A Modeling and Application Method for a State-Space Small-Signal Model of a Direct-Drive Permanent Magnet Wind Power Grid-Connected System under AC Asymmetric Operating Conditions

Abstract

This invention discloses a modeling and application method for a state-space small-signal model of a direct-drive permanent magnet wind power grid-connected system under AC asymmetric operating conditions. The modeling method includes establishing mathematical models of each core component of the direct-drive permanent magnet wind power grid-connected system; converting the mathematical models of the AC-DC-AC power converter and filter circuit to obtain the corresponding dq-sequence dynamic phasor models; processing the mathematical models of the wind turbine shaft system, permanent magnet synchronous generator, phase-locked loop, and turbine-side converter control system at the steady-state operating point to obtain a linear time-invariant model; processing the mathematical models of the phase sequence separation stage, grid-side converter control system, and the dq-sequence dynamic phasor model to obtain a linear periodic time-varying model; and integrating the linear time-invariant model and the linear periodic time-varying model to obtain the state-space small-signal model. The state-space small-signal model obtained by this invention can accurately and completely characterize the small-disturbance characteristics of a direct-drive permanent magnet wind power grid-connected system under AC asymmetric operating conditions.

Description

Technical Field

[0001] This invention relates to the field of wind power generation system technology, and more specifically, to a modeling and application method for a state space small-signal model of a direct-drive permanent magnet wind power grid-connected system under AC asymmetric operating conditions. Background Technology

[0002] Direct-drive permanent magnet wind power generation, as one of the main technologies in the global wind power market, belongs to high-order, nonlinear converter power sources. It has significant coupling and interaction with the power grid, and under certain conditions, it may induce broadband oscillation accidents, posing a serious threat to system stability, equipment safety, and power quality. For the small-signal stability analysis of wind power grid-connected systems, the academic community mainly adopts two modeling methods: LTP (Linear Time-Periodic) and LTI (Linear Time-Invariant). Among them, LTP modeling preserves time-varying characteristics and the model is accurate, but the mathematical expression of the state matrix is ​​complex. LTI modeling uses a constant state matrix and the analysis theory is mature, but it is prone to truncation errors and increases the model order. Current research is mostly based on idealized assumptions about the three-phase balance of the power grid and the positive sequence control of converter equipment, which makes it difficult to adapt to the common power grid voltage imbalance conditions in actual engineering. Power grid voltage imbalance will significantly increase the modeling difficulty of wind power grid-connected systems. On the one hand, the LTP method faces decoupling challenges in motor system modeling due to the complexity of the small disturbance expression of flux linkage. On the other hand, the LTI method cannot accurately describe the frequency components derived from key variables and the transient process of the control system, resulting in insufficient model accuracy.

[0003] In the existing technology, there is no research on LTP models for modeling direct-drive permanent magnet wind power grid-connected systems under AC asymmetric operating conditions. Existing LTI models are mainly divided into two categories: one is the model established by the impedance method, which ignores the generator modeling and simply replaces the generator with a current or voltage source; the other is the state-space model, which takes into account the impact of AC voltage asymmetry at the grid connection point on the grid-side converter. However, neither the impedance method nor the state-space method considers the phase sequence separation link when modeling the grid-side control system, and ignores the second harmonic component in the outer loop control variable of the current vector control. As a result, the model cannot accurately and completely describe the small disturbance characteristics of the direct-drive permanent magnet wind power grid-connected system. Summary of the Invention

[0004] To overcome the shortcomings of existing modeling techniques that cannot accurately and completely describe the small-interference characteristics of direct-drive permanent magnet wind power grid-connected systems, this invention proposes the following technical solution:

[0005] Firstly, this invention proposes a modeling method for a small-signal state-space model of a direct-drive permanent magnet wind power grid-connected system under AC asymmetric operating conditions, comprising:

[0006] Mathematical models of the core components of a direct-drive permanent magnet wind power grid-connected system are established. The core components include the wind turbine shaft system, permanent magnet synchronous generator, AC-DC-AC power converter, filter circuit and control system. The control system includes a phase sequence separation link, a phase-locked loop, a turbine-side converter control system and a grid-side converter control system.

[0007] The dq-sequence dynamic phasor modeling method is used to transform the mathematical models of the AC-DC-AC power converter and the filter circuit respectively, so as to obtain the corresponding dq-sequence dynamic phasor models.

[0008] The mathematical models of the wind turbine shaft system, permanent magnet synchronous generator, phase-locked loop and generator-side converter control system are linearized at the steady-state operating point to obtain a linear time-invariant model;

[0009] The mathematical models of the phase sequence separation stage, the grid-side converter control system, and the dq sequence dynamic phasor model are linearized to obtain a linear periodic time-varying model.

[0010] By integrating the linear time-invariant model and the linear periodic time-varying model, and eliminating algebraic variables, a state-space small-signal model of the direct-drive permanent magnet wind power grid-connected system is obtained.

[0011] As a preferred technical solution, the mathematical model of the wind turbine shaft system is expressed as follows:

[0012]

[0013] In the formula, Ω s This refers to the mechanical angular velocity of the generator rotor. ρ a air density; R t The radius of the wind turbine blades; v C represents wind speed. p The wind energy utilization coefficient; J The total moment of inertia of the equivalent concentrated mass of the wind turbine and permanent magnet synchronous generator; n p This represents the number of pole pairs of the generator. ψ f It is a permanent magnet flux chain; AC current at the output of the machine-side converter positive sequence fundamental frequency q Axial components; D m This is the self-damping coefficient;

[0014] The mathematical model of a permanent magnet synchronous generator is expressed as follows:

[0015]

[0016] In the formula, R s Stator resistance; ω s= n p Ω s The electrical angular velocity of the generator rotor; and These are the output voltages of the machine-side converter. positive sequence fundamental frequency d shaft and q Axial components; L sd and L sq stator d shaft and q Shaft inductance.

[0017] As a preferred technical solution, the mathematical model of the AC-DC-AC power converter includes a mathematical model of the DC capacitor voltage in the time domain, a mathematical model of the three-phase modulation signal of the machine-side converter and the grid-side converter, and a mathematical model of the machine-side converter and the grid-side converter in the time domain.

