Inverter working mode switching method and device based on impedance change

Abstract

The invention discloses an inverter working mode switching method and device based on impedance change. The method comprises the following steps: acquiring voltage information of an electrical connection point between a power grid side and a user side; determining the output angular frequency of the inverter according to the voltage information; determining a plurality of harmonic amplitudes of the inverter according to the output angular frequency; determining a diagnosis value of the inverter according to the plurality of harmonic amplitudes and the current component of the inverter; and switching the working mode of the inverter according to the relationship between the diagnosis numerical value and a preset numerical value. According to the inverter working mode switching method provided by the invention, the influence of the inverter on the power quality of the power grid can be reduced to the greatest extent through real-time operation voltage information processing, so that the robustness of the system is improved.

Description

Technical Field

[0001] This invention relates to the field of inverter control technology, and in particular to a method and apparatus for switching inverter operating modes based on impedance changes. Background Technology

[0002] The traditional power grid, dominated by synchronous generators, is gradually being challenged. The interface of new energy inverters is continuously increasing. Since new energy power plants are often located at the end of the grid (such as desert photovoltaic and offshore wind power), the low short-circuit ratio (SCR) of the grid leads to a large equivalent impedance, which greatly increases the risk of system resonance. Identifying the grid-connected impedance of inverters has become an important technology. Analyzing the stability of inverters at the grid connection point can improve the reliability of the system by changing control parameters and control structure.

[0003] Current impedance identification methods are mainly divided into active injection and passive measurement methods, and their basic principles are as follows:

[0004] 1. Active Injection Method: A small signal disturbance is actively superimposed on the output voltage or current of the inverter, and the voltage or current at the point of common coupling (PCC) is measured at the same time. The impedance at the corresponding frequency point is calculated by analyzing the frequency components of the injected signal.

[0005] II. Passive Measurement Method: Without actively injecting interference signals, the impedance is estimated by continuously detecting the fluctuations in the natural voltage and current at the grid connection point and using the spectral information of the natural fluctuations through certain analysis methods.

[0006] While active injection methods offer a high signal-to-noise ratio and can acquire relatively accurate impedance information over a wide frequency band, they generate additional harmonics, affecting power quality. Furthermore, the injected signal can interfere with other devices, causing unnecessary electromagnetic interference. Additionally, active injection methods have high computational complexity, resulting in poor real-time performance for resource-constrained microcontroller units (MCUs), making them impractical for real-time applications. Passive measurement methods do not require additional injection and do not affect power quality, but they rely on the presence and spectral characteristics of natural disturbances. If the disturbance does not contain the desired frequency components, the impedance at that point cannot be estimated; the estimation accuracy and resolution are generally lower than those of active injection methods. Summary of the Invention

[0007] This invention provides a method and apparatus for switching inverter operating modes based on impedance changes. By acquiring the operating voltage information of the grid connection point (i.e., the electrical connection point between the grid side and the user side) in real time, the diagnostic value of the inverter is determined by the operating voltage information, the harmonic amplitude at different output angular frequencies, and the current component of the inverter. The operating mode of the inverter is adjusted in real time according to the diagnostic value, which reduces the impact of the inverter on the power quality of the grid and greatly improves the robustness of the grid system.

[0008] According to a first aspect of the present invention, a method for switching the operating mode of an inverter based on impedance variation is provided, comprising:

[0009] Obtain voltage information at the electrical connection points between the power grid and the user side;

[0010] The output angular frequency of the inverter is determined based on the voltage information;

[0011] The multiple harmonic amplitudes of the inverter are determined based on the output angular frequency;

[0012] The diagnostic values ​​of the inverter are determined based on multiple harmonic amplitudes and the current components of the inverter.

[0013] The inverter's operating mode is switched based on the relationship between the diagnostic values ​​and preset values.

[0014] Optionally, before obtaining the voltage information at the electrical connection point between the grid side and the user side, the following steps are included:

[0015] The inverter is loaded with default control parameters and a control algorithm; wherein the default control parameters include: phase-locked loop coefficients, control loop coefficients, grid feedforward coefficients, and damping coefficients; and the control algorithm is a grid-following control algorithm.

