Wind and solar power generation unit fault active voltage support method based on extended controllable boundary

Abstract

The application discloses a wind and light power generation unit fault active voltage support control method based on an extended controllable boundary, and aims at the fact that the strength of a power grid connected with large-scale wind and light power stations decreases year by year, the system voltage lacks effective support during a fault, and the new energy is prone to large-area disconnection. In view of the safety of equipment stress and system response, the wind and light unit extended fault controllable boundary is provided, 10 binary quadratic analytical equations are used to determine the controllable area of the new energy under complex fault conditions, and a group dispersion mapping matrix algorithm is provided, so that the maximum support instruction value of the wind and light power generation unit can be safely, limitedly, quickly and flexibly calculated from the controllable area. Compared with the current national standard, the fault voltage support capacity of the new energy can be improved by more than 50%, and the strength of the power grid during the fault is significantly improved, and secondary chain accidents such as large-area disconnection of the new energy are avoided. The application has the advantages of fast calculation speed, low application cost, high program portability and the like, and has high practical application value.

Description

Technical Field

[0001] This invention relates to a method for active voltage support during faults in wind and solar power generation units based on extended controllable boundaries, belonging to the field of power transmission system automation. Background Technology

[0002] In scenarios with weak system support, a significant drop in system voltage during a fault could lead to large-scale grid disconnection of renewable energy sources and trigger various cascading accidents. Therefore, the control strategy for renewable energy power sources must not only ensure their own safe power-through, but also safely, efficiently, quickly, and flexibly utilize controllable resources to provide fault support for the system voltage. Thus, renewable energy power plants, during a fault, not only need to ensure their own safe power-through, but also fully utilize their controllable resources to provide safe, rapid, and flexible voltage support to the system.

[0003] Currently, the fault control strategies for wind and solar power generation units already in operation typically refer to the existing national standards GB / T37408-2019 and GB / T 19963.1-2021. The reactive power output of the renewable energy source is only related to the degree of AC voltage drop at the PCC point, and can be regarded as an unconstrained voltage-controlled current source. This is a single-objective control method, which has the advantages of low computational load, high safety, and fast response speed, but it is difficult to flexibly and fully exploit the voltage support capability of the wind and solar power generation unit in different fault scenarios. As the strength of the opposite system continues to decline, the system response is increasingly significantly affected by the renewable energy output, and the fault control strategy must take into account various safety constraint boundaries.

[0004] Therefore, in recent years, new fault control strategies for wind and solar power generation units have continuously enriched the controllable constraints and constructed controllable boundaries for new energy faults. However, as the intensity of large-scale new energy grid integration gradually decreases, the constraint characteristics of the multi-stage transformer connection group transformation process on new energy control strategies become increasingly significant. During faults, there is a risk of local node voltage exceeding limits, a problem that existing methods have not considered. Furthermore, existing methods require dynamic searching for optimal control commands during the control process, resulting in relatively slow computation speed.

[0005] Therefore, in the face of the severe situation that the intensity of large-scale new energy grid connection is becoming weaker, the existing fault control methods have problems such as imperfect theory and slow speed, making it difficult to meet the four core requirements of safety, limit, speed and flexibility. Summary of the Invention

[0006] The technical problem to be solved by this invention is to overcome the shortcomings of the prior art and propose an active voltage support method for wind and solar power generation units based on extended controllable boundaries. This method, for the first time, proposes an extended controllable boundary for wind and solar power units that considers the propagation characteristics of fault disturbances, and proposes a clustered discrete mapping matrix, which can quickly and accurately calculate the power command of wind and solar power units, thereby improving the safety, limitability, speed, and flexibility of fault control for wind and solar power units.

[0007] To address the aforementioned technical problems, this invention provides a fault active voltage support control method for wind and solar power generation units based on extended controllable boundaries, applied to the controller of the grid-side converter of a wind and solar power generation unit, comprising the following steps:

[0008] 1) Upon detecting a fault, the wind and solar power generation unit activates the fault control function. The equivalent positive and negative sequence voltages V on the grid side are calculated using an online impedance estimator. g + , and equivalent impedance R g +jL g Three-phase voltage and current data at point PCC are collected, and the voltage v along the αβ axis is obtained through Clark transformation. α v β Current component i α i β The current components are then subjected to Park transform and sequence component separation control to obtain the positive and negative sequence dq-axis current components U. d + U q + , Finally, after the power decoupling coordinate transformation matrix K... PQ / dq The positive and negative sequence PQ axis current components I are obtained. P + I Q + ,

[0009]

[0010] 2) Initialize the control target parameters, including: I lim Indicates the maximum allowable output phase current amplitude of power electronic equipment, V lim Indicates the maximum allowable phase voltage amplitude of the system, P lim This indicates the maximum active power amplitude allowed to be output by the DC bus capacitor of the wind and solar unit, I. P + This represents the active power required during the fault period, and m represents the calculation resolution parameter.