[0018] The mathematical model of the DC capacitor voltage in the time domain is expressed as follows:

[0019]

[0020] In the formula, This is the DC capacitor voltage; It is a DC capacitor; This indicates that a, b, and c are in phase; and This indicates the AC voltage and current output from the machine-side converter; and This indicates the AC voltage and current output of the grid-side converter;

[0021] The mathematical model expression for the three-phase modulation signal of the machine-side converter is shown below:

[0022]

[0023] In the formula, , and These represent the three-phase modulation signals of the machine-side converter; and These are the modulation ratio and phase shift angle of the positive sequence modulation signal of the machine-side converter, respectively.

[0024] The mathematical model expression for the three-phase modulation signal of the grid-side converter is shown below:

[0025]

[0026] In the formula, , and These represent the three-phase modulation signals of the grid-side converter. and These represent the modulation ratio and phase shift angle of the positive sequence modulation signal of the grid-side converter, respectively. and These represent the modulation ratio and phase shift angle of the negative sequence modulation signal of the grid-side converter, respectively. ω The angular frequency of the AC power grid;

[0027] The mathematical models of the generator-side converter and the grid-side converter in the time domain are expressed as follows:

[0028]

[0029] In the formula, express , or ; express , or .

[0030] As a preferred technical solution, the dq-sequence dynamic phasor modeling method is used to transform the mathematical model of the AC-DC-AC power converter to obtain the corresponding dq-sequence dynamic phasor model, including:

[0031] The dq-sequence dynamic phasor modeling method is used to transform the mathematical model of the DC capacitor voltage in the time domain into a dq-sequence dynamic phasor model, the expression of which is shown below:

[0032]

[0033] In the formula, the superscript of the variable , 0 and 0 represent positive, negative, and zero sequence, respectively; the subscript numbers 0, 1, and 2 represent DC, fundamental frequency, and second harmonic frequency components, respectively; subscript d and q They represent d and q Axis components; subscripts r and i represent the real and imaginary parts, respectively; Indicates DC capacitor voltage The zero-sequence DC real component; and These represent the DC capacitor voltages respectively. The real and imaginary parts of the zero-sequence second harmonic; and These represent the modulation signals of the machine-side converter. The positive-sequence fundamental frequency d-axis and q-axis components; and These represent the modulation signals of the grid-side converter. The positive-sequence fundamental frequency d-axis and q-axis components; and These represent the modulation signals of the grid-side converter. The negative-order fundamental frequency d-axis and q-axis components; Indicates the AC output current of the machine-side converter. positive sequence fundamental frequency d Axial components; and These represent the output current of the grid-side converter, respectively. positive sequence fundamental frequency d shaft and q Axial components; and These represent the output current of the grid-side converter, respectively. negative sequence fundamental frequency d q-axis and q-axis components;

[0034] The dq-sequence dynamic phasor modeling method is used to transform the mathematical models of the machine-side converter and the grid-side converter in the time domain into dq-sequence dynamic phasor models, the expressions of which are shown below:

[0035]

[0036] In the formula, and These represent the AC output voltages of the grid-side converter, respectively. The positive-sequence fundamental frequency d-axis and q-axis components; and These represent the AC output voltages of the grid-side converter, respectively. The negative-order fundamental frequency d-axis and q-axis components;

[0037] in,

[0038]

[0039]

[0040] In the formula, for Reference value; for Reference value; for Reference value; for Reference value; for Reference value; for Reference values.

[0041] As a preferred technical solution, the mathematical model of the filter circuit is expressed as follows:

[0042]

[0043] In the formula, Indicates the inductance of the filter circuit. Indicates the resistance of the filter circuit;

[0044] The mathematical model of the filter circuit is transformed using the dq-order dynamic phasor modeling method, and the corresponding dq-order dynamic phasor model is obtained, the expression of which is shown below:

[0045]

[0046] In the formula, and PCC voltage The positive-sequence fundamental frequency d-axis and q-axis components; and PCC voltage The negative-sequence fundamental frequency d-axis and q-axis components.

[0047] As a preferred technical solution, the output current of the grid-side converter i g and PCC voltage u g Each is equipped with a set of phase sequence separation stages, in order to i g For example, the mathematical model expression for the phase sequence separation stage is shown below:

[0048]

[0049] In the formula, , , and The grid-side converter output current extracted by the phase sequence separation stage is respectively positive sequence fundamental frequency d Axial components, positive sequence fundamental frequency q Axial components, negative sequence fundamental frequency d Axial components and negative sequence fundamental frequency q Axial components; ω i This is the cutoff frequency of the current phase sequence separation stage; θ pll This refers to the phase output of the phase-locked loop; , , , It is an intermediate variable.

[0050] The mathematical model of a phase-locked loop is expressed as follows:

[0051]

[0052] In the formula, x a1 and x a2 These are the state variables of the phase-locked loop. k ppll , k ipll These are the proportional and integral parameters of the phase-locked control, respectively. PCC voltage extracted for phase sequence separation stage positive sequence fundamental frequency q Axial components; ω pll and θ pll These are the angular velocity and angle output by the phase-locked loop.

[0053] As a preferred technical solution, the mathematical model of the machine-side converter control system is expressed as follows:

[0054]

[0055] In the formula, x 1. x 2 and x 3 are machine-side converters d Shaft current control, and state variables introduced by outer and inner loop constant speed control; for Reference value; for Reference value; for Reference value; for Reference value; for Reference value; k p1 and k i1 For machine-side converters d The proportional and integral parameters of the inner-loop control. k p2 and k i2 For machine-side converters q The proportional and integral parameters of the outer loop control. k p3 and k i3 For machine-side converters qThe proportional and integral parameters of the inner-loop control.

[0056] As a preferred technical solution, the mathematical model of the grid-side converter control system is expressed as follows:

[0057]

[0058] In the formula, x 4. x 5 and x 6 represents the positive sequence outer and inner loops of the grid-side converter. d shaft and q State variables introduced by shaft current control; x 7 and x 8 represents the negative sequence of the inner loop of the grid-side converter. d and q State variables introduced by shaft current control; and PI parameters for outer loop DC voltage control; k p5 and k i5 Inner ring d PI parameters for shaft current control; k p6 and k i6 Inner ring q PI parameters for shaft current control; for Reference value; for Reference value; for Reference value; for Reference value; for Reference value; for Reference value; for Reference value; for Reference value; u gd1m + , u gq1m + The PCC voltage extracted from the phase sequence separation stage is respectively positive sequence fundamental frequency d, q Axial components; u gd1m - and u gq1m -PCC voltage extracted for phase sequence separation stage negative sequence fundamental frequency d, q Axial components.

