Online detection method and system for grid impedance of grid-forming converter

Abstract

The invention provides an on-line detection method for grid impedance of a grid-forming converter. The method comprises the following steps: acquiring a phase angle difference delta between a voltage phase angle of the grid-forming converter and a voltage phase angle of a power grid through a phase-locked loop of a synchronous rotating coordinate system; and calculating a resistive component Rg and an inductive component Lg of the power grid impedance based on the phase angle difference delta and active power P and reactive power Q output by the grid-forming converter during grid connection. The phase angle difference between the phase angle of the converter voltage and the phase angle of the power grid voltage is obtained through the SRF-PLL; and on the basis of an impedance calculation expression deduced through an output power expression of the grid-forming converter, online estimation of the power grid impedance is realized, and the accuracy of online estimation of the power grid impedance is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of grid-type energy storage converter control, and more particularly to an online detection method and system for grid impedance of a grid-type converter. Background Art

[0002] With the development and promotion of renewable energy generation technologies, the penetration rate of new energy power electronic power supplies continues to increase. Grid-connected converters (GCCs) that are compatible with weak grids have become a research focus in this field. GCCs are key devices that connect renewable energy generation devices to the grid. However, in weak grids, a large grid impedance exists between the point of common coupling (PCC) and the grid. This grid impedance can affect the stability of the converter and may even cause system instability. Therefore, to ensure the stable operation of GCCs in weak grids, grid impedance detection technology is required to obtain grid impedance information, which can then guide converter stability analysis and control system design.

[0003] Traditional online detection methods for grid impedance mainly calculate impedance values by indirectly measuring parameters such as voltage and current, ignoring the influence of phase on the detection results. As a result, there are problems such as large fluctuations in measurement results and insufficient accuracy. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for online estimation of grid impedance suitable for a grid-type converter, so as to improve the accuracy of online estimation of grid impedance.

[0005] According to one aspect of the present invention, there is provided a method for online detection of grid impedance of a grid-type converter, comprising the following steps:

[0006] Obtaining a phase angle difference δ between the voltage phase angle of the grid-type converter and the voltage phase angle of the grid through a synchronous rotating coordinate system phase-locked loop;

[0007] Based on the phase angle difference δ, the active power P and reactive power Q output by the grid-connected converter, the resistive component R of the grid impedance is calculated. g and the inductive component L g .

[0008] In the online detection method for grid impedance of a grid-type converter provided by the present invention, the phase angle difference Among them, ω pll is the angular frequency obtained by PLL, and ω0 is the fundamental angular frequency of the power grid.

[0009] In the online detection method for the grid impedance of the grid-type converter provided by the present invention, the resistive component R of the grid impedance is calculated based on the phase angle difference δ, the active power P and reactive power Q output by the grid-type converter when connected to the grid. g and the inductive component L g The steps include:

[0010] Calculating the grid line impedance Z and the grid line impedance angle α based on the phase angle difference δ, the active power P, and the active power Q;

[0011] Based on the grid line impedance Z and the grid line impedance angle α, the inductive component L of the grid is calculated. g and the resistive component R g .

[0012] In the online detection method for the grid impedance of the grid-type converter provided by the present invention, the inductive component The resistive component R g =|Z|*cosα,

[0013] in, ω0 is the grid fundamental angular frequency, U is the grid voltage, and E is the grid-connected converter voltage.

[0014] According to another aspect of the present invention, there is also provided an online detection system for grid impedance of a grid-type converter, comprising:

[0015] A phase angle difference acquisition module is used to obtain a phase angle difference δ between the voltage phase angle of the grid-type converter and the voltage phase angle of the grid through a synchronous rotating coordinate system phase-locked loop;

[0016] A calculation module is used to calculate the resistive component R of the grid impedance based on the phase angle difference δ, the active power P and reactive power Q output by the grid-connected converter when connected to the grid. g and the inductive component L g .

[0017] In the online detection system for grid impedance of a grid-type converter provided by the present invention, the phase angle difference Among them, ω pll is the angular frequency obtained by PLL, and ω0 is the fundamental angular frequency of the power grid.

[0018] In the online detection system for grid impedance of a grid-type converter provided by the present invention, the calculation module includes:

[0019] a first calculation unit, configured to calculate a grid line impedance Z and a grid line impedance angle α based on the phase angle difference δ, the active power P, and the active power Q;

[0020] The second calculation unit is used to calculate the inductive component L of the power grid based on the power grid line impedance Z and the power grid line impedance angle α. g and the resistive component R g .

[0021] In the online detection system for grid impedance of a grid-type converter provided by the present invention, the inductive component The resistive component R g =|Z|*cosα,

[0022] in, ω0 is the grid fundamental angular frequency, U is the grid voltage, and E is the grid-connected converter voltage.