[0011] 3) According to I P+ Value will I Q + Discretize at resolution m to obtain discrete vector I + Q.map :

[0012]

[0013] In the formula, m is the discrete resolution parameter, which determines the control accuracy.

[0014] 4) Convert the discrete vector I + Q.map Substituting into equation (3) to solve the two linear equations in two variables, we obtain the m terms in the equation. The combined values ​​are the discrete vector I under the active power amplitude constraint. − Q.map.P

[0015]

[0016] In the formula, ω represents the system frequency, and L represents the inductance of the output filter of the wind-solar unit converter.

[0017] 5) Convert the discrete vector I + Q.map Substitute into equation (4) to solve these three linear equations in two variables. Each equation yields m solutions. The value of , combining all the solutions of the three equations, yields the m×3 dimensional discrete matrix under the phase current amplitude constraint. .map.I

[0018]

[0019] in

[0020]

[0021] In the formula, γ represents the phase difference between the positive and negative sequence voltages at point PCC.

[0022] 6) Convert the discrete vector I + Q.map Substitute each equation into equation (6) to solve these 6 linear equations in two variables. Each equation yields m solutions. The value of , combining all the solutions of the 6 equations, yields the m×3 dimensional discrete matrix under the extended phase voltage magnitude constraint. .map.U

[0023]

[0024] in

[0025]

[0026] In the formula, I + P.|0| This indicates the command value of the active current component of the wind and solar power generation unit before the fault.

[0027] 7) The values ​​calculated in steps 4), 5), and 6) .map.P , .map.I , .map.U Perform grouping, and define the upper boundary group matrix including .map.P , .map.I , .map.U The lower boundary group matrix is ​​defined as having only .map.U Based on the clustering results, generate an m×10 dimensional upper bound discrete mapping matrix B. up and the lower bound discrete mapping matrix B of m×6 dimensions up The mathematical expressions for the two matrices are:

[0028]

[0029] 8) Extract the row maximum element of the upper and lower bound discrete mapping matrix. .map1 Vector and row minimum element .map2 Vector, and with I + Q.map A numerical matrix is ​​constructed to represent the graphical boundary line of the controllable fault area of ​​the wind and solar power generation unit, denoted as:

[0030]

[0031] 9) Define the control target and determine if the positive sequence voltage amplitude U at point PCC is... + PCC If the value is less than 0.4pu, then it belongs to case 1; if 0.4pu ≤ U + PCC If ≤0.6pu, it belongs to case 2; if 0.6pu≤U + PCC If the value is ≤0.9 pu, it falls under case 3. Different instruction value calculation methods are used for each of the three case types.

[0032]

[0033] In the formula, I + Q.ref , .ref These are the positive and negative sequence reactive current command values ​​output by the control program.

[0034] 10) The calculated instruction value I + Q.ref , .ref I is obtained through power decoupling inverse transformation d + I q + , This current is then input to the inner current loop of the converter. The power decoupling inverse transform can be expressed as:

[0035]

[0036] In step 1) above, the fault detection method involves extracting the effective value of the AC voltage at the PCC point and determining whether the voltage drop meets the low-voltage ride-through requirements stipulated in the current national standard. Considering that the online impedance estimator typically requires 13-20ms to calculate the equivalent impedance on the grid side, after starting the fault control module, the wind and solar units first calculate I according to the current national standard control method. d + I q + , Instruction. When the algorithm provided by this invention executes to step 10), the original instruction value is overwritten.

[0037] In step 1) above, the negative sequence active and reactive power are coupled in the dq axis and cannot be controlled independently. Transformation (1) solves this problem, so that the positive and negative sequence active and reactive power of the wind and solar unit can be controlled independently through the current component.

[0038] In step 2) above, I lim V lim P lim The value should be set according to the actual converter performance, and is usually set to 1.1~1.2 pu, typically 1.1 pu. lim Typically calculated based on the maximum withstand voltage of the DC bus capacitor.

[0039]

[0040] In the formula, ω represents the system angular frequency, and C dc This represents the DC bus capacitance value, V. dc This represents the rated DC bus voltage, V. dc.lim This indicates the maximum permissible DC bus voltage amplitude.