[0016] Optionally, determining the inverter's output angular frequency based on the voltage information includes:

[0017] The voltage information is used as the input to the phase-locked loop control algorithm;

[0018] The output angular frequency of the inverter is determined based on the phase-locked loop control algorithm and the voltage information.

[0019] Optionally, determining multiple harmonic amplitudes of the inverter based on the output angular frequency includes:

[0020] Perform a Fast Fourier Transform analysis on the output angular frequency;

[0021] Based on the analysis results, multiple harmonic amplitude values ​​of the inverter are derived; wherein the number of harmonic amplitude values ​​is less than 20.

[0022] Optionally, the diagnostic values ​​of the inverter are determined based on multiple harmonic amplitudes and the current components of the inverter, including:

[0023] The diagnostic values ​​are calculated using formula (I):

[0024]

[0025] Where, diag_value is the diagnostic value, k1 and k2 are allocation coefficients, and ω i Here, A is the harmonic proportion coefficient, k is the harmonic amplitude, and A is the harmonic amplitude. i The harmonic amplitudes are extracted from the first k iterations. harmonic_id is the d-axis component minus the DC value in the phase-locked loop control algorithm, and harmonic_iq is the q-axis component minus the DC value in the phase-locked loop control algorithm.

[0026] Optionally, the inverter's operating mode can be switched based on the relationship between the diagnostic values ​​and preset values, including:

[0027] When the diagnostic value is greater than the first preset value, the value of the default control parameter is adjusted.

[0028] When the diagnostic value is less than or equal to the first preset value, the inverter's operating mode is switched from grid-connected to grid-connected.

[0029] Optionally, when the diagnostic value is greater than a first preset value, adjusting the default control parameter includes:

[0030] When the diagnostic value is greater than the first preset value and less than the second preset value, the diagnostic value continues to be monitored.

[0031] When the diagnostic value is greater than the first preset value and greater than or equal to the second preset value, the diagnostic value is compared with the third preset value.

[0032] Optionally, when the diagnostic value is greater than the first preset value and greater than or equal to the second preset value, the diagnostic value is compared with a third preset value, including:

[0033] When the diagnostic value is greater than or equal to the third preset value, the value of the default control parameter is adjusted.

[0034] When the diagnostic value is less than the third preset value, the default control parameter is loaded; wherein the first preset value is less than the second preset value, and the second preset value is less than the third preset value.

[0035] Optionally, after switching the inverter's operating mode based on the relationship between the diagnostic value and the preset value, the method further includes:

[0036] When the inverter is in the grid-connected operating mode, the impedance of the electrical connection point between the grid side and the user side is calculated by the active injection method.

[0037] According to a second aspect of the present invention, an inverter operating mode switching device based on impedance change is provided, for executing any of the inverter operating mode switching methods based on impedance change described in the first aspect of the present invention, the inverter operating mode switching device comprising:

[0038] The acquisition module is used to acquire voltage information at the electrical connection points between the power grid side and the user side;

[0039] An output angular frequency determination module is used to determine the output angular frequency of the inverter based on the voltage information.

[0040] The harmonic amplitude determination module is used to determine multiple harmonic amplitudes of the inverter based on the output angular frequency.

[0041] The diagnostic value determination module is used to determine the diagnostic value of the inverter based on multiple harmonic amplitudes and the current component of the inverter.

[0042] The working mode switching module is used to switch the working mode of the inverter according to the relationship between the diagnostic value and the preset value.

[0043] This invention discloses a method and apparatus for switching inverter operating modes based on impedance changes. The method includes acquiring voltage information at the electrical connection point between the grid side and the user side; determining the inverter's output angular frequency based on the voltage information; determining multiple harmonic amplitudes of the inverter based on the output angular frequency; determining diagnostic values ​​of the inverter based on the multiple harmonic amplitudes and the inverter's current components; and switching the inverter's operating mode based on the relationship between the diagnostic values ​​and preset values. The method for switching inverter operating modes based on impedance changes provided by this invention acquires the operating voltage information at the grid connection point (i.e., the electrical connection point between the grid side and the user side) in real time, determines the inverter's diagnostic values ​​based on the operating voltage information, harmonic amplitudes at different output angular frequencies, and the inverter's current components, and adjusts the inverter's operating mode in real time based on the diagnostic values. This reduces the inverter's impact on the power quality of the grid and greatly improves the robustness of the power grid system.

