VSG-based inverter phase-locked loop-free pre-synchronization method, system and device, and medium

Abstract

The invention relates to the technical field of inverter control, and discloses a VSG-based inverter phase-locked loop-free pre-synchronization method, system and device and a medium, and the method comprises the steps: eliminating the voltage deviation between the VSG inverter voltage of a virtual synchronous generator and the output voltage of a micro-grid through a deviation integral feedback method; a general signal delay superposition operator is adopted to filter the power grid voltage so as to construct virtual power, then the virtual power is introduced into an active-frequency loop of the virtual synchronous generator as a feedback signal, and a power angle feedback control model is formed so as to adjust the VSG inverter voltage; and detecting the voltage deviation between the power grid voltage and the adjusted VSG inverter voltage in real time, and when it is judged that the voltage deviation is smaller than a deviation threshold value, generating a grid-connected connection point switching-on instruction and controlling a switch of a grid-connected connection point to be switched on, so that phase-locked loop-free pre-synchronization of the distributed power supply inverter is realized, the grid-connected stability of the distributed power supply inverter is enhanced, and the grid-connected stability of the distributed power supply inverter is improved. And the current and voltage impact of the grid-connected instant system is reduced.

Description

Technical Field

[0001] The present invention relates to the field of inverter control technology, and in particular to a VSG-based inverter phase-locked loop-free pre-synchronization method, system, device and medium. Background Art

[0002] Since the virtual synchronous generator (VSG) can imitate various characteristics of the synchronous generator, such as providing the ability to generate power and regulate frequency, and providing the distributed generator (DG) with inertia and damping properties similar to those of the synchronous generator, it has been widely used in the grid construction of distributed power inverters.

[0003] In the prior art, the VSG-based DG inverter pre-synchronization grid-connected control method can be divided into: dual phase-locked loop pre-synchronization, single phase-locked loop pre-synchronization and no phase-locked loop pre-synchronization according to the number of phase-locked loops used as needed. However, the introduction of heavy phase-locked loops in this process will increase the complexity of the system, and its phase-locked accuracy will also affect whether the pre-synchronization can be accurately achieved. At the same time, the grid voltage at the pre-synchronization grid-connected point of the VSG-based DG inverter is usually not an ideal voltage source, and will contain a large number of high-order harmonics, which will easily cause output power oscillations, and will also affect the accuracy of grid pre-synchronization information extraction, thereby affecting the grid-connected stability of the DG inverter based on the VSG control strategy.

[0004] It can be seen that how to improve the stability of distributed power inverters when connected to the grid has become a technical problem that needs to be urgently solved by those skilled in the art. Summary of the invention

[0005] The present invention provides a VSG-based inverter phase-locked loop-free pre-synchronization method, system, device and medium to solve the problem of how to improve the stability of a distributed power inverter when it is connected to the grid.

[0006] In order to solve the above technical problems, the first aspect of the present invention provides a VSG-based inverter phase-locked loop-free pre-synchronization method, comprising:

[0007] When it is detected that the microgrid is in an off-grid mode, a deviation integral feedback method is used to eliminate a first voltage deviation between a VSG inverter voltage output by a virtual synchronous generator and a grid voltage output by the microgrid;

[0008] filtering high-order harmonic interference in the grid voltage by a universal signal delay superposition operator, and constructing virtual power according to the filtered grid voltage;

[0009] Introducing the virtual power as a feedback signal into the active power-frequency loop of the virtual synchronous generator to form a work angle feedback control model to adjust the VSG inverter voltage;

[0010] The second voltage deviation between the grid voltage and the adjusted VSG inverter voltage is detected in real time. When the second voltage deviation is less than the deviation threshold, a grid connection point closing instruction is generated and the switch of the grid connection point is controlled to close, so as to realize the phase-locked loop-free pre-synchronization of the distributed power inverter.

[0011] As one of the preferred solutions, when it is detected that the microgrid is in an off-grid mode, a deviation integral feedback method is used to eliminate a first voltage deviation between a VSG inverter voltage output by a virtual synchronous generator and a grid voltage output by the microgrid, including:

[0012] When detecting that the microgrid is in an off-grid mode, responding to the off-grid mode and generating a pre-synchronization instruction to send to the virtual synchronous generator;

[0013] Controlling the virtual synchronous generator to introduce secondary frequency and secondary voltage based on deviation integral feedback into its own active-frequency loop and reactive-voltage loop based on the pre-synchronization instruction for adjustment, so as to eliminate the first voltage deviation between the VSG inverter voltage and the grid voltage;

[0014] The deviation between the adjusted VSG inverter voltage and the grid voltage is expressed by the following formula:

[0015]

[0016] Where Δω and ΔU are the voltage angular frequency and amplitude deviation respectively; s is a complex variable; J and D are the virtual inertia and damping coefficient of the virtual synchronous generator respectively; ω 0 is the rated angular frequency; P ref (s), Q ref (s) are the rated active and reactive power of the virtual synchronous generator respectively; P L (s), Q L (s) are local active and reactive loads respectively; k 1 , k 2 are the integral feedback coefficients of frequency deviation and voltage deviation respectively; k q , k i They are the reactive droop coefficient and reactive loop integral coefficient of the virtual synchronous generator respectively.

[0017] As one of the preferred solutions, filtering the high-order harmonic interference in the grid voltage by a universal signal delay superposition operator and constructing virtual power according to the filtered grid voltage includes:

[0018] Performing Clark transformation on the grid voltage to obtain two-phase voltage signals in a two-phase stationary coordinate system;

[0019] Performing a filtering operation on the two-phase voltage signal according to the universal signal delay superposition operator to obtain a two-phase fundamental voltage signal to extract a fundamental positive sequence component, thereby obtaining a three-phase voltage fundamental positive sequence component;

[0020] The virtual power is constructed based on the three-phase voltage fundamental positive sequence component.

[0021] As one preferred solution, the universal signal delay addition operator includes a first universal signal delay addition operator and a second universal signal delay addition operator; wherein,

[0022] The filtering operation is performed on the two-phase voltage signal according to the universal signal delay superposition operator to obtain the two-phase fundamental voltage signal to extract the fundamental positive sequence component to obtain the three-phase voltage fundamental positive sequence component, including:

[0023] The harmonic frequency signal to be extracted from the two-phase voltage signal is extracted by the first universal signal delay superposition operator, and the orthogonal signal corresponding to the harmonic frequency signal to be extracted is extracted from the two-phase voltage signal by the second universal signal delay superposition operator, so as to obtain a two-phase fundamental voltage signal; wherein the first universal signal delay superposition operator and the second universal signal delay superposition operator are expressed by the following formula:

[0024]

[0025] Where GDSS1 and GDSS2 are the first general signal delay superposition operator and the second general signal delay superposition operator respectively; u(t) is the two-phase voltage signal; m, k, n are any integers; h s is the harmonic frequency signal to be extracted; T is the fundamental wave period;

[0026] A positive sequence extraction model is used to extract the fundamental positive sequence component in the two-phase fundamental voltage signal to obtain the three-phase voltage fundamental positive sequence component; wherein the positive sequence extraction model is expressed by the following formula:

[0027]

[0028] In the formula, is the positive sequence component of the three-phase voltage fundamental wave in the αβ coordinate system; T abc is the Clark transformation matrix; T + is the voltage positive sequence component calculation matrix; u αβ is the two-phase fundamental voltage signal in the αβ coordinate system; q is the 90° lagging operator.