[0041] In step 2) above, I P +The calculation of I is not within the scope of this invention. P + It is only used as a parameter input in the algorithm for calculation. The value of m depends on the actual computing performance of the controller chip; the higher the chip performance, the larger the m setting, and the better the control effect.

[0042] In steps 4), 5), and 6) above, considering that wind and solar units typically do not need to output negative-sequence active power, the formulas (3), (4), and (6) are... This can be ignored, thus reducing the computational load.

[0043] In step 6) above, considering that the zero-sequence voltage component of the fault in actual engineering only exists in the 220kV voltage level system, and that after the voltage drop of multiple transformers and 35kV lines, the 220kV node usually will not experience overvoltage due to the zero-sequence component, the zero-sequence voltage component can be ignored. Therefore, only the positive and negative sequence components of the system voltage are considered.

[0044] In step 9) above, the controller extracts the positive sequence voltage amplitude U at the PCC point of the wind and solar power generation unit. + PCC Determine when U + PCC When 0.4pu is less than U, the wind and solar units preferentially emit positive-sequence reactive power; when 0.4pu ≤ U + PCC When ≤0.6pu, the wind and solar power units should ensure that the sum of the positive and negative sequence reactive power output is maximized. When 0.6pu≤U + PCC When the power consumption is ≤0.9 pu, the wind and solar units prioritize the emission of negative sequence reactive power.

[0045] In step 10) above, the transformation matrix (11) is the inverse of the transformation matrix (1) in step 1).

[0046] The fault control module provided by this invention has an input quantity of U. d + U q + , R g +jL g The output quantity is I d + I q + , The controllable parameter is: I lim V lim P lim I P + .

[0047] Beneficial effects:

[0048] This invention provides a control strategy during wind and solar power generation unit failures. Addressing the issue that renewable energy sources cannot safely, fully, quickly, and flexibly support system fault voltages when large-scale renewable energy is integrated into weak power grids, this invention constructs a controllable boundary for extended renewable energy faults, overcoming the shortcomings of existing theories. Furthermore, it proposes a clustered discrete mapping matrix algorithm, which can safely, fully, quickly, and flexibly calculate the maximum voltage support output that renewable energy can provide, increasing the active voltage support capability of renewable energy by more than 50%. This significantly improves grid strength during faults and avoids secondary cascading accidents such as large-scale renewable energy disconnection from the grid. Moreover, this invention has advantages such as fast calculation speed, low application cost, and high program portability, making it highly valuable for practical applications. Attached Figure Description

[0049] 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.

[0050] Figure 1 This is a schematic diagram of the large-scale wind and solar power station grid connection system in an embodiment of the present invention;

[0051] Figure 2 This is a schematic diagram of the transformer connection group wiring in an embodiment of the present invention;

[0052] Figure 3 This is a diagram showing the phase voltage vectors on both sides of the transformer during an asymmetrical fault, as described in an embodiment of the present invention.

[0053] Figure 4 This is a flowchart of the active voltage control for wind and solar unit faults in an embodiment of the present invention;

[0054] Figure 5 This is a graphical representation of the calculation principle of active voltage control for wind and solar unit faults in this embodiment of the invention.

[0055] Figure 6 This is a performance comparison chart between the control strategy provided in this embodiment of the invention and the current national standard. Detailed Implementation

[0056] The present invention will be further described below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present invention and should not be construed as limiting the scope of protection of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0057] With the continuous increase in installed capacity of wind and solar power, the grid strength of large-scale renewable energy aggregation stations is gradually decreasing. During faults, the lack of effective voltage support can easily lead to large-scale grid disconnection of renewable energy. This places higher demands on the fault control of renewable energy, namely, to provide rapid and flexible support for system voltage by utilizing controllable resources to the greatest extent possible while ensuring its own safety. However, existing methods can only ensure the safe passage of renewable energy, and do not adequately consider the safety constraints of system response, thus failing to fully tap the voltage support capacity of renewable energy or flexibly cope with complex fault conditions. Currently, in areas with a high proportion of renewable energy integration, such as Northwest, North, and Northeast my country, where grid strength is relatively low, there is an urgent need for a control method that can safely, fully, quickly, and flexibly improve the voltage support capacity of renewable energy during faults.