[0044] It should be understood that the description in this section is not intended to identify key or essential features of the embodiments of the present invention, nor is it intended to limit the scope of the invention. Other features of the invention will become readily apparent from the following description. Attached Figure Description

[0045] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0046] Figure 1 This is a flowchart of an inverter operating mode switching method based on impedance change provided in an embodiment of the present invention;

[0047] Figure 2 This is a flowchart of another inverter operating mode switching method based on impedance change provided in an embodiment of the present invention;

[0048] Figure 3 This is a flowchart of another inverter operating mode switching method based on impedance change provided in an embodiment of the present invention;

[0049] Figure 4 This is a flowchart of another inverter operating mode switching method based on impedance change provided in an embodiment of the present invention;

[0050] Figure 5 This is a flowchart of another inverter operating mode switching method based on impedance change provided in an embodiment of the present invention;

[0051] Figure 6 This is a flowchart of another inverter operating mode switching method based on impedance change provided in an embodiment of the present invention;

[0052] Figure 7 This is a flowchart of another inverter operating mode switching method based on impedance change provided in an embodiment of the present invention;

[0053] Figure 8 This is a flowchart of another inverter operating mode switching method based on impedance change provided in an embodiment of the present invention;

[0054] Figure 9 This is a typical three-phase inverter dual closed-loop control block diagram provided in the embodiments of the present invention;

[0055] Figure 10 This is a block diagram of an inverter operating mode switching device based on impedance change, provided in an embodiment of the present invention. Detailed Implementation

[0056] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0057] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0058] It should be understood that the various forms of processes shown above can be used, with steps reordered, added, or deleted. For example, the steps described in this invention can be executed in parallel, sequentially, or in different orders, as long as the desired result of the technical solution of this invention can be achieved, and this is not limited herein.

[0059] Figure 1 This is a flowchart of an inverter operating mode switching method based on impedance change provided in an embodiment of the present invention. (Refer to...) Figure 1 The inverter operating mode switching method based on impedance change provided in this embodiment of the invention includes:

[0060] S101. Obtain voltage information of the electrical connection points between the power grid side and the user side.

[0061] The electrical connection point between the grid side and the user side, known as the grid connection point (PCC), refers to the electrical connection point between the power system (grid) and user equipment (user side, such as new energy power plants, energy storage systems, industrial loads, etc.). It is also the assessment point for power quality (such as harmonics and voltage fluctuations). The core feature of the PCC is that the grid side and the user side share the same voltage and frequency, and it is a monitoring point for power quality and power exchange.

[0062] Specifically, voltage information at the electrical connection point (PCC point) between the grid side and the user side can be obtained in real time through voltage transformers or smart meters.

[0063] S102. Determine the output angular frequency of the inverter based on the voltage information.

[0064] Specifically, the output angular frequency of the inverter refers to the angular frequency of the AC voltage output by the inverter. The voltage information is obtained in step S101 above. The voltage information may include voltage vectors with a 120° phase angle difference. After the abc / dq transformation in the phase-locked loop, the phase angle of the power grid can be obtained. Finally, the AC voltage angular frequency output by the inverter can be calculated based on the voltage information and the phase angle. The open-loop control and closed-loop control of the phase-locked loop are mature existing technologies, and the working principle of the phase-locked loop will not be elaborated here.

[0065] S103. Determine the amplitude values ​​of multiple harmonics of the inverter based on the output angular frequency.

[0066] Specifically, based on the AC voltage angular frequency of the inverter output calculated in step S102 above, the AC voltage angular frequency is analyzed (for example, the method for determining multiple harmonic amplitudes of the inverter includes: 1. determining the fundamental angular frequency; 2. determining the harmonic angular frequency; 3. calculating the harmonic amplitude according to the modulation method), and multiple harmonic amplitudes of the inverter are calculated.

[0067] S104. Determine the diagnostic values ​​of the inverter based on multiple harmonic amplitudes and the inverter's current components.

