A multi-machine group equivalent method for full-power inverter-based new energy power supply

Abstract

The application discloses a multi-machine group equivalent method of a full-power inverter new energy power source, and comprises the following steps: establishing a multi-machine group short-circuit current analytical model of the full-power inverter new energy power source and performing phase conversion; dividing into two categories according to whether the machine group enters low penetration control, wherein the weighted average voltage method is used for equivalent for the machine group which does not enter low penetration control; for the machine group which enters low penetration control, firstly, equivalent modeling is performed on two machine groups; the relative error and the electrical quantity relationship generated by the equivalent modeling are used, and the electrical quantity boundary corresponding to the corresponding category is calculated in combination with a given error upper limit, so that the group equivalent is realized; meanwhile, based on the equivalent idea of the two machine groups, the method can also be extended to the scene of more than two machine groups. By using the method, the equivalent modeling precision of the new energy power source can be ensured, the equivalent model complexity is simplified, the simulation time is reduced, and the calculation efficiency of the network short-circuit current is improved.

Description

Technical Field

[0001] This invention relates to the field of power system equivalent modeling technology, and in particular to a multi-machine grouping equivalent method for full-power inverter-type new energy power sources. Background Technology

[0002] my country's wind power installed capacity has grown rapidly. As of April 2021, the national installed power generation capacity reached 2.23 billion kilowatts, a year-on-year increase of 9.5%, of which wind power installed capacity reached 290 million kilowatts, a year-on-year increase of 34.6%, far exceeding the growth rate of the total installed power generation capacity. The large-scale integration of wind power, photovoltaic, and other new energy sources into the power grid has altered the grid topology and power flow distribution, highlighting the fault characteristics of power electronic devices in the system. Their controlled and distorted short-circuit currents differ significantly from those of synchronous power sources, affecting the performance of protection devices and the safe operation level of the system under grid short-circuit fault disturbances. However, current equivalent modeling methods for new energy power plants often employ single-machine multiplication. When performing equivalent modeling on a large number of new energy power sources with different operating states, the accuracy of single-machine equivalent models is poor, severely reducing the accuracy of fault currents after short circuits and hindering the analysis of relay protection device performance.

[0003] With the rapid increase in the proportion of renewable energy sources such as wind and solar power connected to the grid, traditional single-unit equivalent models can no longer meet the needs of actual production and operation. Moreover, compared with synchronous generators, renewable energy sources such as wind and solar power, which utilize power electronics technology for grid connection, exhibit differences in their operating mechanisms, grid topologies, and control methods. This leads to complex and unique fault transient characteristics of renewable energy sources, posing new challenges to the modeling of power plants with high-density renewable energy connections. Therefore, it is urgent to develop equivalent modeling methods suitable for power plants containing renewable energy sources. Summary of the Invention

[0004] The purpose of this invention is to provide a multi-machine grouping equivalent method for full-power inverter-type new energy power supplies, which can ensure the accuracy of equivalent modeling of new energy power supplies, simplify the complexity of equivalent models, reduce simulation time, and improve the calculation efficiency of network short-circuit current.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] A multi-machine grouping equivalent method for full-power inverter-type new energy power supplies includes:

[0007] An analytical model of the short-circuit current of a multi-unit full-power inverter power supply is established, and phase conversion is performed on the analytical model and the equivalent model of the short-circuit current of the multi-unit power supply respectively.

[0008] Based on whether the unit enters low-temperature control, it is divided into two categories;

[0009] If the model belongs to the category of not entering the low-voltage transmission range, then the single-unit equivalent model is used for equivalent modeling based on the analytical relationship between the multi-unit short-circuit current analytical model and the equivalent model after phase conversion. If the model belongs to the category of entering the low-voltage transmission range, then the multi-unit equivalent model is used for multi-unit equivalent modeling based on the analytical relationship between the multi-unit short-circuit current analytical model and the equivalent model after phase conversion. The electrical quantity boundary is calculated using the relative error generated by the multi-unit equivalent modeling and the electrical quantity relationship, and the units are grouped according to the electrical quantity boundary.

[0010] As can be seen from the technical solution provided by the present invention, the fault characteristics of full-power inverter-type new energy power supply are fully considered. Equivalent modeling is performed according to different fault characteristics, and then the relationship between the error of equivalent modeling and electrical quantities is established. Combined with the established error boundary, the electrical quantity boundary is determined to achieve clustering. Simulation experiments show that the equivalent model of full-power inverter-type new energy power supply that is suitable for engineering application obtained by the present invention is simple, reduces the simulation time required, maintains a certain accuracy, and improves the network current calculation performance of new energy power supply. Attached Figure Description

[0011] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0012] Figure 1 A flowchart illustrating a multi-machine grouping equivalent method for a full-power inverter-type new energy power supply provided in an embodiment of the present invention;

[0013] Figure 2 A detailed model topology diagram provided for embodiments of the present invention;

[0014] Figure 3 This is a schematic diagram of the equivalent model topology provided in an embodiment of the present invention;

[0015] Figure 4 The voltage drop to 0.5 pu is a simulation verification diagram provided in an embodiment of the present invention;

[0016] Figure 5 The voltage drop to 0.3 pu is a simulation verification diagram provided in an embodiment of the present invention.

