Method for calculating limit proportion of DC capacity of power transmission channel containing embedded DC, electronic equipment and medium

Abstract

The invention discloses a power transmission channel direct current capacity limit proportion calculation method containing embedded direct current, electronic equipment and a medium. The method comprises the steps that an alternating current and direct current hybrid system model containing the embedded direct current is constructed based on a target power grid; selecting collocation points at equal intervals in a direct current transmission capacity parameter range based on an embedded direct current-containing alternating current-direct current hybrid system model to obtain a collocation point configuration completion model; calculating transient voltage stability index values under different collocation points based on the collocation point configuration completion model; and based on polynomial approximation, fitting the direct current capacity of the power transmission channel and the transient voltage stability index value into a polynomial function. And solving the polynomial function to obtain the direct current capacity limit proportion. According to the method, through dynamic coupling modeling, equal-interval collocation and polynomial fitting, the whole working condition can be covered by the limited calculation amount, and therefore the simulation efficiency and the result precision are improved.

Description

Technical Field

[0001] This invention belongs to the field of power system safety verification technology, specifically involving a method for calculating the DC capacity limit ratio of transmission channels with embedded DC, electronic equipment, and media. Background Technology

[0002] With the continuous expansion of new energy installed capacity and the increasing demand for optimized allocation of power resources between regions, DC transmission, as a high-efficiency and high-capacity transmission method, is showing a gradual upward trend in its proportion in the power grid. This increase in the proportion of DC transmission power leads to significant changes in the development process and instability patterns of faults, affecting the safe and stable operation of the system.

[0003] In related technologies, current transient voltage assessment methods can be mainly categorized into two types. The first is based on the system voltage instability mechanism, which can clearly reveal the principle of voltage instability but is difficult to apply to complex systems. The second is based on assessment methods derived from engineering experience, which perform a series of numerical calculations on measured fault response data and set corresponding thresholds for transient voltage assessment. The calculation results of these methods deviate significantly from the actual system, failing to provide a reliable basis for channel planning and operational control.

[0004] In summary, there is an urgent need for a method to calculate the DC capacity limit ratio that balances computational accuracy and efficiency and fully considers the coupling characteristics of AC / DC systems, in order to solve the problems of low simulation efficiency and insufficient accuracy caused by model simplification in existing technologies. Summary of the Invention

[0005] The purpose of this invention is to provide a method for calculating the DC capacity limit ratio of transmission channels with embedded DC, which can achieve full coverage of operating conditions with limited computational resources through dynamic coupling modeling, equidistant point allocation, and polynomial fitting, thereby improving simulation efficiency and result accuracy.

[0006] To achieve the above objectives, this invention proposes a method for calculating the DC capacity limit ratio of a transmission channel containing embedded DC, comprising: constructing an AC / DC hybrid system model containing embedded DC based on the target power grid; selecting distribution points at equal intervals within the DC transmission capacity parameter range based on the AC / DC hybrid system model containing embedded DC to obtain a completed distribution point configuration model; calculating transient voltage stability index values ​​under different distribution points based on the completed distribution point configuration model; fitting the DC capacity of the transmission channel and the transient voltage stability index values ​​into a polynomial function based on polynomial approximation; and solving the polynomial function to obtain the DC capacity limit ratio.

[0007] In one optional implementation, the AC / DC hybrid system model with embedded DC simplifies the sending-end AC system to active power injection. Based on the AC / DC hybrid system model with embedded DC, points are selected at equal intervals within the DC transmission capacity parameter range to obtain a complete point configuration model. Specifically, this includes: determining the initial approximation order; selecting the points within the DC transmission capacity parameter range according to the initial approximation order: number of points = N+1; where N is the initial approximation order; for each point, adjusting the embedded DC transmission capacity to an absolute target value using an embedded DC control strategy; and adjusting the proportion of DC transmission capacity under normal operation of the simulation model to the required target value based on the absolute target value. In the formula, p i is the absolute target value; p is the active power injection; after all the matching points are configured, the completed matching point configuration model is obtained.

[0008] In one optional implementation, the transient voltage stability index values ​​under different configuration points are calculated based on the completed configuration point model. Specifically, this includes: setting a three-phase short-circuit fault on the AC line based on the completed configuration point model, obtaining transient voltage response curves when each bus recovers from the fault; selecting an index calculation bus based on the transient voltage response curves, and determining whether the index calculation bus is experiencing a voltage dip or overvoltage; if the index calculation bus is experiencing a voltage dip problem, then constructing a transient voltage dip safety margin index, and calculating the transient voltage stability index value under voltage dip conditions. The expression for the transient voltage dip safety margin index is: In the formula: η i.d.n This refers to the voltage sag safety margin indicator; V cr.d.n For the k-th voltage threshold; t i.d.n The voltage recovery threshold V after the fault cr.d.k The moment; K d.k V represents the weighting coefficient. i (t) represents the bus voltage; if the bus voltage problem is an overvoltage issue, then a transient overvoltage safety margin index is constructed, and the transient voltage stability index value under overvoltage is calculated. The expression for the transient overvoltage safety margin index is: In the formula: η i.d.m For overvoltage safety margin indicators; V cr.r.k For the k-th voltage threshold; t i.r.k When the voltage first exceeds the threshold V cr.r.k The moment; t′ i.r.k When the voltage first drops below V during voltage recovery cr.r.k The moment; K r.k These are the weighting coefficients.

[0009] In an optional implementation, the method for calculating the DC capacity limit ratio of the transmission channel with embedded DC further includes: determining whether there is a critical stable point within the range of DC transmission capacity parameters based on the transient voltage stability index values ​​under different matching points; if not, adjusting the range of DC transmission capacity parameters.

[0010] In an optional implementation, the method for calculating the DC capacity limit ratio of the transmission channel with embedded DC further includes: comparing the transient voltage stability index value under different matching points with the critical stability index value respectively; if the transient voltage stability index value is less than the critical stability index value, the corresponding matching point is a stable matching point, and the range of the critical stability index value is [0,1]; if the transient voltage stability index value is greater than the critical stability index value, the corresponding matching point is an unstable matching point; if the number of stable matching points and the number of unstable matching points are not the same, the range of DC transmission capacity parameters is adjusted.

