Switchable converter capacity configuration and switching boundary setting method, equipment and medium

Abstract

The invention discloses a switchable converter capacity configuration and switching boundary setting method and device and a medium, and the method comprises the steps: enabling a switchable converter to be switched into a network construction control mode, and obtaining the mode switchable converter capacity in the network construction control mode; the method comprises the following steps: establishing a small signal model of a grid following converter and a grid following / constructing mode switchable converter series-parallel field station according to working conditions, calculating whether a current dominant characteristic root damping ratio of the small signal model meets a stability margin requirement or not, and if the requirement is met, constructing a switching boundary of a hysteresis control strategy setting mode switchable converter by taking an operation short circuit ratio as an index. According to the method, the capacity required by the mode switchable converter is determined under the specified working condition, the switchable converter is converted comprehensively based on the change of the short-circuit ratio and the active power output, the sufficient stability margin is ensured, the operating short-circuit ratio index is introduced, the stability of the active power non-full-power working condition can be reflected, and the stability of the mode switchable converter is improved. The set switching boundary is more reasonable and accurate compared with the short circuit ratio.

Description

Technical Field

[0001] The present invention relates to the technical field of intelligent distribution network control, and in particular to a method, device and medium for configuring the capacity of a switchable converter and setting a switching boundary. Background Art

[0002] As the penetration rate of new energy in my country's power system continues to increase, new energy power generation equipment such as wind power and photovoltaic power generation are connected to the grid with converters as ports. At present, grid-connected converters usually adopt grid-following control, which has the risk of oscillation instability under weak grid conditions, affecting the safe consumption of new energy. Grid-building control has good weak grid stability, but it also has disadvantages such as slow power response speed and difficulty in achieving maximum power point tracking. Therefore, the capacity configuration of grid-building converters should comprehensively weigh economic and technical factors. The current technical methods for capacity configuration of grid-building converters can be mainly divided into two categories, one based on time domain simulation and the other based on small signal mathematical models. In terms of time domain simulation method, studies have established electromagnetic transient models of regional power grids in Ireland, the United Kingdom, and southeastern Australia, and analyzed the small signal stability of the system by means of time domain simulation. The common conclusion is that if the power generation units of the entire power grid are composed of converters, in order to maintain the stability of the system, some converters must adopt grid-building control. However, the proportion of grid-forming converters required to maintain system stability is related to multiple factors such as system scale, grid structure, and line parameters, and no unified conclusion can be reached at present. In terms of methods based on small-signal mathematical models, Professor Zhang Xing's team at Hefei University of Technology proposed to configure a part of grid-forming mode switchable converters in the station to switch the control mode as the short-circuit ratio changes, in response to the problem of large fluctuations in the equivalent impedance of the grid at the grid connection point caused by the intermittent, random, and volatile nature of new energy. However, the short-circuit ratio reflects the small-signal stability under working conditions and lacks consideration for the fluctuation of the active power of new energy. The active power has a significant impact on the small-signal stability. Ignoring this point will cause deviations in capacity configuration and switching boundary setting. Summary of the invention

[0003] The technical problem to be solved by the present invention is that the existing new energy station capacity configuration of the grid-connected / grid-forming converter and the switching boundary based on the short-circuit ratio index ignore the influence of the new energy power fluctuation on the small signal stability, and the deviation of the capacity configuration and the switching boundary setting is large. The purpose is to provide a method, equipment and medium for the capacity configuration and switching boundary setting of the switchable converter. First, through the capacity configuration, the influence of the two factors of short-circuit ratio and active power are comprehensively considered to determine the capacity required by the mode switchable converter under the specified working conditions. As the short-circuit ratio decreases, the active output increases, and the risk of oscillation instability of the full grid-connected operation station increases. At this time, the switchable converter is converted to the grid-forming mode to ensure sufficient stability margin. Secondly, in terms of the switching boundary setting, the introduction of the operating short-circuit ratio index can reflect the stability of the working condition where the active power is not fully generated, and the set switching boundary is more reasonable and accurate than the short-circuit ratio.

[0004] The present invention is achieved through the following technical solutions:

[0005] A first aspect of the present invention provides a method for configuring the capacity of a switchable converter and setting the switching boundary, comprising the following specific steps:

[0006] S1. Build a new energy station, switch the switchable converter to a grid-building control mode, and obtain the capacity of the mode-switchable converter in the grid-building control mode;

[0007] S2. Define the working condition. Under the current working condition, based on the capacity of the mode-switchable converter, establish a small signal model of the hybrid station of the grid-following converter and the grid-following / grid-building mode-switchable converter;

[0008] S3, calculating whether the current dominant characteristic root damping ratio of the small signal model meets the stability margin requirement, if so, executing step S4, otherwise returning to step S1;

[0009] S4. Taking the operating short-circuit ratio as an indicator, a hysteresis control strategy is constructed to set the switching boundary of the switchable converter.