[0068] Specifically, the diagnostic values ​​of the inverter are determined based on the multiple harmonic amplitudes of the inverter calculated in step S103 above and the current components of the inverter (i.e., the current components of the inverter in the phase-locked loop in the dq coordinate system in step S102 above). The diagnostic values ​​are the main criteria for judging whether the inverter needs to switch operating modes, which will be explained in detail below and will not be repeated here.

[0069] S105. Switch the inverter's operating mode based on the relationship between the diagnostic values ​​and the preset values.

[0070] The inverter operates in two modes: Grid-Following (GFL) and Grid-Forming (GFM).

[0071] Grid-connected systems are mainly used in photovoltaic grid-connected, wind power grid-connected, and energy storage systems. They have current source characteristics (i.e., the output current is controlled and the voltage is determined by the grid), and rely on the grid voltage and frequency (synchronizing the grid phase through a phase-locked loop, and cannot independently establish voltage and frequency).

[0072] The grid-type is mainly used in islanded microgrids, black start, and weak grid support. It has voltage source characteristics (i.e., directly controls the output voltage amplitude and frequency) and autonomously establishes voltage and frequency (without needing a phase-locked loop, it can simulate the inertial characteristics of a synchronous generator).

[0073] Specifically, based on the diagnostic values ​​of the inverter determined in step S104 above, and pre-stored preset values, the inverter's operating mode is switched according to the relationship between the diagnostic values ​​and the preset values ​​(e.g., a size relationship). (e.g., switching from grid-following mode to grid-connecting mode, or vice versa).

[0074] Based on the above embodiments, the present invention further refines the process before acquiring voltage information at the electrical connection point between the power grid side and the user side. Figure 2 This is a flowchart of another inverter operating mode switching method based on impedance change provided in an embodiment of the present invention, for reference. Figure 2 The inverter operating mode switching method based on impedance change provided in this embodiment of the invention includes:

[0075] S201, Load default control parameters and control algorithm into the inverter.

[0076] Specifically, in the initial stage, the default operating mode loaded into the inverter is grid-connected. At the same time, grid-connected control parameters and grid-connected control algorithms are loaded into the inverter to enable the inverter to operate in grid-connected mode. The default control parameters include: phase-locked loop coefficients, control loop coefficients, grid feedforward coefficients, and damping coefficients; the control algorithm is the grid-connected control algorithm.

[0077] S202. Obtain voltage information of the electrical connection points between the power grid side and the user side.

[0078] S203. Determine the output angular frequency of the inverter based on the voltage information.

[0079] S204. Determine the amplitude values ​​of multiple harmonics of the inverter based on the output angular frequency.

[0080] S205. Determine the diagnostic values ​​of the inverter based on multiple harmonic amplitudes and the inverter's current components.

[0081] S206. Switch the inverter's operating mode based on the relationship between the diagnostic values ​​and the preset values.

[0082] Based on the above embodiments, the present invention further refines the determination of the inverter's output angular frequency according to voltage information. Figure 3 This is a flowchart of another inverter operating mode switching method based on impedance change provided in an embodiment of the present invention, for reference. Figure 3 The inverter operating mode switching method based on impedance change provided in this embodiment of the invention includes:

[0083] S301. Obtain voltage information of the electrical connection point between the power grid side and the user side.

[0084] S302. Use voltage information as input to the phase-locked loop control algorithm.

[0085] Specifically, voltage information can be obtained through voltage transformers. The obtained voltage information includes voltage vectors with a 120° difference in three-phase angles, and is input into the phase-locked loop control algorithm.

[0086] S303. Determine the output angular frequency of the inverter based on the phase-locked loop control algorithm and voltage information.

[0087] Specifically, the three-phase voltage of the power grid acquired in step S302 above is used as the input of the phase-locked loop control algorithm. For example, taking a synchronous rotating coordinate system as an example, after coordinate transformation, the proportional-integral (PI) controller controls and outputs the synchronous angular frequency of the inverter. Finally, the inverter's pulse width modulator (PWM) generates a sinusoidal pulse width modulation (SPWM) signal that is synchronized with the power grid, ensuring stable grid-connected power transmission.