[0011] In an optional implementation, the method for calculating the DC capacity limit ratio of the transmission channel with embedded DC further includes: selecting two consecutive points whose transient voltage stability index values ​​are on both sides of the critical stability index; calculating the interval between the two consecutive points; and selecting new points outward from the two consecutive points at the same interval.

[0012] In one optional implementation, the expression for the polynomial function is: In the formula, To approximate the index polynomial; ψ k (p i ) represents the parameter vector p i A system of orthogonal polynomials; ψ(p i basis functions in ); c k The coefficients are the ones corresponding to the basis functions; N is the approximation order.

[0013] In an optional implementation, the method for calculating the DC capacity limit ratio of the transmission channel with embedded DC further includes: constructing a quantitative index polynomial error. In the formula, To approximate the result of the index polynomial calculation at the collocation point; η(p i ) represents the transient voltage stability index result; p i m Let ε be the m-th collocation point; compare the error of the quantization index polynomial with the error threshold. If ε > μ, then increase the approximation order of the polynomial function to re-select collocation points for simulation; if ε ≤ μ, then let the calculation result of the approximation index polynomial at the collocation point be... And solve for the DC limit ratio at critical stability.

[0014] The present invention also proposes an electronic device, comprising: at least one processor; a memory communicatively connected to the at least one processor; wherein the memory stores instructions executable by the at least one processor, the instructions being executed by the at least one processor to enable the at least one processor to execute any of the methods for calculating the DC capacity limit ratio of a transmission channel with embedded DC as described in the present invention.

[0015] The present invention also proposes a medium storing a computer program, which, when executed by a processor, implements the method for calculating the DC capacity limit ratio of a power transmission channel with embedded DC as described in any one of the claims.

[0016] The beneficial effects of this invention are: by using dynamic coupling modeling, equidistant point collocation, and polynomial fitting, it is possible to cover all working conditions with a limited amount of computation, thereby improving simulation efficiency and result accuracy. Attached Figure Description

[0017] Figure 1 A flowchart illustrating the method for calculating the DC capacity limit ratio of a power transmission channel containing embedded DC, provided in an embodiment of the present invention;

[0018] Figure 2 A flowchart illustrating an example of a method for calculating the DC capacity limit ratio of a power transmission channel containing embedded DC, provided for implementation of the present invention;

[0019] Figure 3 A schematic diagram of the channel topology in a cross-river section, illustrating an example of the method for calculating the DC capacity limit ratio of a power transmission channel containing embedded DC, provided in an embodiment of the present invention.

[0020] Figure 4 The transient response waveforms of characteristic bus voltage under different configuration points are shown in the example of the DC capacity limit ratio calculation method for transmission channels with embedded DC provided in the embodiments of the present invention.

[0021] Figure 5 The diagram illustrates the relationship between the DC transmission capacity ratio and the system transient voltage stability index, as an example of the DC capacity limit ratio calculation method for a transmission channel with embedded DC provided in this embodiment of the invention. Detailed Implementation

[0022] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0023] like Figure 1 As shown in the embodiments of the present invention, in one aspect, a method for calculating the DC capacity limit ratio of a power transmission channel containing embedded DC is provided, comprising the following steps:

[0024] Step S101: Construct an AC / DC hybrid system model with embedded DC based on the target power grid.

[0025] Step S103: Based on the AC / DC hybrid system model with embedded DC, select matching points at equal intervals within the range of DC transmission capacity parameters to obtain the completed matching point configuration model.

[0026] Step S105: Calculate the transient voltage stability index values ​​under different matching points based on the completed matching point configuration model.

[0027] Step S107: Based on polynomial approximation, fit the DC capacity of the transmission channel and the transient voltage stability index values ​​to a polynomial function.

[0028] Step S109: Solve the polynomial function to obtain the DC capacity limit ratio.

[0029] In this embodiment, a hybrid model that accurately reflects the coupling relationship of AC / DC systems is built based on the actual topology, equipment parameters, and operating characteristics of the target power grid. Specifically, an electromagnetic transient simulation model of the AC / DC channel containing embedded DC is established by selecting the appropriate embedded DC type (embedded LCC-HVDC / embedded SLCC-HVDC / embedded VSC-HVDC).

[0030] First, determine the reasonable parameter range for DC transmission capacity: the lower limit is taken as the current DC capacity operating value of the target power grid or the planned minimum capacity, and the upper limit is taken as the physical transmission limit of the channel (such as the rated capacity of the converter valve and the current carrying capacity limit of the DC line).

[0031] Within this parameter range, N+1 matching points are selected according to the principle of equal intervals (the number of matching points is set according to the calculation accuracy requirements, usually no less than 4), and each matching point corresponds to a specific DC capacity value.

[0032] Substitute the DC capacity parameters of each configuration point into the hybrid system model constructed in step S101 to generate N+1 complete configuration point models of "hybrid system model + specific DC capacity", covering typical operating conditions from minimum to maximum DC capacity.

[0033] For each completed point configuration model, simulate common transient disturbance scenarios of the target power grid.

[0034] The dynamic response of the model under disturbance is solved using electromagnetic transient simulation tools, and the voltage time-domain curves of key monitoring nodes (such as AC busbars of converter stations and load center buses) are extracted. Transient voltage stability indices are calculated based on the voltage time-domain curves, and finally a one-to-one correspondence dataset of "DC capacity - transient voltage stability index values" is obtained.

[0035] The least squares method can be used for polynomial approximation: based on the distribution characteristics of the data samples, select an appropriate polynomial order (usually 2-4; too high an order can easily lead to overfitting, while too low an order will result in insufficient fitting accuracy) and construct a polynomial function.

[0036] By minimizing the sum of squared residuals between the fitted value and the actual index value, the polynomial coefficients are obtained, and finally the polynomial function that can accurately characterize the mapping relationship between DC capacity and transient voltage stability index is determined.

[0037] First, a critical threshold for transient voltage stability is set, and this threshold is used as the critical value y0 of the dependent variable of the polynomial function.

[0038] Solve the equation y = y0 to obtain the corresponding independent variable x0 (i.e., the DC capacity value when the transient voltage just reaches the critical stable state).