[0017] Figure 6 This is a system topology for a region with centralized access to new energy sources in an artificial experiment provided in an embodiment of the present invention;

[0018] Figure 7 The diagram shows the experimental verification provided in the embodiments of the present invention. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0020] First, the following explanations are provided for the terms that may be used in this article:

[0021] The terms “including,” “comprising,” “containing,” “having,” or other similar semantic descriptions should be interpreted as non-exclusive inclusion. For example, “including a technical feature element (such as raw material, component, ingredient, carrier, dosage form, material, size, part, component, mechanism, device, step, process, method, reaction conditions, processing conditions, parameter, algorithm, signal, data, product or article of manufacture, etc.)” should be interpreted as including not only the expressly listed technical feature element, but also other technical feature elements that are not expressly listed and are well-known in the art.

[0022] The following is a detailed description of the multi-unit grouping equivalent method for a full-power inverter-type new energy power supply provided by this invention. Contents not described in detail in the embodiments of this invention are prior art known to those skilled in the art. Where specific conditions are not specified in the embodiments of this invention, they shall be performed according to conventional conditions in the art or conditions recommended by the manufacturer. Where the manufacturers of the equipment involved in the embodiments of this invention are not specified, they are all conventional products that can be purchased commercially.

[0023] like Figure 1 As shown, a multi-machine grouping equivalent method for a full-power inverter-type new energy power supply mainly includes the following steps:

[0024] Step 1: Establish a multi-unit short-circuit current analytical model for a full-power inverter power supply, and perform phase conversion on both the multi-unit short-circuit current analytical model and the equivalent model.

[0025] The current of a full-power inverter-type new energy power supply is entirely output from the grid-side converter. Its fault characteristics are mainly divided into the low-voltage control stage (0.2U). N <U s ≤0.8U N ) and outer loop control phase (0.8U N <U s ), U s U is the per-unit voltage input to the phase-locked loop of the new energy (unit). N This is the rated voltage at the station terminal.

[0026] In this embodiment of the invention, according to relevant technical regulations (specifically, the "Technical Regulations for Wind Farm Access to Power Systems"), a multi-unit short-circuit current analytical model for a full-power inverter power supply is established, expressed as follows:

[0027]

[0028]

[0029] Among them, i d i q These are the d-axis and q-axis currents of the short-circuit current output by the full-power inverter power supply, respectively. N I is the rated current of the station. max P0 is the maximum allowable output circuit current of the new energy power station, K is the reactive current support coefficient (for example, K can be set to 1.5), and P0 is the output power of the power station before the fault.

[0030] Since the reference phases of each unit are different, they need to be reduced to the same reference system. The reference phase can be the synchronous machine phase; or, if the new energy capacity is smaller than the system capacity, the fault point phase can be selected as the reference phase. After selecting the reference phase, the phase conversion is performed on the multi-unit short-circuit current analytical model of the full-power inverter power supply to obtain the steady-state short-circuit current analytical model, which is expressed as:

[0031]

[0032] Among them, i d∑ i q∑ These are the d-axis and q-axis currents of the short-circuit current converted to the reference phase from the full-power inverter power supply model (which can be considered a detailed model in comparison) before the equivalent calculation; i di i qi Let θ be the d-axis and q-axis currents of the short-circuit current output by the phase-locked loop of unit i, respectively. These can be obtained from equations (1) and (2). i This is the difference between the output phase and the reference phase of the unit's i-phase-locked loop.

[0033] Similarly, for the equivalent model, we have:

[0034]

[0035] In the formula: i d∑eq i q∑eq These are the d-axis and q-axis currents of the short-circuit current output after phase conversion from the equivalent model, respectively, and θ. eq Let i be the difference between the phase output of the equivalent model phase-locked loop and the reference phase. deq i qeq The d-axis and q-axis currents of the short-circuit current output before phase conversion of the equivalent model can be obtained according to equations (1) and (2).

[0036] Those skilled in the art will understand that the equivalent model is a conventional model for power systems.

[0037] Step 2: Divide into two categories based on whether the unit enters low-temperature penetration control.

[0038] In this embodiment of the invention, the category classification method includes: if U is satisfied s >0.8U N If it falls into the category of not entering the low-crossing zone; if it satisfies 0.2U N s <0.8U N If so, it belongs to the category of entering the low-passing zone;

[0039] Furthermore, the present invention does not distinguish the execution order of the aforementioned steps 1 and 2; they can be executed simultaneously or sequentially.

[0040] Step 3: If the unit belongs to the category of not entering the low-voltage transmission range, then the single-unit equivalent model is used for equivalent modeling based on the analytical relationship between the multi-unit short-circuit current analytical model and the equivalent model after phase conversion. If the unit belongs to the category of entering the low-voltage transmission range, then the multi-unit equivalent model is used for multi-unit equivalent modeling based on the analytical relationship between the multi-unit short-circuit current analytical model and the equivalent model after phase conversion. The electrical quantity boundary is calculated using the relative error and electrical quantity relationship generated by the multi-unit equivalent modeling, and the units are grouped according to the electrical quantity boundary.