[0010] Furthermore, the step S1 specifically includes:

[0011] Obtain a grid-following converter with a single-machine multiplication equivalent value and a mode-switchable converter with a single-machine multiplication equivalent value, connect the grid-following converter with a single-machine multiplication equivalent value and the mode-switchable converter with a single-machine multiplication equivalent value in parallel, multiply and scale the power data in the grid-following converter and the grid-building converter based on the single-machine parameters, and build a new energy station;

[0012] Increase the capacity of the mode-switchable converter in the new energy station from scratch, with each capacity increase being the rated capacity of a single converter.

[0013] Furthermore, the increasing the capacity of the mode-switchable converter in the new energy station specifically includes:

[0014] The rated capacity of a single mode-switchable converter and the number of mode-switchable converters configured in the station at the i-th iteration are obtained. The number of mode-switchable converters configured in the i-th iteration is one more than that in the (i-1)-th iteration, thereby obtaining the total capacity of the mode-switchable converters configured in the station.

[0015] The rated capacity of a single grid-following converter, the number of mode-switchable converters configured in the station at the i-th iteration, and the total number of converters in the station are obtained to obtain the total number of grid-following converters in the station, and then the total capacity of the grid-following converters configured in the station is obtained.

[0016] Furthermore, the defined working condition specifically includes: defining the maximum output active power of the converter and the minimum short-circuit ratio of the grid connection point as the target working condition, and the step of obtaining the defined working condition includes:

[0017] Adjust the output active power of the converter to the maximum and the short-circuit ratio of the grid point to the minimum value SCR min Set to 1, and adjust the line inductance to make the short-circuit ratio of the grid connection point reach the target value. The calculation formula is as follows:

[0018] In the formula, SCR min Indicates the minimum short-circuit ratio of the grid connection point, U B Indicates rated voltage, S B Indicates rated power, L g represents the line inductance value to be calculated, ω0 represents the reference angular frequency, which is related to the rated frequency of the system, and R g Indicates the line resistance value.

[0019] Furthermore, the step S2 specifically includes:

[0020] Construct the dynamic equations of each link of the grid-following mode and grid-building mode of the converter, construct the dynamic equations of the grid-following mode converter connection transformer, the grid-building mode converter connection transformer, and the line between the grid connection point and the infinite power source, convert the physical quantities of the two-phase rotating coordinate system of the following / grid-building mode to the global coordinate system equation, perform linearization at the steady-state operation point, and obtain the small signal model of the hybrid station of the following / grid-building mode switchable converter;

[0021] Among them, the dynamic equations of each link of the grid-following mode include: the dynamic equation of the LC filter part of the converter, the dynamic equation of the current inner loop of the grid-following converter, the dynamic equation of the d-axis of the grid-following outer loop, the dynamic equation of the q-axis of the grid-following outer loop, and the dynamic equation of the phase-locked loop;

[0022] Among them, the dynamic equations of each link of the grid-forming mode include: the dynamic equation of the current inner loop of the grid-forming converter, the dynamic equation of the d-axis of the grid-forming outer loop, the dynamic equation of the q-axis of the grid-forming outer loop, the dynamic equation of the power synchronization loop, and the dynamic equation of the LC filter of the grid-forming mode converter.

[0023] Furthermore, the step S3 specifically includes:

[0024] According to the small signal model, the state matrix is ​​extracted, and the characteristic roots of the state matrix are calculated to obtain a pair of conjugate characteristic roots, wherein a pair of conjugate characteristic roots represents an oscillation mode of the grid-connected system of the new energy station;

[0025] The conjugate characteristic root with the largest real part among the conjugate characteristic roots of the state matrix is ​​defined as the dominant characteristic root, and the damping ratio and frequency of the oscillation mode corresponding to the dominant characteristic root are calculated;

[0026] According to the damping ratio threshold, when the dominant characteristic root damping ratio is greater than the damping ratio threshold, the stability margin meets the requirement, and the process goes to step S4; otherwise, the process returns to step S1.