[0023] The implementation of the online detection method and system for the grid impedance of a grid-type converter of the present invention has the following beneficial effects: the present invention obtains the phase angle difference between the phase angle of the converter voltage and the phase angle of the grid voltage through SRF-PLL; and then realizes online estimation of the grid impedance based on the impedance calculation expression derived from the output power expression of the grid-type converter, thereby improving the accuracy of online estimation of the grid impedance. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only embodiments of the present invention. Those skilled in the art can also derive other drawings based on the provided drawings without inventive work.

[0025] Figure 1 FIG2 is a flow chart of an online detection method for grid impedance of a grid-type converter proposed by the present invention;

[0026] Figure 2 The figure shows a schematic diagram of the grid-connected principle of a grid-connected converter provided by the present invention;

[0027] Figure 3 FIG. 1 is a control block diagram of a SRF-PLL grid-type converter provided by the present invention;

[0028] Figure 4 The figure shows the experimental results of online detection of grid resistance of a grid-forming converter provided by the present invention;

[0029] Figure 5 The figure shows the experimental results of online detection of grid resistance of a grid-type converter provided by the present invention. DETAILED DESCRIPTION

[0030] To facilitate understanding of the present invention, the present invention will be described more fully below with reference to the accompanying drawings. The drawings illustrate exemplary embodiments of the present invention. However, the present invention may be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and comprehensive understanding of the present invention.

[0031] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in this specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0032] Figure 1 FIG. 1 is a flow chart of an online detection method for grid impedance of a grid-type converter proposed by the present invention. Figure 1 As shown, the online detection method for the grid impedance of a grid-type converter provided by the present invention includes the following steps:

[0033] Step S1, obtaining a phase angle difference δ between the voltage phase angle of the grid-type converter and the voltage phase angle of the grid through a synchronous rotating coordinate system phase-locked loop;

[0034] Specifically, in one embodiment of the present invention, a phase angle difference between a voltage phase angle of the converter and a voltage phase angle of the grid is obtained by a synchronous reference frame phase-locked loop (SRF-PLL).

[0035] Figure 2 The control block diagram of SRF-PLL, where K p,pll and K i,pll are the proportional and integral gains of the PI controller in the SRF-PLL, Δω pll is the frequency difference between the angular frequency of the PLL output and the angular frequency of the grid, ω pll is the angular frequency obtained by PLL, ω0 is the grid fundamental angular frequency, θ pll is the PLL output phase angle, U PCC is the voltage at PCC, u d 、u q is the component of the voltage at the PCC in the two-phase rotating coordinate system, and δ is the phase angle difference between the PLL output phase angle and the grid phase angle. Through SRF-PLL, we can obtain Among them, ω pll is the angular frequency obtained by PLL, and ω0 is the fundamental angular frequency of the power grid.

[0036] Step S2: Calculate the resistive component R of the grid impedance based on the phase angle difference δ, the active power P and reactive power Q output by the grid-connected converter when connected to the grid. g and the inductive component L g .

[0037] Figure 3 The schematic diagram of the grid-connected converter is shown in Figure 1. U∠0 is the grid voltage, the converter is simplified to E∠δ, δ is the phase angle difference between the voltage phase angle of the grid-connected converter and the grid voltage phase angle, and is connected to the grid through the grid line resistance. The grid impedance is composed of the resistive component R g and the inductive component L g constitute.

[0038] according to Figure 3 , the output active power P and reactive power Q of the grid-connected converter can be calculated as follows:

[0039]

[0040] Where Z is the line impedance, α is the line impedance angle, and it satisfies α=tan -1 (ω0L / R)ω0 is the fundamental angular frequency of the power grid.

[0041] According to the above output power expressions (1) and (2), the grid line impedance Z can be expressed as

[0042]

[0043] From the line impedance expression (3), the grid line impedance angle α can be obtained:

[0044] QEcos(α-δ)-QUcosα-PEsin(α-δ)+PUsinα=0

[0045]

[0046] From this, the grid line impedance Z and impedance angle α are obtained. Then the resistive component R can be obtained by the grid line impedance Z and impedance angle α. g and the inductive component L g They are:

[0047]

[0048] R g =|Z|*cosα.

[0049] Furthermore, in one embodiment of the present invention, the grid impedance resistive component estimated value R can be calculated from the grid line impedance Z expression and the grid line impedance angle α. gand the estimated value of the perceptual component L g However, due to the coupling of power during calculation, the grid line impedance Z and grid line impedance angle α cannot be estimated by one-time R g and L g The experiment found that when the active power P is not 0 and the reactive power Q is 0, the inductive component L of the grid impedance can be accurately estimated. g ; Assume that the reactive power Q is not 0, and when the active power P is 0, the resistive component R of the grid impedance can be accurately estimated g The grid voltage U can be directly read at the PCC point when the converter is not working, that is, the real voltage.

