High-resistance grid-connected inverter transient stability method, system, device and medium

Abstract

The present application relates to a kind of high resistance network configuration network type inverter transient stability method, system, equipment and medium, the method includes obtaining operating electrical quantity, power reference, maximum allowable current, virtual impedance and grid impedance;Based on operating electrical quantity and power reference, reverse droop control is carried out, internal potential and original current reference are obtained;The original current reference is carried out ring current limiting, obtains current limiting coefficient, and is adjusted according to this virtual impedance and is superimposed with grid impedance, obtains equivalent impedance;Based on internal potential, operating electrical quantity and equivalent impedance, the transient relationship that reactive power changes with power angle is determined, and the transient balance point determination result and virtual impedance parameter relationship are obtained in combination with transient balance constraint;Accordingly determine target virtual impedance and configure to network configuration type inverter.The present application has the effect of improving fault transient stability.

Description

Technical Field

[0001] This invention belongs to the technical field of grid-connected inverter control, and in particular relates to a transient stabilization method, system, equipment and medium for a high-impedance grid-connected inverter. Background Technology

[0002] Currently, with the continuous grid connection of renewable energy sources such as wind and solar power, the proportion of power sources with inverter interfaces in the power grid is constantly increasing. Low-voltage distribution networks and microgrids typically have high resistance-to-reactance ratios, and grid-connected inverters are susceptible to operational constraints such as power coupling changes, reduced system strength, and limited overcurrent margins of devices during load surges and grid voltage dips.

[0003] Existing grid-connected inverters typically configure control parameters for current-limited operation based on conventional power control relationships. However, during voltage drops in high-impedance distribution networks, changes in impedance characteristics under current-limited conditions can cause the judgment of transient operation to deviate from reality, easily leading to a continuous increase in the power angle and power oscillations, which can affect the stable recovery after a fault. Summary of the Invention

[0004] The purpose of this invention is to provide a transient stabilization method, system, device and medium for high-resistance grid-connected inverters, so as to solve the technical problem of inaccurate stability judgment in the current-limiting transient process of existing control methods.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a transient stabilization method for a high-resistivity grid-connected inverter, the method comprising: Obtain operating electrical quantities, power reference, maximum allowable current, virtual impedance, and grid impedance; Under high-resistance distribution network conditions, reverse droop control is performed based on the operating electrical quantities and the power reference to obtain the internal potential and the original current reference. Based on the original current reference and the maximum allowable current, a ring current limit is performed to obtain a current limit coefficient. The virtual impedance is adjusted according to the current limit coefficient, and then the adjusted virtual impedance is superimposed with the grid impedance to obtain the equivalent impedance. Based on the internal potential, the operating electrical quantities, and the equivalent impedance, the transient relationship of reactive power changing with the power angle is determined. Based on the current limiting coefficient, the maximum allowable current, and the power reference, the transient balance constraint is determined. Based on the transient balance constraint, the transient relationship is analyzed to obtain the transient balance point determination result and the parameter relationship between the transient balance point angle and the virtual impedance. The target virtual impedance is determined based on the transient equilibrium point determination result and the parameter relationship between the transient equilibrium point angle and the virtual impedance, and the target virtual impedance is configured to the grid-type inverter.

[0006] By adopting the above technical solutions, and by acquiring operating electrical quantities, power reference, maximum allowable current, virtual impedance, and grid impedance, a unified operational basis can be provided for reverse droop control, current limiting analysis, and impedance configuration, thereby improving the accuracy of subsequent transient analysis results. By implementing reverse droop control under high-resistance distribution network conditions, and obtaining the internal potential and original current reference, the power control relationship can be adapted to the power coupling characteristics of high-resistance and high-reactance distribution networks, thereby reducing the mutual interference between active and reactive power regulation. Through ring current limiting based on the original current reference and maximum allowable current, and adjusting the virtual impedance according to the current limiting coefficient, the relationship with the grid impedance can be improved. Superposition can reflect the change in impedance state before and after current limiting triggering, thus providing an accurate equivalent impedance basis for the transient behavior of the inverter during faults; by determining the transient relationship of reactive power with power angle and combining it with transient balance constraints for analysis, it is possible to determine whether a transient balance point exists and the influence of virtual impedance on the transient balance point angle, thereby avoiding power oscillations and transient instability caused by the continuous increase of power angle; by determining the target virtual impedance based on the transient balance point determination result and the virtual impedance parameter relationship and configuring it to the grid-type inverter, the virtual impedance parameters can be matched with the current transient operating state, thereby improving the stable recovery capability after voltage drop.

[0007] In one example, the invention can be further configured such that: the step of performing reverse droop control based on the operating electrical quantity and the power reference to obtain the internal potential and the original current reference includes: Determine the active power and reactive power from the operating electrical quantities; The preset reference grid angular frequency is adjusted based on the deviation between the reactive power reference and the reactive power in the power reference to obtain the angular frequency; The voltage amplitude reference is determined based on the deviation between the active power reference and the active power in the power reference. The internal voltage angle reference is determined based on the angular frequency, and the internal potential is determined based on the internal voltage angle reference and the voltage amplitude reference. The internal potential is used as the control reference for the voltage and current inner loop, and the original current reference is generated through virtual admittance control.

[0008] By adopting the above technical solutions, active and reactive power can be determined from operating electrical quantities, and the angular frequency can be adjusted according to the reactive power deviation. The voltage amplitude reference can be determined according to the active power deviation, thereby forming a reverse droop control quantity adapted to high-resistance distribution networks. This improves the power regulation adaptability of grid-type inverters under high resistance and reactance ratio conditions. By determining the internal voltage angle reference according to the angular frequency and combining it with the voltage amplitude reference to determine the internal potential, an internal voltage control basis containing both amplitude and phase information can be formed, thereby enabling grid-type inverters to have stable voltage build-up capability. By using the internal potential as the control reference for the voltage and current inner loop and generating the original current reference through virtual admittance control, the internal potential change can be converted into the corresponding current control quantity, thereby providing a reliable input for subsequent loop current limiting.

[0009] In one example, the present invention can be further configured such that determining the internal voltage angle reference based on the angular frequency includes: Integrating the angular frequency yields the change in internal voltage angle; The internal voltage angle is updated based on the change in internal voltage angle to obtain the current internal voltage angle; The current internal voltage angle is determined as the internal voltage angle reference.

[0010] By adopting the above technical solution, the change in internal voltage angle is obtained by integrating the angular frequency, and the current internal voltage angle is updated according to the change in internal voltage angle. This allows the internal voltage angle to be continuously adjusted according to the angular frequency change caused by reactive power deviation, thereby avoiding abrupt changes in the internal potential phase. By determining the current internal voltage angle as the internal voltage angle reference, real-time phase basis can be continuously provided for the generation of internal potential, thereby improving the power angle tracking stability in the reverse droop control process.

[0011] In one example, the present invention can be further configured as follows: performing ring current limiting based on the original current reference and the maximum allowable current to obtain a current limiting coefficient, adjusting the virtual impedance according to the current limiting coefficient, and then superimposing the adjusted virtual impedance and the grid impedance to obtain an equivalent impedance, including: Determine the amplitude of the original current reference; The amplitude of the original current reference is compared with the maximum allowable current; When the amplitude of the original current reference does not exceed the maximum allowable current, the current limiting coefficient is determined to be: When the amplitude of the original current reference exceeds the maximum allowable current, the amplitude of the original current reference is limited while the phase angle remains unchanged, and the current limiting coefficient is determined based on the ratio of the amplitude of the original current reference to the maximum allowable current. The virtual impedance is adjusted according to the current limiting coefficient to obtain the adjusted virtual impedance. The adjusted virtual impedance is then superimposed with the grid impedance to obtain the equivalent impedance.

[0012] By adopting the above technical solutions, the triggering state of the ring current limiter can be accurately identified by determining the amplitude of the original current reference and comparing it with the maximum allowable current, thereby preventing the output current of the grid-connected inverter from exceeding the allowable range. By determining the current limiting coefficient to 1 when the amplitude of the original current reference does not exceed the maximum allowable current, the virtual impedance under normal operating conditions can be kept unchanged, thereby avoiding unnecessary impedance adjustments from affecting steady-state power output. By limiting the amplitude of the original current reference and keeping the phase angle unchanged when it exceeds the maximum allowable current, the current reference direction can be maintained while protecting power devices, thereby reducing the disturbance of the current limiting process to the power control state. By adjusting the virtual impedance according to the current limiting coefficient and superimposing it with the grid impedance, the equivalent impedance under current limiting conditions can be obtained, thereby providing impedance parameters that are consistent with the actual operating state for subsequent transient balance analysis.