[0059] As a preferred technical solution, the linear time-invariant model and the linear periodic time-varying model are integrated, and algebraic variables are eliminated to obtain the state-space small-signal model of the direct-drive permanent magnet wind power grid-connected system, the expression of which is shown below:

[0060]

[0061] In the formula, Indicates small perturbation quantities; For state variables, The state matrix, For the input matrix, For input variables;

[0062] in, The expression is as follows:

[0063]

[0064] In the formula, all The quantity represents a small perturbation to the corresponding variable;

[0065] The expression is as follows:

[0066]

[0067] In the formula, all The quantity represents a small perturbation to the corresponding variable;

[0068] The expression is as follows:

[0069]

[0070] The expression is as follows:

[0071] .

[0072] Secondly, this invention also proposes an application method for a state-space small-signal model of a direct-drive permanent magnet wind power grid-connected system under AC asymmetric operating conditions. The method constructs a state-space small-signal model of the direct-drive permanent magnet wind power grid-connected system using the modeling method described in any of the above schemes, including:

[0073] Apply a small disturbance to the direct-drive permanent magnet wind power grid-connected system, obtain the dynamic response of the direct-drive permanent magnet wind power grid-connected system through the state space small-signal model of the direct-drive permanent magnet wind power grid-connected system, or directly perform small disturbance stability analysis based on the state space small-signal model of the direct-drive permanent magnet wind power grid-connected system.

[0074] The beneficial effects of the present invention include at least the following:

[0075] This invention establishes a mathematical model that includes core components such as the phase sequence separation stage, thus fully incorporating the key components and control links of a direct-drive permanent magnet wind power grid-connected system, avoiding model incompleteness due to component omissions. Linearization of components such as the wind turbine shaft system yields the LTI model. The power converter and filter circuit models are transformed using the dq-sequence dynamic phasor modeling method. Furthermore, the trajectories of the phase sequence separation stage, the grid-side converter control system model, and the dq-sequence dynamic phasor model are linearized to obtain the LTP model, which can adapt to the time-varying characteristics and key variable-derived frequency components under grid voltage imbalance conditions, overcoming the accuracy limitations of single modeling methods. Finally, by integrating the two models and eliminating algebraic variables, the resulting state-space small-signal model can more accurately and completely characterize the small-interference characteristics of a direct-drive permanent magnet wind power grid-connected system under AC asymmetric conditions. Attached Figure Description

[0076] Figure 1 This is a flowchart illustrating the modeling method for the state space small-signal model of a direct-drive permanent magnet wind power grid-connected system provided in an embodiment of the present invention.

[0077] Figure 2 This is a schematic diagram of the electromagnetic transient simulation main circuit and control system of the direct-drive permanent magnet wind power grid-connected system provided in an embodiment of the present invention. Figure I .

[0078] Figure 3 This is a schematic diagram of the electromagnetic transient simulation main circuit and control system of the direct-drive permanent magnet wind power grid-connected system provided in an embodiment of the present invention. Figure II .

[0079] Figure 4 (a) is a simulation result diagram of the DC capacitor voltage of the electromagnetic transient and small-signal model provided by the embodiment of the present invention, in which the reference value of udc changes from 1800V to 95% of the original value at 4s.

[0080] Figure 4 (b) is a simulation result diagram of the grid-side phase a current of the electromagnetic transient and small-signal model provided by the embodiment of the present invention, in which the reference value of udc changes from 1800V to 95% of the original electromagnetic transient and small-signal model at 4s.

[0081] Figure 4(c) is a simulation result diagram of the grid-side active power of the electromagnetic transient and small-signal model provided by the embodiment of the present invention, in which the UDC reference value is changed from 1800V to 95% of the original value at 4s.

[0082] Figure 4 (d) is a simulation result diagram of the grid-side reactive power of the electromagnetic transient and small-signal model provided by the embodiment of the present invention, in which the UDC reference value changes from 1800V to 95% of its original value at 4s.

[0083] Figure 5 (a) is a rotational speed diagram of the DC capacitor voltage in the electromagnetic transient and small-signal model provided in the embodiment of the present invention, where the wind speed changes from 10 m / s to 11 m / s in 4 seconds.

[0084] Figure 5 (b) is a simulation result of the DC capacitor voltage of the electromagnetic transient and small-signal model provided in the embodiment of the present invention when the wind speed changes from 10 m / s to 11 m / s in 4 seconds.

[0085] Figure 5 (c) is a simulation result diagram of the grid-side active power of the electromagnetic transient and small-signal model provided in the embodiment of the present invention when the seasonal wind speed changes from 10m / s to 11m / s in 4s.

[0086] Figure 5 (d) is a simulation result of the grid-side phase a current in the electromagnetic transient and small-signal model provided by the embodiment of the present invention when the wind speed changes from 10 m / s to 11 m / s in 4 seconds.

[0087] Figure 6 Parameters of the grid-side controller for AC asymmetry provided in the embodiments of the present invention k p4 Simulation diagram of the time-domain response of the electromagnetic transient model during a step jump. Detailed Implementation

[0088] The embodiments of the present invention will be described below with reference to the accompanying drawings and preferred technical solutions. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be understood that the preferred technical solutions are only for illustrating the present invention and not for limiting the scope of protection of the present invention.

[0089] It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. Therefore, the drawings only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0090] In the following description, numerous details are explored to provide a more thorough explanation of embodiments of the invention. However, it will be apparent to those skilled in the art that embodiments of the invention may be practiced without these specific details. In other embodiments, well-known structures and devices are shown in block diagram form rather than in detail to avoid obscuring embodiments of the invention.

[0091] Example 1

[0092] This embodiment proposes a modeling method for the state-space small-signal model of a direct-drive permanent magnet wind power grid-connected system under AC asymmetric operating conditions, such as... Figure 1 As shown, Figure 1 This is a flowchart illustrating a modeling method for a small-signal state-space model of a direct-drive permanent magnet wind power grid-connected system under AC asymmetric operating conditions, provided by an embodiment of the present invention. The method includes the following steps:

[0093] S1: Establish mathematical models for each core component of the direct-drive permanent magnet wind power grid-connected system. The core components include the wind turbine shaft system, permanent magnet synchronous generator, AC-DC-AC power converter, filter circuit and control system. The control system includes a phase sequence separation link, a phase-locked loop, a turbine-side converter control system and a grid-side converter control system.

