A flexible direct-current converter parameter identification method and device and a storage medium

Abstract

This invention discloses a method, device, and storage medium for parameter identification of flexible DC-DC converters, belonging to the field of power electronic equipment modeling technology. The method includes: establishing an electromagnetic transient average state model of the flexible DC-DC converter based on its dynamic characteristics and control strategy; converting the electromagnetic transient average state model of the flexible DC-DC converter into a polynomial function form using Taylor series expansion; transforming the parameter identification problem of the flexible DC-DC converter into a parameter fitting problem of a nonlinear system, designing a parameter identification algorithm based on the Koopman operator to identify the physical parameters of the flexible DC-DC converter; and comparing the identified values ​​obtained through MATLAB simulation with reference values ​​to achieve parameter identification of the flexible DC-DC converter. This invention obtains a globally linearized representation of the system without neglecting any nonlinear characteristics, eliminating the influence of strongly nonlinear modules in the control system of advanced power electronic equipment.

Description

Technical Field

[0001] This invention relates to the field of power electronic equipment modeling technology, and in particular to a method, device and storage medium for identifying parameters of a flexible DC converter. Background Technology

[0002] With the rapid evolution of power electronics technology and its widespread application in power generation, transmission, and consumption, the impact of key high-capacity power electronic equipment on the power flow distribution and stability of power systems is becoming increasingly prominent. As a result, there is a growing demand for accurate modeling and state prediction of advanced power electronic equipment in online control decision-making.

[0003] Currently, parameter identification methods commonly used in advanced power electronic equipment can be divided into data-based methods and mechanism-based methods. Traditional data-driven modeling methods can only improve inaccurate model parameters and cannot handle problems related to deviations in model structure and modeling function type. Simple mechanism models cannot achieve online updates of model structure or online correction of model parameters. Online parameter identification methods based on neural networks, machine learning, and deep learning all involve online training, which is computationally intensive and has poor timeliness. In modeling and online analysis calculations on electromagnetic transient time scales, such parameter identification algorithms involving training processes are not ideal. In addition, advanced power electronic equipment generally has a large amount of state information. Its control systems include modules with strong nonlinearity such as saturation limiting, signal change rate limiting, time delay, and control loop switching. Conventional modeling methods result in large errors in parameter identification. Summary of the Invention

[0004] In order to at least partially solve one of the technical problems existing in the prior art, the present invention aims to provide a method, device and storage medium for identifying parameters of flexible DC converters based on the Koopman operator.

[0005] The technical solution adopted in this invention is:

[0006] A method for identifying parameters of a flexible DC converter includes the following steps:

[0007] Based on the dynamic characteristics and control strategy of the flexible DC converter, an electromagnetic transient average state model of the flexible DC converter is established.

[0008] The electromagnetic transient average state model of the flexible DC converter is converted into a polynomial function form by Taylor series expansion.

[0009] The parameter identification problem of flexible DC converters is transformed into a parameter fitting problem of nonlinear systems. A parameter identification algorithm based on the Koopman operator is designed to identify the physical parameters of flexible DC converters.

[0010] The parameters of the flexible DC converter are identified by comparing the identified values ​​obtained through MATLAB simulation with the reference values.

[0011] Furthermore, the electromagnetic transient average state model of the flexible DC converter includes:

[0012] Internal dynamics model:

[0013]

[0014] In the formula, i c This is the internal circulating current of a flexible DC-DC converter, measured in pJ. and These represent the sum of the upper and lower bridge arm capacitor voltages of the flexible DC converter, respectively, in volts (V). R is the parasitic bridge arm resistance in pU, L is the bridge arm inductance in pU, N is the number of submodules in each bridge arm, C is the capacitance of the submodule in volts (F), and n is the capacitance of the submodule. u It is the insertion index (0~1) of the upper bridge arm submodule, n l It is the insertion index (0~1) of the lower bridge arm submodule, v d It is the pole-to-pole DC bus voltage measured on the inverter side or rectifier side, and the unit is volts (V). s The output current of a flexible DC-DC converter is measured in pu (unit: pu).