[0041] In this embodiment of the invention, the overall approach to multi-unit equivalent modeling is as follows: equalization is performed based on the short-circuit current error generated by the equalization method, with a time scale between 200 and 300 milliseconds (this range is merely an example; in practical applications, users can adjust the time scale according to their needs or experience). Therefore, the dynamic processes of the mechanical parts or photovoltaic arrays during the fault process are not considered. Since the degree of fault varies across different control modes, the current fault characteristics are also inconsistent. First, the units are divided into two categories based on whether they have entered the low-voltage passthrough control zone. Units not entering the low-voltage passthrough zone are modeled using a single-unit equivalent method. For units entering the low-voltage passthrough zone, the calculation method for the equivalent impedance is derived based on the voltage-controlled current source characteristics of the inverter power supply. Furthermore, based on the boundary of the short-circuit current error, the electrical quantity boundary that determines the current error is calculated. The grouping of units is then achieved based on the differences in electrical quantities among the units.

[0042] In this embodiment of the invention, the equivalent method for two generating units is first discussed, and it can be extended to application scenarios with more than two generating units. The equivalent site topology is as follows: Figure 3 As shown, Figure 2 The chain structure shown in the detailed model is equivalent to a parallel structure.

[0043] ​The equivalent modeling methods for the two types of cases will be introduced below.

[0044] 1. Not entered the low-crossing zone.

[0045] When a shallow voltage drop occurs in the system and the inverter voltage outer loop is not disconnected, according to the aforementioned equations (1), (2), and (3), we can obtain:

[0046]

[0047] In the formula: i d∑ i q∑ These are the d-axis and q-axis currents, respectively, of the short-circuit current converted to the reference phase from the full-power inverter power supply model before equivalence, i. d1 i d2 The d-axis currents of the short-circuit currents output by Unit 1 and Unit 2 are respectively obtained from Equation (2), and θ1 and θ2 are the differences between the voltage phase output by the phase-locked loop of Unit 1 and Unit 2 and the reference phase, respectively.

[0048] Similarly, the short-circuit current after reduction using the equivalent model can be obtained as follows:

[0049]

[0050] In the formula: i deq =2(P1+P2) / (3u deq The short-circuit current (d-axis current) output by the equivalent model is given by equation (u), where P1 and P2 are the active power outputs of units 1 and 2, respectively. deq For the d-axis voltage of the equivalent model, i d∑eq i q∑eq These represent the short-circuit currents on the d-axis and q-axis, respectively, converted from the equivalent model to the reference phase.

[0051] Because the station's collection line is relatively short, its reactance is relatively small, and the voltage drop is shallow as it does not enter the low-voltage break-through zone, the voltage transverse component on the line is small, and the phase difference between each node is small. Ignoring the voltage phase difference and subtracting equation (6) from equation (5), the equivalent error of the dq-axis short-circuit current can be obtained as follows:

[0052]

[0053] In the formula: u d1 u d2 The equivalent error Δi of the d-axis voltage and dq-axis short-circuit current of units 1 and 2. dq Includes Δi d With Δi qTwo parts; according to the above formula, the short-circuit current dq axis current error brought about by the equivalent is mainly caused by the difference in voltage amplitude. Therefore, the impedance equivalent method of weighted average voltage is adopted, and the units that have not entered the low-break-through range are classified into one category and the single-unit equivalent method is adopted.

[0054] The formula for calculating the weighted average voltage method is as follows:

[0055]

[0056] In the formula, M represents the number of wind turbine units, n represents the number of wind turbine units in the main wind turbine branch of the wind farm, and Z represents the number of wind turbine units in the main wind turbine branch of the wind farm. eq Z is the equivalent line impedance. k Let P be the impedance of line k. i P j The rated active power of units i and j are respectively, and the subscripts i, j, and h are the unit serial numbers.

[0057] In existing technologies, single-machine equivalent methods are applied to both entry and non-entry low-voltage crossing control. The above description of this invention theoretically demonstrates the feasibility for non-entry low-voltage crossing control. To maintain the integrity of the method (including multi-machine modeling for both control types), a weighted average voltage impedance equivalent method is used, and its feasibility is theoretically proven. Specifically, in this embodiment, the single-machine equivalent method is directly used to represent one machine for non-entry low-voltage crossing control, while group equivalent methods are used for entry low-voltage crossing control (see details below).

[0058] 2. Enter the low-pass zone.

[0059] As mentioned earlier, we will first introduce the equivalent method for two generating units (referred to as Unit 1 and Unit 2). When the voltage drop is significant, the renewable energy power station enters low-voltage protection control. By combining equations (1), (2), and (3), we can obtain:

[0060]

[0061] Among them, i d∑ i q∑ θ1 and θ2 are the d-axis and q-axis currents of the short-circuit current converted to the reference phase from the full-power inverter power supply model before equivalence, respectively. θ1 and θ2 are the voltage phase differences between the output voltage phases of Unit 1 and Unit 2 phase-locked loops and the reference phase, respectively. m1 I m2 These represent the maximum allowable currents for the inverters in Unit 1 and Unit 2, respectively, and the power factor angle of the units is... i di i qi These are the d-axis and q-axis currents of the short-circuit current output by the i-th phase-locked loop of the unit, i = 1, 2.