[0088] S304. Determine the amplitude values ​​of multiple harmonics of the inverter based on the output angular frequency.

[0089] S305. Determine the diagnostic values ​​of the inverter based on multiple harmonic amplitudes and the inverter's current components.

[0090] S306. Switch the inverter's operating mode based on the relationship between the diagnostic values ​​and the preset values.

[0091] Based on the above embodiments, the present invention further refines the determination of multiple harmonic amplitudes of the inverter according to the output angular frequency. Figure 4 This is a flowchart of another inverter operating mode switching method based on impedance change provided in an embodiment of the present invention, for reference. Figure 4 The inverter operating mode switching method based on impedance change provided in this embodiment of the invention includes:

[0092] S401. Obtain voltage information at the electrical connection points between the power grid side and the user side.

[0093] S402. Use voltage information as input to the phase-locked loop control algorithm.

[0094] S403. Determine the output angular frequency of the inverter based on the phase-locked loop control algorithm and voltage information.

[0095] S404. Perform Fast Fourier Transform analysis on the output angular frequency.

[0096] The Fast Fourier Transform (FFT) is an efficient algorithm for calculating the Discrete Fourier Transform, used to convert time-domain signals into frequency-domain signals and analyze their frequency components.

[0097] Specifically, the output angular frequency of the inverter obtained in step S403 above is subjected to a fast Fourier transform. The steps include: signal sampling (i.e., acquiring the output voltage of the inverter through an analog-to-digital converter), windowing (to reduce spectral leakage), FFT calculation, frequency mapping, and harmonic extraction.

[0098] S405. Derive multiple harmonic amplitude values ​​of the inverter based on the analysis results.

[0099] Specifically, according to step S404 above, the output angular frequency of the inverter is analyzed by FFT transformation, and multiple harmonic amplitudes of the inverter are derived based on the analysis results. The number of harmonic amplitudes is less than k, k is less than 20, and k is related to the bandwidth of the dynamic filter and the sampling frequency.

[0100] S406. Determine the diagnostic values ​​of the inverter based on multiple harmonic amplitudes and the inverter's current components.

[0101] S407. Switch the inverter's operating mode based on the relationship between the diagnostic values ​​and the preset values.

[0102] Optionally, diagnostic values ​​for the inverter can be determined based on multiple harmonic amplitudes and the inverter's current components, including:

[0103] The diagnostic values ​​are calculated using formula (1):

[0104]

[0105] Where diag_value is the diagnostic value, k1 and k2 are the allocation coefficients, and ω i Here, A is the harmonic proportion coefficient, k is the harmonic amplitude, and A is the harmonic amplitude. i The values ​​are the amplitudes of each harmonic extracted in the first k iterations. harmonic_id is the d-axis component minus the DC value in the phase-locked loop control algorithm, and harmonic_iq is the q-axis component minus the DC value in the phase-locked loop control algorithm.

[0106] Based on the above embodiments, the present invention further refines the switching of inverter operating modes according to the relationship between diagnostic values ​​and preset values. Figure 5 This is a flowchart of another inverter operating mode switching method based on impedance change provided in an embodiment of the present invention, for reference. Figure 5 The inverter operating mode switching method based on impedance change provided in this embodiment of the invention includes:

[0107] S501. Obtain voltage information of the electrical connection point between the power grid side and the user side.

[0108] S502. Determine the output angular frequency of the inverter based on the voltage information.

[0109] S503. Determine the amplitude values ​​of multiple harmonics of the inverter based on the output angular frequency.

[0110] S504. Determine the diagnostic values ​​of the inverter based on multiple harmonic amplitudes and the inverter's current components.

[0111] S505. Switch the inverter's operating mode based on the relationship between the diagnostic values ​​and the preset values.

[0112] S506. Compare the diagnostic values ​​with the preset values.

[0113] Specifically, the diagnostic value calculated in step S505 is compared with the preset value stored in advance. If the diagnostic value is greater than the first preset value, step S5061 is executed; if the diagnostic value is less than or equal to the first preset value, step S5062 is executed.

[0114] S5061. When the diagnostic value is greater than the first preset value, the size of the default control parameter is adjusted.

