A method for measuring impedance of a doubly-fed wind turbine based on secondary-side disturbance

Abstract

The present invention discloses a method for measuring impedance of a doubly-fed wind turbine based on secondary-side disturbance, comprising: S1, injecting voltage disturbance at the voltage sampling point of the grid-side converter, recording the disturbance voltage and disturbance current output by the doubly-fed wind turbine side and the grid-side converter; S2, calculating the equivalent impedance of the wind turbine side port by the disturbance voltage and disturbance current on the wind turbine side; S3, injecting current disturbance at the current sampling point of the grid-side converter, recording the disturbance voltage and disturbance current output by the grid-side converter, and calculating the equivalent impedance of the grid-side converter by combining the disturbance voltage and disturbance current output by the grid-side converter; S4, calculating the equivalent impedance value of the doubly-fed wind turbine as a whole; S5, changing the frequency of the injected disturbance, repeating the above steps until the full-band impedance measurement is completed. The present invention adopts the above method to inject secondary-side disturbance into the voltage and current sampling points of the grid-side converter, and realizes the rapid measurement of the broadband impedance value of the doubly-fed wind turbine through the theoretical calculation formula.

Description

Technical Field

[0001] The invention relates to the technical field of wind power generation, and in particular to a method for measuring impedance of a double-fed wind turbine based on secondary-side disturbance. Background Art

[0002] With the continuous development of wind power generation technology, doubly-fed induction generation (DFIG) is an important wind turbine and is widely used in modern wind power generation systems. However, during the operation of wind turbines, especially in variable speed operation, they are often affected by various disturbance factors, such as wind speed fluctuations, load fluctuations, etc. These disturbances may cause the instability of the wind turbine working state, thereby affecting the output power quality and system safety of the wind farm. Therefore, accurate and real-time measurement of the impedance of wind turbines and the broadband impedance characteristics of doubly-fed wind turbines are of great significance for analyzing the small signal stability of wind farms. In practice, the broadband impedance characteristics of doubly-fed wind turbines are difficult to obtain. Especially in doubly-fed wind turbine systems, they are of great significance for fault diagnosis, operation optimization and system scheduling.

[0003] The broadband impedance characteristics of doubly-fed wind turbines are of great significance for analyzing the small signal stability of wind farms. By studying the broadband impedance characteristics, the impedance characteristics of wind turbines in different frequency ranges can be revealed, thus providing an important reference for the stability analysis of wind farms. However, in practice, the broadband impedance characteristics of doubly-fed wind turbines are difficult to obtain, mainly because their measurement process involves complex system behavior and dynamic response.

[0004] The existing wind turbine impedance measurement methods mainly include two categories: one is the impedance measurement method based on the actual device injection disturbance, and the other is the measurement method based on the hardware-in-the-loop experiment. The first method is the impedance measurement method based on the actual device injection disturbance. For example, Liu Wei et al. provided an online test method for wind farm impedance, in which the disturbance signal is superimposed on the reference wave signal in the static synchronous compensator (STATCOM) control link, so that STATCOM can output a disturbance voltage containing a disturbance component of a specific frequency, generate a disturbance current after passing through the export reactor, and then inject it into the wind farm through the AC bus. By extracting the disturbance current and voltage components of each branch current and each bus voltage, the impedance of each wind turbine branch is calculated. Similarly, Yu Yongjun et al. used a three-phase cascaded H-bridge converter as a harmonic disturbance source, injected a harmonic current of a specific frequency into the 35kV common bus of the wind farm, and measured the voltage and current of the disturbance injection port to obtain the input impedance of the wind farm.

[0005] This method involves modifying the controller of an existing device, such as using a STATCOM as a disturbance source to generate disturbances. This method has low applicability and cannot be implemented if the original system does not have extra STATCOMs. At the same time, the method of using an actual disturbance device is costly, complex to operate, and the switching process has a large impact on the original system.

[0006] The second method is a measurement method based on hardware-in-the-loop experiments. For example, Li Guanghui et al. took a doubly-fed asynchronous wind turbine as the research object and proposed a wind turbine impedance measurement method based on control hardware-in-the-loop. This method measures the impedance of the doubly-fed wind turbine by means of controller hardware-in-the-loop, but it is an offline measurement and cannot achieve real-time online wind turbine impedance measurement; in addition, the main circuit is built on the simulator and cannot fully reflect the actual main circuit characteristics.

[0007] Therefore, the existing impedance measurement methods have certain limitations and cannot meet the needs of wind turbines for accurate impedance measurement in actual operation. Summary of the invention

[0008] The purpose of the present invention is to provide a method for measuring impedance of a doubly-fed wind turbine based on secondary-side disturbance to solve the problems mentioned in the background technology.