[0027] Furthermore, the step S4 specifically includes:

[0028] Obtain the actual active power per unit value injected into the grid connection point by the new energy station and the short-circuit ratio of the grid connection point to calculate the operating short-circuit ratio;

[0029] Based on the operating short-circuit ratio, the operating short-circuit ratio changes from large to small and crosses the boundary value C1 and the operating short-circuit ratio changes from large to small and crosses the boundary value C2;

[0030] When the station output active power increases, the short-circuit ratio decreases, and the operating short-circuit ratio changes from large to small and crosses the boundary value C1, the mode of the switchable converter is changed from the grid-following mode to the grid-building mode;

[0031] When the station output active power decreases, the short-circuit ratio increases, and the operating short-circuit ratio increases from small to large and crosses the boundary value C2, the mode of the switchable converter is converted from the grid-building mode to the grid-following mode.

[0032] Furthermore, the boundary values ​​C1 and C2 are specifically set including:

[0033] All switchable converters in the station adopt the grid-following control mode to reduce the short-circuit ratio of the grid connection point. When the dominant characteristic root damping ratio of the station is detected until it is lower than the set threshold, the critical OSCR value is C 11 ;

[0034] Fixed SCR value, increased station active power, detected the station dominant characteristic root damping ratio until it is lower than the set threshold, and obtained the critical OSCR value is C 12 ;

[0035] Take C11 and C 12 The largest one among them is taken as the value of C1;

[0036] An incremental value is added to the value of C1 to obtain the value of C2, that is, C2=C1+1.

[0037] A second aspect of the present invention provides an electronic device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein when the processor executes the program, a method for configuring the capacity of a switchable converter and setting the switching boundary is implemented.

[0038] A third aspect of the present invention provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements a method for capacity configuration and switching boundary setting of a switchable converter.

[0039] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0040] First, through capacity configuration, the influence of short-circuit ratio and active power is comprehensively considered to determine the capacity required for the mode-switching converter under specified working conditions. As the short-circuit ratio decreases, the active output increases, and the risk of oscillation instability in the full-grid operation station increases. At this time, the switchable converter is converted to the grid-forming mode to ensure sufficient stability margin. Secondly, in terms of switching boundary setting, the introduction of the operating short-circuit ratio indicator can reflect the stability of the active power under-generation condition. The set switching boundary is more reasonable and accurate than the short-circuit ratio. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In order to more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and should not be regarded as limiting the scope. For those of ordinary skill in the art, other relevant drawings can be obtained based on these drawings without creative work. In the drawings:

[0042] Figure 1 is a flow chart of a capacity configuration and boundary setting method in an embodiment of the present invention;

[0043] Figure 2 It is a new energy station model in the embodiment of the present invention;

[0044] Figure 3 is a specific control structure of the converter in the embodiment of the present invention;

[0045] Figure 4 It is a schematic diagram of the transformation of voltage and current in a three-phase stationary coordinate system to a two-phase rotating coordinate system in an embodiment of the present invention;

[0046] Figure 5 Schematic diagram of converter mode switching based on hysteresis control in an embodiment of the present invention;

[0047] Figure 6 It is a simulation result diagram in an embodiment of the present invention. DETAILED DESCRIPTION

[0048] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments and drawings. The exemplary embodiments of the present invention and their description are only used to explain the present invention and are not intended to limit the present invention.

[0049] As a possible implementation, Figure 1 As shown, this embodiment provides a method for configuring the capacity of a switchable converter and setting the switching boundary. First, through capacity configuration, the influence of the short-circuit ratio and active power is comprehensively considered to determine the capacity required for the mode switchable converter under specified working conditions. As the short-circuit ratio decreases, the active output increases, and the risk of oscillation instability in the full-grid operation station increases. At this time, the switchable converter is converted to the grid-forming mode to ensure sufficient stability margin. Secondly, in terms of switching boundary setting, the introduction of the operating short-circuit ratio indicator can reflect the stability of the active power under-generation working conditions, and the set switching boundary is more reasonable and accurate than the short-circuit ratio.

[0050] The specific implementation scheme of this embodiment is:

[0051] S1. Construct a new energy station and make the mode-switchable converter work in the grid-building mode. Increase the capacity of the mode-switchable converter in the new energy station from zero, with each capacity increase being the rated capacity of a single converter.

