Method for acquiring three-phase short-circuit current of doubly-fed fan considering grid-side converter GSC feed-out current

Abstract

The invention discloses a method for acquiring three-phase short-circuit current of a doubly-fed fan by considering the feed-out current of a grid-side converter GSC, and the method comprises the steps: when a three-phase short circuit occurs in a power grid, under the condition of considering RSC control, power fluctuation exists between RSC and GSC; solving the DC bus voltage fluctuation between the RSC and the GSC according to the power fluctuation of the DC side; obtaining a reference value of the current of the grid-side converter according to the voltage fluctuation of the direct-current bus; and obtaining the feed-out current of the grid-side converter according to the d-axis current reference value and the q-axis current reference value. And adding the stator short-circuit current under the static coordinate system considering RSC control and the feed-out current of the GSC to obtain the double-fed fan three-phase short-circuit current of the DFIG considering the feed-out current of the GSC. According to the method, the transient characteristics of the DFIG can be analyzed more accurately, the short-circuit characteristic analysis of the DFIG is perfected, and a basis reference is provided for the fault characteristic analysis of the DFIG.

Description

Technical Field

[0001] The invention relates to a method for acquiring a three-phase short-circuit current of a double-fed wind turbine taking into account a current fed out by a grid-side converter GSC, and belongs to the technical field of fault analysis of wind power generation systems. Background Art

[0002] The statements in this section merely provide background information related to the present invention and do not necessarily constitute prior art.

[0003] With the proposal of the "carbon peak and carbon neutrality" goals and under the new situation of "building a new power system with new energy as the main body", new energy is showing a new trend of accelerated development. Among them, new energy power generation energy represented by wind power generation technology has received great attention. The doubly-fed induction generator has become the most widely used in wind farms because of its good operating characteristics, active and reactive decoupling control, and small converter capacity.

[0004] According to the technical regulations for wind power grid connection, all wind turbines connected to the grid must have low voltage ride through (LVRT) capabilities. The low voltage ride through capabilities of existing wind turbines can be divided into LVRT achieved by hardware circuits and LVRT achieved by converter control strategies. Among them, LVRT achieved by hardware circuits includes crowbar circuits, unloading circuits, and GSC dual parallel connections, all of which have been studied. Regarding the method of achieving LVRT by converter control strategies, the fault characteristics of DFIG are affected by the converter excitation control and the electromagnetic process of the generator, showing the characteristics of nonlinear strong coupling. Therefore, the present invention is aimed at the situation where the rotor-side converter is not locked and still plays a regulating role when the three-phase symmetry of the machine-end voltage occurs.

[0005] The fault current of a doubly-fed wind turbine generator system consists of two parts: the stator side short-circuit current provided by the stator side and the short-circuit current provided by the grid-side converter. Existing studies have mainly focused on the short-circuit current on the stator side, and have given less consideration to the short-circuit current provided by the grid side. When the rotor side is not locked, there is a power imbalance between the rotor side and the grid side during a fault, which will cause current fluctuations on the GSC side. Therefore, if the GSC side current is ignored, it will inevitably cause errors in the calculation results of the DFIG short-circuit current. Therefore, it is of great significance to study the DFIG three-phase short-circuit current characteristics taking into account the GSC feed-in current. Summary of the invention

[0006] The present invention provides a method for obtaining the three-phase short-circuit current of a doubly-fed wind turbine taking into account the feed-out current of a grid-side converter GSC. The method realizes the acquisition of the three-phase short-circuit current of the doubly-fed wind turbine taking into account the feed-out current of the grid-side converter GSC through the stator three-phase short-circuit current and the grid-side converter three-phase feed-out current in a three-phase stationary coordinate system.

[0007] The technical solution of the present invention is:

[0008] According to a first aspect of the present invention, a method for obtaining a three-phase short-circuit current of a doubly-fed wind turbine taking into account the current fed out by a grid-side converter GSC is provided, comprising the following steps: when a three-phase short circuit occurs in the power grid, taking into account the control of the rotor-side converter RSC, there is a power fluctuation between the rotor-side converter RSC and the grid-side converter GSC, and the power fluctuation between the rotor-side converter RSC and the grid-side converter GSC is solved; based on the power fluctuation between the rotor-side converter RSC and the grid-side converter GSC, the DC bus voltage fluctuation between the rotor-side converter RSC and the grid-side converter GSC is solved; based on the DC bus voltage fluctuation, a reference value of the grid-side converter current based on a d, q synchronous rotating coordinate system is obtained; wherein the grid-side converter current based on the d, q synchronous rotating coordinate system is obtained. The reference value of the converter current includes the reference value of the d-axis current and the reference value of the q-axis current of the grid-side converter; according to the reference values ​​of the d-axis and q-axis currents of the grid-side converter based on the d, q synchronous rotating coordinate system, the grid-side converter feed-in current based on the d, q synchronous rotating coordinate system is obtained; wherein the grid-side converter feed-in current based on the d, q synchronous rotating coordinate system includes the d-axis and q-axis components of the grid-side converter feed-in current; the stator short-circuit current and the grid-side converter feed-in current based on the d, q synchronous rotating coordinate system are converted into the stator three-phase short-circuit current and the grid-side converter three-phase feed-in current in the three-phase stationary coordinate system; the stator three-phase short-circuit current in the three-phase stationary coordinate system is added to the three-phase feed-in current of the grid-side converter to obtain the three-phase short-circuit current of the doubly-fed wind turbine taking into account the feed-in current of the grid-side converter GSC.

[0009] Furthermore, when a three-phase short circuit fault occurs in the power grid at time t=t1, an approximate power fluctuation value ΔP' between the rotor-side converter RSC and the grid-side converter GSC is obtained; the approximate power fluctuation value ΔP' between the rotor-side converter RSC and the grid-side converter GSC is used as the power fluctuation ΔP between the rotor-side converter RSC and the grid-side converter GSC, and the specific expression is as follows:

[0010]

[0011] Among them, P g Indicates grid-side power, P r represents the rotor side power; s is the slip rate; k is the magnitude of the voltage drop at the machine end after a power grid failure; U s0 is the amplitude of the terminal voltage of the machine during steady-state operation; i rq is the q-axis component of the rotor current; e represents the natural constant; τ1 represents the stator transient flux attenuation constant of the doubly fed wind turbine.

