power electronic equipment it contains may become unstable after grid connection. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the purpose of this application is to provide an optimal power flow method that takes into account the stability boundary of the subsynchronous frequency band of the grid-connected converter, aiming to solve the problem that the prior art cannot guarantee the stability of power electronic equipment after grid connection.

[0006] To achieve the above objectives, in a first aspect, this application provides an optimal power flow method that considers the stability boundary of the subsynchronous frequency band of the grid-connected converter, comprising:

[0007] Based on the branch data of the power system, the node admittance matrix of the power system is constructed. Based on the node admittance matrix, the grid-connected admittance margin of the grid-connected converter is calculated. Based on the topology and control loop of the grid-connected converter, the admittance model of the grid-connected converter in the dq coordinate system is constructed.

[0008] The admittance model of the grid-connected converter in the dq coordinate system is transformed from the complex frequency domain to the frequency domain. Combined with the grid-connectable admittance margin of the grid-connected converter, the subsynchronous frequency band stability constraint of the grid-connected converter is constructed.

[0009] By embedding the subsynchronous frequency band stability constraint of the grid-connected converter into the optimal power flow model of the power system and solving it, the power output boundary of the grid-connected converter is obtained.

[0010] Preferably, the stability constraint of the subsynchronous frequency band of the grid-connected converter is:

[0011]

[0012] in, , , and Let d, dq, qd, and qq be the real part expressions of the frequency domain admittance model of the grid-connected converter, respectively. Each component expression contains three related physical variables. The angular frequency of the subsynchronous oscillation. To match the active power output of the grid converter, To match the reactive power output of the grid converter, The voltage at the node where the grid converter is located The direct-axis component, , , and They are respectively The dd component, dq component, qd component, and qq component. For nodes The grid-connected converter has a grid admittance margin.

[0013] Preferably, the expressions for each component are as follows:

[0014]

[0015] in,

[0016]

[0017]

[0018]

[0019]

[0020] in, This indicates taking the real part of the expression. Let represent the dd component, dq component, qd component, and qq component expressions of the frequency domain admittance model of the grid-connected converter, respectively. The imaginary unit, and Let represent the transfer functions of the direct-axis current loop and quadrature-axis current loop of the grid-connected converter, respectively. and These represent the proportional and integral coefficients of the DC voltage loop controller for the grid-connected converter, respectively. and These represent the proportional and integral coefficients of the reactive power loop controller of the grid converter, respectively. This indicates the DC-side capacitance value of the grid-connected converter. This represents the steady-state value of the DC voltage of the grid-connected converter.

[0021] Preferably, the angular frequency of the subsynchronous oscillation Satisfy the angular frequency constraints of the optimal power flow model of the power system; and These represent the node voltages where the grid converter is located. The direct-axis components and quadrature-axis components, Locked to 0, ,in, As the decision variable for optimal power flow in the power system, the optimal power flow model of the power system, which takes into account the stability constraints of the subsynchronous frequency band of the grid-connected converter, is solved by combining a commercial solver.

[0022] Preferably, The dd, dq, qd, and qq components are determined in the following way:

[0023] calculate ,in, This indicates taking the real part of the expression. The node admittance matrix is ​​the first Line number Column elements, The node admittance matrix is ​​the first Line number Column elements, Let be the order of the nodal admittance matrix of the power system. Let be the order of the nodal admittance matrix of the power system;

[0024] calculate The dd component, dq component, qd component, and qq component:

[0025]

[0026] in, and These are the sine and cosine values ​​of the voltage phase at the node where the grid-connected converter is located, respectively. They serve as decision variables for the optimal power flow of the power system. The optimal power flow model of the power system, which takes into account the stability constraints of the subsynchronous frequency band of the grid-connected converter, is solved using a commercial solver.

[0027] Preferably, the node admittance matrix of the power system is as follows:

[0028]

[0029] in, The node admittance matrix is ​​the first Line number Column elements, For nodes To the node The admittance value of the branch between them. For nodes The set of all directly connected nodes. for A node in the process.

[0030] Preferably, based on the topology and control loop of the grid-connected converter, an admittance model of the grid-connected converter in the dq coordinate system is constructed, as follows:

[0031] Based on the grid-connected converter topology, the power balance equations for the DC side of the grid-connected converter are constructed.

[0032] Based on the grid-connected converter control loop, construct the logic control equations for the grid-connected converter;

[0033] Small-signal linearization is performed on the power balance equation, logic control equation, and output power equation of the grid-connected converter to obtain the corresponding linearized expressions.