[0009] To achieve the above object, the present invention provides a method for measuring impedance of a doubly-fed wind turbine based on secondary-side disturbance, comprising the following steps:

[0010] S1. At a certain disturbance frequency, a voltage disturbance is injected into the voltage sampling point of the grid-side converter, and the disturbance voltage and disturbance current output by the double-fed wind turbine side and the grid-side converter are recorded at the same time;

[0011] S2. Extract the disturbance component at the corresponding frequency through Fourier decomposition and calculate the equivalent impedance of the fan side port ;

[0012] S3, injecting current disturbance at the current sampling point of the grid-side converter, recording the disturbance voltage and disturbance current output by the grid-side converter, and combining the disturbance voltage and disturbance current output by the grid-side converter recorded in step S1 to calculate the equivalent impedance of the grid-side converter ;

[0013] S4. Calculate the overall impedance value of the doubly-fed wind turbine at the frequency;

[0014] S5. Change the frequency of the injected disturbance and repeat steps S1-S4 until the full-band impedance measurement of the doubly-fed wind turbine is completed.

[0015] Preferably, in S1, the injected voltage disturbance generates a three-phase voltage containing a disturbance component after passing through the controller of the grid-side converter, and outputs a three-phase current containing a disturbance component after passing through the filter inductor in the main circuit of the grid-side converter. The three-phase current is used as an external disturbance current source to inject a disturbance current into the wind turbine side port and the grid to obtain

[0016] ;

[0017] in, , are the port voltages of the grid-side converter under voltage disturbance v 2 , output current The disturbance component of is the injected voltage disturbance component, is the grid-side converter filter impedance The sum of the grid equivalent impedance from the perspective of the grid-side converter, at this time, the grid-side converter filter is a pure inductor.

[0018] Preferably, in S2, for the wind turbine side port, the grid side converter after injecting the secondary side disturbance is equivalent to an external disturbance current source, and the equivalent impedance of the wind turbine side port is It can be calculated by the following formula:

[0019] ;

[0020] In the formula, , They are the port voltages on the fan side. , output current The disturbance component.

[0021] Preferably, in S3, a current disturbance is injected into the current sampling point of the grid-side converter,

[0022] ;

[0023] in, , are respectively the terminal voltages of the grid-side converter under the second current disturbance , output current The disturbance component of is the injected current disturbance component.

[0024] Preferably, in S3, the theoretical model of the grid-side converter port impedance is:

[0025] ;

[0026] in, and is the s-domain transfer function related to the grid-side converter port filter parameters.

[0027] Preferably, the disturbance component of the output current of the grid-side converter under voltage disturbance is and the disturbance component of the output current of the grid-side converter under the second current disturbance The calculation formula of is combined to get A (s) and B (s) at the disturbance frequency, and then calculate the A (s) and B Substitute the value of (s) into The theoretical model formula is used to obtain the measured value of the grid-side converter port impedance.

[0028] Preferably, in S4, the equivalent impedance value of the doubly-fed wind turbine as a whole is and The parallel impedance of .

[0029] Preferably, the changing of the frequency of the injected disturbance in S5 may be replaced by changing the type of the injected disturbance signal.

[0030] Preferably, the types of the injected disturbance signal include injected pulse waves, random binary sequences and various broadband signals.

[0031] Therefore, the present invention adopts the above-mentioned doubly-fed wind turbine impedance measurement method based on secondary-side disturbance, which has the following beneficial effects: the present invention provides a low-cost, simple-to-operate doubly-fed wind turbine broadband impedance measurement method to overcome the disadvantages of high cost and complex operation of the impedance measurement method based on primary-side disturbance; the method changes the disturbance injection method from the traditional main circuit disturbance source injection (primary-side disturbance) to the injection of secondary-side disturbance at the voltage and current sampling points of the grid-side converter, and realizes rapid measurement of the broadband impedance value of the doubly-fed wind turbine through theoretical calculation formulas.

[0032] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 A flow chart of a method for measuring impedance of a doubly-fed wind turbine based on secondary-side disturbance according to an embodiment of the present invention;

[0034] Figure 2 It is a structural schematic diagram of an embodiment of the present invention;

[0035] Figure 3 is a diagram showing the measurement results of the primary side disturbance and the equivalent impedance of the fan side port according to an embodiment of the present invention;

[0036] Figure 4 is a diagram showing the measurement results of the primary side disturbance and the equivalent impedance of the grid side converter according to an embodiment of the present invention;

[0037] 1. Wind turbine; 2. Induction generator; 3. Transformer. DETAILED DESCRIPTION

[0038] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. The components of the embodiments of the present invention generally described and shown in the drawings here can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0039] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0040] Example