[0012] Further, according to the power fluctuation ΔP between the rotor-side converter RSC and the grid-side converter GSC, the DC bus voltage fluctuation ΔU between the rotor-side converter RSC and the grid-side converter GSC is solved. dc , the expression is:

[0013]

[0014] Among them, C dc is the DC side capacitance; ω1 is the synchronous speed; s is the slip rate; k is the magnitude of the voltage drop at the generator end after a grid fault occurs; U s0 is the amplitude of the terminal voltage of the machine during steady-state operation; i rq is the q-axis component of the rotor current; e represents the natural constant; τ1 represents the stator transient flux attenuation constant of the doubly fed wind turbine; t1 represents the time when a three-phase short circuit fault occurs; U dc1 , U dc2 , U dc3 , U dc4 、m dc ,η1,η2, Represents a mnemonic.

[0015] Furthermore, the grid-side converter d-axis current reference value based on the d, q synchronous rotating coordinate system The expression is:

[0016]

[0017] Among them, A0, A1, A2, A3, A4, η1, η2 represent mnemonics; e represents a natural constant; j represents an imaginary number; ω1 represents the synchronous speed; t represents time; τ1 represents the stator transient flux attenuation constant of the doubly fed wind turbine;

[0018] Without taking into account the reactive support of the grid-side converter GSC, the grid-side converter q-axis current reference value based on the d, q synchronous rotating coordinate system is is 0.

[0019] Furthermore, the grid-side converter feed-out current based on the d, q synchronous rotating coordinate system is expressed as:

[0020]

[0021] Among them, i gd 、i gq They are the d-axis and q-axis components of the current fed out by the grid-side converter respectively; Indicates the grid-side converter d-axis current reference value, represents the reference value of the q-axis current of the grid-side converter; c1, c2, c3, c4, r1, r2 represent mnemonics; e represents a natural constant; t represents time.

[0022] Furthermore, the stator short-circuit current i based on the d, q synchronous rotating coordinate system s , the expression is:

[0023]

[0024] Among them, B1, B2, B3, represents a mnemonic; e represents a natural constant; j represents an imaginary number; ω1 represents the synchronous speed; t represents time; τ1 represents the stator transient flux attenuation constant of the doubly fed wind turbine.

[0025] Furthermore, in the three-phase stationary coordinate system, the three-phase short-circuit current of the doubly fed wind turbine, taking phase A as an example, is expressed as:

[0026] i DFIGa =i sa +i ga ;

[0027]

[0028] Where: i DFIGa is the short-circuit current of phase A of the doubly-fed wind turbine; i sa are the stator A phase short-circuit current in the three-phase stationary coordinate system, i ga is the A-phase feed current of the grid-side converter in the three-phase stationary coordinate system; e is a natural constant; j is an imaginary number; ω1 is the synchronous speed; t is time; τ1 is the stator transient flux attenuation constant of the doubly fed wind turbine; A0, A1, A2, A3, A4, A5, A6, η1, η2, r1, r2, B1, B2, B3 represent mnemonics; Re() means taking the real part.

[0029] According to a second aspect of the present invention, there is provided a device for acquiring the three-phase short-circuit current of a doubly-fed wind turbine taking into account the current fed by the grid-side converter GSC, comprising a module for executing a method for acquiring the three-phase short-circuit current of a doubly-fed wind turbine taking into account the current fed by the grid-side converter GSC as described in any one of the above items.

[0030] According to a third aspect of the present invention, there is provided a terminal device, comprising a memory, a processor, and a program stored in the memory and executable by the processor, wherein when the processor executes the program, the method for obtaining the three-phase short-circuit current of a doubly-fed wind turbine taking into account the current fed out by the grid-side converter GSC as described in any one of the above items is implemented.

[0031] According to a fourth aspect of the present invention, a computer-readable storage medium is provided, the computer-readable storage medium comprising a stored program, wherein when the program is running, the device where the computer-readable storage medium is located is controlled to execute any one of the above-mentioned methods for obtaining the three-phase short-circuit current of a doubly-fed wind turbine taking into account the current fed out by the grid-side converter GSC.

[0032] The beneficial effects of the present invention are:

[0033] The present invention is based on the fact that when a fault occurs, the power imbalance between the RSC and the GSC causes a disturbance in the DC bus voltage, thereby affecting the d-axis current command value of the voltage outer loop of the grid-side converter. According to the command value, the GSC feed current can be obtained. Further, the DFIG output current is obtained by adding it to the stator side short-circuit current. According to the proposed short-circuit current calculation method, the transient characteristics of the DFIG can be analyzed more accurately, the short-circuit characteristic analysis of the DFIG can be improved, and a reference for the fault characteristic analysis of the DFIG is provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 is the equivalent circuit of the doubly-fed wind turbine in the dq coordinate system;

[0035] Figure 2 It is a doubly-fed wind turbine system structure;

[0036] Figure 3 This is the GSC control block diagram;

[0037] Figure 4 This is the RSC control block diagram;

[0038] Figure 5 is the q-axis current of the doubly-fed wind turbine rotor;

[0039] Figure 6 is the DC bus voltage fluctuation;

[0040] Figure 7 The current fed out of phase A of the grid-side converter of the doubly-fed wind turbine;

[0041] Figure 8 is the short-circuit current of phase A of the doubly-fed wind turbine stator;

[0042] Fig. 9 is the short-circuit current of phase A of the doubly-fed wind turbine. DETAILED DESCRIPTION

[0043] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. It should be noted that the embodiments in this application and the features in the embodiments can be combined with each other arbitrarily without conflict.

