Secondary side injection disturbance signal setting method and device for converter impedance measurement

Abstract

The application relates to a secondary-side injection disturbance signal setting method and device for converter impedance measurement, and the method comprises the following steps: obtaining grid impedance; determining a grid type according to the grid impedance, wherein the grid type comprises a strong grid, a normal grid and a weak grid; determining the amplitude of a disturbance signal according to the grid type; the disturbance signal is a disturbance voltage signal or a disturbance current signal. The amplitude of the secondary-side injection disturbance signal is reasonably set to avoid the threat of excessive disturbance signal injection to the steady operation of the system, and the signal-to-noise ratio of the disturbance signal is as large as possible to improve the accuracy of the disturbance signal waveform measurement.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of converter impedance measurement, and particularly relates to a method and device for setting a secondary-side injected disturbance signal in converter impedance measurement. BACKGROUND

[0002] At present, a large amount of new energy such as wind power and photovoltaic power is connected to the power system, which brings small signal stability problems to the traditional power system. Impedance method is an important method for analyzing small signal stability problems, and the wideband impedance characteristics of the converter of each new energy station are the basis for analysis. In order to obtain the wideband impedance of each converter, the disturbance signal injection method is one of the most commonly used methods. The converter impedance measurement method based on disturbance signal injection includes primary-side injection of disturbance signal and secondary-side injection of disturbance signal, and the disturbance signal includes current disturbance signal and voltage disturbance signal.

[0003] The design of the amplitude of the disturbance signal is one of the key steps for converter impedance measurement, and the purpose is to avoid the threat of the safe and stable operation of the system caused by the injected disturbance signal being too large. The existing setting method of the amplitude of the disturbance signal generally sets the amplitude of the injected disturbance signal to about 5% of the size of the steady-state voltage and the steady-state current of the system to be measured. This is set according to the measurement experience of actual engineering, and the amplitude of the disturbance signal involved in this method is generally for the primary-side injected disturbance signal. The amplitude of the secondary-side injected disturbance signal has not been disclosed in the literature. SUMMARY

[0004] The purpose of the present application is to provide a method for setting a secondary-side injected disturbance signal in converter impedance measurement, which reasonably sets the amplitude of the secondary-side injected disturbance signal to avoid the threat of the stable operation of the system caused by the injected disturbance signal being too large, and at the same time, increases the signal-to-noise ratio of the disturbance signal as much as possible to improve the accuracy of the measurement of the disturbance signal waveform.

[0005] To achieve the above purpose, the present application provides a method for setting a secondary-side injected disturbance signal in converter impedance measurement, comprising:

[0006] obtaining a grid impedance;

[0007] determining a grid type according to the grid impedance, wherein the grid type includes a strong grid, a normal grid and a weak grid;

[0008] determining the amplitude of the disturbance signal according to the grid type, wherein the disturbance signal is a disturbance voltage signal or a disturbance current signal.

[0009] Preferably, the determination of the grid type according to the grid impedance further comprises:

[0010] The grid type is determined according to the size of the grid impedance, when the grid impedance is greater than a first preset impedance, the grid type is determined as a weak grid; when the grid impedance is greater than a second preset impedance and less than the first preset impedance, the grid type is determined as a normal grid; when the grid impedance is less than the second preset impedance, the grid type is determined as a strong grid.

[0011] Preferably, the amplitude of the disturbance signal is determined according to the grid type, further comprising:

[0012] When the grid type is a weak grid, the amplitude of the injected disturbance current signal is set as k2V N / Z g , and the amplitude of the injected voltage disturbance signal is set as k1V N , V N is a steady-state voltage value of the grid-connected converter, k1 is less than k2, Z g is the grid impedance, and k1 and k2 are preset values.

[0013] Preferably, the amplitude of the disturbance signal is determined according to the grid type, further comprising:

[0014] When the grid type is a strong grid, the amplitude of the injected disturbance current signal is set as k1I N , and the amplitude of the injected voltage disturbance signal is set as k2Z g I N , I N is a steady-state current value of the grid-connected converter, k1 is less than k2,

[0015] Z g is the grid impedance, and k1 and k2 are preset values.

[0016] Preferably, the amplitude of the disturbance signal is determined according to the grid type, further comprising:

[0017] A coordinate system is established with current as the abscissa and current as the ordinate, a rectangular region is generated in the coordinate system, and the boundaries of the rectangular region are 5%I N , 10%I N , 5%V N and 10%V N .

