Voltage synchronization signal detection method based on improved DSOGI-PLL

Abstract

A voltage synchronizing signal detection method based on an improved DSOGI-PLL is characterized in that a DSOGI-QSG algorithm is adopted in a phase-locked loop, a difference node is introduced on a second-order generalized integrator SOGI structure in the DSOGI-QSG to improve the DSOGI structure, and the improved DSOGI-QSG structure is obtained and can suppress the influence of a direct current component on extraction of each parameter; a specific subharmonic elimination module structure is additionally arranged at the front end of the SOGI structure to serve as a front harmonic filtering cascade module, then the amplitude is corrected through a correction coefficient, and finally filtered signals are input into the SRF-PLL. A cascade harmonic elimination module is constructed in front of the QSG to suppress the distortion harmonic influence, and meanwhile, the QSG structure is optimized, so that the QSG structure can eliminate the direct current amount in the signal, the good characteristics of the traditional DSOGI-PLL are reserved, and meanwhile, the influence of the current bias amount, harmonic distortion and three-phase imbalance of the power grid synchronization signal on the phase locking speed and accuracy can be effectively reduced; and the system performance and applicability are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of offshore wind power, and in particular to a voltage synchronization signal detection method based on an improved DSOGI-PLL. Background Art

[0002] Power electronic converters are widely used in modern power systems, and grid voltage synchronization signal detection technology is a key component of the converter's grid connection process. In practical projects, power grids are often affected by external factors, resulting in power quality issues such as DC deviation, three-phase imbalance, and harmonic distortion. To ensure the normal operation of systems and equipment, converters must be able to quickly and accurately acquire information such as the amplitude, phase, and frequency of the fundamental grid voltage.

[0003] The Dual Second Order Generalized Integrator (DSOGI-PLL) utilizes the quadrature separation properties of the SOGI to derive the fundamental component and its quadrature component for symmetrical component calculation. While it has a certain degree of harmonic suppression capability, its phase-locking accuracy is affected by excessive DC or certain harmonics. This paper proposes a novel, improved PLL by adding a structure to filter specific subharmonics and DC to the traditional DSOGI-PLL. This method incorporates a cascaded harmonic cancellation module before the QSG to suppress the effects of distortion harmonics. The QSG structure is optimized to eliminate DC content in the signal, preserving the favorable characteristics of the traditional DSOGI-PLL while effectively mitigating the effects of current offset, harmonic distortion, and three-phase imbalance in the grid synchronization signal on phase-locking speed and accuracy, thereby improving system performance and applicability. Summary of the Invention

[0004] The present invention provides a voltage synchronization signal detection method based on an improved DSOGI-PLL, which solves the problem that the phase-locking accuracy of a traditional DSOGI-PLL is interfered with by excessive DC or certain harmonics.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is: A voltage synchronization signal detection method based on an improved DSOGI-PLL is proposed. The phase-locked loop adopts the DSOGI-QSG algorithm. A difference node is introduced into the second-order generalized integrator SOGI structure in the DSOGI-QSG to improve it. The improved DSOGI-QSG structure is obtained, which can suppress the influence of the DC component on the extraction of various parameters.

[0006] The second-order generalized integrator SOGI structure in the improved DSOGI-QSG mentioned above adds a subharmonic elimination module structure at the front end as a pre-harmonic filtering cascade module, then corrects the amplitude by the correction coefficient, and finally inputs the filtered signal into the SRF-PLL.

[0007] The steps of the voltage synchronization signal detection method in the above-mentioned improved DSOGI-QSG structure are as follows: The three-phase balanced voltage of the power grid is calculated and transformed into a two-phase rotating coordinate system by Parker transformation. The relationship between the amplitude and phase of the power grid voltage is analyzed using the current harmonic detection method and the two-phase rotating coordinate system. The symmetrical component method is used to obtain the positive and negative component expressions under the three-phase coordinate axis. The positive and negative component expressions under the three-phase coordinate axis are used as the improved DSOGI-QSG positive and negative sequence component calculation module. The positive and negative sequence components after filtering out the interference are input into the SRF-PLL to obtain the power grid voltage synchronization information.

