A method and system for determining short-circuit current in a full-power conversion wind turbine generator set

Abstract

The present invention provides a method and system for determining short-circuit current in a full-power conversion wind turbine, including: based on the topological structure of a full-power conversion wind turbine composed of an LCL filter, obtaining the operating parameters of the LCL-VSC type full-power conversion wind turbine; substituting the operating parameters into a pre-constructed short-circuit current calculation formula to obtain the short-circuit current when a fault occurs in the full-power conversion wind turbine composed of an LCL filter; the short-circuit current calculation formula is determined based on: the topological structure of the full-power conversion wind turbine, the internal potential and the operational reactance, and the equivalent voltage of the external circuit. The present invention realizes the rapid calculation of short-circuit current through the obtained short-circuit current expression of the LCL-VSC type full-power conversion wind turbine.

Description

Technical Field

[0001] The present invention relates to the field of simulation in new energy power generation grid connection, and specifically relates to a method and system for determining short-circuit current in an LCL-VSC full-power conversion wind turbine under the influence of initial values of each frequency of short-circuit current. Background Art

[0002] The full-power conversion wind turbine is connected to the grid through a voltage source converter of Pulse Width Modulation (PWM). Since the frequency of the full-power conversion wind turbine and the frequency of the grid are independent of each other, there are no problems such as inrush current, inrush torque during grid connection, and out-of-step after grid connection. Moreover, it can also adjust active power and reactive power, so it is widely used. In photovoltaic and wind power, more and more power electronic devices rely on voltage source converters (VSCs) to access the grid. Among them, the LCL-type VSC is widely used in medium and high-capacity occasions due to its good effect of reducing current harmonics of switching frequency, low cost, and small volume. As the proportion of wind power in the power generation system increases, calculating the operating parameters of the wind farm during a fault after a fault occurs in the wind farm plays a key role in solving the fault. However, the fault characteristics of LCL-VSC are very different from those of traditional synchronous machines. The fault characteristics of synchronous machines mainly depend on their physical structure model, which is a pure physical circuit process, while the fault characteristics of LCL-VSC are jointly determined by the external physical circuit and the internal control loop, which is more complex. Therefore, there is an urgent need in engineering for a method to calculate the short-circuit current of an LCL-VSC full-power conversion wind turbine. Summary of the Invention

[0003] In order to solve the lack of a method for quickly calculating the short-circuit current in an LCL-VSC full-power conversion wind turbine in the prior art, the technical solution provided by the present invention is: a method for determining the short-circuit current in a full-power conversion wind turbine, including:

[0004] Based on the topological structure of the full-power conversion wind turbine composed of an LCL filter, obtain the operating parameters of the LCL-VSC full-power conversion wind turbine;

[0005] Substitute the operating parameters into a pre-constructed short-circuit current calculation formula to obtain the short-circuit current when the full-power conversion wind turbine composed of an LCL filter fails;

[0006] The short-circuit current calculation formula is determined based on: the topological structure of the full-power conversion wind turbine, the internal electromotive force and operational reactance, and the equivalent voltage of the external circuit.

[0007] Preferably, the construction of the short-circuit current calculation formula includes:

[0008] Draw the system block diagram in the frequency domain based on the topological structure of the full-power conversion wind turbine generator set;

[0009] Construct the frequency-domain expression of the short-circuit current based on the system block diagram in the frequency domain;

[0010] Set the attenuation frequency components based on the frequency-domain expression, and set the initial values for the attenuation frequency components;

[0011] Calculate the amplitudes of the respective attenuation frequency components in the short-circuit current based on the short-circuit current frequency division circuit and the initial values;

[0012] Construct the short-circuit current calculation formula based on the amplitudes of the respective attenuation frequency components in the short-circuit current.

[0013] Preferably, the frequency-domain expression is as shown in the following formula:

[0014]

[0015] In the formula: I 2dq (s): Grid-side current vector; Z c (s): Impedance on the wind power side; Z g (s): Equivalent impedance on the grid side; I 1dq (s): Converter-side current vector; V gdq (s): Grid voltage vector; L g : Grid-side filter inductor; I 2dq_0 : Initial value of the grid-side current vector; V cfdq_0 : Initial value of the filter capacitor voltage vector; ω: Synchronous rotation angular velocity; s: Laplace operator;

[0016] Among them, the converter-side current vector I 1dq (s) is calculated according to the following formula:

[0017]

[0018] In the formula: k p : Proportional parameter of the current loop controller; L f : Converter filter inductor; k i : Integral parameter of the current loop controller; Converter-side current command value; I 1dq_0 : Initial value of the converter-side current vector.