[0018] A straight line is generated in the coordinate system according to the grid impedance as the slope;

[0019] Two intersection points of the straight line and the boundaries of the rectangular region are obtained, and a line segment is determined according to the two intersection points;

[0020] The amplitude of the injected disturbance current signal is set as the horizontal coordinate value of the midpoint of the line segment, and the amplitude of the injected disturbance voltage signal is set as the vertical coordinate value of the midpoint of the line segment.

[0021] The application further provides a secondary side injected disturbance signal setting device for converter impedance measurement, which comprises:

[0022] a power grid impedance obtaining module, configured to obtain a power grid impedance;

[0023] a power grid type determining module, configured to determine a power grid type according to the power grid impedance, wherein the power grid type comprises a strong power grid, a normal power grid and a weak power grid;

[0024] a disturbance amplitude setting module, configured to determine the amplitude of a disturbance signal according to the power grid type, wherein the disturbance signal is a disturbance voltage signal or a disturbance current signal.

[0025] Preferably, the power grid impedance obtaining module is further configured to:

[0026] determine the power grid type according to the size of the power grid impedance, wherein when the power grid impedance is greater than a first preset impedance, the power grid type is determined as a weak power grid; when the power grid impedance is greater than a second preset impedance and smaller than the first preset impedance, the power grid type is determined as a normal power grid; and when the power grid impedance is smaller than the second preset impedance, the power grid type is determined as a strong power grid.

[0027] Preferably, the disturbance amplitude setting module is further configured to:

[0028] when the power grid type is a weak power grid, the amplitude of the injected disturbance current signal is set as k2V N / Z g , and the amplitude of the injected voltage disturbance signal is set as k1V N , V N is a steady-state voltage value of the grid-connected converter, k1 is smaller than k2, Z g is the power grid impedance, and k1 and k2 are preset values.

[0029] Preferably, the disturbance amplitude setting module is further configured to:

[0030] when the power grid type is a strong power grid, the amplitude of the injected disturbance current signal is set as k1I N , and the amplitude of the injected voltage disturbance signal is set as k2Z g I N , I N is a steady-state current value of the grid-connected converter, k1 is smaller than k2,

[0031] Z g is the power grid impedance, and k1 and k2 are preset values.

[0032] Preferably, the disturbance amplitude setting module is further used for:

[0033] A rectangular region is generated in the coordinate system with current as the abscissa and current as the ordinate, and the boundary of the rectangular region is 5% I N , 10% I N , 5% V N , and 10% V N ;

[0034] A straight line is generated in the coordinate system according to the grid impedance as the slope;

[0035] Two intersection points of the straight line and the boundary of the rectangular region are obtained, and a line segment is determined according to the two intersection points;

[0036] The amplitude of the injected disturbance current signal is set as the abscissa value of the midpoint of the line segment, and the amplitude of the injected disturbance voltage signal is set as the ordinate value of the midpoint of the line segment.

[0037] The method provides a more fine and adaptive secondary side injected disturbance signal setting method for converter impedance measurement, and the beneficial effects of the method are as follows:

[0038] The amplitude of the disturbance signal is adjusted by recognizing the grid type, so that the measurement method can adapt to different grid conditions; by generating disturbance signals of multiple frequencies, the impedance of the converter in the full frequency band can be measured, improving the comprehensiveness of the measurement; by reasonably designing the amplitude of the disturbance signal, it is ensured that the measurement process will not affect the stable operation of the grid. The application is helpful to improve the accuracy and reliability of converter impedance measurement in practical application, and has important significance for ensuring the stable operation of new energy access power system. At the same time, the method also provides technical support for the optimization control and protection strategy of power system. BRIEF DESCRIPTION OF DRAWINGS

[0039] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0040] Figure 1 The flow chart of a secondary side injected disturbance signal setting method for converter impedance measurement in an embodiment of the present application.

[0041] Figure 2 The structural diagram of a grid impedance measurement circuit in an embodiment of the present application.

[0042] Figure 3 A schematic diagram of a method for setting a disturbance signal injected on the secondary side of a converter impedance measurement according to an embodiment of the application. DETAILED DESCRIPTION

[0043] The detailed description of the drawings is intended as a description of the current embodiment of the application and is not intended to represent the only form in which the present application can be practiced. It is believed that the same or equivalent functions could be accomplished by different embodiments that are intended to be encompassed within the spirit and scope of the application.

