A method and system for calculating the pry bar action boundary of a doubly-fed wind generator

Abstract

The application discloses a kind of for the calculation method and system of double-fed wind generator crowbar action boundary, comprising: the short-circuit current response expression of double-fed wind turbine under the control of rotor sustained excitation is established;Based on the short-circuit current response expression of double-fed wind turbine, through simultaneous flux equation, voltage equation and current loop control equation, obtain the dynamic analytical solution of rotor current in synchronous rotating coordinate system;According to the dynamic analytical solution of rotor current in synchronous rotating coordinate system, determine the quantitative relationship of transient component attenuation coefficient and current inner loop control parameter;Based on the quantitative relationship of transient component attenuation coefficient and current inner loop control parameter, obtain the relationship formula of crowbar action demarcation line about voltage drop degree and slip;If the crowbar action of double-fed wind turbine is located above the crowbar action demarcation line, then crowbar action after fault.The problem that crowbar protection action boundary is not clear and field group sub-group equivalent model accuracy is insufficient in the process of double-fed wind farm low voltage ride through is solved.

Description

Technical Field

[0001] This invention relates to the field of short-circuit current calculation technology for power system relay protection, specifically to a calculation method and system for the crowbar action boundary of a doubly fed wind turbine. Background Technology

[0002] With the goal of "carbon peaking and carbon neutrality" being proposed, a high proportion of new energy sources, a high proportion of power electronic equipment, and ultra-high / extra-high voltage long-distance power transmission will become the main characteristics of my country's new power system. By the end of 2024, China's total installed capacity of new energy exceeded 1.45 billion kilowatts, accounting for 43.4% of the total installed power generation capacity. New energy units connect to the grid through power electronic equipment. Compared with traditional synchronous generators, their control is more flexible, but their inertia is lower, and their tolerance to voltage and frequency deviations is weaker. To meet the requirement of not disconnecting from the grid during faults in the "Technical Regulations for Wind Farm Connection to the Power System," new energy units are designed with high / low voltage ride-through and crowbar control strategies, which are switched according to the operating status. Under the influence of complex fault ride-through control strategies and different control parameters, the short-circuit current characteristics of wind turbines are significantly different from those of traditional synchronous generators, which may degrade the operating performance of current power system protection devices and affect the safe and stable operation of the system.

[0003] Existing methods for calculating short-circuit current do not adequately consider the dynamic process of the entire fault cycle in wind turbines. The dynamic process of a doubly-fed induction generator (DFIG) wind turbine after a fault includes the converter unresponsive phase, the crowbar engagement-asynchronous motor phase, and the crowbar disengagement-RSC control phase. Most existing methods only calculate a single phase, failing to accurately reflect the entire dynamic fault cycle of the entire power system. Therefore, analyzing the impact of low-voltage ride-through and crowbar control on the short-circuit current during a fault and establishing an accurate wind farm model is crucial for the analysis of new power systems. Summary of the Invention

[0004] To address the challenges of unclear crowbar protection action boundaries and insufficient accuracy of equivalent models for farm clusters during low-voltage ride-through in doubly-fed induction generator (DFIG) wind farms, this invention provides a method for calculating the crowbar action boundaries of DFIG wind turbines, comprising:

[0005] Establish the short-circuit current response expression of a doubly-fed wind turbine generator under continuous rotor excitation control;

[0006] Based on the short-circuit current response expression of the doubly fed wind turbine, the dynamic analytical solution of the rotor current in the synchronous rotating coordinate system is obtained by simultaneously solving the flux linkage equation, voltage equation and current loop control equation.

[0007] Based on the dynamic analytical solution of the rotor current in the synchronous rotating coordinate system, the quantitative relationship between the transient component attenuation coefficient and the inner loop control parameters of the current is determined.

[0008] Based on the quantitative relationship between the transient component attenuation coefficient and the current inner loop control parameters, the relationship between the crowbar action boundary line and the voltage drop and slip rate is obtained; if the crowbar action of the doubly fed wind turbine is above the crowbar action boundary line, then the crowbar will act after the fault.

[0009] Furthermore, the short-circuit current response expression of a doubly-fed wind turbine under continuous rotor excitation control is established, including:

[0010] The equations for the stator and rotor flux linkages of a doubly fed wind turbine generator set on the synchronous rotating coordinate axis dq are as follows:

[0011]

[0012] In the formula: ψ s ψ r For the stator and rotor flux linkage vectors of a doubly-fed wind turbine; i s i r The stator and rotor current vectors; L s L r The stator and rotor windings of the doubly fed wind turbine are fully inductive.

[0013] The equations for the stator and rotor voltages of a doubly fed wind turbine generator set on the dq synchronous rotating coordinate axis are as follows:

[0014]

[0015] In the formula: U s U r These are the stator and rotor currents and voltage vectors of the doubly fed wind turbine.

[0016] Furthermore, based on the short-circuit current response expression of the doubly-fed wind turbine, by simultaneously solving the flux linkage equation, voltage equation, and current loop control equation, the dynamic analytical solution of the rotor current in the synchronous rotating coordinate system is obtained, including:

[0017] The control equations for the rotor-side current loop of a doubly-fed wind turbine can be written in vector form as follows:

[0018]

[0019] Where ω p =sω s The angular frequency of the rotor current before coordinate transformation;

[0020] The stator flux linkage after the fault is analyzed. Based on the voltage flux linkage equation of the doubly fed wind turbine given in equations (1) and (2), the stator and rotor flux linkages are rewritten as follows:

[0021]

[0022] in Let k be the leakage flux coefficient of the generator. s =L m / L s The inductive coupling coefficient of the stator winding;

[0023] Substituting equation (4) into equation (1), we solve the first-order differential equation of the stator voltage with respect to the stator flux linkage, and obtain the expression for the DFIG stator flux linkage when the stator terminal voltage undergoes a sudden change, as shown in equation (5), where t0 is the fault initiation time.