[0041] like Figure 1 As shown, the present invention provides a method for measuring impedance of a doubly-fed wind turbine based on secondary-side disturbance. The doubly-fed wind turbine includes a wind turbine 1, an induction generator 2, a rotor-side converter, a grid-side converter, a rotor-side controller and a grid-side controller. The rotor-side converter of the doubly-fed wind turbine controls the speed of the wind turbine, and the grid-side converter controls the DC bus voltage stability between the rotor side and the grid-side converter. Figure 2 , v 1 , i 1 are the voltage and current output by the induction generator 2, v 2 , i 2 The equivalent impedance of the double-fed wind turbine consists of two parts: one is the equivalent impedance of the wind turbine port, which is related to the controller of the rotor-side converter and the parameters of the induction generator 2; the other is the equivalent impedance of the grid-side converter, which is related to its controller parameters and main circuit parameters.

[0042] S1. At a certain disturbance frequency, a voltage disturbance is injected into the voltage sampling point of the grid-side converter, and the disturbance voltage and disturbance current output by the doubly-fed wind turbine side and the grid-side converter are recorded at the same time.

[0043] Assuming that the main circuit parameters of the grid-side converter are known, a voltage disturbance is injected into the voltage sampling point of the grid-side converter. The injected voltage disturbance generates a three-phase voltage containing a disturbance component after passing through the controller of the grid-side converter. After passing through the filter inductor in the main circuit of the grid-side converter, a three-phase current containing a disturbance component is output. This current is used as an external disturbance current source to inject a disturbance current into the wind turbine side port and the grid. Then,

[0044] (1)

[0045] in, , are the port voltages of the grid-side converter under voltage disturbance v 2 , output current The disturbance component of is the grid-side converter filter impedance and the sum of the grid equivalent impedance from the perspective of the grid-side converter (when the grid-side converter filter is a pure inductor), is the injected voltage disturbance component. The grid equivalent impedance from the perspective of the grid-side converter can be expressed as , The ratio is calculated.

[0046] S2. Extract the disturbance component at the corresponding frequency through Fourier decomposition and calculate the equivalent impedance of the fan side port .

[0047] Relative to the wind turbine side port, the grid side converter after injecting the secondary side disturbance can be equivalent to an external disturbance current source, so the equivalent impedance of the wind turbine side port is It can be calculated by the following formula:

[0048] (2)

[0049] In the formula, , They are the port voltages on the fan side. v 1 , output current The calculation method of formula (1) is essentially equivalent to the impedance calculation under the primary side current disturbance injection, but the disturbance source is generated by the secondary side current disturbance injection.

[0050] S3, injecting current disturbance at the current sampling point of the grid-side converter, recording the disturbance voltage and disturbance current output by the grid-side converter, and combining the disturbance voltage and disturbance current output by the grid-side converter recorded in step S1 to calculate the equivalent impedance of the grid-side converter .

[0051] The current disturbance is injected into the current sampling point of the grid-side converter,

[0052] (3)

[0053] in, , are respectively the terminal voltages of the grid-side converter under the second current disturbance v 2 , output current The disturbance component of is the injected current disturbance component.

[0054] The theoretical model of the grid-side converter port impedance can be simplified as follows:

[0055] (4)

[0056] in, and is the s-domain transfer function related to the grid-side converter port filter parameters.

[0057] Combining equations (1) and (3), we can calculate A (s) and B (s) at the perturbation frequency (two equations with two unknowns). A (s) and B Substitute the value of (s) into The theoretical model (4) can be used to obtain the measured value of the grid-side converter port impedance.

[0058] S4. Calculate the overall impedance value of the doubly fed wind turbine at this frequency. The equivalent impedance value of the doubly fed wind turbine is and If the main circuit topology of the doubly fed wind turbine contains a transformer 3, then based on the measurement obtained by the present invention and , and then the equivalent impedance value of the doubly fed wind turbine as a whole is obtained according to the existing transformer 3 impedance conversion method.

[0059] S5, changing the frequency of the injected disturbance, repeating steps S1-S4 until the full-band impedance measurement of the doubly-fed wind turbine is completed. The purpose of this method can also be achieved by changing the type of injected disturbance signal, such as injecting pulse waves, random binary sequences, and various broadband signals.