[0039] Calculate the DC capacity limit ratio: Based on the total transmission capacity (DC capacity + AC capacity) of the AC / DC transmission channel, the ratio of x0 to the total transmission capacity is defined as the DC capacity limit ratio. This ratio is the optimal critical value that balances the system's transient voltage stability and the channel's transmission efficiency.

[0040] This method accurately constructs a hybrid AC / DC system model (including equipment dynamic characteristics and AC / DC coupling relationship) and calculates transient voltage stability index based on actual disturbance scenarios. It avoids the errors caused by neglecting key dynamic factors in traditional simplified models, and makes the solved DC capacity limit ratio more in line with the actual operating characteristics of the power grid. It can effectively prevent accidents such as commutation failure and voltage collapse caused by excessive DC capacity, and ensure the transient safety of the power grid.

[0041] Compared to the traditional offline simulation model that "traverses all DC capacity operating conditions", this method uses "equal-interval point allocation + polynomial fitting" to calculate the transient indices of only a finite number of points. It can then cover the characteristics of the entire capacity range through function fitting, significantly reducing the amount of simulation calculations and lowering the time cost and computing power consumption for power grid planning and operation analysis in engineering. It is especially suitable for rapid analysis scenarios of large-scale complex power grids.

[0042] The method can clearly give the critical value of the limit ratio of DC capacity, providing a quantitative basis for the planning, design and operation control of AC and DC channels: in the planning stage, the optimal construction scale of DC capacity can be determined based on this, avoiding the problem of insufficient capacity wasting channel potential or excessive capacity sacrificing stability; in the operation stage, this ratio can be used as a constraint condition for DC power regulation, achieving a precise balance between channel transmission efficiency and system stability, and improving the overall resource utilization efficiency of the power grid.

[0043] The model construction process takes into account complex scenarios such as high proportion of renewable energy grid connection, dynamic load changes, and multiple types of fault disturbances. The polynomial fitting method can flexibly adapt to the nonlinear relationship between DC capacity and transient voltage index under different grid topologies. It can be extended to various scenarios such as cross-regional UHV AC / DC channels and embedded DC channels in urban power grids, and has strong engineering practicality and scenario adaptability.

[0044] Further, in step S103, the AC / DC hybrid system model with embedded DC simplifies the sending-end AC system to active power injection. Based on the AC / DC hybrid system model with embedded DC, distribution points are selected at equal intervals within the range of DC transmission capacity parameters to obtain the completed distribution point configuration model. Specifically, this includes the following steps:

[0045] Step S1031: Determine the initial approximation order;

[0046] Step S1033: Within the range of DC transmission capacity parameters, select matching points based on the initial approximation order:

[0047] Number of points = N+1;

[0048] In the formula, N is the initial approximation order;

[0049] Step S1035: For each distribution point, adjust the embedded DC transmission capacity to the absolute target value using the embedded DC control strategy;

[0050] Step S1037: Adjust the DC transmission capacity ratio under normal operation of the simulation model to the required target value based on the absolute target value:

[0051]

[0052] In the formula, p i p represents the absolute target value; p is the active power injection.

[0053] Step S1039: All collocation points are configured, and the completed collocation point configuration model is obtained.

[0054] In this embodiment, the electromagnetic transient simulation model of the AC / DC channel with embedded DC simplifies the sending-end AC system to active power injection, while the receiving-end AC system adopts the Thevenin equivalent. The system model is run in simulation to verify its similarity to the real system.

[0055] By simplifying the sending-end AC system to active power injection, the model complexity and computational load are significantly reduced, while retaining the key characteristic of the sending end supporting the active power of the AC / DC hybrid system. This achieves a good balance between model simplification and computational accuracy, making subsequent calculations more efficient and the results still reliable.

[0056] First, the range of DC transmission capacity parameters should be clearly defined. This range is usually determined by the physical limitations of the DC transmission system (such as the rated capacity of the converter valve, the maximum current carrying capacity of the DC line, etc.) and the actual power grid operation requirements, covering the range from the minimum feasible DC capacity to the maximum possible DC capacity.

[0057] The initial approximation order is determined to be N, and N+1 collocation points are selected. For example, when N=3, the number of collocation points is 4. The DC transmission capacity adjustment range is set, and collocation points are selected at equal intervals. These collocation points are evenly distributed within the DC transmission capacity parameter range, which can relatively uniformly cover the entire capacity interval, providing representative sample points for subsequent polynomial fitting. Selecting collocation points at equal intervals based on the initial approximation order can uniformly cover the DC transmission capacity parameter range, providing reasonably distributed and representative sample points for subsequent polynomial fitting, ensuring that the fitted polynomial function accurately reflects the relationship between the DC transmission capacity and the transient voltage stability index.

[0058] For each selected point of connection, the embedded DC system utilizes its own control strategies, such as constant power control and current control. Taking constant power control as an example, by adjusting control parameters such as the firing angle of the converter valve, the transmission capacity of the embedded DC system is precisely adjusted to the absolute target value p corresponding to that point of connection. i By modifying the embedded DC control strategy parameters, the embedded DC transmission capacity can be adjusted to the target value p. i When adjusting the embedded DC transmission capacity, the DC voltage is not modified; instead, the rated DC transmission capacity is changed by adjusting the rated DC current. Changes in the DC power transmission level affect the reactive power absorption of the AC system by the LCC converter. Therefore, when adjusting the transmission capacity of embedded LCC-HVDC and SLCC-HVDC converters, the parameters of the filter device need to be adjusted to meet the reactive power support requirements of the DC line. By adjusting the DC transmission capacity to the absolute target value through the embedded DC control strategy, the accurate DC capacity setting for each distribution point is ensured, providing accurate input conditions for simulation calculations and improving the accuracy of subsequent transient voltage stability index numerical calculations.

[0059] Adjusting the active power 'p' injected into the AC system at the sending end allows you to adjust the DC transmission capacity ratio under normal operating conditions in the simulation model to the desired target value. To maintain the rated active power transmitted by AC lines in AC / DC channels

[0060] The DC transmission capacity ratio under normal operating conditions is adjusted according to the calculated target value, so that the DC transmission capacity accounts for the required target value in the power transmission of the entire AC / DC transmission channel, thereby simulating the system operation under different DC capacity ratios.