[0013] In one example, the present invention can be further configured as follows: adjusting the virtual impedance according to the current limiting coefficient to obtain the adjusted virtual impedance, and then superimposing the adjusted virtual impedance with the grid impedance to obtain the equivalent impedance, includes: The virtual impedance is decomposed into virtual resistance and virtual reactance determined by virtual inductance, and the grid impedance is decomposed into grid resistance and grid reactance. The virtual resistance and the virtual reactance are adjusted proportionally according to the current limiting coefficient to obtain the adjusted virtual resistance and the adjusted virtual reactance. The adjusted virtual resistance is superimposed on the grid resistance to obtain the equivalent resistance; The adjusted virtual reactance is superimposed with the grid reactance to obtain the equivalent reactance; The equivalent impedance is determined based on the equivalent resistance and the equivalent reactance.

[0014] By adopting the above technical solutions, and by decomposing virtual impedance into virtual resistance and virtual reactance, and grid impedance into grid resistance and grid reactance, the resistive and inductive components of the impedance can be processed separately, thereby improving the clarity of the equivalent impedance construction. By proportionally adjusting the virtual resistance and virtual reactance according to the current limiting coefficient, the dynamic amplification characteristics of the virtual impedance after the ring current limiting is triggered can be reflected, thus ensuring that the equivalent impedance remains consistent with the current limiting state. By superimposing the adjusted virtual resistance with the grid resistance and the adjusted virtual reactance with the grid reactance respectively, the equivalent resistance and equivalent reactance under the current limiting state can be obtained, thereby accurately characterizing the comprehensive impedance characteristics between the inverter and the grid. By determining the equivalent impedance based on the equivalent resistance and equivalent reactance, a complete impedance basis can be provided for the transient relationship analysis between reactive power and power angle, thereby improving the reliability of transient stability determination.

[0015] In one example, the present invention can be further configured as follows: determining the transient relationship of reactive power changing with power angle based on the internal potential, the operating electrical quantity, and the equivalent impedance; determining transient balance constraints based on the current limiting coefficient, the maximum allowable current, and the power reference; and analyzing the transient relationship based on the transient balance constraints to obtain the transient balance point determination result and the parametric relationship between the transient balance point angle and the virtual impedance, including: Based on the internal potential, the grid voltage in the operating electrical quantities, and the equivalent impedance, the relationship between reactive power and output current amplitude and power angle is determined, and the transient relationship is obtained. The current limiting constraint corresponding to the output current amplitude is determined based on the relationship between the output current amplitude and the power angle, the current limiting coefficient and the maximum allowable current, and the reactive power balance constraint is determined based on the reactive power reference in the power reference, thus obtaining the transient balance constraint. Based on the comparison between the reactive power reference and the maximum and minimum reactive power values ​​in the transient relationship, the existence state of the transient equilibrium point is determined, and the grid voltage that makes the reactive power reference equal to the maximum or minimum reactive power value is determined as the critical grid drop voltage, thus obtaining the transient equilibrium point determination result. When the transient equilibrium point determination result indicates the existence of a transient equilibrium point, a constraint relationship is established between the power angle, the current limiting coefficient, and the virtual impedance based on the current limiting constraint and the reactive power balance constraint. Using the virtual resistance and virtual inductance in the virtual impedance as parameters to be analyzed, the relationship between the transient equilibrium point angle and the virtual resistance and virtual inductance is determined according to the constraint relationship, thus obtaining the parameter relationship between the transient equilibrium point angle and the virtual impedance.

[0016] By adopting the above technical solution, and determining the relationship between reactive power and output current amplitude and power angle variation based on internal potential, grid voltage, and equivalent impedance, a nonlinear transient relationship under reverse droop control can be established, thus reflecting the impact of power angle variation on reactive power and output current during voltage dips. By determining current limiting constraints and reactive power balance constraints based on output current amplitude relationship, current limiting coefficient, maximum allowable current, and reactive power reference, current boundaries and power balance conditions under transient operating conditions can be defined, thus providing a unified basis for determining the transient balance point. Furthermore, by comparing the reactive power reference with the reactive power... By determining the maximum and minimum power values ​​and identifying the critical grid voltage drop, we can judge whether a transient equilibrium point exists and the allowable voltage drop range of the grid, thereby identifying in advance operating states where the power angle may continuously increase. By establishing the constraint relationship between the power angle, current limiting coefficient, and virtual impedance, we can reveal the coupling effect between the current limiting state and virtual impedance, thereby improving the pertinence of virtual impedance parameter analysis. By analyzing the relationship between the transient equilibrium point angle and the changes in virtual resistance and virtual inductance, we can obtain the adjustment direction of virtual impedance parameters, thus providing a basis for reducing the transient equilibrium point angle and improving the transient stability margin.

[0017] In one example, the present invention can be further configured as follows: determining the target virtual impedance based on the transient equilibrium point determination result and the parametric relationship between the transient equilibrium point angle and the virtual impedance includes: Based on the transient equilibrium point existence status in the transient equilibrium point determination result, and the comparison result between the critical grid drop voltage and the grid voltage in the operating electrical quantity, virtual impedance parameter combinations that do not satisfy the transient equilibrium constraint are screened out in the preset virtual impedance parameter search space to obtain candidate virtual impedance parameter combinations. Based on the parameter relationship between the transient equilibrium point angle and the virtual impedance, determine the parameter adjustment direction of the virtual resistance and virtual inductance in the candidate virtual impedance parameter combination; A multi-objective cost function is constructed based on the candidate virtual impedance parameter combination. The multi-objective cost function includes the transient equilibrium point angle cost, the absolute error integral index of dynamic power fluctuation, and the steady-state active power loss penalty term. Using a Gaussian process as a probabilistic proxy model, a posterior probability distribution is constructed based on the candidate virtual impedance parameter combination and the multi-objective cost function. The target virtual impedance is determined from the candidate virtual impedance parameter combinations based on the posterior probability distribution, the desired improvement acquisition function, and the parameter adjustment direction.

[0018] By adopting the above technical solutions, virtual impedance parameter combinations that do not meet the transient balance constraints can be screened out based on the existence of the transient equilibrium point and the comparison between the critical grid drop voltage and the grid voltage. This allows for the pre-elimination of parameter regions that cannot maintain transient balance, thus avoiding invalid calculations within infeasible parameter ranges. Furthermore, by determining the parameter adjustment direction of virtual resistance and virtual inductance based on the parameter relationship between the transient equilibrium point angle and virtual impedance, stability guidance can be provided for the selection of candidate virtual impedance parameter combinations, thereby improving the effectiveness of target virtual impedance determination. Constructing a multi-objective cost function based on candidate virtual impedance parameter combinations, which includes the transient equilibrium point angle cost, the dynamic power fluctuation absolute error integral index, and the steady-state active power reduction penalty term, can balance transient stability margin, dynamic power fluctuation, and steady-state load-carrying capacity, thus avoiding a decrease in steady-state power output capacity due to solely pursuing damping. Finally, by constructing a posterior probability distribution and combining it with the desired improvement acquisition function and parameter adjustment direction to determine the target virtual impedance, both known excellent regions and regions to be explored can be considered within the candidate parameter range, thereby improving the efficiency and globality of virtual impedance parameter optimization.

[0019] In a second aspect, the present invention provides a transient stability system for a high-resistivity grid-connected inverter, the system comprising: The data acquisition module is used to acquire operating electrical quantities, power reference, maximum allowable current, virtual impedance, and grid impedance; The droop control module is used to perform reverse droop control under high-resistance distribution network conditions based on the operating electrical quantities and the power reference to obtain the internal potential and the original current reference. The current limiting modeling module is used to perform ring current limiting based on the original current reference and the maximum allowable current to obtain the current limiting coefficient, adjust the virtual impedance according to the current limiting coefficient, and then superimpose the adjusted virtual impedance and the grid impedance to obtain the equivalent impedance. The balance analysis module is used to determine the transient relationship of reactive power changing with power angle based on the internal potential, the operating electrical quantity and the equivalent impedance, determine the transient balance constraint based on the current limiting coefficient, the maximum allowable current and the power reference, and analyze the transient relationship based on the transient balance constraint to obtain the transient balance point determination result and the parameter relationship between the transient balance point angle and the virtual impedance. The impedance configuration module is used to determine the target virtual impedance based on the transient equilibrium point determination result and the parameter relationship between the transient equilibrium point angle and the virtual impedance, and to configure the target virtual impedance to the grid-type inverter.