[0115] Specifically, when the diagnostic value is greater than the first preset value, the default control parameters loaded into the inverter before step S501 are adjusted, that is, the size of the default control parameters is adjusted (the default control parameters are the grid-connected control parameters). The control parameters include: phase-locked loop coefficient, grid feedforward coefficient, damping coefficient, etc.

[0116] S5062. When the diagnostic value is less than or equal to the first preset value, the inverter's operating mode is switched from grid-following to grid-connecting.

[0117] Specifically, when the diagnostic value is less than or equal to the first preset value, the inverter's working module will be switched from the default grid-following mode to the grid-building mode.

[0118] Based on the above embodiments, the present invention further refines the process of adjusting the default control parameter when the diagnostic value is greater than a first preset value. Figure 6 This is a flowchart of another inverter operating mode switching method based on impedance change provided in an embodiment of the present invention, for reference. Figure 6 The inverter operating mode switching method based on impedance change provided in this embodiment of the invention includes:

[0119] S601. Obtain voltage information of the electrical connection point between the power grid side and the user side.

[0120] S602. Determine the output angular frequency of the inverter based on the voltage information.

[0121] S603. Determine the amplitude values ​​of multiple harmonics of the inverter based on the output angular frequency.

[0122] S604. Determine the diagnostic values ​​of the inverter based on multiple harmonic amplitudes and the inverter's current components.

[0123] S605. Switch the inverter's operating mode based on the relationship between the diagnostic values ​​and the preset values.

[0124] S606. Compare the diagnostic values ​​with the preset values.

[0125] S607. When the diagnostic value is greater than the first preset value, the size of the default control parameter is adjusted.

[0126] S608. Compare the diagnostic value with the second preset value.

[0127] Specifically, when the diagnostic value is greater than the first preset value and less than the second preset value, step S6081 is executed; when the diagnostic value is greater than the first preset value and greater than or equal to the second preset value, step S6082 is executed.

[0128] S6081. When the diagnostic value is greater than the first preset value and less than the second preset value, the diagnostic value will continue to be monitored.

[0129] Specifically, after obtaining the diagnostic value in step S604 above, the diagnostic value is compared with the first preset value and the second preset value. When the diagnostic value is greater than the first preset value and less than the second preset value, since the power grid is running and the inverter is also running, the voltage information of the inverter is also changing, which leads to a change in the diagnostic value of the inverter. At this time, the diagnostic value of the inverter is monitored.

[0130] S6082. When the diagnostic value is greater than the first preset value and greater than or equal to the second preset value, the diagnostic value is compared with the third preset value.

[0131] Specifically, after obtaining the diagnostic value in step S604 above, the diagnostic value is compared with the first preset value and the second preset value. When the diagnostic value is greater than the first preset value and greater than or equal to the second preset value, proceed to the next step, that is, compare the diagnostic value with the third preset value.

[0132] Based on the above embodiments, the present invention further refines the comparison of the diagnostic value with a third preset value when the diagnostic value is greater than a first preset value and greater than or equal to a second preset value. Figure 7 This is a flowchart of another inverter operating mode switching method based on impedance change provided in an embodiment of the present invention, for reference. Figure 7 The inverter operating mode switching method based on impedance change provided in this embodiment of the invention includes:

[0133] S701. Obtain voltage information of the electrical connection point between the power grid side and the user side.

[0134] S702. Determine the output angular frequency of the inverter based on the voltage information.

[0135] S703. Determine the amplitude values ​​of multiple harmonics of the inverter based on the output angular frequency.

[0136] S704. Determine the diagnostic values ​​of the inverter based on multiple harmonic amplitudes and the inverter's current components.

[0137] S705. Switch the inverter's operating mode based on the relationship between the diagnostic values ​​and the preset values.

[0138] S706. Compare the diagnostic values ​​with the preset values.

[0139] S707. When the diagnostic value is greater than the first preset value, the size of the default control parameter is adjusted.

[0140] S708. Compare the diagnostic value with the second preset value.

[0141] S709. When the diagnostic value is greater than the first preset value and greater than or equal to the second preset value, the diagnostic value is compared with the third preset value.