[0061] Once all N+1 distribution points have completed the adjustment of DC transmission capacity and the setting of simulation models according to the above steps, a complete distribution point configuration model is obtained. Each complete distribution point configuration model corresponds to a specific DC transmission capacity ratio operating condition, providing a basic model for subsequent calculation of transient voltage stability index values ​​under different distribution points.

[0062] The DC transmission capacity ratio was calculated and adjusted to the required target value based on the absolute target value. This clearly quantifies the proportion of DC capacity in channel power transmission under different configuration points, making the subsequent analysis of the relationship between transient voltage stability and DC capacity ratio more targeted and operable.

[0063] Further, step S105, calculating the transient voltage stability index values ​​under different matching points based on the completed matching point configuration model, specifically includes the following steps:

[0064] Step S1051: Based on the completed point configuration model, a three-phase short-circuit fault is set in the AC line to obtain the transient voltage response curves when each bus recovers from the fault.

[0065] Step S1053: Select the index calculation bus based on the transient voltage response curve, and determine whether the index calculation bus is a voltage drop or an overvoltage.

[0066] Based on existing practical indicators, multiple sets of voltage threshold values ​​and their maximum allowable recovery time can be designed to determine whether the transient voltage drop of the bus is within the stable range.

[0067] By combining multiple low-voltage binary meter criteria, a transient voltage drop safety margin index can be constructed.

[0068] Step S1055: If the index calculation bus is a voltage sag problem, then construct a transient voltage sag safety margin index, calculate the transient voltage stability index value under voltage sag, and the expression of the transient voltage sag safety margin index is:

[0069]

[0070] In the formula: η i.d.n This refers to the voltage sag safety margin indicator; V cr.d.n For the k-th voltage threshold; t i.d.n The voltage recovery threshold V after the fault cr.d.k The moment; K d.k V represents the weighting coefficient. i (t) represents the bus voltage. K d.k The weighting coefficient can be obtained from equation (2).

[0071]

[0072] A three-phase short-circuit fault was simulated, and the bus voltage curve with the most significant deviation from normal operating value after the fault was selected as the index calculation curve. A transient voltage stability index based on a multi-binary meter was used to reflect the drop in transient voltage response curve and the degree of overvoltage as a value greater than 0.

[0073] Based on the calculation results of the indicators, it can be determined whether a critical stable point exists in the parameter space. If it is determined that no critical stable point exists in the parameter space, the parameter space needs to be adjusted.

[0074] To improve the accuracy of the approximation polynomial, the number of unstable collocations should be equal to the number of stable collocations. Otherwise, the parameter space needs to be adjusted. Select two consecutive collocations on both sides of the critical stability index, and then reselect collocations at equal intervals on both sides of these two collocations.

[0075] In this embodiment, a three-phase short-circuit fault is set on the AC line for fault simulation. After the simulation runs, the voltage changes over time of each bus in the system during the fault occurrence, duration, and recovery process after fault clearance are recorded, resulting in transient voltage response curves for each bus during fault recovery. These curves can intuitively reflect the transient impact of the fault on the voltage of different buses.

[0076] The transient voltage response curves of each busbar during fault recovery are obtained. The busbar with the most significant deviation from the rated value is selected as the index busbar, as its voltage transient characteristics best characterize the transient voltage stability of the entire system. The voltage curves are observed to determine whether the transient voltage stability problem under the current fault is primarily a voltage drop problem (voltage below the rated value by a certain margin) or an overvoltage problem (voltage above the rated value by a certain margin). Based on this, an appropriate transient voltage stability index is selected.

[0077] Step S1057: If the index calculation bus is an overvoltage problem, then construct a transient overvoltage safety margin index, calculate the transient voltage stability index value under overvoltage, and the expression for the transient overvoltage safety margin index is:

[0078]

[0079] In the formula: η i.d.m V is the overvoltage safety margin index under the constraint of m overvoltage multi-binary tables; cr.r.k The voltage threshold of the k-th binary table; t i.r.k When the voltage first exceeds the threshold V cr.r.k The moment; t′ i.r.k When the voltage first drops below V during voltage recovery cr.r.k The moment; K r.k The weighting coefficient can be obtained from equation (4).

[0080]

[0081] Equation (4) integrates multiple factors such as voltage threshold and time to determine the weight, so that the index can accurately measure the degree of harm of overvoltage.

[0082] To minimize changes to the system architecture, the DC voltage is not modified when adjusting the embedded DC transmission capacity; therefore, there is no need to change the transformer ratios on both sides of the DC line. The current control in the embedded DC control strategy is adjusted, thereby changing the embedded DC rated transmission capacity by regulating the operating DC current.

[0083] Changes in power transmission levels can affect the reactive power absorption of the AC system by the LCC converter. Therefore, when adjusting the transmission capacity of embedded LCC-HVDC and SLCC-HVDC converters, it is necessary to adjust the parameters of the filter device to ensure that it can meet the reactive power support requirements of the DC line.

[0084] Using the above indicators, the degree to which the transient voltage response curve obtained from system fault simulation under each matching point deviates from the rated value is expressed as a numerical value. Specifically, by substituting the data of the deviation of the transient voltage response curve obtained from system fault simulation under each matching point from the rated value into this formula, the transient overvoltage safety margin index value under the corresponding matching point is calculated, thereby quantifying the transient voltage stability under overvoltage.

[0085] By distinguishing between two different transient voltage problems, voltage dips and overvoltages, and constructing corresponding safety margin indices for each, we can accurately quantify and analyze different types of transient voltage problems. Compared with general indices, these indices can more accurately characterize the stability of the system under specific transient voltage problems.

[0086] This step covers the two main transient voltage problems that may occur on each bus of the system under a three-phase short-circuit fault in the AC line: voltage drop and overvoltage. It comprehensively covers the typical scenarios of transient voltage stability analysis and provides comprehensive transient voltage stability index data support for the subsequent calculation of the DC capacity limit ratio.