[0015] External dynamics model:

[0016] In a three-phase power system, considering the average model of a three-phase flexible DC converter and using a synchronous rotating dq reference frame, the dynamic characteristics of the output current and effective DC bus voltage of the flexible DC converter connected to node i are as follows:

[0017]

[0018] In the formula, v di It is the pole-to-pole DC bus voltage measured on the inverter side or rectifier side of a flexible DC converter, in volts (V). di P represents the DC current of the flexible DC converter, in amperes (A). ei This represents the power output on the inverter or rectifier side of the flexible DC-DC converter connected to node i, in watts (W). It is the effective DC bus capacitance, C di This represents the DC bus capacitance of the flexible DC converter, where M represents the number of phases and N represents the number of phases. i Indicates the number of submodules in each arm, C i This indicates the capacitance of the submodule capacitor, in F; i dsi and iqsi These are the d-axis and q-axis output currents of the flexible DC-DC converter, measured in units of pu (units per kilobyte). L i and R i These represent the arm inductance and parasitic arm resistance in units of p (pu), respectively. dsi and v qsi These represent the output voltages on the d-axis and q-axis, respectively, expressed in units of pu. di and v qi These are the d-axis and q-axis voltages of the common coupling point (PCC) bus of the flexible DC converter, where i is the node and ω is the q-axis voltage. s This represents the system frequency in PU (pu).

[0019] Furthermore, the output current of the flexible DC converter is controlled by a proportional-integral (PI) controller, and the output voltage v dsi and v qsi It is generated by the following formula:

[0020]

[0021] Where v Rdi and v Rqi These are the state variables of the proportional-integral controller, and their dynamics are as follows:

[0022]

[0023] K pi and K Ii These are the proportional and integral coefficients of the proportional-integral controller. and They are i dsi and i qsi Reference values.

[0024] Furthermore, for the inverter side of the flexible DC converter transmission system, the control objective is to maintain the DC bus voltage and regulate reactive power output; the inverter side of the flexible DC converter... and It is generated by the following formula:

[0025]

[0026] In the formula, x dci These are the state variables of the DC bus voltage controller, and their dynamics are as follows:

[0027]

[0028] In the formula, v di This indicates the magnitude of the PCC bus voltage in the flexible DC converter. Indicates v di Reference; S* It is the basic power of the entire power system's MVA. α represents the reference reactive power output of the flexible DC converter. di and α idi These are all parameters of the controller.

[0029] Furthermore, in converting the electromagnetic transient average state model of the flexible DC converter into a polynomial function form, only the state variable v... d The state equations need to be expanded into polynomial functions using Taylor series, and the state variable v d The second-order Taylor series expansion expression near the value x0 (stable operating value) is:

[0030]

[0031] Furthermore, the parameter identification problem of the flexible DC converter is transformed into a parameter fitting problem of a nonlinear system. A parameter identification algorithm is designed based on the Koopman operator to identify the physical parameters of the flexible DC converter, including:

[0032] The parameter identification problem of flexible DC converters can be described as the parameter fitting problem of a nonlinear system as follows:

[0033]

[0034] In the formula, Given a polynomial function, These are the parameters to be determined;

[0035] Input: Measurement data System vector field basis functions

[0036] Output: Estimated value of polynomial vector field function and parameters to be determined

[0037] Choose M ≤ N basis functions

[0038] Calculate the M×N matrix P x and P y :

[0039]

[0040] Calculate the M×M matrix

[0041] Calculate the M×M matrix

[0042] calculate

[0043] For each j, the following regression problem is computed:

[0044] in

[0045] Furthermore, the basis functions ψ k Gausky function ψ k (x)=exp(-γ‖xx k || 2 ).

[0046] Furthermore, the flexible DC converter parameter identification method also includes a data acquisition step:

[0047] The data of six state variables of the flexible DC converter during stable operation were obtained by MATLAB simulation: circulating current, upper arm capacitor voltage, lower arm capacitor voltage, DC bus voltage, d-axis component of output current, and q-axis component of output current.

[0048] From the running data of six state variables, n initial points are randomly selected. Using numerical integration, a trajectory is generated from each initial point, resulting in n trajectories. Each trajectory takes M points, with a time interval of Δt. k It is a column vector consisting of N state variables:

[0049] x k =x(t) k )=x(kΔt)

[0050] Data snapshot by (x k ,y k Composed of data, for a given initial point, a set of data snapshots is represented as:

[0051]

[0052] Another technical solution adopted in this invention is:

[0053] A flexible DC converter parameter identification device includes:

[0054] At least one processor;

[0055] At least one memory for storing at least one program;

[0056] When the at least one program is executed by the at least one processor, the at least one processor performs the method as described above.

[0057] Another technical solution adopted in this invention is:

[0058] A computer-readable storage medium storing a processor-executable program, which, when executed by a processor, performs the method described above.