[0024]

[0025] As can be seen from equation (5), after a three-phase short-circuit fault occurs in the power grid, according to the principle of flux conservation, the stator flux generates a DC attenuation component with an attenuation coefficient of τ. sn The steady-state value of the magnetic flux linkage is related to the stator voltage after the fault.

[0026] By combining equations (2), (3), and (5) and taking the first derivative simultaneously, we obtain the dynamic equation of rotor current under symmetrical faults:

[0027]

[0028] in

[0029]

[0030] From equation (6), it can be seen that the rotor circuit of the three-phase short circuit in the power grid under the continuous excitation control strategy of the converter is a second-order dynamic circuit. Solving this non-homogeneous second-order differential equation yields the analytical solution of the rotor current in the synchronous rotating coordinate system as follows:

[0031]

[0032] As can be seen from equation (7), during the fault, the DFIG rotor current in the synchronous rotating coordinate system contains a value equal to the rotor current given value i. rref The steady-state component and the attenuation coefficient are τ sn The power frequency oscillation component, the harmonic components with attenuation coefficients p1 and p2, and m1, m2, and m3 are the amplitude coefficients of the two harmonic components and the power frequency oscillation component, respectively.

[0033] The attenuation coefficients p1 and p2 are the opposites of the two roots of the characteristic equation of equation (6), as shown in equation (8):

[0034]

[0035] Furthermore, based on the dynamic analytical solution of the rotor current in the synchronous rotating coordinate system, the quantitative relationship between the transient component attenuation coefficient and the inner loop control parameters of the current is determined, including:

[0036] At the instant of the fault, the rotor current cannot change abruptly, but the initial value of the rotor current rate of change will change due to the stator terminal voltage and the rotor voltage. According to the impulse function matching method, the coefficients of each transient component can be obtained as follows:

[0037]

[0038] Combining equations (5) and (7), the expression for the DFIG stator current during the fault period can be obtained:

[0039]

[0040] Where i sf The steady-state value of the stator current during a fault is generally determined by the control strategy. The expressions for the coefficients m4, m5, and m6 of the transient attenuation components of the stator current are as follows:

[0041]

[0042] According to equation (11), the transient response of the stator current in the stationary coordinate system also consists of four parts: the steady-state component, the attenuation coefficient τ, and the constant-state component. sn The transient DC component and the transient harmonic components with attenuation coefficients p1 and p2; according to equation (8), the attenuation coefficients p1 and p2 depend on the current inner loop control parameters of the rotor converter, when the proportional coefficient k p When the integral coefficient increases, the real parts of p1 and p2 increase, and the decay rate of the free component accelerates; when the integral coefficient increases, the real parts of p1 and p2 decrease, and the decay rate of the free component slows down; according to equation (5), the decay coefficient τ sn It is only related to the motor impedance parameters;

[0043] The attenuation coefficient is τ sn The amplitude m6 of the transient component is affected by the system control parameters. According to equation (11), the size of m6 depends on m3. According to equation (9), the influence of different current inner loop control parameters on the size of m3 can be obtained.

[0044] Furthermore, based on the quantitative relationship between the transient component attenuation coefficient and the current inner loop control parameters, the relationship between the crowbar action boundary line and the voltage drop degree and slip rate is obtained, including:

[0045] Combining equations (5), (6), (7), (8), and (9), we can obtain the relationship between the crowbar action boundary line and the voltage drop degree k and slip rate s:

[0046]

[0047] in

[0048]

[0049] In equation (13), the synchronous speed ω of the doubly fed wind turbine is... s The frequency is 50Hz, and the rotor speed ω of the doubly fed wind turbine is... r The variation range is 10Hz to 100Hz, and the slip s varies from 0.8 to -1.

[0050] The crowbar action boundary can be obtained based on the relationship between voltage drop degree k and slip rate s.

[0051] This invention also provides a calculation system for the action boundary of a doubly-fed wind turbine crowbar, comprising:

[0052] The response expression establishment module is used to establish the short-circuit current response expression of a doubly-fed wind turbine under continuous rotor excitation control.

[0053] The current dynamic analysis module is used to obtain the dynamic analytical solution of the rotor current in the synchronous rotating coordinate system by simultaneously solving the flux linkage equation, voltage equation and current loop control equation based on the short-circuit current response expression of the doubly fed wind turbine.

[0054] The quantitative relationship determination module is used to determine the quantitative relationship between the transient component attenuation coefficient and the inner loop control parameters of the current based on the dynamic analytical solution of the rotor current in the synchronous rotating coordinate system.

[0055] The crowbar action module is used to obtain the relationship between the crowbar action boundary line and the voltage drop and slip rate based on the quantitative relationship between the transient component attenuation coefficient and the current inner loop control parameters; if the crowbar action of the doubly fed wind turbine is above the crowbar action boundary line, the crowbar will act after the fault.

[0056] Furthermore, the response expression building module includes:

[0057] The flux linkage equation submodule is used to express the flux linkage equations on the stator and rotor sides of a doubly fed wind turbine generator set on the dq synchronous rotating coordinate axis.

[0058]

[0059] In the formula: ψ s ψ r For the stator and rotor flux linkage vectors of a doubly-fed wind turbine; i s i r The stator and rotor current vectors; L s L r The stator and rotor windings of the doubly fed wind turbine are fully inductive.

[0060] The voltage equation submodule is used to express the stator and rotor voltage equations of a doubly fed wind turbine generator set on the dq synchronous rotating coordinate axis.

[0061]

[0062] In the formula: U s U r These are the stator and rotor currents and voltage vectors of the doubly fed wind turbine.