[0062] Simplifying, we get:

[0063]

[0064] In the above formula:

[0065]

[0066] The variables in equation (11) are all intermediate variables in the process of deriving the expression.

[0067] Similarly, the short-circuit current of the equivalent modeling unit can be determined based on the phase-converted multi-unit short-circuit current analytical model and equation (4), expressed as:

[0068]

[0069] In the formula: i d∑eq i q∑eq These are the d-axis and q-axis currents of the short-circuit current output after phase conversion from the equivalent model, respectively. i deq i qeq The d-axis and q-axis currents are the short-circuit currents output before phase conversion in the equivalent model.

[0070] Comparing equations (12) and (10), it can be seen that the dq-axis current error caused by the equivalent value consists of two parts: 1. The output current of the detailed model is the vector sum of the output currents of each unit, and the amplitude (limit value) of the total current is less than I. m1 +I m2 If the capacity remains constant, the current limit is typically 1.2 times the rated current. The equivalent model is calculated by adding the previous unit limits, therefore the current amplitude output by the equivalent model is I. m1 +I m2 Therefore, the resulting dq-axis current amplitude error is unavoidable. 2. Cosine term error due to different current phases. As analyzed above, due to the voltage-controlled current source characteristics of the inverter power supply, If it is a continuous function of the voltage drop, then let... An equivalent voltage can be obtained to eliminate the cosine term error between the equivalent model and the detailed model. Assuming the voltage at the fault point remains unchanged before and after equivalence, the equivalent impedance can be calculated using the equivalent voltage. Specifically:

[0071] Since the fault point current is mainly supplied by the system side, it is assumed that the grid connection point voltage remains unchanged before and after the equivalent value, and is a known quantity. Therefore, the current phases before and after the equivalent value are assumed to be equal: The power factor is the same before and after the equivalence. Ignoring power losses on the line, the equivalent voltage of the equivalent model is obtained as follows:

[0072]

[0073] Among them, P eq The active power output of the unit for equivalent modeling, U eq For the equivalent voltage of the equivalent model, u di For detailed modeling, the terminal voltage of each unit, i.e., U s .

[0074] The equivalent line length is calculated using the following formula:

[0075]

[0076] Where δU and ΔU are the longitudinal and transverse components of the voltage drop, respectively, l is the line length of the equivalent model, and r and x are the unit resistance and reactance of the line, respectively.

[0077] Based on the previous analysis, the amplitude error caused by the equivalent impedance is unavoidable, and the cosine term error caused by the different current phases can be eliminated by the equivalent impedance. Therefore, by deriving the relationship between the current error and the electrical quantity, and calculating the electrical quantity boundary based on the given upper limit of error, grouping can be achieved.

[0078] Subtracting equation (12) from equation (10) yields the equivalent error:

[0079]

[0080] Where, Δi d With Δi q These represent the equivalent errors of the short-circuit current on the d-axis and q-axis, respectively.

[0081] Since the voltage drop at the outlet of each wind turbine is similar, δ is relatively small. Therefore, the above equation is linearized, a Taylor expansion is performed, and higher-order terms are ignored, resulting in:

[0082]

[0083] The relative error caused by equivalence is defined as:

[0084]

[0085] Among them, ε(i d ) and ε(i q ) represent the relative errors of the d-axis and q-axis short-circuit currents generated by equivalent values, respectively;

[0086] From the above formula:

[0087]

[0088] The cosine term error in the above equation is eliminated through voltage equivalence. Therefore, the second term in equation (18) equals 1, and the relative error generated by the equivalent is:

[0089]

[0090] Equation (19) shows that the error generated by equivalence of wind fields entering low-voltage control is mainly determined by the current limit value of each wind field and the phase of the outlet voltage of each wind field. Therefore, the electrical quantity boundary (group boundary) of wind fields entering low-voltage control can be defined according to the total relative error generated by equivalence, and group equivalence can be achieved.

[0091] The previous section introduced the equivalent method for two generating units entering the low-voltage transmission range, which can also be extended to the scenario of N (N>2) generating units. For the low-voltage transmission range category, the two generating units are first modeled using the phase-converted multi-unit short-circuit current analytical model and the equivalent model to obtain the equivalent generating units. Then, the equivalent model is performed with the next generating unit, and a total of N-1 equivalent modeling operations are performed. The electrical quantity boundary is calculated using the relationship between the total relative error generated by the N-1 equivalent modeling operations and the electrical quantity. Based on the relationship between the phase angle difference between the relevant generating units and the electrical quantity boundary during the equivalent modeling process, the generating units are grouped.