[0034] By combining the linearized expressions, we obtain the admittance model of the grid converter in the dq coordinate system.

[0035] To achieve the above objectives, in a second aspect, this application provides a computer-readable storage medium including instructions that, when executed on an electronic device, cause the electronic device to perform the optimal power flow method as described in the first aspect.

[0036] It is understandable that the beneficial effects of the second aspect can be found in the relevant descriptions in the first aspect above, and will not be repeated here.

[0037] Overall, the technical solutions conceived in this application have the following beneficial effects compared with the prior art:

[0038] This application proposes an optimal power flow method that considers the stability boundary of the sub-synchronous frequency band of grid-connected converters. By using a dq admittance model of the grid-connected converter, quantifying the grid-connectable admittance margin, constructing stability constraints for the sub-synchronous frequency band of the grid-connected converter, and embedding these constraints into the optimal power flow model for solution, this method can accurately characterize the output power boundary of the grid-connected converter during stable operation. Through this approach, this application can effectively guarantee the grid-connected stability of each converter, thereby ensuring the stability of the power system and providing strong technical support for the safe and stable operation of the power system. This method is adaptable to system optimization under multiple operating conditions, not limited to a single operating scenario, and has strong practicality. Attached Figure Description

[0039] Figure 1 This is the flow intention of the optimal power flow method that takes into account the stability boundary of the subsynchronous frequency band of the grid converter provided in the embodiments of this application.

[0040] Figure 2 This is a topology diagram of a 33-node system provided in an embodiment of this application.

[0041] Figure 3 This is a schematic diagram of the grid-connected converter topology and control loop provided in the embodiments of this application.

[0042] Figure 4 This is a schematic diagram of the 24-hour active power output boundary characteristics of the grid-connected converter provided in the embodiments of this application.

[0043] Figure 5 This is a characteristic value distribution diagram of the active power output of the grid-connected converter according to the subsynchronous frequency band of the grid-connected system when it is at full power output, provided in the embodiments of this application.

[0044] Figure 6 This is a partially enlarged view of the characteristic value distribution diagram of the active power output of the grid-connected converter in the subsynchronous frequency band of the grid-connected system when the output is at full power, provided in the embodiments of this application.

[0045] Figure 7 This is a characteristic value distribution diagram of the subsynchronous frequency band of the grid-connected system when the active power output of the grid-connected converter is optimized according to the power output provided in the embodiments of this application.

[0046] Figure 8 This is a partially enlarged view of the characteristic value distribution diagram of the subsynchronous frequency band of the grid-connected system when the active power output of the grid-connected converter is optimized according to the power output provided in the embodiments of this application. Detailed Implementation

[0047] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0048] In this application, the term "and / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent three cases: A existing alone, A and B existing simultaneously, and B existing alone. In this application, the symbol " / " indicates that the related objects are in an "or" relationship, for example, A / B means A or B.

[0049] In this application, the terms "first" and "second," etc., are used to distinguish different objects, not to describe a specific order of objects. For example, "first response message" and "second response message," etc., are used to distinguish different response messages, not to describe a specific order of response messages.

[0050] In the embodiments of this application, the terms "exemplary" or "for example" are used to indicate that something is an example, illustration, or description. Any embodiment or design that is described as "exemplary" or "for example" in the embodiments of this application should not be construed as being more preferred or advantageous than other embodiments or design. Specifically, the use of the terms "exemplary" or "for example" is intended to present the relevant concepts in a specific manner.

[0051] In the description of the embodiments of this application, unless otherwise stated, "multiple" means two or more, for example, multiple processing units means two or more processing units, multiple elements means two or more elements, etc.

[0052] The embodiments of this application are described below with reference to the accompanying drawings.

[0053] like Figure 1 As shown, this application provides an optimal power flow method that considers the stability boundary of the subsynchronous frequency band of the grid-connected converter, including:

[0054] S1. Based on the given grid-connected converter topology, construct the power balance equation for the DC side of the grid-connected converter; based on the given grid-connected converter control loop, construct the logic control equation for the grid-connected converter; perform small-signal linearization on the power balance equation, logic control equation, and output power equation of the grid-connected converter to obtain the linearized expressions; combine the linearized expressions to obtain the admittance model of the grid-connected converter in the dq coordinate system.

[0055] Furthermore, the power balance equation for the DC side of the grid-connected converter in step S1 is:

[0056]

[0057] in, To match the DC-side capacitor value of the grid converter, To match the DC voltage on the DC side of the grid converter, The active power input to the grid-connected converter for renewable energy sources This refers to the direct-axis component of the voltage at the node where the grid converter is located. This refers to the direct-axis current on the filter inductor side of the grid converter.

