A method and system for identifying parameters of an equivalent model of a grid-connected inverter power supply

Abstract

The application provides a grid-connection type inverter power supply equivalent model parameter identification method and system, and belongs to the parameter identification technical field in grid-connection type inverter control and relay protection, and comprises the following steps: based on the three-phase voltage and three-phase current measurement values collected at the protection installation place of the equivalent model, voltage and current phasors at the outlet of the grid-connection type inverter power supply are obtained; based on the reactive power and outlet voltage amplitude under the steady-state operation state after small disturbance, the reactive-voltage droop coefficient of the grid-connection type inverter power supply is identified; virtual internal potential calculation values and virtual internal potential measurement values are constructed, and the reactive ring integral coefficient and virtual inductance value are identified through a particle swarm optimization algorithm; the virtual internal potential before the fault of the grid-connection type inverter power supply is determined; and based on the virtual internal potential before the fault and the positive sequence voltage and current phasors during the fault, the positive sequence equivalent impedance of the grid-connection type inverter power supply under the fault state is determined.

Description

Technical Field

[0001] This invention belongs to the field of parameter identification technology in grid-type inverter control and relay protection, and particularly relates to a method and system for parameter identification of equivalent model of grid-type inverter power supply. Background Technology

[0002] The statements in this section are merely background information related to the present invention and do not necessarily constitute prior art.

[0003] Grid-based inverters, by simulating the operating characteristics of synchronous generators, have the ability to actively support system voltage and frequency, and have good application prospects in weak grid operation, islanded operation, and high-proportion renewable energy access scenarios.

[0004] Currently, grid-connected inverters typically employ virtual synchronous machine control and droop control to achieve voltage source characteristics, and utilize strategies such as virtual impedance and current limiting control to achieve fault ride-through functionality. When a system fault occurs, the control mode and output characteristics of the grid-connected inverter change, and its equivalent impedance characteristics are no longer fixed but dynamically change with the control strategy, fault type, and operating state. Existing relay protection analysis and fault characteristic studies usually require the equivalent model parameters of the grid-connected inverter.

[0005] However, the equivalent model parameters of grid-connected inverters typically include internal variables such as virtual internal potentials and control loop parameters, which are difficult to obtain directly through protection installations. Furthermore, the dynamic switching of inverter control states during fault ride-through causes changes in equivalent impedance, further increasing the difficulty of online parameter acquisition.

[0006] Therefore, it can be concluded that the core internal parameters of the existing grid-type inverter power supply equivalent model cannot be directly measured by the protection measurement point, and the inverter control state switching during fault ride causes dynamic changes in the equivalent impedance, making it difficult to achieve online and accurate acquisition of model parameters. Summary of the Invention

[0007] To overcome the shortcomings of the prior art, this invention provides a method and system for identifying equivalent model parameters of grid-type inverter power supplies. It can achieve online identification of equivalent model parameters of grid-type inverter power supplies by relying solely on measurable electrical quantities at the protection installation point, so as to accurately obtain equivalent model parameters under normal operation and fault ride-through conditions, and provide a foundation for relay protection adaptability analysis and fault characteristic research.

[0008] To achieve the above objectives, one or more embodiments of the present invention provide the following technical solutions: Firstly, a method for parameter identification of the equivalent model of a grid-type inverter power supply is disclosed, including: Establish equivalent models of grid-connected inverters under normal operating conditions and fault ride-through conditions; Based on the three-phase voltage and three-phase current measurements collected at the protection installation point, the voltage and current phasors at the output of the grid-type inverter power supply are obtained; Based on the reactive power and output voltage amplitude under steady-state operation after small disturbances, the reactive power-voltage droop coefficient of the grid-type inverter is identified. Based on the reactive power, output voltage amplitude, voltage phasor and current phasor in the transient process of grid-type inverter power supply, virtual internal potential calculation value and virtual internal potential measurement value are constructed, and the reactive power loop integral coefficient and virtual inductance value are identified by particle swarm optimization algorithm. Based on the virtual inductance value and the voltage and current phasors at the output of the grid-type inverter, the virtual internal potential of the grid-type inverter before the fault is determined. Based on the virtual internal potential before the fault and the positive sequence voltage and current phasors during the fault, the positive sequence equivalent impedance of the grid-type inverter power supply under fault conditions is determined.

[0009] As a further technical solution, corresponding equivalent models are established based on the control structure of the grid-type inverter power supply under normal operating conditions and fault ride-through conditions, respectively. Based on the active-frequency control loop, reactive-voltage control loop, and virtual inductive reactance, the virtual internal potential and virtual inductive reactance of the grid-type inverter are determined, and the grid-type inverter under normal operation is equivalent to a controlled voltage source model in series with virtual internal potential and virtual inductive reactance. When the output voltage amplitude of the grid-type inverter is lower than the fault ride-through threshold set by the control, the grid-type inverter is determined to have entered the fault ride-through state. Based on the positive sequence voltage and current characteristics of the grid-type inverter under virtual impedance current limiting or direct current limiting, the positive sequence network of the grid-type inverter under fault ride-through condition is equivalent to a voltage source model in series with the virtual internal potential and the positive sequence equivalent impedance before the fault.

[0010] As a further technical solution, the voltage and current phasors at the output of the grid-type inverter power supply are obtained as follows: Acquire the time-domain signals of three-phase voltage and three-phase current at the protection installation location; Extract the fundamental components of the three-phase voltage and three-phase current to obtain the fundamental phasors of the voltage and current at the protection installation location; By combining the line parameters or transformer parameters, the fundamental phasors of voltage and current at the protection installation point are converted to the output of the grid-type inverter power supply to obtain the voltage phasors and current phasors at the output of the grid-type inverter power supply.