[0052] like Figure 2 As shown in the figure, the modeling method of the new energy station is shown, in which the new energy station is modeled as a single-machine multiplied equivalent grid-following converter and a single-machine multiplied equivalent mode switchable converter in parallel, the station is connected to the grid connection point, and the grid connection point is connected to the infinite power supply through a resistance-inductance line, R g Indicates line resistance, L g Indicates line inductance, U sabc It represents the three-phase AC voltage at the grid connection point, and represents the three-phase AC voltage of the infinite power supply. The single-machine multiplication and equivalence are based on the single-machine models of the grid-following converter and the mode-switchable converter. The grid-following converter in the station can be understood as the mode-switchable converter fixedly adopting the grid-following control mode. Among them, the single-machine model of the mode-switchable converter is as follows Figure 3As shown in the figure, the control links used in the grid-following mode are the phase-locked loop, the grid-following outer loop d-axis and the grid-following outer loop q-axis, and the control links used in the grid-building mode are the power synchronization loop, the grid-building outer loop d-axis and the grid-building outer loop q-axis. The remaining links are the same in the grid-following mode and the grid-building mode. F 、Filter inductor L F And the connection transformer inductance L T The value is multiplied and scaled based on the single machine parameters. When the multiplication simulation multiple is n, the capacitance is n times the single machine parameters, and the inductance parameters are reduced to 1 / n of the single machine parameters. In addition, the voltage value obtained after the Parker change remains unchanged, and the current value is reduced to 1 / n of the original value. The active power P and reactive power Q injected into the grid point are 1 / n of the actual value. Figure 3 The other parameters involved and their meanings will be described in detail in step S2.

[0053] The calculation formula for increasing the capacity of the switchable converter in the new energy station mode in step S1 is:

[0054]

[0055] Where: S swits Indicates the rated capacity of a single unit of a mode-switching converter, S gfls It represents the rated capacity of a single grid-following converter. Assuming that the rated capacity of converters with different control strategies (grid-following or grid-building) in the station is the same, that is, S swits and S gfls Equal. swit Indicates the total capacity of the configuration mode switchable converters in the station, S gfl Represents the total capacity of the grid-following converters configured in the station. i represents the number of mode-switchable converters configured in the station at the i-th iteration, N represents the total number of converters in the station, and the value of N remains unchanged. Each iteration only adjusts the capacity ratio of the grid-following converters to the mode-switchable converters in the station.

[0056] S2. Establish a small signal model of a hybrid station with a grid-following converter and a converter switchable in the grid-following / grid-building mode under target operating conditions.

[0057] Based on the capacity of the switchable converter in the current station using the grid control mode determined in step S1, a small signal model of the hybrid station is established. First, the dynamic equations of the converter's grid-following mode and grid-forming mode need to be established. The dynamic equation of the converter LC filter part is established according to Kirchhoff's voltage law and Kirchhoff's current law:

[0058]

[0059] Among them, u tdGFL 、utqGFL are the d-axis and q-axis components of the filter capacitor voltage, respectively, dGFL 、i qGFL are the d-axis and q-axis components of the AC grid current respectively, i vdGFL 、i vqGFL are the d-axis and q-axis components of the converter output current, respectively, and u vdGFL 、u vqGFL are the d-axis and q-axis components of the converter terminal voltage, respectively, and ω0 is the fundamental angular frequency. The above voltages, currents, and impedances are all converted to the low-voltage side of the connection transformer. The subscript GFL represents the electrical quantity related to the grid-mode converter.

[0060] The current inner loop dynamic equation of the grid-following converter is:

[0061]

[0062] Among them, z1, z2, x1, x2 are introduced intermediate variables, K p1 , K i1 , K p2 , K i2 is the proportional-integral parameter of the current inner loop, U vdrefGFL , U vqrefGFL is the voltage reference value of the grid-following converter terminal, T F is the inertia time constant of the voltage feedforward link.

[0063] The dynamic equations of the d-axis of the outer ring of the network and the dynamic equations of the q-axis of the outer ring of the network are:

[0064]

[0065] Among them, x3 and x4 are introduced intermediate variables, K p3 , K i3 , K p4 , K i4 is the voltage outer loop proportional-integral link parameter, P refGFL , Q refGFL is the reference value of active and reactive power of the converter, i vdrefGFL 、i vqrefGFL It is the reference value of the d and q axes of the inner loop of the current in the grid-following mode.

[0066] The dynamic equation of the phase-locked loop is:

[0067]

[0068] Among them, x5 is the introduced intermediate variable, θ GFL is the phase-locked loop output angle, K p5 , K i5 are the proportional-integral parameters of the phase-locked loop, ω GFLIt is the angular frequency of the dq rotation coordinate system of the control system in the network following mode.