[0044] As shown in Figure 1 , one embodiment of the application provides a method for setting a disturbance signal injected on the secondary side of a converter impedance measurement, comprising the following steps:

[0045] Step S1, obtaining the grid impedance;

[0046] Specifically, in the embodiment, the grid impedance is set as Z g ; There are many ways to obtain the grid impedance, such as direct measurement method, online monitoring method, short circuit test method, simulation analysis method, power flow calculation method, model-based estimation method, each method has its advantages and limitations, suitable for different occasions and needs. The converter is a bridge between the new energy system and the grid, used to realize the grid connection of the new energy system, for example, as shown in Figure 2 , a disturbance signal can be injected on the secondary side of the converter, and the grid-connected converter system will produce a corresponding disturbance response under the injection of the disturbance signal, which is specifically manifested as: the grid-connected point voltage and output current of the converter contain harmonic components with the same frequency as the injected disturbance, because the injected disturbance passes through the control loop of the converter, and a disturbance response with the corresponding frequency is generated. Then, the disturbance response component of the grid-connected converter output is extracted, and the size of the equivalent grid impedance is calculated, specifically: the disturbance component v g in the grid-connected point voltage is equal to the product of the disturbance component i g in the output current of the converter and the grid impedance Z g at the disturbance frequency,

[0047] i.e.

[0048] v g = Z g × i g

[0049] Therefore, the disturbance component v g of the grid-connected point voltage is divided by the disturbance component i g of the output current of the converter, and the grid impedance Z g is calculated.

[0050] Step S2: Determine the power grid type based on the power grid impedance. The power grid type includes strong power grid, ordinary power grid, and weak power grid.

[0051] Specifically, such as Figure 3 As shown, a coordinate system is established with current as the horizontal axis and current as the horizontal axis. Ideally, the desired output disturbance response of the converter is 5%-10% of the original system's steady-state voltage and current values, i.e. Figure 2 The dashed rectangular area in the middle (the boundary of the rectangular area is 5% I) N 10% I N 5% V N and 10% V N The method in this embodiment determines the power grid impedance based on the magnitude of the impedance. Figure 3 The region enclosed by the coordinate axes is divided into three parts: a weak power grid, a normal power grid, and a strong power grid, corresponding to the area to the left of line OA, the area between line OA and line OB, and the area to the right of line OB, respectively. The power grid impedance Z is obtained from step S1. g With the grid impedance Z g The slope can be represented by a straight line in the coordinate system, and the equation of the line is v. g =Z g ×i g By determining the area where the line is located, the type of power grid can be identified. When the line falls to the left of the line OA, it is a weak power grid; when it falls between the lines OA and OB, it is a normal power grid; and when it falls to the right of the line OB, it is a strong power grid.

[0052] Therefore, step S2 may further include:

[0053] The power grid type is determined based on the magnitude of the power grid impedance. When the power grid impedance is greater than a first preset impedance, the power grid type is determined to be a weak power grid. When the power grid impedance is greater than a second preset impedance and less than a first preset impedance, the power grid type is determined to be a normal power grid. When the power grid impedance is less than a second preset impedance, the power grid type is determined to be a strong power grid.

[0054] Step S3: Determine the amplitude of the disturbance signal according to the power grid type; the disturbance signal is a disturbance voltage signal or a disturbance current signal.

[0055] Specifically, there are two design objectives for the amplitude of the secondary-side disturbance: First, the disturbance response generated by the grid-connected converter system after the secondary-side disturbance is injected should not be too large to threaten the safe operation of the system, that is, the injected disturbance amplitude should not be too large; Second, the disturbance response generated by the grid-connected converter system after the secondary-side disturbance is injected should not be too small to result in a very low signal-to-noise ratio and affect the accuracy of subsequent disturbance waveform measurement and extraction, that is, the injected disturbance amplitude should not be too small.

[0056] Therefore, the embodiment method gives the following design according to the size of the calculated grid impedance value.

[0057] (1) When the grid type is a weak grid, at this time, the injected current disturbance cannot be too large, otherwise it is easy to cause the disturbance voltage of the grid-connected point of the converter to be too large, therefore, the amplitude of the injected disturbance current signal is set to k2V N / Z g , the amplitude of the injected voltage disturbance signal is set to k1V N , V N is the steady-state voltage value of the grid-connected converter, k1 is less than k2, Z g is the grid impedance, and k1 and k2 are preset values.