[0059] The beneficial effects of this invention are: the parameter identification method proposed in this invention, based on the Koopman operator, can obtain a global linearized representation of the system without ignoring any nonlinear characteristics, thus eliminating the influence of modules with strong nonlinearity such as saturation limiting, signal change speed limiting, time delay, and control loop switching in the control system of advanced power electronic equipment. Attached Figure Description

[0060] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following description is provided with accompanying drawings of the relevant technical solutions in the embodiments of the present invention or the prior art. It should be understood that the accompanying drawings described below are only for the purpose of clearly illustrating some embodiments of the technical solutions of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0061] Figure 1 This is a flowchart of the electromagnetic transient average state model parameter identification method for a flexible DC converter based on the Koopman operator in an embodiment of the present invention;

[0062] Figure 2 This is a topology diagram of the single-phase and sub-module structure of the flexible DC converter in this embodiment of the invention;

[0063] Figure 3 This is a topology diagram of a 3-machine, 9-node power system with a flexible DC converter in an embodiment of the present invention;

[0064] Figure 4 This is a diagram showing the circulating current trajectory of the rectifier side of the flexible DC converter in this embodiment of the invention.

[0065] Figure 5 This is a diagram showing the voltage and operating trajectory of the upper bridge arm capacitor on the rectifier side of the flexible DC converter in this embodiment of the invention.

[0066] Figure 6 This is a diagram showing the voltage and operating trajectory of the lower bridge arm capacitor on the rectifier side of the flexible DC converter in this embodiment of the invention.

[0067] Figure 7 This is a diagram showing the d-axis component trajectory of the output current on the rectifier side of the flexible DC converter in this embodiment of the invention.

[0068] Figure 8 This is a diagram showing the q-axis component trajectory of the output current on the rectifier side of the flexible DC converter in this embodiment of the invention.

[0069] Figure 9This is a diagram showing the operating trajectory of the DC bus voltage on the rectifier side of the flexible DC converter in this embodiment of the invention.

[0070] Figure 10 This is a diagram showing the circulating current trajectory of the inverter side of the flexible DC converter in an embodiment of the present invention.

[0071] Figure 11 This is a diagram showing the voltage and operating trajectory of the upper bridge arm capacitor on the inverter side of the flexible DC converter in this embodiment of the invention.

[0072] Figure 12 This is a diagram showing the voltage and operating trajectory of the lower bridge arm capacitor on the inverter side of the flexible DC converter in this embodiment of the invention.

[0073] Figure 13 This is a diagram showing the d-axis component trajectory of the output current on the inverter side of the flexible DC converter in this embodiment of the invention.

[0074] Figure 14 This is a diagram showing the q-axis component trajectory of the output current on the inverter side of the flexible DC converter in this embodiment of the invention.

[0075] Figure 15 This is a diagram showing the operating trajectory of the DC bus voltage on the inverter side of the flexible DC converter in this embodiment of the invention.

[0076] Figure 16 This is a comparison diagram of the true and identified values ​​of the circulating current vector field on the rectifier side of the flexible DC converter in this embodiment of the invention;

[0077] Figure 17 This is a comparison diagram of the actual and identified values ​​of the upper bridge arm capacitor voltage and vector field on the rectifier side of the flexible DC converter in this embodiment of the invention.

[0078] Figure 18 This is a comparison diagram of the actual and identified values ​​of the lower bridge arm capacitor voltage and vector field on the rectifier side of the flexible DC converter in this embodiment of the invention.

[0079] Figure 19 This is a comparison diagram of the true and identified values ​​of the d-axis component vector field of the rectifier-side output current of the flexible DC converter in this embodiment of the invention.

[0080] Figure 20 This is a comparison diagram of the true and identified values ​​of the q-axis component vector field of the output current on the rectifier side of the flexible DC converter in this embodiment of the invention;

[0081] Figure 21 This is a comparison diagram of the true and identified values ​​of the DC bus voltage vector field on the rectifier side of the flexible DC converter in this embodiment of the invention;

[0082] Figure 22 This is a comparison diagram of the true and identified values ​​of the circulating current vector field on the inverter side of the flexible DC converter in this embodiment of the invention;

[0083] Figure 23 This is a comparison diagram of the actual and identified values ​​of the upper bridge arm capacitor voltage and vector field of the flexible DC converter on the inverter side in this embodiment of the invention.

[0084] Figure 24 This is a comparison diagram of the actual and identified values ​​of the lower bridge arm capacitor voltage and vector field on the inverter side of the flexible DC converter in this embodiment of the invention.