[0092] The idea of ​​equivalence between two generator units in the previous step can also be extended to scenarios with more than two generator units. During the 2nd to N-1th equivalence modeling processes, considering the error generated by multiple equivalence models, the case where the relative error is largest in the k-th equivalence modeling is as follows:

[0093]

[0094] Where k = [2, N-1], the subscript j represents the sequence number of the unit j that performs equivalent operations with the equivalent unit in the k-th equivalent operation process, and the equivalent unit and unit j in the k-th equivalent operation process are simply referred to as the two units, ε k With ε(i dq ) represents the relative error of the equivalent dq-axis short-circuit current (including ε(i) in the aforementioned formula 19). d ) and ε(i q (Two parts), phase angle difference θ k θ represents the difference between the phase-locked loop output phase and the reference phase of the equivalent unit (covering all units that have already been equivalently equivalent) during the k-th equivalent process. j This is the difference between the output phase and the reference phase of the unit's phase-locked loop (PLL). i dj i qj These are the d-axis and q-axis currents of the short-circuit current output by the phase-locked loop of unit j, respectively. dk i qk These are the d-axis and q-axis currents of the short-circuit current output by the equivalent generator unit during the k-th equivalent process, respectively. It can be calculated according to equation (21):

[0095]

[0096] In the formula: I M(k-1) The current limiting value of the equivalent model after the (k-1)th equivalent calculation is expressed as: When k=1, the above equation degenerates into the calculation expression of δ in equation (11).

[0097] Therefore, the short-circuit current of the equivalent unit output obtained through N-1 equivalent modeling can be expressed as:

[0098]

[0099] Where, when r = 1, i dq1 The d-axis and q-axis currents (i.e., including i) represent the short-circuit current output phase of the phase-locked loop of unit 1. d1 with i q1 ), ε1 represents the dq-axis short-circuit current error caused by equating units 1 and 2 to equivalent unit 1 (i.e., the relative error generated by the first equivalent modeling), when r>1, i dqr ε represents the d-axis and q-axis currents of the equivalent generator output short-circuit current during the r-th equivalent operation. r This represents the relative error of the dq-axis short-circuit current generated during the r-th equalization (generated by the equalization of all units that have been equalized and the next unit).

[0100] As can be seen from equation (22), during the k-th equalization modeling process, δ k,j Less than the maximum phase angle difference δ between two units classified as the same type of unit max Then, the relative error of the multi-machine current equivalent model after N-1 times is:

[0101]

[0102] In the formula: i dq∑ ε0 represents the short-circuit current after reduction from the full-power inverter power supply model before equivalent modeling; p and t both represent the unit number, and ε0 is the relative error generated by the equivalent modeling of the two units with the largest phase angle difference.

[0103] Simplifying, we get:

[0104]

[0105] Where ε is the total relative error generated by multi-machine equivalent modeling, i dqeq Includes i deq with i qeq Two parts, i deq i qeq The d-axis and q-axis currents are the short-circuit currents output before phase conversion in the equivalent model.

[0106] The relationship between the upper limit of the phase angle difference of similar units and the total relative error ε generated by multiple units being of equal value is as follows:

[0107]

[0108] Since the phase angle difference is determined by both the voltage drop and the voltage phase, the upper limit of the phase angle difference δ max This can be understood as the boundary of electrical quantities. The above formula (25) shows the relationship between the relative error generated by equivalent modeling and electrical quantities. The upper limit of the phase angle difference δ can be calculated from the total relative error ε. max The upper limit of the phase angle difference δ max The phase angle difference δ of the relevant units during each equivalent modeling is respectively compared with that of the other units. a,b Compare, if δ a,b Less than the upper limit of phase angle difference δ max If the relevant units are grouped together, then a and b are the serial numbers of two units when the current model is the first equivalent modeling. When the current model is not the first equivalent modeling, a is the equivalent unit (covering all units that have been equivalently modeled), and b is the serial number of a single unit.

[0109] The previous section introduced how to group electrical quantities during equivalent modeling. The following section describes the parameters of the equivalent model. The parameter calculation formulas for multi-machine equivalent models are as follows:

[0110]

[0111] In the formula: S eqy S is the capacity of the equivalent unit y. w Let N be the capacity of unit w. y S represents the number of units divided into group y. Teqy For the equivalent model y transformer capacity, S Te Let x be the capacity of transformer e. Teqy Let x be the transformer reactance of the equivalent model y. Tu Let u be the reactance of the transformer.

[0112] The above-described scheme in this embodiment mainly achieves the following beneficial effects: Based on the derived relationship between electrical quantity boundaries and errors, this invention can determine the electrical quantity boundaries of the clusters according to the required modeling accuracy, i.e., the upper limit of error. Furthermore, based on the electrical quantity boundaries, the clustering results of the wind farms are determined, with each cluster equivalent to one wind turbine. The multi-turbine equivalent modeling method proposed in this invention can guarantee the modeling accuracy of new energy power sources. Compared with detailed wind farm models, it simplifies the complexity of equivalent models, reduces simulation time, and improves the calculation efficiency of network short-circuit current.

[0113] To verify the above effects, a simulation experiment was conducted.

[0114] Taking the actual topology and parameters of a wind farm in Inner Mongolia as an example, a topology was built in PSCAD as follows: Figure 2 The detailed model of the wind farm shown is a wind farm containing 5×10×2MW permanent magnet direct-drive wind turbines. The wind turbines are connected to the grid connection point via a transformer substation (0.69kV / 35kV) and to the external power grid via an overhead line through a main transformer (35kV / 220kV). The short-circuit impedance of the transformer substation is 6.39%, and that of the main transformer is 13.54%. Considering more stringent operating conditions, the cable line between the wind turbines is 1km. The accuracy of the invention was verified under two scenarios: voltage drop at the grid connection point.