[0142] S7091. When the diagnostic value is greater than or equal to the third preset value, the value of the default control parameter shall be adjusted.

[0143] Specifically, when the diagnostic value is greater than or equal to the third preset value, the default control parameters loaded into the inverter before step S701 are adjusted, that is, the size of the default control parameters is adjusted (the default control parameters are the grid-connected control parameters). The control parameters include: phase-locked loop coefficient, grid feedforward coefficient, damping coefficient, etc.

[0144] S7092. When the diagnostic value is less than the third preset value, the default control parameters are loaded. Wherein, the first preset value is less than the second preset value, and the second preset value is less than the third preset value.

[0145] Specifically, when the diagnostic value is less than the third preset value, the default control parameters will continue to be loaded, that is, the inverter will maintain its grid-connected working mode.

[0146] Based on the above embodiments, the present invention further refines the switching of the inverter's operating mode according to the relationship between diagnostic values ​​and preset values. Figure 8 This is a flowchart of another inverter operating mode switching method based on impedance change provided in an embodiment of the present invention, for reference. Figure 8 The inverter operating mode switching method based on impedance change provided in this embodiment of the invention further includes:

[0147] S801. Obtain voltage information of the electrical connection point between the power grid side and the user side.

[0148] S802. Determine the output angular frequency of the inverter based on the voltage information.

[0149] S803. Determine the amplitude values ​​of multiple harmonics of the inverter based on the output angular frequency.

[0150] S804. Determine the diagnostic values ​​of the inverter based on multiple harmonic amplitudes and the inverter's current components.

[0151] S805. Switch the inverter's operating mode based on the relationship between the diagnostic values ​​and the preset values.

[0152] S806. When the inverter is in grid-connected operation mode, the impedance of the electrical connection point between the grid side and the user side is calculated by active injection method.

[0153] Specifically, in step S805 above, when the inverter is in grid-connected working mode, also known as strong grid, the impedance of the electrical connection point between the grid side and the user side can be calculated by the active injection method. In this working mode, the use of the active injection method will not have a significant impact on the stability of the grid system and the power quality. Figure 9 This is a typical three-phase inverter dual closed-loop control block diagram provided in an embodiment of the present invention, for reference. Figure 9 V d * V q * G is the outer ring reference value. c For the outer loop regulator, G d For inner loop regulator, H il This is the current coefficient. When it is determined that the inverter is under strong grid conditions (i.e., grid-connected), a small disturbance can be injected into the outer or inner loop, and the corresponding voltage / current can be measured to obtain the impedance at the PCC point under this operating condition, thereby further improving the accuracy of this method.

[0154] Based on the same inventive concept, embodiments of the present invention also provide an inverter operating mode switching device based on impedance change, used to execute the inverter operating mode switching method based on impedance change in any of the above embodiments. Figure 10 This is a block diagram of an inverter operating mode switching device based on impedance change provided in an embodiment of the present invention. (Refer to...) Figure 10 The inverter operating mode switching device includes:

[0155] Module 1 is used to acquire voltage information of the electrical connection points between the power grid side and the user side.

[0156] Output angular frequency determination module 2 is used to determine the output angular frequency of the inverter based on voltage information.

[0157] Harmonic amplitude determination module 3 is used to determine multiple harmonic amplitudes of the inverter based on the output angular frequency.

[0158] The diagnostic value determination module 4 is used to determine the diagnostic values ​​of the inverter based on multiple harmonic amplitudes and the inverter's current components.

[0159] The working mode switching module 5 is used to switch the working mode of the inverter according to the relationship between the diagnostic value and the preset value.

[0160] The inverter operating mode switching device based on impedance change provided in this embodiment of the invention can achieve the same technical effect as the inverter operating mode switching method based on impedance change provided in the above-mentioned embodiment of the invention, and will not be described again here.

[0161] The specific embodiments described above do not constitute a limitation on the scope of protection of this invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A method for switching the operating mode of an inverter based on impedance change, characterized in that, include: Obtain voltage information at the electrical connection points between the power grid and the user side; The output angular frequency of the inverter is determined based on the voltage information; The multiple harmonic amplitudes of the inverter are determined based on the output angular frequency; The diagnostic values ​​of the inverter are determined based on multiple harmonic amplitudes and the current components of the inverter. The inverter's operating mode is switched based on the relationship between the diagnostic values ​​and preset values.