[0020] By adopting the above technical solutions, and by acquiring operating electrical quantities, power reference, maximum allowable current, virtual impedance, and grid impedance, a unified operational basis can be provided for reverse droop control, current limiting analysis, and impedance configuration, thereby improving the accuracy of subsequent transient analysis results. By implementing reverse droop control under high-resistance distribution network conditions, and obtaining the internal potential and original current reference, the power control relationship can be adapted to the power coupling characteristics of high-resistance and high-reactance distribution networks, thereby reducing the mutual interference between active and reactive power regulation. Through ring current limiting based on the original current reference and maximum allowable current, and adjusting the virtual impedance according to the current limiting coefficient, the relationship with the grid impedance can be improved. Superposition can reflect the change in impedance state before and after current limiting triggering, thus providing an accurate equivalent impedance basis for the transient behavior of the inverter during faults; by determining the transient relationship of reactive power with power angle and combining it with transient balance constraints for analysis, it is possible to determine whether a transient balance point exists and the influence of virtual impedance on the transient balance point angle, thereby avoiding power oscillations and transient instability caused by the continuous increase of power angle; by determining the target virtual impedance based on the transient balance point determination result and the virtual impedance parameter relationship and configuring it to the grid-type inverter, the virtual impedance parameters can be matched with the current transient operating state, thereby improving the stable recovery capability after voltage drop.

[0021] In a third aspect, the present invention provides an electronic device, including a memory and a processor, wherein the memory stores a computer program, and the processor executes the computer program to implement the steps of the transient stabilization method for a high-impedance distribution network inverter.

[0022] In a fourth aspect, the present invention provides a computer-readable storage medium having a computer program stored thereon, wherein the computer program, when executed by a processor, implements the steps of the transient stabilization method for a high-impedance grid-type inverter. Attached Figure Description

[0023] The accompanying drawings, which form part of this specification, 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 undue limitation of the invention. In the drawings: Figure 1 This is a flowchart of a transient stabilization method for a high-resistance grid-connected inverter in an embodiment of the present invention; Figure 2 This is a schematic diagram of the GFM inverter system structure based on reverse droop control in an embodiment of the present invention; Figure 3 This is a schematic diagram of the equivalent circuit model of the GFM inverter containing a ring current limiter in an embodiment of the present invention; Figure 4 This is a schematic diagram of the Q-δ trajectory analysis when the grid voltage drops from 1 p.u. to 0.5 p.u. in an embodiment of the present invention; Figure 5 This is a schematic diagram of the Q-δ trajectory analysis when the grid voltage drops from 1 p.u. to 0.05 p.u. in an embodiment of the present invention. Figure (a) shows the case with a short fault duration, and Figure (b) shows the case with a long fault duration. Figure 6 This is a three-dimensional surface diagram showing the variation of δTEP with virtual resistance Rv and virtual inductance Lv in an embodiment of the present invention. Figure 7 This is a schematic diagram of the iterative process of the Bayesian optimization algorithm in an embodiment of the present invention; Figure 8 These are time-domain experimental waveforms at different voltage drop depths in embodiments of the present invention, wherein Figures (a), (b), and (c) are time-domain experimental waveforms at voltage drop depths of 0.5 pu, 0.3 pu, and 0.2 pu, respectively. Figure 9 These are time-domain experimental waveforms of different fault durations when the grid voltage depth drops to 0.01 pu in an embodiment of the present invention. Figure (a) shows the case where the fault recovers after 3 seconds, and Figure (b) shows the case where the fault recovers after 5 seconds. Figure 10 This is a comparison diagram of the transient time-domain response of the traditional droop control diagram (a) and the reverse droop control diagram (b) of the present invention when the grid voltage drops to 0.5 pu in an embodiment of the present invention. Figure 11 This is a comparison of the transient time-domain response of the traditional droop control diagram (a) and the reverse droop control diagram (b) of the present invention when the grid voltage drops to 0.3 pu in an embodiment of the present invention. Figure 12 This is a comparison diagram of the transient time-domain response of the traditional droop control diagram (a) and the reverse droop control diagram (b) of the present invention when the grid voltage drops to 0.1 pu in an embodiment of the present invention. Figure 13 This is a structural block diagram of the transient stability system of a high-resistance grid-connected inverter in an embodiment of the present invention; Figure 14 This is a structural block diagram of an electronic device according to an embodiment of the present invention. Detailed Implementation

[0024] The present invention will now be described in detail with reference to the accompanying drawings and embodiments. It should be noted that, unless otherwise specified, the embodiments and features described herein can be combined with each other.

[0025] The following detailed description is exemplary and intended to provide further detailed explanation of the invention. Unless otherwise specified, all technical terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art. The terminology used in this invention is for describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention.

[0026] Example 1 like Figure 1 As shown, this invention discloses a transient stabilization method for a high-resistivity grid-connected inverter, specifically including the following steps: S10: Obtain operating electrical quantities, power reference, maximum allowable current, virtual impedance, and grid impedance.

[0027] Specifically, the operating electrical quantities include the voltage at the common coupling point, the inverter output current, and the power quantities used to characterize the inverter's operating status. The power reference includes active power reference and reactive power reference. The maximum allowable current is set according to the output current amplitude that the grid-connected inverter can withstand. The virtual impedance includes impedance parameters used for voltage and current inner loop control. The grid impedance includes the line impedance parameters corresponding to the grid-connected inverter when it is connected to the AC grid through the common coupling point. All data are acquired at the same control moment and a corresponding relationship is established.

[0028] S20: Under high-impedance distribution network conditions, reverse droop control is performed based on the operating electrical quantities and power reference to obtain the internal potential and original current reference.

[0029] Specifically, such as Figure 2 The diagram shows the structure of a GFM inverter system based on reverse droop control. The grid-type inverter is powered by a DC voltage source Vdc, connected to the common coupling point PCC via a filter inductor Lf and a filter capacitor Cf, and connected to the AC grid via a grid impedance including grid resistance Rg and grid inductor Lg. The reverse droop control section generates an internal potential based on active and reactive power. The internal potential generates an initial current reference through a voltage-current inner loop, a virtual impedance, and a ring current limiter. Among them, Qf droop control is used to adjust the angular frequency based on reactive power deviation, and PV droop control is used to adjust the voltage amplitude based on active power deviation.

[0030] S30: Based on the original current reference and the maximum allowable current, a ring current limit is performed to obtain the current limit coefficient. The virtual impedance is adjusted according to the current limit coefficient, and then the adjusted virtual impedance is superimposed with the grid impedance to obtain the equivalent impedance.

[0031] Specifically, the ring current limit restricts the current reference amplitude based on the relationship between the original current reference amplitude and the maximum allowable current, while keeping the current reference phase angle unchanged. The current limiting coefficient is used to characterize the degree of change in virtual impedance after the ring current limit is triggered. The adjusted virtual impedance and the grid impedance together constitute the inverter equivalent impedance under the current limiting operation state.

[0032] S40: Based on the internal potential, operating electrical quantities and equivalent impedance, determine the transient relationship of reactive power as a function of power angle. Based on the current limiting coefficient, maximum allowable current and power reference, determine the transient balance constraints. Based on the transient balance constraints, analyze the transient relationship to obtain the transient balance point determination result and the parameter relationship between the transient balance point angle and the virtual impedance.

[0033] Specifically, the internal potential, grid operating voltage, and equivalent impedance jointly determine the changes in reactive power, output current amplitude, and power angle during grid voltage dips. Transient balance constraints are used to characterize the balance conditions of output current and reactive power under current-limiting conditions. Based on transient relationships and transient balance constraints, it is determined whether a transient balance point exists, and further, the influence of virtual impedance changes on the transient balance point angle is determined.

[0034] S50: Determine the target virtual impedance based on the transient equilibrium point determination result and the parameter relationship between the transient equilibrium point angle and the virtual impedance, and configure the target virtual impedance to the grid-type inverter.

[0035] Specifically, based on whether a transient equilibrium point exists, the power angle state corresponding to the transient equilibrium point, and the change in the transient equilibrium point angle caused by the change in virtual impedance parameters, the target virtual impedance that satisfies the transient equilibrium constraint is determined, and the target virtual impedance is written into the voltage and current inner loop control parameters of the grid-type inverter.