[0115] 1. Voltage drop at grid connection point by 50%

[0116] When the grid connection point voltage drops to 50%, the equivalent boundary is calculated based on the error of the short-circuit current before and after the equivalent value. The wind turbines are classified by (17) and (22). The error of the dq axis current after the equivalent value calculation of two single units is less than 0.4%. The wind farm grouping results are shown in Table 1.

[0117]

[0118]

[0119] Table 1 Wind Field Clustering Results

[0120] The fault currents and their errors in wind farms using traditional single-unit equivalent models, the equivalent model proposed in this invention, and detailed models are as follows: Figure 4 As shown. Figure 4 In the diagram, the left side shows the A-phase current curve, with three types of curves (the curves corresponding to the detailed model, the single-machine model, and the equivalent model overlap). The right side shows the equivalent error, with the curves with smaller amplitudes corresponding to the equivalent model proposed in this invention, and the curves with larger amplitudes corresponding to the traditional single-machine equivalent model.

[0121] The maximum error of the total current and the error of the dq-axis current before and after the equivalence are shown in Table 2. Setting the dq-axis current error to 0.4%, the final error should be less than: 1 - (1 - 0.4%)³ + 1 - (1 - 0.4%)² = 2%. The current error is slightly larger than the theoretically analyzed error range because the theoretical analysis of this invention ignores the power loss on the line. When the voltage drop is shallow, the power loss is small and can be ignored. However, when the voltage drops deeply, ignoring the power loss introduces a certain error. In this case, the impedance equivalence method derived earlier does not completely eliminate the cosine term in the error, but its accuracy is still higher than the traditional single-machine equivalence method and the traditional equivalence method, proving the accuracy of the equivalence method.

[0122]

[0123] Table 2 Comparison of the equivalent measurement error between the proposed equivalent measurement method and the traditional single-machine equivalent measurement method.

[0124] 2. Voltage drop at grid connection point is 30%.

[0125] When the grid connection point voltage drops to 30%, the equivalent boundary is calculated based on the error of the short-circuit current before and after the equivalent value. The wind turbines are classified according to (17) and (22). The error of the dq axis current after the equivalent value reduction of two single units is less than 0.4%. The wind farm grouping results are shown in Table 3.

[0126]

[0127] Table 3 Wind Field Clustering Results

[0128] The fault currents and their errors in wind farms using traditional single-unit equivalent models, the equivalent model proposed in this invention, and detailed models are as follows: Figure 5 As shown. Figure 5 In the table, the left side shows the A-phase current curve, with three types of curves (the curves corresponding to the detailed model, single-machine model, and equivalent model coincide). The right side shows the equivalent error, with the smaller curve corresponding to the equivalent model proposed in this invention, and the larger curve corresponding to the traditional single-machine equivalent model. The maximum error of the total current and the dq-axis current error generated before and after the equivalent model are shown in Table 4. The accuracy of the equivalent method proposed in this invention is good, and the final dq-axis current error satisfies the group boundary and error relationship obtained by equation (21).

[0129]

[0130] Table 4 Comparison of the equivalent measurement error between the proposed equivalent measurement method and the traditional single-machine equivalent measurement method.

[0131] As shown in Tables 2 and 4, the fault current error is significantly reduced by the proposed equivalent method compared to traditional single-unit equivalent methods and traditional impedance equivalent methods. The method for classifying wind farm groups based on the current error before and after equivalent methods is more accurate than traditional equivalent methods.

[0132] To further verify the rationality of the proposed equivalent modeling method, an artificial short-circuit experiment was conducted in a concentrated wind farm grid connection area in Shaanxi Province. The network topology of this area is as follows: Figure 6 As shown.

[0133] In the diagram, sections AB of the 35kV bus are numbered 1-6 as wind farm collection lines, each connecting 8-13 wind turbine units. System parameters are shown in Table 5. A short-circuit fault is located on the 330kV transmission line approximately 10km away from the No. 2 main transformer. The fault type is a single-phase ground fault, and the fault duration is 40ms. Waveform data from the permanent magnet wind turbine collection lines at the measuring points are used to verify the proposed equivalent modeling method. The output short-circuit current of the equivalent model established using the proposed method is compared with the waveform data. Figure 7 As shown, the experimental results demonstrate the practical value of the proposed equivalent modeling method.

[0134]

[0135] Table 5 System Component Parameters in Areas with Centralized Access to New Energy

[0136] The equivalent model proposed in this invention for wind farms and the experimental data from artificial short circuits are compared, for example... Figure 7 As shown. Figure 7 In the diagram, phases a, b, and c are represented from top to bottom. The solid line represents the short-circuit current curve corresponding to the artificial short-circuit experimental data, and the dashed line represents the short-circuit current curve of the equivalent model proposed in this invention. The results show that the equivalent method proposed in this invention has good accuracy and certain engineering applicability.