[0029] As one of the preferred solutions, constructing the virtual power based on the positive sequence component of the three-phase voltage fundamental wave includes:

[0030] quantizing a virtual current according to a virtual inductance between the virtual synchronous generator and the microgrid, a fundamental positive sequence component of the three-phase voltage, and a VSG inverter voltage, and determining a virtual voltage based on the VSG inverter voltage;

[0031] Determine initial power by using the virtual current and the virtual voltage, and average the initial power using a sliding time window to obtain average power;

[0032] The average power is subjected to inertial processing to generate the virtual power.

[0033] As one of the preferred solutions, the power angle feedback control model is expressed by the following formula:

[0034]

[0035] Where δ is the power angle of the virtual synchronous generator; Δω V is the virtual angular frequency deviation; P V is the virtual power; U is the VSG inverter voltage; U g is the grid voltage; X V is the reactance in the virtual impedance; t is the time.

[0036] As one of the preferred solutions, after the real-time detection of the second voltage deviation between the grid voltage and the adjusted VSG inverter voltage, the method further includes:

[0037] When the second voltage deviation is not less than the deviation threshold, the first voltage deviation elimination step and the virtual power construction step are iteratively performed based on the adjusted VSG inverter voltage to update the second voltage deviation, and the relationship between the updated second voltage deviation and the deviation threshold is re-judged according to the update result, until the iterative process is terminated when the second voltage deviation is less than the deviation threshold, a grid connection point closing instruction is generated, and the switch of the grid connection point is controlled to be closed, so as to realize the phase-locked loop-free pre-synchronization of the distributed power supply inverter.

[0038] A second aspect of the present invention provides a VSG-based inverter phase-locked loop-free presynchronization system, comprising:

[0039] A deviation elimination module, for eliminating a first voltage deviation between a VSG inverter voltage output by a virtual synchronous generator and a grid voltage output by the microgrid by using a deviation integral feedback method when detecting that the microgrid is in an off-grid mode;

[0040] A power construction module, used for filtering high-order harmonic interference in the grid voltage through a universal signal delay superposition operator, and constructing virtual power according to the filtered grid voltage;

[0041] A voltage regulation module, used for introducing the virtual power as a feedback signal into the active power-frequency loop of the virtual synchronous generator, forming a work angle feedback control model to regulate the VSG inverter voltage;

[0042] The pre-synchronization module is used to detect in real time the second voltage deviation between the grid voltage and the adjusted VSG inverter voltage. When the second voltage deviation is less than the deviation threshold, it generates a grid connection point closing instruction and controls the switch of the grid connection point to close, so as to realize the phase-locked loop-free pre-synchronization of the distributed power inverter.

[0043] A third aspect of the present invention provides an electronic device, comprising a processor, a memory, and a computer program stored in the memory and configured to be executed by the processor, wherein when the processor executes the computer program, the VSG-based inverter non-phase-locked loop pre-synchronization method as described above is implemented.

[0044] A fourth aspect of the present invention provides a computer-readable storage medium, which includes a stored computer program, wherein when the device where the computer-readable storage medium is located executes the computer program, the VSG-based inverter phase-locked loop pre-synchronization method as described above is implemented.

[0045] Compared with the prior art, the embodiments of the present invention have the following advantages:

[0046] (1) The deviation integral feedback method can accurately calculate and eliminate the voltage deviation between the voltage output by the VSG and the voltage output by the microgrid, thereby ensuring the voltage consistency between the two and improving the voltage stability. The high-order harmonic interference in the grid voltage can be filtered out by the universal signal delay superposition operator, which can effectively reduce the impact of harmonics on the grid voltage and further improve the voltage quality.

[0047] (2) The introduction of virtual power feedback can realize dynamic adjustment of the VSG inverter voltage, thereby accurately reflecting the actual state of the power grid, improving the accuracy and response speed of active power-frequency control, and adjusting the output power angle of the VSG through the power angle feedback control model to achieve synchronous operation with the power grid, which helps to ensure the stability and reliability of distributed power sources during the grid connection process;

[0048] (3) A phase-locked loop-free grid-connected pre-synchronization process is realized, which reduces the complexity and uncertainty of the grid-connected process and improves the success rate of grid-connected. The scheme can adapt to changes in different microgrid environments and distributed power supply characteristics and has strong adaptability and flexibility. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] In order to more clearly illustrate the technical solution of the present invention, the drawings required for use in the implementation mode will be briefly introduced below. Obviously, the drawings described below are only some implementation modes of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0050] Figure 1 It is an active frequency characteristic diagram of a distributed power inverter provided by a certain embodiment of the present invention under the condition of a virtual synchronous machine with different loads in an off-grid mode;

[0051] Figure 2 It is a flow chart of a VSG-based inverter phase-locked loop-free pre-synchronization method provided by an embodiment of the present invention;

[0052] Figure 3 is a frequency deviation integral feedback structure diagram provided by a certain embodiment of the present invention;

[0053] Figure 4 is a voltage deviation integral feedback structure diagram provided by a certain embodiment of the present invention;

[0054] Figure 5 It is a diagram of a process of generating a positive sequence component of a fundamental wave of a three-phase voltage provided by a certain embodiment of the present invention;

[0055] Figure 6 is a phase plane diagram of a power angle feedback control model provided by a certain embodiment of the present invention;

[0056] Figure 7 It is a diagram of an active-frequency loop and a reactive-voltage loop after introducing deviation integral feedback regulation and power angle regulation based on virtual power provided by a certain embodiment of the present invention;

[0057] Figure 8 It is a diagram showing the synchronization between the VSG inverter voltage and the grid voltage when directly connected to the grid according to an embodiment of the present invention;

[0058] Fig. 9 is a diagram showing the frequency variation of the VSG inverter voltage when directly connected to the grid provided by an embodiment of the present invention;

[0059] Fig.10 This is a diagram showing the change in output current of a VSG grid connection point when directly connected to the grid, provided by an embodiment of the present invention;

[0060] Fig.11 It is a diagram showing changes of pre-synchronization instructions and PCC point closing instructions when the solution of the present invention is adopted, provided by a certain embodiment of the present invention;

[0061] Fig.12 It is a diagram showing the synchronization between the VSG inverter voltage and the grid voltage when the solution of the present invention is adopted, provided in a certain embodiment of the present invention;

[0062] Fig.13 It is a diagram of the frequency variation of the VSG inverter voltage when the solution of the present invention is adopted, provided by a certain embodiment of the present invention;

[0063] Fig.14 A diagram showing the change of the output current of the VSG grid connection point when the solution of the present invention is adopted, provided in a certain embodiment of the present invention;

[0064] Fig.15 It is a structural diagram of a VSG-based inverter non-phase-locked loop pre-synchronization system provided by a certain embodiment of the present invention;

[0065] Fig.16 It is a structural diagram of an electronic device provided by a certain embodiment of the present invention. DETAILED DESCRIPTION

[0066] The following is a clear and complete description of the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings and embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. The purpose of providing these embodiments is to make the disclosure of the present invention more thorough and comprehensive. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0067] In the description of this application, the terms "first", "second", "third", etc. are used for descriptive purposes only and are not to be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first", "second", "third", etc. may explicitly or implicitly include one or more of the feature. In the description of this application, unless otherwise specified, "plurality" means two or more.