[0058] To address the aforementioned technical problems, this invention provides a method for active voltage support control of wind and solar power generation units based on extended controllable boundaries, comprising the following steps:

[0059] 1) For example Figure 1 As shown, this invention presents a typical large-scale renewable energy power plant integrated into a weak grid system. During faults, the renewable energy source disconnects the outer power loop, retaining only the inner current loop. To achieve independent control of positive and negative sequence power, both positive and negative sequence loops employ a fixed d-axis voltage control strategy. The positive and negative sequence components are extracted using a time-delay cancellation method, and then processed through a set of transformation matrices K. PQ / dq and K dq / PQ Achieved. The short-circuit ratio of the 35kV node system is adjustable within the range of 1.5 to 10. The connection group of the 0.38 / 35kV transformer T1 in the substation is Dyn11, and the connection group of the 35kV / 220kV step-up main transformer T2 in the substation is YNd11. The photovoltaic power station has a capacity of 100MW, with a 35kV line length of 4km and a 220kV line length of 517.13km. After the wind and solar power generation unit detects a fault, the fault control function is activated. The equivalent positive and negative sequence voltages V on the grid side are calculated through an online impedance estimator. g + , and equivalent impedance R g +jL g Three-phase voltage and current data at point PCC are collected, and the voltage v along the αβ axis is obtained through Clark transformation. α v β Current component i α i β The current components are then subjected to Park transform and sequence component separation control to obtain the positive and negative sequence dq-axis current components U. d + U q + , Finally, after the power decoupling coordinate transformation matrix K... PQ / dqThe positive and negative sequence PQ axis current components I are obtained. P + I Q + ,

[0060]

[0061] In the dq axis, the negative sequence active and reactive power are coupled and cannot be controlled independently. Transformation (1) solves this problem, so that the positive and negative sequence active and reactive power of the wind and solar unit can be controlled independently through the current component.

[0062] 2) Initialize the control target parameters, including: I lim This represents the maximum allowable phase current amplitude of the power electronic equipment. Clearly, the switching transistors in the wind-solar unit converter have limited current-carrying capacity; once this capacity is exceeded, they will quickly lock out. Therefore, during control, the converter arm current needs to be limited to the allowable range. lim This represents the maximum allowable phase voltage amplitude of the system. In weak power grids, the equivalent impedance of the opposite grid is very high. Since the power loop of a wind and solar power unit is disconnected, it can be considered a current source during a fault. Changes in the output current have a more significant impact on the system voltage. Therefore, it is necessary to limit the system voltage within the allowable range during the control process. lim This indicates the maximum allowable active power amplitude of the DC bus capacitor of the wind and solar power unit. During an imbalance fault, the output active power exhibits second-harmonic oscillation, causing the DC bus voltage of the new energy unit to oscillate at the same frequency, thereby resulting in overvoltage of the DC bus capacitor, affecting its service life and even equipment safety. Therefore, the active power amplitude needs to be limited to the allowable range during the control process; P + This represents the active power required during the fault period, and m represents the calculation resolution parameter. P + The calculation of I is not within the scope of this invention. P + It is only used as a parameter input in the algorithm for calculation. The value of m depends on the actual computing performance of the controller chip; the higher the chip performance, the larger the m setting, and the better the control effect. lim V lim P lim The value should be set according to the actual converter performance, and is usually set to 1.1~1.2 pu, typically 1.1 pu. lim Typically calculated based on the maximum withstand voltage of the DC bus capacitor.

[0063]

[0064] In the formula, ω represents the system angular frequency, and Cdc This represents the DC bus capacitance value, V. dc This represents the rated DC bus voltage, V. dc.lim This indicates the maximum permissible DC bus voltage amplitude.

[0065] 3) There are three controllable variables in the entire wind and solar unit fault control process, namely I Q + , .in, It is usually set to 0, so there are only two actual controllable variables I. Q + , In order to quickly calculate the required new energy output current command while minimizing the use of the controller's computing power, I... Q + Set it as a discrete array and substitute it into a linear equation in two variables to solve. Therefore, it is necessary to base it on I. P + Value will I Q + Discretize at resolution m to obtain discrete vector I + Q.map :

[0066]

[0067] In the formula, m is the discrete resolution parameter, which determines the control accuracy.

[0068] 4) According to Figure 1 From the system topology shown, the mathematical relationship between the voltage at point PCC and the output current of the new energy source can be obtained.

[0069]

[0070] The mathematical relationship between the active power amplitude and the output current of new energy sources can also be given.

[0071]

[0072] Combining equations (4) and (5), we can obtain the active power amplitude constraint equation as shown in equation (6). The discrete vector I... + Q.map Substituting into equation (6) to solve the two linear equations in two variables, we obtain the m terms in the equation. The combined values ​​constitute the discrete vector under the active power amplitude constraint. .map.P .