[0008] The steps for calculating the three-phase balanced voltage of the power grid and transforming it into a two-phase rotating coordinate system are as follows: Assume that the three-phase balanced voltage can be expressed as: ; in, 、 、 is the three-phase voltage of A, B, and C in the three-phase stationary coordinate system; The three-phase grid voltage can be converted from the three-phase stationary coordinate system to the two-phase stationary coordinate system as follows: ; in, 、 A two-phase stationary coordinate system 、 Shaft voltage; Coordinate transformation matrix for converting three-phase stationary coordinate system into two-phase stationary coordinate system; Then perform Park transformation on the above equation and transfer it to the two-phase rotating coordinate system, which can be expressed as: ; in, 、 Two-phase rotating coordinate system 、 Shaft voltage; The coordinate transformation matrix for converting the three-phase stationary coordinate system into the two-phase stationary coordinate system.

[0009] The relationship between the above current harmonic detection method and the two-phase rotating coordinate system analysis of the grid voltage amplitude and phase is: On the axis 、 The relationship between the phase and amplitude of the grid voltage. hour, , at this time the grid voltage vector and The axes coincide, that is ;when hour, , the grid voltage leads Axis phase; when hour, , The axis leads the grid voltage phase. According to this principle, PI control can be used to make The axis is always zero, at this time Axis and grid voltage vector The phase is the same, and the angular frequency is dynamically adjusted to track the real-time angular frequency of the power grid. ,integral To achieve real-time detection of the grid phase.

[0010] The specific steps for obtaining the positive and negative component expressions under the three-phase coordinate axis using the above-mentioned symmetrical component method are as follows: The three-phase voltage three-sequence positive and negative zero-sequence voltages can be expressed as: ; A, B, C three-phase voltage, three-phase positive, negative, and zero-sequence voltage; Using the three-sequence voltage representation method, the positive and negative sequence components under the three-phase coordinate axis can be expressed as:

[0011] The above formula can be used as the basis for calculating the positive and negative sequence components, and as the DSOGI positive and negative sequence component calculation module after positive and negative sequence separation. The positive and negative sequence components after filtering out interference are input into the SRF-PLL to obtain the grid voltage synchronization information.

[0012] The transfer function of the improved DSOGI-QSG structure is: ; ; in, : gain coefficient; : system angular frequency; Improved DSOGI-PLL quadrature output In the frequency domain it can be expressed as: ; The output frequency domain signal Converted into the time domain, it can be expressed as: .

[0013] When the grid voltage is unbalanced and distorted, the improved DSOGI-PLL injects nth-order specific harmonics into the input signal. At this time, the voltage input signal is expressed as: ; in, 、 、 : Shaft voltage positive sequence, negative sequence, and nth harmonic; 、 、 : Shaft voltage positive sequence, negative sequence, and nth harmonic; When only specific nth harmonics are present, the voltage signal can be decomposed into positive and negative sequence and nth harmonics on the αβ coordinate axes. When the fundamental frequency is used as the resonant frequency, the system can track the fundamental frequency without static error. At this time, after orthogonal decomposition, the amplitude and phase angle of the grid fundamental voltage signal remain unchanged. However, the nth harmonic is not filtered out by the DSOGI-QSG, but rather causes a certain change in amplitude and phase. The resulting amplitude and phase can be expressed as: ; ; 、 After orthogonal decomposition 、 Shaft output; 、 After orthogonal decomposition 、 Output quadrature.

[0014] When the grid voltage is unbalanced and distorted, the improved DSOGI-PLL injects nth order specific harmonics into the input signal. The amplitude and phase formulas generated by the harmonics are: and The amplitude is the same, but the phase is shifted. From the amplitude and phase formulas, we can see that the amplitude and phase of the orthogonal decomposition of the specific nth harmonic component have changed to a certain extent, and the amplitude is always 90° different, while the amplitude and phase of the fundamental component have not changed. After PNSC positive and negative sequence separation calculation, it can be expressed as: ; From the above formula, we can see that there are nth harmonic components in the fundamental component, which can be eliminated before obtaining the positive and negative sequence components of the grid voltage; from the mathematical derivation of the previous formula, we can see that by mathematically canceling them, the n-fold harmonic components can be eliminated. Plus 、 Subtract n times The subharmonic component, at this time, the voltage in the two-phase stationary coordinate system can be expressed as ; The voltage in the above formula eliminates the specific order n harmonics after decomposition calculation by the specific order harmonic elimination module.