[0068] In the description of the present application, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be a connection between the two components. The terms "vertical", "horizontal", "left", "right", "upper", "lower" and similar expressions used herein are for illustrative purposes only, and do not indicate or imply that the system or component referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention. The term "and / or" used herein includes any and all combinations of one or more related listed items. For those of ordinary skill in the art, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0069] In the description of this application, it should be noted that, unless otherwise defined, all technical and scientific terms used in the present invention have the same meaning as those commonly understood by those skilled in the art. The terms used in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. For those of ordinary skill in the art, the specific meanings of the above terms in this application can be understood by specific circumstances.

[0070] Normally, a distributed power inverter can be equivalent to a voltage source when working. When a planned or unplanned grid-connected mode switches to an off-grid mode, the output of the inverter can maintain the voltage and phase in the grid-connected mode. Therefore, in the process of switching from grid-connected to off-grid, the transient process of the system is relatively stable, and will not have a great impact on the local load, and the switching between grid-connected and off-grid can be smoothly realized; and when the distributed power inverter needs to switch from off-grid mode (i.e., the distributed power supply independently supplies power to the local load) to grid-connected mode (i.e., the distributed power supply and the distribution network jointly supply power to the local load), since the distributed power inverter is previously in an off-grid state, the output power is determined by the local load, and the voltage amplitude and phase output by the active and reactive power regulation system are not necessarily consistent with the grid system of the microgrid. If it is directly connected to the grid at this time, it will lead to grid connection failure and seriously affect the power quality of the grid.

[0071] The active frequency characteristics of the virtual synchronous machine of the distributed power inverter in off-grid mode with different loads are as follows: Figure 1 As shown, straight line 4 is the frequency droop curve of the distributed power inverter, straight lines 1-3 are the frequency characteristic curves of different loads, and the frequency represented by the intersection of straight line 4 and straight line 1-3 is the system operating frequency value when the distributed power inverter carries different loads. Figure 1 It can be seen that when the load is P L1When the distributed power inverter operates at a frequency of ω 1 , at this time P L1 <P ref ,ω 1 >ω ref ; When the load is P L2 When the distributed power inverter operates at a frequency of ω 2 , at this time P L2 >P ref , ω2<ωref; the grid frequency is generally 50Hz, ω ref =100πrad / s, so when the local load is not P ref When the operating frequency of the distributed power inverter is not ω ref ,With the accumulation of running time, there will be a phase difference between the phase angle of the distributed power inverter and the grid phase angle. Similarly, according to the reactive power-voltage characteristics of VSG, the output voltage amplitude of the distributed power inverter will be different depending on the type of local load.

[0072] During off-grid operation, the grid voltage V output by the microgrid g The VSG inverter voltage V output by the virtual synchronous generator o As shown below:

[0073] V g =V 1 sin(ω g t+θ g )

[0074] V o =V 2 sin(ω o t+θ o )

[0075] Where V 1 ,ω g and θ g are the voltage amplitude, angular frequency and phase angle of the grid voltage respectively; V 2 ,ω o and θ o are the voltage amplitude, angular frequency and phase angle of the VSG inverter voltage respectively; t is time.

[0076] During off-grid operation, the VSG inverter voltage is approximately equal to the grid voltage, V 2 ≈V 1 = V. Therefore, the transient voltage difference between the two voltages V e It can be expressed as follows:

[0077] V e =V g -V o =V 1sin(ω g t+θ g )-V 2 sin(ω o t+θ o )

[0078] By using trigonometric identities, V e The simplified representation is:

[0079]

[0080] When the VSG inverter operates in off-grid mode, V e A simplified representation of can be characterized as the possibility of frequency and phase differences between the grid voltage and the VSG inverter voltage. Therefore, substantial deviations of up to 2V may occur at the point of common connection (PCC, i.e., the grid connection point). In order to synchronize the VSG inverter voltage with the grid voltage, it is crucial to ensure that their frequency, voltage, and phase angle are aligned with each other, as any mismatch in these parameters can lead to sudden changes in power flow, which may cause instability or damage to both the VSG inverter and the grid.

[0081] In AC power grid, due to the extensive application of many nonlinear electrical devices, its voltage and current waveforms are not actually completely sinusoidal waveforms, but non-sinusoidal waves with varying degrees of distortion. In a balanced three-phase system, due to the symmetry relationship, even harmonics have been eliminated, and only odd harmonics exist. The harmonic voltage and current that appear are mainly 6n±1 harmonics, such as 5th, 7th, 11th, 13th, etc. The existence of harmonic voltage causes the grid voltage to no longer be a single sinusoidal voltage form, resulting in a transient voltage difference V between the grid voltage and the VSG inverter voltage. e Contains multiple harmonic components, as shown in the following formula:

[0082]

[0083] Where n is the harmonic order; V gn is the amplitude of the nth harmonic, which is generally 1 / n of the fundamental amplitude; θ gn is the phase angle of the nth harmonic. Under the condition of grid voltage containing harmonics, the transient voltage difference between the grid voltage and the VSG inverter voltage contains multiple harmonic components, which interferes with the extraction of grid pre-synchronization information.

[0084] In order to solve the problem of grid-connected pre-synchronization of distributed power inverters based on the VSG control strategy and eliminate grid voltage harmonic interference, in one embodiment, as Figure 2 As shown, the first aspect of the present invention provides a VSG-based inverter non-phase-locked loop pre-synchronization method, which is applied to a distributed power inverter based on a VSG control strategy, comprising:

[0085] S1. When it is detected that the microgrid is in an off-grid mode, a deviation integral feedback method is used to eliminate a first voltage deviation between a VSG inverter voltage output by a virtual synchronous generator and a grid voltage output by the microgrid;

[0086] S2. filtering the high-order harmonic interference in the grid voltage by a universal signal delay superposition operator, and constructing virtual power according to the filtered grid voltage;

[0087] S3, introducing the virtual power as a feedback signal into the active power-frequency loop of the virtual synchronous generator, forming a work angle feedback control model to adjust the VSG inverter voltage;

[0088] S4. Real-time detection of a second voltage deviation between the grid voltage and the adjusted VSG inverter voltage. When the second voltage deviation is less than a deviation threshold, a grid connection point closing instruction is generated and the switch of the grid connection point is controlled to close, so as to realize phase-locked loop-free pre-synchronization of the distributed power inverter.