[0058] Furthermore, the logic control equation for the grid-connected converter control loop in step S1 is as follows:

[0059]

[0060]

[0061]

[0062]

[0063]

[0064]

[0065] in, and These are the direct-axis and quadrature-axis components of the given current in the grid-connected converter control circuit, respectively. To connect the quadrature-axis current on the filter inductor side of the grid converter, This is the setpoint value for the DC-side direct-axis voltage of the grid-connected converter. and These are the proportional and integral coefficients of the DC voltage loop controller, respectively. and These are the proportional and integral coefficients of the reactive power loop controller, respectively. and These are the proportional and integral coefficients of the direct-axis current loop controller, respectively. and These are the proportional and integral coefficients of the quadrature-axis current loop controller, respectively. and These represent the setpoint and actual reactive power values ​​of the renewable energy input grid converter, respectively. and These are the transfer functions of the direct-axis current loop and quadrature-axis current loop of the grid converter, respectively. It is a complex frequency.

[0066] Furthermore, the small-signal linearization of the power balance equation, logic control equation, and output power equation of the grid converter in step S1 is as follows:

[0067]

[0068]

[0069]

[0070]

[0071]

[0072]

[0073]

[0074] in, , , , and These represent the DC voltage value of the grid converter under steady-state operating conditions, the direct-axis component of the node voltage, the direct-axis current value on the filter inductor side, the quadrature-axis component of the node voltage, and the quadrature-axis current value on the filter inductor side, respectively. , , , , , , , and These are the small disturbance variables of the grid-connected converter's output active power, DC voltage, output reactive power, the direct-axis component of the node voltage, the quadrature-axis component of the node voltage, the direct-axis given current of the control loop, the quadrature-axis given current of the control loop, the direct-axis current on the filter inductor side, and the quadrature-axis current on the filter inductor side.

[0075] Furthermore, the admittance model of the grid converter in the dq coordinate system in step S1 is as follows:

[0076]

[0077] in,

[0078]

[0079] S2. Calculate the node admittance matrix based on the power system branch data; according to the theorem "when the real part of the diagonal element of the node admittance matrix of the converter grid-connected system is less than the negative of the sum of the moduli of the off-diagonal elements in the same row, then the real part of all eigenvalues ​​of the admittance matrix is ​​negative", calculate the grid-connectable admittance margin of the grid-connected converter.

[0080] Furthermore, the derivation process of the theorem in step S2 is as follows:

[0081] According to the Gerschgöring disk theorem, any eigenvalue of the admittance matrix of a converter grid-connected system must lie within a certain row of the Gerschgöring disk, that is:

[0082]

[0083] in, This is an eigenvalue of the admittance matrix of the converter grid-connected system. The node admittance matrix is ​​the first Line number Column elements, which are diagonal elements. The node admittance matrix is ​​the first Line number Column elements are non-diagonal elements. The row number of the admittance matrix of the converter grid-connected system. The column number of the admittance matrix of the converter grid-connected system. Let be the order of the admittance matrix of the converter grid-connected system.

[0084] According to the properties of vector triangles,

[0085]

[0086] in, Let be the real part of the eigenvalues ​​of the converter grid-connected admittance matrix. This represents the real part of the diagonal elements of the converter's grid-connected admittance matrix.

[0087] According to equations (17) and (18),

[0088]

[0089] Therefore, when the real part of the diagonal element of the admittance matrix of the converter grid-connected system is less than the negative of the sum of the moduli of the off-diagonal elements in the same row, the real part of the eigenvalue of the admittance matrix is ​​less than 0.

[0090] Further, the expression for calculating the nodal admittance matrix of the system in step S2 is as follows:

[0091]

[0092] in, Here is the nodal admittance matrix. For nodes To the node The admittance value of the branch between them. For nodes The set of all directly connected nodes. for A node in the process.

[0093] Furthermore, the expression for the grid-connected admittance margin of the grid-connected converter in step S2 is as follows:

[0094]

[0095] in, This indicates taking the real part of the expression. For nodes The grid-connected converter has a grid admittance margin.

[0096] Furthermore, the dd, dq, qd, and qq components of the grid-connectable admittance margin expression for the grid-connected converter in step S2 are:

[0097]

[0098] in, , , and They are respectively The dd component, dq component, qd component, and qq component. and These are the nodes where the grid converter is located. The sine and cosine values ​​of the voltage phase.