[0019] Preferably, the setting of the attenuation frequency components based on the frequency-domain expression and setting the initial values for the attenuation frequency components includes:

[0020] Simplify the common denominator in the frequency-domain expression to obtain the zero and real poles corresponding to the DC component in the short-circuit current, and the complex poles corresponding to the AC component in the short-circuit current;

[0021] Set the DC component and the AC component as the attenuation frequency components;

[0022] Based on the internal electromotive force of the full-power conversion wind turbine, the operational reactance corresponding to each attenuation frequency component, and the equivalent voltage of the external circuit, set an initial value for the attenuation frequency component;

[0023] Among them, the operational reactance corresponding to each attenuation frequency component is determined by the oscillation frequencies corresponding to the real poles and the complex poles.

[0024] Preferably, the initial value of each attenuation frequency component is set according to the following formula:

[0025]

[0026] In the formula: A Σi : The initial value of each attenuation frequency component; E: The internal electromotive force of the full-power conversion wind turbine; V: The equivalent voltage of the external circuit when calculating each amplitude; L op (s): The operational reactance corresponding to each attenuation frequency component; ω: Synchronous rotation angular velocity; s: Laplace operator;

[0027] Among them, the operational reactance L op corresponding to each frequency component is calculated according to the following formula:

[0028]

[0029] In the formula: L g : Filter inductor; ω n : Rated frequency; ω n + ω: The oscillation frequency corresponding to the real pole; ω - ω n : The oscillation frequency corresponding to the complex pole.

[0030] Preferably, calculating the amplitudes of the attenuation frequency components in the short-circuit current based on the short-circuit current frequency division circuit and the initial value includes:

[0031] Based on the equivalent internal electromotive force, grid voltage in the equivalent circuit of the initial values of the amplitudes of DC component 1 and DC component 2, and the equivalent operational reactance of DC component 1 and DC component 2, calculate the initial value of the amplitude of DC component 1;

[0032] Based on the equivalent internal electromotive force in the equivalent circuit of the initial values of the amplitudes of DC component 1 and DC component 2, the equivalent external voltage of the equivalent circuit of the initial value of the amplitude of DC component 2, and the equivalent operational reactance of DC component 1 and DC component 2, calculate the initial value of the amplitude of DC component 2;

[0033] Calculate the initial value of the amplitude of AC component 3 based on the internal electromotive force, grid voltage in the equivalent circuit, and the equivalent operational reactance of AC component 3;

[0034] Calculate the initial value of the amplitude of AC component 4 based on the internal electromotive force, grid voltage in the equivalent circuit, and the equivalent operational reactance of AC component 4;

[0035] Among them, the amplitude of the DC component 1 is determined by the zero-pole; the amplitude of the DC component 2 is determined by the real pole; the amplitude of the AC component 3 is determined by the complex pole 3; the amplitude of the AC component 4 is determined by the complex pole 4.

[0036] Preferably, the initial values of the amplitudes of the DC component 1 and the DC component 2 are as shown in the following formula:

[0037]

[0038] In the formula: A Σ1 : The initial value of the amplitude of the DC component 1; A Σ2 : The initial value of the amplitude of the DC component 2; E: The internal electromotive force of the full-power conversion wind turbine; V gdq : The grid voltage vector; L op : The equivalent operational reactances of the DC component 1 and the DC component 2; E0: The equivalent external voltage vector; ω: The synchronous rotational angular velocity.

[0039] Preferably, the initial values of the amplitudes of the AC component 3 and the AC component 4 are calculated according to the following formula:

[0040]

[0041] In the formula: A Σ3 : The initial value of the amplitude of the AC component 3; A Σ4 : The initial value of the amplitude of the AC component 4; V gdq : The grid voltage vector; E': The VSC internal electromotive force in the equivalent circuit when calculating the initial value of the amplitude of the AC component 3; L' op : The equivalent operational reactance of the AC component 3; E”: The VSC internal electromotive force in the equivalent circuit when calculating the initial value of the amplitude of the AC component 4; L” op : The equivalent operational reactance of the AC component 4.

[0042] Preferably, constructing the short-circuit current calculation formula based on the amplitudes of the attenuation frequency components in the short-circuit current includes:

[0043] Construct the time-domain expression of the DC component in the short-circuit current based on the initial values of the amplitudes of the DC component 1 and the DC component 2;

[0044] Based on the initial amplitude value of the AC component 3 and the initial amplitude value of the AC component 4, construct the time-domain expression of the AC component in the short-circuit current;

[0045] Based on the time-domain expression of the DC component in the short-circuit current and the time-domain expression of the AC component in the short-circuit current, construct the short-circuit current calculation formula.