[0011] As a further technical solution, the steps for identifying the reactive power-voltage droop coefficient of a grid-connected inverter are as follows: When the output voltage of the grid-connected inverter is not lower than the fault ride-through threshold, obtain the reactive power and output voltage amplitude under steady-state operation after small disturbances. Based on the condition that the rate of change of virtual internal potential is zero under steady-state operation, the reactive power-voltage droop coefficient of the grid-type inverter power supply is determined.

[0012] As a further technical solution, the steps for identifying the reactive power loop integral coefficient and the virtual inductance value are as follows: Based on the reactive-voltage control equations in the equivalent model of a grid-type inverter under normal operating conditions, the virtual internal potential amplitude is obtained by utilizing the reactive power and output voltage amplitude during the transient process. Based on the voltage phasor, current phasor, and virtual inductive reactance relationship at the output of the grid-type inverter power supply, a virtual internal potential measurement value is constructed. The reactive power loop integral coefficient, virtual inductance value, and initial value of virtual internal potential are used as the parameter vector to be identified. The fitness function is the early weighted mean square error between the calculated virtual internal potential and the measured virtual internal potential. The early weighted mean square error is determined based on the time weighting coefficient, which decreases with the sampling time to increase the weight of the dynamic data in the initial stage of the disturbance in the parameter identification process. The particle swarm optimization algorithm is used to optimize the vector of parameters to be identified, and the reactive power loop integral coefficient, virtual inductance value and initial value of virtual internal potential are obtained.

[0013] As a further technical solution, determining the virtual internal potential of a grid-connected inverter before a fault includes: Under normal operating conditions of the grid-type inverter, the virtual internal potential of the grid-type inverter is calculated based on the identified virtual inductance value and the voltage phasor and current phasor at the output of the grid-type inverter. The virtual internal potential under steady-state operation before the fault occurs is used as the voltage source parameter in the positive sequence equivalent model under fault ride-through state.

[0014] As a further technical solution, determining the positive sequence equivalent impedance of a grid-type inverter under fault conditions includes: When the output voltage amplitude of the grid-connected inverter is lower than the set threshold, the grid-connected inverter is determined to have entered the fault ride-through state. Extract the positive sequence voltage phasor and positive sequence current phasor at the output of the grid-type inverter during the fault period; Based on the virtual internal potential before the fault, the positive sequence voltage phasor during the fault, and the positive sequence current phasor during the fault, the positive sequence equivalent impedance of the grid-type inverter under fault conditions is calculated. Under fault ride-through conditions, the positive sequence network of a grid-type inverter power supply can be equivalently represented as a voltage source model consisting of a virtual internal potential before the fault and a positive sequence equivalent impedance connected in series. The positive sequence voltage phasor and positive sequence current phasor during the fault period are subjected to moving average filtering. Calculate the positive sequence equivalent impedance of a grid-type inverter under fault conditions.

[0015] As a further technical solution, the fault ride-through state includes a fault ride-through state using virtual impedance current limiting and a fault ride-through state using direct current limiting. The direct current limiting method includes prioritizing the control of the current vector angle, prioritizing the control of the d-axis current, and prioritizing the control of the q-axis current.

[0016] Secondly, a parameter identification system for the equivalent model of a grid-type inverter power supply is disclosed, including: The equivalent model construction module is configured to: establish equivalent models for the normal operation state and positive sequence equivalent models for the fault ride-through state of the grid-connected inverter based on the control structure under the normal operation state and fault ride-through state of the grid-connected inverter, respectively.

[0017] The data acquisition module is configured to: obtain the voltage and current phasors at the output of the grid-type inverter power supply based on the three-phase voltage and three-phase current measurements collected at the protection installation point using the equivalent model; The parameter identification module is configured to: identify the reactive power-voltage droop coefficient of the grid-type inverter based on the reactive power and output voltage amplitude under steady-state operation after small disturbances; Based on the reactive power, output voltage amplitude, voltage phasor and current phasor in the transient process of grid-type inverter power supply, virtual internal potential calculation value and virtual internal potential measurement value are constructed, and the reactive power loop integral coefficient and virtual inductance value are identified by particle swarm optimization algorithm. The internal potential determination module is configured to: determine the virtual internal potential of the grid-type inverter before the fault based on the virtual inductance value and the voltage and current phasors at the output of the grid-type inverter. The impedance calculation module is configured to determine the positive sequence equivalent impedance of the grid-type inverter power supply under fault conditions based on the virtual internal potential before the fault and the positive sequence voltage and current phasors during the fault.

[0018] The above one or more technical solutions have the following beneficial effects: In the technical solution of this invention, the virtual inductive reactance parameter is first identified by the measurable electrical quantities under normal operating conditions, then the virtual internal potential before the fault is calculated based on the virtual inductive reactance parameter, and finally the positive sequence equivalent impedance is calculated by the positive sequence voltage and current under the fault ride-through state, thereby forming a parameter acquisition path from virtual inductance value to virtual internal potential and then to fault equivalent impedance.

[0019] Based on the three-phase voltage and three-phase current measurements collected at the protection installation point, the technical solution of this invention sequentially identifies the reactive power-voltage droop coefficient, reactive power loop integral coefficient, and virtual inductance value of the grid-type inverter power supply. Based on the virtual inductance value, the virtual internal potential before the fault is determined. Then, the positive sequence voltage and current phasors during the fault period are used to calculate the positive sequence equivalent impedance, thus realizing the progressive identification from reactive power control parameters, virtual inductive reactance parameters to the equivalent impedance under fault conditions.

[0020] The equivalent model parameter identification process in this invention does not rely on the internal controller parameters of the grid-type inverter, but only on the measurable electrical quantities at the protection installation point. This allows for direct application to the protection device side, providing a parameter basis for relay protection adaptability analysis and fault characteristic research. By constructing virtual internal potential calculation values ​​and virtual internal potential measurement values, and using the prior weighted mean square error between the two as the fitness function, the ability of the transient process parameter identification results to characterize the dynamic characteristics of the grid-type inverter can be improved.