[0089] Specifically, when it is detected that the microgrid is in off-grid mode, the deviation integral feedback method is used to eliminate the voltage deviation between the VSG inverter voltage output by the virtual synchronous generator and the grid voltage output by the microgrid to ensure the initial matching of the voltage and lay the foundation for the subsequent synchronization process; and the generalized delayed signal superposition operator (Generalized Delayed Signal Superposition Operator, GDSS) is used to filter out the high-order harmonic interference in the grid voltage, and the filtered grid voltage information is used to construct virtual power to improve the purity of the voltage signal, providing a reliable basis for power feedback control; the virtual power is then introduced into the active loop of the VSG through the filtering link to make the output voltage gradually synchronized with the grid fundamental voltage, that is, the VSG inverter voltage is dynamically adjusted according to the change of virtual power, and the voltage stability and synchronization are further improved; finally, in the process of introducing the virtual power signal to realize the power angle adjustment, the voltage deviation between the grid voltage and the VSG inverter voltage (that is, the voltage amplitude deviation ΔU, the angular frequency deviation Δω and the phase deviation Δθ) is detected in real time, when its relationship with the deviation threshold satisfies the following formula:

[0090]

[0091] Where U T ,ω T ,θ T Both are deviation thresholds.

[0092] That is, when the voltage deviation between the grid voltage and the adjusted VSG inverter voltage is less than the deviation threshold, a grid connection point closing command is generated and the switch of the grid connection point is controlled to close, and the deviation integral feedback and virtual power angle adjustment links are cut off at the same time to achieve phase-locked loop-free pre-synchronization of the distributed power inverter and enter the grid-connected mode. It should be noted that the first voltage deviation and the second voltage deviation both refer to the voltage deviation between the VSG inverter voltage and the grid voltage.

[0093] The present invention uses the deviation integral feedback method and the power angle feedback control model to more accurately adjust the VSG inverter voltage to keep it consistent with the grid voltage, thereby improving the synchronization accuracy; at the same time, the use of the general signal delay superposition operator effectively removes the high-order harmonic interference in the grid voltage, improves the purity of the voltage signal and the stability of the system, avoids the use of the traditional phase-locked loop, simplifies the synchronization process, and reduces the difficulty and cost of synchronization.

[0094] In one embodiment, step S1 includes:

[0095] When detecting that the microgrid is in an off-grid mode, responding to the off-grid mode and generating a pre-synchronization instruction to send to the virtual synchronous generator;

[0096] Controlling the virtual synchronous generator to introduce secondary frequency and secondary voltage based on deviation integral feedback into its own active-frequency loop and reactive-voltage loop based on the pre-synchronization instruction for adjustment, so as to eliminate the first voltage deviation between the VSG inverter voltage and the grid voltage;

[0097] Specifically, in off-grid mode, the VSG rated power does not match the load power, causing the VSG frequency and phase to deviate from the grid frequency and phase. Similarly, the VSG rated power does not match the load power, causing the VSG voltage to deviate from the grid voltage. The frequency deviation and amplitude deviation values ​​are as follows:

[0098]

[0099] Where Δω and ΔU are the voltage angular frequency and amplitude deviation respectively; s is a complex variable; J and D are the virtual inertia and damping coefficient of the virtual synchronous generator respectively; ω 0 is the rated angular frequency; P ref (s), Q ref (s) are the rated active and reactive power of the virtual synchronous generator respectively; P L (s), Q L (s) are local active and reactive loads respectively; k q , k i They are the reactive droop coefficient and reactive loop integral coefficient of the virtual synchronous generator respectively.

[0100] Therefore, before grid connection, measures must be taken to eliminate frequency deviation and voltage deviation. The present invention adopts a deviation integral feedback method to eliminate the error caused by power mismatch. The frequency deviation integral feedback structure and the voltage deviation integral feedback structure are respectively as follows: Figure 3 , 4 As shown in the figure, when the power does not match, when the deviation Δω, ΔU is not 0, the deviation is fed through the integral negative feedback link (k 1 / s and k 2 / s link) is introduced into the input end to reduce the equivalent input, and the deviation is adjusted to 0 in the final stable state, so that the angular frequency and amplitude of the VSG inverter voltage are consistent with the distribution network frequency and voltage rating; wherein the deviation between the adjusted VSG inverter voltage and the grid voltage is expressed by the following formula:

[0101]

[0102] In the formula, k 1 , k 2 They are the frequency deviation and voltage deviation integral feedback coefficients respectively.

[0103] The present invention can more accurately adjust the output of VSG to keep it consistent with the grid voltage by introducing secondary frequency and secondary voltage regulation of deviation integral feedback, greatly improving the synchronization accuracy and reducing the impact and oscillation during grid connection; in the microgrid off-grid mode, through precise pre-synchronization control, it can ensure that VSG is synchronized with the grid voltage before grid connection, which helps to enhance the stability of the system and avoid problems such as voltage fluctuations and frequency instability that may occur during the grid connection process.

[0104] In one embodiment, step S2 includes:

[0105] Performing Clark transformation on the grid voltage to obtain two-phase voltage signals in a two-phase stationary coordinate system;

[0106] Performing a filtering operation on the two-phase voltage signal according to the universal signal delay superposition operator to obtain a two-phase fundamental voltage signal to extract a fundamental positive sequence component, thereby obtaining a three-phase voltage fundamental positive sequence component;

[0107] The virtual power is constructed based on the three-phase voltage fundamental positive sequence component.

[0108] Specifically, any single-phase voltage or current signal u(t) can be regarded as a combination of fundamental and harmonic signals, and its expression is as follows:

[0109]

[0110] Where h is the harmonic order (for the fundamental component, h = 1); H is the maximum harmonic order considered; ω, are the fundamental angular frequency and the initial phase of the hth harmonic respectively.

[0111] When constructing virtual power, the present invention first converts the grid voltage, that is, the three-phase voltage signal, into a two-phase voltage signal in the αβ coordinate system through Clark transformation; wherein the Clark transformation T abc / αβ With the Clark inverse transform They are shown as follows:

[0112]

[0113] Then, a universal signal delay superposition operator is used to filter the two-phase voltage signal, the purpose of which is to remove the high-order harmonic interference in the signal. Then, through delay and superposition operations, the fundamental positive sequence component in the signal, that is, the three-phase voltage fundamental positive sequence component, can be extracted; finally, based on the extracted three-phase voltage fundamental positive sequence component, virtual power is constructed. The present invention enhances the adaptability of the system to grid voltage changes through precise signal processing and virtual power construction. In the case of grid voltage fluctuations or failures, the system can respond more quickly and take corresponding control measures to ensure the stable operation of the power system.