[0015] The decomposition operation of the above-mentioned specific harmonic elimination module eliminates the specific nth harmonic. However, the positive and negative sequence components of the input signal in the two-phase stationary coordinate system are offset to a certain extent. A correction coefficient is introduced based on the offset. When the input signal has nth harmonic, the correction coefficient after decomposition can be expressed as: ; in, : Axis correction factor; : Axis correction factor.

[0016] The present invention provides a voltage synchronization signal detection method based on an improved DSOGI-PLL. A cascaded harmonic elimination module is constructed in front of the QSG to suppress the influence of distortion harmonics. At the same time, the QSG structure is optimized to eliminate the DC content in the signal, retaining the good characteristics of the traditional DSOGI-PLL. At the same time, it can effectively reduce the influence of the current bias, harmonic distortion and three-phase imbalance in the power grid synchronization signal on the phase-locking speed and accuracy, thereby improving the system performance and applicability. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The present invention will be further described below with reference to the accompanying drawings and examples: Figure 1 This is a schematic diagram of the current harmonic detection method of the present invention; Figure 2 This is a schematic diagram of the SRF-PLL control principle of the present invention; Figure 3 This is the traditional DSOGI phase-locked loop structure diagram; Figure 4 This is the traditional DSOGI-QSG structure diagram; Figure 5 This is a structural diagram of the improved DSOGI-QSG of the present invention; Figure 6 This is a structural diagram of a specific subharmonic elimination module of the present invention; Figure 7 This is the structural diagram of the improved DSOGI phase-locked loop of the present invention. DETAILED DESCRIPTION

[0018] In order to make the purpose, technical solutions and advantages of the present invention clearer, the following content will systematically and completely describe the specific technical solutions of the present invention in combination with the drawings provided according to the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0019] Example 1: This paper proposes a novel, improved phase-locked loop (PLL) by adding a structure to filter specific subharmonics and DC content to the traditional DSOGI-PLL. This approach incorporates a cascaded harmonic cancellation module before the QSG to suppress the effects of distortion harmonics. The QSG structure is optimized to eliminate DC content in the signal, preserving the favorable characteristics of the traditional DSOGI-PLL while effectively mitigating the effects of current offset, harmonic distortion, and three-phase imbalance in the grid synchronization signal on phase-lock speed and accuracy, thereby improving system performance and applicability.

[0020] Assume that the three-phase balanced voltage can be expressed as: ; 、 、 : Three-phase voltages of A, B, and C in the three-phase stationary coordinate system; The three-phase grid voltage is converted from the three-phase stationary coordinate system to the two-phase stationary coordinate system and can be expressed as ; 、 : Two-phase stationary coordinate system Shaft voltage; : Coordinate transformation matrix of the three-phase stationary coordinate system into the two-phase stationary coordinate system; Then perform Park transformation on the above equation and transfer it to the two-phase rotating coordinate system, which can be expressed as: ; 、 : Two-phase rotating coordinate system Shaft voltage; : Coordinate transformation matrix of the two-phase stationary coordinate system into the two-phase rotating coordinate system; - Conversion diagram Figure 1 shown.

[0021] It can be seen from the current harmonic detection method principle diagram and the two-phase rotating coordinate system formula On the axis 、 The relationship between the phase and amplitude of the grid voltage. hour, , at this time the grid voltage vector and The axes coincide, that is ;when hour, , the grid voltage leads Axis phase; when hour, , The axis leads the grid voltage phase. According to this principle, PI control can be used to The axis is always zero, at this time Axis and grid voltage vector The phase is the same, and the angular frequency is dynamically adjusted to track the real-time angular frequency of the power grid. ,integral To achieve real-time detection of the grid phase.

[0022] like Figure 2 The SRF-PLL control principle shown in is often used to analyze the asymmetric three-phase voltage of the unbalanced power grid signal using the symmetrical component method. The three-phase voltage, three-sequence positive and negative zero-sequence voltage can be expressed as: ; A, B, C three-phase voltage, three-phase positive, negative, and zero-sequence voltage; Using the three-sequence voltage representation method, the positive and negative sequence components under the three-phase coordinate axis can be expressed as:

[0023] It can be seen that the extraction of positive and negative sequence components is closely related to the input quantity. The above formula can be used as the basis for the calculation of positive and negative sequence components and as the DSOGI positive and negative sequence component calculation module after the positive and negative sequence separation. Inputting the positive and negative sequence components after filtering out the interference into the SRF-PLL should be able to obtain more accurate grid voltage synchronization information; the DSOGI phase-locked loop structure is as follows Figure 3 shown.