[0137] Through the above description of the embodiments, those skilled in the art can clearly understand that the above embodiments can be implemented by software, or by using software plus necessary general-purpose hardware platforms. Based on this understanding, the technical solutions of the above embodiments can be embodied in the form of a software product, which can be stored in a non-volatile storage medium (such as a CD-ROM, USB flash drive, external hard drive, etc.), including several instructions to cause a computer device (such as a personal computer, server, or network device, etc.) to execute the methods described in the various embodiments of the present invention.

[0138] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A multi-machine grouping equivalent method for full-power inverter-type new energy power supplies, characterized in that, include: An analytical model of the short-circuit current of a multi-unit full-power inverter power supply is established, and phase conversion is performed on the analytical model and the equivalent model of the short-circuit current of the multi-unit power supply respectively. Based on whether the unit enters low-temperature control, it is divided into two categories; If the model belongs to the category of not entering the low-voltage transmission range, then the single-unit equivalent model is used for equivalent modeling based on the analytical relationship between the multi-unit short-circuit current analytical model and the equivalent model after phase conversion. If the model belongs to the category of entering the low-voltage transmission range, then the multi-unit equivalent model is used for multi-unit equivalent modeling based on the analytical relationship between the multi-unit short-circuit current analytical model and the equivalent model after phase conversion. The electrical quantity boundary is calculated using the relative error generated by the multi-unit equivalent modeling and the electrical quantity relationship, and the units are grouped according to the electrical quantity boundary.

2. The multi-machine grouping equivalent method for a full-power inverter-type new energy power supply according to claim 1, characterized in that, The establishment of a multi-unit short-circuit current analytical model for a full-power inverter power supply, and the phase conversion of the multi-unit short-circuit current analytical model and the equivalent model, respectively, include: An analytical model of the short-circuit current of a multi-unit full-power inverter power supply is established, expressed as: Among them, i d i q These are the d-axis and q-axis currents of the short-circuit current output by the full-power inverter power supply, respectively. N I is the rated current of the station. max Where U is the maximum allowable circuit current output of the renewable energy power station, K is the reactive current support coefficient, P0 is the power station output power before the fault, and U is the maximum allowable circuit current output of the renewable energy power station. s U is the per-unit voltage value input to the unit's phase-locked loop. N This refers to the rated voltage at the station terminal. By selecting a reference phase, phase conversion is performed on the multi-unit short-circuit current analytical model of the full-power inverter power supply, resulting in a steady-state short-circuit current analytical model, expressed as: Among them, i d∑ i q∑ These are the d-axis and q-axis currents of the short-circuit current converted to the reference phase from the analytical model of the multi-unit short-circuit current before equivalent conversion; i di i qi Let θ represent the d-axis and q-axis currents of the short-circuit current output by unit i, respectively, calculated using a multi-unit short-circuit current analytical model. i This is the difference between the output phase and the reference phase of the unit's i-phase-locked loop; The equivalent model is also subjected to phase conversion, resulting in the phase-converted equivalent model, which is represented as follows: In the formula: i d∑eq i q∑eq These are the d-axis and q-axis currents of the short-circuit current output after phase conversion from the equivalent model, respectively, and θ. eq Let i be the difference between the phase output of the equivalent model phase-locked loop and the reference phase. deq i qeq The d-axis and q-axis currents are the short-circuit currents output before phase conversion in the equivalent model.

3. The multi-machine grouping equivalent method for a full-power inverter-type new energy power supply according to claim 1, characterized in that, The classification based on whether the unit enters low-temperature control is divided into two categories, including: If U is satisfied s >0.8U N If so, it belongs to the category of not entering the low-crossing zone; If 0.2U is satisfied N s <0.8U N If so, it belongs to the category of entering the low-passing zone;​ Among them, U s U is the per-unit voltage value input to the unit's phase-locked loop. N This is the rated voltage at the station terminal.

4. The multi-machine grouping equivalent method for a full-power inverter-type new energy power supply according to claim 1, 2, or 3, characterized in that, For the category that has not entered the low-voltage penetration range, the equivalent modeling method using a single machine includes: using the impedance equivalent modeling method with weighted average voltage.

5. The multi-machine grouping equivalent method for a full-power inverter-type new energy power supply according to claim 1, characterized in that, If the scenario falls under the category of entering the low-voltage transmission range, then based on the analytical relationship between the multi-unit short-circuit current analytical model and the equivalent model after phase conversion, a grouping equivalent model is used for multi-unit equivalent modeling. The relative error generated by the multi-unit equivalent modeling and the relationship with electrical quantities are used to calculate the electrical quantity boundaries. Based on these electrical quantity boundaries, the units are grouped, including: The total number of generating units is set to N. When N>2, the two generating units are first modeled equivalently based on the analytical relationship between the phase-converted multi-unit short-circuit current analytical model and the equivalent model to obtain the equivalent generating units. Then, the equivalent modeling is performed with the next generating unit, and a total of N-1 equivalent modeling is performed. The electrical quantity boundary is calculated using the relationship between the total relative error generated by the N-1 equivalent modeling and the electrical quantity. The generating units are grouped according to the relationship between the phase angle difference between related generating units and the electrical quantity boundary during the multi-unit equivalent modeling process.

