Double-fed wind power plant resonance stability analysis method considering current measurement error

Abstract

The invention belongs to the technical field of transient stability of a power system, and particularly relates to a double-fed wind power plant resonance stability analysis method considering current measurement errors. According to the method, an alternating-current power transmission line model containing a series compensator and a doubly-fed wind power plant control link considering current measurement errors are modeled through an impedance analysis method, the transmission characteristic influence of the current measurement link is also considered, and positive and negative sequence impedance of an electromagnetic current transformer and a secondary cable thereof and a sampling resistor is modeled; the defects of an existing analysis method are overcome, on the basis of an existing doubly-fed wind power plant oscillation stability analysis method containing a series compensation power transmission line, transmission characteristics of a current measurement link are introduced into an inner loop current controller of a fan converter, and the defects of the existing analysis method are overcome.

Description

Technical Field

[0001] The invention belongs to the technical field of transient stability of electric power systems, and in particular relates to a method for analyzing resonance stability of a double-fed wind farm taking current measurement errors into consideration. Background Art

[0002] Subsynchronous oscillations in systems connected by doubly-fed wind turbines and containing series compensation lines will have an adverse impact on the safe and stable operation of the power grid. Although many scholars have explained the oscillation mechanism from multiple angles, they still cannot cover all actual subsynchronous oscillation accidents. For example, in December 2023, the subsynchronous oscillation phenomenon was monitored by the new energy station in Guyuan, northern Hebei. When the accident occurred, there was no switching equipment in the nearby station, and the oscillation divergence caused by external disturbances was excluded; the previous oscillation risk assessment also failed to explain the cause of this oscillation phenomenon. Subsynchronous oscillations contain a lot of energy. If their divergence cannot be suppressed in time, it will affect the stable operation of the power system and damage the life of electrical equipment. Therefore, considering a more complete impedance characteristic analysis method of the doubly-fed wind farm transmitted by series compensation in the subsynchronous frequency band is extremely important for evaluating the oscillation risk of the system.

[0003] The existing research methods for analyzing the oscillation stability of the double-fed wind farm transmitted by series compensation are mainly based on the impedance analysis method and the state space method. In terms of considerations, Wu Xi and others from Southeast University proposed a method for determining the cause of subsynchronous oscillation in the double-fed wind power grid-connected system in 2022 (publication number: CN115000982A). This method is to calculate and analyze the properties of each term in the subsynchronous modal energy balance equation on the source side and the grid side, and determine the cause of the subsynchronous oscillation according to the properties of the energy term, and provide a mechanism explanation for the subsynchronous oscillation problem of the double-fed wind power grid-connected system from the energy perspective; Chen Xiaolu and others from the Electric Power Research Institute of State Grid Inner Mongolia Eastern Electric Power Co., Ltd. proposed an analysis method for the influence of the control parameters of the double-fed wind farm on the subsynchronous oscillation in 2023 (publication number: CN116054190A). By establishing a non-time-varying model of each submodule of the double-fed wind turbine system, the eigenvalue analysis method was used to explore the influence of the PI parameters of the controller, and the sensitivity of each controller parameter to the subsynchronous oscillation was calculated to obtain the key parameters affecting the stable operation of the system, providing guidance and suggestions for the safe operation of the power grid. The above methods provide tools for analyzing oscillation stability, but do not consider more factors that may be involved in inducing oscillations. In 2021, Xue Ancheng and others from North China Electric Power University proposed a subsynchronous oscillation analysis method for doubly fed systems considering nonlinear links (publication number: CN112886644A), considering the participation of the limiting link and saturation characteristics in the control process of doubly fed wind turbines in the oscillation, and using the describing function method to approximate the nonlinear link. The influence of the static VAR generator is also taken into account, revealing the mechanism by which the limiting saturation link causes changes in system impedance. However, the wind turbine control strategy considered in this method is relatively simple, and the actual risk of subsynchronous oscillation of wind turbines is not accurately portrayed.

[0004] In summary, there is an urgent need for a resonant stability analysis method for a doubly fed wind farm that takes into account the current measurement error, considers the influence of the current measurement error in the controller, and does not simplify the original control mode of the doubly fed wind turbine generator set, so as to further improve the accuracy and reliability of subsynchronous oscillation risk assessment. Summary of the invention

[0005] The present invention provides a doubly-fed wind farm resonance stability analysis method taking into account current measurement errors, so as to solve the technical problems in the prior art that the existing analysis methods do not consider all factors and the wind turbine control strategy is simple, resulting in the inability to explain some actual oscillation phenomena and accurately evaluate the system stability.