[0044] Example 1: Figure 1-9 As shown, according to the first aspect of an embodiment of the present invention, a method for obtaining the three-phase short-circuit current of a doubly fed wind turbine taking into account the current fed out by the grid-side converter GSC is provided, comprising the following steps: when a three-phase short circuit occurs in the power grid, taking into account the control of the rotor-side converter RSC, there is a power fluctuation between the rotor-side converter RSC and the grid-side converter GSC, and the power fluctuation between the rotor-side converter RSC and the grid-side converter GSC is solved; based on the power fluctuation between the rotor-side converter RSC and the grid-side converter GSC, the DC bus voltage fluctuation between the rotor-side converter RSC and the grid-side converter GSC is solved; based on the DC bus voltage fluctuation, a reference value of the grid-side converter current based on the d, q synchronous rotating coordinate system is obtained; wherein, the grid-side converter current based on the d, q synchronous rotating coordinate system is obtained. The reference value of the side converter current includes the reference value of the d-axis current and the reference value of the q-axis current of the grid-side converter; according to the reference values ​​of the d-axis and q-axis currents of the grid-side converter based on the d, q synchronous rotating coordinate system, the grid-side converter feed-in current based on the d, q synchronous rotating coordinate system is obtained; wherein the grid-side converter feed-in current based on the d, q synchronous rotating coordinate system includes the d-axis and q-axis components of the grid-side converter feed-in current; the stator short-circuit current and the grid-side converter feed-in current based on the d, q synchronous rotating coordinate system are converted into the stator three-phase short-circuit current and the grid-side converter three-phase feed-in current in the three-phase stationary coordinate system; the stator three-phase short-circuit current in the three-phase stationary coordinate system is added to the three-phase feed-in current of the grid-side converter to obtain the three-phase short-circuit current of the doubly-fed wind turbine taking into account the feed-in current of the grid-side converter GSC.

[0045] Furthermore, when a three-phase short circuit fault occurs in the power grid at time t=t1, an approximate power fluctuation value ΔP' between the rotor-side converter RSC and the grid-side converter GSC is obtained; the approximate power fluctuation value ΔP' between the rotor-side converter RSC and the grid-side converter GSC is used as the power fluctuation ΔP between the rotor-side converter RSC and the grid-side converter GSC, and the specific expression is as follows:

[0046]

[0047] Among them, the grid side power P g ≈3kU s0 si rq, rotor side power s is the slip rate, s = 1-ω r / ω1,ω r represents the rotor speed; ω1 is the synchronous speed; k is the magnitude of the voltage drop at the machine end after a power grid failure; U s0 is the amplitude of the terminal voltage of the machine during steady-state operation; i rq is the q-axis component of the rotor current; e represents the natural constant; τ1 represents the stator transient flux attenuation constant of the doubly fed wind turbine, τ1=R s / L s +jω1,L s =L ls +L m ; L s , L m are the equivalent stator inductance and mutual inductance respectively; L ls is the stator leakage inductance of the doubly-fed machine, R s Represents the equivalent stator resistance.

[0048] Further, according to the power fluctuation between the rotor-side converter RSC and the grid-side converter GSC, the DC bus voltage fluctuation ΔU between the rotor-side converter RSC and the grid-side converter GSC is solved. dc , the expression is:

[0049]

[0050] Among them, C dc is the DC side capacitance; ω1 is the synchronous speed; U dc1 , U dc2 , U dc3 , U dc4 、m dc ,η1,η2, Represents a mnemonic, σ is the magnetic flux leakage coefficient, L s , L r , L m are the equivalent stator inductance, rotor inductance and the mutual inductance between the stator and rotor respectively; β1=(R p +k p ) / (σL r );β2=k i / (σL r );k p Rotor side current inner loop proportionality coefficient, k i is the integral coefficient of the inner loop of the rotor side current; is the q-axis forced component of the rotor current; irqm is the transient DC component of the rotor current q axis; i rq1 ,i rq2 is the q-axis decay speed component of the rotor current; i r0 is the rotor current in steady state; R r is the rotor resistance.

[0051] Furthermore, the grid-side converter d-axis current reference value based on the d, q synchronous rotating coordinate system The expression is:

[0052]

[0053] Among them, A0, A1, A2, A3, A4, η1, η2 represent mnemonics; e represents a natural constant; j represents an imaginary number; t represents time; τ1 represents the stator transient flux attenuation constant of the doubly fed wind turbine;

[0054] Without taking into account the reactive support of the grid-side converter GSC, the grid-side converter q-axis current reference value based on the d, q synchronous rotating coordinate system is is 0.

[0055] The mnemonics involved in the above are explained as follows: A2=(2k vp τ1-k vi ) dc2 / 2τ1; A 01 =2U dc1 +U dc2 +2U dc3 +2U dc4 ; A 02 =2U dc1 +U dc2 +2U dc3 ; A 03 =2U dc1 +U dc2 +2U dc4 ; A 04 =2U dc1 +U dc2 ;k vp Indicates the voltage outer loop proportional coefficient of the grid-side converter; k vi Indicates the voltage outer loop integral coefficient of the grid-side converter; U dc1 , U dc2 , U dc3 , U dc4 , Represents a mnemonic, the expression is the same as above.

[0056] Furthermore, the grid-side converter feed-out current based on the d, q synchronous rotating coordinate system is expressed as:

[0057]

[0058] Among them, i gd 、i gq They are the d-axis and q-axis components of the current fed out by the grid-side converter respectively; Indicates the grid-side converter d-axis current reference value, represents the q-axis current reference value of the grid-side converter; c1, c2, c3, c4, r1, r2 represent mnemonics;

[0059] The mnemonics involved in the above are explained as follows: m1=(R g +k pg )ω1 / L g ; i gd0 、i gq0 In steady state, they are the d-axis and q-axis components of the current fed from the grid-side converter; ω1 is the synchronous speed; R g , L g are the resistance and inductance of the grid side and the machine end respectively; k pg , k ig are the proportional and integral parameters of the inner loop of the grid-side converter current respectively; u sq Represents the q-axis component of the stator voltage.

[0060] Furthermore, the stator short-circuit current i based on the d, q synchronous rotating coordinate system s , the expression is:

[0061]

[0062] Among them, B1, B2, B3, represents a mnemonic; e represents a natural constant; j represents an imaginary number; t represents time; τ1 represents the stator transient flux attenuation constant of the doubly fed wind turbine;

[0063] The mnemonics involved in the above are explained as follows: β1=(R p +k p )L s / L D ; β2=k i L s / L D; L s =L ls +L m ; L r =L lr +L m ; L s , L r , L m are the equivalent stator inductance, rotor inductance and the mutual inductance between the stator and rotor respectively; k is the magnitude of the voltage drop at the machine end after a fault occurs in the power grid; u s Indicates the stator voltage; Indicates the rotor current reference value; R r is the rotor resistance; k p Rotor side current inner loop proportionality coefficient, k i is the integral coefficient of the inner loop of the rotor side current; σ is the magnetic leakage coefficient, L ls is the stator leakage inductance of the doubly-fed generator; L lr is the rotor leakage inductance of the doubly-fed machine; τ1 represents the stator transient flux attenuation constant, τ1=R s / L s +jω1;R s Represents the equivalent stator resistance.