[0021] Advantages of additional aspects of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0022] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0023] Figure 1 This is a schematic diagram of the main circuit and control structure of a grid-type inverter power supply under normal operating conditions. Figure 2 A schematic diagram of the equivalent model of a grid-connected inverter under normal operating conditions; Figure 3 A schematic diagram of a fault ride-through control structure using virtual impedance current limiting for grid-connected inverter power supplies; Figure 4(a) is a schematic diagram of the priority control current vector angle of a grid-type inverter power supply; Figure 4(b) is a schematic diagram of priority control of the d-axis current in a grid-type inverter power supply; Figure 4(c) is a schematic diagram of priority control of the q-axis current in a grid-type inverter power supply; Figure 5 A schematic diagram of the positive sequence equivalent model of a grid-type inverter power supply under fault ride-through condition; Figure 6 This is a flowchart of the progressive identification method for the equivalent model of a grid-type inverter power supply based on protection measurement quantities in an embodiment of the present invention. Figure 7(a) is a schematic diagram showing the comparison between the amplitude of the calculated impedance and the actual input impedance in the inverter in the embodiment of the present invention; Figure 7(b) is a schematic diagram showing the phase comparison results between the calculated impedance and the actual input impedance in the inverter in an embodiment of the present invention; Figure 7(c) is a schematic diagram of the magnitude error between the calculated impedance and the actual input impedance in the inverter in the embodiment of the present invention; Figure 7(d) is a schematic diagram of the phase error results between the calculated impedance and the actual input impedance in the inverter in an embodiment of the present invention; Figure 7(e) is a schematic diagram of the calculated impedance trajectory between the calculated impedance and the actual input impedance in the inverter in an embodiment of the present invention. Figure 8(a) is a schematic diagram of the calculation results of the two-phase short-circuit amplitude error under different fault types in the embodiment of the present invention; Figure 8(b) is a schematic diagram of calculating the two-phase short-circuit phase error under different fault types in an embodiment of the present invention; Figure 8(c) is a schematic diagram of calculating the amplitude error of a two-phase ground fault under different fault types in an embodiment of the present invention; Figure 8(d) is a schematic diagram of calculating the phase error of a two-phase ground fault under different fault types in an embodiment of the present invention; Figure 8(e) is a schematic diagram of calculating the amplitude error of a single-phase ground fault under different fault types in an embodiment of the present invention; Figure 8(f) is a schematic diagram of calculating the phase error of a single-phase ground fault under different fault types in an embodiment of the present invention; Figure 9 This is a schematic diagram comparing the equivalent impedance trajectories of grid-type inverters under different current limiting strategies in embodiments of the present invention. Detailed Implementation

[0024] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0025] It should be noted that the terminology used herein is for the purpose of describing particular implementations only and is not intended to limit the exemplary implementations of the present invention.

[0026] Where there is no conflict, the embodiments and features in the embodiments of the present invention can be combined with each other.

[0027] Example 1 Parameter identification methods for grid-connected inverters mainly focus on the identification of control parameters such as inertia and damping, with limited research on the online identification of reactive power control parameters, virtual internal potential, and equivalent impedance under fault conditions. Furthermore, existing methods typically rely on internal inverter control parameters or controller models, making them difficult to apply directly to protection devices.

[0028] Therefore, see appendix Figure 6 As shown in the figure, this embodiment discloses a progressive identification method for equivalent model parameters of a grid-connected inverter based on protection measurement. This method achieves online acquisition of equivalent model parameters under normal operation and fault ride-through conditions of the grid-connected inverter without relying on the internal controller parameters. The method ultimately outputs the reactive power-voltage droop coefficient K. q Reactive power loop integral coefficient K, virtual inductance value L IBR Virtual internal potential and positive sequence equivalent impedance under fault conditions Specifically, it includes: Step 1: Based on the control structure of the grid-connected inverter under normal operation and fault ride-through conditions, establish equivalent models for the grid-connected inverter under normal operation and positive sequence equivalent models for the grid-connected inverter under fault ride-through conditions, respectively. Step 2: Based on the three-phase voltage and three-phase current measurements collected at the protection installation point, obtain the voltage and current phasors at the output of the grid-type inverter power supply; Step 3: Based on the reactive power and output voltage amplitude under steady-state operation after small disturbance, identify the reactive power-voltage droop coefficient of the grid-type inverter. Step 4: Based on the reactive power, output voltage amplitude, voltage phasor and current phasor in the transient process of the grid-type inverter, construct the virtual internal potential calculation value and virtual internal potential measurement value, and identify the reactive power loop integral coefficient and virtual inductance value through the particle swarm optimization algorithm. Step 5: Based on the virtual inductance value and the voltage and current phasors at the output of the grid-type inverter, determine the virtual internal potential of the grid-type inverter before the fault. Step 6: Based on the virtual internal potential before the fault and the positive sequence voltage and current phasors during the fault, determine the positive sequence equivalent impedance of the grid-type inverter power supply under fault conditions.

[0029] This embodiment first identifies virtual inductive reactance parameters using measurable electrical quantities under normal operating conditions, then calculates the virtual internal potential before the fault based on the virtual inductive reactance parameters, and finally calculates the positive sequence equivalent impedance using positive sequence voltage and current under fault ride-through conditions. This forms a parameter acquisition path from virtual inductance value to virtual internal potential and then to fault equivalent impedance. It does not require obtaining the internal control parameters of the inverter, and can achieve progressive identification of equivalent model parameters of grid-type inverter power supply by relying only on measurable electrical quantities at the protection installation location. This can provide a model parameter basis for relay protection adaptability analysis and fault characteristic research.