[0094] S2: Using the dq-sequence dynamic phasor modeling method, the mathematical models of the AC-DC-AC power converter and the filter circuit are transformed to obtain the corresponding dq-sequence dynamic phasor models;

[0095] S3: Linearize the mathematical models of the wind turbine shaft system, permanent magnet synchronous generator, phase-locked loop and generator-side converter control system at the steady-state operating point to obtain a linear time-invariant model;

[0096] S4: The mathematical models of the phase sequence separation link, the grid-side converter control system, and the dq sequence dynamic phasor model are linearized to obtain a linear periodic time-varying model.

[0097] S5: Integrate the linear time-invariant model and the linear periodic time-varying model, and eliminate algebraic variables to obtain the state-space small-signal model of the direct-drive permanent magnet wind power grid-connected system.

[0098] Understandably, this invention, by establishing a mathematical model that includes core components such as the phase sequence separation stage, can fully incorporate the key components and control links of a direct-drive permanent magnet wind power grid-connected system, avoiding model incompleteness due to component omissions. Linearization of components such as the wind turbine shaft system yields the LTI model. The dq-sequence dynamic phasor modeling method is used to transform the power converter and filter circuit models. Furthermore, the trajectories of the phase sequence separation stage, the grid-side converter control system model, and the dq-sequence dynamic phasor model are linearized to obtain the LTP model, which can adapt to the time-varying characteristics and key variable-derived frequency components under grid voltage imbalance conditions, overcoming the accuracy limitations of single modeling methods. Finally, by integrating the two models and eliminating algebraic variables, the resulting state-space small-signal model can more accurately and completely characterize the small-interference characteristics of a direct-drive permanent magnet wind power grid-connected system under AC asymmetric conditions.

[0099] Example 2

[0100] This embodiment improves upon the modeling method of the state space small-signal model of the direct-drive permanent magnet wind power grid-connected system proposed in Embodiment 1.

[0101] It should be noted that, as Figure 2 and Figure 3 As shown, Figure 2 This is a schematic diagram of the electromagnetic transient simulation main circuit and control system of the direct-drive permanent magnet wind power grid-connected system provided in an embodiment of the present invention. Figure I , Figure 3 This is a schematic diagram of the electromagnetic transient simulation main circuit and control system of the direct-drive permanent magnet wind power grid-connected system provided in an embodiment of the present invention. Figure II The electromagnetic transient simulation main circuit and control system of the direct-drive permanent magnet wind power grid-connected system consists of a wind turbine and a permanent magnet synchronous generator (perm). a nent m a gnet synchronousgener a tor, PMSG), machine-side converter (m a It consists of a chine-side converter (MSC), a grid-side converter (GSC), DC capacitors, filter circuits, and a control system. (See diagram.) u sj , i sj This refers to the AC voltage and current output from the machine-side converter. u cj , i gj This refers to the AC voltage and current output from the grid-side converter. u dc This is the DC capacitor voltage; P s ,P g This refers to the power output from the DC capacitor to the machine-side converter and the grid-side converter. u gj The voltage is the PCC (Point of Common Coupling) voltage. R f , L f For the filter circuit's resistor and inductor. Of the voltage and current variables mentioned above, j = a b and c represent respectively a The three phases are b and c.

[0102] Due to the isolation provided by DC capacitors, wind turbines, permanent magnet synchronous generators (PMSGs), and turbine-side converters (MSCs) are less affected by grid imbalances. However, grid-side converters (GSCs), connected to the grid via filter circuits, are significantly affected by AC grid imbalances. Therefore, during modeling... u dc The left circuit is considered as a symmetrical case, and the right circuit (including) u dc The impact of grid voltage imbalance is then taken into account. Accordingly, the generator-side converter is only equipped with positive sequence control; the grid-side converter is equipped with both positive and negative sequence control, phase sequence separation circuit and phase-locked loop.

[0103] Machine-side converters typically employ rotor flux-oriented current vector control. Among these, q Shaft current corresponds to active power control. d Shaft current corresponds to reactive power control. The outer loop is typically set to zero reactive power. d The reference value for the shaft current is set to zero. When the wind speed changes, if the turbine-side converter adopts constant speed control, the value can be determined according to the maximum power point tracking requirement. q Reference value of rotor speed on outer ring Then, an inner loop is generated through PI control. q shaft current reference signal i sqref .

[0104] Positive sequence control of grid-side converters typically employs grid voltage-oriented vector control technology. Among these, d Shaft current corresponds to active power control. q The shaft current corresponds to reactive power control. This is achieved by adjusting the positive sequence. d Shaft current, maintaining constant DC bus voltage; by setting positive sequence q The shaft current reference value is zero, and the reactive power exchanged between the grid-side converter and the grid is zero. Negative-sequence control of the grid-side converter typically employs current suppression control. d Shaft current corresponds to active power control. qShaft current corresponds to reactive power control. Generally, negative sequence is set. d, q The shaft current reference value is zero. To implement the control strategy of the grid-side converter, a multiple repetition filter (MCCF) is used for phase sequence separation, and a phase-locked loop is used to obtain the phase of the point of common coupling (PCC) voltage.

[0105] In this embodiment, the mathematical model of the wind turbine shaft system is expressed as follows:

[0106]

[0107] In the formula, Ω s This refers to the mechanical angular velocity of the generator rotor. ρ a air density; R t The radius of the wind turbine blades; v C represents wind speed. p The wind energy utilization coefficient; J The total moment of inertia of the equivalent concentrated mass of the wind turbine and permanent magnet synchronous generator; n p This represents the number of pole pairs of the generator. ψ f It is a permanent magnet flux chain; AC current at the output of the machine-side converter positive sequence fundamental frequency q Axial components; D m This is the self-damping coefficient;

[0108] The mathematical model of a permanent magnet synchronous generator is expressed as follows:

[0109]

[0110] In the formula, R s Stator resistance; ω s= n p Ω s The electrical angular velocity of the generator rotor; and These are the output voltages of the machine-side converter. positive sequence fundamental frequency d shaft and q Axial components; L sd and L sq stator d shaft and q Shaft inductance.

[0111] It should be noted that the mathematical models of the wind turbine shaft system and the permanent magnet synchronous generator are both nonlinear time-invariant dynamic models.

[0112] In this embodiment, the mathematical model of the AC-DC-AC power converter includes the mathematical model of the DC capacitor voltage in the time domain, the mathematical model of the three-phase modulation signal of the machine-side converter and the grid-side converter, and the mathematical model of the machine-side converter and the grid-side converter in the time domain.