[0064] Furthermore, in the three-phase stationary coordinate system, the three-phase short-circuit current of the doubly fed wind turbine, taking phase A as an example, is expressed as:

[0065] i DFIGa =i sa +i ga ;

[0066] in,

[0067] Among them, i DFIGa is the short-circuit current of phase A of the doubly-fed wind turbine; i sa are the stator A phase short-circuit current in the three-phase stationary coordinate system, i ga is the A-phase feed current of the grid-side converter in the three-phase stationary coordinate system; A0, A1, A2, A3, A4, A5, A6, η1, η2, r1, r2, B1, B2, B3 represent mnemonics, and the expressions are as follows: A1=(k vp τ1-k vi ) dc1 / τ1;A2=(2k vp τ1-k vi ) dc2 / 2τ1; A 01 =2U dc1 +U dc2 +2U dc3 +2U dc4 ; A 02 =2U dc1 +U dc2 +2U dc3 ; A 03 =2U dc1 +U dc2 +2U dc4 ; A 04 =2U dc1 +U dc2 ; τ1=R s / L s +jω1; k vp Indicates the voltage outer loop proportional coefficient of the grid-side converter; k vi Represents the voltage outer loop integral coefficient of the grid-side converter; R r is the rotor resistance; L s , L r , L m are the equivalent stator inductance, rotor inductance and the mutual inductance between the stator and rotor respectively; k is the magnitude of the voltage drop at the machine end after a fault occurs in the power grid; k p is the proportional parameter of the rotor current inner loop PI controller.

[0068] According to the second aspect of an embodiment of the present invention, there is provided a device for acquiring the three-phase short-circuit current of a doubly-fed wind turbine taking into account the current fed out by the grid-side converter GSC, including a module for executing the method for acquiring the three-phase short-circuit current of a doubly-fed wind turbine taking into account the current fed out by the grid-side converter GSC as described in any one of the above items. Specifically comprising: a first module for solving the power fluctuation between the rotor-side converter RSC and the grid-side converter GSC when a three-phase short circuit occurs in the power grid, taking into account the power fluctuation between the rotor-side converter RSC and the grid-side converter GSC under the control of the rotor-side converter RSC; for solving the DC bus voltage fluctuation between the rotor-side converter RSC and the grid-side converter GSC based on the power fluctuation between the rotor-side converter RSC and the grid-side converter GSC; a second module for obtaining a reference of the grid-side converter current based on the d, q synchronous rotating coordinate system according to the DC bus voltage fluctuation. value; a third module, for obtaining the grid-side converter feed-out current based on the d, q synchronous rotating coordinate system according to the grid-side converter d-axis and q-axis current reference values ​​based on the d, q synchronous rotating coordinate system; a fourth module, for converting the stator short-circuit current and grid-side converter feed-out current based on the d, q synchronous rotating coordinate system into the stator three-phase short-circuit current and grid-side converter three-phase feed-out current in the three-phase stationary coordinate system; for adding the stator three-phase short-circuit current in the three-phase stationary coordinate system to the grid-side converter three-phase feed-out current to obtain the doubly-fed wind turbine three-phase short-circuit current taking into account the grid-side converter GSC feed-out current. The term "module" as used above may be a combination of software and / or hardware that implements a predetermined function. Although the system described in the above embodiment is preferably implemented in software, the implementation of hardware, or a combination of software and hardware, is also possible and conceivable. For parts not described in detail in each module, please refer to the relevant description of this embodiment.

[0069] According to a third aspect of an embodiment of the present invention, there is provided a terminal device, comprising a memory, a processor, and a program stored on the memory and executable by the processor, wherein when the processor executes the program, the method for obtaining the three-phase short-circuit current of a doubly-fed wind turbine taking into account the current fed out by the grid-side converter GSC as described in any one of the above items is implemented.

[0070] According to a fourth aspect of an embodiment of the present invention, a computer-readable storage medium is provided, the computer-readable storage medium comprising a stored program, wherein when the program is running, the device where the computer-readable storage medium is located is controlled to execute any one of the above-mentioned methods for obtaining the three-phase short-circuit current of a doubly-fed wind turbine taking into account the current fed out of the grid-side converter GSC. In an exemplary embodiment, the computer-readable storage medium may include, but is not limited to: a U disk, a read-only memory (ROM), a random access memory (RAM), a mobile hard disk, a magnetic disk or an optical disk, and other media that can store computer programs.

[0071] Obviously, those skilled in the art should understand that the above modules or steps of the present invention can be implemented by a general computing device, they can be concentrated on a single computing device, or distributed on a network composed of multiple computing devices, they can be implemented by a program code executable by a computing device, so that they can be stored in a storage device and executed by the computing device, and in some cases, the steps shown or described can be executed in a different order than here, or they can be made into individual integrated circuit modules, or multiple modules or steps therein can be made into a single integrated circuit module for implementation. Thus, the present invention is not limited to any specific combination of hardware and software.

[0072] Example 2: Based on experimental data, an optional implementation of the present invention is described in detail below:

[0073] Taking a grid-connected doubly-fed wind turbine as an example, assuming that a three-phase short-circuit fault occurs in the power grid at 1.5s, taking into account the RSC control, there is a power fluctuation between the RSC and the GSC. The DC bus voltage fluctuation between the RSC and the GSC is solved by the power fluctuation on the DC side. According to the DC bus voltage fluctuation, the reference value of the d and q axis currents of the grid-side converter can be obtained. According to the reference value of the d and q axis currents of the grid-side converter, the d and q axis components of the grid-side converter output current can be obtained. The stator short-circuit current in the stationary coordinate system is added to the grid-side converter output current to obtain the three-phase short-circuit current of the doubly-fed wind turbine DFIG taking into account the grid-side converter GSC output current. After the grid fails, the amplitude of the voltage drop at the machine end is k=0.22. The specific parameters of the doubly-fed wind turbine are shown in Table 1:

[0074] Table 1 Specific parameters of double-fed wind turbine

[0075]

[0076] S1. According to the specific parameters of the doubly fed wind turbine in Table 1, the power fluctuation between GSC and RSC is calculated. The expression is:

[0077]

[0078] Among them, s = -0.2; k = 0.22; U s0 =1; τ1 = 0.0694; t1 is the time when the fault occurs; t is the time.