[0114] In one embodiment, the filtering operation is performed on the two-phase voltage signal according to the universal signal delay superposition operator to obtain the two-phase fundamental voltage signal to extract the fundamental positive sequence component to obtain the three-phase voltage fundamental positive sequence component, including:

[0115] Extracting the harmonic frequency signal to be extracted from the two-phase voltage signal by using the first universal signal delay superposition operator, and extracting the orthogonal signal corresponding to the harmonic frequency signal to be extracted from the two-phase voltage signal by using the second universal signal delay superposition operator, to obtain a two-phase fundamental voltage signal;

[0116] A positive sequence extraction model is used to extract the fundamental positive sequence component in the two-phase fundamental voltage signal to obtain the three-phase voltage fundamental positive sequence component.

[0117] Specifically, the generalized delayed signal superposition operator mainly includes two types of generalized delayed signal operators (GDS), which are represented as GDS1 and GDS2 respectively. Applying them to the two-phase voltage signal u(t) respectively can obtain:

[0118]

[0119] Where T is the fundamental period; k and n are arbitrary integers, which are coefficients related to the phase and amplitude operations on u(t); h z is the harmonic frequency that needs to be extracted;

[0120] GDS1[u(t)] and GDS2[u(t)] are converted to <h s n) and multiply them by 2 / (m+1), we can get two GDSS operators, namely the first general signal delay superposition operator and the second general signal delay superposition operator included in the general signal delay superposition operator:

[0121]

[0122] Wherein, GDSS1 and GDSS2 are the first general signal delay superposition operator and the second general signal delay superposition operator respectively; h s is the harmonic frequency signal to be extracted.

[0123] The present invention uses the operations of superposition and multiplication by appropriate coefficients. When the m and n parameters are reasonably selected, the GDSS1 operator is used to extract the harmonic frequency signal to be extracted from the two-phase voltage signal, and the GDSS2 operator is used to extract the orthogonal signal corresponding to the harmonic frequency signal to be extracted from the two-phase voltage signal, so as to obtain a two-phase fundamental voltage signal, which can separate specific harmonic components from a complex voltage waveform.

[0124] In particular, when h s =1, m=14, n=15, the universal delayed signal superposition operator can extract harmonics of h=1, 14, 16, 29... etc. Since the content of harmonics of 14th order and above is very small in the distribution network, it can be regarded as extracting only the pure fundamental wave and its orthogonal signal, achieving the function of filtering out high-order harmonics. However, the extracted signal still contains the fundamental negative sequence component, which will have an adverse effect on the accuracy and speed of power grid information extraction. Therefore, it is necessary to add a positive sequence component processing process to extract the fundamental positive sequence component; wherein, the positive sequence extraction model is expressed by the following formula:

[0125]

[0126] In the formula, is the positive sequence component of the three-phase voltage fundamental wave in the αβ coordinate system; T + is the voltage positive sequence component calculation matrix; u αβ is the two-phase fundamental voltage signal in the αβ coordinate system; q = e -jπ / 2 is the 90° lagged operator.

[0127] The generation process of the three-phase voltage fundamental positive sequence component is as follows: Figure 5As shown in the figure, the three-phase voltage signal output by the microgrid is converted into a two-phase voltage signal in the αβ coordinate system through Clark transformation, and then two GDSS operators are used to filter the two-phase voltage signals respectively to obtain the two-phase fundamental voltage signal and its orthogonal signal. Then, the three-phase voltage fundamental positive sequence component in the αβ coordinate system is extracted through the positive sequence extraction model, and the three-phase voltage fundamental positive sequence component u of the power grid is obtained after Clark inverse transformation. + g , for use in the subsequent pre-synchronization phase.

[0128] The present invention improves the versatility and flexibility of signal processing by introducing a universal signal delay superposition operator to adapt to the requirements of harmonic signal extraction of different frequencies; the target harmonic component and its orthogonal component can be more effectively extracted from complex signals through the generation of orthogonal signals, thereby improving the accuracy and reliability of signal extraction; the extracted three-phase voltage fundamental positive sequence component is of great significance for the steady-state and dynamic analysis of the power system, and helps to more accurately evaluate the operating status and performance of the system; through the accurate extraction and analysis of the fundamental positive sequence component, the method helps to timely discover and deal with potential problems in the power system, thereby improving the stability and safety of the system.

[0129] In one embodiment, constructing the virtual power based on the three-phase voltage fundamental positive sequence component includes:

[0130] quantizing a virtual current according to a virtual inductance between the virtual synchronous generator and the microgrid, a fundamental positive sequence component of the three-phase voltage, and a VSG inverter voltage, and determining a virtual voltage based on the VSG inverter voltage;

[0131] Determine initial power by using the virtual current and the virtual voltage, and average the initial power by using a sliding time window to obtain average power;

[0132] The average power is subjected to inertial processing to generate the virtual power.

[0133] Specifically, the present invention calculates the virtual power by quantizing the virtual current and virtual voltage when constructing the virtual power; wherein the virtual current i V It is quantified by the virtual inductance between the virtual synchronous generator and the microgrid, the fundamental positive sequence component of the three-phase voltage, and the VSG inverter voltage, as shown in the following formula:

[0134]

[0135] Where, L V is the virtual inductance between the virtual synchronous generator and the microgrid.

[0136] The virtual current can be expressed in integral form:

[0137]

[0138] And the VSG inverter voltage is used as the virtual voltage. According to the instantaneous power theory, the initial power P V1 It can be expressed as:

[0139]

[0140] In the formula, u ox It is the virtual voltage, that is, the three-phase voltage output by VSG.

[0141] In order to reduce the fluctuation of initial power during transient process, a sliding average function is usually used to calculate the average power P within the "sliding time window". V2 :

[0142]

[0143] Where SlidingWindow is the sliding average function.

[0144] The average power is processed by inertia link to realize the smooth signal function, and the virtual power P can be obtained. V , and at the same time, the continuity of the power loop input signal is maintained after the virtual power feedback is removed to prevent the signal mutation from affecting the stability of the power loop; among them, the inertia link processing is shown in the following formula:

[0145]

[0146] In the formula, ω c is the cut-off frequency of the inertia link.

[0147] The present invention introduces virtual inductance and virtual voltage, and performs averaging and inertial processing on power, so that the output power of VSG is more stable, which helps to improve the overall stability of the microgrid; the scheme allows VSG to be dynamically adjusted according to the actual operation of the microgrid, thereby enhancing the flexibility and adaptability of the system; by performing inertial processing on the average power, VSG can simulate the dynamic response characteristics of a real synchronous generator, thereby improving the compatibility and reliability of VSG in the microgrid; using a sliding time window to average the initial power can effectively reduce power fluctuations and improve the accuracy and stability of power control.