[0063] Furthermore, the current dynamic analysis module includes:

[0064] The vector equation submodule is used to write the rotor-side current loop control equations of a doubly-fed wind turbine in vector form, specifically:

[0065]

[0066] Where ω p =sω s The angular frequency of the rotor current before coordinate transformation;

[0067] The stator and rotor flux linkage rewriting submodule is used to analyze the stator flux linkage after a fault occurs. Based on the voltage flux linkage equations of the doubly fed wind turbine given in equations (1) and (2), the stator and rotor flux linkages are rewritten as follows:

[0068]

[0069] in Let k be the leakage flux coefficient of the generator. s =L m / L s The inductive coupling coefficient of the stator winding;

[0070] The differential equation solving submodule is used to substitute equation (4) into equation (1) to solve the first-order differential equation of the stator voltage with respect to the stator flux linkage. The expression for the DFIG stator flux linkage when the stator terminal voltage changes abruptly is shown in equation (5), where t0 is the fault initiation time.

[0071]

[0072] As can be seen from equation (5), after a three-phase short-circuit fault occurs in the power grid, according to the principle of flux conservation, the stator flux generates a DC attenuation component with an attenuation coefficient of τ. sn The steady-state value of the magnetic flux linkage is related to the stator voltage after the fault.

[0073] The current dynamic equation submodule is used to combine equations (2), (3), and (5) and simultaneously take the first derivative to obtain the rotor current dynamic equation under symmetrical faults:

[0074]

[0075] in

[0076]

[0077] The rotor current solution module is used to solve the rotor current in the synchronous rotating coordinate system. As shown in equation (6), the rotor circuit under the continuous excitation control strategy of the converter with a three-phase short circuit in the power grid is a second-order dynamic circuit. Solving this non-homogeneous second-order differential equation yields the analytical solution of the rotor current.

[0078]

[0079] As can be seen from equation (7), during the fault, the DFIG rotor current in the synchronous rotating coordinate system contains a value equal to the rotor current given value i. rref The steady-state component and the attenuation coefficient are τ sn The power frequency oscillation component, the harmonic components with attenuation coefficients p1 and p2, and m1, m2, and m3 are the amplitude coefficients of the two harmonic components and the power frequency oscillation component, respectively.

[0080] The attenuation coefficients p1 and p2 are the opposites of the two roots of the characteristic equation of equation (6), as shown in equation (8):

[0081]

[0082] Furthermore, the quantitative relationship determination module includes:

[0083] The submodule for solving the coefficients of transient components is used when, at the instant of a fault, the rotor current cannot change abruptly, but the initial value of the rotor current rate of change will change due to the stator terminal voltage and the rotor voltage. Based on the impulse function matching method, the coefficients of each transient component can be solved as follows:

[0084]

[0085] Combining equations (5) and (7), the expression for the DFIG stator current during the fault period can be obtained:

[0086]

[0087] Where i sf The steady-state value of the stator current during a fault is generally determined by the control strategy. The expressions for the coefficients m4, m5, and m6 of the transient attenuation components of the stator current are as follows:

[0088]

[0089] The first quantitative relational submodule is used to determine, according to equation (11), that the transient response of the stator current in the stationary coordinate system also consists of four parts: the steady-state component, the attenuation coefficient τ, and the constant-state component. sn The transient DC component and the transient harmonic components with attenuation coefficients p1 and p2; according to equation (8), the attenuation coefficients p1 and p2 depend on the current inner loop control parameters of the rotor converter, when the proportional coefficient k pWhen the integral coefficient increases, the real parts of p1 and p2 increase, and the decay rate of the free component accelerates; when the integral coefficient increases, the real parts of p1 and p2 decrease, and the decay rate of the free component slows down; according to equation (5), the decay coefficient τ sn It is only related to the motor impedance parameters;

[0090] The second quantitative relationship submodule is used for attenuation coefficient τ. sn The amplitude m6 of the transient component is affected by the system control parameters. According to equation (11), the size of m6 depends on m3. According to equation (9), the influence of different current inner loop control parameters on the size of m3 can be obtained.

[0091] Furthermore, the crowbar action module includes:

[0092] The relation determination submodule, used to solve equations (5), (6), (7), (8), and (9), yields the relation between the crowbar action boundary line and the voltage drop degree k and slip rate s:

[0093]

[0094] in

[0095]

[0096] In equation (13), the synchronous speed ω of the doubly fed wind turbine is... s The frequency is 50Hz, and the rotor speed ω of the doubly fed wind turbine is... r The variation range is 10Hz to 100Hz, and the slip s varies from 0.8 to -1.

[0097] The action boundary line determination submodule is used to determine the crowbar action boundary line based on the relationship between the voltage drop degree k and the slip rate s.

[0098] This invention provides a method and system for calculating the crowbar action boundary of a doubly-fed induction generator (DFIG) wind turbine. First, it establishes the short-circuit current response expression of the DFIG wind turbine under continuous rotor excitation control. By simultaneously solving the flux linkage equation, voltage equation, and control equation, it derives the dynamic analytical solution of the rotor current in a synchronous rotating coordinate system, revealing the quantitative relationship between the transient component attenuation coefficient and the inner current loop control parameters. Based on this, and combined with the crowbar action threshold condition, it proposes an analytical formula for the crowbar action boundary line describing the mapping relationship between voltage drop depth and slip rate. Under known wind speed and voltage drop conditions, it achieves accurate judgment of whether the crowbar will act. This solves the problems of unclear crowbar protection action boundaries and insufficient accuracy of the equivalent model for wind farm grouping during low-voltage ride-through in DFIG wind farms. Attached Figure Description

[0099] Figure 1This is a flowchart illustrating a method for calculating the action boundary of a doubly fed wind turbine crowbar, as provided in an embodiment of the present invention.