[0073]

[0074] In the formula, ω represents the system frequency, and L represents the inductance of the output filter of the wind-solar unit converter.

[0075] 5) Convert the discrete vector I + Q.map Substitute into equation (4) to solve these three linear equations in two variables. Each equation yields m solutions. The value of , combining all the solutions of the three equations, yields the m×3 dimensional discrete matrix under the phase current amplitude constraint. .map.I

[0076]

[0077] in

[0078]

[0079] In the formula, γ represents the phase difference between the positive and negative sequence voltages at point PCC.

[0080] 6) Convert the discrete vector I + Q.map Substitute each equation into equation (6) to solve these 6 linear equations in two variables. Each equation yields m solutions. The value of , combining all the solutions of the 6 equations, yields the m×3 dimensional discrete matrix under the extended phase voltage magnitude constraint. .map.U

[0081]

[0082] In the formula, Δδ + , These represent the phase shifts of the positive and negative sequence voltages at point PCC, respectively.

[0083] The phase difference shift between positive and negative sequence voltages can be calculated from the formula.

[0084]

[0085] In the formula, the active and reactive current components of the new energy source are coupled in the arcsine function. If further substituted into the phase voltage calculation formula, the higher-order equations become difficult to solve. Three reasonable simplifications are made: the system is an inductive grid, so the resistance can be approximately ignored; considering the small phase shift, the arcsin function can be linearized; and the negative-sequence active current component of the new energy source is usually zero. Based on the above three simplification and decoupling principles, the following is obtained:

[0086]

[0087] The positive and negative sequence voltage amplitudes (Equation (4)) and phases (Equation (11)) at point PCC are transformed into three-phase voltage amplitudes using the following transformation formula:

[0088]

[0089] In the formula, V a V b V c These represent the amplitudes of the three-phase voltages at point PCC.

[0090] Furthermore, the impact of the transformer connection group must be considered. To filter out third harmonics and isolate zero-sequence paths, transformers typically employ a Y-Δ connection group. The Y-Δ transformation of a transformer refers to the change in the phase of the three-phase AC quantities during the connection group conversion process. Its wiring method is as follows: Figure 2 As shown. According to the symmetrical component method, the sequence component voltages on both sides of the transformer have the following relationship:

[0091]

[0092] In the formula, These represent the positive and negative sequence voltage components on the Y and Δ sides of the transformer, respectively. α represents the phase shift caused by the Y-Δ transformation, which is usually a multiple of 30°.

[0093] Substituting equation (13) into the three-phase voltage amplitude calculation formula, it can be found that during an asymmetrical fault, from the Y side to the Δ side, at least one phase voltage amplitude is always increased, such as... Figure 3 As shown. Considering the presence of multiple transformers in the system, merely checking whether the voltage at a single node meets the limits is insufficient. While it can ensure that the phase voltage amplitude at that point does not exceed the limit, other voltage level nodes after Y-Δ transformation still face the risk of phase voltage exceeding the limit. Therefore, multi-stage Y-Δ transformation needs to be incorporated into the fault control process of the wind and solar power generation unit.

[0094] Combining equations (4), (11), and (13), the extended phase voltage amplitude constraint equation can be derived as shown in equation (14). Considering that the zero-sequence voltage component of the fault in actual engineering only exists in the 220kV voltage level system, and after the voltage drop of multiple transformers and 35kV lines, the 220kV node usually will not experience overvoltage due to the zero-sequence component, so the zero-sequence voltage component can be ignored. Therefore, only the positive and negative sequence components of the system voltage are considered. The discrete vector I + Q.map Substituting each variable into equation (14) and solving the system of two linear equations, we obtain the discrete vector under the extended phase voltage amplitude constraint. .map.U

[0095]

[0096] in

[0097]

[0098] In the formula, I + P.|0| This indicates the command value of the active current component of the wind and solar power generation unit before the fault.

[0099] Considering that wind and solar units typically do not require the output of negative-sequence active power, the formulas (6), (7), and (14) are as follows: This can be ignored, thus reducing the computational load.