[0085] Figure 25 This is a comparison diagram of the true and identified values ​​of the d-axis component vector field of the output current on the inverter side of the flexible DC converter in this embodiment of the invention.

[0086] Figure 26 This is a comparison diagram of the true and identified values ​​of the q-axis component vector field of the output current on the inverter side of the flexible DC converter in this embodiment of the invention;

[0087] Figure 27 This is a comparison diagram of the actual value and the identified value of the DC bus voltage vector field on the inverter side of the flexible DC converter in an embodiment of the present invention. Detailed Implementation

[0088] The embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention. The step numbers in the following embodiments are set only for ease of explanation, and there is no limitation on the order between the steps. The execution order of each step in the embodiments can be adaptively adjusted according to the understanding of those skilled in the art.

[0089] In the description of this invention, it should be understood that the orientation descriptions, such as up, down, front, back, left, right, etc., are based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention.

[0090] In the description of this invention, "several" means one or more, "more than" means two or more, "greater than," "less than," and "exceeding" are understood to exclude the stated number, while "above," "below," and "within" are understood to include the stated number. The use of "first" and "second" in the description is merely for distinguishing technical features and should not be construed as indicating or implying relative importance, or implicitly indicating the number of indicated technical features, or implicitly indicating the order of the indicated technical features.

[0091] Furthermore, in the description of this invention, unless otherwise stated, "multiple" means two or more. "And / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A alone, A and B simultaneously, or B alone. The character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0092] In the description of this invention, unless otherwise explicitly defined, terms such as "set up," "install," and "connect" should be interpreted broadly, and those skilled in the art can reasonably determine the specific meaning of the above terms in this invention in conjunction with the specific content of the technical solution.

[0093] like Figure 1 As shown, this embodiment provides a parameter identification method for flexible DC-DC converters based on the Koopman operator, specifically a parameter identification method for the electromagnetic transient average state model of flexible DC-DC converters based on the Koopman operator. This method overcomes the limitations of conventional algorithms in terms of data dimensionality, computational load, runtime efficiency, and the ability to track and simulate the real modes and nonlinear characteristics of the equipment. It leverages the advantages of both mechanism-based and data-driven modeling to achieve accurate identification of the physical parameters of flexible DC-DC converters. The method specifically includes the following steps:

[0094] S1: Based on the dynamic characteristics and control strategy of the flexible DC converter, establish the electromagnetic transient average state model of the flexible DC converter.

[0095] The topology diagram of a flexible DC converter single phase and submodule is as follows: Figure 2 As shown. In Figure 2 in,i d The DC current of a flexible DC converter is measured in amperes (A), v d The pole-to-pole DC bus voltage, measured in volts (V), is the voltage across the inverter or rectifier side of a flexible DC converter. du The DC bus voltage to ground, measured in volts (V), is the voltage across the inverter or rectifier side upper arm of a flexible DC converter. dl C is the pole-to-ground DC bus voltage measured in volts (V) on the lower bridge arm of the inverter or rectifier side of a flexible DC converter. d R is the DC bus capacitance of the flexible DC converter in F units, R is the parasitic bridge arm resistance in pu units, L is the bridge arm inductance in pu units, M represents the number of phases, N represents the number of submodules per arm, and i s The output current of a flexible DC-DC converter is measured in units of pu (p). a The AC bus voltage is measured in volts (V), and S1 and S2 represent switches.

[0096] Internal dynamics model of flexible DC converter:

[0097]

[0098] Where i c This is the internal circulating current of the flexible DC converter, measured in pJ. and These represent the sum of the voltages across the upper and lower bridge arm capacitors of the flexible DC-DC converter, respectively, in volts (V). R is the parasitic bridge arm resistance in pU, L is the bridge arm inductance in pU, N is the number of submodules per bridge arm, C is the capacitance of the submodule, and n... u It is the insertion index (0~1) of the upper bridge arm submodule, n l It is the insertion index (0~1) of the lower bridge arm submodule, v d It is the pole-to-pole DC bus voltage measured on the inverter side or rectifier side, and the unit is volts (V). s It is the output current of a flexible DC-DC converter, measured in pu.