[0069] The dynamic equation form of the current inner loop of the grid-type converter is consistent with the grid-following mode. For the sake of distinction, the subscript GFL of the relevant physical quantity in equation (3) is replaced by GFM, and the subscript GFM represents the physical quantity related to the grid-type converter. Replace z1 and z2 with k1 and k2, and replace x1 and x2 with y1 and y2, and we can get:

[0070]

[0071] The dynamic equations of the d-axis of the outer ring of the network and the dynamic equations of the q-axis of the outer ring of the network are:

[0072]

[0073] Among them, z3, x6, x7 are introduced intermediate variables, K G , K T , K p6 , K i6 , K p7 , K i7 It is the parameter of the proportional-integral link of the voltage outer loop.

[0074] The dynamic equation of the power synchronization ring is:

[0075]

[0076] Among them, θ GFM is the output angle of the power synchronization ring, z4 is the introduced intermediate variable, J is the virtual synchronous machine rotor inertia coefficient, K D is the virtual synchronous damping coefficient.

[0077] The dynamic equation of the LC filter of the grid-connected mode converter is:

[0078]

[0079] The dynamic equations of the grid-following mode converter connection transformer, the grid-building mode converter connection transformer, and the line between the grid connection point and the infinite power source can be expressed as:

[0080]

[0081] Where: u sdg 、u sqg They represent the d-axis component and q-axis component of the grid connection point voltage in the global coordinate system, respectively. The global coordinate system refers to a two-phase rotating coordinate system in which the d-axis coincides with the infinite power supply voltage vector. d 、u qThey represent the d-axis and q-axis components of the infinite power supply voltage in the global coordinate system, and the other electrical quantities with subscript g represent their values ​​in the global coordinate system. Figure 3 It can be seen that the network following mode is based on the phase-locked loop output θ GFL The voltage and current in the three-phase stationary coordinate system are transformed into the two-phase rotating coordinate system. The network mode is based on the θ output of the phase-locked loop. GFM The voltage and current in the three-phase stationary coordinate system are transformed into the two-phase rotating coordinate system. The above two rotating coordinate systems are not consistent with the global coordinate system, so conversion between different rotating coordinate systems is required. Figure 4 As shown in the figure, the formula for converting the physical quantities of the two-phase rotating coordinate system of the grid-following mode to the global coordinate system is:

[0082]

[0083] Where: m d and m q Represents the d-axis and q-axis components of the physical quantity in the global coordinate system, m dGFL and m qGFL It represents the d-axis and q-axis components of the physical quantity in the two-phase rotating coordinate system of the grid-following mode converter.

[0084] The formula for converting the physical quantities of the two-phase rotating coordinate system of the network mode to the global coordinate system is:

[0085]

[0086] Where: m dGFM and m qGFM It represents the d-axis and q-axis components of the physical quantity in the two-phase rotating coordinate system of the grid-connected mode converter.

[0087] By combining equations (2) to (12) and linearizing them at the steady-state operation point, we can obtain the small signal model of the new energy station grid-connected system:

[0088]

[0089] Where:

[0090] ΔX=[Δi dGFL ,Δi qGFL ,Δu tdGFL ,Δu tqGFL ,Δi vdGFL ,Δi vqGFL ,Δθ GFL ,Δx1,Δx2,Δx3,Δx4,Δx5,Δz1,Δz2,Δi dGFM ,Δ

[0091] i qGFM ,Δu tdGFM ,ΔutqGFM ,Δi vdGFM ,Δi vqGFM ,Δθ GFM ,Δy1,Δy2,Δk1,Δk2,Δz3,Δx6,Δx7,Δz4] T ;

[0092] ΔU=[ΔP refGFL ,ΔQ refGFL ,ΔP refGFM ,ΔQ refGFM ,Δu d ,Δu q ] T ;

[0093] The above formulas are the state matrix and input matrix respectively.

[0094] It should be noted that the grid-following mode converter and grid-forming mode converter described in equations (2) to (10) are converter models after single-machine multiplication. The current, power, inductance and capacitance involved are processed accordingly according to the multiplication number of the single-machine multiplication. The corresponding processing method has been described in step S1.

[0095] Existing studies have shown that when all converters in new energy stations adopt grid-following control, their small signal stability is inversely correlated with their output active power and positively correlated with the short-circuit ratio of the station grid connection point. Therefore, the present invention defines the worst working condition as the condition where the converter outputs the maximum active power and the grid connection point short-circuit ratio is the minimum. This condition is reflected in the small signal model as shown in the appendix of the specification. Figure 3 The active power reference value P in ref Take 1p.u., without loss of generality, consider the converter to operate at unity power factor, the reactive power reference value Q ref Take 0p.u.. Considering the existence of the working point, the short-circuit ratio of the grid-connected point is usually not less than 1. The present invention takes the minimum short-circuit ratio as 1. Figure 2 When the resistance and inductance of the power grid satisfy the relationship of formula (14), the short-circuit ratio of the grid connection point can be 1.