[0099] S3. Transform the admittance model of the grid-connected converter derived in S1 from the complex frequency domain to the frequency domain, and combine it with the admittance margin of the grid-connected converter in S2 to construct the subsynchronous frequency band stability constraint of the grid-connected converter.

[0100] Subsynchronous frequency bands typically refer to the range of 2.5 Hz to 49 Hz. The stability constraint of the subsynchronous frequency band for grid-connected converters is essentially that the real part of the dq admittance model of the grid-connected converter in S1 must be less than the stability margin calculated in S2.

[0101] Furthermore, the subsynchronous frequency band stability constraint of the grid-connected converter in step S3 is:

[0102]

[0103] in, , , and Let d, dq, qd, and qq be the real part of the frequency domain admittance model of the grid converter, respectively. The angular frequency of the subsynchronous oscillation. To match the grid converter output power, This refers to the direct-axis component of the node voltage of the grid converter under steady-state operating conditions. , , and They are respectively The dd component, dq component, qd component, and qq component. The imaginary unit is . The left half of formula (23) comes from formula (1)-(16), and the right half comes from formula (17)-(22).

[0104] S4. Embed the subsynchronous frequency band stability constraints of the grid-connected converter constructed in S3 into the optimal power flow model of the power system, and use a commercial solver to solve the above model to obtain the power output boundary of the grid-connected converter.

[0105] Furthermore, the optimal AC power flow model of the power system embedding the stability constraints of the subsynchronous frequency band of the grid-connected converter in step S4 is as follows:

[0106]

[0107]

[0108]

[0109]

[0110]

[0111]

[0112]

[0113]

[0114]

[0115]

[0116]

[0117]

[0118]

[0119] Equation (24) is the optimization objective function, representing the minimization of system network loss. express Time Node With nodes The square of the branch current between them, Represents a node With nodes The resistance value of the branch between them, This represents the number of system nodes.

[0120] Equations (25) and (26) are the active power injection constraint and reactive power injection constraint at the node, respectively. and They represent Time Node Active and reactive loads, and They represent Time Node The active and reactive power outputs of thermal power units. and They represent Time Node The active and reactive power outputs of the grid converter are connected. and They represent Time Node Flow to Node Active power and reactive power, and They represent Time Node Flow to Node Active power and reactive power, Represents a node With nodes The reactance value of the branch circuit.

[0121] Equation (27) is a constraint of Ohm's law. express Time Node voltage The square of.

[0122] Equations (28) and (29) represent the active power output constraints and reactive power output constraints of thermal power units, respectively. and These represent the maximum and minimum threshold values ​​for the active power output of thermal power units, respectively. and These represent the maximum and minimum threshold values ​​for reactive power output of thermal power units, respectively.

[0123] Equations (30) and (31) are the constraints for the square of the node voltage and the square of the branch current, respectively. and They represent Time Node Maximum and minimum threshold values ​​for voltage squared. express Time Node With nodes The maximum threshold for the square of the branch current.

[0124] Equation (32) represents the power constraint at the beginning of the branch. This represents the L2 norm.

[0125] Equation (33) takes into account the stability constraints of the subsynchronous frequency band of the grid-connected converter. and They represent Always keep track of the node where the grid converter is located Active output and reactive output, express Always keep track of the node where the grid converter is located The voltage direct-axis component.

[0126] Equation (34) is the angular frequency constraint, and the constraint range is the subsynchronous frequency band.

[0127] Equation (35) is the node voltage phase constraint. for Time Node The square of the voltage phase sine value, for Time Node The square of the voltage phase cosine.

[0128] Equation (36) is the node voltage amplitude constraint. for Always keep track of the node where the network converter is located The square of the direct-axis component of the voltage, for Always keep track of the node where the grid converter is located The square of the voltage.

[0129] The optimal power flow model for the power system that takes into account the stability constraints of the subsynchronous frequency band of the grid-connected converter proposed in this application requires solving for the following variables: , , , , and .

[0130] When a commercial solver is used to solve the optimal power flow model of a power system that takes into account the stability constraints of the subsynchronous frequency band of the grid converter, the solution obtained is the unique global optimal solution. Other methods can also be used to solve it.

[0131] Example

[0132] This embodiment was tested in a 33-node system. The topology of the 33-node system is as follows: Figure 2 As shown, the system contains 33 nodes. Nodes 1, 3, 5, and 7 are each connected to a thermal power unit, and node 2 is connected to a grid-connected converter with its reactive power output set to 0. The topology and control loop of the grid-connected converter are as follows. Figure 3 As shown, it includes the direct-axis current loop, quadrature-axis current loop, DC voltage loop, and reactive power loop of the grid-connected converter.