[0113] The mathematical model of the DC capacitor voltage in the time domain is expressed as follows:

[0114]

[0115] In the formula, This is the DC capacitor voltage; It is a DC capacitor; This indicates that a, b, and c are in phase; and This indicates the AC voltage and current output from the machine-side converter; and This indicates the AC voltage and current output of the grid-side converter;

[0116] The mathematical model expression for the three-phase modulation signal of the machine-side converter is shown below:

[0117]

[0118] In the formula, , and These represent the three-phase modulation signals of the machine-side converter; and These are the modulation ratio and phase shift angle of the positive sequence modulation signal of the machine-side converter, respectively.

[0119] The mathematical model expression for the three-phase modulation signal of the grid-side converter is shown below:

[0120]

[0121] In the formula, , and These represent the three-phase modulation signals of the grid-side converter. and These represent the modulation ratio and phase shift angle of the positive sequence modulation signal of the grid-side converter, respectively. and These represent the modulation ratio and phase shift angle of the negative sequence modulation signal of the grid-side converter, respectively. ω The angular frequency of the AC power grid;

[0122] The mathematical models of the generator-side converter and the grid-side converter in the time domain are expressed as follows:

[0123]

[0124] In the formula, express , or ; express , or .

[0125] It should be noted that the mathematical model of the AC-DC-AC power converter is established in the abc stationary coordinate system and is a nonlinear periodic time-varying model.

[0126] In this embodiment, the dq-sequence dynamic phasor modeling method is used to transform the mathematical model of the AC-DC-AC power converter to obtain the corresponding dq-sequence dynamic phasor model, including:

[0127] The dq-sequence dynamic phasor modeling method is used to transform the mathematical model of the DC capacitor voltage in the time domain into a dq-sequence dynamic phasor model, the expression of which is shown below:

[0128]

[0129] In the formula, the superscript of the variable , 0 and 0 represent positive, negative, and zero sequence, respectively; the subscript numbers 0, 1, and 2 represent DC, fundamental frequency, and second harmonic frequency components, respectively; subscript d and q They represent d and q Axis components; subscripts r and i represent the real and imaginary parts, respectively; Indicates DC capacitor voltage The zero-sequence DC real component; and These represent the DC capacitor voltages respectively. The real and imaginary parts of the zero-sequence second harmonic; and These represent the modulation signals of the machine-side converter. The positive-sequence fundamental frequency d-axis and q-axis components; and These represent the modulation signals of the grid-side converter. The positive-sequence fundamental frequency d-axis and q-axis components; and These represent the modulation signals of the grid-side converter. The negative-order fundamental frequency d-axis and q-axis components; Indicates the AC output current of the machine-side converter. positive sequence fundamental frequency d Axial components; and These represent the output current of the grid-side converter, respectively. positive sequence fundamental frequency d shaft and q Axial components; and These represent the output current of the grid-side converter, respectively. negative sequence fundamental frequency d q-axis and q-axis components;

[0130] The dq-sequence dynamic phasor modeling method is used to transform the mathematical models of the machine-side converter and the grid-side converter in the time domain into dq-sequence dynamic phasor models, the expressions of which are shown below:

[0131]

[0132] In the formula, and These represent the AC output voltages of the grid-side converter, respectively. The positive-sequence fundamental frequency d-axis and q-axis components; and These represent the AC output voltages of the grid-side converter, respectively. The negative-order fundamental frequency d-axis and q-axis components;

[0133] in,

[0134]

[0135]

[0136] In the formula, for Reference value; for Reference value; for Reference value; for Reference value; for Reference value; for Reference values.

[0137] In this embodiment, the mathematical model of the filter circuit is expressed as follows:

[0138]

[0139] In the formula, Indicates the inductance of the filter circuit. This represents the resistance of the filter circuit.

[0140] It should be noted that the mathematical model of the filter circuit is established in the abc stationary coordinate system and is a nonlinear periodic time-varying dynamic model.

[0141] The mathematical model of the filter circuit is transformed using the dq-order dynamic phasor modeling method, and the corresponding dq-order dynamic phasor model is obtained, the expression of which is shown below:

[0142]

[0143] In the formula, and PCC AC voltage The positive-sequence fundamental frequency d-axis and q-axis components; and PCC AC voltage The negative-sequence fundamental frequency d-axis and q-axis components.

[0144] It should be noted that, using dq The sequential dynamic phasor modeling method, after processing the original model of the electrical system (AC-DC-AC power converter, filter circuit) affected by the AC system, significantly reduces the periodic time-varying characteristics and significantly enhances the time-invariant characteristics. However, due to the consideration of DC capacitor voltage... u dc The second harmonic component in the model still results in a nonlinear periodic time-varying model.

[0145] In this embodiment, it is the output current of the grid-side converter. i g and PCC voltage u g Each is equipped with a set of phase sequence separation stages, in order to i g For example, the mathematical model expression for the phase sequence separation stage is shown below:

[0146]

[0147] In the formula, , , and The grid-side converter output current extracted by the phase sequence separation stage is respectively positive sequence fundamental frequency d Axial components, positive sequence fundamental frequency q Axial components, negative sequence fundamental frequency d Axial components and negative sequence fundamental frequency q Axial components; ω i This is the cutoff frequency of the current phase sequence separation stage; θ pllThis refers to the phase output of the phase-locked loop; , , , It is an intermediate variable.

[0148] It should be noted that, θ pll Since it is a function of time, the mathematical model of the phase sequence separation stage is a nonlinear periodic time-varying model.

[0149] The mathematical model of a phase-locked loop is expressed as follows:

[0150]

[0151] In the formula, x a1 and x a2 These are the state variables of the phase-locked loop. k ppll , k ipll These are the proportional and integral parameters of the phase-locked control, respectively. PCC voltage extracted for phase sequence separation stage positive sequence fundamental frequency q Axial components; ω pll and θ pll These are the angular velocity and angle output by the phase-locked loop.

[0152] It should be noted that the mathematical model of the phase-locked loop in the time domain is a nonlinear time-invariant model.

[0153] In this embodiment, the mathematical model of the machine-side converter control system is expressed as follows:

[0154]

[0155] In the formula, x 1. x 2 and x 3 are machine-side converters d Shaft current control, and state variables introduced by outer and inner loop constant speed control; for Reference value; for Reference value; for Reference value; for Reference value; for Reference value; k p1 and ki1 For machine-side converters d The proportional and integral parameters of the inner-loop control. k p2 and k i2 For machine-side converters q The proportional and integral parameters of the outer loop control. k p3 and k i3 For machine-side converters q The proportional and integral parameters of the inner-loop control.