[0148] When the microgrid is in off-grid mode, the VSG is disconnected from the grid. Assume that there is a virtual impedance Z between the VSG and the grid. V ∠α V =R V +jX V , then the expression of VSG virtual output active power is:

[0149]

[0150] Where δ is the power angle of the virtual synchronous generator; U is the VSG inverter voltage; U g is the grid voltage; α V is the virtual impedance angle.

[0151] Let R V =0, that is, assuming that the system is inductive, then α V =90°, then:

[0152]

[0153] The present invention will -P V As a feedback signal, it is introduced into the active power-frequency loop of the virtual synchronous generator to form a power angle feedback control model to adjust the VSG inverter voltage; wherein, the power angle feedback control model is expressed by the following formula:

[0154]

[0155] Where, X V is the reactance in the virtual impedance; Δω V is the virtual angular frequency deviation.

[0156] The phase plane of the power angle feedback control model is as follows Figure 6 As shown, δ=2kπ is a stable equilibrium point, and δ=(2k+1)π is an unstable equilibrium point. Therefore, the VSG is in phase with the power grid in steady state.

[0157] Finally, the calculated virtual power is introduced into the frequency loop as a feedback signal to adjust the VSG power angle, and finally the VSG inverter voltage is synchronized with the grid voltage; among them, after the deviation integral feedback regulation and the power angle regulation based on virtual power are introduced, the active-frequency loop and reactive-voltage loop are as follows Figure 7 As shown, when the voltage deviation between the adjusted VSG inverter voltage and the grid voltage is less than the deviation threshold, a grid connection point closing command is generated and the switch Sv of the grid connection point is controlled to close, indicating that the pre-synchronization control takes effect, thereby realizing the phase-locked loop-free pre-synchronization of the distributed power inverter.

[0158] The present invention uses deviation integral feedback regulation to enable the system to accumulate voltage deviations and make adjustments accordingly, which helps to eliminate static errors and improve the matching accuracy between the VSG output voltage and the grid voltage; at the same time, the power angle regulation based on virtual power can simulate the dynamic response of a real synchronous generator, making the VSG more stable during the grid connection process; the introduction of deviation integral feedback regulation and virtual power power angle regulation enables the VSG to respond more quickly and adjust the output power when facing grid voltage fluctuations or load changes, thereby enhancing the robustness of the system and helping to reduce the risk of VSG disconnection due to grid failures or load mutations.

[0159] In one embodiment, after the real-time detection of the second voltage deviation between the grid voltage and the adjusted VSG inverter voltage, the method further includes:

[0160] When the second voltage deviation is not less than the deviation threshold, the first voltage deviation elimination step and the virtual power construction step are iteratively performed based on the adjusted VSG inverter voltage to update the second voltage deviation, and the relationship between the updated second voltage deviation and the deviation threshold is re-judged according to the update result, until the iterative process is terminated when the second voltage deviation is less than the deviation threshold, a grid connection point closing instruction is generated, and the switch of the grid connection point is controlled to be closed, so as to realize the phase-locked loop-free pre-synchronization of the distributed power supply inverter.

[0161] Specifically, when the voltage deviation between the grid voltage and the adjusted VSG inverter voltage is not less than the deviation threshold, the voltage deviation elimination step and the virtual power construction step are iteratively executed based on the adjusted VSG inverter voltage to gradually reduce the voltage deviation until the grid connection condition is met and a grid connection point closing instruction is generated. The present invention gradually reduces the deviation between the VSG output voltage and the grid voltage through iterative processing until the grid connection condition is met, thereby improving the accuracy and stability of the grid connection; the solution can cope with fluctuations in grid voltage and load changes, and by dynamically adjusting the control parameters of the VSG, the VSG can better adapt to changes in the grid, thereby enhancing the adaptability of the system.

[0162] In one embodiment, R V =0Ω, L V =1.2*10 -3 H; PCC point closing condition U T =4,ω T =0.1*2π,θ T =5. Figure 8-10 Indicates that no other pre-synchronization measures are taken, that is, the synchronization of the VSG inverter voltage with the grid voltage, the frequency change of the VSG inverter voltage, and the output current change of the VSG grid connection point when directly connected to the grid. Figure 8-10It can be seen that when the PCC point is closed at 0.5s for direct grid connection, although the voltage can be synchronized instantly, the VSG output voltage frequency deviates from the grid power frequency by -0.6Hz, and the current impact at the grid connection point is as high as 80A, which is about 4 times the rated operating condition (20A), which does not meet the requirements for safe grid connection. Figure 11-14 It shows the changes of pre-synchronization instruction and PCC point closing instruction, the synchronization of VSG inverter voltage and grid voltage, the frequency change of VSG inverter voltage and the output current change of VSG grid connection point after adopting the scheme of the present invention. It can be seen that the grid connection command is sent in 0.5s, the grid connection conditions are met in about 0.7s, the VSG output voltage frequency deviates from the grid power frequency by no more than +0.25Hz, no impact current is generated, and the system stabilizes at the rated operating condition after about 1s, meeting the safety grid connection requirements.

[0163] In the embodiment of the present application, based on the problem of how to improve the stability of the distributed power inverter when connected to the grid, a VSG-based inverter phase-locked loop pre-synchronization method is designed. The method issues a pre-synchronization instruction in the off-grid mode of the microgrid, and introduces the secondary frequency and secondary voltage based on the deviation integral feedback into the active-frequency loop (P-ω loop) and reactive-voltage loop (QV loop) of the VSG for adjustment respectively; at the same time, a general signal delay superposition operator is used to filter out the high-order harmonic interference of the grid voltage, and the filtered grid voltage information is used to construct virtual power, and the virtual power is introduced into the VSG active loop through the filtering link to make the output voltage gradually synchronized with the grid fundamental voltage; in addition, the voltage amplitude deviation, angular frequency deviation and phase deviation between the grid voltage and the output voltage of the VSG inverter are detected in real time. When the deviation threshold condition is met, a PCC point closing instruction is sent, the PCC point switch is closed, and the deviation integral feedback and virtual power angle adjustment links are cut off at the same time, and the grid-connected mode is entered, thereby enhancing the grid-connected stability of the distributed power inverter based on the VSG control strategy and reducing the instantaneous system current and voltage impact at the time of grid connection.

[0164] It should be noted that although the steps in the above flowchart are shown in sequence according to the arrows, these steps are not necessarily executed in the order indicated by the arrows. Unless otherwise specified in this document, there is no strict order restriction for the execution of these steps, and these steps can be executed in other orders.

[0165] In another embodiment, if Fig.15 As shown, the second aspect of the present invention provides a VSG-based inverter phase-locked loop-free pre-synchronization system, comprising:

[0166] The deviation elimination module 10 is used to eliminate the first voltage deviation between the VSG inverter voltage output by the virtual synchronous generator and the grid voltage output by the microgrid by using a deviation integral feedback method when it is detected that the microgrid is in an off-grid mode;

[0167] A power construction module 20, configured to filter the high-order harmonic interference in the grid voltage by a universal signal delay superposition operator, and construct virtual power according to the filtered grid voltage;

[0168] A voltage regulating module 30, used for introducing the virtual power as a feedback signal into the active power-frequency loop of the virtual synchronous generator, forming a work angle feedback control model to regulate the VSG inverter voltage;

[0169] The pre-synchronization module 40 is used to detect in real time the second voltage deviation between the grid voltage and the adjusted VSG inverter voltage. When the second voltage deviation is less than the deviation threshold, it generates a grid connection point closing instruction and controls the closure of the switch of the grid connection point to achieve phase-locked loop-free pre-synchronization of the distributed power inverter.