[0030] The following is a detailed explanation of the progressive identification method for the equivalent model of a grid-type inverter power supply based on protection measurements proposed in this embodiment: In one implementation example, regarding step 1: Based on the control structure of the grid-connected inverter under normal operating conditions and fault ride-through conditions, equivalent models for the grid-connected inverter under normal operating conditions and positive-sequence equivalent models for the fault ride-through conditions are established respectively. To determine the relationship between the port voltage and current of the grid-connected inverter under different operating conditions, and thus establish the corresponding equivalent models, the control structures for normal operating conditions and fault ride-through conditions are described below.

[0031] Under normal operating conditions, the control structure of a grid-type inverter power supply is as follows: Figure 1 As shown. The control structure of a grid-type inverter includes an active-frequency control loop, a reactive-voltage control loop, a virtual inductive reactance loop, and voltage and current inner loops. The basic control equations of the power loop include the active-frequency control equation shown in equation (1) and the reactive-voltage control equation shown in equation (2): (1) (2) Equation (1) describes the relationship between active power deviation and virtual angular frequency dynamics. In the equation, D p The active power loop damping coefficient; J This is virtual inertia; P set , P These are the reference value and the actual value of active power, respectively. ω n and ω These are the virtual rated speed and the actual speed, respectively. Equation (2) describes the regulatory effect of reactive power deviation and voltage deviation on the amplitude of the virtual internal potential. Where, E This represents the amplitude of the virtual internal potential. Q set , Q These are the reference value and the actual value of reactive power, respectively. U n , U m These are the base voltage and the grid connection point voltage, respectively. K The reactive power loop integral coefficient; K q This is the reactive power-voltage droop coefficient. K q and K Identify them in steps 3 and 4 respectively.

[0032] Equations (1) and (2) are used to establish the equivalent model of normal operation. The parameters in equation (1) are not used as the variables to be identified in subsequent parameter identification. Equation (2) is then simplified by steady-state conditions to obtain equations (6) and (7), and then integrated to obtain equation (8), which is used to construct the virtual internal potential calculation value.

[0033] The virtual inductive reactance is used to simulate the internal reactance of the synchronous generator. The virtual inductive reactance will reduce the voltage inner loop reference value. Equations (3) and (4) respectively represent the generation relationship of the d-axis and q-axis voltage reference values: (3) (4) In the formula, u dref , u qref This is the reference value for the dq-axis voltage after virtual inductive reactance; i d and i q This refers to the dq-axis current output by the inverter; L IBR The virtual inductance value is given. Equations (3) and (4) are used to convert the virtual inductance control relationship into the port phasor relationship shown in equation (5), and further construct the virtual internal potential measurement value in equation (9).

[0034] When the grid-type inverter is in normal operation, according to equations (1) to (4), it can be equivalent to a controlled voltage source model consisting of a virtual internal potential and a virtual inductive reactance in series, such as... Figure 2 As shown, the magnitude and phase angle of the virtual internal potential E are determined by the power outer loop equation, and the virtual inductive reactance X in the figure... IBR The virtual inductance values ​​in equations (3) and (4) L IBR Decide. L IBR The corresponding virtual inductive reactance in the power frequency phasor domain is X. IBR =ω L IBR Therefore, the phasor relationship of the grid-type inverter power supply ports is obtained: (5) In the formula, E For grid-connected inverters, the virtual internal potential phasor is used. U v This refers to the voltage phasor at the output of a grid-connected inverter power supply. I v ω is the current phasor at the output of the grid-type inverter power supply, and ω is the angular frequency.

[0035] When the output voltage amplitude of the grid-connected inverter is lower than the set fault ride-through threshold, the grid-connected inverter switches from normal operation control state to fault ride-through control state, and suppresses the fault current through current limiting control. The fault ride-through threshold can be set according to the control requirements of the grid-connected inverter; in this embodiment, it can be set to 0.9 times the rated voltage.

[0036] Fault ride-through current limiting methods for grid-connected inverters include virtual impedance current limiting and direct current limiting. The virtual impedance current limiting method applies an additional virtual impedance based on the voltage drop at the grid-connected inverter's output voltage; the greater the voltage drop, the larger the virtual impedance applied. Simultaneously, during fault ride-through, the power outer loop is blocked, maintaining the virtual internal potential and frequency at their pre-fault states. Its control structure is as follows: Figure 3 As shown.

[0037] Direct current limiting limits the current reference value to ensure that the output current of the grid-connected inverter does not exceed the set maximum allowable current. Depending on the priority control quantity maintained during the current limiting process, the direct current limiting method includes three types: priority control of the current vector angle, priority control of the d-axis current, and priority control of the q-axis current, as shown in Figures 4(a), 4(b), and 4(c). Different direct current limiting methods correspond to different active and reactive current distribution relationships, causing the grid-connected inverter to exhibit different port voltage and current characteristics during fault periods.

[0038] Virtual impedance current limiting alters the port characteristics of a grid-connected inverter by adding virtual impedance, while direct current limiting alters the port characteristics by constraining the current reference value. Although their current limiting mechanisms differ, both methods, based on the external characteristics of the positive-sequence voltage and current at the grid-connected inverter port, can be equivalent to a positive-sequence voltage source connected in series with a positive-sequence equivalent impedance, such as... Figure 5 As shown.

[0039] In the fault ride-through state, the virtual internal potential under the steady-state operation before the fault occurs is used as the voltage source parameter in the positive-sequence equivalent model. The positive-sequence equivalent impedance is used to comprehensively characterize the influence of virtual impedance control, direct current limiting control, and the internal control loops of the grid-connected inverter on the positive-sequence voltage and current relationship at the port. Therefore, the positive-sequence equivalent model of the grid-connected inverter under fault ride-through state includes the virtual internal potential before the fault and the positive-sequence equivalent impedance connected in series with it.