2. The inverter operating mode switching method based on impedance change according to claim 1, characterized in that, Before obtaining voltage information at the electrical connection points between the grid side and the user side, the following steps are included: The inverter is loaded with default control parameters and a control algorithm; wherein the default control parameters include: phase-locked loop coefficients, control loop coefficients, grid feedforward coefficients, and damping coefficients; and the control algorithm is a grid-following control algorithm.

3. The inverter operating mode switching method based on impedance change according to claim 1, characterized in that, Determining the inverter's output angular frequency based on the voltage information includes: The voltage information is used as the input to the phase-locked loop control algorithm; The output angular frequency of the inverter is determined based on the phase-locked loop control algorithm and the voltage information.

4. The inverter operating mode switching method based on impedance change according to claim 3, characterized in that, The inverter's multiple harmonic amplitudes are determined based on the output angular frequency, including: Perform a Fast Fourier Transform analysis on the output angular frequency; Based on the analysis results, multiple harmonic amplitude values ​​of the inverter are derived; wherein the number of harmonic amplitude values ​​is less than 20.

5. The inverter operating mode switching method based on impedance change according to claim 3, characterized in that, The diagnostic values ​​of the inverter are determined based on multiple harmonic amplitudes and the current components of the inverter, including: The diagnostic values ​​are calculated using formula (I): Where, diag_value is the diagnostic value, k1 and k2 are allocation coefficients, and ω i Here, A is the harmonic proportion coefficient, k is the harmonic amplitude, and A is the harmonic amplitude. i The harmonic amplitudes are extracted from the first k iterations. harmonic_id is the d-axis component minus the DC value in the phase-locked loop control algorithm, and harmonic_iq is the q-axis component minus the DC value in the phase-locked loop control algorithm.

6. The inverter operating mode switching method based on impedance change according to claim 2, characterized in that, The inverter's operating mode is switched based on the relationship between the diagnostic values ​​and preset values, including: When the diagnostic value is greater than the first preset value, the value of the default control parameter is adjusted. When the diagnostic value is less than or equal to the first preset value, the inverter's operating mode is switched from grid-connected to grid-connected.

7. The inverter operating mode switching method based on impedance change according to claim 6, characterized in that, When the diagnostic value is greater than the first preset value, adjusting the default control parameter includes: When the diagnostic value is greater than the first preset value and less than the second preset value, the diagnostic value continues to be monitored. When the diagnostic value is greater than the first preset value and greater than or equal to the second preset value, the diagnostic value is compared with the third preset value.

8. The inverter operating mode switching method based on impedance change according to claim 7, characterized in that, When the diagnostic value is greater than the first preset value and greater than or equal to the second preset value, the diagnostic value is compared with a third preset value, including: When the diagnostic value is greater than or equal to the third preset value, the value of the default control parameter is adjusted. When the diagnostic value is less than the third preset value, the default control parameter is loaded; wherein the first preset value is less than the second preset value, and the second preset value is less than the third preset value.

9. The inverter operating mode switching method based on impedance change according to claim 2, characterized in that, After switching the inverter's operating mode based on the relationship between the diagnostic values ​​and preset values, the process further includes: When the inverter is in the grid-connected operating mode, the impedance of the electrical connection point between the grid side and the user side is calculated by the active injection method.

10. An inverter operating mode switching device based on impedance change, characterized in that, For executing the inverter operating mode switching method based on impedance change as described in any one of claims 1-9, the inverter operating mode switching device comprises: The acquisition module is used to acquire voltage information at the electrical connection points between the power grid side and the user side; An output angular frequency determination module is used to determine the output angular frequency of the inverter based on the voltage information. The harmonic amplitude determination module is used to determine multiple harmonic amplitudes of the inverter based on the output angular frequency. The diagnostic value determination module is used to determine the diagnostic value of the inverter based on multiple harmonic amplitudes and the current component of the inverter. The working mode switching module is used to switch the working mode of the inverter according to the relationship between the diagnostic value and the preset value.

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