Virtual inertia control method for netted converter based on parallel heterogeneous SOGI-FLL

Abstract

The application discloses a virtual inertia control method for a grid-following converter based on a parallel heterogeneous second order generalized integrator-based frequency locked loop (SOGI-FLL), which comprises the following steps: a plurality of SOGI are connected in parallel in a SOGI-FLL control loop to obtain a multi-parallel SOGI-FLL (MSOGI-FLL); an FLL is constructed by using different output signals of the parallel SOGI; a multi-parallel heterogeneous SOGI-FLL (MHSOGI-FLL) structure is formed; the MHSOGI-FLL structure is used to directly realize accurate evaluation of a power grid angular frequency differential signal; and the power grid angular frequency differential signal is applied to a virtual inertia control method for a grid-following converter. The method effectively avoids the harmonic interference problem caused by traditional angular frequency differential operation, effectively suppresses the adverse influence of characteristic harmonic disturbance in a power grid voltage on the virtual inertia response performance of the grid-following converter, and is suitable for a grid-following converter grid-connected control scene in power electronic technology.

Description

Technical Field

[0001] This invention relates to the field of renewable energy grid connection control technology, and in particular to a virtual inertia control method for grid-connected converters based on parallel heterogeneous SOGI-FLL. This method is applicable to the integration of a high proportion of renewable energy into the power system, in order to address the system inertia deficiency problem caused by the grid connection of a high proportion of renewable energy. By simulating the inertia response characteristics of synchronous generators, it provides fast and reliable inertia support for the power grid, and is especially suitable for various grid-connected converters that need to be connected to the grid. Background Technology

[0002] With the increasing prevalence of renewable energy and power electronic equipment in new power systems, large-scale wind and solar power generation units are primarily connected to the grid via power conversion systems (PCS), altering the traditional power system dominated by synchronous generators. Due to the lack of mechanical inertia support, renewable energy generation units struggle to effectively participate in grid frequency regulation, leading to a decline in the power system's inertia level and operational stability. Weakened inertia support can easily cause frequency instability issues such as excessively high frequency change rates and large frequency amplitude deviations. On the one hand, excessively high frequency change rates can trigger malfunctions in synchronous generator sliding pole protection, increasing the risk of cascading failures; on the other hand, excessively large frequency amplitude deviations may trigger safety mechanisms such as low-frequency load shedding, inducing large-scale power outages. Faced with the risks of insufficient system inertia and frequency instability brought about by the continuous increase in renewable energy penetration, it is urgent to improve the control methods of existing power converters, namely, by introducing virtual inertia control to enhance the dynamic support capability for grid frequency changes.

[0003] To this end, various studies have been conducted, such as the article entitled "A family of gradient descent gridfrequency estimators for the SOGI filter", MATAS J, MARTIN H, HOZ J, et al, IEEE Transactions on Power Electronics, 2018, 33(7), 5796-5810 ("A family of gradient descent grid frequency estimators for the SOGI filter", IEEE Transactions on Power Electronics, 2018, Vol. 33, No. 7, pp. 5796-5810). This article forms a grid angular frequency differential signal detection method based on heterogeneous second-order generalized integrator-based frequency locked loop (HSOGI-FLL) by constructing frequency-locked loop control loops using different output signals of the second-order generalized integrator. This method can directly extract the frequency differential signal without performing differential operations on the grid angular frequency, thus effectively avoiding the noise sensitivity and implementation complexity inherent in traditional differential operations. Compared to the traditional SOGI-FLL structure, the HSOGI-FLL exhibits superior response performance in the dynamic detection of the differential signal of the grid angular frequency. However, the HSOGI-FLL still suffers from significant shortcomings in disturbance suppression when the grid voltage contains non-ideal components such as characteristic subharmonics, DC bias, and interharmonics. Furthermore, current research on the HSOGI-FLL does not yet cover its specific applications and control methods in the virtual inertia control of grid-connected converters.