6. The multi-machine grouping equivalent method for a full-power inverter-type new energy power supply according to claim 5, characterized in that, For the category of entering the low-crossing interval, the multi-machine equivalent modeling process using the cluster equivalent method includes: First, equivalent modeling is performed on the two units, which are referred to as Unit 1 and Unit 2. The short-circuit current is determined based on the analytical model of multi-unit short-circuit current after phase conversion, and is expressed as follows: Among them, i d∑ i q∑ These are the d-axis and q-axis currents of the short-circuit current converted to the reference phase from the analytical model of the multi-unit short-circuit current before equivalence, respectively. θ1 and θ2 are the differences between the voltage phase output of unit 1 and unit 2's phase-locked loop and the reference phase, respectively. m1 I m2 These represent the maximum allowable currents for the inverters in Unit 1 and Unit 2, respectively, and the power factor angle of the units is... i di i qi These are the d-axis and q-axis currents of the short-circuit current output phase of unit i's phase-locked loop, respectively, calculated using a multi-unit short-circuit current analytical model, where i = 1, 2; The short-circuit current of the equivalent modeling unit is determined based on the equivalent model after phase conversion, and is expressed as: In the formula: i d∑eq i q∑eq These are the d-axis and q-axis currents of the short-circuit current output after phase conversion from the equivalent model, respectively. i deq i qeq The d-axis and q-axis currents of the short-circuit current output before phase conversion in the equivalent model; Combining the two sets of short-circuit current calculation formulas above, the equivalent error is obtained: Where, Δi d With Δi q These represent the equivalent errors of the short-circuit current on the d-axis and q-axis, respectively. The relative error caused by equivalence is defined as: Among them, ε(i d ) and ε(i q ) represent the relative errors of the d-axis and q-axis short-circuit currents generated by equivalent values, respectively; The electrical quantity boundary of the wind field entering the low-voltage control is defined by the total relative error generated by the N-1th equal-value modeling, thus achieving group equal-value.

7. The multi-machine grouping equivalent method for a full-power inverter-type new energy power supply according to claim 6, characterized in that, The relationship between the total relative error generated by N-1 equivalent modeling and electrical quantities is used to calculate the electrical quantity boundaries. Based on the relationship between the phase angle difference between relevant units and the electrical quantity boundaries during the equivalent modeling process, unit grouping is performed, including: During the 2nd to N-1th isometry modeling processes, the case where the kth isometry modeling produces the largest relative error is: Where k = [2, N-1], the subscript j represents the sequence number of the unit that performs equivalent operations with the equivalent unit in the k-th equivalent operation process, and ε k With ε(i dq Both represent the relative errors in the d-axis and q-axis short-circuit currents produced by equivalent values, and the phase angle difference. θ k θ represents the difference between the output phase of the phase-locked loop of the equivalent unit and the reference phase during the k-th equivalent process. The equivalent units include all units that have been equivalently equivalent. j This is the difference between the output phase and the reference phase of the unit's phase-locked loop (PLL). i dj i qj These are the d-axis and q-axis currents of the short-circuit current output by the phase-locked loop of unit j, respectively. dk i qk These are the d-axis and q-axis currents of the short-circuit current output by the equivalent generator unit during the k-th equivalent process, respectively. The equivalent short-circuit current of the generator unit, obtained through N-1 equivalent measurements, is expressed as follows: Where, when r = 1, i dq1 The d-axis and q-axis currents represent the short-circuit current output phase of the phase-locked loop of Unit 1. ε1 represents the d-axis and q-axis short-circuit current error caused by equivaling Unit 1 and Unit 2 to equivalent Unit 1, i.e., the relative error generated by the first equivalent modeling; when r>1, i dqr ε represents the d-axis and q-axis currents of the equivalent generator output short-circuit current during the r-th equivalent operation. r This represents the relative error of the dq-axis short-circuit current generated during the r-th equalization. The relative error of the multi-machine current equivalent model after N-1 times is: Among them, i dq∑ Includes i d∑ with i q∑ Two parts, i d∑ i q∑ These are the d-axis and q-axis currents of the short-circuit current converted from the analytical model of the multi-unit short-circuit current to the reference phase, respectively; p and t both represent the unit number, and ε0 is the relative error generated by the equivalent modeling of the two units with the largest phase angle difference; The relative error of the multi-machine current equivalent modeling after N-1 times is simplified as follows: Where ε is the total relative error generated by multi-machine equivalent modeling, i dqeq Includes i deq with i qeq Two parts, i deq i qeq The d-axis and q-axis currents of the short-circuit current output before phase conversion in the equivalent model; The relationship between the upper limit of the phase angle difference of similar units and the total relative error ε generated by multiple units being of equal value is as follows: Upper limit of phase angle difference δ max This refers to the electrical quantity boundary, and the upper limit of the phase angle difference δ is calculated using the total relative error ε. max The upper limit of the phase angle difference δ max The phase angle difference δ of the relevant units during each equivalent modeling is respectively compared with that of the other units. a,b Compare, if δ a,b Less than the upper limit of phase angle difference δ max If the relevant units are grouped together, then when it is the first time of equivalent modeling, a and b are the serial numbers of two units. When it is not the first time of equivalent modeling, a is the equivalent unit and b is the serial number of a single unit.

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