[0024] Depend on Figure 3 It can be seen that the traditional DSOGI-PLL structure consists of the following components: the orthogonal generator structure QSG, the positive and negative sequence component calculation module PNSC and the synchronous reference frame phase-locked loop SRF-PLL. The entire phase-locked process is the three-phase grid voltage signal in Orthogonal decomposition is performed in the coordinate system, the positive and negative sequences of the decomposed signal are separated and calculated, and then converted into the synchronous rotating coordinate system input required by the SRF-PLL to complete the closed-loop phase locking.

[0025] The orthogonal signal generator QSG in the second-order generalized integral can generate an orthogonal signal with a 90° deviation from the input signal to calculate the positive and negative sequence components, and the QSG has a certain ability to filter out harmonic interference. Figure 4 shown.

[0026] The SOGI output can be obtained and The transfer functions are as follows: ; ; : gain coefficient; : system angular frequency; Assuming that the input signal contains only DC components, let the DC quantity in the time domain be: , which can be expressed in the frequency domain as: ; DC flow The output signal can be expressed in the frequency domain as: ; The output signal Converted into the time domain, it can be expressed as: ; When the input is a DC disturbance, the output The output is sinusoidal and does not contain DC. Similarly, the analysis of the orthogonal output The frequency domain output can be expressed as: ; The output signal Transformed into the time domain, it can be expressed as: ; It is obvious that when the input contains a DC component, the output signal In addition to the sine and cosine components, there is also a DC component When the input signal When it is a DC component, Q(s) behaves as an equivalent low-pass filter, and the output signal is The DC component cannot be eliminated, and after orthogonal decomposition, it is input into the synchronous reference coordinate system phase-locked loop to improve the accuracy of grid voltage phase detection.

[0027] When the input signal contains a DC component, it will affect the phase-locked performance of the SOGI-PLL. In order to solve the problem that the SOGI-FLL method cannot handle the DC component, a difference node is introduced based on the SOGI structure to improve it, so that it can suppress the influence of the DC component on the extraction of various parameters and can accurately extract the DC component.

[0028] like Figure 5 As shown in , the optimized SOGI-QSG transfer function can be obtained as follows: ; ; Similarly, it can be analyzed that the improved SOGI-PLL has orthogonal output after adding the difference node In the frequency domain it can be expressed as: ; The output frequency domain signal Converted into the time domain, it can be expressed as: ; It can be clearly seen that there is no DC component. From the above analysis, it can be concluded that the improved SOGI-PLL construction difference node can effectively eliminate the DC component and eliminate DC interference on the basis of orthogonal output. When the grid voltage is unbalanced and distorted, the nth specific harmonic is injected into the input signal. From the analysis principle in the previous section, we can see that the voltage input signal at this time is expressed as: ; 、 、 : Shaft voltage positive sequence, negative sequence, and nth harmonic; 、 、 : Shaft voltage positive sequence, negative sequence, and nth harmonic; When the analysis only includes specific nth harmonics, you can The voltage signal is decomposed into positive and negative sequence and nth harmonics on the coordinate axis. From the analysis of SOGI's quadrature generation module mentioned above, we know that when the fundamental frequency is used as the resonant frequency, the system can track the fundamental frequency without static error. In this case, after the orthogonal decomposition, the amplitude and phase angle of the grid fundamental voltage signal remain unchanged. However, the nth harmonic is not filtered out by SOGI-QSG, but instead causes a certain change in amplitude and phase. The resulting amplitude and phase can be expressed as: ; ; 、 After orthogonal decomposition 、 Shaft output; 、 After orthogonal decomposition 、 Output quadrature; in, and The amplitude is the same, but the phase is shifted. From the above two equations, we can see that the amplitude and phase of the orthogonal decomposition of the specific nth harmonic component have changed to a certain extent, and the amplitude is always 90° different, while the amplitude and phase of the fundamental component have not changed. After PNSC positive and negative sequence separation calculation, it can be expressed as: ; From the above formula, we know that there are nth harmonic components in the fundamental component, which can be eliminated before obtaining the positive and negative sequence components of the grid voltage. From the mathematical derivation of the previous formula, we know that by mathematically canceling them, the nth harmonic component can be eliminated. Plus 、 Subtract n times The subharmonic component, at this time, the voltage in the two-phase stationary coordinate system can be expressed as ; The structure diagram of the specific subharmonic elimination module is as follows: Figure 6 As shown in , after the decomposition operation, the specific nth harmonic is eliminated, but the positive and negative sequence components of the input signal in the two-phase stationary coordinate system are offset to a certain extent. The correction coefficient is introduced according to the offset. When the input signal has nth harmonic, the correction coefficient after decomposition can be expressed as: ; : Axis correction factor; : Axis correction factor.