[0036] In one embodiment, step S20, namely, performing reverse droop control based on the operating electrical quantities and power reference to obtain the internal potential and original current reference, includes: S21: Determine active power and reactive power from operating electrical quantities.

[0037] Specifically, the three-phase voltage and the three-phase current of the inverter output collected at the common coupling point are subjected to Park transformation to obtain the voltage and current components in the synchronous rotating coordinate system. Then, the active power P and reactive power Q are calculated based on the voltage and current components through P / Q transformation. The active power P is used to characterize the active power output or absorbed by the inverter to the AC grid, and the reactive power Q is used to characterize the reactive power output or absorbed by the inverter to the AC grid.

[0038] S22: Based on the deviation between the reactive power reference and the reactive power in the power reference, adjust the preset reference grid angular frequency to obtain the angular frequency.

[0039] Specifically, the angular frequency is calculated according to the reverse droop control law, and the angular frequency satisfies the formula. Where ω is the adjusted angular frequency, ω ref To preset the reference grid angular frequency, K q For Qf droop gain, Q ref Q is the reactive power reference, and Q is the step reactive power. When the reactive power deviates from the reactive power reference, Qf droop control adjusts the angular frequency according to the reactive power deviation.

[0040] S23: Determine the voltage amplitude reference based on the deviation between the active power reference and the active power in the power reference.

[0041] Specifically, the voltage amplitude reference is calculated according to the reverse droop control law, and the voltage amplitude reference satisfies the formula. Where E is the voltage amplitude reference, E ref K is the preset reference voltage. p PV droop gain, Pref is the active power reference, and P is the active power. When the active power deviates from the active power reference, the PV droop control adjusts the voltage amplitude reference according to the active power deviation.

[0042] S24: Determine the internal voltage angle reference based on the angular frequency, and determine the internal potential based on the internal voltage angle reference and the voltage amplitude reference.

[0043] Specifically, by integrating the angular frequency, the internal voltage angle reference θ is obtained. ref The internal potential uses voltage amplitude reference E as its amplitude and internal voltage angle reference θ as its angle. ref As a phase formation, the internal potential in a synchronously rotating coordinate system can be expressed as E∠θ. ref In a coordinate system with the internal potential as a reference, the internal potential is expressed as E=Ee. j0 .

[0044] S25: Use the internal potential as the control reference for the voltage and current inner loop, and generate the original current reference through virtual admittance control.

[0045] Specifically, the internal potential is compared with the feedback voltage at the common coupling point to obtain the voltage deviation. This voltage deviation is then input into the virtual admittance control path corresponding to the virtual impedance. The virtual admittance control path converts the voltage deviation into a current control reference based on the impedance relationship formed by the virtual resistance and virtual inductance. The current control path outputs the original current references for the d-axis and q-axis. The original current reference is not subjected to amplitude saturation processing before entering the ring current limiter.

[0046] In one embodiment, step S24, namely determining the internal voltage angle reference based on the angular frequency, includes: S241: Integrate the angular frequency to obtain the change in internal voltage angle.

[0047] Specifically, taking the current internal voltage angle as the initial state of integration, the angular frequency ω is integrated over time. The change in the internal voltage angle is determined by the integral result of the angular frequency within the current control period. The larger the angular frequency, the larger the corresponding change in the internal voltage angle; the smaller the angular frequency, the smaller the corresponding change in the internal voltage angle.

[0048] S242: Update the internal voltage angle based on the change in internal voltage angle to obtain the current internal voltage angle.

[0049] Specifically, the change in internal voltage angle is superimposed on the internal voltage angle at the start of integration to obtain the current internal voltage angle. The current internal voltage angle is used to reflect the real-time angle state of the internal potential of the grid-connected inverter relative to the AC grid voltage.

[0050] S243: Determine the current internal voltage angle as the internal voltage angle reference.

[0051] Specifically, the current internal voltage angle is used as the phase reference for the internal potential at the next moment, and the current internal voltage angle is continuously input into the internal potential generation path so that the phase of the internal potential can be updated synchronously with the angular frequency change caused by the reactive power deviation.

[0052] In one embodiment, in step S30, a ring current limiting is performed based on the original current reference and the maximum allowable current to obtain a current limiting coefficient. The virtual impedance is then adjusted according to the current limiting coefficient, and the adjusted virtual impedance is superimposed with the grid impedance to obtain the equivalent impedance, including: S31: Determine the amplitude of the original current reference.

[0053] Specifically, the original current reference vector is determined based on the original current reference along the d-axis and the original current reference along the q-axis. The magnitude, the original current reference amplitude is in the form of || ‖express, The original current reference is the virtual admittance control output and has not yet undergone ring current limiting.

[0054] S32: Compares the magnitude of the original current reference with the maximum permissible current.

[0055] Specifically, the original current reference amplitude || || with the maximum allowable current I max Comparison, I max For the maximum allowable amplitude of the output current on the grid-connected inverter side, when the original current reference amplitude is not greater than I...max At this time, the ring current limiter is in an untriggered state, when the original current reference amplitude is greater than I. max At that time, the ring current limiter is in the triggered state.

[0056] S33: When the amplitude of the original current reference does not exceed the maximum allowable current, the current limiting factor is determined to be .

[0057] Specifically, when‖ || No more than I max At this time, the original current reference does not need to be amplitude compressed, and the ring current limiter directly outputs the original current reference, with a current limiting coefficient k. lim When the value is set to 1, the virtual impedance remains unscaled.

[0058] S34: When the amplitude of the original current reference exceeds the maximum allowable current, the amplitude of the original current reference is limited while the phase angle remains unchanged, and the current limiting coefficient is determined based on the ratio of the amplitude of the original current reference to the maximum allowable current.

[0059] Specifically, when‖ When || is greater than Imax, the ring current limiter operates according to the formula Generate saturated current reference ,in, The saturation current reference is after processing by the ring current limiter. As the original current reference, I max For the maximum allowable current, Used to limit the original current reference amplitude to I max The phase angle of the original current reference remains unchanged, and the current limiting factor is calculated according to the formula. Confirmed, when the ring current limiter is triggered, k lim Greater than 1.

[0060] S35: Adjust the virtual impedance according to the current limiting coefficient to obtain the adjusted virtual impedance. Then, superimpose the adjusted virtual impedance with the grid impedance to obtain the equivalent impedance.

[0061] Specifically, after the ring current limiter is triggered, the original current reference before saturation flows through the virtual impedance, while the actual output current after ring current limiting flows through the grid impedance. According to Kirchhoff's voltage law, the voltage drop of the two parts is kept consistent. The virtual impedance is amplified according to the current limiting factor, making the effective virtual impedance from Z... v Adjusted to Z v ·k lim Among them, Z v For the virtual impedance before adjustment, k lim The current limiting factor is the virtual impedance that is adjusted and then superimposed in series with the grid impedance to form the equivalent impedance under the current limiting condition. Furthermore, such as Figure 3The diagram shows the equivalent circuit model of a GFM inverter with a ring current limiter. When the ring current limiter is triggered, the internal potential is equivalent to a voltage source. The adjusted virtual impedance is connected in series with the grid impedance between the internal potential and the AC grid. The adjusted virtual impedance is the impedance amplified by the current limiting factor. The common coupling point PCC is located between the adjusted virtual impedance and the grid impedance, thus forming an equivalent circuit model for transient stability analysis.

[0062] In one embodiment, in step S35, the virtual impedance is adjusted according to the current limiting coefficient to obtain the adjusted virtual impedance. The adjusted virtual impedance is then superimposed with the grid impedance to obtain the equivalent impedance, including: S351: Decompose the virtual impedance into virtual resistance and virtual reactance determined by the virtual inductance, and decompose the mains impedance into mains resistance and mains reactance.

[0063] Specifically, the virtual impedance is represented as Z. v =R v +jX v , where R v X is a virtual resistance. v For virtual reactance, X v =ω g ·L v ω g L is the angular frequency of the power grid. v For virtual inductance, the mains impedance is represented by Z. g =R g +jX g , where R g X is the resistance of the power grid. g Let be the grid reactance, and j be the imaginary unit. The virtual impedance and grid impedance correspond to the virtual impedance voltage drop in the inverter control loop and the grid impedance voltage drop in the connected line, respectively.