[0004] The article, titled "Frequency derivative-based inertia enhancement by grid-connected power converters with a frequency-locked-loop", Fang J, Zhang R, Li H, et al, IEEE Transactions on Smart Grid, 2019, 10(5), 4918-4927 ("Frequency derivative-based virtual inertia control strategy for grid-connected power converters with a frequency-locked loop", IEEE Smart Grid Journal, 2019, Vol. 10, No. 5, pp. 4918-4927), proposes a virtual inertia control algorithm based on SOGI-FLL. By associating the gain coefficient with the active power reference value and applying it to the PCS, the algorithm can improve the system inertia while avoiding the high-frequency noise introduced by the differential operation. However, this method has limited disturbance suppression capability and high harmonic content in grid-connected current when the grid has characteristic subharmonics, DC components and interharmonics.

[0005] The article, titled "Research on Virtual Inertia Control Strategy of Energy Storage Converter Based on Frequency Differentiation Principle," published in the Proceedings of the Chinese Society for Electrical Engineering, Vol. 41, No. 6, 2021, pp. 2088-2101, proposes embedding an SOGI frequency adaptive filter into the SOGI-FLL control loop to form a virtual inertia control strategy based on a cascaded SOGI-FLL. This strategy effectively suppresses the interference of characteristic subharmonics, DC components, and interharmonics in the grid voltage on the angular frequency differential signal, improving the accuracy of the virtual inertia response. However, its performance and grid-connected current quality under distorted grid conditions containing characteristic subharmonics and interharmonics still require further optimization.

[0006] The article, titled "Inertia Simulation Method for Energy Storage Converter Based on Improved Second-Order Generalized Integrator-Frequency Locked Loop," published in the *Acta Energiae Solaris Sinica*, Vol. 42, No. 12, 2021, pp. 428-434, proposes a virtual inertia simulation method based on an improved SOGI-FLL. This method embeds multiple frequency adaptive notch filters into the SOGI-FLL structure, improving the suppression effect on interharmonic component disturbances and enhancing the control performance of the virtual inertia response. However, the dynamic coupling between the notch filter and the SOGI-FLL is neglected in small-signal modeling, and the impact of coupling on the system under extreme grid conditions still needs to be analyzed. Furthermore, the disturbance suppression effect needs to be further improved.

[0007] As can be seen from the above, among the existing virtual inertia control methods for grid-connected converters based on the detection of the differential signal of the grid angular frequency, the SOGI-FLL control method is often used. However, when dealing with disturbances in the grid that include characteristic subharmonics, DC components and interharmonics, there are problems such as insufficient disturbance suppression capability, which leads to the deterioration of the virtual inertia response performance of the grid-connected converter and the quality of the grid-connected current. Summary of the Invention

[0008] To overcome the limitations of various technical solutions presented in the background art, this invention addresses the problems of excessively high system frequency change rate and increased frequency amplitude deviation caused by the reduction of equivalent inertia in grid-connected renewable energy systems. It provides a virtual inertia control method for grid-connected converters based on a parallel heterogeneous SOGI-FLL. This method connects multiple SOGIs in parallel within the control loop of the SOGI-FLL to obtain a parallel SOGI-FLL (Multi-parallel SOGI-FLL, MSOGI-FLL). By using different output signals of the parallel SOGIs to construct FLLs, a parallel heterogeneous SOGI-FLL (Multi-parallel Heterogeneous SOGI-FLL, MHSOGI-FLL) structure is formed. The MHSOGI-FLL structure is used to directly and accurately evaluate the differential signal of the grid angular frequency, and this differential signal is then applied to the virtual inertia control method of the grid-connected converter. This method effectively avoids the harmonic interference problem caused by traditional angular frequency differentiation operations, and at the same time can effectively suppress the adverse effects of characteristic subharmonic disturbances in the grid voltage on the virtual inertia response performance of grid-connected converters, so that grid-connected converters can effectively provide virtual inertia support for the grid and ensure grid-connected current quality.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0010] A virtual inertia control method for a grid-connected converter based on parallel heterogeneous SOGI-FLL includes the following steps:

[0011] Step 1: First, collect the inductor current i on the bridge arm side of the grid converter. 1a i 1b i 1c and grid voltage u ga u gb u gc The αβ component u of the grid voltage is obtained by transforming from a three-phase stationary coordinate system to a two-phase stationary coordinate system. gα u gβ The α-axis and β-axis components u of the grid voltage after decoupling are obtained through the harmonic decoupling network control equations. gαi u gβi(i = 1, 2, ..., n), and then the α-axis orthogonal output component u after grid voltage filtering is obtained by the second-order generalized integrator control equation. αdi with u αqi (i = 1, 2, ..., n), β-axis orthogonal output component u βdi with u βqi (i = 1, 2, ..., n) and intermediate output components u αai with u βai (i = 1, 2, ..., n);

[0012] Step 2, based on the bridge arm side inductor current i obtained in Step 1 1a i 1b i 1c and the α-axis and β-axis components u after decoupling from the grid voltage gα1 u gβ1 After the grid voltage phase angle θ g The dq component I of the inductor current on the arm side of the grid-type converter is obtained by a single synchronous rotating coordinate transformation with orientation reference. 1d I 1q With the decoupled dq component U gd U gq Then, the voltage amplitude U of the grid phase voltage is obtained through the voltage amplitude calculation equation. g ;

[0013] Step 3, based on the filtered output component u obtained in Step 1 gα1 u gβ1 u αa1 u βa1 u αd1 u βd1 The amplitude U of the grid phase voltage obtained in step 2 g And the angular frequency command ω given by the grid converter. ref The angular frequency ω of the power grid is obtained through the frequency-locked loop control equation. g and the differential signal dω of angular frequency g / dt, representing the angular frequency ω of the power grid. g The phase angle θ of the grid voltage is obtained through integration. g ;

[0014] Step 4, based on the differential signal dω of the power grid angular frequency obtained in Step 3. g The reference active power P of the grid-connected converter is obtained by using the virtual inertia control equations, along with the active power command P0 and the inertia time constant H of the grid-connected converter. ref ;

[0015] Step 5, based on the d-axis component U of the grid voltage obtained in Step 1 gd and the reference active power P obtained in step 4ref The reference active current I of the grid-type converter is obtained through the current calculation equation. dref and reference reactive current I qref ;

[0016] Step 6, based on the reference active current I obtained in Step 5 dref Reference reactive current I qref And the dq component I of the bridge arm side inductor current in step 1 1d I 1q dq component of grid voltage U gd U gq And the angular frequency ω of the power grid in step 3 g The control signal U is obtained through the current control equation. d U q ;

[0017] Step 7, first according to the control signal U obtained in step 6 d U q and the grid voltage phase angle θ obtained in step 3 g After the grid voltage phase angle θ g The three-phase bridge arm voltage control signal U is obtained by inverse transformation of the single synchronous rotating coordinates with the orientation reference. a U b U c Then, the three-phase bridge arm voltage control signal U a U b U c The SVPWM modulation stage generates the drive signal for the inverter bridge switching transistors of the grid converter.

[0018] Preferably, the harmonic decoupling network control equations in step 1 are:

[0019]

[0020] The control equation for the second-order generalized integrator is:

[0021]

[0022] in:

[0023]

[0024]

[0025] In the formula, n is a positive integer, i and j are both positive integers from 1 to n, and ω g ω is the angular frequency of the power grid, k is the gain coefficient of the second-order generalized integrator, and s is the Laplace operator.

[0026] Preferably, the amplitude U of the grid phase voltage in step 2 g The calculation formula used is:

[0027]

[0028] Preferably, the frequency-locked loop control equation in step 3 is:

[0029]

[0030] Phase angle θ of grid voltage g The calculation formula used is:

[0031]

[0032] In the formula, λ is the integral coefficient of the second-order generalized integrator, and s is the Laplace operator.

[0033] Preferably, the virtual inertia control equation in step 4 is:

[0034]

[0035] Preferably, the reference active current I in step 5 dref The calculation formula used is:

[0036]

[0037] Reference reactive current I qref The calculation formula used is:

[0038] I qref =0.

[0039] Preferably, the current control equation in step 6 is:

[0040]

[0041] In the formula, k pc k is the proportionality coefficient of the current loop. ic is the integral coefficient of the current loop, L is the filter inductance on the bridge arm side, and s is the Laplace operator.