[0040] In one implementation example, regarding step 2: Based on the three-phase voltage and three-phase current measurements collected at the protection installation point, the voltage and current phasors at the output of the grid-type inverter power supply are obtained.

[0041] The protection device synchronously acquires the three-phase voltage and three-phase current time-domain signals at the protection installation location according to a set sampling frequency, and performs a discrete Fourier transform using one power frequency cycle as the data window to obtain the fundamental phasors of the three-phase voltage and current at the protection installation location. Under fault conditions, a symmetrical component transform is further performed on the three-phase fundamental phasors to extract the positive sequence voltage and current phasors. Using fundamental extraction can reduce the influence of harmonics, switching ripple, and measurement noise on the parameter identification results.

[0042] The parameters of the lines and transformers between the protection installation point and the grid-type inverter power supply outlet are converted to a unified per-unit standard and equivalent to the series impedance Z. eq =R eq +jω L eq , where R eq and L eq The values ​​are determined by the known resistance and inductance parameters of the line and transformer, respectively. Taking the positive current direction as flowing from the grid-connected inverter output to the system side, the output current phasor is consistent with the current phasor at the protection installation point, and the output voltage phasor is equal to the sum of the voltage phasor at the protection installation point and the equivalent series impedance voltage drop. When the voltage levels on both sides are different, the values ​​are converted to the grid-connected inverter output side reference according to the transformer turns ratio, thus obtaining the output voltage phasor. U v and current phasor I v .

[0043] Step 2 obtained U v and I v The required output reactive power Q for calculating steps 3 and 4. calc and the output voltage amplitude U calc The virtual internal potential measurement value is used in equation (9), the virtual internal potential before the fault is calculated in equation (13), and the value is extracted during the fault. and Substitute into equation (14) to calculate the positive sequence equivalent impedance. This conversion process only relies on the measurements at the protection installation location and the known line and transformer parameters, without needing to read the internal variables of the grid-type inverter power controller, making it easy to implement directly on the protection device side.

[0044] In one implementation example, regarding step 3: Based on the reactive power and output voltage amplitude under steady-state operation after a small disturbance, identify the reactive-voltage droop coefficient of the grid-type inverter. K q This information is then used to identify the reactive power loop integral coefficient and the virtual inductance value.

[0045] Rearranging the reactive power-voltage control equation in equation (2), when U n U m When it is not equal to 0, we can obtain the reactive power-voltage droop coefficient. K q The expression: (6) This embodiment does not directly use equation (6) to solve. K qInstead, at the new steady-state operating point, dE / dt=0 is set to simplify equation (6) to equation (7).

[0046] Under small disturbance conditions where the output voltage of the grid-connected inverter remains above the fault ride-through threshold, the system enters a new steady-state operating point after a transient process, at which point dE / dt = 0. At the rated operating point, Q set =0, and per-unit processing is performed based on the rated voltage, then U n With a per-unit value of 1, the above formula can be simplified to: (7) In equation (7), Q calc The reactive power output of the grid-type inverter is calculated based on the output voltage and current phasors obtained in step 2. U calc The output voltage amplitude of the grid-type inverter power supply is calculated based on the measurements taken at the protection installation location.

[0047] In one implementation example, regarding step 4: based on the reactive power, output voltage amplitude, voltage phasor, and current phasor during the transient process of the grid-connected inverter, virtual internal potential calculation values ​​and virtual internal potential measurement values ​​are constructed respectively, and the reactive power loop integral coefficient and virtual inductance value are identified through particle swarm optimization algorithm. Specifically, equation (2) is integrated over time under per-unit conditions to obtain the virtual internal potential calculation value shown in equation (8); the amplitude of equation (5) is taken to obtain the virtual internal potential measurement value shown in equation (9). Theoretically, the two should be consistent, so the unknown parameters can be identified by minimizing the error between them. Among them, the reactive power and output voltage amplitude are obtained based on the voltage and current at the output of the grid-connected inverter obtained in step 2.

[0048] Based on the reactive-voltage control equation (2), the magnitude of the virtual internal potential is expressed as: (8) In the formula, E calc (t) represents the calculated virtual internal potential value obtained from the reactive-voltage control equation at time t; E0 represents the initial value of the virtual internal potential at the start of integration; K q The reactive power-voltage droop coefficient identified in step 3; Q calc (τ) represents the output reactive power at time τ; U calc (τ) represents the output voltage amplitude at time τ; E0 and K are the alternative identification quantities. Equation (8) forms the first calculation path for obtaining the virtual internal potential from the reactive power control equation.

[0049] Based on the voltage phasor, current phasor, and virtual inductive reactance relationships at the output of the grid-type inverter, a virtual internal potential measurement is constructed: (9) In the formula, E meas (t) represents the virtual internal potential measurement at time t. Let be the voltage phasor at the output of the grid-type inverter at time t. Let be the current phasor at the output of the grid-type inverter at time t, and be the voltage phasor and current phasor at the output of the grid-type inverter obtained in step 2, respectively. Equation (9) forms the second calculation path to obtain the virtual internal potential from the externally measurable port voltage and current.

[0050] The reactive power loop integral coefficient, the virtual inductance value, and the initial value of the virtual internal potential are used as the parameter vector to be identified: θ =[ K , L IBR , E 0] T (10) In equation (10), θ Let K be the parameter vector to be identified in the particle swarm optimization algorithm, and L be the integral coefficient of the reactive power loop. IBR Here, E0 represents the virtual inductance value, and T denotes the initial virtual internal potential at the start of integration. The search range for each parameter is preset based on the rated parameters of the grid-type inverter and the allowable range for the project. q Since it has already been obtained from step 3, it will not be included in the parameter vector again.