[0006] In order to achieve the above object, the present invention adopts the following technical solution: A method for analyzing resonance stability of a doubly-fed wind farm considering current measurement errors comprises the following steps: Step 1: According to the structure and parameters of the AC transmission line with series compensator, a positive and negative sequence impedance network model of the AC transmission line is established; Step 2: According to the control method of the doubly-fed wind turbine generator set and taking into account the current measurement error, an equivalent impedance model of the doubly-fed wind farm containing multiple machines is established in the dq coordinate system; Step 3: According to the Nyquist impedance stability criterion, the positive and negative sequence impedance models of the AC transmission line and the equivalent impedance model of the doubly fed wind farm are plotted in the Bode diagram, and the system stability is judged based on the intersection of the two in the amplitude-frequency characteristic curve.

[0007] The positive and negative sequence impedance network model in step 1 is based on the Thevenin theorem, which equates the AC transmission line with series compensator to a circuit structure with resistors, inductors and capacitors in series, and establishes impedance two-port models of the transmission line with series compensator in the positive and negative sequence network respectively.

[0008] The positive and negative sequence impedance network model in step 1, when considering the coupling effect, is a 2-input 2-output network, that is, the impedance matrix size is 2×2.

[0009] When establishing the equivalent impedance model of the doubly fed wind farm, the rotating control vector in the abc three-phase stationary coordinate system is transferred to the stationary vector in the dq rotating coordinate system through Park transformation, and the corresponding dq domain two-port impedance network model is established according to the control logic of the doubly fed wind turbine.

[0010] According to the impedance transformation formula, the dq domain two-port impedance model is converted into a positive and negative sequence impedance network model, and finally the equivalent impedance model of the doubly fed wind farm is obtained. The impedance transformation formula is:

[0011]

[0012] In the formula, and They represent the impedance matrix and positive and negative sequence impedance matrix in the dq domain two-port impedance model respectively. Considering the coupling effect, both are 2×2 structures; V represents the rotation transformation matrix.

[0013] The equivalent impedance model of the doubly-fed wind farm is a 2-input 2-output model in the dq coordinate system, that is, the impedance matrix size is 2×2.

[0014] The equivalent impedance model of the doubly-fed wind farm includes a wind turbine impedance model. The wind turbine impedance model uses an asymmetric control of the wind turbine in the dq coordinate system. Therefore, the wind turbine impedance model should also be established in the dq coordinate system.

[0015] The doubly-fed wind farm equivalent impedance model also includes a circulating current controller impedance model. The wind turbine impedance model and the circulating current controller impedance model constitute a complete doubly-fed wind farm equivalent impedance model. When establishing the impedance model of the circulating current controller, the measurement error of the current inner loop controller should be introduced into the calculation of the impedance transfer function when calculating its impedance transfer function.

[0016] The measurement error of the current inner loop controller is calculated. According to the influence of the current measurement link, based on the electromagnetic current transformer, the current measurement environment impedance transfer function is established, and then the impedance network model of the current measurement link is established. The amplitude and phase errors introduced by the line current are calculated as the total error of the measurement link. The impedance network model of the current measurement link is substituted into the position of the current inner loop controller first to establish an equivalent impedance model of the doubly fed wind turbine considering the current measurement error. Several equivalent impedance models of doubly fed wind turbines are connected in parallel to form an equivalent impedance model of the doubly fed wind farm.

[0017] Comparing the impedance characteristics of the wind farm and the AC transmission line on both sides in the Bode diagram, there is a resonance point at the intersection of the amplitude-frequency characteristics of the two. If the phase margin corresponding to this point is insufficient, unstable oscillation will occur; otherwise, there is no oscillation risk.

[0018] Compared with the prior art, the present invention has the following beneficial effects: The present invention discloses a method for analyzing the resonance stability of a doubly-fed wind farm considering the current measurement error. The method uses an impedance analysis method to model an AC transmission line model containing a series compensator and a control link of a doubly-fed wind farm considering the current measurement error. Compared with similar research methods, the analysis method proposed in the present invention adopts the control link of a typical doubly-fed wind turbine set without simplified equivalence, and the obtained oscillation stability analysis result is more reliable. Considering the influence of the transmission characteristics of the current measurement link, the positive and negative sequence impedances of the electromagnetic current transformer and its secondary cable and sampling resistor are modeled, which makes up for the shortcomings of the existing analysis method, and the influence of the current measurement error on the stability analysis of the new energy station is introduced. Using the Nyquist impedance stability criterion, the positive and negative sequence network impedance model of the AC transmission line and the equivalent impedance model of the doubly-fed wind farm are plotted in the Bode diagram, and the system stability is judged based on the intersection of the two in the amplitude-frequency characteristic curve and the corresponding phase margin, which provides a clear, intuitive and reliable judgment basis for the stability evaluation of the system.