[0100] Figure 2 This is a schematic diagram of the control system of a doubly fed wind turbine generator according to an embodiment of the present invention;

[0101] Figure 3 This is a schematic diagram of the T-type equivalent circuit of DFIG vector form in the dq synchronous rotating coordinate system according to an embodiment of the present invention;

[0102] Figure 4 This is a schematic diagram of the voltage amplitude of a symmetrical fault in a power grid according to an embodiment of the present invention;

[0103] Figure 5 This is a schematic diagram illustrating the influence of the control parameters involved in this embodiment of the invention on the transient DC component amplitude coefficient m3;

[0104] Figure 6 This is a schematic diagram illustrating the analytical boundary of the crowbar action in an embodiment of the present invention;

[0105] Figure 7 This is a schematic diagram comparing the dividing line of the crowbar analysis action with the crowbar action situation in the embodiments of the present invention;

[0106] Figure 8 This is a schematic diagram of the structure of a calculation system for the action boundary of a doubly fed wind turbine crowbar, provided in an embodiment of the present invention. Detailed Implementation

[0107] Numerous specific details are set forth in the following description to provide a full understanding of the invention. However, the invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0108] This invention derives an analytical formula for the crowbar actuation boundary of a doubly-fed induction generator (DFIG) wind turbine. Under known wind speed and voltage drop conditions, it enables accurate determination of whether the crowbar actuates, which is of great significance for fault analysis and protection scheme design. Based on this, this invention provides a method for calculating the crowbar actuation boundary of a DFIG wind turbine, such as... Figure 1 As shown, it includes the following steps:

[0109] Step S101: Establish the short-circuit current response expression of the doubly fed wind turbine under continuous rotor excitation control.

[0110] The block diagram of the DFIG control system for a doubly fed wind turbine is as follows: Figure 2 As shown.

[0111] The stator and rotor windings of the DFIG both adopt the conventional method for electric motors. Its T-shaped equivalent circuit in vector form under the dq synchronous rotating coordinate system is as follows: Figure 3 As shown in the figure, L ls L lr For the self-inductance of the DFIG stator and rotor windings, L m For the mutual inductance between the stator and rotor windings of the DFIG, R s R r These are the stator and rotor resistances, respectively.

[0112] The equations for the stator and rotor flux linkages of a doubly fed wind turbine generator set on the synchronous rotating coordinate axis dq are as follows:

[0113]

[0114] In the formula: ψ s ψ r For the stator and rotor flux linkage vectors of a doubly-fed wind turbine; i s i r The stator and rotor current vectors; L s L r The stator and rotor windings of the doubly fed wind turbine are fully inductive.

[0115] The equations for the stator and rotor voltages of a doubly fed wind turbine generator set on the dq synchronous rotating coordinate axis are as follows:

[0116]

[0117] In the formula: U s U r These are the stator and rotor currents and voltage vectors of the doubly fed wind turbine.

[0118] Step S102: Based on the short-circuit current response expression of the doubly fed wind turbine, the dynamic analytical solution of the rotor current in the synchronous rotating coordinate system is obtained by simultaneously solving the flux linkage equation, voltage equation and current loop control equation.

[0119] As shown in the block diagram of the DFIG control system of the doubly fed wind turbine, the control equation of the rotor-side current loop of the doubly fed wind turbine is written in vector form, as shown in equation (3):

[0120]

[0121] Where ω p =sω s The angular frequency of the rotor current before coordinate transformation;

[0122] To analyze and derive the short-circuit current of a DFIG wind turbine under a symmetrical grid fault, a three-phase voltage amplitude step is used to represent the symmetrical grid fault, neglecting the impact of phase transitions on the short-circuit current. The voltage amplitudes during the fault process are as follows: Figure 4 As shown, K represents the symmetrical voltage drop depth of the power grid.

[0123] To calculate and analyze the stator and rotor short-circuit currents of the DFIG after a fault, the stator flux linkage after the fault must first be analyzed. Based on the voltage flux linkage equations of the doubly fed wind turbine given in equations (1) and (2), the stator and rotor flux linkages are rewritten as follows:

[0124]

[0125] in Let k be the leakage flux coefficient of the generator. s =L m / L s The inductive coupling coefficient of the stator winding;

[0126] Substituting equation (4) into equation (1), we solve the first-order differential equation of the stator voltage with respect to the stator flux linkage, and obtain the expression for the DFIG stator flux linkage when the stator terminal voltage undergoes a sudden change, as shown in equation (5), where t0 is the fault initiation time.

[0127]

[0128] As can be seen from equation (5), after a three-phase short-circuit fault occurs in the power grid, according to the principle of flux conservation, the stator flux generates a DC attenuation component with an attenuation coefficient of τ. sn The steady-state value of the magnetic flux linkage is related to the stator voltage after the fault.

[0129] By combining equations (2), (3), and (5) and taking the first derivative simultaneously, we obtain the dynamic equation of rotor current under symmetrical faults:

[0130]

[0131] in

[0132]

[0133] From equation (6), it can be seen that the rotor circuit of the three-phase short circuit in the power grid under the continuous excitation control strategy of the converter is a second-order dynamic circuit. Solving this non-homogeneous second-order differential equation yields the analytical solution of the rotor current in the synchronous rotating coordinate system as follows:

[0134]

[0135] As can be seen from equation (7), during the fault, the DFIG rotor current in the synchronous rotating coordinate system contains a value equal to the rotor current given value i. rref The steady-state component and the attenuation coefficient are τ sn The power frequency oscillation component, the harmonic components with attenuation coefficients p1 and p2, and m1, m2, and m3 are the amplitude coefficients of the two harmonic components and the power frequency oscillation component, respectively.

[0136] The attenuation coefficients p1 and p2 are the opposites of the two roots of the characteristic equation of equation (6), as shown in equation (8):

[0137]

[0138] Step S103: Based on the dynamic analytical solution of the rotor current in the synchronous rotating coordinate system, determine the quantitative relationship between the transient component attenuation coefficient and the inner loop control parameters of the current.