[0156] It should be noted that the mathematical model of the machine-side converter control system is a nonlinear time-invariant model.

[0157] In this embodiment, the mathematical model of the grid-side converter control system is expressed as follows:

[0158]

[0159] In the formula, x 4. x 5 and x 6 represents the positive sequence outer and inner loops of the grid-side converter. d shaft and q State variables introduced by shaft current control; x 7 and x 8 represents the negative sequence of the inner loop of the grid-side converter. d and q State variables introduced by shaft current control; and PI parameters for outer loop DC voltage control; k p5 and k i5 Inner ring d PI parameters for shaft current control; k p6 and k i6 Inner ring q PI parameters for shaft current control; for Reference value; for Reference value; for Reference value; for Reference value; for Reference value; for Reference value; for Reference value; for Reference value; u gd1m + , u gq1m + The PCC voltage extracted from the phase sequence separation stage is respectively positive sequence fundamental frequency d, q Axial components; u gd1m - and u gq1m - PCC voltage extracted for phase sequence separation stage negative sequence fundamental frequency d, q Axial components.

[0160] It should be noted that the coefficients of the mathematical model for the grid-side converter control system include time variables. t This model is a nonlinear periodic time-varying model.

[0161] In this embodiment, the linear time-invariant model and the linear periodic time-varying model are integrated, and algebraic variables are eliminated to obtain the state-space small-signal model of the direct-drive permanent magnet wind power grid-connected system, the expression of which is as follows:

[0162]

[0163] In the formula, Indicates small perturbation quantities; For state variables, The state matrix, For the input matrix, For input variables;

[0164] in, The expression is as follows:

[0165]

[0166] In the formula, all The quantity represents the small perturbation of the corresponding variable.

[0167] The expression is as follows:

[0168]

[0169] In the formula, all The quantity represents the small perturbation of the corresponding variable.

[0170] The expression is as follows:

[0171]

[0172] The expression is as follows:

[0173]

[0174] Where the number *×* in the subscript parentheses represents the size of the matrix, and:

[0175]

[0176]

[0177] Example 3

[0178] This embodiment proposes an application method for the state-space small-signal model of a direct-drive permanent magnet wind power grid-connected system under AC asymmetric operating conditions. The method constructs the state-space small-signal model of the direct-drive permanent magnet wind power grid-connected system using the modeling method described in any of the above embodiments, including: applying a small disturbance to the direct-drive permanent magnet wind power grid-connected system, obtaining the dynamic response of the direct-drive permanent magnet wind power grid-connected system through the state-space small-signal model, or directly performing small-disturbance stability analysis based on the state-space small-signal model of the direct-drive permanent magnet wind power grid-connected system.

[0179] Build using Simulink Figure 2 and Figure 3 The electromagnetic transient model simulation main circuit and control system diagram of the direct-drive permanent magnet wind power grid-connected system is shown in Table 1. The system parameters are also shown in Table 1. Meanwhile, the system described in Example 2 is encapsulated in the Simulink platform. Figure 2 and Figure 3 The state-space small-signal model of the corresponding direct-drive permanent magnet wind power grid-connected system. The initial wind speed of the system is known to be 10 m / s, the rated voltage amplitude of the PCC is 690 V, and the voltage imbalance of the PCC is 4% (i.e., 27.6 V).

[0180] Table 1 Parameters of Direct-Drive Permanent Magnet Wind Power Grid-Connected System

[0181]

[0182] This embodiment verifies the accuracy and effectiveness of the present invention from two perspectives. First, two small disturbances are set up, and the consistency between the electromagnetic transient simulation and the simulation results of the small-signal model of the present invention is compared. Second, a sudden change in control parameters is set up to cause the system to become unstable due to small disturbances. At this time, the dominant oscillation mode of the system is fully excited, and the consistency between the oscillation frequency shown by the time-domain simulation curve and the oscillation frequency obtained by the small-signal model analysis is compared.

[0183] like Figure 4 As shown, Figure 4 (a) The 4s time command provided in the embodiment of the present invention u dc The simulation results of the DC capacitor voltage in the electromagnetic transient and small-signal model are shown, with the reference value changing from 1800V to 95% of the original value. Figure 4 (b) The 4s time command provided in the embodiment of the present invention u dc The simulation results of the grid-side phase a current under the electromagnetic transient and small-signal model are shown in the figure, where the reference value is changed by a step from 1800V to 95% of the original value. Figure 4 (c) The 4s time command provided in the embodiment of the present invention u dc The simulation results of the grid-side active power under the electromagnetic transient and small-signal model are shown in the figure, where the reference value changes by a step from 1800V to 95% of the original value. Figure 4 (d) is the 4s time command provided in the embodiment of the present invention. u dc The simulation results of the grid-side reactive power under the electromagnetic transient and small-signal models are shown in the figure. The green and black solid lines represent the simulation results of the electromagnetic transient and small-signal models, respectively.

[0184] like Figure 5 As shown, Figure 5 (a) is a rotational speed diagram of the DC capacitor voltage in the electromagnetic transient and small-signal model provided in the embodiment of the present invention when the wind speed changes from 10 m / s to 11 m / s in 4 seconds. Figure 5 (b) is a simulation result of the DC capacitor voltage of the electromagnetic transient and small-signal model provided in the embodiment of the present invention when the seasonal wind speed changes from 10 m / s to 11 m / s in 4 seconds. Figure 5 (c) is a simulation result diagram of the grid-side active power of the electromagnetic transient and small-signal model provided in the embodiment of the present invention when the seasonal wind speed changes from 10 m / s to 11 m / s in 4 seconds. Figure 5 (d) is a simulation result diagram of the grid-side phase a current of the electromagnetic transient and small-signal model provided by the embodiment of the present invention when the seasonal wind speed changes from 10m / s to 11m / s in 4s. The green and black solid lines represent the simulation results of the electromagnetic transient and small-signal models, respectively.

[0185] Depend on Figure 4 and Figure 5 It can be seen that the DC capacitor voltage, grid-side active power, and grid-side reactive power exhibit second harmonic fluctuations. The second harmonic fluctuations of grid-side active power and grid-side reactive power are particularly significant. The simulation results of the small-signal model and the electromagnetic transient model are in good agreement, demonstrating the correctness of the state-space small-signal model given in this invention.