[0019] Furthermore, when establishing the equivalent impedance model of the doubly fed wind farm, the asymmetric control characteristics of the wind turbine in the dq coordinate system are fully taken into account, and the measurement error of the current inner loop controller is introduced into the impedance transfer function calculation of the circulating current controller. Compared with the existing method of simply handling the wind turbine control strategy, it can more accurately characterize the impact of the operating state of the wind turbine under complex working conditions on the system stability.

[0020] Furthermore, by considering the current measurement error and establishing the corresponding current measurement link impedance network model, and incorporating it into the equivalent impedance model of the doubly fed wind farm, compared with the existing analysis method, it can more accurately simulate the actual operating state of the system, avoid the deviation in the judgment of system stability caused by ignoring these errors, and improve the accuracy of the system stability analysis results.

[0021] Furthermore, when analyzing the resonant stability of the doubly-fed wind farm's transmission system via the series-compensated line, by judging the phase margin of the positive and negative sequence network impedance model of the AC transmission line and the equivalent impedance model of the doubly-fed wind farm in the Bode diagram, it is possible to accurately determine whether the system has an unstable oscillation risk, avoiding the ambiguity and uncertainty that may exist in previous analysis methods, and being able to better quantitatively evaluate the system stability, thereby providing strong support for the safe and stable operation of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 : The structure diagram of the double-fed wind farm system after series compensation; Figure 2 :Typical control block diagram of wind turbine grid-side and machine-side converters; Figure 3 :Schematic diagram of equivalent impedance of doubly-fed wind farm and transmission line; Figure 4 : Equivalent circuit diagram of the current measurement link proposed in the present invention; Figure 5 : Impedance spectrum of the double-fed wind farm transmitted through series compensation when the present invention is not implemented; Figure 6 : Control block diagram of wind turbine grid-side and machine-side converters after the introduction of the present invention; Figure 7 : Impedance spectrum of the doubly-fed wind farm after the implementation of the present invention. DETAILED DESCRIPTION

[0023] In order to further understand the content of the present invention, the present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the embodiments are only for explaining the present invention and are not intended to limit it.

[0024] The embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0025] The invention provides a method for analyzing resonance stability of a doubly-fed wind farm considering current measurement errors, comprising two parts: impedance modeling of an AC transmission line including series compensation and equivalent impedance modeling of a doubly-fed wind farm considering current measurement link errors.

[0026] Firstly, according to the structure and parameters of the AC transmission line with series compensator, the positive and negative sequence network impedance model of the AC transmission line with series compensator is established. According to the Thevenin theorem, the AC transmission line with series compensator is equivalent to a circuit structure of resistance, inductance and capacitance in series, and the impedance two-port model of the transmission line with series compensator in the positive and negative sequence network is established respectively. When the coupling effect is considered, the impedance model is a 2-input 2-output network, that is, the impedance matrix scale is 2×2.

[0027] Considering the influence of the current measurement link, the impedance network model of the current measurement link is established. Based on the electromagnetic current transformer, the impedance transfer function of the current measurement link is established, and then the impedance network model of the current measurement link is established. The current measurement circuit consists of an electromagnetic current transformer, an 800-meter cable on the secondary side, and a sampling resistor. Among them, the electromagnetic current transformer adopts the Г-type circuit equivalent, and the secondary side cable adopts the π-type circuit equivalent. The relevant parameters depend on the parameters of the actual transformer and cable.

[0028] Then, according to the typical control structure and control method of the doubly-fed wind turbine, the impedance model of the wind turbine and the converter controller is established in the dq coordinate system. The wind turbine impedance model and the circulating current controller impedance model together constitute the doubly-fed wind farm group impedance model. Several doubly-fed wind farm group impedance models are connected in parallel to form the doubly-fed wind farm equivalent impedance model. Among them, when establishing the wind turbine impedance model, since the wind turbine adopts asymmetric control in the dq coordinate system, when establishing the impedance model of the wind turbine, it should also be carried out in the dq coordinate system. The established equivalent impedance model of the doubly-fed wind turbine is a 2-input 2-output model in the dq coordinate system, that is, the impedance matrix scale is 2×2. When establishing the converter controller impedance model, the impedance transfer function of the converter controller is established, and the above-mentioned current measurement link impedance network model is substituted into the corresponding position of the current inner loop controller to establish the converter controller impedance model considering the current measurement error, thereby realizing the doubly-fed wind farm equivalent impedance model considering the current measurement error.