[0079] S2. According to the specific parameters of the doubly fed wind turbine in Table 1, the voltage fluctuation between GSC and RSC is calculated. The expression is:

[0080]

[0081] in, t1 is the time when the fault occurs; t is the time; is the q-axis forced component of the rotor current; i rqm is the transient DC component of the rotor current q axis; i rq1 ,i rq2 is the q-axis attenuated speed component of the rotor current.

[0082] S3. According to the specific parameters of the double-fed wind turbine in Table 1, the reference value of the d-axis current of the grid-side converter is expressed as:

[0083]

[0084] in:

[0085] A0=20.1686A 0m ;

[0086]

[0087] A 0m =0.0048A 01 +45.5376A 02 +3.4128A 03 +2.4283A 04 ;

[0088]

[0089] S4. According to the specific parameters of the double-fed wind turbine in Table 1, the grid-side converter output current expression is:

[0090]

[0091] in:

[0092] c1=-0.2162+j0.0102; c2=-0.2162-j0.0102; c3=-0.03+j0.0014; c4=-0.03-j0.0014;

[0093] r1=-1.4334+j12.8260; r2=-1.4334-j12.8260.

[0094] S5. According to the specific parameters of the doubly-fed wind turbine in Table 1, the three-phase current components on the stator side are expressed as follows:

[0095]

[0096] in:

[0097] B1=-0.8474+j0.3617; B2=0.0019-j0.2174; B3=0.0448+j0.0876; τ1=0.0694.

[0098] Based on the three-phase current components on the stator side, the stator short-circuit current i is obtained s =i sa +i sb +i sc .

[0099] S6. According to the specific parameters of the double-fed wind turbine in Table 1, take the short-circuit current of phase A as an example. Figures 7 to 9 As shown in the figure, the expression of the DFIG and GSC feed-in current in the three-phase stationary coordinate system is:

[0100] i DFIGa =i sa +i ga ;

[0101] in:

[0102]

[0103] B1=-0.8474+j0.3617; B2=0.0019-j0.2174; B3=0.0448+j0.0876;

[0104] A0=20.1686A 0m ;

[0105]

[0106] A 0m =0.0048A 01 +45.5376A 02 +3.4128A 03 +2.4283A04 ;

[0107]

[0108] c1=-0.2162+j0.0102; c2=-0.2162-j0.0102; c3=-0.03+j0.0014; c4=-0.03-j0.0014;

[0109] τ1=0.0694; eta1=0.496; eta2=5.7616; r1=-1.4334+j12.8260; r2=-1.4334-j12.8260.

[0110] At present, existing studies have been able to simultaneously consider the impact of one or more factors on the short-circuit current when analyzing the short-circuit current characteristics of DFIG. However, in actual calculations, existing work rarely considers the contribution of GSC feed current to short-circuit current. The present invention analyzes the short-circuit current of a doubly-fed wind turbine in a scenario where the grid voltage drops slightly, analyzes the effects of the converter (RSC and GSC) control respectively, and regards the short-circuit current as the sum of the stator short-circuit current and the GSC feed current. Figure 1 As shown. Therefore, the present invention takes into account the DFIG three-phase short-circuit current characteristics of the GSC feed-in current, first obtains the GSC feed-in current and the short-circuit current on the stator side, and then obtains the three-phase short-circuit current of the doubly fed wind turbine taking into account the GSC feed-in current based on the above. Specifically, when a fault occurs in the power grid, the electromagnetic power output by it will change significantly, resulting in a disturbance in the DC bus voltage, which will in turn affect the GSC feed-in current. Therefore, the GSC feed-in current solution process is as follows: when a three-phase short circuit occurs in the power grid, taking into account the RSC control, there is a power fluctuation between the RSC and the GSC; the DC bus voltage fluctuation between the RSC and the GSC is solved from the power fluctuation on the DC side; according to the DC bus voltage fluctuation, the reference value of the grid-side converter current can be obtained; according to the d and q axis current reference values, the grid-side converter feed-in current can be obtained. The stator short-circuit current in the stationary coordinate system taking into account the RSC control is added to the GSC feed-in current to obtain the DFIG doubly fed wind turbine three-phase short-circuit current taking into account the GSC feed-in current. The present invention can more accurately analyze the transient characteristics of DFIG, improve the short-circuit characteristic analysis of DFIG, and provide a reference for the fault characteristic analysis of DFIG. The principle of the present invention is further described as follows:

[0111] 1) The control of the grid-side converter and the calculation model of the stator current are described as follows:

[0112] The control of the grid-side converter is specifically to set the reactive power command value to zero, that is, the grid-side converter does not control the grid voltage, which is the main mode of operation of the grid-side converter at present. Figure 3As shown, under its control mode, the influence of the grid-side converter on the rotor current of the generator is mainly transmitted through the DC bus voltage, and the degree of influence depends on the control performance of the grid-side converter on the DC voltage. During steady-state operation, under the control of the grid-side converter, the active power exchange of the two converters remains balanced and the DC bus voltage remains stable. When a short circuit occurs in the power grid, the present invention operates in a super-synchronous state, the voltage drop at the machine end causes the active power flowing out of the grid-side converter to decrease, and the rotor winding has overcurrent and overvoltage, so that the active power flowing out of the rotor-side converter increases, causing the DC voltage to increase rapidly at the moment of short circuit. The more serious the grid fault is, the greater the difference between the two powers, and the greater the maximum value of the DC voltage. When the capacity of the grid-side converter is large enough, due to the increase in the voltage deviation of the DC voltage control loop, the power flowing out of the grid-side converter will also increase accordingly, so that the DC voltage is gradually reduced under the control of the grid-side converter, and finally stabilized near the DC voltage command value. It can be seen that when a three-phase short circuit occurs in the power grid, taking into account the control of the rotor-side converter RSC, there is power fluctuation between the rotor-side converter RSC and the grid-side converter GSC.