[0186] like Figure 6 As shown, Figure 6 Parameters of the grid-side controller for AC asymmetry provided in the embodiments of the present invention k p4 The time-domain response simulation diagram of the electromagnetic transient model during a step jump is shown. Keeping other parameters constant, the proportional gain kp4 of the DC voltage outer loop controller in the electromagnetic transient simulation model is set to jump from 1 to 0.15 in 5s. It can be seen that the system exhibits divergent oscillations with a period of 0.271s and a corresponding oscillation frequency of 1 / 0.271 = 3.690Hz. The characteristic exponent is then calculated using the LTP small-signal model established in this invention, yielding the dominant oscillation mode as (0.7696 ± 23.2134i). The real part of the characteristic exponent is positive, indicating system instability; the oscillation frequency corresponding to the imaginary part is 23.2134 / (2π) = 3.695Hz, which matches well with the oscillation frequency of 3.690Hz obtained from the electromagnetic transient simulation, further verifying the correctness of the small-signal model.

[0187] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0188] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "N" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0189] Any process or method description in the flowchart or otherwise herein can be understood as representing a module, segment, or portion of code comprising one or more N executable instructions for implementing custom logic functions or processes, and the scope of preferred embodiments of the invention includes additional implementations in which functions may be performed not in the order shown or discussed, including substantially simultaneously or in reverse order depending on the functions involved, as should be understood by those skilled in the art to which embodiments of the invention pertain.

[0190] It should be understood that various parts of the present invention can be implemented in hardware, software, firmware, or a combination thereof. In the above embodiments, the N steps or methods can be implemented in software or firmware stored in memory and executed by a suitable instruction execution system. For example, if implemented in hardware as in another embodiment, it can be implemented using any of the following techniques known in the art, or a combination thereof: discrete logic circuits having logic gates for implementing logical functions on data signals, application-specific integrated circuits (ASICs) having suitable combinational logic gates, programmable gate arrays (FPGAs), field-programmable gate arrays (FPGAs), etc.

[0191] Those skilled in the art will understand that all or part of the steps of the methods described in the above embodiments can be implemented by a program instructing related hardware, and the program can be stored in a computer-readable storage medium. When executed, the program includes one or a combination of the steps of the method embodiments.

[0192] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for modeling a state space small signal model of a direct-drive permanent-magnet wind power grid-connected system under an AC asymmetric operating condition, characterized in that, include: Mathematical models of the core components of a direct-drive permanent magnet wind power grid-connected system are established. The core components include the wind turbine shaft system, permanent magnet synchronous generator, AC-DC-AC power converter, filter circuit and control system. The control system includes a phase sequence separation link, a phase-locked loop, a turbine-side converter control system and a grid-side converter control system. The output current of the grid-side converter i g and PCC voltage u g Each is equipped with a phase sequence separation circuit, wherein the grid-side converter output current is... i g The mathematical model for the phase sequence separation process is expressed as follows: In the formula, , , and The grid-side converter output current extracted by the phase sequence separation stage is respectively positive sequence fundamental frequency d Axial components, positive sequence fundamental frequency q Axial components, negative sequence fundamental frequency d Axial components and negative sequence fundamental frequency q Axial components; ω i This is the cutoff frequency of the current phase sequence separation stage; θ pll This refers to the phase output of the phase-locked loop; , , , As an intermediate variable; The dq-sequence dynamic phasor modeling method is used to transform the mathematical model of the DC capacitor voltage in the time domain into a dq-sequence dynamic phasor model, the expression of which is shown below: In the formula, the superscript of the variable , 0 and 0 represent positive, negative, and zero sequence, respectively; the subscript numbers 0, 1, and 2 represent DC, fundamental frequency, and second harmonic frequency components, respectively; subscript d and q They represent d and q Axis components; subscripts r and i represent the real and imaginary parts, respectively; Indicates DC capacitor voltage The zero-sequence DC real component; and These represent the DC capacitor voltages respectively. The real and imaginary parts of the zero-sequence second harmonic; and These represent the modulation signals of the machine-side converter. The positive-sequence fundamental frequency d-axis and q-axis components; and These represent the modulation signals of the grid-side converter. The positive-sequence fundamental frequency d-axis and q-axis components; and These represent the modulation signals of the grid-side converter. The negative-order fundamental frequency d-axis and q-axis components; Indicates the AC output current of the machine-side converter. positive sequence fundamental frequency d Axial components; and These represent the output current of the grid-side converter, respectively. positive sequence fundamental frequency d shaft and q Axial components; and These represent the output current of the grid-side converter, respectively. negative sequence fundamental frequency d q-axis and q-axis components; It is a DC capacitor; Indicates the AC output current of the machine-side converter. positive sequence fundamental frequency q Axial components; The dq-sequence dynamic phasor modeling method is used to transform the mathematical models of the machine-side converter and the grid-side converter in the time domain into dq-sequence dynamic phasor models, the expressions of which are shown below: In the formula, and These represent the AC output voltages of the grid-side converter, respectively. The positive-sequence fundamental frequency d-axis and q-axis components; and These represent the AC output voltages of the grid-side converter, respectively. The negative-order fundamental frequency d-axis and q-axis components; and These are the output voltages of the machine-side converter. positive sequence fundamental frequency d shaft and q Axial components; in, In the formula, for Reference value; for Reference value; for Reference value; for Reference value; for Reference value; for Reference value; and These are the modulation ratio and phase shift angle of the positive sequence modulation signal of the machine-side converter, respectively. and These represent the modulation ratio and phase shift angle of the positive sequence modulation signal of the grid-side converter, respectively. and These represent the modulation ratio and phase shift angle of the negative sequence modulation signal of the grid-side converter, respectively. ω The angular frequency of the AC power grid; The mathematical models of the wind turbine shaft system, permanent magnet synchronous generator, phase-locked loop and generator-side converter control system are linearized at the steady-state operating point to obtain a linear time-invariant model; The mathematical models of the phase sequence separation stage, the grid-side converter control system, and the dq sequence dynamic phasor model are linearized to obtain a linear periodic time-varying model. By integrating the linear time-invariant model and the linear periodic time-varying model, and eliminating algebraic variables, a state-space small-signal model of the direct-drive permanent magnet wind power grid-connected system is obtained.