[0046] Preferably, the short-circuit current calculation formula is as shown in the following formula:

[0047]

[0048] In the formula: I 2dq (t): short-circuit current; I 2dq_DC (t): time-domain expression of the DC component in the short-circuit current; I 2dq_AC (t): time-domain expression of the AC component in the short-circuit current; E: internal electromotive force of the full-power conversion wind turbine; L op : equivalent operation reactance of DC component 1 and DC component 2; E0: equivalent external voltage vector; ω: synchronous rotation angular velocity; V gdq : grid voltage vector; E': internal electromotive force of the VSC in the equivalent circuit when calculating the initial amplitude value of AC component 3; L' op : equivalent operation reactance of AC component 3; E”: internal electromotive force of the VSC in the equivalent circuit when calculating the initial amplitude value of AC component 4; L” op : equivalent operation reactance of AC component 4; τ2: attenuation factor corresponding to the real pole; τ3: attenuation factor corresponding to the complex pole; ω n +ω: oscillation frequency corresponding to the real pole; ω - ω n : oscillation frequency corresponding to the complex pole.

[0049] Preferably, the operating parameters include:

[0050] Internal electromotive force of the LCL-VSC type full-power conversion wind turbine, proportional parameter of the current loop controller, synchronous rotation angular velocity, converter filter inductor, grid-side filter inductor, grid-side filter resistor, resistor of the filter, and capacitor of the filter.

[0051] Based on the same inventive concept, the present invention also provides a system for determining the short-circuit current in a full-power conversion wind turbine, including:

[0052] An acquisition module, configured to acquire the operating parameters of the LCL-VSC type full-power conversion wind turbine based on the topological structure of the full-power conversion wind turbine constituted by the LCL filter;

[0053] A calculation module, configured to substitute the operating parameters into the pre-constructed short-circuit current calculation formula to obtain the short-circuit current when a fault occurs in the full-power conversion wind turbine constituted by the LCL filter;

[0054] The short-circuit current calculation formula is determined based on the topology structure, internal electromotive force, operational reactance of the full-power conversion wind turbine generator set, and the equivalent voltage of the external circuit.

[0055] Preferably, the system further includes a construction module for constructing the short-circuit current calculation formula.

[0056] The construction module includes:

[0057] A drawing unit for drawing a system block diagram in the frequency domain based on the topology structure of the full-power conversion wind turbine generator set.

[0058] A frequency-domain expression construction unit for constructing a frequency-domain expression of the short-circuit current based on the system block diagram in the frequency domain.

[0059] An initial value setting unit for setting the attenuation frequency component based on the frequency-domain expression and setting an initial value for the attenuation frequency component.

[0060] An amplitude calculation unit for calculating the amplitude of each attenuation frequency component in the short-circuit current based on the short-circuit current frequency division circuit and the initial value.

[0061] A construction unit for constructing the short-circuit current calculation formula based on the amplitudes of each attenuation frequency component in the short-circuit current.

[0062] Compared with the prior art, the beneficial effects of the present invention are:

[0063] The technical solution provided by the present invention is based on the topology structure of the full-power conversion wind turbine generator set composed of an LCL filter, and obtains the operating parameters of the LCL-VSC type full-power conversion wind turbine generator set; substituting the operating parameters into the pre-constructed short-circuit current calculation formula, the short-circuit current during the fault of the full-power conversion wind turbine generator set composed of an LCL filter is obtained; wherein, the short-circuit current calculation formula is determined by the topology structure, internal electromotive force, operational reactance of the full-power conversion wind turbine generator set, and the equivalent voltage of the external circuit. The present invention realizes the rapid calculation of the short-circuit current through the obtained short-circuit current calculation formula of the LCL-VSC type full-power conversion wind turbine generator set.

[0064] The technical solution provided by the present invention is verified through experiments and then deduced that the real part of the corresponding decaying pole only affects the decay of the AC component, and its effect on the initial value can be ignored. On this basis, a unified expression for the initial value of each decaying frequency component is obtained, and a frequency division circuit can be used to depict the change of the initial value corresponding to each frequency component, thereby obtaining the conclusion that in the external short-circuit circuit, the LCL filter circuit and the current control respectively determine the corresponding short-circuit current component and its corresponding decay time constant, but the initial value of each frequency component is jointly determined by the LCL filter circuit and the current control.

[0065] The technical solution provided by the present invention combines the accuracy and practicality of calculations, and also provides a feasible theoretical basis for the practical calculation of short-circuit currents in wind farms.

[0066] The technical solution provided by the present invention lays a good foundation for the protection setting and other work of the power system of a wind farm with LCL-VSC full-power conversion wind turbines. BRIEF DESCRIPTION OF THE DRAWINGS

[0067] Figure 1 is a flow chart for determining the short-circuit current of the present invention;

[0068] Figure 2 is a typical control structure block diagram of the LCL-VSC system;

[0069] Figure 3 is a block diagram of the LCL-VSC system in the frequency domain of the present invention;

[0070] Figure 4-a is a schematic diagram of an equivalent circuit for calculating the initial value of the amplitude of DC component 1 in an embodiment of the present invention;

[0071] Figure 4-b is a schematic diagram of an equivalent circuit for calculating the initial value of the amplitude of DC component 2 in an embodiment of the present invention;

[0072] Figure 4-c is a schematic diagram of an equivalent circuit for calculating the initial value of the amplitude of AC component 3 in an embodiment of the present invention;

[0073] Figure 4-d is a schematic diagram of an equivalent circuit for calculating the initial value of the amplitude of AC component 4 in an embodiment of the present invention;

[0074] Figure 5 is a comparison diagram of the short-circuit current time-domain waveforms of three models in the dq coordinate system in an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0075] To better understand the present invention, the content of the present invention will be further described below in conjunction with the accompanying drawings of the specification and examples.