[0096]

[0097] In the formula, SCR represents the short-circuit ratio of the grid connection point, U B Indicates rated voltage, S B Indicates rated power.

[0098] S3. Calculate whether the current dominant characteristic root damping ratio meets the stability margin requirement. If so, proceed to S4; otherwise, return to S1.

[0099] Solve the characteristic roots of the state matrix A in equation (13). Each pair of conjugate characteristic roots represents an oscillation mode of the grid-connected system of the new energy station. Assuming that a pair of conjugate characteristic roots of A is a+jb, the calculation formula for the damping ratio ζ and frequency f (unit: Hz) of the oscillation mode corresponding to the conjugate characteristic root is:

[0100]

[0101] The conjugate characteristic root with the largest real part among the conjugate characteristic roots of matrix A is defined as the dominant characteristic root, and the small signal stability depends on the damping ratio of this pair of conjugate characteristic roots. The damping ratio threshold ζ is calculated according to formula (16): cr When the dominant characteristic root damping ratio is greater than the damping ratio threshold, the stability margin meets the requirement and the process goes to step S4, otherwise it returns to step S1.

[0102]

[0103] Where c is the normalized coefficient (based on the oscillation frequency f std =2.5Hz, damping ratio ζ std =5% low-frequency mode as the benchmark, we can get c = 63.84).

[0104] S4. Use the hysteresis control strategy to adjust the mode switching boundary of the mode-switchable converter.

[0105] After determining the capacity configuration scheme of the mode-switchable converter based on steps S1 to S3, the switching boundary of the following / forming control mode is adjusted with the operating short-circuit ratio as an indicator. The calculation formula of the operating short-circuit ratio OSCR is shown in formula (17).

[0106]

[0107] Where P* represents the actual active power per unit value injected into the grid by the new energy station.

[0108] The schematic diagram of converter mode switching based on hysteresis control is shown in Figure 5As shown, when the station output active power increases, the short-circuit ratio decreases, and the OSCR changes from large to small and crosses the boundary value C1, the stability of the station converters all adopting the grid-following mode is weakened, and there is a risk of oscillation instability. The mode of the switchable converter is converted from the grid-following mode to the grid-building mode. In order to avoid the control mode of the converter being repeatedly switched near the switching boundary due to the fluctuation of new energy power, a hysteresis switching strategy is adopted. When the OSCR changes from small to large and crosses the boundary value C2, the switchable converter is converted from the grid-building mode back to the grid-following mode. Specifically, when C1 is set, all converters in the station adopt the grid-following control mode. Referring to step S2, a small signal model of the full grid-following converter station is established. The station active power is fixed to 1p.u., and the SCR is gradually reduced (i.e., the grid impedance is increased). The small signal model of the full grid-following station is used to calculate the dominant characteristic root damping ratio of the station at this time until it is lower than the critical OSCR value of the threshold calculated by formula (16) C 11 Then fix the SCR value to 1, gradually increase the station active power, and determine the station dominant characteristic root damping ratio until it is lower than the critical OSCR value of the threshold calculated by formula (16) C 12 , take C 11 and C 12 The larger one is used as the value of C1. The switching boundary C2 can be obtained by adding an increment ΔC to C1. In this embodiment, the value of ΔC can be 1.

[0109] like Figure 3 As shown, the red signal line indicates that the mode-switchable converter switches from the following grid mode to the building grid mode, and the blue signal line indicates the switch from the building grid mode to the following grid mode. The switching principle is to assign signals to the integral link to maintain the inner loop current d, q-axis current reference value and the phase of the two-phase rotating coordinate system without sudden change at the switching moment.

[0110] As a possible implementation method, this embodiment provides an electronic device, including a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the program, a method for configuring the capacity of a switchable converter and setting the switching boundary is implemented.

[0111] As a possible implementation, this embodiment provides a computer-readable storage medium having a computer program stored thereon, and when the program is executed by a processor, a method for configuring the capacity of a switchable converter and setting a switching boundary is implemented.