[0170] It should be noted that each module in the above-mentioned VSG-based inverter without phase-locked loop pre-synchronization system can be fully or partially implemented by software, hardware and their combination. The above-mentioned modules can be embedded in or independent of the processor in the computer device in the form of hardware, or can be stored in the memory of the computer device in the form of software, so that the processor can call and execute the operations corresponding to the above modules. For the specific definition of a VSG-based inverter without phase-locked loop pre-synchronization system, please refer to the definition of a VSG-based inverter without phase-locked loop pre-synchronization method above. The two have the same functions and effects, which will not be repeated here.

[0171] A third aspect of the present invention provides an electronic device, the electronic device comprising:

[0172] processor, memory, and bus;

[0173] The bus is used to connect the processor and the memory;

[0174] The memory is used to store operation instructions;

[0175] The processor is used to call the operation instruction, and the executable instruction enables the processor to perform operations corresponding to the VSG-based inverter non-phase-locked loop pre-synchronization method as shown in the first aspect of the present application.

[0176] In an alternative embodiment, an electronic device is provided, such as Fig.16 As shown, Fig.16The electronic device 5000 shown includes: a processor 5001 and a memory 5003. The processor 5001 and the memory 5003 are connected, such as through a bus 5002. Optionally, the electronic device 5000 may also include a transceiver 5004. It should be noted that in actual applications, the transceiver 5004 is not limited to one, and the structure of the electronic device 5000 does not constitute a limitation on the embodiments of the present application.

[0177] Processor 5001 may be a CPU, a general-purpose processor, a DSP, an ASIC, an FPGA or other programmable logic device, a transistor logic device, a hardware component or any combination thereof. It may implement or execute various exemplary logic blocks, modules and circuits described in conjunction with the disclosure of this application. Processor 5001 may also be a combination that implements computing functions, such as a combination of one or more microprocessors, a combination of a DSP and a microprocessor, etc.

[0178] The bus 5002 may include a path to transmit information between the above components. The bus 5002 may be a PCI bus or an EISA bus, etc. The bus 5002 may be divided into an address bus, a data bus, a control bus, etc. For ease of representation, Fig.16 Only one thick line is used in the diagram, but this does not mean that there is only one bus or only one type of bus.

[0179] The memory 5003 may be a ROM or other type of static storage device that can store static information and instructions, a RAM or other type of dynamic storage device that can store information and instructions, or an EEPROM, a CD-ROM or other optical disk storage, an optical disk storage (including a compressed optical disk, a laser disk, an optical disk, a digital versatile disk, a Blu-ray disk, etc.), a magnetic disk storage medium or other magnetic storage device, or any other medium that can be used to carry or store the desired program code in the form of instructions or data structures and can be accessed by a computer, but is not limited to these.

[0180] The memory 5003 is used to store application code for executing the solution of the present application, and the execution is controlled by the processor 5001. The processor 5001 is used to execute the application code stored in the memory 5003 to implement the content shown in any of the above method embodiments.

[0181] Among them, electronic devices include but are not limited to: mobile terminals such as mobile phones, laptops, digital broadcast receivers, PDAs (personal digital assistants), PADs (tablet computers), PMPs (portable multimedia players), vehicle-mounted terminals (such as vehicle-mounted navigation terminals), etc., and fixed terminals such as digital TVs, desktop computers, etc.

[0182] The fourth aspect of the present invention provides a computer-readable storage medium, on which a computer program is stored. When the program is executed by a processor, the method for pre-synchronization of an inverter without a phase-locked loop based on a VSG is implemented as shown in the first aspect of the present application.

[0183] Another embodiment of the present application provides a computer-readable storage medium, on which a computer program is stored. When the computer-readable storage medium is run on a computer, the computer can execute the corresponding content in the aforementioned method embodiment.

[0184] In addition, an embodiment of the present invention further provides a computer-readable storage medium on which a computer program is stored, and when the program is executed by a processor, the steps of the above method are implemented.

[0185] In summary, the present invention relates to the field of inverter control technology, and discloses a VSG-based inverter phase-locked loop (PLL)-free pre-synchronization method, system, device and medium. The voltage deviation between the VSG inverter voltage of the virtual synchronous generator and the output voltage of the microgrid is eliminated by the deviation integral feedback method, and then the grid voltage is filtered by a general signal delay superposition operator to construct virtual power. Then, the virtual power is introduced into the active-frequency loop of the virtual synchronous generator as a feedback signal to form an angle feedback control model to adjust the VSG inverter voltage, and the voltage deviation between the grid voltage and the adjusted VSG inverter voltage is detected in real time. When it is determined that the voltage deviation is less than the deviation threshold, a grid connection point closing instruction is generated and the switch of the grid connection point is controlled to close, so as to realize the phase-locked loop-free pre-synchronization of the distributed power inverter, enhance the grid-connected stability of the distributed power inverter, and reduce the instantaneous system current and voltage impact of the grid connection.

[0186] Each embodiment in this specification is described in a progressive manner, and the same or similar parts of each embodiment can be directly referred to each other, and each embodiment focuses on the differences from other embodiments. In particular, for the system embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and the relevant parts can be referred to the partial description of the method embodiment. It should be noted that the technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, all possible combinations of the technical features in the above-mentioned embodiments are not described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0187] The above-mentioned embodiments only express several preferred implementation modes of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in the technical field, several improvements and substitutions can be made without departing from the technical principles of the present invention, and these improvements and substitutions should also be regarded as the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be based on the protection scope of the claims.

Claims

1. A VSG-based inverter phase-locked loop-free pre-synchronization method, characterized in that: include: When it is detected that the microgrid is in an off-grid mode, a deviation integral feedback method is used to eliminate a first voltage deviation between a VSG inverter voltage output by a virtual synchronous generator and a grid voltage output by the microgrid; filtering high-order harmonic interference in the grid voltage by a universal signal delay superposition operator, and constructing virtual power according to the filtered grid voltage; Introducing the virtual power as a feedback signal into the active power-frequency loop of the virtual synchronous generator to form a work angle feedback control model to adjust the VSG inverter voltage; The second voltage deviation between the grid voltage and the adjusted VSG inverter voltage is detected in real time. When the second voltage deviation is less than the deviation threshold, a grid connection point closing instruction is generated and the switch of the grid connection point is controlled to close, so as to realize the phase-locked loop-free pre-synchronization of the distributed power inverter.