[0050] In order to verify the feasibility of the above method, a grid-connected converter simulation model is built on MATLAB / Simulink, and the line impedance is set to R g =0.5Ω、L g =6mH, the effective value of the grid line voltage is 380V, and the grid power frequency cycle is 50Hz.

[0051] The active power P * is 10kW, reactive power Q * If it is 0, the estimated value of the inductance component of the online impedance detection can be obtained. like Figure 4 As shown, the maximum relative error is 1.1%, which can better estimate the line inductance component.

[0052] The active power P * is 0, reactive power Q * For 10kW, the estimated value of the online impedance detection resistor component can be obtained like Figure 5 As shown, the maximum relative error is 4.5%, which can better estimate the line inductance component.

[0053] The method for online estimation of grid impedance of a grid-forming type provided by the present invention improves on the traditional method for online estimation of grid impedance. The phase angle difference between the phase angle of the converter voltage and the phase angle of the grid voltage is obtained through SRF-PLL. Then, based on the impedance calculation expression derived from the output power expression of the grid-forming type converter, online estimation of grid impedance is realized, thereby improving the accuracy of online estimation of grid impedance.

[0054] Accordingly, the present invention also provides an online detection system for the grid impedance of a grid-type converter, comprising: a phase angle difference acquisition module for acquiring a phase angle difference δ between the voltage phase angle of the grid-type converter and the grid voltage phase angle through a synchronous rotating coordinate system phase-locked loop; a calculation module for calculating the resistive component R of the grid impedance based on the phase angle difference δ and the active power P and reactive power Q output by the grid-type converter when connected to the grid. g and the inductive component L g .

[0055] Specifically, in one embodiment of the present invention, the phase angle difference is δ.

[0056] Specifically, in one embodiment of the present invention, the calculation module includes: a first calculation unit, which is used to calculate the grid line impedance Z and the grid line impedance angle α based on the phase angle difference δ, the active power P and the active power Q; a second calculation unit, which is used to calculate the inductive component L of the grid based on the grid line impedance Z and the grid line impedance angle α. g and the resistive component R g The perceptual component sinα, the resistive component R g =|Z|*cosα, where ω0 is the grid fundamental angular frequency, U is the grid voltage, and E is the grid-connected converter voltage.

[0057] An embodiment of the present invention further provides an online detection device for grid impedance of a grid-type converter, which may include:

[0058] memory for storing computer programs;

[0059] The processor, when used to execute the computer program stored in the above-mentioned memory, can implement the following steps:

[0060] The phase angle difference δ between the voltage phase angle of the grid-type converter and the grid voltage phase angle is obtained through a synchronous rotating coordinate system phase-locked loop; based on the phase angle difference δ, the active power P and reactive power Q output by the grid-type converter when connected to the grid, the resistive component R of the grid impedance is calculated. g and the inductive component L g .

[0061] An embodiment of the present invention further provides a computer-readable storage medium, wherein the computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, the following steps can be implemented:

[0062] The phase angle difference δ between the voltage phase angle of the grid-type converter and the grid voltage phase angle is obtained through a synchronous rotating coordinate system phase-locked loop; based on the phase angle difference δ, the active power P and reactive power Q output by the grid-type converter when connected to the grid, the resistive component R of the grid impedance is calculated. g and the inductive component L g .

[0063] The computer-readable storage medium may include: a USB flash drive, a mobile hard disk, a read-only memory (ROM)> a random access memory (RAM), a magnetic disk or an optical disk, and other media that can store program codes.

[0064] In the description provided herein, numerous specific details are described. However, it is understood that embodiments of the present invention may be practiced without these specific details. In some instances, well-known methods, structures, and techniques are not shown in detail so as not to obscure the understanding of this description.

[0065] Similarly, it should be understood that in order to streamline the present disclosure and aid in understanding one or more of the various inventive aspects, in the above description of exemplary embodiments of the invention, various features of the invention are sometimes grouped together into a single embodiment, figure, or description thereof. However, this disclosed method should not be interpreted as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as reflected in the claims below, inventive aspects lie in less than all the features of the individual embodiments disclosed above. Accordingly, the claims following the detailed description are hereby expressly incorporated into this detailed description, with each claim standing on its own as a separate embodiment of the invention.

[0066] Those skilled in the art will appreciate that the modules in the devices in the embodiments may be adaptively changed and arranged in one or more devices different from the embodiments. The modules or units or components in the embodiments may be combined into one module or unit or component, and in addition may be divided into multiple submodules or subunits or subcomponents. All features disclosed in this specification (including the accompanying claims, abstracts and drawings) and all processes or units of any method or device disclosed herein may be combined in any combination, except that at least some of such features and / or processes or units are mutually exclusive. Unless expressly stated otherwise, each feature disclosed in this specification (including the accompanying claims, abstracts and drawings) may be replaced by an alternative feature providing the same, equivalent or similar purpose.