[0064] S352: Adjust the virtual resistance and virtual reactance proportionally according to the current limiting coefficient to obtain the adjusted virtual resistance and virtual reactance.

[0065] Specifically, the virtual resistance R v With the current limiting coefficient k lim Multiplying them together yields the adjusted virtual resistance R. v ·k lim Virtual reactance X v With the current limiting coefficient k lim Multiplying them together yields the adjusted virtual reactance X. v ·k lim When the current limiting factor is 1, the virtual resistance and virtual reactance remain at their original values. When the current limiting factor is greater than 1, the virtual resistance and virtual reactance increase by the same proportion.

[0066] S353: The adjusted virtual resistance is superimposed on the mains resistance to obtain the equivalent resistance.

[0067] Specifically, the adjusted virtual resistance R v ·k lim With grid resistance R g By superimposing the values, the equivalent resistance R under current-limited conditions can be obtained. eq The equivalent resistance satisfies R eq =R v ·k lim +R g R eq It is used to characterize the equivalent resistive component formed by the combined action of the original current reference through the virtual impedance path and the actual output current through the grid impedance path.

[0068] S354: The adjusted virtual reactance is superimposed with the grid reactance to obtain the equivalent reactance.

[0069] Specifically, the adjusted virtual reactance X v ·k lim With grid reactance X g By superimposing the values, the equivalent reactance X under current-limited conditions is obtained. eq The equivalent reactance satisfies X eq =X v ·k lim +X g X eq Used to characterize the equivalent inductive component formed by the virtual inductance and the grid inductance.

[0070] S355: Determine the equivalent impedance based on the equivalent resistance and equivalent reactance.

[0071] Specifically, based on the equivalent resistance R eq and equivalent reactance X eq Determine the equivalent impedance Z eq The equivalent impedance satisfies Z eq =R eq +jX eq When the ring current limiter is not triggered and k lim When = 1, the equivalent impedance satisfies Z eq =Z v +Z g = (R) v +R g )+j(X v +X g ), when the ring current limiter is triggered and k lim When it is greater than 1, the equivalent impedance is determined by R. eq =R v ·k lim +R g and Xeq =X v ·k lim +X g To be determined jointly.

[0072] In one embodiment, in step S40, the transient relationship of reactive power changing with power angle is determined based on internal potential, operating electrical quantities, and equivalent impedance. Transient balance constraints are determined based on current limiting coefficient, maximum allowable current, and power reference. The transient relationship is then analyzed based on these constraints to obtain the transient balance point determination result and the parametric relationship between the transient balance point angle and virtual impedance, including: S41: Based on the internal potential, grid voltage and equivalent impedance in the operating electrical quantities, determine the relationship between reactive power and output current amplitude and power angle, and obtain the transient relationship.

[0073] Specifically, ignoring the effect of the filter capacitor Cf on transient stability, the internal potential is expressed as E = Ee in the internal potential coordinate system. j0 The grid voltage is expressed as Vgdq = Vge -jδ Where E is the internal potential amplitude, Vg is the grid voltage amplitude, and δ is the power angle. The nonlinear relationships between active power P, reactive power Q, and output current amplitude with the power angle δ are determined based on the equivalent impedance. The reactive power relationship is then simplified using trigonometric identities. , where Q o To determine the dynamic DC bias that determines the overall vertical and horizontal orientation of the reactive power curve, Q m The dynamic AC amplitude determines the oscillation amplitude of the reactive power curve, and φ is the dynamic phase angle that determines the horizontal offset of the reactive power curve.

[0074] S42: Determine the current limiting constraint corresponding to the output current amplitude based on the relationship between the output current amplitude and the power angle, the current limiting coefficient and the maximum allowable current, and determine the reactive power balance constraint based on the reactive power reference in the power reference to obtain the transient balance constraint.

[0075] Specifically, based on the output current amplitude relationship, the current amplitude is made to reach the maximum allowable current I. max The condition is used as a current limiting constraint, let D 2 =E 2 +Vg 2 -2E·Vg·cosδ, where D 2 The voltage drop term between the internal potential and the grid voltage is squared, and the current limiting constraint satisfies... The reactive power balance constraint is based on the reactive power Q reaching the reactive power reference Q. ref The conditions are determined, Q ref The reactive power reference in the power reference, the current limiting constraint and the reactive power balance constraint together constitute the transient balance constraint.

[0076] S43: Based on the comparison between the maximum and minimum reactive power values ​​in the reactive power reference and transient relationship, determine the existence state of the transient equilibrium point. The grid voltage that makes the reactive power reference equal to the maximum or minimum reactive power value is determined as the critical grid drop voltage, and the transient equilibrium point determination result is obtained.

[0077] Specifically, the reactive power curve The maximum value is Q o +Q m The minimum value is Q o -Q m ,when At that time, reactive power reference Q ref Located within the range of values ​​of the reactive power curve, such as Figure 4 The diagram shows the Q-δ trajectory analysis when the grid voltage drops from 1 p.u. to 0.5 p.u. When the grid voltage drops from its rated value to 0.5 p.u., the reactive power fault curve intersects with the reactive power reference line. This intersection point corresponds to the transient equilibrium point. The power angle changes along the reactive power trajectory to the transient equilibrium point and then stops increasing. After the fault is cleared, it can recover to the initial stable equilibrium point. When Q... ref Less than Q o -Q m or greater than Q o +Q m At this point, the reactive power curve and the reactive power reference line do not intersect, and the transient equilibrium point does not exist. When the grid voltage experiences an extreme deep drop, the minimum value of the reactive power curve degenerates to 3E²Xg / 2Zeq², where X... g For the grid reactance, Z eq As the equivalent impedance, when the reactive power reference and the reactive power curve do not intersect, the power angle continues to increase during the fault. This can be achieved by solving for Q. o -Q m =Q ref The critical grid sag voltage is obtained. A transient equilibrium point exists when the grid voltage Vg is higher than the critical grid sag voltage; a transient equilibrium point does not exist when the grid voltage Vg is not higher than the critical grid sag voltage. Figure 5 The diagram shows the Q-δ trajectory analysis for different fault durations when the grid voltage drops from 1 p.u. to 0.05 p.u. When the grid voltage drops to 0.05 p.u., the reactive power fault curve and the reactive power reference line no longer intersect to meet the stable operation conditions, and the transient equilibrium point does not exist. When the fault duration is short, the power angle continues to increase along the transient trajectory. When the fault duration is long, the power angle further increases and crosses the recoverable region, indicating that it is difficult to maintain a transient stable state when the grid voltage is below the critical grid drop voltage.

[0078] S44: When the transient equilibrium point determination result indicates the existence of a transient equilibrium point, establish the constraint relationship between the power angle, the current limiting coefficient and the virtual impedance based on the current limiting constraint and the reactive power balance constraint.

[0079] Specifically, the equivalent resistance R under current-limited conditions eq =R v ·k lim +R g and equivalent reactance X eq =X v ·k lim +X g Substituting the current limiting constraint and reactive power balance constraint, we construct a function relating the power angle δ and the current limiting coefficient k. lim The full-dimensional implicit function system of equations, the first implicit function satisfies The second implicit function satisfies ,in, NQ = Xeq·A - Req·B + Xg·D 2 A = E·Vg·cosδ-Vg 2 B = E·Vg·sinδ, D 2 =E 2 +Vg 2 -2E·Vg·cosδ, F1 is used to characterize the constraint that the output current amplitude reaches the maximum allowable current, and F2 is used to characterize the constraint that the reactive power at the transient equilibrium point reaches the reactive power reference.

[0080] S45: Using the virtual resistance and virtual inductance in the virtual impedance as parameters to be analyzed, determine the relationship between the transient equilibrium point angle and the virtual resistance and virtual inductance according to the constraint relationship, and obtain the parameter relationship between the transient equilibrium point angle and the virtual impedance.