2. The modeling method for the state-space small-signal model of a direct-drive permanent magnet wind power grid-connected system under AC asymmetric operating conditions as described in claim 1, characterized in that, The mathematical model of the wind turbine shaft system is expressed as follows: In the formula, Ω s This refers to the mechanical angular velocity of the generator rotor. ρ a air density; R t The radius of the wind turbine blades; v C represents wind speed. p Wind energy utilization coefficient; J The total moment of inertia of the equivalent concentrated mass of the wind turbine and permanent magnet synchronous generator; n p This represents the number of pole pairs of the generator. ψ f For permanent magnet flux linkage; AC current at the output of the machine-side converter positive sequence fundamental frequency q Axial components; D m This is the self-damping coefficient; The mathematical model of a permanent magnet synchronous generator is expressed as follows: In the formula, R s Stator resistance; ω s= n p Ω s The electrical angular velocity of the generator rotor; and These are the output voltages of the machine-side converter. positive sequence fundamental frequency d shaft and q Axial components; L sd and L sq stator d shaft and q Shaft inductance.

3. The modeling method for the state-space small-signal model of a direct-drive permanent magnet wind power grid-connected system under AC asymmetric operating conditions as described in claim 2, characterized in that, The mathematical model of the AC-DC-AC power converter includes the mathematical model of the DC capacitor voltage in the time domain, the mathematical model of the three-phase modulation signal of the machine-side converter and the grid-side converter, and the mathematical model of the machine-side converter and the grid-side converter in the time domain. The mathematical model of the DC capacitor voltage in the time domain is expressed as follows: In the formula, This is the DC capacitor voltage; It is a DC capacitor; This indicates that a, b, and c are in phase; and This indicates the AC voltage and current output from the machine-side converter; and This indicates the AC voltage and current output of the grid-side converter; The mathematical model expression for the three-phase modulation signal of the machine-side converter is shown below: In the formula, , and These represent the three-phase modulation signals of the machine-side converter; and These are the modulation ratio and phase shift angle of the positive sequence modulation signal of the machine-side converter, respectively. The mathematical model expression for the three-phase modulation signal of the grid-side converter is shown below: In the formula, , and These represent the three-phase modulation signals of the grid-side converter. and These represent the modulation ratio and phase shift angle of the positive sequence modulation signal of the grid-side converter, respectively. and These represent the modulation ratio and phase shift angle of the negative sequence modulation signal of the grid-side converter, respectively. ω The angular frequency of the AC power grid; The mathematical models of the generator-side converter and the grid-side converter in the time domain are expressed as follows: In the formula, express , or ; express , or .

4. The modeling method for the state-space small-signal model of a direct-drive permanent magnet wind power grid-connected system under AC asymmetric operating conditions as described in claim 3, characterized in that, The mathematical model of the filter circuit is expressed as follows: In the formula, Indicates the inductance of the filter circuit. Indicates the resistance of the filter circuit; The mathematical model of the filter circuit is transformed using the dq-order dynamic phasor modeling method, and the corresponding dq-order dynamic phasor model is obtained, the expression of which is shown below: In the formula, and PCC voltage The positive-sequence fundamental frequency d-axis and q-axis components; and PCC voltage The negative-sequence fundamental frequency d-axis and q-axis components.

5. The modeling method for the state-space small-signal model of a direct-drive permanent magnet wind power grid-connected system under AC asymmetric operating conditions as described in claim 4, characterized in that, The mathematical model of a phase-locked loop is expressed as follows: In the formula, x a1 and x a2 These are the state variables of the phase-locked loop. k ppll , k ipll These are the proportional and integral parameters of the phase-locked control, respectively. PCC voltage extracted for phase sequence separation stage positive sequence fundamental frequency q Axial components; ω pll and θ pll These are the angular velocity and angle output by the phase-locked loop.

6. The modeling method for the state-space small-signal model of a direct-drive permanent magnet wind power grid-connected system under AC asymmetric operating conditions as described in claim 5, characterized in that, The mathematical model of the machine-side converter control system is expressed as follows: In the formula, x 1. x 2 and x 3 are machine-side converters d Shaft current control, and state variables introduced by outer and inner loop constant speed control; for Reference value; for Reference value; for Reference value; for Reference value; for Reference value; k p1 and k i1 For machine-side converters d The proportional and integral parameters of the inner-loop control. k p2 and k i2 For machine-side converters q The proportional and integral parameters of the outer loop control. k p3 and k i3 For machine-side converters q The proportional and integral parameters of the inner-loop control.

7. The modeling method for the state-space small-signal model of a direct-drive permanent magnet wind power grid-connected system under AC asymmetric operating conditions as described in claim 6, characterized in that, The mathematical model of the grid-side converter control system is expressed as follows: In the formula, x 4. x 5 and x 6 represents the positive sequence outer and inner loops of the grid-side converter. d shaft and q State variables introduced by shaft current control; x 7 and x 8 represents the negative sequence of the inner loop of the grid-side converter. d and q State variables introduced by shaft current control; and PI parameters for outer loop DC voltage control; k p5 and k i5 Inner ring d PI parameters for shaft current control; k p6 and k i6 Inner ring q PI parameters for shaft current control; for Reference value; for Reference value; for Reference value; for Reference value; for Reference value; for Reference value; for Reference value; for Reference value; u gd1m + , u gq1m + The PCC voltage extracted from the phase sequence separation stage is respectively positive sequence fundamental frequency d, q Axial components; u gd1m - and u gq1m - PCC voltage extracted for phase sequence separation stage negative sequence fundamental frequency d, q Axial components.

8. The modeling method for the state-space small-signal model of a direct-drive permanent magnet wind power grid-connected system under AC asymmetric operating conditions as described in claim 7, characterized in that, By integrating the linear time-invariant model and the linear periodic time-varying model, and eliminating algebraic variables, the state-space small-signal model of the direct-drive permanent magnet wind power grid-connected system is obtained, and its expression is shown below: In the formula, Indicates small perturbation quantities; For state variables, The state matrix, For the input matrix, For input variables; in, The expression is as follows: In the formula, all The quantity represents a small perturbation to the corresponding variable; The expression is as follows: In the formula, all The quantity represents a small perturbation to the corresponding variable; The expression is as follows: The expression is as follows: 。 9. A method for applying a state-space small-signal model of a direct-drive permanent magnet wind power grid-connected system under AC asymmetric operating conditions, comprising constructing a state-space small-signal model of the direct-drive permanent magnet wind power grid-connected system using the modeling method described in any one of claims 1 to 8, characterized in that, include: Apply a small disturbance to the direct-drive permanent magnet wind power grid-connected system, obtain the dynamic response of the direct-drive permanent magnet wind power grid-connected system through the state space small-signal model of the direct-drive permanent magnet wind power grid-connected system, or directly perform small disturbance stability analysis based on the state space small-signal model of the direct-drive permanent magnet wind power grid-connected system.

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