[0139] At the instant of the fault, the rotor current cannot change abruptly, but the initial value of the rotor current rate of change will change due to the stator terminal voltage and the rotor voltage. According to the impulse function matching method, the coefficients of each transient component can be obtained as follows:

[0140]

[0141] Combining equations (5) and (7), the expression for the DFIG stator current during the fault period can be obtained:

[0142]

[0143] Where i sf The steady-state value of the stator current during a fault is generally determined by the control strategy. The expressions for the coefficients m4, m5, and m6 of the transient attenuation components of the stator current are as follows:

[0144]

[0145] According to equation (11), the transient response of the stator current in the stationary coordinate system also consists of four parts: the steady-state component, the attenuation coefficient τ, and the constant-state component. sn The transient DC component and the transient harmonic components with attenuation coefficients p1 and p2; according to equation (8), the attenuation coefficients p1 and p2 depend on the current inner loop control parameters of the rotor converter, when the proportional coefficient k p When the integral coefficient increases, the real parts of p1 and p2 increase, and the decay rate of the free component accelerates; when the integral coefficient increases, the real parts of p1 and p2 decrease, and the decay rate of the free component slows down; according to equation (5), the decay coefficient τ sn It is only related to the motor impedance parameters;

[0146] The attenuation coefficient is τ sn The amplitude m6 of the transient component is affected by the system control parameters. According to equation (11), the magnitude of m6 depends on m3. According to equation (9), the influence of different current inner loop control parameters on the magnitude of m3 can be obtained, such as... Figure 5 As shown.

[0147] according to Figure 5 (a) It can be seen that m3 is related to k iThe graph of the function is not monotonic, when k i When the value is greater than this extreme point, m3 monotonically decreases, and the amplitude of the corresponding transient component fluctuation changes with k. i Increase and decrease; when k i When the value is less than this extreme point, m3 monotonically increases, causing the amplitude of the corresponding transient component fluctuation to change with k. i It increases as the ratio of the proportional coefficient to the integral coefficient of the current inner loop regulator, k. p / k i When k is larger, i It has virtually no impact on the size of m3. According to Figure 5 (b) It can be seen that the proportionality constant k p The larger k is, the smaller m3 will be. p / k i The smaller the hour, the more k p The greater the impact on m3.

[0148] In summary, the short-circuit current output by a doubly-fed induction generator (DFIG) wind turbine comprises three transient components with different attenuation coefficients. The inner current loop parameters determine the magnitude of the attenuation coefficients of two of these transient components and influence the attenuation coefficient τ. sn The amplitude of the transient component. Appropriately increasing the proportional coefficient and decreasing the integral coefficient of the rotor converter's inner current loop is beneficial for accelerating the decay of the corresponding transient component. Increasing k p / k i It can reduce the corresponding attenuation coefficient by τ sn The amplitude of the transient component is beneficial to the rapid stabilization of the short-circuit current.

[0149] Step S104: Based on the quantitative relationship between the transient component attenuation coefficient and the current inner loop control parameters, obtain the relationship between the crowbar action boundary line and the voltage drop degree and slip rate; if the crowbar action of the doubly fed wind turbine is above the crowbar action boundary line, then the crowbar will act after the fault.

[0150] Based on the rotor short-circuit current formula, the functional relationship between voltage drop depth K and slip rate s can be derived, which is the analytical formula for the crowbar action boundary line.

[0151] Combine equations (5), (6), (7), (8), and (9). In equation (7), due to the action delay of the crowbar, the time t is taken as 3ms. The action condition of the crowbar is that the rotor short-circuit current exceeds 1.5 times the rotor rated current, so the rotor short-circuit current i r The value is taken as 1.5 times the rated rotor current. The relationship between the crowbar action boundary and the voltage drop degree k and slip s can be obtained:

[0152]

[0153] in

[0154]

[0155] In equation (13), the synchronous speed ω of the doubly fed wind turbine is... s The frequency is 50Hz, and the rotor speed ω of the doubly fed wind turbine is... r The variation range is 10Hz to 100Hz. The slip s varies from 0.8 to -1; the higher the wind speed and power, the higher the rotor speed and the lower the slip.

[0156] The crowbar action boundary can be obtained based on the relationship between the voltage drop degree k and the slip rate s. Furthermore, the voltage drop depth during crowbar action at any slip rate can be determined, such as... Figure 6 As shown.

[0157] If the fan's (s, K) is above the action boundary line, the pry bar will move after a fault; otherwise, the pry bar will not move.

[0158] Based on the MPPT curve of the wind turbine, a one-to-one correspondence between the wind speed and slip rate of the DFIG can be obtained. Therefore, when a fault occurs, by combining the wind speed and the voltage drop depth of the wind turbine, it is possible to accurately determine whether the crowbar of each wind turbine in the field group has been activated, making the group modeling of fault stages feasible.

[0159] To verify the correctness of the analytical formula for the crowbar action boundary line derived in the aforementioned theory, a typical DFIG wind turbine model was built based on the PSCAD simulation platform. The transformer voltage level was 690V / 35kV, and the wind turbine rated power was 2MW.

[0160] In the doubly-fed induction generator (DFIG) model, the fault type is set as a three-phase short circuit, with the short circuit point located on the collector line and the voltage measurement point located at the transformer substation outlet. When a fault occurs, if the rotor short-circuit current exceeds 1.5 times the rated rotor current, the crowbar protection is activated. Considering the control delay of the DFIG control system in actual engineering and taking into account the crowbar movement process, the crowbar protection device is set to activate 3ms after the fault in the simulation model to simulate the real-world operating scenario.

[0161] By adjusting the slip rate *s* inside the fan, the operation of the DFIG under different wind speeds is simulated. At a given wind speed (or slip rate), the transition resistance value at the short-circuit point is changed, thereby altering the electrical distance between the short-circuit point and the measuring point, and consequently changing the voltage drop *ΔU*. Through extensive simulations, the movement of the crowbar under different slip rates and voltage drop degrees is statistically analyzed. The simulated crowbar movement boundary line can be determined and compared with the analytical boundary line. The simulation comparison results are as follows: Figure 7As shown, simulation results based on several different voltage drop levels and slip rates demonstrate that the analytical formula for the crowbar action boundary can accurately characterize the actual crowbar action. The analytical curve is basically consistent with the action boundary in the simulation, with a small error.

[0162] The higher the wind speed (or initial power) before the short circuit, the deeper the voltage drop during the short circuit, and the easier it is for the crowbar to move. By combining the wind turbine's MPPT curve with the initial wind speed and voltage drop depth, the crowbar's movement can be accurately determined.