[0099] External dynamics model of flexible DC converter:

[0100] Considering the average model of a three-phase flexible DC converter and using a synchronous rotating dq reference frame, the dynamic characteristics of the output current and effective DC bus voltage of the flexible DC converter connected to node i are as follows:

[0101]

[0102] Among them, v di It is the pole-to-pole DC bus voltage measured on the inverter side or rectifier side of a flexible DC converter, in volts (V). di P represents the DC current of the flexible DC converter, in amperes (A). ei This represents the power output on the inverter or rectifier side of the flexible DC-DC converter connected to node i, in watts (W). It is the effective DC bus capacitance. C di This represents the DC bus capacitance of the flexible DC converter, where M represents the number of phases and N represents the number of phases. i Indicates the number of submodules in each arm, C i Indicates the capacitance of the submodule capacitor, i dsi and i qsi The L represents the d-axis and q-axis output current of a flexible DC-DC converter, measured in units of pu. i and R i This represents the arm inductance and parasitic arm resistance in units of p (pu), and v (v). dsi and v qsiThese represent the output voltages on the d-axis and q-axis, respectively, expressed in units of pu. di and v qi These are the d-axis and q-axis voltages of the common coupling point (PCC) bus of the flexible DC converter, where i is the node and ω is the q-axis voltage. s This represents the system frequency in PU (pu).

[0103] The output current of the flexible DC-DC converter is controlled by a proportional-integral (PI) controller, and the output voltage is v. dsi and v qsi It is generated by the following formula:

[0104]

[0105] Where v Rdi and v Rqi These are the state variables of the PI controller, and their dynamics are as follows:

[0106]

[0107] K pi and K Ii These are the proportional and integral coefficients of the PI controller, and and is i dsi and i qsi Reference values.

[0108] For flexible DC-DC converters at the inverter end of a power transmission system, the control objectives are to maintain the DC bus voltage and regulate reactive power output. and It is generated by the following formula:

[0109]

[0110] Where x dci These are the state variables of the DC bus voltage controller, and their dynamics are as follows:

[0111]

[0112] V i This indicates the magnitude of the PCC bus voltage in the flexible DC converter. Indicates v di Reference. S * It is the basic power of the entire power system's MVA. α represents the reference reactive power output of the flexible DC converter. di and α idi These are the parameters of the controller.

[0113] S2: The electromagnetic transient average state model of the flexible DC converter is converted into a system represented by a polynomial function by Taylor series expansion.

[0114] The electromagnetic transient average state model of a flexible DC converter only contains the state variable v. d It is not represented by a polynomial function; its state equations need to be expanded using Taylor series. d The second-order Taylor series expansion expression near its stable operating point x0 is:

[0115]

[0116] S3: The parameter identification problem of flexible DC converters is transformed into a parameter fitting problem of nonlinear systems. Based on the Koopman operator, a parameter identification algorithm is designed to identify the physical parameters of flexible DC converters.

[0117] (1) Data acquisition:

[0118] Taking the IEEE 3-machine 9-bus system as an example, with the flexible DC converter connected between node 2 and node 8, the power system topology including the flexible DC converter is as follows: Figure 3 As shown. The flexible DC converter is designed as a 3-phase unit, with 12 sub-modules per arm, and a DC bus voltage of 1.40 × 10⁻⁶. 5 V, the maximum output voltage is 7.00 × 10 4 V, the maximum output current is 2.00×10 3 A, with an initial phase of 0°. Wherein, Figure 3 In the diagram, Bus1-Bus9 represent busbars 1-9 respectively, G1-G3 represent synchronous generators 1-3 respectively, and Load1-Load3 represent load outputs 1-3 respectively.

[0119] The system was simulated in the time domain using MATLAB to obtain data on six state variables when the flexible DC converter was operating stably: circulating current, upper arm capacitor voltage, lower arm capacitor voltage, DC bus voltage, d-axis component of output current, and q-axis component of output current.

[0120] in, Figures 4-9 These are the rectifier-side circulating current, upper arm capacitor voltage, lower arm capacitor voltage, d-axis component of output current, q-axis component of output current, and DC bus voltage trajectory diagrams of the flexible DC converter.

[0121] in, Figures 10-15 These are the operating trajectory diagrams of the inverter-side circulating current, upper arm capacitor voltage, lower arm capacitor voltage, output current d-axis component, output current q-axis component, and DC bus voltage of the flexible DC converter.

[0122] Five initial points are randomly selected from the trajectories of six state variables. Using numerical integration, a trajectory is generated from each initial point, resulting in five trajectories. Each trajectory has M = 20 points, with a time interval of Δt = 0.5 milliseconds. k It is a column vector consisting of 6 state variables:

[0123] x k =x(t) k )=x(kΔt)

[0124] Data snapshot by (x k ,y k Composed of data, for a given initial point, a set of data snapshots can be represented as:

[0125]

[0126] (2) Koopman-based parameter identification:

[0127] The parameter identification problem of flexible DC converters can be described as the parameter fitting problem of a nonlinear system:

[0128]

[0129] in Given a polynomial function, These are the parameters to be determined.