[0058] (2) A rectangular region is generated in the coordinate system, and the boundaries of the rectangular region are 5%I N , 10%I N , 5%V N , and 10%V N .

[0059] A straight line is generated in the coordinate system according to the grid impedance as the slope; the straight line equation is v g =Z g ×i g .

[0060] Two intersection points of the straight line (v g =Z g ×i g ) and the boundaries of the rectangular region are obtained, and a line segment is determined according to the two intersection points.

[0061] The amplitude of the injected disturbance current signal is set to the horizontal coordinate value of the midpoint of the line segment, and the amplitude of the injected disturbance voltage signal is set to the vertical coordinate value of the midpoint of the line segment.

[0062] (3) When the grid type is a strong grid, the injected voltage disturbance cannot be too large, otherwise it is easy to cause the disturbance current output by the converter to be too large, therefore, the amplitude of the injected disturbance current signal is set to k1I N , and the amplitude of the injected voltage disturbance signal is set to k2Z g I N , I N is the steady-state current value of the grid-connected converter, k1 is less than k2, Z g is the grid impedance, and k1 and k2 are preset values.

[0063] It should be noted that the technology of injecting a disturbance signal into the secondary side of the converter for impedance measurement is already part of the prior art, and the innovation of the embodiment method is to propose a magnitude design method for injecting a disturbance signal into the secondary side, rather than the measurement method itself. The magnitude design method of the embodiment improves the adaptability and safety of the measurement, making the converter impedance measurement under different grid conditions more accurate and reliable.

[0064] Another embodiment of the application also proposes a secondary side disturbance signal setting device for converter impedance measurement, which comprises:

[0065] A grid impedance obtaining module is configured to obtain a grid impedance.

[0066] A grid type determining module is configured to determine a grid type according to the grid impedance, wherein the grid type comprises a strong grid, a normal grid and a weak grid.

[0067] A disturbance magnitude setting module is configured to determine a magnitude of a disturbance signal according to the grid type, wherein the disturbance signal is a disturbance voltage signal or a disturbance current signal.

[0068] The grid impedance obtaining module is further configured to:

[0069] The grid type is determined according to the size of the grid impedance, when the grid impedance is greater than a first preset impedance, the grid type is determined as a weak grid; when the grid impedance is greater than a second preset impedance and less than the first preset impedance, the grid type is determined as a normal grid; and when the grid impedance is less than the second preset impedance, the grid type is determined as a strong grid.

[0070] The disturbance magnitude setting module is further configured to:

[0071] When the grid type is a weak grid, the magnitude of the injected disturbance current signal is set as k2V N / Z g , and the magnitude of the injected voltage disturbance signal is set as k1V N , V N is a steady-state voltage value of the grid-connected converter, k1 is less than k2, Z g is the grid impedance, and k1 and k2 are preset values.

[0072] The disturbance magnitude setting module is further configured to:

[0073] When the grid type is a strong grid, the magnitude of the injected disturbance current signal is set as k1I N , and the magnitude of the injected voltage disturbance signal is set as k2Z g I N , I N is a steady-state current value of the grid-connected converter, k1 is less than k2,

[0074] Z g is the grid impedance, and k1 and k2 are preset values.

[0075] The disturbance amplitude setting module is further configured to:

[0076] establish a coordinate system with current as the abscissa and current as the ordinate, generate a rectangular region in the coordinate system, the boundary of the rectangular region being 5%I N , 10%I N , 5%V N , and 10%V N ;

[0077] generate a straight line with the grid impedance as the slope in the coordinate system;

[0078] obtain two intersection points of the straight line and the boundary of the rectangular region, and determine a line segment according to the two intersection points;

[0079] set the amplitude of the injected disturbance current signal to the abscissa value of the midpoint of the line segment, and set the amplitude of the injected disturbance voltage signal to the ordinate value of the midpoint of the line segment.

[0080] The device of the embodiment corresponds to the method of the above-described embodiments, and thus, the unexplained contents of the device of the embodiment can be obtained by referring to the method of the above-described embodiments, which will not be described here again.