[0113] The calculation model of stator short-circuit current based on d, q synchronous rotating coordinate system:

[0114] When the voltage at the terminal of the doubly-fed wind turbine drops slightly during a grid fault, the rotor surge voltage generated is insufficient to trigger the crowbar protection action. The rotor-side converter can maintain the connection with the rotor winding and suppress the rotor surge current by adjusting the output voltage of the rotor-side converter. Figure 2 As shown in the figure. The stator short-circuit current of the doubly fed wind turbine is mainly determined by the stator flux and the rotor current. During steady-state operation, the synchronous rotating magnetic motive force formed by the rotor excitation current of the doubly fed induction generator generates an induced electromotive force in the stator winding. At the moment of short circuit, due to the conservation of flux, the stator induced electromotive force remains constant while the machine-end voltage drops, and a voltage difference is formed between the stator induced electromotive force and the machine-end voltage, thereby generating a periodic short-circuit current component. During the grid short circuit, the stator DC flux causes an overcurrent in the rotor winding. When the rotor transient current is controllable, the rotor overcurrent continues to decay and regains stability under the hysteresis correction of the rotor-side converter. When the closed-loop bandwidth of the controller is large enough, the AC side voltage of the rotor-side converter can track the command value well, so the periodic component is considered constant. The stator DC flux generates a static magnetic field in the air gap, and the rotor rotation cuts the magnetic field to generate a transient DC current in the rotor winding.

[0115] Through the above, the present invention obtains the short-circuit current of the doubly-fed wind turbine taking into account the GSC feed-in current based on the stator short-circuit current provided by the stator side and the feed-in current provided by the grid-side converter. According to the power characteristics of the DFIG, the active power exchanged with the grid by the grid-side converter under normal operation is regarded as the slip times of the stator active power fluctuation, and the GSC current will also fluctuate during a fault. Therefore, if the influence of the GSC current is ignored, it will inevitably cause errors in the calculation results of the DFIG short-circuit current. Therefore, the method for obtaining the three-phase short-circuit current of the doubly-fed wind turbine taking into account the GSC feed-in current of the grid-side converter of the present invention is more accurate for the calculation results of the DFIG short-circuit current.

[0116] 2) Establish the mathematical model of DFIG in dq synchronous rotating coordinate system

[0117] According to the equivalent circuit diagram of the doubly fed wind turbine (see attached Figure 1 ), the mathematical model of DFIG in the dq coordinate system is obtained as:

[0118]

[0119] Among them, u s 、u r are the stator and rotor voltages in the dq axis synchronous rotating coordinate system respectively; i s 、i r are the stator and rotor currents in the dq axis synchronous rotating coordinate system; ψ s , r are the stator and rotor flux in the dq axis synchronous rotating coordinate system; R s , R r are stator and rotor resistance respectively; ω1 is synchronous speed, ω=ω1-ω r is the slip angular velocity, ω r is the rotor angular velocity; P is the differential operator; L s , L r , L m They are the equivalent stator inductance, rotor inductance and the mutual inductance between the stator and rotor respectively.

[0120] Since the doubly-fed induction generator rotor converter adopts stator flux directional vector control, the stator voltage dq axis component u sd =0,u sq =U s , the stator and rotor flux under steady-state operation can be obtained as:

[0121]

[0122] Among them, U s is the grid voltage amplitude; ω1 is the synchronous speed; ψ sd , sq They are the d-axis and q-axis components of the stator flux respectively.

[0123] Due to L m >>L ls ; L m >>L lr , so it is approximately considered that L m =L s ; L m =L r , then the rotor voltage and grid-side current in steady-state operation can be expressed as:

[0124]

[0125] Among them, i rq is the q-axis component of the rotor current; ψ s Stator flux; i gq is the q-axis component of the grid-side current; s is the slip rate.

[0126] When a three-phase short circuit occurs at the machine end, the stator flux expression is:

[0127]

[0128] Among them, ψ' s is the stator flux after short circuit; a short circuit fault occurs at time t=t1; k is the magnitude of the voltage drop at the machine end after the power grid fault occurs; τ1 represents the stator transient flux attenuation constant, τ1=R s / L s +jω1.

[0129] 3) Using the full current method, the specific process of solving the rotor short-circuit current of the rotor-side converter in the two-phase synchronous rotating coordinate system is as follows:

[0130] According to the control principle of the rotor side converter RSC Figure 4 As shown, the rotor voltage u in the dq rotating coordinate system can be obtained r The equation is:

[0131]

[0132] in, is the rotor current reference value; i r is the rotor current; k p Rotor side current inner loop proportionality coefficient, k i is the integral coefficient of the inner loop of the rotor side current; σ is the leakage magnetic coefficient.

[0133] Combining equation (1) and equation (7), we can get the second-order differential equation of the rotor current:

[0134]

[0135] Where β1=(R r +kp ) / (σL D );β2=k i / (σL D );m r =L m τ1(1-s)U s0 / (σL r L s );U s0 is the amplitude of the terminal voltage during steady-state operation.

[0136] Solving the second-order differential equation of the rotor current (8) yields:

[0137]

[0138] in, L s =L ls +L m ; L r =L lr +L m ; L ls , L lr is the stator and rotor leakage inductance of the doubly-fed generator; i rm is the transient DC component of the rotor current; i r1 ,i r2 is the rotor current decay speed component; i r0 is the initial value of the rotor current.

[0139] 4) The specific process of solving the power disturbance is:

[0140] Ignoring the losses of the reactor and the switching power devices, the grid-side converter input power P g and rotor-side converter input power P r for:

[0141] P g ≈3kU s0 si rq (10)

[0142]

[0143] At t=t1, a short circuit occurs. According to the DC bus voltage balance formula, The power fluctuation on the DC side is:

[0144]

[0145] Among them, the q-axis component of the rotor current

[0146] 5) The specific process of solving the DC bus voltage fluctuation is:

[0147] Since the grid-side converter adopts the grid voltage oriented vector control strategy, the static gain of the DC bus voltage G pedc (jω1) can be approximately expressed as:

[0148]

[0149] Among them, C dc is the DC side capacitance; ω1 is the synchronous speed.

[0150] From equations (12) and (13), the DC bus voltage fluctuation can be obtained as:

[0151]

[0152] in,

[0153] The DC bus voltage fluctuation is transformed by Laplace transform, and the corresponding Laplace equation is:

[0154]

[0155] 6) Solve the feed-in current command value of the grid-side converter in the dq synchronous rotating coordinate system:

[0156] The Laplace equation of the d-axis component of the grid-side converter reference value is:

[0157]

[0158] Among them, k vp Indicates the voltage outer loop proportional coefficient of the grid-side converter; k vi Indicates the integral coefficient of the grid-side converter voltage outer loop;

[0159] When considering that the GSC does not provide reactive support, the q-axis reference current of the grid-side converter based on the d, q synchronous rotating coordinate system is 0.