[0100] 7) The values ​​calculated in steps 4), 5), and 6) .map.P , .map.I , .map.U Perform grouping, and define the upper boundary group matrix including .map.P , .map.I , .map.U The lower boundary group matrix is ​​defined as having only .map.U Based on the clustering results, generate an m×10 dimensional upper bound discrete mapping matrix B. up and the lower bound discrete mapping matrix B of m×6 dimensions up The mathematical expressions for the two matrices are:

[0101]

[0102] 8) Extract the row maximum element of the upper and lower bound discrete mapping matrix (8). .map1 Vector and row minimum element .map2 Vector, and with I + Q.map A numerical matrix is ​​constructed to represent the graphical boundary line of the controllable fault area of ​​the wind and solar power generation unit, denoted as:

[0103]

[0104] 9) Defining Control Objectives. To meet different system support requirements under various fault conditions, this paper proposes three flexibly switchable active fault voltage support strategies for selection: 1. Prioritizing the output of maximum positive-sequence reactive power to support positive-sequence voltage, suitable for severe fault scenarios, such as metallic two-phase ground faults or three-phase faults; 2. Prioritizing the output of maximum negative-sequence reactive power to support negative-sequence voltage, suitable for slightly asymmetrical fault scenarios, such as high-resistance faults; 3. Maximizing the sum of positive and negative-sequence reactive power, suitable for single-phase faults, two-phase faults, and two-phase high-resistance ground faults. Based on the above principles, if the positive-sequence voltage amplitude U at point PCC is... + PCCIf the value is less than 0.4pu, then it belongs to case 1; if 0.4pu ≤ U + PCC If ≤0.6pu, it belongs to case 2; if 0.6pu≤U + PCC If the value is ≤0.9 pu, it falls under case 3. Different instruction value calculation methods are used for each of the three case types.

[0105]

[0106] In the formula, I + Q.ref , .ref These are the positive and negative sequence reactive current command values ​​output by the control program.

[0107] According to equation (18), the positive sequence voltage amplitude U at point PCC of the wind and solar power generation unit is extracted. + PCC Determine when U + PCC When 0.4pu is less than U, the wind and solar units preferentially emit positive-sequence reactive power; when 0.4pu ≤ U + PCC When ≤0.6pu, the wind and solar power units should ensure that the sum of the positive and negative sequence reactive power output is maximized. When 0.6pu≤U + PCC When the power consumption is ≤0.9 pu, the wind and solar units prioritize the emission of negative sequence reactive power.

[0108] 10) The calculated instruction value I + Q.ref , .ref I is obtained through power decoupling inverse transformation d + I q + , This current is then input to the inner current loop of the converter. The power decoupling inverse transform can be expressed as:

[0109]

[0110] The transformation matrix (19) in this step is the inverse of the transformation matrix (1) in step 1).

[0111] The fault detection method involves extracting the effective value of the AC voltage at the PCC point and determining whether the voltage drop meets the low-voltage ride-through requirements stipulated in the current national standard. Considering that the online impedance estimator typically takes 13-20ms to calculate the equivalent impedance on the grid side, after starting the fault control module, the wind and solar units first calculate I according to the current national standard control method. d+ I q + , Instruction. When the algorithm provided by this invention executes to step 10), the original instruction value is overwritten.

[0112] The input quantity of the fault control module provided by this invention is The output is The controllable parameter is: I lim V lim P lim I P + The complete flowchart of the active voltage support control for wind and solar unit faults provided by this invention is as follows: Figure 4 As shown.

[0113] To further illustrate the performance of the present invention, a detailed description is provided in conjunction with an embodiment. Referring to the construction of a photovoltaic power plant transmission system as follows... Figure 1 The research example is shown below. Specific system parameters are shown in Tables 1 and 2.

[0114] Table 1 Parameters of New Energy Converter Equipment and Filters

[0115]

[0116] Table 2. Other parameters such as line and transformer impedance.

[0117]

[0118] The fault occurred on the grid side at 0s and lasted for 150ms. This invention compares the latest national standard for low-voltage ride-through control of wind and solar power plants in 2021 to illustrate the advancement of the provided control strategy. According to power system safety guidelines, the upper limit of phase voltage amplitude is set to 1.1pu, the upper limit of phase current amplitude to 1.2pu, the active power amplitude to 0.35pu, and the positive-sequence active current after the fault to 0.35pu. With a weak grid SCR of 1.5, in the event of an AG metallic fault, the positive and negative sequence voltages at the PCC point of the photovoltaic power plant drop to 0.7pu and 0.3pu, respectively. Figure 5 A graphical representation of the proposed active voltage support control module for wind and solar power generation units is presented under the fault scenario and preset conditions.