[0081] The above has described the embodiments of the present application, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and changes are obvious to those skilled in the art without departing from the scope and spirit of the described embodiments. The selection of the terms used herein is intended to best explain the principles of the embodiments, practical application, or technical improvement in the market, or to enable other ordinary skilled persons in the art to understand the embodiments disclosed herein.

Claims

1. A method for setting a secondary-side disturbance signal for converter impedance measurement, characterized in that, The method includes: Obtain the grid impedance; The power grid type is determined based on the power grid impedance. The power grid type includes a strong power grid, a normal power grid, and a weak power grid. When the power grid impedance is greater than a first preset impedance, the power grid type is determined to be a weak power grid. When the power grid impedance is greater than a second preset impedance and less than the first preset impedance, the power grid type is determined to be a normal power grid. When the power grid impedance is less than the second preset impedance, the power grid type is determined to be a strong power grid. The amplitude of the disturbance signal is determined according to the power grid type; the disturbance signal is a disturbance voltage signal or a disturbance current signal. Establish a coordinate system with current as the x-axis and voltage as the y-axis, and generate a rectangular region within this coordinate system, the boundary of which is 5%. 10% 5% and 10% , This represents the steady-state current value of the grid-connected converter. This represents the steady-state voltage value of the grid-connected converter. A straight line is generated in the coordinate system with the slope of the power grid impedance. Obtain two intersection points between the straight line and the boundary of the rectangular region, and determine a line segment based on the two intersection points; The amplitude of the injected disturbance current signal is set as the abscissa value of the midpoint of the line segment, and the amplitude of the injected disturbance voltage signal is set as the ordinate value of the midpoint of the line segment.

2. The method according to claim 1, characterized in that, The step of determining the amplitude of the disturbance signal based on the power grid type further includes: When the power grid type is a weak power grid, the amplitude of the injected disturbance current signal is set to... The amplitude of the injected voltage disturbance signal is set to , k 1 less than k 2, Z g For grid impedance, k 1 and k 2 is the default value.

3. The method according to claim 1, characterized in that, The step of determining the amplitude of the disturbance signal based on the power grid type further includes: When the power grid type is a strong power grid, the amplitude of the injected disturbance current signal is set to... The amplitude of the injected voltage disturbance signal is set to , k 1 less than k 2, Z g For grid impedance, k 1 and k 2 is the default value.

4. A device for setting a secondary-side disturbance signal for converter impedance measurement, characterized in that, The device includes: A power grid impedance acquisition module is used to acquire the power grid impedance. A power grid type determination module is used to determine the power grid type based on the power grid impedance. The power grid type includes a strong power grid, a normal power grid, and a weak power grid. When the power grid impedance is greater than a first preset impedance, the power grid type is determined to be a weak power grid; when the power grid impedance is greater than a second preset impedance and less than the first preset impedance, the power grid type is determined to be a normal power grid; when the power grid impedance is less than the second preset impedance, the power grid type is determined to be a strong power grid. The disturbance amplitude setting module is used to determine the amplitude of the disturbance signal according to the power grid type; the disturbance signal is a disturbance voltage signal or a disturbance current signal; The disturbance amplitude setting module is further configured to: when the power grid type is a normal power grid, establish a coordinate system with current as the abscissa and voltage as the ordinate, and generate a rectangular region in the coordinate system, wherein the boundary of the rectangular region is 5%. 10% 5% and 10% , This represents the steady-state current value of the grid-connected converter. The steady-state voltage value of the grid-connected converter is given; a straight line is generated in the coordinate system with the grid impedance as the slope; two intersection points of the straight line and the boundary of the rectangular area are obtained, and a line segment is determined based on the two intersection points; the amplitude of the injected disturbance current signal is set as the abscissa value of the midpoint of the line segment, and the amplitude of the injected disturbance voltage signal is set as the ordinate value of the midpoint of the line segment.

5. The apparatus according to claim 4, characterized in that, The disturbance amplitude setting module is further used for: When the power grid type is a weak power grid, the amplitude of the injected disturbance current signal is set to... The amplitude of the injected voltage disturbance signal is set to , k 1 less than k 2, Z g For grid impedance, k 1 and k 2 is the default value.

6. The apparatus according to claim 4, characterized in that, The disturbance amplitude setting module is further used for: When the power grid type is a strong power grid, the amplitude of the injected disturbance current signal is set to... The amplitude of the injected voltage disturbance signal is set to , k 1 less than k 2, Z g For grid impedance, k 1 and k 2 is the default value.

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