[0076] The present invention provides a method and system for determining short-circuit current in a full-power conversion wind turbine generator set. For an LCL-VSC device, the switching of current commands and the drop of terminal voltage make the original multi-input multi-output system exhibit high-order complex short-circuit characteristics. During the short-circuit process, each transient component and the corresponding decay time constant are determined by the inherent characteristics at the system fault moment. The complexity of its short-circuit characteristic analysis lies in the complexity of calculating the initial values of each frequency. The present invention simplifies the calculation process of each frequency amplitude by using concepts such as operational reactance and frequency division circuits, and combining experimental situations, thereby achieving obtaining a simple and unified mathematical analytical form to describe the short-circuit current characteristics of the LCL-VSC device.

[0077] As Figure 1 shown, a method for determining short-circuit current in a full-power conversion wind turbine generator set provided by the present invention includes:

[0078] Step S1: Based on the topological structure of a full-power conversion wind turbine generator set composed of an LCL filter, obtain the operating parameters of the LCL-VSC type full-power conversion wind turbine generator set;

[0079] Step S2: Substitute the operating parameters into a pre-constructed short-circuit current calculation formula to obtain the short-circuit current when a fault occurs in the full-power conversion wind turbine generator set composed of an LCL filter;

[0080] The short-circuit current calculation formula is determined based on: the topological structure of the full-power conversion wind turbine generator set, the internal electromotive force, the operational reactance, and the equivalent voltage of the external circuit.

[0081] Step S1: Based on the topological structure of a full-power conversion wind turbine generator set composed of an LCL filter, obtain the operating parameters of the LCL-VSC type full-power conversion wind turbine generator set, including:

[0082] Based on the topological structure of a full-power conversion wind turbine generator set composed of an LCL filter, obtaining the operating parameters includes: the internal electromotive force of the LCL-VSC type full-power conversion wind turbine generator set, the proportional parameter of the current loop controller, the synchronous rotational angular velocity, the converter filter inductor, the grid-side filter inductor, the grid-side filter resistor, the resistor of the filter, and the capacitor of the filter.

[0083] Step S2: Substitute the operating parameters into a pre-constructed short-circuit current calculation formula to obtain the short-circuit current when a fault occurs in the full-power conversion wind turbine generator set composed of an LCL filter, specifically including:

[0084] First, construct the short-circuit current calculation formula according to the following steps:

[0085] I. Draw the system block diagram of the LCL-VSC type full-power converter in the frequency domain;

[0086] II. Deduce the frequency-domain expression of the short-circuit current;

[0087] III. Simplify the fault current frequency expression;

[0088] IV. Set the initial values of the decaying frequency components;

[0089] V. Calculate the amplitudes of each frequency in the short - circuit current.

[0090] Then, according to the constructed short - circuit current calculation formula, the short - circuit current of the full - power conversion wind turbine based on the LCL filter during a fault is obtained.

[0091] Furthermore, in the step I, the drawing of the system block diagram of the LCL - VSC full - power converter in the frequency domain includes:

[0092] In this embodiment, taking Figure 2 the LCL - VSC full - power wind turbine under the typical control method shown, the system block diagram in the frequency domain as shown in Figure 3 can be simplified.

[0093] Furthermore, in the step II, the frequency - domain expression of the short - circuit current is derived, and then the relationship between the short - circuit current and the topological structure is established.

[0094] According to Figure 2 and Figure 3 the frequency - domain expression of the short - circuit current can be derived as:

[0095]

[0096] And

[0097]

[0098]

[0099] where I 1dq is the converter - side current vector; is the converter - side current command value; V gdq is the grid voltage vector; V cfdq_0 is the filter capacitor voltage vector; I 2dq is the grid - side current vector, I 1dq_0 is the initial value of the converter - side current vector, I 2dq_0 is the initial value of the grid - side current vector, and V cfdq_0 is the initial value of the filter capacitor voltage vector, which is determined by the initial state of the pre - fault system. k p and k i are the proportional and integral parameters of the current - loop controller respectively; ω is the synchronous rotation angular velocity; L f is the converter filter inductor; L g 、R gis the resistance of the grid-side filter inductor; R and C are the resistance and capacitance of the C branch of the filter respectively; s is the Laplace operator.