[0081] Specifically, for =0 and The system of full-dimensional implicit function equations consisting of =0 is subjected to total differentials, and the transient equilibrium point angle δ is solved according to Cramer's rule. TEP The partial derivatives with respect to the virtual resistance Rv and the virtual inductance Lv are obtained respectively. as well as , where δ TEP Rv is the power angle corresponding to the transient equilibrium point, Rv is the virtual resistance, and Lv is the virtual inductance. When the virtual resistance increases, the transient equilibrium point angle decreases; when the virtual inductance increases, the transient equilibrium point angle increases. Figure 6The diagram shows a three-dimensional surface diagram of δTEP varying with virtual resistance Rv and virtual inductance Lv. The angle of the transient equilibrium point forms a three-dimensional surface as the virtual resistance and virtual inductance change. When the virtual inductance remains constant, the angle of the transient equilibrium point gradually decreases as the virtual resistance increases. When the virtual resistance remains constant, the angle of the transient equilibrium point gradually increases as the virtual inductance increases. This surface corresponds to the parameter relationship between the angle of the transient equilibrium point and the virtual resistance and virtual inductance.

[0082] In one embodiment, step S50, namely determining the target virtual impedance based on the transient equilibrium point determination result and the parametric relationship between the transient equilibrium point angle and the virtual impedance, includes: S51: Based on the transient equilibrium point existence status in the transient equilibrium point determination results, and the comparison results between the critical grid drop voltage and the grid voltage in the operating electrical quantities, virtual impedance parameter combinations that do not meet the transient equilibrium constraints are screened out in the preset virtual impedance parameter search space to obtain candidate virtual impedance parameter combinations.

[0083] Specifically, within the preset virtual impedance parameter search space X, transient equilibrium points are determined for different combinations of virtual resistance Rv and virtual inductance Lv. When there is no transient equilibrium point for the corresponding combination, or the grid voltage Vg is not higher than the critical grid drop voltage corresponding to the combination, the corresponding virtual impedance parameter combination is removed from the search space. When there is a transient equilibrium point for the corresponding combination and the grid voltage Vg is higher than the critical grid drop voltage, the corresponding virtual impedance parameter combination is retained as a candidate virtual impedance parameter combination.

[0084] S52: Based on the parameter relationship between the transient equilibrium point angle and the virtual impedance, determine the parameter adjustment direction of the virtual resistance and virtual inductance in the candidate virtual impedance parameter combination.

[0085] Specifically, according to and Determine the adjustment direction of the candidate virtual impedance parameter combination. Within the range that satisfies the transient balance constraint, the adjustment direction of the virtual resistance is to increase the virtual resistance, and the adjustment direction of the virtual inductance is to decrease the virtual inductance, so that the angle of the transient balance point changes in the direction of decreasing.

[0086] S53: Construct a multi-objective cost function based on the combination of candidate virtual impedance parameters. The multi-objective cost function includes the transient equilibrium point angle cost, the absolute error integral index of dynamic power fluctuation, and the steady-state active power reduction penalty term.

[0087] Specifically, the candidate virtual impedance parameter combination is x = [Rv, Lv]. T As decision variables, construct a multi-objective cost function. Where Jδ is the transient equilibrium point angle cost, used to characterize the transient synchronization margin, J IAEJcap is the absolute error integral index used to quantify dynamic power fluctuations. Jcap = |Pref - Pinit| is the steady-state active power reduction penalty term, where Pref is the active power reference and Pinit is the initial active power. , and These are the normalized baseline values ​​for the corresponding objectives, and w1, w2, and w3 are multi-objective weight coefficients that satisfy w1+w2+w3=1.

[0088] S54: Using a Gaussian process as a probabilistic surrogate model, a posterior probability distribution is constructed based on the combination of candidate virtual impedance parameters and a multi-objective cost function.

[0089] Specifically, the evaluated candidate virtual impedance parameter combinations and their corresponding multi-objective cost function values ​​are used as sampled data input into the Gaussian process. The Gaussian process constructs the posterior probability distribution of the multi-objective cost function in the virtual impedance parameter search space based on the sampled data. The posterior probability distribution outputs the mean of the predicted cost and the variance of the predicted uncertainty for the unsampled candidate virtual impedance parameter combinations. The mean of the predicted cost is used to characterize the expected cost of the candidate virtual impedance parameter combinations, and the variance of the predicted uncertainty is used to characterize the degree of exploration of the candidate virtual impedance parameter combinations. Furthermore, such as Figure 7 The diagram illustrates the iterative process of the Bayesian optimization algorithm. Within the parameter search space composed of virtual resistance and virtual inductance, the multi-objective cost function forms a nonlinear cost surface. The sampled virtual impedance parameter combinations are distributed on the cost surface. The optimal parameter combination is located in the region that satisfies the transient equilibrium constraint and has a small cost function. The Gaussian process estimates the prediction cost and uncertainty of the unsampled region based on the sampled parameter combinations and their cost function values, aiming to improve the acquisition function data and thus determine the subsequent sampled parameter combinations.

[0090] S55: Determine the target virtual impedance from the candidate virtual impedance parameter combinations based on the posterior probability distribution, the desired improvement of the acquisition function, and the parameter adjustment direction.

[0091] Specifically, the expected improvement acquisition function calculates the sampling priority of each candidate virtual impedance parameter combination based on the mean of the prediction cost and the variance of the prediction uncertainty in the posterior probability distribution. Within the candidate range limited by the parameter adjustment direction, the virtual impedance parameter combination with the larger expected improvement value is selected for evaluation, and the evaluation result is updated to the sampling data corresponding to the Gaussian process. The candidate parameter selection and posterior probability distribution update are repeated until the virtual resistance and virtual inductance with a smaller multi-objective cost function and satisfying the transient balance constraint are determined, and the corresponding virtual impedance is determined as the target virtual impedance. Furthermore, after completing the target virtual impedance configuration, the time-domain response of the grid-connected inverter under different grid voltage dip depths and different fault durations is verified. The changes in grid voltage, output current, active power, reactive power, and power angle are collected, such as... Figure 8 The time-domain experimental waveforms shown are illustrated under different voltage drop depths. When the grid voltage drops to 0.5 pu, 0.3 pu, and 0.2 pu respectively and lasts for 2 seconds, the output current, active power, reactive power, and power angle of the grid-connected inverter all undergo transient changes with the grid voltage drop, and return to a stable state after the fault is cleared. Figure 9 The time-domain experimental waveforms shown are for different fault durations when the grid voltage drops to 0.01 pu. Under the condition of a deep fault with the grid voltage dropping to 0.01 pu, there are differences in the time-domain response when the fault lasts for 3 seconds and 5 seconds. The power angle increases further with the extension of the fault duration. The output current, active power and reactive power response after the grid voltage is restored reflect the transient recovery process under different fault durations. like Figures 10 to 12 The diagram shows a comparison of the transient time-domain responses of conventional droop control and reverse droop control when the grid voltage drops to 0.5, 0.3, and 0.1 pu. When the grid voltage drops to 0.5 pu, 0.3 pu, and 0.1 pu, respectively, the time-domain responses of conventional droop control and reverse droop control are compared. Under high-impedance distribution network conditions, the power angle change under reverse droop control is more easily converged, and the power oscillation amplitude is smaller. Especially under the 0.1 pu voltage drop condition, the power angle of conventional droop control continues to increase, while the power angle of reverse droop control can converge towards the transient equilibrium point.

[0092] Example 2 like Figure 13 As shown, based on the same inventive concept as the above embodiments, the present invention also provides a transient stability system for a high-resistance grid-connected inverter, comprising: The data acquisition module is used to acquire operating electrical quantities, power reference, maximum allowable current, virtual impedance, and grid impedance; The droop control module is used to perform reverse droop control under high-resistance distribution network conditions based on the operating electrical quantities and power reference to obtain the internal potential and original current reference. The current limiting modeling module is used to perform ring current limiting based on the original current reference and the maximum allowable current to obtain the current limiting coefficient. The virtual impedance is then adjusted according to the current limiting coefficient, and the adjusted virtual impedance is superimposed with the grid impedance to obtain the equivalent impedance. The balance analysis module is used to determine the transient relationship of reactive power as a function of power angle based on internal potential, operating electrical quantities and equivalent impedance. It determines transient balance constraints based on current limiting coefficient, maximum allowable current and power reference, and analyzes the transient relationship based on the transient balance constraints to obtain the transient balance point determination result and the parameter relationship between the transient balance point angle and virtual impedance. The impedance configuration module is used to determine the target virtual impedance based on the transient equilibrium point determination result and the parameter relationship between the transient equilibrium point angle and the virtual impedance, and to configure the target virtual impedance to the grid-type inverter.