[0042] Compared with the prior art, the present invention has the following beneficial effects:

[0043] This invention discloses a virtual inertia control method for grid-connected converters based on parallel heterogeneous SOGI-FLL. This method involves connecting multiple SOGIs in parallel within the SOGI-FLL control loop to obtain a parallel SOGI-FLL (Multi-parallel SOGI-FLL, MSOGI-FLL). By using different output signals from the parallel SOGIs to construct an FLL, a parallel heterogeneous SOGI-FLL (Multi-parallel Heterogeneous SOGI-FLL, MHSOGI-FLL) structure is formed. The MHSOGI-FLL structure is then used to directly and accurately evaluate the differential angular frequency signal of the grid, and this differential angular frequency signal is applied to the virtual inertia control method of the grid-connected converter. This method effectively avoids the harmonic interference problem caused by traditional angular frequency differentiation operations, and can effectively suppress the adverse effects of characteristic subharmonic disturbances in the grid voltage on the virtual inertia response performance of grid-connected converters. It provides a reliable input signal for the realization of virtual inertia of grid-connected converters, enabling grid-connected converters to effectively provide virtual inertia support for the grid and ensure grid-connected current quality. It is applicable to the grid-connected control field of grid-connected converters in power electronics technology. Attached Figure Description

[0044] Figure 1 This is a topology diagram of a grid-type converter according to an embodiment of the present invention.

[0045] Figure 2 This is a structural diagram of a second-order generalized integrator according to an embodiment of the present invention.

[0046] Figure 3 This is a control structure diagram of the parallel heterogeneous SOGI-FLL according to an embodiment of the present invention.

[0047] Figure 4 This is a small-signal model diagram of the parallel heterogeneous SOGI-FLL according to an embodiment of the present invention.

[0048] Figure 5 A schematic diagram of coordinate transformation and modulation in an embodiment of the present invention.

[0049] Figure 6 This is a diagram of the virtual inertia control structure according to an embodiment of the present invention.

[0050] Figure 7 This is a comparison of simulation waveforms before and after the application of this invention to a grid converter.

[0051] Figure 8 This is a comparison of simulation waveforms before and after the application of this invention to a grid converter. Detailed Implementation

[0052] The following detailed embodiments will be further described in conjunction with the above-mentioned figures, as follows:

[0053] Please see Figure 1 The present invention proposes a virtual inertia control method for grid-connected converters based on parallel heterogeneous SOGI-FLL, comprising the following steps:

[0054] Step 1: First, collect the inductor current i on the bridge arm side of the grid converter. 1a i 1b i 1c and grid voltage u ga u gb u gc The αβ component u of the grid voltage is obtained by transforming from a three-phase stationary coordinate system to a two-phase stationary coordinate system. gα u gβ The α-axis and β-axis components u of the grid voltage after decoupling are obtained through the harmonic decoupling network control equations. gαi u gβi (i = 1, 2, ..., n), and then the α-axis orthogonal output component u after grid voltage filtering is obtained by the second-order generalized integrator control equation. αdi with u αqi (i = 1, 2, ..., n), β-axis orthogonal output component u βdi with u βqi (i = 1, 2, ..., n) and intermediate output components u αai with u βai (i = 1, 2, ..., n);

[0055] The governing equations for the harmonic decoupling network are as follows:

[0056]

[0057] The control equation for the second-order generalized integrator is:

[0058]

[0059] in:

[0060]

[0061] In the formula, n is a positive integer, i and j are both positive integers from 1 to n, and ω g ω is the angular frequency of the power grid, k is the gain coefficient of the second-order generalized integrator, and s is the Laplace operator.

[0062] Step 2, based on the bridge arm side inductor current i obtained in Step 1 1a i 1b i 1c and the α-axis and β-axis components u after decoupling from the grid voltage gα1 ugβ1 After the grid voltage phase angle θ g The dq component I of the inductor current on the arm side of the grid-type converter is obtained by a single synchronous rotating coordinate transformation with orientation reference. 1d I 1q With the decoupled dq component U gd U gq Then, the voltage amplitude U of the grid phase voltage is obtained through the voltage amplitude calculation equation. g ;

[0063] Among them, the amplitude U of the grid phase voltage g The calculation formula used is:

[0064]

[0065] Based on the above control, the structural diagram of the second-order generalized integrator of this invention can be obtained, as shown in the figure below. Figure 2 As shown.