[0100] Further, in step III, simplifying the fault current frequency expression includes:

[0101] In a typical industrial control design, the parameters of the internal current loop controller are usually set to overdamping parameters, that is, k p and k i ; thus, the decaying DC component generated due to the integral coefficient has a very small amplitude and its influence on the dynamic characteristics of the entire short-circuit current can be ignored. Therefore, the common denominator in the frequency-domain expression of the short-circuit current can be simplified to:

[0102]

[0103] where: k p is the proportional parameter of the current loop controller; ω is the synchronous rotation angular velocity; L f is the converter filter inductor; L g , R g are the resistances of the grid-side filter inductors; R and C are the resistance and capacitance of the C branch of the filter respectively; s is the Laplace operator; j represents the imaginary part. Among them, the filter branch is composed of the capacitor C, inductor L, and the corresponding resistors in series and parallel, so it can be said to be the L branch and the C branch.

[0104] Through the above process, the LCL-VSC system is reduced to a third-order system, and its common denominator contains a real pole and two complex poles as follows:

[0105]

[0106] where

[0107]

[0108] τ2 is the decay factor corresponding to the real pole s2, τ3 is the decay factor corresponding to the two complex poles, ω n + ω and ω - ω n represent the oscillation frequencies corresponding to the poles s2 and s3 respectively.

[0109] Further, in step IV, setting the initial values of the decaying frequency components includes:

[0110] In the synchronous rotating coordinate system, the real pole s2 corresponds to the DC component in the system short-circuit current, and the other two complex poles correspond to two AC transient current components with similar oscillation frequencies; moreover, the DC component decays exponentially.

[0111] In the traditional fault analysis of synchronous machines, when calculating the initial values of each frequency component, the influence of resistance on the calculation of the initial values of components is usually ignored. It is assumed that the resistance only affects the attenuation of each frequency component, rather than the initial values of each frequency component. In the LCL-VSC system, each component no longer decays with the short-circuit current transient characteristics of the synchronous machine in a simple monotonic form, and the amplitudes of its frequency components can no longer be simply calculated by the initial value theorem. For the LCL-VSC, a similar assumption can be made, that is, it is considered that the real part of the poles corresponding to the attenuation only affects the attenuation of the AC components, and its effect on the initial values can be ignored.

[0112] Therefore, the initial values of the amplitudes of each frequency can be uniformly expressed by the following formula:

[0113]

[0114]

[0115] where E is the internal electromotive force of the LCL-VSC, which is determined by the operating state of the system itself; L op (s) is the operational reactance corresponding to each frequency component, A ∑i (i = 1, 2, 3, 4) represents the initial values of each frequency component; V is the equivalent voltage of the external circuit when calculating each amplitude; ω n is the rated frequency.

[0116] Based on the above formula, the influence of the initial values of each frequency component in the short-circuit current can be analyzed from the circuit perspective. As Figures 4-a to 4-d shown, a frequency division circuit is adopted to depict the change of the initial values corresponding to each frequency component.

[0117] Furthermore, in step V, calculating the amplitudes of each frequency in the short-circuit current includes:

[0118] The calculation of the amplitudes of each frequency in the short-circuit current is as follows:

[0119] Forced component and decaying DC component

[0120]

[0121]

[0122] where: A Σ1 is the initial value of the amplitude of DC component 1 determined by zero poles, A Σ2 is the initial value of the amplitude of decaying DC component 2 determined by the decaying real pole s2. L op is the unified equivalent operational reactance of DC components 1 and 2. E is the equivalent internal electromotive force of the VSC in the equivalent circuit for calculating the initial values of the amplitudes of DC component 1 and DC component 2, V gdqis the grid voltage vector, and E0 is the equivalent external voltage vector of the equivalent circuit for calculating the initial value of the amplitude of the decaying DC component 2. The frequency-divided circuit is a circuit at different frequencies. In these frequency-divided circuits, for the sake of simplified analysis, a certain frequency-divided circuit can be regarded as the equivalent circuit.

[0123] And there is

[0124]

[0125]

[0126] The time-domain expression of the DC component in the corresponding short-circuit current is

[0127]

[0128] The initial value of the decaying AC component is

[0129]

[0130]

[0131] Among them, A Σ3 is the initial value of the amplitude of the decaying AC component 3 corresponding to the complex pole 3, and A Σ4 is the initial value of the amplitude of the decaying AC component 4 corresponding to the complex pole 4. L' op is the equivalent operational reactance of the AC component 3, and L” op is the equivalent operational reactance of the AC component 4. E' is the internal potential of the VSC in the equivalent circuit for calculating the initial value of the amplitude of the decaying AC component 3, E” is the internal potential of the VSC in series with the fan and internal resistance in the equivalent circuit for calculating the initial value of the amplitude of the decaying AC component 4, and V gdq is the grid voltage vector.