[0093] Optional, the droop control module includes: The power determination submodule is used to determine active and reactive power from operating electrical quantities; The frequency adjustment submodule is used to adjust the preset reference grid angular frequency based on the deviation between the reactive power reference and the reactive power in the power reference, so as to obtain the angular frequency; The amplitude determination submodule is used to determine the voltage amplitude reference based on the deviation between the active power reference and the active power in the power reference. The potential determination submodule is used to determine the internal voltage angle reference based on the angular frequency, and to determine the internal potential based on the internal voltage angle reference and the voltage amplitude reference. The current generation submodule is used to generate the original current reference by using the internal potential as the control reference for the voltage and current inner loop and controlling the virtual admittance.

[0094] Optional, the potential determination submodule includes: An angle integration unit is used to integrate the angular frequency to obtain the internal voltage angle change. Angle update unit is used to update the internal voltage angle according to the change in internal voltage angle to obtain the current internal voltage angle. Angle setting unit is used to determine the current internal voltage angle as the internal voltage angle reference.

[0095] Optional, the current limiting modeling module includes: The amplitude determination submodule is used to determine the amplitude of the original current reference. The amplitude comparison submodule is used to compare the amplitude of the original current reference with the maximum allowable current; The current limiting determination submodule is used to determine the current limiting factor as 1 when the amplitude of the original current reference does not exceed the maximum allowable current; The ring current limiting submodule is used to limit the amplitude of the original current reference while keeping the phase angle unchanged when the amplitude of the original current reference exceeds the maximum allowable current. The current limiting coefficient is determined based on the ratio of the amplitude of the original current reference to the maximum allowable current. The impedance superposition submodule is used to adjust the virtual impedance according to the current limiting coefficient to obtain the adjusted virtual impedance. The adjusted virtual impedance is then superimposed with the grid impedance to obtain the equivalent impedance.

[0096] Optional, the impedance superposition submodule includes: Impedance decomposition unit is used to decompose virtual impedance into virtual resistance and virtual reactance determined by virtual inductance, and to decompose grid impedance into grid resistance and grid reactance; The impedance adjustment unit is used to proportionally adjust the virtual resistance and virtual reactance according to the current limiting coefficient to obtain the adjusted virtual resistance and virtual reactance. The resistance superposition unit is used to superimpose the adjusted virtual resistance with the grid resistance to obtain the equivalent resistance; The reactance superposition unit is used to superimpose the adjusted virtual reactance with the grid reactance to obtain the equivalent reactance; Impedance determination unit, used to determine equivalent impedance based on equivalent resistance and equivalent reactance.

[0097] Optional, the balance analysis module includes: The transient relationship submodule is used to determine the relationship between reactive power and output current amplitude as a function of power angle based on internal potential, grid voltage and equivalent impedance in operating electrical quantities, and to obtain transient relationships. The constraint determination submodule is used to determine the current limiting constraint corresponding to the output current amplitude based on the relationship between the output current amplitude and the power angle, the current limiting coefficient and the maximum allowable current, and to determine the reactive power balance constraint based on the reactive power reference in the power reference, so as to obtain the transient balance constraint. The balance determination submodule is used to determine the existence state of the transient balance point based on the comparison results between the maximum and minimum reactive power values ​​in the reactive power reference and the transient relationship. The grid voltage that makes the reactive power reference equal to the maximum or minimum reactive power value is determined as the critical grid drop voltage, and the transient balance point determination result is obtained. The constraint establishment submodule is used to establish the constraint relationship between power angle, current limiting coefficient and virtual impedance based on current limiting constraint and reactive power balance constraint when the transient equilibrium point determination result indicates the existence of a transient equilibrium point; The parameter analysis submodule is used to take the virtual resistance and virtual inductance in the virtual impedance as the parameters to be analyzed, and determine the relationship between the transient equilibrium point angle and the virtual resistance and virtual inductance according to the constraint relationship, so as to obtain the parameter relationship between the transient equilibrium point angle and the virtual impedance.

[0098] Optional, the impedance configuration module includes: The parameter filtering submodule is used to filter out virtual impedance parameter combinations that do not meet the transient balance constraints in the preset virtual impedance parameter search space based on the transient balance point existence status in the transient balance point determination results and the comparison results between the critical grid drop voltage and the grid voltage in the operating electrical quantities, so as to obtain candidate virtual impedance parameter combinations. The direction determination submodule is used to determine the parameter adjustment direction of virtual resistance and virtual inductance in the candidate virtual impedance parameter combination based on the parameter relationship between the transient equilibrium point angle and the virtual impedance. The cost construction submodule is used to construct a multi-objective cost function based on the combination of candidate virtual impedance parameters. The multi-objective cost function includes the transient equilibrium point angle cost, the absolute error integral index of dynamic power fluctuation, and the steady-state active power reduction penalty term. The probabilistic modeling submodule is used to construct a posterior probability distribution based on the combination of candidate virtual impedance parameters and a multi-objective cost function, using a Gaussian process as a probabilistic surrogate model. The parameter optimization submodule is used to determine the target virtual impedance from candidate virtual impedance parameter combinations based on the posterior probability distribution, the desired improvement of the acquisition function, and the parameter adjustment direction.

[0099] Example 3 like Figure 14 As shown, the present invention also provides an electronic device 100 for implementing a transient stabilization method for a high-resistivity grid-connected inverter; The electronic device 100 includes a memory 101, at least one processor 102, a computer program 103 stored in the memory 101 and executable on at least one processor 102, and at least one communication bus 104.

[0100] The memory 101 can be used to store the computer program 103. The processor 102 implements the steps of the transient stabilization method for a high-resistance grid-type inverter in Embodiment 1 by running or executing the computer program stored in the memory 101 and calling the data stored in the memory 101.

[0101] The memory 101 may primarily include a program storage area and a data storage area. The program storage area may store the operating system, application programs required for at least one function (such as sound playback function, image playback function, etc.), etc.; the data storage area may store data created based on the use of the electronic device 100 (such as audio data), etc. In addition, the memory 101 may include non-volatile memory, such as hard disk, RAM, plug-in hard disk, smart media card (SMC), secure digital (SD) card, flash card, at least one disk storage device, flash memory device, or other non-volatile solid-state storage device.

[0102] At least one processor 102 may be a Central Processing Unit (CPU), or other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. Processor 102 may be a microprocessor or any conventional processor. Processor 102 is the control center of electronic device 100, connecting various parts of electronic device 100 via various interfaces and lines.

[0103] The memory 101 in the electronic device 100 stores multiple instructions to implement a transient stabilization method for a high-impedance grid-connected inverter, and the processor 102 can execute multiple instructions to achieve the following: Obtain operating electrical quantities, power reference, maximum allowable current, virtual impedance, and grid impedance; Under high-resistance distribution network conditions, reverse droop control is performed based on the operating electrical quantities and power reference to obtain the internal potential and original current reference. A ring current limit is performed based on the original current reference and the maximum allowable current to obtain the current limit coefficient. The virtual impedance is then adjusted according to the current limit coefficient, and the adjusted virtual impedance is superimposed with the grid impedance to obtain the equivalent impedance. Based on the internal potential, operating electrical quantities and equivalent impedance, the transient relationship of reactive power with power angle is determined. The transient balance constraint is determined based on the current limiting coefficient, maximum allowable current and power reference. The transient relationship is analyzed based on the transient balance constraint to obtain the transient balance point determination result and the parameter relationship between the transient balance point angle and the virtual impedance. The target virtual impedance is determined based on the transient equilibrium point determination result and the parameter relationship between the transient equilibrium point angle and the virtual impedance, and then the target virtual impedance is configured to the grid-type inverter.

[0104] Example 4 If the modules / units integrated in the electronic device 100 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, all or part of the processes in the methods of the above embodiments of the present invention can also be implemented by a computer program instructing related hardware. The computer program can be stored in a computer-readable storage medium, and when executed by a processor, it can implement the steps of the various method embodiments described above. The computer program includes computer program code, which can be in the form of source code, object code, executable files, or certain intermediate forms. The computer-readable medium can include: any entity or system capable of carrying computer program code, recording media, USB flash drives, portable hard drives, magnetic disks, optical disks, computer memory, and read-only memory (ROM).

[0105] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0106] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A system that specifies functions in one or more boxes.

[0107] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including an instruction set implemented in a process. Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0108] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0109] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the 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.