[0087] By utilizing the constructed transient voltage drop safety margin index and transient overvoltage safety margin index, the changes in the transient voltage response curve are transformed into specific numerical indicators, realizing the quantitative analysis of transient voltage stability. This makes the subsequent polynomial fitting and DC capacity limit ratio solution based on these indicators more reliable and scientific.

[0088] The weighting coefficients in the index are calculated using a reasonable formula, taking into account the impact of factors such as voltage threshold and time on transient voltage stability. This allows the index to more realistically reflect the actual impact of different transient voltage stages on system stability, further improving its accuracy and practicality.

[0089] Furthermore, the method for calculating the DC capacity limit ratio of transmission channels containing embedded DC also includes the following steps:

[0090] Based on the transient voltage stability index values ​​under different matching points, determine whether there is a critical stability point within the range of DC transmission capacity parameters;

[0091] If not, adjust the range of DC transmission capacity parameters.

[0092] In this embodiment, by determining whether a critical stability point exists within the range of DC transmission capacity parameters, it is possible to promptly identify whether the current parameter range covers the key variation range of transient voltage stability. If no critical stability point exists, it indicates that the selected parameter range may be too narrow or deviate from the key region of the actual system's transient stability characteristics. Therefore, by adjusting the parameter range, complete and effective data support is ensured when subsequently solving the DC capacity limit ratio based on polynomial fitting, making the entire calculation logic more rigorous and complete.

[0093] The critical stability point is the key inflection point from stability to instability of transient voltage, and it is crucial for determining the DC capacity limit ratio. Only by performing calculations within the parameter range that includes the critical stability point can the fitted polynomial function accurately reflect the relationship between DC capacity and transient voltage stability, thereby improving the accuracy of the final calculated DC capacity limit ratio and avoiding result deviations caused by inappropriate parameter ranges.

[0094] Different power grids have varying AC / DC system characteristics, and their critical conditions for transient voltage stability also differ. This step allows for flexible adjustment of the DC transmission capacity parameter range based on the actual system's transient voltage response, enabling the method to adapt to AC / DC transmission channels with embedded DC lines of different scales and topologies, thus enhancing the method's versatility and adaptability.

[0095] Furthermore, the method for calculating the DC capacity limit ratio of a transmission channel containing embedded DC is characterized by further including the following steps:

[0096] Step S201: Compare the transient voltage stability index values ​​under different matching points with the critical stability index values ​​respectively. If the transient voltage stability index value is less than the critical stability index value, the corresponding matching point is a stable matching point. The range of the critical stability index value is [0,1].

[0097] Step S203: If the transient voltage stability index value is greater than the critical stability index value, then the corresponding matching point is an unstable matching point.

[0098] Step S205: If the number of stable and unstable connection points are not the same, adjust the range of DC transmission capacity parameters.

[0099] The safety range for both of the above indicators is [0,1]: the closer the indicator is to 0, the better the transient voltage stability; the closer the indicator is to 1, the worse the transient voltage stability; when the indicator is equal to 1, the transient voltage is critically stable. When the indicator is greater than 1, the transient voltage becomes unstable.

[0100] If the calculated results of the selected collocation points are all greater than 1 or all less than 1, it is determined that there is no critical stable point in the parameter space, and the parameter space needs to be adjusted and collocation points need to be reselected for simulation.

[0101] By comparing the transient voltage stability index with the critical stability index, it is possible to clearly distinguish between stable and unstable matching points, and accurately delineate the stability and instability boundaries of the DC transmission capacity under different operating conditions. Compared with traditional empirical assessments, this quantitative judgment method can more objectively and accurately identify the critical state of transient voltage stability of the system, providing a reliable basis for determining the subsequent limit ratio of DC capacity.

[0102] Using the equality of the number of stable and unstable connection points as the basis for adjusting the range of DC transmission capacity parameters allows for dynamic optimization of parameter range selection. If the number of the two types of connection points differs, it means that the current parameter range may not fully cover the critical stability region. Adjusting the parameter range in this case ensures that subsequent calculations can capture key changes in transient voltage stability, avoiding deviations from actual conditions in the DC capacity limit ratio calculation due to an unreasonable parameter range, thus improving the effectiveness and relevance of the calculation.

[0103] This step endows the calculation method with self-optimization capabilities, enabling it to adaptively adjust the range of DC transmission capacity parameters based on the transient voltage response characteristics of different power grid systems. Whether the AC / DC transmission channel is simple or complex with embedded DC, this mechanism can obtain a suitable calculation range, thereby improving the method's versatility and ensuring accurate calculation of the DC capacity limit ratio in various practical engineering scenarios.

[0104] By identifying stable and unstable collocation points and adjusting parameter ranges, misjudgments caused by improper selection of calculation intervals can be effectively avoided, ensuring that the collocation point data used for polynomial fitting accurately reflects the system's transition from stability to instability. This helps to construct a more accurate functional relationship between DC capacity and transient voltage stability indicators, thereby improving the reliability of the final calculated DC capacity limit ratio and providing more valuable decision-making basis for power grid planning and operation scheduling.

[0105] Furthermore, the method for calculating the DC capacity limit ratio of transmission channels with embedded DC also includes the following steps:

[0106] Step S207: Select two consecutive points on both sides of the critical stability index where the transient voltage stability index value is located.

[0107] Step S209: Calculate the interval between two consecutive collocation points.

[0108] Step S2011: Select new collocation points outward from each of the two consecutive collocation points at equal intervals.

[0109] By selecting two consecutive points where the transient voltage stability index values ​​are on either side of the critical stability index, we can focus on the transition region from stability to instability in the system's transient voltage. This region is the core key area for determining the DC capacity limit ratio. Detailed analysis of this region allows for a more accurate capture of the changing patterns of transient voltage stability, laying the foundation for subsequent precise calculations of the DC capacity limit ratio.

[0110] Calculating the interval between two consecutive matching points and selecting new matching points outwards at the same interval is equivalent to performing denser sampling around the critical region. By increasing the number of matching points in this region, the relationship curve between "DC transmission capacity and transient voltage stability index" can be depicted more meticulously in the critical region, thereby improving the accuracy of subsequent polynomial fitting and ultimately enhancing the accuracy of the DC capacity limit ratio calculation results.