2. The inverter non-phase-locked loop pre-synchronization method based on VSG according to claim 1, characterized in that: When it is detected that the microgrid is in an off-grid mode, a deviation integral feedback method is used to eliminate a first voltage deviation between a VSG inverter voltage output by a virtual synchronous generator and a grid voltage output by the microgrid, including: When detecting that the microgrid is in an off-grid mode, responding to the off-grid mode and generating a pre-synchronization instruction to send to the virtual synchronous generator; Controlling the virtual synchronous generator to introduce secondary frequency and secondary voltage based on deviation integral feedback into its own active-frequency loop and reactive-voltage loop based on the pre-synchronization instruction for adjustment, so as to eliminate the first voltage deviation between the VSG inverter voltage and the grid voltage; The deviation between the adjusted VSG inverter voltage and the grid voltage is expressed by the following formula: Where Δω and ΔU are the voltage angular frequency and amplitude deviation respectively; s is a complex variable; J and D are the virtual inertia and damping coefficient of the virtual synchronous generator respectively; ω0 is the rated angular frequency; P ref (s), Q ref (s) are the rated active and reactive power of the virtual synchronous generator respectively; P L (s), Q L (s) are local active and reactive loads respectively; k1 and k2 are frequency deviation and voltage deviation integral feedback coefficients respectively; k q , k i They are the reactive droop coefficient and reactive loop integral coefficient of the virtual synchronous generator respectively.

3. The inverter non-phase-locked loop pre-synchronization method based on VSG according to claim 2, characterized in that: The filtering of the high-order harmonic interference in the grid voltage by a universal signal delay superposition operator and constructing virtual power according to the filtered grid voltage includes: Performing Clark transformation on the grid voltage to obtain two-phase voltage signals in a two-phase stationary coordinate system; Performing a filtering operation on the two-phase voltage signal according to the universal signal delay superposition operator to obtain a two-phase fundamental voltage signal to extract a fundamental positive sequence component, thereby obtaining a three-phase voltage fundamental positive sequence component; The virtual power is constructed based on the three-phase voltage fundamental positive sequence component.

4. The method for pre-synchronization of an inverter without a phase-locked loop based on a VSG according to claim 3, characterized in that: The universal signal delay addition operator includes a first universal signal delay addition operator and a second universal signal delay addition operator; wherein, The filtering operation is performed on the two-phase voltage signal according to the universal signal delay superposition operator to obtain the two-phase fundamental voltage signal to extract the fundamental positive sequence component to obtain the three-phase voltage fundamental positive sequence component, including: The harmonic frequency signal to be extracted from the two-phase voltage signal is extracted by the first universal signal delay superposition operator, and the orthogonal signal corresponding to the harmonic frequency signal to be extracted is extracted from the two-phase voltage signal by the second universal signal delay superposition operator, so as to obtain a two-phase fundamental voltage signal; wherein the first universal signal delay superposition operator and the second universal signal delay superposition operator are expressed by the following formula: Where GDSS1 and GDSS2 are the first general signal delay superposition operator and the second general signal delay superposition operator respectively; u(t) is the two-phase voltage signal; m, k, n are any integers; h s is the harmonic frequency signal to be extracted; T is the fundamental wave period; A positive sequence extraction model is used to extract the fundamental positive sequence component in the two-phase fundamental voltage signal to obtain the three-phase voltage fundamental positive sequence component; wherein the positive sequence extraction model is expressed by the following formula: In the formula, is the positive sequence component of the three-phase voltage fundamental wave in the αβ coordinate system; T abc is the Clark transformation matrix; T + is the voltage positive sequence component calculation matrix; u αβ is the two-phase fundamental voltage signal in the αβ coordinate system; q is the 90° lagging operator.

5. The method for pre-synchronization of an inverter without a phase-locked loop based on a VSG according to claim 3, characterized in that: The constructing the virtual power based on the three-phase voltage fundamental positive sequence component comprises: quantizing a virtual current according to a virtual inductance between the virtual synchronous generator and the microgrid, a fundamental positive sequence component of the three-phase voltage, and a VSG inverter voltage, and determining a virtual voltage based on the VSG inverter voltage; Determine initial power by using the virtual current and the virtual voltage, and average the initial power by using a sliding time window to obtain average power; The average power is subjected to inertial processing to generate the virtual power.

6. The method for pre-synchronization of an inverter without a phase-locked loop based on a VSG according to claim 1, characterized in that: The power angle feedback control model is expressed by the following formula: Where δ is the power angle of the virtual synchronous generator; Δω V is the virtual angular frequency deviation; P V is the virtual power; U is the VSG inverter voltage; U g is the grid voltage; X V is the reactance in the virtual impedance; t is the time.

7. The method for pre-synchronization of an inverter without a phase-locked loop based on a VSG according to claim 1, characterized in that: After the real-time detection of the second voltage deviation between the grid voltage and the adjusted VSG inverter voltage, the method further includes: When the second voltage deviation is not less than the deviation threshold, the first voltage deviation elimination step and the virtual power construction step are iteratively performed based on the adjusted VSG inverter voltage to update the second voltage deviation, and the relationship between the updated second voltage deviation and the deviation threshold is re-judged according to the update result, until the iterative process is terminated when the second voltage deviation is less than the deviation threshold, a grid connection point closing instruction is generated, and the switch of the grid connection point is controlled to be closed, so as to realize the phase-locked loop-free pre-synchronization of the distributed power supply inverter.

8. A VSG-based inverter non-phase-locked loop pre-synchronization system, characterized in that: include: A deviation elimination module, for eliminating a first voltage deviation between a VSG inverter voltage output by a virtual synchronous generator and a grid voltage output by the microgrid by using a deviation integral feedback method when detecting that the microgrid is in an off-grid mode; A power construction module, used for filtering high-order harmonic interference in the grid voltage through a universal signal delay superposition operator, and constructing virtual power according to the filtered grid voltage; A voltage regulation module, used for introducing the virtual power as a feedback signal into the active power-frequency loop of the virtual synchronous generator, forming a work angle feedback control model to regulate the VSG inverter voltage; The pre-synchronization module is used to detect in real time the second voltage deviation between the grid voltage and the adjusted VSG inverter voltage. When the second voltage deviation is less than the deviation threshold, it generates a grid connection point closing instruction and controls the switch of the grid connection point to close, so as to realize the phase-locked loop-free pre-synchronization of the distributed power inverter.

9. An electronic device, characterized in that: It comprises a processor, a memory, and a computer program stored in the memory and configured to be executed by the processor, and when the processor executes the computer program, it implements the VSG-based inverter non-phase-locked loop pre-synchronization method as described in any one of claims 1 to 7.

10. A computer-readable storage medium, characterized in that: The computer-readable storage medium includes a stored computer program, wherein when the device where the computer-readable storage medium is located executes the computer program, the VSG-based inverter non-phase-locked loop pre-synchronization method as described in any one of claims 1 to 7 is implemented.

Images