[0163] Based on the same inventive concept, this invention also provides a calculation system 800 for the boundary of movement of a doubly-fed wind turbine crowbar, such as... Figure 8 As shown, it includes:

[0164] The response expression establishment module 810 is used to establish the short-circuit current response expression of the doubly fed wind turbine under rotor continuous excitation control.

[0165] The current dynamic analysis module 820 is used to obtain the dynamic analytical solution of the rotor current in the synchronous rotating coordinate system by simultaneously solving the flux linkage equation, voltage equation and current loop control equation based on the short-circuit current response expression of the doubly fed wind turbine.

[0166] The quantitative relationship determination module 830 is used to determine the quantitative relationship between the transient component attenuation coefficient and the inner loop control parameters of the current based on the dynamic analytical solution of the rotor current in the synchronous rotating coordinate system.

[0167] The crowbar action module 840 is used to obtain the relationship between the crowbar action boundary line and the voltage drop and slip rate based on the quantitative relationship between the transient component attenuation coefficient and the current inner loop control parameters; if the crowbar action of the doubly fed wind turbine is above the crowbar action boundary line, the crowbar will act after the fault.

[0168] Furthermore, the response expression building module includes:

[0169] The flux linkage equation submodule is used to express the flux linkage equations on the stator and rotor sides of a doubly fed wind turbine generator set on the dq synchronous rotating coordinate axis.

[0170]

[0171] In the formula: ψ s ψ r For the stator and rotor flux linkage vectors of a doubly-fed wind turbine; i s i r The stator and rotor current vectors; L s L r The stator and rotor windings of the doubly fed wind turbine are fully inductive.

[0172] The voltage equation submodule is used to express the stator and rotor voltage equations of a doubly fed wind turbine generator set on the dq synchronous rotating coordinate axis.

[0173]

[0174] In the formula: U s U r These are the stator and rotor currents and voltage vectors of the doubly fed wind turbine.

[0175] Furthermore, the current dynamic analysis module includes:

[0176] The vector equation submodule is used to write the rotor-side current loop control equations of a doubly-fed wind turbine in vector form, specifically:

[0177]

[0178] Where ω p =sω s The angular frequency of the rotor current before coordinate transformation;

[0179] The stator and rotor flux linkage rewriting submodule is used to analyze the stator flux linkage after a fault occurs. Based on the voltage flux linkage equations of the doubly fed wind turbine given in equations (1) and (2), the stator and rotor flux linkages are rewritten as follows:

[0180]

[0181] in Let k be the leakage flux coefficient of the generator. s =L m / L s The inductive coupling coefficient of the stator winding;

[0182] The differential equation solving submodule is used to substitute equation (4) into equation (1) to solve the first-order differential equation of the stator voltage with respect to the stator flux linkage. The expression for the DFIG stator flux linkage when the stator terminal voltage changes abruptly is shown in equation (5), where t0 is the fault initiation time.

[0183]

[0184] As can be seen from equation (5), after a three-phase short-circuit fault occurs in the power grid, according to the principle of flux conservation, the stator flux generates a DC attenuation component with an attenuation coefficient of τ. sn The steady-state value of the magnetic flux linkage is related to the stator voltage after the fault.

[0185] The current dynamic equation submodule is used to combine equations (2), (3), and (5) and simultaneously take the first derivative to obtain the rotor current dynamic equation under symmetrical faults:

[0186]

[0187] in

[0188]

[0189] The rotor current solution module is used to solve the rotor current in the synchronous rotating coordinate system. As shown in equation (6), the rotor circuit under the continuous excitation control strategy of the converter with a three-phase short circuit in the power grid is a second-order dynamic circuit. Solving this non-homogeneous second-order differential equation yields the analytical solution of the rotor current.

[0190]

[0191] As can be seen from equation (7), during the fault, the DFIG rotor current in the synchronous rotating coordinate system contains a value equal to the rotor current given value i. rref The steady-state component and the attenuation coefficient are τ sn The power frequency oscillation component, the harmonic components with attenuation coefficients p1 and p2, and m1, m2, and m3 are the amplitude coefficients of the two harmonic components and the power frequency oscillation component, respectively.

[0192] The attenuation coefficients p1 and p2 are the opposites of the two roots of the characteristic equation of equation (6), as shown in equation (8):

[0193]

[0194] Furthermore, the quantitative relationship determination module includes:

[0195] The submodule for solving the coefficients of transient components is used when, at the instant of a fault, the rotor current cannot change abruptly, but the initial value of the rotor current rate of change will change due to the stator terminal voltage and the rotor voltage. Based on the impulse function matching method, the coefficients of each transient component can be solved as follows:

[0196]

[0197] Combining equations (5) and (7), the expression for the DFIG stator current during the fault period can be obtained:

[0198]

[0199] Where i sf The steady-state value of the stator current during a fault is generally determined by the control strategy. The expressions for the coefficients m4, m5, and m6 of the transient attenuation components of the stator current are as follows:

[0200]

[0201] The first quantitative relational submodule is used to determine, according to equation (11), that the transient response of the stator current in the stationary coordinate system also consists of four parts: the steady-state component, the attenuation coefficient τ, and the constant-state component. snThe transient DC component and the transient harmonic components with attenuation coefficients p1 and p2; according to equation (8), the attenuation coefficients p1 and p2 depend on the current inner loop control parameters of the rotor converter, when the proportional coefficient k p When the integral coefficient increases, the real parts of p1 and p2 increase, and the decay rate of the free component accelerates; when the integral coefficient increases, the real parts of p1 and p2 decrease, and the decay rate of the free component slows down; according to equation (5), the decay coefficient τ sn It is only related to the motor impedance parameters;

[0202] The second quantitative relationship submodule is used for attenuation coefficient τ. sn The amplitude m6 of the transient component is affected by the system control parameters. According to equation (11), the size of m6 depends on m3. According to equation (9), the influence of different current inner loop control parameters on the size of m3 can be obtained.