[0132] And there is

[0133]

[0134]

[0135]

[0136] The time-domain expression of the AC component in the corresponding short-circuit current is

[0137]

[0138] Among them, V gdq is the grid voltage vector, E' is the internal potential of the VSC in the equivalent circuit for calculating the initial value of the amplitude of the decaying AC component 3, E” is the internal potential of the VSC in the equivalent circuit for calculating the initial value of the amplitude of the decaying AC component 4, and L' opis the equivalent operational reactance of the AC component 3, L” op is the equivalent operational reactance of the AC component 4, τ3 is the attenuation factor corresponding to the two complex poles, ω n +ω and ω - ω n respectively represent the oscillation frequencies corresponding to the poles s2 and s3, and ω is the synchronous rotating angular velocity.

[0139] Thus, the time-domain expression of the short-circuit current can be expressed by the following formula:

[0140]

[0141] Among them, E is the equivalent internal potential of the VSC in the equivalent circuit for calculating the initial values of the amplitudes of the DC components 1 and 2, E' is the internal potential of the VSC in the equivalent circuit for calculating the initial value of the amplitude of the decaying AC component 3, E” is the internal potential of the VSC in the equivalent circuit for calculating the initial value of the amplitude of the decaying AC component 4, V gdq is the grid voltage vector, E0 is the equivalent external voltage vector of the equivalent circuit for calculating the initial value of the amplitude of the decaying DC component 2; L op is the unified equivalent operational reactance of the DC components 1 and 2, L' op is the equivalent operational reactance of the AC component 3, L” op is the equivalent operational reactance of the AC component 4; τ2 is the attenuation factor corresponding to the real pole s2, τ3 is the attenuation factor corresponding to the two complex poles, ω n +ω and ω n -ω respectively represent the oscillation frequencies corresponding to the poles s2 and s3, and ω is the synchronous rotating angular velocity.

[0142] With the drop of the grid voltage and the jump of the current command, the equivalent internal potentials E, E', E” and the grid voltage V gdq are all variables, and the rest of the parameters are parametric parameters.

[0143] In this embodiment, it is verified through MATLAB / Simulink experimental simulation. The simulation parameters are shown in Table 1. By comparing the physical model, mathematical model and the above analytical model of an LCL-VSC system, the correctness of its analytical results can be verified. The fault scenario is set as the grid voltage drops by 0.2 p.u., and the current command changes from 1 + 0j to 0.7 + j0.125. As Figure 5 shown by the simulation results, the simulation results of the physical model, mathematical model and analytical analysis results are basically the same.

[0144] Table 1 Simulation model parameter settings

[0145]

[0146] Obviously, in a short - circuit circuit, the LCL filter circuit and the current control respectively determine the corresponding short - circuit current components and their corresponding decay time constants. However, the initial values of each frequency component are jointly determined by the LCL filter circuit and the current control. Through the above - mentioned analysis, it can be seen that the current control part affects the initial values of each frequency component by determining the magnitude of the internal potential, while the external LCL filter circuit affects the initial values of each frequency component by influencing the magnitude of the operational reactance.

[0147] Embodiment 2

[0148] Based on the same inventive concept, an embodiment of the present invention provides a system for determining short - circuit current in a full - power conversion wind turbine, including:

[0149] An acquisition module, configured to acquire the operating parameters of an LCL - VSC type full - power conversion wind turbine based on the topological structure of the full - power conversion wind turbine composed of an LCL filter.

[0150] A calculation module, configured to substitute the operating parameters into a pre - constructed short - circuit current calculation formula to obtain the short - circuit current when a fault occurs in the full - power conversion wind turbine composed of an LCL filter.

[0151] The short - circuit current calculation formula is determined based on: the topological structure of the full - power conversion wind turbine, the internal potential, the operational reactance, and the equivalent voltage of the external circuit.

[0152] In the embodiment, the system further includes: a construction module, configured to construct a short - circuit current calculation formula.

[0153] The construction module includes:

[0154] A drawing unit, configured to draw a system block diagram in the frequency domain based on the topological structure of the full - power conversion wind turbine.

[0155] A frequency - domain expression construction unit, configured to construct a frequency - domain expression of the short - circuit current based on the system block diagram in the frequency domain.

[0156] An initial - value setting unit, configured to set the decay frequency components based on the frequency - domain expression and set initial values for the decay frequency components.

[0157] An amplitude calculation unit, configured to calculate the amplitudes of the decay frequency components in the short - circuit current based on the short - circuit current frequency - division circuit and the initial values.

[0158] A construction unit, configured to construct a short - circuit current calculation formula based on the amplitudes of the decay frequency components in the short - circuit current.

[0159] Those skilled in the art should understand that the embodiments of the present application can be provided as a method, a system, or a computer program product. Therefore, the present application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present application can take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) that contain computer-usable program code.