[0067] Furthermore, those skilled in the art will appreciate that although some embodiments herein include certain features included in other embodiments but not other features, combinations of features from different embodiments are intended to be within the scope of the present invention and to form different embodiments. For example, in the claims below, any of the claimed embodiments may be used in any combination.

[0068] The various component embodiments of the present invention can be implemented in hardware, or in software modules running on one or more processors, or in a combination thereof. It will be appreciated by those skilled in the art that a microprocessor or digital signal processor (DSP) can be used in practice to implement some or all of the functions of some or all of the components in accordance with the embodiments of the present invention. The present invention can also be implemented as a device or apparatus program (e.g., a computer program and a computer program product) for executing a portion or all of the methods described herein. Such a program implementing the present invention can be stored on a computer-readable medium, or can have the form of one or more signals. Such a signal can be downloaded from an Internet website, or provided on a carrier signal, or provided in any other form.

[0069] It should be noted that the above embodiments illustrate rather than limit the invention, and that those skilled in the art may devise alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between brackets should not be construed as limiting the claims. The word "comprising" does not exclude the presence of elements or steps not listed in the claims. The word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. The present invention may be implemented by means of hardware comprising several different elements and by means of appropriately programmed computers. In a unit claim enumerating several means, several of these means may be embodied by the same item of hardware. The use of the words first, second, and third etc. does not indicate any order. These words may be interpreted as names.

Claims

1. A method for online detection of grid impedance of a grid-type converter, characterized in that: The following steps are involved: Obtaining a phase angle difference δ between the voltage phase angle of the grid-type converter and the voltage phase angle of the grid through a synchronous rotating coordinate system phase-locked loop; Based on the phase angle difference δ, the active power P and reactive power Q output by the grid-connected converter, the resistive component R of the grid impedance is calculated. g and the inductive component L g .

2. The online detection method for grid impedance of a grid-type converter according to claim 1, characterized in that: The phase angle difference Among them, ω pll is the angular frequency obtained by PLL, and ω0 is the fundamental angular frequency of the power grid.

3. The online detection method for grid impedance of a grid-type converter according to claim 2, characterized in that: Based on the phase angle difference δ, the active power P and reactive power Q output by the grid-connected converter, the resistive component R of the grid impedance is calculated. g and the inductive component L g The steps include: Calculating the grid line impedance Z and the grid line impedance angle α based on the phase angle difference δ, the active power P, and the active power Q; Based on the grid line impedance Z and the grid line impedance angle α, the inductive component L of the grid is calculated. g and the resistive component R g .

4. The online detection method for grid impedance of a grid-type converter according to claim 3, characterized in that: The perceptual component The resistive component R g =|Z|*cosα, where ω0 is the grid fundamental angular frequency, U is the grid voltage, and E is the grid-connected converter voltage.

5. An online detection system for grid impedance of a grid-type converter, characterized in that: include: A phase angle difference acquisition module is used to obtain a phase angle difference δ between the voltage phase angle of the grid-type converter and the voltage phase angle of the grid through a synchronous rotating coordinate system phase-locked loop; A calculation module is used to calculate the resistive component R of the grid impedance based on the phase angle difference δ, the active power P and reactive power Q output by the grid-connected converter when connected to the grid. g and the inductive component L g .

6. The online detection system for grid impedance of a grid-type converter according to claim 5, characterized in that: The phase angle difference Among them, ω pll is the angular frequency obtained by PLL, and ω0 is the fundamental angular frequency of the power grid.

7. The online detection system for grid impedance of a grid-type converter according to claim 5, characterized in that: The calculation module includes: a first calculation unit, configured to calculate a grid line impedance Z and a grid line impedance angle α based on the phase angle difference δ, the active power P, and the active power Q; The second calculation unit is used to calculate the inductive component L of the power grid based on the power grid line impedance Z and the power grid line impedance angle α. g and the resistive component R g .

8. The online detection system for grid impedance of a grid-type converter according to claim 7, characterized in that: The perceptual component The resistive component R g =|Z|*cosα, where ω0 is the grid fundamental angular frequency, U is the grid voltage, and E is the grid-connected converter voltage.

9. An online detection device for grid impedance of a grid-type converter, characterized in that: The method comprises a processor and a memory, wherein the memory stores a computer program, and when the computer program is executed by the processor, the steps of the online detection method for the grid impedance of a grid-type converter according to any one of claims 1 to 4 are implemented.

10. A computer-readable storage medium storing a computer program, wherein: When the computer program is executed by a processor, the method according to any one of claims 1 to 4 is implemented.

Images