[0111] Selecting new points on the outer side expands the coverage of the points, which not only reflects the changes in transient voltage stability near the critical region more comprehensively, but also avoids calculation deviations caused by accidental factors in the initial point selection to a certain extent. This allows the entire calculation method to maintain good stability and reliability when facing different power grid conditions, thus enhancing the robustness of the method.

[0112] Specifically, the expression for the polynomial function is:

[0113]

[0114] Mode, To approximate the index polynomial; ψ k (p i ) represents the parameter vector p i A system of orthogonal polynomials; ψ(p i basis functions in ); c k The coefficients are the ones corresponding to the basis functions; N is the approximation order.

[0115] Orthogonal polynomial system ψ(p i The recursive expression for ) is shown in the following equation:

[0116]

[0117] In the formula: ψ m (p i ) represents parameter p i orthogonal polynomial system ψ(pi The m-th order polynomial within )

[0118] The calculation method for the DC capacity limit ratio of transmission channels with embedded DC also includes the following steps:

[0119] Step S301: Construct the quantitative index polynomial error:

[0120]

[0121] In the formula, To approximate the result of the index polynomial calculation at the collocation point; η(p i ) represents the transient voltage stability index result; p i m Let m be the collocation point;

[0122] Step S303: Compare the quantitative index polynomial error with the error threshold. If ε>μ, increase the approximation order of the polynomial function to re-select collocation points for simulation.

[0123] Step S305: If ε≤μ, then let the calculation result of the approximation index polynomial at the collocation point be: And solve for the DC limit ratio at critical stability.

[0124] In this embodiment, after obtaining the approximation index polynomial function, error calculation is still required. When the error is large, the critical stable point obtained by solving the polynomial will differ significantly from the actual value. The index polynomial error is quantified by equation (7), and when the error is large, the simulation is performed by increasing the approximation order.

[0125] If the error is within the allowable range, the obtained approximation index polynomial function can approximately express the relationship between transient voltage stability and DC transmission capacity. When the transient voltage is critically stable, the limit value of the DC transmission capacity can be obtained using this polynomial function. Since the transient voltage stability index of 1 indicates critical stability, let the approximation index polynomial... Solve for the DC transmission capacity p at critical stability. i Value selection. An approximate index polynomial function curve can be plotted. The point where the ordinate of the curve is exactly equal to 1 is selected, and its abscissa value is read to solve for the value. Finally, the DC transmission capacity limit ratio at the system's critical stability is obtained.

[0126] Based on the calculation results, a simulation model was set up to perform fault simulation and obtain the transient voltage response curve. The transient voltage stability index was calculated to verify the correctness of the calculation results.

[0127] Application Examples

[0128] like Figure 2 As shown, step one: target system modeling and point allocation.

[0129] First, determine the parameter space of the DC transmission capacity, select matching points, and set the system parameters based on the matching points.

[0130] Based on the target system, an appropriate embedded DC type (embedded LCC-HVDC / embedded SLCC-HVDC / embedded VSC-HVDC) is selected to establish an electromagnetic transient simulation model of the AC / DC channel containing embedded DC. The sending-end AC system is simplified to active power injection, and the receiving-end AC system adopts the Thevenin equivalent. The system model is run in simulation to verify its similarity to the real system.

[0131] The initial approximation order is determined to be N, and N+1 calibration points are selected. The DC transmission capacity adjustment range is set, and calibration points are selected at equal intervals. By modifying the embedded DC control strategy parameters, the embedded DC transmission capacity can be adjusted to the target value p. i When adjusting the embedded DC transmission capacity, the DC voltage is not modified; instead, the rated DC transmission capacity is changed by adjusting the rated DC current. Changes in the DC power transmission level will affect the reactive power absorption of the AC system by the LCC converter. Therefore, when adjusting the transmission capacity of embedded LCC-HVDC and SLCC-HVDC converters, the parameters of the filter device need to be adjusted to ensure that it can meet the reactive power support requirements of the DC line.

[0132] Adjusting the active power 'p' injected into the AC system at the sending end allows you to adjust the DC transmission capacity ratio under normal operating conditions in the simulation model to the desired target value. To maintain the rated active power transmitted by AC lines in AC / DC channels.

[0133] like Figure 3 As shown, this embodiment takes a channel in a cross-river section as an example. Let the active power transmitted by the embedded LCC-HVDC be a variable parameter p1, and let the parameter range be p1∈[1200,1800]MW. The initial approximation order is determined to be 3. Four points are uniformly selected within the parameter range, and the simulation system parameters are set according to the points.

[0134] Step 2: Calculate the stability index of each collocation point.

[0135] After setting the system parameters, a short-circuit fault is introduced at an appropriate location in the system to determine the transient voltage stability index. The fault will cause voltage fluctuations on multiple buses; therefore, a small number of critical buses need to be selected, and the transient voltage safety margin index of these critical buses will be used to characterize the system's transient voltage stability. Among the buses with similar voltage response characteristics, the transient voltage problem is most severe on the critical buses.

[0136] A three-phase short-circuit fault is set at bus 1525 for a duration of 5 power frequency cycles.

[0137] Since the fault occurred near busbar 2525, and simulation results show that, apart from busbar 1525, the voltage drop at busbar 2525 is the most significant, the transient stability index of busbar 2525 is selected as the transient voltage stability index η of the system.

[0138] The voltage response curve obtained from the fault simulation is as follows: Figure 4 As shown in Table 1, the overvoltage safety margin index was selected, and the transient voltage stability index data was calculated.

[0139] Table 1. Transient voltage stability indices corresponding to the four sets of parameters within the point set.

[0140]

[0141] Step 3: Select the dominant transient voltage stability index and determine whether the parameter range and the selected points are reasonable.

[0142] Transient voltage stability indices are obtained based on simulations at each matching point. To determine whether the system's transient voltage stability problem is a voltage dip or overvoltage problem, the dominant index among the transient voltage dip safety margin and transient overvoltage safety margin indices is selected.

[0143] Determine if the parameter space can reach a critical stable value. If all simulation results are greater than 1 or less than 1, it is determined that there is no critical stable point in the parameter space, and the parameter space needs to be adjusted.