[0203] Furthermore, the crowbar action module includes:

[0204] The relation determination submodule, used to solve equations (5), (6), (7), (8), and (9), yields the relation between the crowbar action boundary line and the voltage drop degree k and slip rate s:

[0205]

[0206] in

[0207]

[0208] In equation (13), the synchronous speed ω of the doubly fed wind turbine is... s The frequency is 50Hz, and the rotor speed ω of the doubly fed wind turbine is... r The variation range is 10Hz to 100Hz, and the slip s varies from 0.8 to -1.

[0209] The action boundary line determination submodule is used to determine the crowbar action boundary line based on the relationship between the voltage drop degree k and the slip rate s.

[0210] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0211] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0212] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0213] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0214] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of the claims of the present invention.

Claims

1. A method for calculating the boundary of movement of a crowbar in a doubly-fed wind turbine, characterized in that, include: The short-circuit current response expression of a doubly-fed induction generator (DFIG) under continuous rotor excitation control is established, specifically including the stator and rotor side flux linkage equations of the DFIG on the dq synchronous rotating coordinate axis: (1) In the formula: ψ s , ψ r For the stator and rotor flux linkage vectors of a doubly-fed wind turbine; i s i r The stator and rotor current vectors; L s L r The stator and rotor windings of the doubly fed wind turbine are fully inductive. The equations for the stator and rotor voltages of a doubly fed wind turbine generator set on the dq synchronous rotating coordinate axis are as follows: (2) wherein: U s , U r are the stator and rotor voltage vectors of the DFIG, respectively. Based on the short-circuit current response expression of the doubly-fed induction generator (DFIG) wind turbine, the dynamic analytical solution of the rotor current in the synchronous rotating coordinate system is obtained by simultaneously solving the flux linkage equation, voltage equation, and current loop control equation. Specifically, this includes writing the rotor-side current loop control equation of the DFIG wind turbine in vector form, as follows: (3) in ω p =s ω s The angular frequency of the rotor current before coordinate transformation; The stator flux linkage after the fault is analyzed. Based on the voltage flux linkage equation of the doubly fed wind turbine given in equations (1) and (2), the stator and rotor flux linkages are rewritten as follows: (4) in Let be the leakage flux coefficient of the generator. The inductive coupling coefficient of the stator winding; Substituting equation (4) into equation (1), we solve the first-order differential equation of the stator voltage with respect to the stator flux linkage, and obtain the expression for the DFIG stator flux linkage when the stator terminal voltage undergoes a sudden change, as shown in equation (5), where t0 is the fault initiation time. (5) As shown in equation (5), after a three-phase short-circuit fault occurs in the power grid, according to the principle of flux conservation, the stator flux generates a DC attenuation component with an attenuation coefficient of . τ sn The steady-state value of the magnetic flux linkage is related to the stator voltage after the fault. By combining equations (2), (3), and (5) and taking the first derivative simultaneously, we obtain the dynamic equation of rotor current under symmetrical faults: (6) in From equation (6), it can be seen that the rotor circuit of the three-phase short circuit in the power grid under the continuous excitation control strategy of the converter is a second-order dynamic circuit. Solving the non-homogeneous second-order differential equation (6) yields the analytical solution of the rotor current in the synchronous rotating coordinate system as follows: (7) As can be seen from equation (7), during the fault, the DFIG rotor current in the synchronous rotating coordinate system contains a value equal to the rotor current given value i. rref The steady-state component and the attenuation coefficient are τ sn The power frequency oscillation component, the harmonic components with attenuation coefficients p1 and p2, and m1, m2, and m3 are the amplitude coefficients of the two harmonic components and the power frequency oscillation component, respectively. The attenuation coefficients p1 and p2 are the opposites of the two roots of the characteristic equation of equation (6), as shown in equation (8): (8) Based on the dynamic analytical solution of the rotor current in the synchronous rotating coordinate system, the quantitative relationship between the transient component attenuation coefficient and the inner loop control parameters of the current is determined. Specifically, at the instant of a fault, the rotor current cannot change abruptly, while the initial value of the rotor current rate of change will change due to the stator terminal voltage and the rotor voltage. According to the impulse function matching method, the coefficients of each transient component can be solved as follows: (9) Combining equations (5) and (7), the expression for the DFIG stator current during the fault period can be obtained: (10) where i sf is the stator current fault steady-state value, determined by the control strategy; the coefficients m4, m5, m6 of the stator current transient decay component are expressed as follows: (11) According to equation (11), the transient response of the stator current in the stationary coordinate system also consists of four parts: the steady-state component, the attenuation coefficient, and the current transient response in the stationary coordinate system. τ sn The transient DC component and the transient harmonic components with attenuation coefficients p1 and p2; according to equation (8), the attenuation coefficients p1 and p2 depend on the current inner loop control parameters of the rotor converter, when the proportional coefficient k p When the integral coefficient increases, the real parts of p1 and p2 increase, and the decay rate of the free component accelerates; when the integral coefficient increases, the real parts of p1 and p2 decrease, and the decay rate of the free component slows down; according to equation (5), the decay coefficient... τ sn It is only related to the motor impedance parameters; Attenuation coefficient is τ sn The amplitude m6 of the transient component is affected by the system control parameters. According to equation (11), the size of m6 depends on m3. According to equation (9), the influence of different current inner loop control parameters on the size of m3 can be obtained. Based on the quantitative relationship between the transient component attenuation coefficient and the current inner loop control parameters, the relationship between the crowbar action boundary line and the voltage drop and slip rate is obtained; if, according to the relationship, the voltage drop and slip rate are determined to be above the crowbar action boundary line, then the crowbar will act after the fault, specifically including: combining equations (5), (6), (7), (8), and (9), the relationship between the crowbar action boundary line and the voltage drop K and slip rate s can be obtained: (12) in (13) In equation (13), the synchronous speed of the doubly fed wind turbine is... ω s The rotor speed of the doubly-fed wind turbine is 50Hz. ω r The variation range is 10Hz to 100Hz, and the slip s varies from 0.8 to -1. The crowbar action boundary can be obtained based on the relationship between voltage drop K and slip s.