[0051] The fitness function is the prior weighted mean square error between the calculated virtual internal potential and the measured virtual internal potential. (11) In the formula, J ( θ ) is the parameter vector θ The corresponding fitness function, N To select the number of sampling points within the transient data window, t k For the k-th sampling time, w k This is the time-weighted coefficient.

[0052] (12) In the formula, λ is the attenuation coefficient, and t0 is the initial time of the disturbance. The time weighting coefficient decreases with time and is used to increase the weight of dynamic data in the initial stage of the disturbance in parameter identification. The particle swarm optimization algorithm is used to optimize the parameter vector θ to be identified, and the reactive power loop integral coefficient K and the virtual inductance value L are obtained. IBR And the initial value of the virtual internal potential E0. Where, L IBR This is used in step 5 to calculate the virtual internal potential before the fault. This step uses the virtual internal potential, which cannot be directly measured, as an intermediate constraint, which can improve the stability of parameter identification under conditions of limited measurement data and noise.

[0053] In one implementation example, regarding step 5: Based on the virtual inductance value and the voltage and current phasors at the output of the grid-type inverter, determine the virtual internal potential of the grid-type inverter before the fault.

[0054] Under normal operating conditions of a grid-connected inverter, based on the identified virtual inductance value L... IBR Combined with the voltage phasor at the output of the grid-type inverter power supply U v and current phasor I v Calculate the virtual internal potential of a grid-type inverter: (13) In equation (13), E IBR This refers to the virtual internal potential phasor of a grid-connected inverter under normal operating conditions. U v and I v These are the output voltage phasors and current phasors obtained in step 2, respectively. IBR Z represents the virtual equivalent impedance under normal operating conditions; when the virtual impedance is mainly inductive reactance, Z IBR =jωL IBR Where ω is determined by the system's rated frequency, and L IBR This was identified in step 4. To reduce measurement fluctuations, the steady-state data obtained before the fault occurred can be calculated within the specified window. E IBR Take the average value.

[0055] The virtual internal potential under steady-state operation before the fault occurs is used as the voltage source parameter in the positive sequence equivalent model under fault ride-through state.

[0056] In one implementation example, regarding step 6: Based on the virtual internal potential before the fault and the positive sequence voltage and current phasors during the fault obtained in step 5, the positive sequence equivalent impedance of the grid-type inverter under fault conditions is determined and used as the final equivalent model parameter of this method in the fault ride-through stage.

[0057] When the output voltage amplitude of a grid-type inverter falls below a set threshold, the grid-type inverter is determined to have entered fault ride-through mode. In fault ride-through mode, the positive-sequence network of the grid-type inverter can be equivalently represented as a voltage source model consisting of a virtual internal potential and a positive-sequence equivalent impedance connected in series before the fault, such as... Figure 5 As shown.

[0058] (14) In the formula, This refers to the positive sequence equivalent impedance of a grid-type inverter under fault conditions. The pre-fault steady-state virtual internal potential obtained in step 5 is... Positive sequence voltage phasor at the output of the grid-connected inverter during a fault. This is the positive sequence current phasor at the output of the grid-type inverter during a fault. and The values ​​are obtained from the three-phase voltage and current at the protection installation point through discrete Fourier transform, symmetrical component transform, and conversion of line and transformer parameters, as detailed in step 2. When the inverter enters the fault ride-through state, the above quantities are substituted into equation (14) to obtain the complex positive sequence equivalent impedance containing amplitude and phase angle.

[0059] Before calculating the positive-sequence equivalent impedance under fault conditions, a moving average filter is applied to the positive-sequence voltage phasor and positive-sequence current phasor during the fault period to reduce the impact of aperiodic components and measurement noise on the positive-sequence equivalent impedance identification results. The calculated... It can be used for fault calculation, relay protection setting, and adaptive analysis of grid-type inverter power supplies, and can reflect the equivalent impedance characteristics formed by different current limiting strategies such as virtual impedance current limiting, priority control of current vector angle, priority control of d-axis current, or priority control of q-axis current online. This step does not require prior knowledge of the impedance or current limiting parameters applied inside the fault-crossing controller, and can adapt to control strategy switching and track changes in equivalent impedance during faults.

[0060] Verification Implementation Examples This embodiment is used to illustrate the specific simulation verification process of the method described in this invention.

[0061] This embodiment uses PSCAD / EMTDC to build a simulation model of a grid-connected inverter power supply connected to the grid via a step-up transformer. The grid-connected inverter power supply adopts a virtual synchronous machine control method. To simulate small disturbance conditions in the actual power grid, a three-phase ground fault with a 20Ω transition resistor is set at the far end of the transmission line, causing the voltage amplitude at the output of the grid-connected inverter power supply to drop to 0.95pu of the rated value, with a fault duration of 80ms.

[0062] Substituting the steady-state data into equation (7), we obtain the reactive power-voltage droop coefficient K. qThe value is 10.4827. The reactive power loop integral coefficient K and the inherent virtual inductance L are identified using process quantities. IBR To reduce the impact of random errors on the identification results, the same dataset was subjected to parameter identification ten times, and the results were statistically processed.

[0063] In this embodiment, the identification results of reactive power control parameters and virtual inductance values ​​are shown in Table 1.

[0064] Table 1. Identification Results of Reactive Power Control Parameters and Virtual Inductance Values

[0065] As shown in Table 1, the identification error of each parameter to be determined is within 4%, which proves that the present invention can accurately identify the virtual inductance value and reactive power control parameters of the grid-type inverter power supply.

[0066] After completing the virtual inductance value L IBR After identification, the virtual internal potential of the grid-type inverter is calculated based on the voltage and current phasors collected at the protection installation point under normal system operation before the fault.