[0160] The present application is described with reference to the flowcharts and / or block diagrams of methods, apparatuses (systems), and computer program products according to the embodiments of the present application. It should be understood that each flow and / or block in the flowchart and / or block diagram, and the combination of flows and / or blocks in the flowchart and / or block diagram, can be realized by computer program instructions. These computer program instructions can be provided to the processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing devices to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing devices generate means for realizing the functions specified in one Figure 1 flow or multiple flows and / or blocks Figure 1 or multiple blocks.

[0161] These computer program instructions can also be stored in a computer-readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer-readable memory generate a manufactured article including instruction means, and the instruction means realizes the functions specified in one Figure 1 flow or multiple flows and / or blocks Figure 1 or multiple blocks.

[0162] These computer program instructions can also be loaded onto a computer or other programmable data processing device, so that a series of operation steps are executed on the computer or other programmable device to generate a computer-implemented process, and thus the instructions executed on the computer or other programmable device provide steps for realizing the functions specified in one Figure 1 flow or multiple flows and / or blocks Figure 1 or multiple blocks.

[0163] The above are only embodiments of the present invention and are not used to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention are included in the scope of the claims of the present invention pending approval.

Claims

1. A method for determining short-circuit current in a full-power conversion wind turbine, characterized in that, Including: Based on the topological structure of the full-power conversion wind turbine composed of an LCL filter, obtain the operating parameters of the LCL-VSC type full-power conversion wind turbine; Substitute the operating parameters into the pre-constructed short-circuit current calculation formula to obtain the short-circuit current of the full-power conversion wind turbine based on the LCL filter during a fault; The short-circuit current calculation formula is determined based on: the topological structure of the full-power conversion wind turbine, the internal electromotive force and the operational reactance, and the equivalent voltage of the external circuit; The construction of the short-circuit current calculation formula includes: Draw a system block diagram in the frequency domain based on the topological structure of the full-power conversion wind turbine; Construct a frequency-domain expression of the short-circuit current based on the system block diagram in the frequency domain; Set the attenuation frequency components based on the frequency-domain expression, and set an initial value for the attenuation frequency components; Calculate the amplitudes of the attenuation frequency components in the short-circuit current based on the short-circuit current frequency division circuit and the initial value; Construct a short-circuit current calculation formula based on the amplitudes of the attenuation frequency components in the short-circuit current; The setting of the attenuation frequency components based on the frequency-domain expression and setting an initial value for the attenuation frequency components includes: Simplify the common denominator in the frequency-domain expression to obtain the zero-poles and real poles corresponding to the DC component in the short-circuit current, and the complex poles corresponding to the AC component in the short-circuit current; Set the DC component and the AC component as the attenuation frequency components; Based on the internal electromotive force of the full-power conversion wind turbine, the operational reactance corresponding to each attenuation frequency component, and the equivalent voltage of the external circuit, set an initial value for the attenuation frequency components; Among them, the operational reactance corresponding to each attenuation frequency component is determined by the oscillation frequency corresponding to the real poles and the complex poles.

2. The method according to claim 1, characterized in that, The frequency-domain expression is as shown in the following formula: Wherein: : Grid-side current vector; : Impedance on the wind power side; : Equivalent impedance on the grid side; : Converter-side current vector; : Grid voltage vector; : Grid-side filter inductor; : Initial value of the grid-side current vector; : Initial value of the filter capacitor voltage vector; : Synchronous rotation angular velocity; : Laplace operator; Among them, the converter side current vector , is calculated according to the following formula: Wherein: : the proportional parameter of the current loop controller; : the converter filter inductor; : the integral parameter of the current loop controller; : the current command value on the converter side; : the initial value of the current vector on the converter side.

3. The method according to claim 1, characterized in that, The initial values of the attenuation frequency components are set according to the following formula: In the formula: : Initial value of each decaying frequency component; : Internal electromotive force of the full-power conversion wind turbine; : Equivalent external circuit voltage when calculating each amplitude; : Operational reactance corresponding to each decaying frequency component; : Synchronous rotational angular velocity; : Laplace operator; Among them, the operational reactance L op (s) corresponding to each frequency component is calculated according to the following formula: In the formula: : Filter inductor; : Rated frequency; : Oscillation frequency corresponding to the real pole; : Oscillation frequency corresponding to the complex pole.

4. The method according to claim 1, wherein The calculation of the amplitudes of the attenuation frequency components in the short-circuit current based on the short-circuit current frequency division circuit and the initial value includes: Based on the equivalent internal electromotive force, grid voltage in the equivalent circuit of the initial amplitudes of DC component 1 and DC component 2, and the equivalent operational reactance of DC component 1 and DC component 2, calculate the initial amplitude of DC component 1; Based on the equivalent internal electromotive force in the equivalent circuit of the initial amplitudes of DC component 1 and DC component 2, the equivalent external voltage of the equivalent circuit of the initial amplitude of DC component 2, and the equivalent operational reactance of DC component 1 and DC component 2, calculate the initial amplitude of DC component 2; Based on the internal electromotive force, grid voltage in the equivalent circuit of the initial amplitude of AC component 3, and the equivalent operational reactance of AC component 3, calculate the initial amplitude of AC component 3; Based on the internal electromotive force, grid voltage in the equivalent circuit of the initial amplitude of AC component 4, and the equivalent operational reactance of AC component 4, calculate the initial amplitude of AC component 4; Among them, the amplitude of DC component 1 is determined by the zero-poles; the amplitude of DC component 2 is determined by the real poles; the amplitude of AC component 3 is determined by the complex pole 3; the amplitude of AC component 4 is determined by the complex pole 4.