[0144] To improve the accuracy of the solution, it is necessary to ensure that the number of unstable collocations is almost equal to the number of stable collocations; otherwise, the parameter space needs to be adjusted.

[0145] When η>1, the system is unstable. The proportion of unstable collocation points in this embodiment is calculated to be λ=50%, which meets the requirements.

[0146] Step 4: Obtain the approximation index polynomial function whose error meets the requirements.

[0147] The transient voltage stability index η can be approximated with the DC transmission capacity p through polynomial approximation. i The function η(p) i It can be approximately expressed as a polynomial function.

[0148]

[0149] In the formula: To approximate the index polynomial, ψ k (p i ) represents the parameter vector p i orthogonal polynomial system ψ(p i basis functions in ); c k The coefficients are the ones corresponding to the basis functions; N is the approximation order.

[0150] Find the parameter vector p i orthogonal polynomial system ψ(p i The calculation formula is shown below.

[0151] <ψ m (p i ),ψ n (p i )>=∫ψ m (p i )·ψ n (p i )·ω(p i )dp i =0;

[0152] In the formula: m and n are the orders of the polynomials and m ≠ n, ω(p i ) is the probability density function.

[0153] In practical applications, p i Typically, they are uniformly distributed within the parameter range, and their orthogonal polynomial system is the Legendre polynomial, with the recursive expression shown in the following equation.

[0154]

[0155] In the formula: ψ m (p i ) represents parameter p i orthogonal polynomial system ψ(p i The m-th order polynomial within )

[0156] Treating the system as a black box, without adjusting the system model, after determining the collocation set, all collocation points are passed to the system black box. The stability index η is then obtained from the black box. Using the index calculation results obtained under each collocation case, the coefficients c corresponding to each order of basis functions are obtained by using the collocation method to calculate the polynomial coefficients. k .

[0157] By combining the basis functions of each order and their coefficients, the approximate polynomial of the transient voltage stability index can be obtained.

[0158] After obtaining the approximation index polynomial function, error calculation is still required. When the error is large, the critical stable point obtained by solving the polynomial will differ significantly from the actual value. The index polynomial error is quantified by equation (7), and the error can be reduced by increasing the approximation order when the error is large.

[0159]

[0160] In the formula The result of the index polynomial calculation at the collocation point, η(p) i ) represents the transient voltage stability index result, pi m Let m be the collocation point. If the error is within the allowable range, the obtained approximate index polynomial function can approximately express the relationship between transient voltage stability and DC transmission capacity.

[0161] The approximation index polynomial function in this embodiment is obtained as follows:

[0162]

[0163] Substituting the collocation points into equation (7), we obtain the error index ε = 0.0304%, which is within the allowable range.

[0164] Based on the approximation index polynomial, the DC limit ratio at critical stability is solved.

[0165] Step 5: Based on the approximation index polynomial, solve for the DC limit ratio at critical stability.

[0166] When the transient voltage reaches critical stability, the limit value of the DC transmission capacity can be obtained using this polynomial function. Since a transient voltage stability index of 1 indicates critical stability, let the approximation index polynomial be... Solve for the DC transmission capacity p at critical stability. i Values.

[0167] The curve of the approximate index polynomial function can be plotted. The point where the ordinate of the curve is exactly equal to 1 can be selected, and its abscissa value can be read to solve the problem. Finally, the maximum DC transmission capacity ratio at which the system reaches critical stability can be obtained.

[0168] Based on the calculation results, a simulation model was set up to perform fault simulation and obtain the transient voltage response curve. The transient voltage stability index was calculated to verify the correctness of the calculation results.

[0169] make The critical stability limit value of p1 in this embodiment is found to be 1464MW, with a DC transmission capacity ratio of 56.29%. The relationship between the DC transmission capacity ratio and the stability index is as follows: Figure 5 As shown.

[0170] This invention targets AC / DC transmission sections with embedded DC current. It utilizes transient voltage stability as a system safety and stability assessment index to determine the DC limit ratio at the system's critical stability, thereby studying the optimal AC / DC ratio for hybrid systems. First, a target system with embedded DC current is modeled. Within the range of DC transmission capacity parameters, a simulation model is selected to configure the distribution points. Fault simulations are performed to obtain transient voltage response curves. Based on the transient voltage stability assessment index, the degree of transient voltage deviation from the rated value is expressed numerically. Using polynomial approximation, the DC capacity of the transmission channel is fitted to the calculated index data into a polynomial function. This function is then used to solve for the DC limit ratio of the hybrid power grid.

[0171] On the other hand, the present invention proposes an electronic device, characterized in that it includes: at least one processor; a memory communicatively connected to the at least one processor; wherein the memory stores instructions executable by the at least one processor, the instructions being executed by the at least one processor to enable the at least one processor to execute any one of the following methods for calculating the DC capacity limit ratio of a transmission channel with embedded DC.

[0172] On the other hand, the present invention proposes a medium, which is a computer storage medium storing a computer program, wherein when the computer program is executed by a processor, it implements any one of the methods for calculating the DC capacity limit ratio of a transmission channel containing embedded DC.

[0173] Computer storage media may be simply referred to as media. Those skilled in the art will understand that all or part of the processes in the methods of the above embodiments can be implemented by a computer program instructing related hardware. The program can be stored in a non-volatile computer-readable storage medium, and when executed, it can include the processes of the embodiments of the above methods. Any references to memory, storage, databases, or other media used in the embodiments provided in this application may include non-volatile and / or volatile memory. Non-volatile memory may include read-only memory (ROM), programmable ROM (PROM), electrically programmable ROM (EPROM), electrically erasable programmable ROM (EEPROM), or flash memory. Volatile memory may include random access memory (RAM) or external cache memory. By way of illustration and not limitation, RAM is available in various forms, such as Static RAM (SRAM), Dynamic RAM (DRAM), Synchronous DRAM (SDRAM), Dual Data SDRAM (DDRSDRAM), Enhanced SDRAM (ESDRAM), Synchlink DRAM (SLDRAM), Rambus Direct RAM (RDRAM), Direct Memory Bus Dynamic RAM (DRDRAM), and Memory Bus Dynamic RAM (RDRAM). The various embodiments described in this specification are presented in a progressive manner, and similar or identical parts between embodiments can be referred to interchangeably. Each embodiment focuses on describing the differences from other embodiments. In particular, for embodiments of apparatus, devices, and non-volatile computer storage media, since they are substantially similar to the method embodiments, the description is relatively simple, and relevant parts can be referred to the description of the method embodiments.