[0029] In this paper, the specific subharmonic filtering structure is used as the pre-link of DSOGI-PLL, and then the amplitude is corrected by the correction coefficient. Finally, the filtered signal is input into SRF-PLL, so that the improved DSOGI phase-locked loop structure is as shown in the figure. Figure 7 shown.

[0030] This paper proposes an improved phase-locked loop (PLL) structure. Based on the traditional DSOGI-PLL, this structure adds a difference node and a pre-harmonic filtering cascade module to the SOGI structure to address the presence of DC components and multiple harmonic distortion in grid voltage signals. This structure effectively suppresses DC components and eliminates the effects of harmonic components on positive and negative sequence signal extraction.

[0031] The improved phase-locked loop structure inherits the advantages of the traditional DSOGI-PLL. Compared to the traditional DSOGI-PLL, it can more accurately and stably measure the fundamental positive-sequence voltage signal even when the grid voltage is unbalanced, has a DC component, and suffers from harmonic distortion. Simulation results show that the improved DSOGI-PLL has better interference suppression capabilities and better phase-locked stability when grid-side information is complex.

Claims

1. A voltage synchronization signal detection method based on an improved DSOGI-PLL, wherein the phase-locked loop adopts the DSOGI-QSG algorithm, characterized in that: A difference node is introduced into the second-order generalized integrator SOGI structure in DSOGI-QSG to improve it, and an improved DSOGI-QSG structure is obtained, which can suppress the influence of DC component on the extraction of various parameters.

2. The voltage synchronization signal detection method based on the improved DSOGI-PLL according to claim 1, characterized in that: The front end of the second-order generalized integrator SOGI structure in the improved DSOGI-QSG is added with a subharmonic elimination module structure as a pre-harmonic filtering cascade module, and then the amplitude is corrected by the correction coefficient, and finally the filtered signal is input into the SRF-PLL.

3. The voltage synchronization signal detection method based on the improved DSOGI-PLL according to claim 2, characterized in that: The steps of the voltage synchronization signal detection method in the improved DSOGI-QSG structure are as follows: The three-phase balanced voltage of the power grid is calculated and transformed into a two-phase rotating coordinate system by Parker transformation. The relationship between the amplitude and phase of the power grid voltage is analyzed using the current harmonic detection method and the two-phase rotating coordinate system. The symmetrical component method is used to obtain the positive and negative component expressions under the three-phase coordinate axis. The positive and negative component expressions under the three-phase coordinate axis are used as the improved DSOGI-QSG positive and negative sequence component calculation module. The positive and negative sequence components after filtering out the interference are input into the SRF-PLL to obtain the power grid voltage synchronization information.

4. The voltage synchronization signal detection method based on the improved DSOGI-PLL according to claim 3, characterized in that: The steps of calculating the three-phase balanced voltage of the power grid and transforming it into a two-phase rotating coordinate system are as follows: Assume that the three-phase balanced voltage can be expressed as: ； in, 、 、 is the three-phase voltage of A, B, and C in the three-phase stationary coordinate system; The three-phase grid voltage can be converted from the three-phase stationary coordinate system to the two-phase stationary coordinate system as follows: ； in, 、 A two-phase stationary coordinate system 、 Shaft voltage; Coordinate transformation matrix for converting three-phase stationary coordinate system into two-phase stationary coordinate system; Then perform Park transformation on the above equation and transfer it to the two-phase rotating coordinate system, which can be expressed as: ； in, 、 Two-phase rotating coordinate system 、 Shaft voltage; The coordinate transformation matrix for converting the three-phase stationary coordinate system into the two-phase stationary coordinate system.