[0130] Input quantity: (1) Measurement data System vector field basis functions

[0131] Output: Estimated value of polynomial vector field function and parameters to be determined

[0132] choose basis functions Where n is the number of state variables, m is the order of the polynomial vector field, and ψ k Chosen as Gaussian function ψ k (x)=exp(-γ‖xx k || 2 );

[0133] Calculate the M×N matrix P x and P y ,in:

[0134]

[0135] Calculate the M×M matrix

[0136] Calculate the M×M matrix

[0137] calculate

[0138] For each j, the following regression problem is computed:

[0139] in

[0140] S4: Compare the identified values ​​obtained through MATLAB simulation with the reference values ​​to achieve parameter identification of the flexible DC converter.

[0141] The parameter estimation results of the flexible DC converter are as follows: Figures 16 to 27 As shown. Figures 16 to 27 The middle circle represents the true values ​​of the vector field f1-f6 of the flexible DC converter dynamic model corresponding to each set of state variable samples, i.e., the values ​​of the scalar functions on the right side of the equals sign in the state equation; while the cross in the figure represents the estimated value of the vector field obtained by the Koopman algorithm. Figures 16 to 27 As can be seen from the figure, the Koopman algorithm can accurately estimate the true value of the vector field in 5 simulation calculations with very small estimation error. After calculation, the standard deviation of the estimation error of all estimated values ​​relative to the actual values ​​in the figure is 3.1317e-04.

[0142] in, Figures 16-21 A comparison diagram of the actual and identified values ​​of the rectifier-side circulating current, upper arm capacitor voltage, lower arm capacitor voltage, d-axis component of output current, q-axis component of output current, and DC bus voltage vector field of a flexible DC converter.

[0143] in, Figures 22-27 A comparison diagram of the actual and identified values ​​of the circulating current on the inverter side of the flexible DC converter, the sum of the upper and lower bridge arm capacitor voltages, the d-axis component of the output current, the q-axis component of the output current, and the DC bus voltage vector field.

[0144] Tables 1 and 2 present the parameter estimates in the electromagnetic transient average state models of the rectifier and inverter sides of the flexible DC converter, respectively.

[0145] Table 1

[0146]

[0147] Table 2

[0148]

[0149] In summary, the method of this embodiment has at least the following advantages and beneficial effects compared to the prior art:

[0150] (1) The parameter identification method proposed in this embodiment of the invention can obtain a global linearized representation of the system without ignoring any nonlinear characteristics based on the Koopman operator, thereby eliminating the influence of modules with strong nonlinearity such as saturation limiting, signal change speed limiting, time delay and control loop switching in the control system of advanced power electronic equipment.

[0151] (2) The parameter identification process in this embodiment of the invention does not involve training calculation, is suitable for online application, and can process high-dimensional and computationally intensive data.

[0152] (3) The electromagnetic transient model obtained in the embodiments of the present invention can be used for online state prediction, as well as auxiliary control decision-making and fault early warning based on state prediction.

[0153] This embodiment also provides a flexible DC converter parameter identification device, including:

[0154] At least one processor;

[0155] At least one memory for storing at least one program;

[0156] When the at least one program is executed by the at least one processor, the at least one processor performs the following: Figure 1 The method shown.

[0157] This embodiment of the flexible DC converter parameter identification device can execute the flexible DC converter parameter identification method provided in the method embodiment of the present invention, and can execute any combination of the implementation steps of the method embodiment, and has the corresponding functions and beneficial effects of the method.

[0158] This application also discloses a computer program product or computer program, which includes computer instructions stored in a computer-readable storage medium. A processor of a computer device can read the computer instructions from the computer-readable storage medium and execute the computer instructions, causing the computer device to perform... Figure 1 The method shown.

[0159] This embodiment also provides a storage medium storing instructions or programs that can execute the flexible DC converter parameter identification method provided in the method embodiment of the present invention. When the instructions or programs are run, any combination of implementation steps of the method embodiment can be executed, and the method has the corresponding functions and beneficial effects.