[0174] The above embodiments are merely illustrative examples and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for calculating the DC capacity limit ratio of a power transmission channel containing embedded DC, characterized in that, include: Construct a hybrid AC / DC system model with embedded DC based on the target power grid; Based on the AC / DC hybrid system model with embedded DC, the matching points are selected at equal intervals within the range of DC transmission capacity parameters to obtain the complete matching point configuration model; Based on the completed point configuration model, calculate the transient voltage stability index values ​​under different point configurations; Based on polynomial approximation, the DC capacity of the power transmission channel is fitted to the transient voltage stability index as a polynomial function. Solve the polynomial function to obtain the DC capacity limit ratio.

2. The method for calculating the DC capacity limit ratio of a transmission channel with embedded DC as described in claim 1, characterized in that, The AC / DC hybrid system model with embedded DC simplifies the sending-end AC system to active power injection. Based on this model, distribution points are selected at equal intervals within the DC transmission capacity parameter range to obtain a complete distribution point configuration model, specifically including: Determine the initial approximation order; Within the range of DC transmission capacity parameters, the matching points are selected according to the initial approximation order: Number of points = N+1; In the formula, N is the initial approximation order; For each distribution point, the embedded DC transmission capacity is adjusted to the absolute target value through an embedded DC control strategy; Based on the absolute target value, adjust the DC transmission capacity ratio under normal operation of the simulation model to the required target value: In the formula, p i p represents the absolute target value; p is the active power injection. Once all the points are configured, the completed point configuration model is obtained.

3. The method for calculating the DC capacity limit ratio of a transmission channel with embedded DC as described in claim 1, characterized in that, Based on the completed point configuration model, the transient voltage stability index values ​​under different point configurations are calculated, specifically including: Based on the completed point configuration model, a three-phase short-circuit fault is set in the AC line to obtain the transient voltage response curves of each bus when the fault is recovered. Based on the transient voltage response curve, select the index calculation bus and determine whether the index calculation bus is a voltage drop or an overvoltage. If the bus for calculating the index is a voltage dip problem, then a transient voltage dip safety margin index is constructed, and the value of the transient voltage stability index under voltage dip is calculated. The expression for the transient voltage dip safety margin index is: In the formula: η i.d.n This refers to the voltage sag safety margin indicator; V cr.d.n For the k-th voltage threshold; t i.d.n The voltage recovery threshold V after the fault cr.d.k The moment; K d.k V represents the weighting coefficient. i (t) represents the bus voltage; If the bus for calculating the index is an overvoltage problem, then a transient overvoltage safety margin index is constructed, and the value of the transient voltage stability index under overvoltage is calculated. The expression for the transient overvoltage safety margin index is: In the formula: η i.d.m For overvoltage safety margin indicators; V cr.r.k For the k-th voltage threshold; t i.r.k When the voltage first exceeds the threshold V cr.r.k The moment; t′ i.r.k When the voltage first drops below V during voltage recovery cr.r.k The moment; K r.k These are the weighting coefficients.

4. The method for calculating the DC capacity limit ratio of a transmission channel containing embedded DC according to any one of claims 1 to 3, characterized in that, Also includes: Based on the transient voltage stability index values ​​under different matching points, determine whether there is a critical stability point within the range of DC transmission capacity parameters; If not, adjust the range of the DC transmission capacity parameters.

5. The method for calculating the DC capacity limit ratio of a transmission channel containing embedded DC according to any one of claims 1 to 3, characterized in that, Also includes: The transient voltage stability index values ​​under different matching points are compared with the critical stability index values. If the transient voltage stability index value is less than the critical stability index value, the corresponding matching point is a stable matching point. The range of the critical stability index value is [0,1]. If the transient voltage stability index value is greater than the critical stability index value, then the corresponding matching point is an unstable matching point; If the number of stable connection points is different from the number of unstable connection points, then the range of DC transmission capacity parameters is adjusted.

6. The method for calculating the DC capacity limit ratio of a transmission channel with embedded DC as described in claim 5, characterized in that, Also includes: Select two consecutive points whose transient voltage stability index values ​​are on either side of the critical stability index; Calculate the interval between two consecutive collocation points; At equal intervals, new collocation points are selected outward from the two consecutive collocation points respectively.

7. The method for calculating the DC capacity limit ratio of a transmission channel containing embedded DC according to any one of claims 1 to 3, characterized in that, The expression for the polynomial function is: Mode, To approximate the index polynomial; ψ k (p i ) represents the parameter vector p i A system of orthogonal polynomials; ψ(p i basis functions in ); c k The coefficients are the ones corresponding to the basis functions; N is the approximation order.

8. The method for calculating the DC capacity limit ratio of a transmission channel with embedded DC as described in claim 7, characterized in that, Also includes: Constructing a quantitative indicator polynomial error: In the formula, To approximate the result of the index polynomial calculation at the collocation point; η(p i ) represents the transient voltage stability index result; p i m Let m be the collocation point; Compare the polynomial error of the quantization index with the error threshold. If ε > μ, then increase the approximation order of the polynomial function to re-select collocation points for simulation. If ε≤μ, then let the result of the approximation index polynomial at the collocation point be: And solve for the DC limit ratio at critical stability.

9. An electronic device, characterized in that, include: At least one processor; A memory that is communicatively connected to the at least one processor; The memory stores instructions that can be executed by the at least one processor, which are executed by the at least one processor to enable the at least one processor to perform the method for calculating the DC capacity limit ratio of a power transmission channel with embedded DC, as described in any one of claims 1 to 8.

10. A medium, characterized in that, The system contains a computer program that, when executed by a processor, implements the method for calculating the DC capacity limit ratio of a power transmission channel with embedded DC as described in any one of claims 1 to 8.

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