2. A calculation system for the boundary of movement of the crowbar in a doubly-fed wind turbine, characterized in that, include: The response expression establishment module is used to establish the short-circuit current response expression of a doubly-fed induction generator (DFIG) under continuous rotor excitation control. Specifically, it includes a flux linkage equation submodule, used to establish the flux linkage equations for the stator and rotor sides of the DFIG on the synchronous rotating coordinate axis dq. The expressions are as follows: (14) In the formula: ψ s , ψ r For the stator and rotor flux linkage vectors of a doubly-fed wind turbine; i s i r The stator and rotor current vectors; L s L r The stator and rotor windings of the doubly fed wind turbine are fully inductive. The voltage equation submodule is used to express the stator and rotor voltage equations of a doubly fed wind turbine generator set on the dq synchronous rotating coordinate axis. (15) In the formula: U s U r These are the stator and rotor voltage vectors of the doubly fed wind turbine generator set, respectively. The current dynamic analysis module is used to obtain the dynamic analytical solution of the rotor current in the synchronous rotating coordinate system based on the short-circuit current response expression of the doubly-fed induction generator (DFIG) by simultaneously solving the flux linkage equation, voltage equation, and current loop control equation. Specifically, it includes a vector equation submodule, used to write the rotor-side current loop control equation of the DFIG in vector form: (16) in ω p =s ω s The angular frequency of the rotor current before coordinate transformation; The stator and rotor flux linkage rewriting submodule is used to analyze the stator flux linkage after a fault occurs. Based on the voltage flux linkage equations of the doubly fed wind turbine given in equations (14) and (15), the stator and rotor flux linkages are rewritten as follows: (17) in Let be the leakage flux coefficient of the generator. The inductive coupling coefficient of the stator winding; The differential equation solving submodule is used to substitute equation (17) into equation (14) to solve the first-order differential equation of the stator voltage with respect to the stator flux linkage. The expression for the DFIG stator flux linkage when the stator terminal voltage changes abruptly is shown in equation (18), where t0 is the fault initiation time. (18) As shown in equation (18), after a three-phase short-circuit fault occurs in the power grid, according to the principle of flux conservation, the stator flux generates a DC attenuation component with an attenuation coefficient of . τ sn The steady-state value of the magnetic flux linkage is related to the stator voltage after the fault. The current dynamic equation submodule is used to combine equations (15), (16), and (18) and simultaneously take the first derivative to obtain the rotor current dynamic equation under symmetrical faults: (19) in The rotor current solution module is used to solve the rotor current in the synchronous rotating coordinate system. As can be seen from equation (19), the rotor circuit of the three-phase short circuit in the power grid under the continuous excitation control strategy of the converter is a second-order dynamic circuit. Solving the non-homogeneous second-order differential equation (19) yields the analytical solution of the rotor current. (20) As can be seen from equation (20), during the fault, the DFIG rotor current in the synchronous rotating coordinate system contains a value equal to the rotor current given value i. rref The steady-state component and the attenuation coefficient are τ sn The power frequency oscillation component, the harmonic components with attenuation coefficients p1 and p2, and m1, m2, and m3 are the amplitude coefficients of the two harmonic components and the power frequency oscillation component, respectively. The attenuation coefficients p1 and p2 are the opposites of the two roots of the characteristic equation of equation (19), as shown in equation (21): (21) The quantitative relationship determination module is used to determine the quantitative relationship between the transient component attenuation coefficient and the inner loop control parameters of the current based on the dynamic analytical solution of the rotor current in the synchronous rotating coordinate system. Specifically, it includes a submodule for solving the coefficients of each transient component. This submodule is used because, at the instant of a fault, the rotor current cannot change abruptly, but the initial value of the rotor current rate of change will change due to the stator terminal voltage and the rotor voltage. Based on the impulse function matching method, the coefficients of each transient component can be solved as follows: (22) Combining equations (18) and (20), the expression for the DFIG stator current during the fault period can be obtained: (23) Where i sf The steady-state value of the stator current during a fault is determined by the control strategy; the expressions for the coefficients m4, m5, and m6 of the transient attenuation components of the stator current are as follows: (24) The first quantitative relational submodule is used to determine, according to equation (24), that the transient response of the stator current in the stationary coordinate system also consists of four parts: the steady-state component, the attenuation coefficient, and the constant-state component. τ sn The transient DC component and the transient harmonic components with attenuation coefficients p1 and p2; according to equation (21), the attenuation coefficients p1 and p2 depend on the current inner loop control parameters of the rotor converter, when the proportional coefficient k p When the integral coefficient increases, the real parts of p1 and p2 increase, and the decay rate of the free component accelerates; when the integral coefficient increases, the real parts of p1 and p2 decrease, and the decay rate of the free component slows down; according to equation (18), the decay coefficient... τ sn It is only related to the motor impedance parameters; The second quantitative relationship submodule is used for attenuation coefficients of... τ sn The amplitude m6 of the transient component is affected by the system control parameters. According to equation (24), the size of m6 depends on m3. According to equation (22), the influence of different current inner loop control parameters on the size of m3 can be obtained. The crowbar action module is used to obtain the relationship between the crowbar action boundary line and the voltage drop and slip rate based on the quantitative relationship between the transient component attenuation coefficient and the current inner loop control parameters; if it is determined according to the relationship that the voltage drop and slip rate are above the crowbar action boundary line, then the crowbar will act after the fault, specifically including: a relationship determination submodule, used to combine equations (18), (19), (20), (21), and (22) to obtain the relationship between the crowbar action boundary line and the voltage drop K and slip rate s: (25) in (26) In equation (26), the synchronous speed of the doubly fed wind turbine is... ω s The rotor speed of the doubly-fed wind turbine is 50Hz. ω r The variation range is 10Hz to 100Hz, and the slip s varies from 0.8 to -1. The action boundary line determination submodule is used to determine the crowbar action boundary line based on the relationship between voltage drop degree K and slip rate s.

Images