[0060] The grid-side converter impedance measurement method proposed in the present invention includes two disturbance injection processes, the first time injecting voltage disturbance at the voltage sampling point of the grid-side converter, and the second time injecting current disturbance at the current sampling point of the grid-side converter, and inputting the voltage and current after the disturbance injection into the controller of the grid-side converter. Since in step S1, the equivalent impedance of the wind turbine side has been calculated by injecting disturbance at the voltage sampling point of the grid-side converter, when measuring the impedance of the grid-side converter, it is only necessary to record the output voltage and output current of the grid-side converter after the voltage disturbance is injected when measuring the equivalent impedance of the wind turbine side, and there is no need to inject an additional voltage disturbance; in addition, the current disturbance is injected at the current sampling point of the grid-side converter for the second time, and the output voltage and output current waveforms of the grid-side converter are recorded, and the corresponding disturbance components are extracted by Fourier transform to perform the equivalent impedance of the doubly fed wind turbine. , Calculation.

[0061] The model was built by PLECS software and the simulation was run to verify the effectiveness of this method. The verification results are as follows: Figure 3-4 As shown, the primary-side measurement result and the secondary-side measurement result of the equivalent impedance of the wind turbine side and the grid side port are basically consistent, so the present invention can more accurately measure the broadband impedance of the doubly-fed wind turbine.

[0062] Therefore, the present invention adopts the above-mentioned doubly-fed wind turbine impedance measurement method based on secondary side disturbance, injects secondary side disturbance into the voltage and current sampling points of the grid-side converter, and calculates the wide-band impedance of the doubly-fed wind turbine at the wind turbine side port and the grid-side converter port through the disturbance voltage and current response generated by the wind turbine side port and the grid-side converter port.

[0063] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for measuring impedance of a doubly-fed wind turbine based on secondary-side disturbance, characterized in that: The following steps are involved: S1. At a certain disturbance frequency, a voltage disturbance is injected into the voltage sampling point of the grid-side converter, and the disturbance voltage and disturbance current output by the double-fed wind turbine side and the grid-side converter are recorded at the same time; S2. Extract the disturbance component at the corresponding frequency through Fourier decomposition and calculate the equivalent impedance of the fan side port ; In S2, for the wind turbine side port, the grid side converter after injecting the secondary side disturbance is equivalent to an external disturbance current source, and the equivalent impedance of the wind turbine side port is Calculated by the following formula: ； In the formula, , They are the port voltages on the fan side. , output current The disturbance component of S3, injecting current disturbance at the current sampling point of the grid-side converter, recording the disturbance voltage and disturbance current output by the grid-side converter, and combining the disturbance voltage and disturbance current output by the grid-side converter recorded in step S1 to calculate the equivalent impedance of the grid-side converter ; In S3, the theoretical model of the grid-side converter port impedance is: ； in, and is related to the grid-side converter port filter parameters s Domain transfer function, and Represents the complex terms related to the control loop in the impedance theory model to simplify the subsequent derivation formulas; The disturbance component of the output current of the grid-side converter under voltage disturbance and the disturbance component of the output current of the grid-side converter under the second current disturbance The calculation formula of is combined to get A(s) and B(s) The value at the disturbance frequency, and then the calculated A(s) and B(s) Substitute the value of The theoretical model formula is used to obtain the measured value of the grid-side converter port impedance; S4. Calculate the overall impedance value of the doubly-fed wind turbine at the frequency; In S4, the equivalent impedance value of the doubly fed wind turbine as a whole is and The parallel impedance of S5. Change the frequency of the injected disturbance and repeat steps S1-S4 until the full-band impedance measurement of the doubly-fed wind turbine is completed.

2. The impedance measurement method of a doubly-fed wind turbine based on secondary-side disturbance according to claim 1, characterized in that: In S1, the injected voltage disturbance generates a three-phase voltage containing a disturbance component after passing through the controller of the grid-side converter, and outputs a three-phase current containing a disturbance component after passing through the filter inductor in the main circuit of the grid-side converter. The three-phase current is used as an external disturbance current source to inject a disturbance current into the wind turbine side port and the grid, and obtains ； in, , are the port voltages of the grid-side converter under voltage disturbance , output current The disturbance component of is the injected voltage disturbance component, is the grid-side converter filter impedance The sum of the grid equivalent impedance from the perspective of the grid-side converter, at this time, the grid-side converter filter is a pure inductor.

3. The impedance measurement method of a doubly-fed wind turbine based on secondary-side disturbance according to claim 2 is characterized in that: In S3, a current disturbance is injected into the current sampling point of the grid-side converter to obtain ； in, , are respectively the terminal voltages of the grid-side converter under the second current disturbance , output current The disturbance component of is the injected current disturbance component.

4. The impedance measurement method of a doubly-fed wind turbine based on secondary-side disturbance according to claim 1, characterized in that: In S5, changing the frequency of the injected disturbance is replaced by changing the type of the injected disturbance signal.

5. The impedance measurement method of a doubly-fed wind turbine based on secondary-side disturbance according to claim 4 is characterized in that: The types of injected disturbance signals include injected pulse waves, random binary sequences and various broadband signals.

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