[0066] Step 3, based on the filtered output component u obtained in Step 1 gα1 u gβ1 u αa1 u βa1 u αd1 u βd1 The amplitude U of the grid phase voltage obtained in step 2 g And the angular frequency command ω given by the grid converter. ref The angular frequency ω of the power grid is obtained through the frequency-locked loop control equation. g and the differential signal dω of angular frequency g / dt, representing the angular frequency ω of the power grid. g The phase angle θ of the grid voltage is obtained through integration. g ;

[0067] The frequency-locked loop control equation is as follows:

[0068]

[0069] Phase angle θ of grid voltage g The calculation formula used is:

[0070]

[0071] In the formula, λ is the integral coefficient of the second-order generalized integrator, and s is the Laplace operator.

[0072] Based on the above control, the control structure diagram of the parallel heterogeneous second-order generalized integrator-frequency-locked loop of this invention and the small-signal model diagram of the second-order generalized integrator-frequency-locked loop after the harmonic decoupling network accurately separates each frequency component can be obtained, as shown in the figures below. Figure 3 and Figure 4 As shown. Figure 4 In this context, ω0 is the rated angular frequency of the power grid, and θ0 and θ g These represent the actual phase of the power grid and the phase of the power grid obtained from the assessment, respectively.

[0073] Step 4, based on the differential signal dω of the power grid angular frequency obtained in Step 3. g The reference active power P of the grid-connected converter is obtained by using the virtual inertia control equations, along with the active power command P0 and the inertia time constant H of the grid-connected converter. ref ;

[0074] The virtual inertia control equation is as follows:

[0075]

[0076] The inertia time constant of the grid converter can be selected based on the inertia time constant of the traditional synchronous generator, with a value range of 4s to 12s, and 6s is recommended. Therefore, in this embodiment, the inertia time constant is H = 6s.

[0077] Step 5, based on the d-axis component U of the grid voltage obtained in Step 1 gd and the reference active power P obtained in step 4 ref The reference active current I of the grid-type converter is obtained through the current calculation equation. dref and reference reactive current I qref ;

[0078] Among them, the reference active current I dref The calculation formula used is:

[0079]

[0080] Reference reactive current I qref The calculation formula used is:

[0081] I qref =0.

[0082] Step 6, based on the reference active current I obtained in Step 5 dref Reference reactive current I qref And the dq component I of the bridge arm side inductor current in step 1 1d I 1q dq component of grid voltage U gd U gq And the angular frequency ω of the power grid in step 3 g The control signal U is obtained through the current control equation. d U q ;

[0083] The current control equation is as follows:

[0084]

[0085] In the formula, k pc k is the proportionality coefficient of the current loop. ic is the integral coefficient of the current loop, L is the filter inductance on the bridge arm side, and s is the Laplace operator.

[0086] In the above current control equation, the parameters mainly consider the current tracking characteristics and dynamic steady-state performance of the control system. Therefore, in this embodiment, k is taken as... pc =0.93, k ic =0.4.

[0087] Step 7, as follows Figure 5 As shown, first, based on the control signal U obtained in step 6... d U q and the power grid phase angle θ obtained in step 1 g via the power grid phase angle θ g The three-phase bridge arm voltage control signal U is obtained by inverse transformation of the single synchronous rotating coordinates with the orientation reference. a U b U c Then, the three-phase bridge arm voltage control signal U a U b U c The SVPWM modulation stage generates the drive signal for the inverter bridge switching transistors of the grid converter.

[0088] Based on the above control, the virtual inertia control structure diagram of this invention can be obtained, as shown in the figure below. Figure 6 As shown.