[0119] from Figure 5 As can be seen, in the current domain, the proposed controllable fault region of new energy is represented by the intersection of ten curves. Based on the clustered discrete mapping matrix, the proposed method can quickly extract the boundary line of this region, as shown by the red and blue dots in the figure. The fault control module provided by this invention gives the maximum support point P of the wind and solar power generation unit. bestThe figures are labeled. Based on the fault controllability boundary, the proposed control strategy is compared with the current national standard as follows: Figure 6 As shown. From Figure 6 As shown in (a) and (b), the maximum phase current amplitude of the current national standard is 1.17 pu, which does not reach the maximum support capacity, and the active power amplitude reaches 0.43 pu, exceeding the limit standard. The maximum phase voltage amplitude of the system is about 0.7 pu, and the positive sequence voltage is only increased by 0.056 pu, which cannot fully tap the fault voltage support capacity of the renewable energy power station. The maximum phase voltage amplitude of the proposed method at the 0.38kV and 35kV nodes is 0.98 pu and 1.08 pu, respectively, with the positive sequence voltage increased by 0.18 pu and the negative sequence voltage suppressed by 0.11 pu. The maximum phase current amplitude is 1.19 pu, and the active power amplitude is within 0.35 pu. In comparison, the proposed control strategy significantly improves the fault voltage support capacity of renewable energy.

[0120] It is worth mentioning that, in Figure 6 In (b), compared to a strong grid, a weak grid provides a smaller short-circuit current. Therefore, the output from the renewable energy source has a greater impact on the voltage at the fault point. Furthermore, because the current national standard adopts a voltage-controlled current source method, the output current will dynamically change with voltage fluctuations. As a result, the transient fluctuation time of the fault voltage is long, taking approximately 175ms to reach steady state. In contrast, the proposed control strategy directly calculates the maximum support capacity of the renewable energy source. The output current is not affected by the transient fluctuations of the system voltage, and it can reach steady state approximately 100ms after the fault, significantly shortening the fault transient response time of the weak grid system.

[0121] As can be seen from this embodiment, compared with the control strategy given by the current national standard, the present invention has the advantages of safety, comprehensiveness, speed, and flexibility, improving the active voltage support capability of new energy sources by more than 50%, significantly enhancing grid strength during faults, and avoiding cascading accidents such as large-scale grid disconnection of new energy sources. Furthermore, the present invention has advantages such as fast calculation speed, low application cost, and high program portability, and has high practical application value.

[0122] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for active voltage support during wind and solar power generation unit faults based on extended controllable boundaries, characterized in that, Includes the following steps: 1) After the wind and solar power generation unit detects a fault, it activates the fault control function: it calculates the equivalent positive and negative sequence voltages V on the grid side using an online impedance estimator. g + V g - and equivalent impedance R g +jL g Collect three-phase voltage and current data at point PCC, and obtain the voltage v along the αβ axis through Clark transformation. α v β Current component i α i β The current components are transformed by Park and separated by sequence component control to obtain positive and negative sequence dq-axis current components U. d + U q + U d - U q - I d + I q + I d - I q - Finally, after the power decoupling coordinate transformation matrix K... PQ / dq The positive and negative sequence PQ axis current components I are obtained. P + I Q + I P - I Q - : （1） 2) Initialize the control target parameters, including: the maximum allowable phase current amplitude I of the power electronic equipment. lim , representing the maximum allowable phase voltage amplitude V of the system. lim The value P represents the maximum active power amplitude allowed to be output by the DC bus capacitor of the wind and solar unit. lim , representing the active power I required to be generated during the fault. P + , indicates the calculated resolution parameter m; 3) According to I P + Value will I Q + Discretize using the resolution parameter m to obtain the discrete vector I. + Q.map : （2） In the formula, m is the discrete resolution parameter, which determines the control accuracy; 4) Convert the discrete vector I + Q.map Substituting into equation (3) to solve the two linear equations, we obtain the m I values ​​in the equation. Q - The combined values ​​are the discrete vector I under the active power amplitude constraint. - Q.map.P : （3） In the formula, ω represents the system frequency, and L represents the inductance of the output filter of the wind-solar unit converter; 5) Convert the discrete vector I + Q.map Substitute into equation (4) to solve these three linear equations in two variables. Each equation yields m I values. Q - The value of is obtained by combining all the solutions of the three equations to form the m×3 dimensional discrete matrix I under the phase current amplitude constraint. - Q.map.I : （4） in, （5） In the formula, γ represents the phase difference between the positive and negative sequence voltages at point PCC; 6) Convert the discrete vector I + Q.map Substitute each variable into equation (6) to solve these 6 linear equations in two variables. Each equation yields m solutions of I. Q - The value of , combining all the solutions of the 6 equations, yields the m×3 dimensional discrete matrix I under the extended phase voltage amplitude constraint. - Q.map.U : （6） in, （7） In the formula, I + P.|0| This indicates the command value of the active current component of the wind and solar power generation unit before the fault. 7) The values ​​I obtained in steps 4), 5), and 6) - Q.map.P I - Q.map.I I - Q.map.U Perform grouping, and define the upper boundary group matrix including I. - Q.map.P I - Q.map.I I - Q.map.U The lower boundary group matrix is ​​defined as having only I. - Q.map.U Based on the clustering results, an m×10 dimensional upper bound discrete mapping matrix B is generated. up and the lower bound discrete mapping matrix B of m×6 dimensions up The mathematical expressions for the two matrices are: （8） 8) Extract the row maximum element vector and row minimum element vector of the upper and lower bound discrete mapping matrix (8), and define them as I respectively. - Q.map1 and I - Q.map2 and with I + Q.map A numerical matrix, BD, is constructed to represent the graphical boundary line of the controllable fault area of ​​the wind and solar power generation unit. Its mathematical expression is as follows: （9） 9) Define the control target and determine if the positive sequence voltage amplitude U at point PCC is... + PCC If the value is less than 0.4pu, then it belongs to case 1; if 0.4pu ≤ U + PCC If ≤0.6pu, it belongs to case 2; if 0.6pu≤U + PCC If the value is ≤0.9 pu, it falls under case 3; different instruction value calculation methods are used for each of the three cases: （10） In the formula, I + Q.ref I - Q.ref These are the positive and negative sequence reactive current command values ​​output by the control program; 10) Calculate the instruction value I + Q.ref I - Q.ref I is obtained through power decoupling inverse transformation d + I q + I d - I q - This leads to the current inner loop of the converter; the power decoupling inverse transformation matrix K dq / PQ It can be represented as （11）。 2. The method for active voltage support for wind and solar power generation units based on extended controllable boundaries according to claim 1, characterized in that, In step 4), formula (3) represents the relationship between the active power amplitude and the output current of the wind and solar power generation unit. The discrete vector I... + Q.map Substituting into formula (3), the corresponding negative sequence reactive current discrete vector I is calculated. - Q.map.P .