[0133] Two scenarios are set up to illustrate the validity of this application: Scenario 1: The active power output of the grid-connected converter is at full power output; Scenario 2: An optimal power flow method considering the voltage-frequency coupling stability boundary of the grid-connected converter is used, and the active power output of the grid-connected converter is at optimized power output. Figure 4 The 24-hour active power output boundary characteristics of the grid-connected converter are given.

[0134] In the first case, the grid-connected converter outputs active power at full power. The characteristic value distribution diagram and its enlarged local view of the system are shown below. Figure 5 and Figure 6 As shown. In the second case, the system is optimized using the method proposed in this application, and the active power output of the grid converter is output according to the optimized power output. The specific implementation steps are as described above. At this time, the characteristic value distribution diagram and its local magnified diagram of the system are shown. Figure 7 and Figure 8 As shown. Comparison Figure 6 and Figure 8 It can be seen that in the first case, the active power output of the grid-connected converter is at full power output, and the system's eigenvalues ​​have positive real parts, leading to system instability. In the second case, the active power output of the grid-connected converter is at optimized power output, and all real parts of the system's eigenvalues ​​are negative, leading to system stability. Therefore, the optimal power flow method of this application, which considers the stability boundary of the sub-synchronous frequency band of the grid-connected converter, achieves optimal power flow in the power system while effectively ensuring system stability after the converter is connected to the grid.

[0135] It should be understood that the above-described device is used to execute the methods in the above embodiments. The implementation principle and technical effect of the corresponding program modules in the device are similar to those described in the above methods. The working process of the device can be referred to the corresponding process in the above methods, and will not be repeated here.

[0136] Based on the methods in the above embodiments, this application provides an electronic device that may include a processor, a communications interface, a memory, and a communication bus, wherein the processor, communications interface, and memory communicate with each other via the communication bus. The processor may invoke logical instructions stored in the memory to execute the methods in the above embodiments.

[0137] Furthermore, the logical instructions in the aforementioned memory can be implemented as software functional units and, when sold or used as independent products, can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of this application, in essence, or the part that contributes to the prior art, or a portion of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of this application.

[0138] Based on the methods in the above embodiments, this application provides a computer-readable storage medium storing a computer program that, when run on a processor, causes the processor to execute the methods in the above embodiments.

[0139] Based on the methods in the above embodiments, this application provides a computer program product that, when run on a processor, causes the processor to execute the methods in the above embodiments.

[0140] It is understood that the processor in the embodiments of this application can be a central processing unit (CPU), or other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, transistor logic devices, hardware components, or any combination thereof. A general-purpose processor can be a microprocessor or any conventional processor.

[0141] The method steps in this application embodiment can be implemented in hardware or by a processor executing software instructions. The software instructions can consist of corresponding software modules, which can be stored in random access memory (RAM), flash memory, read-only memory (ROM), programmable read-only memory (PROM), erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), registers, hard disks, portable hard disks, CD-ROMs, or any other form of storage medium known in the art. An exemplary storage medium is coupled to the processor, enabling the processor to read information from and write information to the storage medium. Of course, the storage medium can also be a component of the processor. The processor and the storage medium can reside in an ASIC.

[0142] In the above embodiments, implementation can be achieved entirely or partially through software, hardware, firmware, or any combination thereof. When implemented using software, it can be implemented entirely or partially as a computer program product. The computer program product includes one or more computer instructions. When the computer program instructions are loaded and executed on a computer, all or part of the processes or functions described in the embodiments of this application are generated. The computer can be a general-purpose computer, a special-purpose computer, a computer network, or other programmable device. The computer instructions can be stored in a computer-readable storage medium or transmitted through the computer-readable storage medium. The computer instructions can be transmitted from one website, computer, server, or data center to another website, computer, server, or data center via wired (e.g., coaxial cable, fiber optic, digital subscriber line (DSL)) or wireless (e.g., infrared, wireless, microwave, etc.) means. The computer-readable storage medium can be any available medium that a computer can access or a data storage device such as a server or data center that integrates one or more available media. The available medium can be a magnetic medium (e.g., floppy disk, hard disk, magnetic tape), an optical medium (e.g., DVD), or a semiconductor medium (e.g., solid-state disk (SSD)).