[0112] As a possible implementation method, this embodiment adopts Figure 2 The multiplied simulation of the new energy station grid-connected system shown in FIG. 1 illustrates the effectiveness of the proposed method. The station is modeled as a grid-type converter multiplier equivalent machine and a mode-switching converter multiplier equivalent machine connected in parallel. The specific control block diagram of the converter is shown in FIG. Figure 3As shown, the values ​​of relevant parameters are shown in Table 1 and Table 2 below.

[0113] Table 1 Converter parameters

[0114]

[0115]

[0116] Table 2 AC grid parameters

[0117]

[0118] Reference Figure 1 , steps S1 to S3 are executed in a loop. During the execution process, the changing trend of the dominant characteristic root of the station as the capacity proportion of the mode-switchable converter in the station increases is shown in Table 3. In the implementation case of the present invention, in the station including 50 converters, when the number of mode-switchable converters using network control reaches 9, the station meets the requirements for stability margin under the worst working condition defined in the present invention (the station outputs active power of 1p.u. and the short-circuit ratio is 1).

[0119] Table 3. Trend of dominant characteristic roots as the capacity proportion of mode-switchable converters in stations increases

[0120]

[0121] Further, step S4 is executed, all 50 converters are controlled by grid-following, the active power reference value is fixed to 1p.u., and the SCR is changed, or the SCR is fixed to 1 and the active power reference value is changed. The trend of the dominant characteristic root damping ratio changing with the operating short-circuit ratio is shown in Table 4. From Table 4, it can be seen that C 11 The value is 2.4, C 12 The value is 2.22, therefore, the value of C1 is 2.4 and the value of C2 is 3.4.

[0122] Table 4 Trend of the dominant characteristic root damping ratio of the full grid station synchronization with the operating short-circuit ratio

[0123]

[0124] PSCAD electromagnetic transient simulation is used to verify the effectiveness of the mode switchable converter and mode switching boundary of the embodiment of the present invention. The simulation conditions are set to the short-circuit ratio SCR change (i.e., grid inductance change) and the fluctuation of the station output active power reference value. The simulation results are shown in the figure below. It can be found that according to the configuration of the mode switchable converter capacity according to the method proposed in the present invention, the switching boundary is set based on the operating short-circuit ratio, which can adapt to the large fluctuations of grid impedance and active power. The station output active power curve is relatively smooth, the oscillation amplitude is small, and the stability is good.

[0125] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for configuring the capacity of a switchable converter and setting the switching boundary, characterized in that: The specific steps include: S1. Build a new energy station, switch the switchable converter to a grid-building control mode, and obtain the capacity of the mode-switchable converter in the grid-building control mode; S2. Define the working condition. Under the current working condition, based on the capacity of the mode-switchable converter, establish a small signal model of the hybrid station of the grid-following converter and the grid-following / grid-building mode-switchable converter; S3, calculating whether the current dominant characteristic root damping ratio of the small signal model meets the stability margin requirement, if so, executing step S4, otherwise returning to step S1; S4. Taking the operating short-circuit ratio as an indicator, a hysteresis control strategy is constructed to set the switching boundary of the switchable converter.

2. The method for capacity configuration and switching boundary setting of a switchable converter according to claim 1, characterized in that: The step S1 specifically includes: Obtain a grid-following converter with a single-machine multiplication equivalent value and a mode-switchable converter with a single-machine multiplication equivalent value, connect the grid-following converter with a single-machine multiplication equivalent value and the mode-switchable converter with a single-machine multiplication equivalent value in parallel, multiply and scale the power data in the grid-following converter and the grid-building converter based on the single-machine parameters, and build a new energy station; Increase the capacity of the mode-switchable converter in the new energy station from scratch, with each capacity increase being the rated capacity of a single converter.

3. The method for capacity configuration and switching boundary setting of a switchable converter according to claim 2, characterized in that: The increasing the capacity of the mode-switchable converter in the new energy station specifically includes: The rated capacity of a single mode-switchable converter and the number of mode-switchable converters configured in the station at the i-th iteration are obtained. The number of mode-switchable converters configured in the i-th iteration is one more than that in the (i-1)-th iteration, thereby obtaining the total capacity of the mode-switchable converters configured in the station. The rated capacity of a single grid-following converter, the number of mode-switchable converters configured in the station at the i-th iteration, and the total number of converters in the station are obtained to obtain the total number of grid-following converters in the station, and then the total capacity of the grid-following converters configured in the station is obtained.