[0067] (15) Since the actual input value of the virtual impedance can be directly obtained in the controller, the virtual impedance current limiting method is tested first to verify the reliability of the method. A three-phase metallic fault is set in the sending line to simulate the fault situation in the actual project. The positive sequence voltage and current are collected in real time during the fault, and the positive sequence equivalent impedance is calculated based on equation (14).

[0068] The calculated impedance was compared with the actual input impedance within the inverter. Figures 7(a) and 7(b) show the amplitude and phase comparison results of the calculated impedance and the actual input impedance within the inverter in the time domain, respectively. Figures 7(c) and 7(d) show the amplitude and phase errors of the calculated impedance and the actual input impedance within the inverter in the time domain, respectively. Figure 7(e) shows the trajectory of the calculated impedance over time. It can be seen that after one half-cycle, the impedance amplitude error is less than 5%, and the phase error is within 5°, indicating that the impedance amplitude and phase can quickly track the changes in the actual equivalent impedance during the dynamic process of the system.

[0069] Furthermore, tests were conducted on two-phase short circuits, two-phase ground faults, and single-phase ground faults. The amplitude and phase errors of the impedance and the actual input impedance within the inverter in the time domain were calculated. Figure 8(a) shows the calculated amplitude error of the two-phase short circuit under different fault types in this embodiment; Figure 8(b) shows the calculated phase error of the two-phase short circuit under different fault types in this embodiment; Figure 8(c) shows the calculated amplitude error of the two-phase ground fault under different fault types in this embodiment; Figure 8(d) shows the calculated phase error of the two-phase ground fault under different fault types in this embodiment; Figure 8(e) shows the calculated amplitude error of the single-phase ground fault under different fault types in this embodiment; Figure 8(f) shows the calculated phase error of the single-phase ground fault under different fault types in this embodiment. Under various fault conditions, the impedance calculation error exhibits brief fluctuations in the initial stage of system disturbance, but within two cycles, the impedance amplitude error can be controlled within 5% and the phase error within 5°, ensuring good results.

[0070] Next, the direct current limiting method is identified. The same method is used to test three current limiting methods: priority control of the current vector angle, priority control of the d-axis current, and priority control of the q-axis current. The equivalent impedance trajectories under different current limiting strategies are shown below. Figure 9 As shown, the equivalent impedance exhibits significant differences under different current limiting strategies: the current limiting strategy that prioritizes controlling the current vector angle exhibits resistive characteristics; the current limiting strategy that prioritizes controlling the d-axis current exhibits capacitive characteristics; and the current limiting strategy that prioritizes controlling the q-axis current and virtual impedance exhibits inductive characteristics. These differences indicate that this invention can obtain the equivalent impedance of a grid-type inverter under fault conditions under different current limiting strategies online.

[0071] Example 2 The purpose of this embodiment is to provide a computer device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the program to implement the steps of the above-described method.

[0072] Example 3 The purpose of this embodiment is to provide a computer-readable storage medium.

[0073] A computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, performs the steps of the above method.

[0074] Example 4 The purpose of this embodiment is to provide a method and system for parameter identification of equivalent models of grid-type inverter power supplies, including: The equivalent model construction module is configured to: build equivalent models of grid-type inverters under normal operating conditions and fault ride-through conditions; The data acquisition module is used to collect the three-phase voltage and three-phase current measurements at the protection installation point, and to obtain the voltage and current phasors at the outlet of the grid-type inverter power supply based on the three-phase voltage and three-phase current measurements.

[0075] The parameter identification module is used to identify the reactive power-voltage droop coefficient based on the reactive power and output voltage amplitude under steady-state operation after small disturbances, and to identify the reactive power loop integral coefficient and virtual inductance value based on the virtual internal potential calculation value and virtual internal potential measurement value during the transient process.

[0076] The internal potential determination module is used to determine the virtual internal potential of the grid-type inverter before a fault, based on the identified virtual inductance value and the voltage and current phasors at the output of the grid-type inverter.

[0077] The impedance calculation module is used to determine the positive sequence equivalent impedance of a grid-type inverter under fault conditions based on the virtual internal potential before the fault and the positive sequence voltage and current phasors during the fault.

[0078] Example 5 The purpose of this embodiment is to provide a computer program product containing instructions that, when run on a computer, cause the computer to perform the methods and functions involved in any of the above embodiments.

[0079] The steps and methods involved in the apparatus of the above embodiments correspond to those in Embodiment 1. For specific implementation details, please refer to the relevant description section of Embodiment 1. The term "computer-readable storage medium" should be understood as a single medium or multiple media including one or more instruction sets; it should also be understood as including any medium capable of storing, encoding, or carrying an instruction set for execution by a processor and enabling the processor to perform any of the methods in this invention.

[0080] Those skilled in the art will understand that the modules or steps of the present invention described above can be implemented using general-purpose computer devices. Optionally, they can be implemented using computer-executable program code, thereby allowing them to be stored in a storage device for execution by a computer device, or they can be fabricated as separate integrated circuit modules, or multiple modules or steps can be fabricated as a single integrated circuit module. The present invention is not limited to any particular combination of hardware and software.

[0081] While the specific embodiments of the present invention have been described above in conjunction with the accompanying drawings, this is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without creative effort based on the technical solutions of the present invention are still within the scope of protection of the present invention.