[0160] The circuit equation of the GSC current inner loop in two-phase synchronous rotating coordinates is:

[0161]

[0162] Among them, u gd 、u gq are the d-axis and q-axis components of the grid-side voltage respectively; U sd , U sq are the d-axis and q-axis components of the stator voltage respectively; R g , Lg are the resistance of the grid side and the machine end, and the inductance of the grid side and the machine end respectively; i gd 、i gq They are the d-axis and q-axis components of the grid-side input current respectively; ω1 is the synchronous speed.

[0163] The basic control equation of the inner current loop of the grid-side converter is:

[0164]

[0165] In the formula, are the grid-side current reference values ​​d and q axis components respectively; k pg , k ig They are the proportional-integral parameters of the inner current loop of the grid-side converter.

[0166] Differentiating both sides of the voltage equation in equation (17) yields:

[0167]

[0168] By differentiating both sides of the basic control equation (18), we can obtain:

[0169]

[0170] Combining equations (19) and (20), the second-order differential equation of the grid-side converter feed-out current is:

[0171]

[0172] Where m1=(R g +k pg )ω1 / L g ;

[0173] Solve the analytical expression of the grid-side converter feed-out current equation (21) in the dq synchronous rotating coordinate system. The analytical expression of the grid-side feed-out current is the sum of the general solution of the homogeneous equation corresponding to the grid-side current second-order differential equation and the special solution corresponding to the grid-side current second-order differential equation, that is:

[0174]

[0175] in,

[0176]

[0177] Substituting the d-axis component and q-axis component of the GSC output current into the GSC short-circuit current, the GSC output current in the dq rotating coordinate system can be obtained:

[0178]

[0179] 7) Solve the short-circuit current on the stator side:

[0180] From the DFIG mathematical model in the dq synchronous rotating coordinate system, it can be seen that the stator flux equation in equation (2) is transformed into the stator short-circuit current equation:

[0181]

[0182] Among them, ψ s is the stator flux, ψ s =L s i s +L m i r ; L s =L ls +L m ; L s , L m are the equivalent stator inductance and the mutual inductance between the stator and rotor respectively; L ls is the stator leakage inductance of the doubly-fed generator; i r is the rotor current.

[0183] Substituting the stator flux analytical formula (2) and the rotor current analytical formula (9) into the stator short-circuit current equation, we can obtain:

[0184]

[0185] in,

[0186] 8) The output current of the DFIG three-phase stationary coordinate system taking into account the GSC feed-in current is:

[0187] The stator short-circuit current based on the d, q synchronous rotating coordinate system is converted to the three-phase stationary coordinate system:

[0188]

[0189] In the formula, i sa 、i sb 、i sc are the currents of the stator phases A, B and C in the three-phase stationary coordinate system respectively; Re is the sign of the real part;

[0190]

[0191] The grid-side converter output current equation (23) obtained in the dq rotating coordinate system is transformed into the three-phase stationary coordinate system as follows:

[0192]

[0193] Where i ga ,i gb ,i gc They are the currents of phases A, B and C of the grid-side converter in the three-phase stationary coordinate system; Re is the sign of the real part;

[0194]

[0195] in, A1=(k vp τ1-k vi ) dc1 / τ1;A2=(2k vp τ1-k vi ) dc2 / 2τ1;

[0196]

[0197] A 01 =2U dc1 +U dc2 +2U dc3 +2U dc4 ; A 02 =2U dc1 +U dc2 +2U dc3 ; A 03 =2U dc1 +U dc2 +2U dc4 ; A 04 =2U dc1 +U dc2 ; τ1=R s / L s +jω1; k vp Indicates the voltage outer loop proportional coefficient of the grid-side converter; k vi Represents the voltage outer loop integral coefficient of the grid-side converter; R r is the rotor resistance; L s , L r , L m are the equivalent stator inductance, rotor inductance and the mutual inductance between the stator and rotor respectively; k is the magnitude of the voltage drop at the machine end after a fault occurs in the power grid; k p is the proportional parameter of the rotor current inner loop PI controller.

[0198] In the three-phase stationary coordinate system, taking phase a as an example, Figures 7 to 9 The three-phase short-circuit current of the doubly-fed wind turbine taking into account the GSC feed-out current is:

[0199] iDFIGa =i sa +i ga (30)

[0200] in,

[0201] It can be known from the application of the above technical solution that when a slight voltage drop occurs in the power grid, the doubly fed wind turbine usually relies on the adjustment of the output voltage of the rotor converter to suppress the rotor impact current in order to cope with low voltage ride-through (LVRT). There is an imbalance in the power exchange between the RSC and the GSC, which leads to the disturbance of the DC bus voltage, making the DFIG transient process more complicated. Therefore, the present invention designs an analytical method for the three-phase short-circuit current of the doubly fed wind turbine taking into account the current fed out by the grid-side converter. Through the present invention, the transient characteristics of the DFIG can be analyzed more accurately, the short-circuit characteristics analysis of the DFIG can be improved, and a reference for the fault characteristics analysis of the DFIG can be provided.

[0202] The specific implementation modes of the present invention are described in detail above in conjunction with the accompanying drawings, but the present invention is not limited to the above implementation modes, and various changes can be made within the knowledge scope of ordinary technicians in this field without departing from the purpose of the present invention.

Claims

1. A method for obtaining the three-phase short-circuit current of a double-fed wind turbine taking into account the current fed out of the grid-side converter GSC, characterized in that: The following steps are involved: When a three-phase short circuit occurs in the power grid, taking into account the control of the rotor-side converter RSC, there is a power fluctuation between the rotor-side converter RSC and the grid-side converter GSC, and the power fluctuation between the rotor-side converter RSC and the grid-side converter GSC is solved; based on the power fluctuation between the rotor-side converter RSC and the grid-side converter GSC, the DC bus voltage fluctuation between the rotor-side converter RSC and the grid-side converter GSC is solved; According to the DC bus voltage fluctuation, a reference value of the grid-side converter current based on the d and q synchronous rotating coordinate system is obtained; wherein the reference value of the grid-side converter current based on the d and q synchronous rotating coordinate system includes a reference value of the d-axis current and a reference value of the q-axis current of the grid-side converter; According to the d-axis and q-axis current reference values ​​of the grid-side converter in the d and q synchronous rotating coordinate systems, the grid-side converter feed-in current based on the d and q synchronous rotating coordinate systems is obtained; wherein the grid-side converter feed-in current based on the d and q synchronous rotating coordinate systems includes the grid-side converter feed-in current d and q-axis components; The stator short-circuit current and the grid-side converter feed-in current based on the d, q synchronous rotating coordinate system are converted into the stator three-phase short-circuit current and the grid-side converter three-phase feed-in current in the three-phase stationary coordinate system; the stator three-phase short-circuit current in the three-phase stationary coordinate system is added to the three-phase feed-in current of the grid-side converter to obtain the three-phase short-circuit current of the doubly-fed wind turbine taking into account the feed-in current of the grid-side converter GSC.