4. The method for capacity configuration and switching boundary setting of a switchable converter according to claim 1, characterized in that: The defined working condition specifically includes defining the maximum output active power of the converter and the minimum short-circuit ratio of the grid connection point as the target working condition, and the step of obtaining the defined working condition includes: Adjust the output active power of the converter to the maximum and the short-circuit ratio of the grid point to the minimum value SCR min Set to 1, adjust the line inductance so that the short-circuit ratio of the grid connection point reaches the target value. The calculation formula is as follows: In the formula, SCR min Indicates the minimum short-circuit ratio of the grid connection point, U B Indicates rated voltage, S B Indicates rated power, L g represents the line inductance value to be calculated, ω0 represents the reference angular frequency, which is related to the rated frequency of the system, and R g Indicates the line resistance value.

5. The method for capacity configuration and switching boundary setting of a switchable converter according to claim 1, characterized in that: The step S2 specifically includes: Construct the dynamic equations of each link of the grid-following mode and grid-building mode of the converter, construct the dynamic equations of the grid-following mode converter connection transformer, the grid-building mode converter connection transformer, and the line between the grid connection point and the infinite power source, convert the physical quantities of the two-phase rotating coordinate system of the following / grid-building mode to the global coordinate system equation, perform linearization at the steady-state operation point, and obtain the small signal model of the hybrid station of the following / grid-building mode switchable converter; Among them, the dynamic equations of each link of the grid-following mode include: the dynamic equation of the LC filter part of the converter, the dynamic equation of the current inner loop of the grid-following converter, the dynamic equation of the d-axis of the grid-following outer loop, the dynamic equation of the q-axis of the grid-following outer loop, and the dynamic equation of the phase-locked loop; Among them, the dynamic equations of each link of the grid-forming mode include: the dynamic equation of the current inner loop of the grid-forming converter, the dynamic equation of the d-axis of the grid-forming outer loop, the dynamic equation of the q-axis of the grid-forming outer loop, the dynamic equation of the power synchronization loop, and the dynamic equation of the LC filter of the grid-forming mode converter.

6. The method for capacity configuration and switching boundary setting of a switchable converter according to claim 1, characterized in that: The step S3 specifically includes: According to the small signal model, the state matrix is ​​extracted, and the characteristic roots of the state matrix are calculated to obtain a pair of conjugate characteristic roots, wherein a pair of conjugate characteristic roots represents an oscillation mode of the grid-connected system of the new energy station; The conjugate characteristic root with the largest real part among the conjugate characteristic roots of the state matrix is ​​defined as the dominant characteristic root, and the damping ratio and frequency of the oscillation mode corresponding to the dominant characteristic root are calculated; According to the damping ratio threshold, when the dominant characteristic root damping ratio is greater than the damping ratio threshold, the stability margin meets the requirement, and the process goes to step S4; otherwise, the process returns to step S1.

7. The method for capacity configuration and switching boundary setting of a switchable converter according to claim 1, characterized in that: The step S4 specifically includes: Obtain the actual active power per unit value injected into the grid connection point by the new energy station and the short-circuit ratio of the grid connection point to calculate the operating short-circuit ratio; Based on the operating short-circuit ratio, the operating short-circuit ratio changes from large to small and crosses the boundary value C1 and the operating short-circuit ratio changes from large to small and crosses the boundary value C2; When the station output active power increases, the short-circuit ratio decreases, and the operating short-circuit ratio changes from large to small and crosses the boundary value C1, the mode of the switchable converter is changed from the grid-following mode to the grid-building mode; When the station output active power decreases, the short-circuit ratio increases, and the operating short-circuit ratio increases from small to large and crosses the boundary value C2, the mode of the switchable converter is converted from the grid-building mode to the grid-following mode.

8. The method for capacity configuration and switching boundary setting of a switchable converter according to claim 7, characterized in that: The boundary values ​​C1 and C2 are specifically set as follows: All switchable converters in the station adopt the grid-following control mode to reduce the short-circuit ratio of the grid connection point. When the dominant characteristic root damping ratio of the station is detected until it is lower than the set threshold, the critical OSCR value is C 11 ; Fixed SCR value, increased station active power, detected the station dominant characteristic root damping ratio until it is lower than the set threshold, and obtained the critical OSCR value is C 12 ; Take C 11 and C 12 The largest one among them is taken as the value of C1; An incremental value is added to the value of C1 to obtain the value of C2, that is, C2=C1+1.

9. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that: When the processor executes the program, the method for capacity configuration and switching boundary setting of the switchable converter as described in any one of claims 1 to 8 is implemented.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the program is executed by a processor, the method for configuring the capacity of a switchable converter and setting the switching boundary as described in any one of claims 1 to 8 is implemented.

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