[0029] When establishing the equivalent impedance model of the doubly fed wind farm, the rotating control vector in the abc three-phase stationary coordinate system is transferred to the stationary vector in the dq rotating coordinate system through Park transformation, and the corresponding dq domain two-port impedance network model is established according to the control logic of the doubly fed wind turbine. Using the impedance transformation relationship between the impedance matrix in the dq coordinate system and the positive and negative sequence impedance matrix, the dq domain two-port impedance model is converted into a positive and negative sequence impedance network model, and finally the equivalent impedance model of the doubly fed wind farm is obtained, and its matrix structure remains unchanged at 2×2. The impedance transformation formula is:

[0030]

[0031] In the above formula, and They represent the impedance matrix and positive and negative sequence impedance matrix in the dq domain two-port impedance model respectively. Considering the coupling effect, both are 2×2 structures; V represents the rotation transformation matrix.

[0032] Finally, according to the Nyquist impedance stability criterion, the positive and negative sequence network impedance model of the AC transmission line and the equivalent impedance model of the doubly fed wind farm are plotted in the Bode diagram, and the system stability is judged based on the intersection of the two in the amplitude-frequency characteristic curve. The impedance characteristics of the doubly fed wind farm and the AC transmission line are compared in the Bode diagram. Taking the positive sequence impedance as an example, based on the Nyquist impedance stability criterion, when the phase margin corresponding to the intersection of the two amplitude-frequency characteristic curves is insufficient, the system will face the risk of unstable oscillation; otherwise, the system does not have the risk of oscillation. Because the positive and negative sequence network impedance model of the AC transmission line and the equivalent impedance model of the doubly fed wind farm are 2×2 matrices, the main diagonal is the positive and negative sequence self-impedance, and the secondary diagonal is the positive and negative sequence coupling impedance.

[0033] The double-fed wind farm system outputted via the AC transmission line with series compensation is as follows Figure 1 As shown in the figure, the system can be divided into three parts: 35kV low-voltage wind farm, 220kV transmission line and 500kV transmission line. Among them, the transmission line is equivalent to a resistor. r R and reactance x L The two step-up transformers step up the 35kV voltage to 220kV and 500kV respectively, and are equivalent to reactance. x T2 and x T3 .like Figure 2 As shown in the figure, it is a typical control block diagram of the back-to-back converter on the rotor side of the doubly-fed wind turbine of the present invention. The machine-side converter controller is used to control the power output of the unit to track the real-time wind speed command. A typical double closed-loop proportional integral (PI) controller is used. Its control logic is as follows Figure 2 (a); wherein: H p ( s ), H q ( s ) represent active power controller and reactive power controller respectively, H ri (s) is the inner loop current controller of the rotor side converter.

[0034] The grid-side commutation controller is used to maintain a constant voltage on the DC-side capacitor and adopts a typical PI control mode. Its control logic is as follows: Figure 2 (b); wherein: H vdc(s), H gi (s) represent the DC voltage controller and the inner loop current controller of the grid-side converter respectively. P g , Q g , V dc , i rdq , i gdq , θ s , θ r , m rabc , m gabc They respectively represent the active and reactive power of the unit, DC voltage, dq axis current of the rotor side and the grid side, synchronization angle of the grid side and the rotor side, and modulation reference signals of the converters of the rotor side and the grid side. The specific working principle does not belong to the core content of the present invention, so it is not repeated in the present invention.

[0035] A typical PI controller transfer function has the following form: (2) Based on the impedance analysis method, the impedance model of the AC transmission line with series compensation and the impedance model of the doubly fed wind farm considering the error of the current measurement link are established. The relationship between the two is as follows: Figure 3 As shown: The AC transmission system with series compensation consists of a step-up transformer, a transmission line and a series compensation capacitor. The positive and negative sequence network impedance model of the entire AC transmission system can be obtained according to the impedance series and parallel connection. The equivalent impedance of the AC transmission system with series compensation can be obtained by the Thevenin equivalent principle: (3) Consider Figure 4 The current measurement equivalent circuit shown in the figure, in which the electromagnetic current transformer is equivalent to a Г-type circuit, and the secondary side cable is equivalent to a π-type circuit. Here, taking phase A as an example, the same applies to phases B and C. R 1 and L 1 is the resistance and inductance of CT converted to the secondary side; R m and L m is the excitation resistance and inductance of CT; R 2 and L 2 is the equivalent resistance and parasitic inductance of the cable, C is the parasitic capacitance; R 0 is the sampling resistance, here it is 1Ω; I primary and I0 are the current to be measured and the sampling current respectively; I 1 and I 2 are the inductor branch currents respectively; U 1. U 2 and U secondary They are the voltage at the primary and secondary terminals of CT and the voltage on the resistor to be measured respectively.