[0160] In some alternative embodiments, the functions / operations mentioned in the block diagrams may not occur in the order shown in the operation diagrams. For example, depending on the functions / operations involved, two consecutively shown blocks may actually be executed substantially simultaneously, or the blocks may sometimes be executed in reverse order. Furthermore, the embodiments presented and described in the flowcharts of this invention are provided by way of example to provide a more comprehensive understanding of the technology. The disclosed methods are not limited to the operations and logic flows presented herein. Alternative embodiments are contemplated in which the order of various operations is altered and sub-operations described as part of a larger operation are executed independently.

[0161] Furthermore, although the invention has been described in the context of functional modules, it should be understood that, unless otherwise stated, one or more of the described functions and / or features may be integrated into a single physical device and / or software module, or one or more functions and / or features may be implemented in a separate physical device or software module. It is also understood that a detailed discussion of the actual implementation of each module is unnecessary for understanding the invention. Rather, given the properties, functions, and internal relationships of the various functional modules in the apparatus disclosed herein, the actual implementation of the module will be understood within the scope of conventional skill of an engineer. Therefore, those skilled in the art can implement the invention as set forth in the claims using ordinary techniques without excessive experimentation. It is also understood that the specific concepts disclosed are merely illustrative and not intended to limit the scope of the invention, which is determined by the full scope of the appended claims and their equivalents.

[0162] If the aforementioned functions are implemented as software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of this invention, essentially, 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 invention. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0163] The logic and / or steps represented in the flowchart or otherwise described herein, for example, can be considered as a sequenced list of executable instructions for implementing logical functions, and can be embodied in any computer-readable medium for use by, or in conjunction with, an instruction execution system, apparatus, or device (such as a computer-based system, a processor-included system, or other system that can fetch and execute instructions from, an instruction execution system, apparatus, or device). For the purposes of this specification, "computer-readable medium" can be any means that can contain, store, communicate, propagate, or transmit programs for use by, or in conjunction with, an instruction execution system, apparatus, or device.

[0164] More specific examples of computer-readable media (a non-exhaustive list) include: electrical connections (electronic devices) having one or more wires, portable computer disk drives (magnetic devices), random access memory (RAM), read-only memory (ROM), erasable and editable read-only memory (EPROM or flash memory), fiber optic devices, and portable optical disc read-only memory (CDROM). Furthermore, computer-readable media can even be paper or other suitable media on which the program can be printed, since the program can be obtained electronically, for example, by optically scanning the paper or other medium, followed by editing, interpreting, or otherwise processing as necessary, and then stored in computer memory.

[0165] It should be understood that various parts of the present invention can be implemented in hardware, software, firmware, or a combination thereof. In the above embodiments, multiple steps or methods can be implemented in software or firmware stored in memory and executed by a suitable instruction execution system. For example, if implemented in hardware, as in another embodiment, it can be implemented using any one or a combination of the following techniques known in the art: discrete logic circuits having logic gates for implementing logical functions on data signals, application-specific integrated circuits (ASICs) having suitable combinational logic gates, programmable gate arrays (PGAs), field-programmable gate arrays (FPGAs), etc.

[0166] In the foregoing description of this specification, references to terms such as "one embodiment," "another embodiment," or "some embodiments" indicate that a specific feature, structure, material, or characteristic described in connection with an embodiment or example is included in at least one embodiment or example of the present invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0167] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

[0168] The above is a detailed description of the preferred embodiments of the present invention. However, the present invention is not limited to the above embodiments. Those skilled in the art can make various equivalent modifications or substitutions without departing from the spirit of the present invention. All such equivalent modifications or substitutions are included within the scope defined by the claims of this application.

Claims

1. A method for identifying parameters of a flexible DC converter, characterized in that, Includes the following steps: Based on the dynamic characteristics and control strategy of the flexible DC converter, an electromagnetic transient average state model of the flexible DC converter is established. The electromagnetic transient average state model of the flexible DC converter is converted into a polynomial function form by Taylor series expansion. The parameter identification problem of flexible DC converters is transformed into a parameter fitting problem of nonlinear systems. A parameter identification algorithm based on the Koopman operator is designed to identify the physical parameters of flexible DC converters. The parameters of the flexible DC converter are identified by comparing the identified values ​​obtained through MATLAB simulation with the reference values. The parameter identification problem of flexible DC converters is described as a parameter fitting problem of a nonlinear system. A parameter identification algorithm based on the Koopman operator is designed to identify the physical parameters of the flexible DC converter, including: The parameter identification problem of flexible DC converters can be described as the parameter fitting problem of a nonlinear system as follows: In the formula, Given a polynomial function, These are the parameters to be determined; Input: Measurement data System vector field basis functions ; Output: Estimated value of polynomial vector field function and parameters to be determined ; choose basis functions ; calculate matrix and : calculate matrix ; calculate matrix ; calculate ; For each j Calculate the following regression problem: , in .