5. The voltage synchronization signal detection method based on the improved DSOGI-PLL according to claim 4, characterized in that: The relationship between the current harmonic detection method and the two-phase rotating coordinate system analysis of the grid voltage amplitude and phase is: On the axis 、 The relationship between the phase and amplitude of the grid voltage. hour, , at this time the grid voltage vector and The axes coincide, that is ;when hour, , the grid voltage leads Axis phase; when hour, , The axis leads the grid voltage phase. According to this principle, PI control can be used to make The axis is always zero, at this time Axis and grid voltage vector The phase is the same, and the angular frequency is dynamically adjusted to track the real-time angular frequency of the power grid. ,integral To achieve real-time detection of the grid phase.

6. The voltage synchronization signal detection method based on the improved DSOGI-PLL according to claim 5, characterized in that: The specific steps of obtaining the positive and negative component expressions under the three-phase coordinate axis by the symmetrical component method are as follows: The three-phase voltage three-sequence positive and negative zero-sequence voltages can be expressed as: ； A, B, C three-phase voltage, three-phase positive, negative, and zero-sequence voltage; Using the three-sequence voltage representation method, the positive and negative sequence components under the three-phase coordinate axis can be expressed as: The above formula can be used as the basis for calculating the positive and negative sequence components, and as the DSOGI positive and negative sequence component calculation module after positive and negative sequence separation. The positive and negative sequence components after filtering out interference are input into the SRF-PLL to obtain the grid voltage synchronization information.

7. The voltage synchronization signal detection method based on the improved DSOGI-PLL according to claim 6, characterized in that: The improved DSOGI-QSG structure transfer function is: ； ； in, : gain coefficient; : system angular frequency; Improved DSOGI-PLL quadrature output In the frequency domain it can be expressed as: ； The output frequency domain signal Converted into the time domain, it can be expressed as: 。 8. The voltage synchronization signal detection method based on the improved DSOGI-PLL according to claim 7, characterized in that: The improved DSOGI-PLL injects nth-order specific harmonics into the input signal when the grid voltage is unbalanced and distorted. At this time, the voltage input signal is expressed as: ； in, 、 、 : Shaft voltage positive sequence, negative sequence, and nth harmonic; 、 、 : Shaft voltage positive sequence, negative sequence, and nth harmonic; When only specific nth harmonics are present, the voltage signal can be decomposed into positive and negative sequence and nth harmonics on the αβ coordinate axes. When the fundamental frequency is used as the resonant frequency, the system can track the fundamental frequency without static error. At this time, after orthogonal decomposition, the amplitude and phase angle of the grid fundamental voltage signal remain unchanged. However, the nth harmonic is not filtered out by the DSOGI-QSG, but rather causes a certain change in amplitude and phase. The resulting amplitude and phase can be expressed as: ； ； 、 After orthogonal decomposition 、 Shaft output; 、 After orthogonal decomposition 、 Output quadrature.

9. The voltage synchronization signal detection method based on the improved DSOGI-PLL according to claim 8, characterized in that: The improved DSOGI-PLL injects nth order specific harmonics into the input signal when the grid voltage is unbalanced and distorted. The amplitude and phase formulas generated by the nth order specific harmonics are: and The amplitude is the same, but the phase is shifted. From the amplitude and phase formulas, we can see that the amplitude and phase of the orthogonal decomposition of the specific nth harmonic component have changed to a certain extent, and the amplitude is always 90° different, while the amplitude and phase of the fundamental component have not changed. After PNSC positive and negative sequence separation calculation, it can be expressed as: ； From the above formula, we can see that there are nth harmonic components in the fundamental component, which can be eliminated before obtaining the positive and negative sequence components of the grid voltage; from the mathematical derivation of the previous formula, we can see that by mathematically canceling them, the n-fold harmonic components can be eliminated. Plus 、 Subtract n times The subharmonic component, at this time, the voltage in the two-phase stationary coordinate system can be expressed as ； The voltage in the above formula eliminates the specific order n harmonics after decomposition calculation by the specific order harmonic elimination module.

10. The voltage synchronization signal detection method based on the improved DSOGI-PLL according to claim 9, characterized in that: The specific harmonic elimination module eliminates the specific nth harmonic after decomposition operation. However, the positive and negative sequence components of the input signal in the two-phase stationary coordinate system are offset to a certain extent. A correction coefficient is introduced according to the offset. When the input signal has nth harmonic, the correction coefficient after decomposition can be expressed as: ； in, : Axis correction factor; : Axis correction factor.

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