2. The method for obtaining the three-phase short-circuit current of a double-fed wind turbine taking into account the feed-out current of the grid-side converter GSC according to claim 1 is characterized in that: When a three-phase short circuit fault occurs in the power grid at time t=t1, an approximate power fluctuation value ΔP' between the rotor-side converter RSC and the grid-side converter GSC is obtained; the approximate power fluctuation value ΔP' between the rotor-side converter RSC and the grid-side converter GSC is used as the power fluctuation ΔP between the rotor-side converter RSC and the grid-side converter GSC. The specific expression is as follows: Among them, P g Indicates grid-side power, P r represents the rotor side power; s is the slip rate; k is the magnitude of the voltage drop at the machine end after a power grid failure; U s0 is the amplitude of the terminal voltage of the machine during steady-state operation; i rq is the q-axis component of the rotor current; e represents the natural constant; τ1 represents the stator transient flux attenuation constant of the doubly fed wind turbine.

3. The method for obtaining the three-phase short-circuit current of a double-fed wind turbine taking into account the feed-out current of the grid-side converter GSC according to claim 1, characterized in that: According to the power fluctuation ΔP between the rotor-side converter RSC and the grid-side converter GSC, the DC bus voltage fluctuation ΔU between the rotor-side converter RSC and the grid-side converter GSC is solved. dc , the expression is: Among them, C dc is the DC side capacitance; ω1 is the synchronous speed; s is the slip rate; k is the magnitude of the voltage drop at the generator end after a grid fault occurs; U s0 is the amplitude of the terminal voltage of the machine during steady-state operation; i rq is the q-axis component of the rotor current; e represents the natural constant; τ1 represents the stator transient flux attenuation constant of the doubly fed wind turbine; t1 represents the time when a three-phase short circuit fault occurs; U dc1 , U dc2 , U dc3 , U dc4 、m dc ,η1,η2, Represents a mnemonic.

4. The method for obtaining the three-phase short-circuit current of a double-fed wind turbine taking into account the feed-out current of the grid-side converter GSC according to claim 1, characterized in that: The grid-side converter d-axis current reference value based on the d, q synchronous rotating coordinate system The expression is: Among them, A0, A1, A2, A3, A4, η1, η2 represent mnemonics; e represents a natural constant; j represents an imaginary number; ω1 represents the synchronous speed; t represents time; τ1 represents the stator transient flux attenuation constant of the doubly fed wind turbine; Without taking into account the reactive support of the grid-side converter GSC, the grid-side converter q-axis current reference value based on the d, q synchronous rotating coordinate system is is 0.

5. The method for obtaining the three-phase short-circuit current of a double-fed wind turbine taking into account the feed-out current of the grid-side converter GSC according to claim 1, characterized in that: The grid-side converter feed-out current based on the d, q synchronous rotating coordinate system is expressed as: Among them, i gd 、i gq They are the d-axis and q-axis components of the current fed out by the grid-side converter respectively; Indicates the grid-side converter d-axis current reference value, represents the reference value of the q-axis current of the grid-side converter; c1, c2, c3, c4, r1, r2 represent mnemonics; e represents a natural constant; t represents time.

6. The method for obtaining the three-phase short-circuit current of the double-fed wind turbine taking into account the feed-out current of the grid-side converter GSC according to claim 1, characterized in that: The stator short-circuit current i based on the d, q synchronous rotating coordinate system s , the expression is: Among them, B1, B2, B3, represents a mnemonic; e represents a natural constant; j represents an imaginary number; ω1 represents the synchronous speed; t represents time; τ1 represents the stator transient flux attenuation constant of the doubly fed wind turbine.

7. The method for obtaining the three-phase short-circuit current of the double-fed wind turbine taking into account the feed-out current of the grid-side converter GSC according to claim 1, characterized in that: In the three-phase stationary coordinate system, the three-phase short-circuit current of the doubly fed wind turbine, taking phase A as an example, is expressed as follows: i DFIGa =i sa +i ga ; Where: i DFIGa is the short-circuit current of phase A of the doubly fed wind turbine; i sa are the stator A phase short-circuit current in the three-phase stationary coordinate system, i ga is the A-phase feed current of the grid-side converter in the three-phase stationary coordinate system; e is a natural constant; j is an imaginary number; ω1 is the synchronous speed; t is time; τ1 is the stator transient flux attenuation constant of the doubly fed wind turbine; A0, A1, A2, A3, A4, A5, A6, η1, η2, r1, r2, B1, B2, B3 represent mnemonics; Re() means taking the real part.

8. A device for acquiring three-phase short-circuit current of a double-fed wind turbine taking into account the current fed out of the grid-side converter GSC, characterized in that: The method comprises a module for executing the method for obtaining the three-phase short-circuit current of a doubly-fed wind turbine taking into account the current fed out by the grid-side converter GSC as described in any one of claims 1 to 7.

9. A terminal device, characterized in that: It includes a memory, a processor, and a program stored in the memory and executable by the processor. When the processor executes the program, it implements the method for obtaining the three-phase short-circuit current of the doubly-fed wind turbine taking into account the current fed out by the grid-side converter GSC as described in any one of claims 1 to 7.

10. A computer-readable storage medium, characterized in that: The computer-readable storage medium includes a stored program, wherein when the program is running, the device where the computer-readable storage medium is located is controlled to execute the method for obtaining the three-phase short-circuit current of the doubly-fed wind turbine taking into account the current fed out of the grid-side converter GSC as described in any one of claims 1 to 7.

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