2. The method for identifying parameters of a flexible DC-DC converter according to claim 1, characterized in that, The electromagnetic transient average state model of the flexible DC converter includes: Internal dynamics model: In the formula, It is the internal circulating current of the flexible DC converter. and These represent the sum of the upper arm capacitor voltages and the sum of the lower arm capacitor voltages of the flexible DC converter, respectively. R is the parasitic arm resistance, L is the arm inductance, N is the number of submodules in each arm, and C is the capacitance of the submodule. n u It is the insertion index of the upper bridge arm submodule. n l It is the insertion index of the lower bridge arm submodule. v d It is the pole-to-pole DC bus voltage measured on the inverter side or rectifier side. i s It is the output current of the flexible DC converter; External dynamics model: In a three-phase power system, consider an average model of a three-phase flexible DC converter, using a synchronous rotating dq reference frame connected to the node. i The output current and effective DC bus voltage dynamic characteristics of the flexible DC converter are as follows: In the formula, v di It is the pole-to-pole DC bus voltage measured on the inverter side or rectifier side of a flexible DC converter. This represents the DC current of the flexible DC converter. P ei Indicates a connection at the node i The power output of the flexible DC converter on the inverter side or rectifier side. It is the effective DC bus capacitance. This refers to the DC bus capacitance of a flexible DC converter. M Indicates the number of phases. Indicates the number of submodules in each arm. This indicates the capacitance of the submodule capacitor; i dsi and i qsi These are the d-axis and q-axis output currents of the flexible DC converter, respectively. L i and R i These represent the arm inductance and parasitic arm resistance, respectively. v dsi and v qsi These represent the output voltages along the d-axis and q-axis, respectively. v di and v qi These are the d-axis and q-axis voltages of the common coupling point bus of the flexible DC converter, respectively. i For nodes, Represents the system frequency.

3. The method for identifying parameters of a flexible DC-DC converter according to claim 2, characterized in that, The output current of the flexible DC-DC converter is controlled by a proportional-integral controller, and the output voltage... v dsi and v qsi It is generated by the following formula: in and These are the state variables of the proportional-integral controller, and their dynamics are as follows: and These are the proportional and integral coefficients of the proportional-integral controller. and They are and Reference values.

4. The method for identifying parameters of a flexible DC-DC converter according to claim 3, characterized in that, For the inverter side of a flexible DC-DC converter transmission system, the control objective is to maintain the DC bus voltage and regulate reactive power output; the inverter side of the flexible DC-DC converter... and It is generated by the following formula: In the formula, These are the state variables of the DC bus voltage controller, and their dynamics are as follows: In the formula, This indicates the magnitude of the PCC bus voltage in the flexible DC converter. express Reference; It is the basic power of the entire power system's MVA. This indicates the reference reactive power output of the flexible DC converter. and These are all parameters of the controller.

5. The method for identifying parameters of a flexible DC-DC converter according to claim 2, characterized in that, In converting the electromagnetic transient average state model of a flexible DC converter into a polynomial function form, only state variables are considered. The state equations need to be expanded into polynomial functions using Taylor series, and the state variables... At its stable operating point x The second-order Taylor series expansion expression near 0 is: 。 6. The method for identifying parameters of a flexible DC-DC converter according to claim 1, characterized in that, basis functions Gaussian function .

7. The method for identifying parameters of a flexible DC converter according to claim 1, characterized in that, The flexible DC converter parameter identification method also includes a data acquisition step: The data of six state variables of the flexible DC converter during stable operation were obtained by MATLAB simulation: circulating current, upper arm capacitor voltage, lower arm capacitor voltage, DC bus voltage, d-axis component of output current, and q-axis component of output current. From the running data of six state variables, n initial points are randomly selected. Using numerical integration, a trajectory is generated from each initial point, resulting in n trajectories. Each trajectory takes M points, with a time interval of Δt. k It is a column vector consisting of N state variables: Data snapshot by Composition, for a given initial point, a set of data snapshots is represented as: 。 8. A parameter identification device for a flexible DC converter, characterized in that, include: At least one processor; At least one memory for storing at least one program; When the at least one program is executed by the at least one processor, the at least one processor implements the method of any one of claims 1-7.

9. A computer-readable storage medium storing a processor-executable program, characterized in that, The processor-executable program, when executed by the processor, is used to perform the method as described in any one of claims 1-7.

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