[0036] According to the Thevenin equivalence theorem, the relationship between the current to be measured and the sampling current can be established: (4) in, (5) The corresponding control links are described in the dq domain coordinates. Combined with the asymmetric control characteristics of the commutation controller in the dq coordinate system, during the Park transformation, the frequency-related quantities will couple nonlinear terms as sub-diagonal elements. The voltage and current equations after Park transformation can be expressed as: (6) (7) (8) (9) (10) Combining equations (4) to (10), we can get the transfer function relationship between the secondary sampling current of the current measurement link and the actual current to be measured: (11) Where, the relevant transfer functions are as follows: (12) The Park transformation converts the electrical quantity in the abc three-phase stationary coordinate system into the electrical quantity in the dq rotating coordinate system. Its key parameter is the reference synchronization angle. θ p The Park transformation can be described by the following formula: (13) according to Figure 2 The typical control block diagram of the wind turbine converter can list the transfer function of the doubly fed wind turbine as follows: Since the wind turbine commutation controller adopts a typical PI control model, in the control of the rotor-side commutation controller, the outer loop is mainly used to track the output power command, while the outer loop of the grid-side commutation controller is used to maintain the constant DC voltage. Therefore, the transfer function relationship of the outer loop controller can be described as: (14) in, P dfig , P ref , Q dfig , Q ref are the output active power and reactive power of the doubly-fed wind turbine and their corresponding reference values ​​respectively; H vr , H vg They are the proportional-integral links of the outer loop controllers of the rotor-side and grid-side converters respectively.

[0037] The inner loop current controller also adopts the PI control mode. When the current measurement link is not considered, the transfer function relationship of the inner loop current controller can be established as follows: (15) The impedance transfer function of the doubly-fed wind turbine can be obtained by combining equations (14) and (15), and then the equivalent impedance model of the doubly-fed wind turbine is established. Several equivalent impedance models of doubly-fed wind turbines are connected in parallel to form an equivalent impedance model of a doubly-fed wind farm containing multiple machines. The impedance Bode diagram of the impedance transfer function of the doubly-fed wind turbine is drawn, as shown in Figure 5 As shown in the figure, the two have a resonance point near 9Hz, and the corresponding phase margin is 3.2°. According to the Nyquist impedance stability criterion, the system is stable at this time.

[0038] By introducing the above current measurement link, that is, equation (11), into the current inner loop controller, the control block diagram of the doubly fed wind turbine converter considering the current measurement error can be obtained as follows: Figure 6 As shown by the red frame line in the middle. At this time, the impedance Bode diagram corresponding to the system can be drawn as follows Figure 7 As shown in the figure, we can see that near the original resonance point (9Hz), the corresponding phase margin is -0.8°. According to the Nyquist impedance stability criterion, the system is unstable at this time.

[0039] It can be seen that after considering the error introduced in the current measurement link, the originally stable system becomes unstable, indicating that the transmission characteristics of the current measurement link play an important role in the oscillation stability analysis of the double-fed wind farm sent through the series-compensated transmission line. When analyzing similar projects in practice, the influence of the current measurement link must be considered to obtain more accurate and reliable stability analysis results.

[0040] The present invention solves the drawbacks of existing subsynchronous oscillation analysis methods, introduces the error of the current measurement link into the impedance stability analysis of the system, realizes the refined modeling of the doubly fed wind farm with series compensation, uses the Nyquist impedance stability criterion to judge the optimized system, achieves the goal of stability analysis of the entire new energy station, and the analysis result is more reliable.

[0041] In addition, it should be understood that although this specification is described in accordance with the implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation modes that can be understood by those skilled in the art. The above content is only to illustrate the technical idea of ​​the present invention, and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution according to the technical idea proposed by the present invention shall fall within the protection scope of the claims of the present invention.