[0143] It is understood that the various numerical designations used in the embodiments of this application are merely for the convenience of description and are not intended to limit the scope of the embodiments of this application.

[0144] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. An optimal power flow method considering the stability boundary of the subsynchronous frequency band of the grid-connected converter, characterized in that, include: Based on the branch data of the power system, the node admittance matrix of the power system is constructed. Based on the node admittance matrix, the grid-connected admittance margin of the grid-connected converter is calculated. Based on the topology and control loop of the grid-connected converter, the admittance model of the grid-connected converter in the dq coordinate system is constructed. The admittance model of the grid-connected converter in the dq coordinate system is transformed from the complex frequency domain to the frequency domain. Combined with the grid-connectable admittance margin of the grid-connected converter, the subsynchronous frequency band stability constraint of the grid-connected converter is constructed. By embedding the subsynchronous frequency band stability constraint of the grid-connected converter into the optimal power flow model of the power system and solving it, the power output boundary of the grid-connected converter is obtained.

2. The optimal power flow method as described in claim 1, characterized in that, The stability constraint of the subsynchronous frequency band of the grid-connected converter is: in, , , and Let d, dq, qd, and qq be the real part expressions of the frequency domain admittance model of the grid-connected converter, respectively. Each component expression contains three related physical variables. The angular frequency of the subsynchronous oscillation. To match the active power output of the grid converter, To match the reactive power output of the grid converter, The node where the grid converter is located under stable operating conditions Voltage The direct-axis component, , , and They are respectively The dd component, dq component, qd component, and qq component. For nodes The grid-connected converter has a grid admittance margin.

3. The optimal power flow method as described in claim 2, characterized in that, The specific expressions for each component are as follows: in, in, This indicates taking the real part of the expression. Let represent the dd component, dq component, qd component, and qq component expressions of the frequency domain admittance model of the grid-connected converter, respectively. The imaginary unit, and Let represent the transfer functions of the direct-axis current loop and quadrature-axis current loop of the grid-connected converter, respectively. and These represent the proportional and integral coefficients of the DC voltage loop controller for the grid-connected converter, respectively. and These represent the proportional and integral coefficients of the reactive power loop controller of the grid converter, respectively. This indicates the DC-side capacitance value of the grid-connected converter. This indicates the DC voltage value of the grid-connected converter under stable operating conditions.

4. The optimal power flow method as described in claim 3, characterized in that, angular frequency of the subsynchronous oscillation Satisfy the angular frequency constraints of the optimal power flow model of the power system; and These represent the node voltages of the grid-connected converter under steady-state operating conditions. The direct-axis components and quadrature-axis components, Locked to 0, ,in, As the decision variable for optimal power flow in the power system, the optimal power flow model of the power system, which takes into account the stability constraints of the subsynchronous frequency band of the grid-connected converter, is solved by combining a commercial solver.

5. The optimal power flow method as described in claim 2, characterized in that, The dd, dq, qd, and qq components are determined in the following way: calculate ,in, This indicates taking the real part of the expression. The node admittance matrix is ​​the first Line number Column elements, The node admittance matrix is ​​the first Line number Column elements, Let be the order of the nodal admittance matrix of the power system; calculate The dd component, dq component, qd component, and qq component: in, and These are the sine and cosine values ​​of the voltage phase at the node where the grid-connected converter is located, respectively. They serve as decision variables for the optimal power flow of the power system. The optimal power flow model of the power system, which takes into account the stability constraints of the subsynchronous frequency band of the grid-connected converter, is solved using a commercial solver.

6. The optimal power flow method as described in claim 5, characterized in that, The nodal admittance matrix of the power system is as follows: in, For nodes To the node The admittance value of the branch between them. For nodes The set of all directly connected nodes. for A node in the process.

7. The optimal power flow method as described in claim 1, characterized in that, Based on the topology and control loop of the grid-connected converter, the admittance model of the grid-connected converter in the dq coordinate system is constructed as follows: Based on the grid-connected converter topology, the power balance equations for the DC side of the grid-connected converter are constructed. Based on the grid-connected converter control loop, construct the logic control equations for the grid-connected converter; Small-signal linearization is performed on the power balance equation, logic control equation, and output power equation of the grid-connected converter to obtain the corresponding linearized expressions. By combining the linearized expressions, we obtain the admittance model of the grid converter in the dq coordinate system.

8. A computer-readable storage medium, characterized in that, Includes instructions that, when executed on an electronic device, cause the electronic device to perform the optimal power flow method as described in any one of claims 1-7.

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