5. The method according to claim 4, characterized in that, The initial amplitudes of the DC component 1 and the DC component 2 are as shown in the following formula: In the formula: : Initial value of the amplitude of DC component 1; : Initial value of the amplitude of DC component 2; : Internal electromotive force of the full-power conversion wind turbine; : Grid voltage vector; : Equivalent operational reactance of DC component 1 and DC component 2; : Equivalent external voltage vector; : Synchronous rotational angular velocity.

6. The method according to claim 5, characterized in that, The initial amplitudes of the AC component 3 and the AC component 4 are calculated according to the following formula: Where: : Initial amplitude value of AC component 3; : Initial amplitude value of AC component 4; : Grid voltage vector; : Internal potential of VSC in the equivalent circuit when calculating the initial amplitude value of AC component 3; : Equivalent operational reactance of AC component 3; : Internal potential of VSC in the equivalent circuit when calculating the initial amplitude value of AC component 4; : Equivalent operational reactance of AC component 4.

7. The method according to claim 4, wherein Constructing a short-circuit current calculation formula based on the amplitudes of the decaying frequency components in the short-circuit current, including: Constructing a time-domain expression of the DC component in the short-circuit current based on the initial value of the amplitude of the DC component 1 and the initial value of the amplitude of the DC component 2; Constructing a time-domain expression of the AC component in the short-circuit current based on the initial value of the amplitude of the AC component 3 and the initial value of the amplitude of the AC component 4; Constructing a short-circuit current calculation formula based on the time-domain expression of the DC component in the short-circuit current and the time-domain expression of the AC component in the short-circuit current.

8. The method according to claim 1, characterized in that, The short-circuit current calculation formula is as shown in the following formula: Wherein: : short-circuit current; : time-domain expression of the DC component in the short-circuit current; : time-domain expression of the AC component in the short-circuit current; : internal electromotive force of the full-power conversion wind turbine; : equivalent operational reactance of DC component 1 and DC component 2; : equivalent external voltage vector; : synchronous rotational angular velocity; : grid voltage vector; : internal electromotive force of the VSC in the equivalent circuit when calculating the initial value of the amplitude of AC component 3; : equivalent operational reactance of AC component 3; : internal electromotive force of the VSC in the equivalent circuit when calculating the initial value of the amplitude of AC component 4; : equivalent operational reactance of AC component 4; : attenuation factor corresponding to the real pole; : attenuation factor corresponding to the complex pole; : oscillation frequency corresponding to the real pole; : oscillation frequency corresponding to the complex pole.

9. The method according to claim 1, wherein The operating parameters include: The internal electromotive force of the LCL-VSC full-power conversion wind turbine, the proportional parameter of the current loop controller, the synchronous rotational angular velocity, the converter filter inductor, the grid-side filter inductor, the grid-side filter resistor, the resistor of the filter, and the capacitor of the filter.

10. A system for determining short-circuit current in a full-power conversion wind turbine unit for the method as described in claim 1, characterized in that, Including: An acquisition module, configured to acquire the operating parameters of the LCL-VSC full-power conversion wind turbine based on the topological structure of the full-power conversion wind turbine constituted by the LCL filter; A calculation module, configured to substitute the operating parameters into a pre-constructed short-circuit current calculation formula to obtain the short-circuit current of the full-power conversion wind turbine constituted by the LCL filter during a fault; The short-circuit current calculation formula is determined based on: the topological structure of the full-power conversion wind turbine, the internal electromotive force, the operational reactance, and the equivalent voltage of the external circuit.

11. The system according to claim 10, wherein The system further includes: a construction module, configured to construct a short-circuit current calculation formula; The construction module includes: A drawing unit, configured to draw a system block diagram in the frequency domain based on the topological structure of the full-power conversion wind turbine; A frequency-domain expression construction unit, configured to construct a frequency-domain expression of the short-circuit current based on the system block diagram in the frequency domain; An initial value setting unit, configured to set the decaying frequency components based on the frequency-domain expression and set initial values for the decaying frequency components; An amplitude calculation unit, configured to calculate the amplitudes of the decaying frequency components in the short-circuit current based on a short-circuit current frequency division circuit and the initial values; A construction unit, configured to construct a short-circuit current calculation formula based on the amplitudes of the decaying frequency components in the short-circuit current.

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