Claims

1. A method for analyzing the resonance stability of a doubly-fed wind farm considering current measurement errors, characterized in that: The following steps are involved: Step 1: According to the structure and parameters of the AC transmission line with series compensator, the positive and negative sequence network impedance model of the AC transmission line is established; Step 2: According to the control method of the doubly-fed wind turbine generator set and taking into account the current measurement error, an equivalent impedance model of the doubly-fed wind farm containing multiple machines is established in the dq coordinate system; Step 3: According to the Nyquist impedance stability criterion, the positive and negative sequence network impedance model of the AC transmission line and the equivalent impedance model of the doubly fed wind farm are plotted in the Bode diagram, and the system stability is judged based on the intersection of the two in the amplitude-frequency characteristic curve.

2. A method for analyzing resonance stability of a doubly-fed wind farm considering current measurement error according to claim 1, characterized in that: The positive and negative sequence network impedance model in step 1 is based on the Thevenin theorem, which equates the AC transmission line containing a series compensator to a circuit structure in which a resistor, an inductor and a capacitor are connected in series, and an impedance two-port model of the transmission line containing a series compensator in the positive and negative sequence network is established respectively.

3. A method for analyzing resonance stability of a doubly-fed wind farm considering current measurement error according to claim 2, characterized in that: The positive and negative sequence network impedance model in step 1, when the coupling effect is considered, is a 2-input 2-output network, that is, the impedance matrix size is 2×2.

4. A method for analyzing resonance stability of a doubly-fed wind farm considering current measurement error according to claim 1, characterized in that: When establishing the equivalent impedance model of the doubly fed wind farm, the rotating control vector in the abc three-phase stationary coordinate system is transferred to the stationary vector in the dq rotating coordinate system through Park transformation, and the corresponding dq domain two-port impedance network model is established according to the control logic of the doubly fed wind turbine.

5. A method for analyzing resonance stability of a doubly-fed wind farm considering current measurement error according to claim 4, characterized in that: According to the impedance transformation formula, the dq domain two-port impedance model is converted into the positive and negative sequence impedance model of the doubly fed wind farm, and finally the equivalent impedance model of the doubly fed wind farm is obtained. The impedance transformation formula is: In the formula, and They represent the impedance matrix and positive and negative sequence impedance matrix in the dq domain two-port impedance model respectively. Considering the coupling effect, both are 2×2 structures; V represents the rotation transformation matrix.

6. A method for analyzing resonance stability of a doubly-fed wind farm considering current measurement error according to claim 5, characterized in that: The equivalent impedance model of the doubly-fed wind farm is a 2-input 2-output model in the dq coordinate system, that is, the impedance matrix size is 2×2.

7. A method for analyzing resonance stability of a doubly-fed wind farm considering current measurement error according to claim 6, characterized in that: The equivalent impedance model of the doubly-fed wind farm includes a wind turbine impedance model. The wind turbine used in the wind turbine impedance model is asymmetrically controlled in the dq coordinate system. Therefore, the wind turbine impedance model should also be established in the dq coordinate system.

8. A method for analyzing resonance stability of a doubly-fed wind farm considering current measurement error according to claim 7, characterized in that: The doubly-fed wind farm equivalent impedance model also includes a circulating current controller impedance model. The wind turbine impedance model and the circulating current controller impedance model constitute a doubly-fed wind farm group impedance model. Several doubly-fed wind turbine group equivalent impedance models are connected in parallel to form the doubly-fed wind farm equivalent impedance model. The impedance model of the circulating current controller is established by calculating its impedance transfer function. When calculating its impedance transfer function, the measurement error of the current inner loop controller should be introduced into the calculation of the impedance transfer function.

9. A method for analyzing resonance stability of a doubly-fed wind farm considering current measurement error according to claim 8, characterized in that: The current inner loop controller measurement error calculation is based on the influence of the current measurement link, and based on the electromagnetic current transformer, the current measurement link impedance transfer function is established, and then the current measurement link impedance network model is established, and the amplitude and phase errors introduced by the model using the line current are calculated as the total error of the measurement link, and the impedance network model of the current measurement link is substituted into the corresponding position of the current inner loop controller to establish the doubly fed wind farm equivalent impedance model considering the current measurement error.

10. The method for analyzing resonance stability of a doubly-fed wind farm considering current measurement error according to claim 1, characterized in that: Comparing the impedance characteristics of the wind farm and the AC transmission line on both sides in the Bode diagram, there is a resonance point at the intersection of the amplitude-frequency characteristics of the two. If the phase margin corresponding to this point is insufficient, unstable oscillation will occur. Otherwise, there is no risk of oscillation.

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