3. The method for active voltage support for wind and solar power generation units based on extended controllable boundaries according to claim 1, characterized in that, In step 5), formula (4) represents the relationship between the amplitude of the three-phase current flowing through the bridge arm of the wind-solar unit converter and the output current. The discrete vector I... + Q.map Substituting into formula (4), the corresponding negative sequence reactive current discrete vector I is calculated. - Q.map.I .

4. The method for active voltage support for wind and solar power generation units based on extended controllable boundaries according to claim 1, characterized in that, In step 8), matrix (9) is derived from discrete vector I. + Q.map and the upper and lower boundary grouping discrete matrix B up B down Combining the components, the calculation method is to take B. up The row maximum element vector I - Q.map1 Take B down The smallest element vector in the row I - Q.map2 , with I + Q.map splicing.

5. The method for active voltage support for wind and solar power generation units based on extended controllable boundaries according to claim 1, characterized in that, Formula (10) defines the control principles for wind and solar power units under three operating conditions, respectively addressing different types of faults; the positive sequence voltage amplitude U at the PCC point of the wind and solar power generation unit is extracted. + PCC , when U + PCC When 0.4pu is less than U, the wind and solar units preferentially emit positive-sequence reactive power; when 0.4pu ≤ U + PCC When ≤0.6pu, the wind and solar power units should ensure that the sum of the positive and negative sequence reactive power output is maximized. When 0.6pu≤U + PCC When the power consumption is ≤0.9 pu, the wind and solar units prioritize the emission of negative sequence reactive power.

6. The method for active voltage support for wind and solar power generation units based on extended controllable boundaries according to claim 1, characterized in that, The power decoupling coordinate inverse transformation The positive and negative sequence PQ axis current components are transformed into positive and negative sequence dq axis current components, and then input into the inner current loop; the transformation matrices in step 10) and step 1) are inverse matrices of each other.

7. A non-volatile storage medium, characterized in that, The non-volatile storage medium includes a stored program, wherein the program, when running, controls the device where the non-volatile storage medium is located to execute the method of claim 1.

8. An electronic device, characterized in that, It includes a processor and a memory; the memory stores computer-readable instructions, and the processor is used to execute the computer-readable instructions, wherein the computer-readable instructions, when executed, perform the method of claim 1.

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