Claims

1. A method for parameter identification of an equivalent model of a grid-connected inverter power supply, characterized in that it includes: Establish equivalent models of grid-connected inverters under normal operating conditions and fault ride-through conditions; Based on the equivalent model, the three-phase voltage and three-phase current measurements collected at the protection installation point are used to obtain the voltage and current phasors at the output of the grid-type inverter power supply. Based on the reactive power and output voltage amplitude under steady-state operation after small disturbances, the reactive power-voltage droop coefficient of the grid-type inverter is identified. Based on the reactive power, output voltage amplitude, voltage phasor and current phasor in the transient process of grid-type inverter power supply, virtual internal potential calculation value and virtual internal potential measurement value are constructed, and the reactive power loop integral coefficient and virtual inductance value are identified by particle swarm optimization algorithm. Based on the virtual inductance value and the voltage and current phasors at the output of the grid-type inverter, the virtual internal potential of the grid-type inverter before the fault is determined. Based on the virtual internal potential before the fault and the positive sequence voltage and current phasors during the fault, the positive sequence equivalent impedance of the grid-type inverter power supply under fault conditions is determined. The steps for identifying the reactive power loop integral coefficient and the virtual inductance value are as follows: Based on the reactive-voltage control equations in the equivalent model of a grid-type inverter under normal operating conditions, the virtual internal potential amplitude is obtained by utilizing the reactive power and output voltage amplitude during the transient process. Based on the voltage phasor, current phasor, and virtual inductive reactance relationship at the output of the grid-type inverter power supply, a virtual internal potential measurement value is constructed. The reactive power loop integral coefficient, virtual inductance value, and initial value of virtual internal potential are used as the parameter vector to be identified. The fitness function is the early weighted mean square error between the calculated virtual internal potential and the measured virtual internal potential. The early weighted mean square error is determined based on the time weighting coefficient, which decreases with the sampling time to increase the weight of the dynamic data in the initial stage of the disturbance in the parameter identification process. The particle swarm optimization algorithm is used to optimize the vector of parameters to be identified, and the reactive power loop integral coefficient, virtual inductance value and initial value of virtual internal potential are obtained.

2. The method for parameter identification of equivalent model of grid-type inverter power supply as described in claim 1, characterized in that, The method for obtaining the voltage and current phasors at the output of a grid-connected inverter is as follows: Acquire the time-domain signals of three-phase voltage and three-phase current at the protection installation location; Extract the fundamental components of the three-phase voltage and three-phase current to obtain the fundamental phasors of the voltage and current at the protection installation location; By combining the line parameters or transformer parameters, the fundamental phasors of voltage and current at the protection installation point are converted to the output of the grid-type inverter power supply to obtain the voltage phasors and current phasors at the output of the grid-type inverter power supply.

3. The method for parameter identification of equivalent model of grid-type inverter power supply as described in claim 1, characterized in that, The steps for identifying the reactive power-voltage droop factor of a grid-connected inverter are as follows: When the output voltage of the grid-connected inverter is not lower than the fault ride-through threshold, obtain the reactive power and output voltage amplitude under steady-state operation after small disturbances. Based on the condition that the rate of change of virtual internal potential is zero under steady-state operation, the reactive power-voltage droop coefficient of the grid-type inverter power supply is determined.

4. The method for parameter identification of equivalent model of grid-type inverter power supply as described in claim 1, characterized in that, When determining the virtual internal potential of a grid-connected inverter before a fault, the following steps are included: Under normal operating conditions of the grid-type inverter, the virtual internal potential of the grid-type inverter is calculated based on the identified virtual inductance value and the voltage phasor and current phasor at the output of the grid-type inverter. The virtual internal potential under steady-state operation before the fault occurs is used as the voltage source parameter in the positive sequence equivalent model under fault ride-through state.

5. The method for parameter identification of equivalent model of grid-connected inverter power supply as described in claim 1, characterized in that, When determining the positive-sequence equivalent impedance of a grid-type inverter under fault conditions, the following is included: When the output voltage amplitude of the grid-connected inverter is lower than the set threshold, the grid-connected inverter is determined to have entered the fault ride-through state. Extract the positive sequence voltage phasor and positive sequence current phasor at the output of the grid-type inverter during the fault period; Based on the virtual internal potential before the fault, the positive sequence voltage phasor during the fault, and the positive sequence current phasor during the fault, the positive sequence equivalent impedance of the grid-type inverter under fault conditions is calculated. Under fault ride-through conditions, the positive sequence network of a grid-type inverter power supply can be equivalently represented as a voltage source model consisting of a virtual internal potential before the fault and a positive sequence equivalent impedance connected in series. The positive sequence voltage phasor and positive sequence current phasor during the fault period are subjected to moving average filtering. Calculate the positive sequence equivalent impedance of a grid-type inverter under fault conditions.

6. A system for identifying parameters of an equivalent model of a grid-connected inverter, employing the parameter identification method for an equivalent model of a grid-connected inverter as described in any one of claims 1-5, characterized in that, include: The equivalent model construction module is configured to: establish equivalent models of grid-type inverters under normal operating conditions and fault ride-through conditions; The data acquisition module is configured to: obtain the voltage and current phasors at the output of the grid-type inverter power supply based on the three-phase voltage and three-phase current measurements collected at the protection installation point using the equivalent model; The parameter identification module is configured to: identify the reactive power-voltage droop coefficient of the grid-type inverter based on the reactive power and output voltage amplitude under steady-state operation after small disturbances; Based on the reactive power, output voltage amplitude, voltage phasor and current phasor in the transient process of grid-type inverter power supply, virtual internal potential calculation value and virtual internal potential measurement value are constructed, and the reactive power loop integral coefficient and virtual inductance value are identified by particle swarm optimization algorithm. The internal potential determination module is configured to: determine the virtual internal potential of the grid-type inverter before the fault based on the virtual inductance value and the voltage and current phasors at the output of the grid-type inverter. The impedance calculation module is configured to determine the positive sequence equivalent impedance of the grid-type inverter power supply under fault conditions based on the virtual internal potential before the fault and the positive sequence voltage and current phasors during the fault.

7. A computer program product, comprising a computer program, characterized in that, When the computer program is executed by a processor, it implements the method of any one of claims 1-5.

8. A computer device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the processor executes the program, it implements the steps of the method described in any one of claims 1-5.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the program is executed by the processor, it performs the steps of the method described in any one of claims 1-5.

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