[0110] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A transient stabilization method for a high-resistivity grid-connected inverter, characterized in that, The method includes: Obtain operating electrical quantities, power reference, maximum allowable current, virtual impedance, and grid impedance; Under high-resistance distribution network conditions, reverse droop control is performed based on the operating electrical quantities and the power reference to obtain the internal potential and the original current reference. Based on the original current reference and the maximum allowable current, a ring current limit is performed to obtain a current limit coefficient. The virtual impedance is adjusted according to the current limit coefficient, and then the adjusted virtual impedance is superimposed with the grid impedance to obtain the equivalent impedance. Based on the internal potential, the operating electrical quantities, and the equivalent impedance, the transient relationship of reactive power changing with the power angle is determined. Based on the current limiting coefficient, the maximum allowable current, and the power reference, the transient balance constraint is determined. Based on the transient balance constraint, the transient relationship is analyzed to obtain the transient balance point determination result and the parameter relationship between the transient balance point angle and the virtual impedance. The target virtual impedance is determined based on the transient equilibrium point determination result and the parameter relationship between the transient equilibrium point angle and the virtual impedance, and the target virtual impedance is configured to the grid-type inverter.

2. The transient stabilization method for high-resistivity grid-connected inverters according to claim 1, characterized in that, The step of performing reverse droop control based on the operating electrical quantities and the power reference to obtain the internal potential and the original current reference includes: Determine the active power and reactive power from the operating electrical quantities; The preset reference grid angular frequency is adjusted based on the deviation between the reactive power reference and the reactive power in the power reference to obtain the angular frequency; The voltage amplitude reference is determined based on the deviation between the active power reference and the active power in the power reference. The internal voltage angle reference is determined based on the angular frequency, and the internal potential is determined based on the internal voltage angle reference and the voltage amplitude reference. The internal potential is used as the control reference for the voltage and current inner loop, and the original current reference is generated through virtual admittance control.

3. The transient stabilization method for a high-resistivity grid-connected inverter according to claim 2, characterized in that, The step of determining the internal voltage angle reference based on the angular frequency includes: Integrating the angular frequency yields the change in internal voltage angle; The internal voltage angle is updated based on the change in internal voltage angle to obtain the current internal voltage angle; The current internal voltage angle is determined as the internal voltage angle reference.

4. The transient stabilization method for a high-resistivity grid-connected inverter according to claim 1, characterized in that, The process involves performing a ring current limit based on the original current reference and the maximum allowable current to obtain a current limiting coefficient. The virtual impedance is then adjusted according to the current limiting coefficient, and the adjusted virtual impedance is superimposed with the grid impedance to obtain an equivalent impedance, including: Determine the amplitude of the original current reference; The amplitude of the original current reference is compared with the maximum allowable current; When the amplitude of the original current reference does not exceed the maximum allowable current, the current limiting factor is determined to be 1; When the amplitude of the original current reference exceeds the maximum allowable current, the amplitude of the original current reference is limited while the phase angle remains unchanged, and the current limiting coefficient is determined based on the ratio of the amplitude of the original current reference to the maximum allowable current. The virtual impedance is adjusted according to the current limiting coefficient to obtain the adjusted virtual impedance. The adjusted virtual impedance is then superimposed with the grid impedance to obtain the equivalent impedance.

5. The transient stabilization method for a high-resistivity grid-connected inverter according to claim 4, characterized in that, The step of adjusting the virtual impedance according to the current limiting coefficient to obtain the adjusted virtual impedance, and then superimposing the adjusted virtual impedance with the grid impedance to obtain the equivalent impedance includes: The virtual impedance is decomposed into virtual resistance and virtual reactance determined by virtual inductance, and the grid impedance is decomposed into grid resistance and grid reactance. The virtual resistance and the virtual reactance are adjusted proportionally according to the current limiting coefficient to obtain the adjusted virtual resistance and the adjusted virtual reactance. The adjusted virtual resistance is superimposed on the grid resistance to obtain the equivalent resistance; The adjusted virtual reactance is superimposed with the grid reactance to obtain the equivalent reactance; The equivalent impedance is determined based on the equivalent resistance and the equivalent reactance.

6. The transient stabilization method for a high-resistivity grid-connected inverter according to claim 1, characterized in that, The process involves determining the transient relationship between reactive power and power angle based on the internal potential, the operating electrical quantities, and the equivalent impedance; determining transient balance constraints based on the current limiting coefficient, the maximum allowable current, and the power reference; and analyzing the transient relationship based on the transient balance constraints to obtain the transient balance point determination result and the parametric relationship between the transient balance point angle and the virtual impedance, including: Based on the internal potential, the grid voltage in the operating electrical quantities, and the equivalent impedance, the relationship between reactive power and output current amplitude and power angle is determined, and the transient relationship is obtained. The current limiting constraint corresponding to the output current amplitude is determined based on the relationship between the output current amplitude and the power angle, the current limiting coefficient and the maximum allowable current, and the reactive power balance constraint is determined based on the reactive power reference in the power reference, thus obtaining the transient balance constraint. Based on the comparison between the reactive power reference and the maximum and minimum reactive power values ​​in the transient relationship, the existence state of the transient equilibrium point is determined; the grid voltage that makes the reactive power reference equal to the maximum or minimum reactive power value is determined as the critical grid drop voltage, and the transient equilibrium point determination result is obtained. When the transient equilibrium point determination result indicates the existence of a transient equilibrium point, a constraint relationship is established between the power angle, the current limiting coefficient, and the virtual impedance based on the current limiting constraint and the reactive power balance constraint. Using the virtual resistance and virtual inductance in the virtual impedance as parameters to be analyzed, the relationship between the transient equilibrium point angle and the virtual resistance and virtual inductance is determined according to the constraint relationship, thus obtaining the parameter relationship between the transient equilibrium point angle and the virtual impedance.

7. The transient stabilization method for a high-resistivity grid-connected inverter according to claim 6, characterized in that, The step of determining the target virtual impedance based on the transient equilibrium point determination result and the parametric relationship between the transient equilibrium point angle and the virtual impedance includes: Based on the transient equilibrium point existence status in the transient equilibrium point determination result, and the comparison result between the critical grid drop voltage and the grid voltage in the operating electrical quantity, virtual impedance parameter combinations that do not satisfy the transient equilibrium constraint are screened out in the preset virtual impedance parameter search space to obtain candidate virtual impedance parameter combinations. Based on the parameter relationship between the transient equilibrium point angle and the virtual impedance, determine the parameter adjustment direction of the virtual resistance and virtual inductance in the candidate virtual impedance parameter combination; A multi-objective cost function is constructed based on the candidate virtual impedance parameter combination. The multi-objective cost function includes the transient equilibrium point angle cost, the absolute error integral index of dynamic power fluctuation, and the steady-state active power loss penalty term. Using a Gaussian process as a probabilistic proxy model, a posterior probability distribution is constructed based on the candidate virtual impedance parameter combination and the multi-objective cost function. The target virtual impedance is determined from the candidate virtual impedance parameter combinations based on the posterior probability distribution, the desired improvement acquisition function, and the parameter adjustment direction.

8. A transient stability system for a high-resistance grid-connected inverter, characterized in that, The system includes: The data acquisition module is used to acquire operating electrical quantities, power reference, maximum allowable current, virtual impedance, and grid impedance; The droop control module is used to perform reverse droop control under high-resistance distribution network conditions based on the operating electrical quantities and the power reference to obtain the internal potential and the original current reference. The current limiting modeling module is used to perform ring current limiting based on the original current reference and the maximum allowable current to obtain the current limiting coefficient, adjust the virtual impedance according to the current limiting coefficient, and then superimpose the adjusted virtual impedance and the grid impedance to obtain the equivalent impedance. The balance analysis module is used to determine the transient relationship of reactive power changing with power angle based on the internal potential, the operating electrical quantity and the equivalent impedance, determine the transient balance constraint based on the current limiting coefficient, the maximum allowable current and the power reference, and analyze the transient relationship based on the transient balance constraint to obtain the transient balance point determination result and the parameter relationship between the transient balance point angle and the virtual impedance. The impedance configuration module is used to determine the target virtual impedance based on the transient equilibrium point determination result and the parameter relationship between the transient equilibrium point angle and the virtual impedance, and to configure the target virtual impedance to the grid-type inverter.

9. An electronic device, characterized in that, It includes a processor and a memory, the processor being used to execute a computer program stored in the memory to implement the transient stabilization method for a high-resistivity grid-type inverter as described in any one of claims 1 to 7.

10. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores at least one instruction, which, when executed by a processor, implements the transient stabilization method for a high-resistivity grid-type inverter as described in any one of claims 1 to 7.

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