[0089] Example

[0090] To verify the control effect of the proposed virtual inertia control method for grid-connected converters based on parallel heterogeneous SOGI-FLL, the proposed virtual inertia control method for grid-connected converters based on parallel heterogeneous SOGI-FLL (hereinafter referred to as MHSOGI-FLL) is compared with an existing virtual inertia control method for grid-connected converters based on SOGI-FLL. The SOGI-FLL control method mentioned in the background section is titled "Frequency derivative-based inertia enhancement by grid-connected power converters with a frequency-locked-loop," Fang JY, Zhang RQ, Li HC, et al., *IEEE Transactions on Smart*. The article “Frequency Differential Virtual Inertia Control Strategy for Grid-Connected Power Converters Based on Frequency Locking Loop” (IEEE Smart Grid Journal, Vol. 10, No. 5, 2019, pp. 4918-4927) provides a simulation comparison, mainly comparing the differential signal dω of the grid angular frequency when dealing with characteristic subharmonic disturbance signals in the grid voltage. g / dt detection performance.

[0091] First, the relevant parameters are set. In this embodiment, the relevant parameter settings in the virtual inertia control method for grid-connected converters based on parallel heterogeneous SOGI-FLL of the present invention are as follows:

[0092] DC bus voltage U of the grid converter dc The voltage rating is 650V, the output AC line voltage is 380V / 50Hz, the rated capacity is 100kVA, the filter inductance on the bridge arm side of the grid converter is L=0.56mH, the filter capacitor is C=90uF, the three-phase isolation transformer is a 100kVA 270V / 400V Dyn11 type transformer, and the angular frequency of the grid converter is the angular frequency corresponding to the rated frequency of 50Hz, i.e., ω. ref = 314.16 rad / s, amplitude U of the grid phase voltage g The value corresponding to a rated voltage of 380V is used, i.e., U g =311V. According to Figure 4 The system frequency closed-loop transfer function can be obtained as follows: Therefore, G1(s) is a typical second-order control system, and the two control parameters k and λ can be selected using the typical second-order system parameter correction method. The natural oscillating angular frequency ω of the MHSOGI-FLL... n The expressions for the damping coefficient ζ are respectively and Set according to the recommended parameter selection principles for second-order control systems. The value of λ is determined by the value of k, and λ also determines ω. n Therefore, the values ​​of k and λ, as well as their dynamic response performance, can be determined by choosing a suitable value for k. To ensure that the system has both good dynamic response performance and harmonic suppression capability, let... And λ can be represented by k and ζ, which gives us... Then λ = 12337.

[0093] Based on the above parameter settings, simulation comparison tests were conducted, as follows:

[0094] The simulation and experimental test conditions were set as follows: Condition 1: Under standard sinusoidal grid voltage, the angular frequency is 6.28 rad / s at 0.5 s. 2 The rate increases and returns to the original state at 1.0s; Operating condition 2: Inject 5th and 7th characteristic harmonic components with an amplitude of 0.01pu into the standard grid voltage.

[0095] Based on the above working conditions, the following is obtained: Figure 7 and Figure 8 The simulation and test comparison chart shown below, in which, Figure 7 and Figure 8 In this context, SOGI-FLL represents an existing method for detecting the differential signal of the power grid angular frequency based on a second-order generalized integrator-frequency-locked loop (PLL), while MHSOGI-FLL represents the proposed method for detecting the differential signal of the power grid angular frequency based on a parallel heterogeneous second-order generalized integrator-frequency-locked loop (PLL). Specifically, the curve pointed to by SOGI-FLL is the simulation waveform before the application of this invention, and more specifically, it is the dynamic response simulation waveform of the differential signal of the power grid angular frequency detected after using the existing second-order generalized integrator-PLL method. The curve pointed to by MHSOGI-FLL is the simulation waveform after the application of this invention, and more specifically, it is the dynamic response simulation waveform of the differential signal of the power grid angular frequency detected after using the proposed parallel heterogeneous second-order generalized integrator-frequency-locked loop.

[0096] Depend on Figure 7 (a) It can be observed that the grid angular frequency signal is 6.28 rad / s 2During the rate increase, both the MHSOGI-FLL proposed in this invention and the existing SOGI-FLL can accurately detect the differential signal of the grid angular frequency without performing grid angular frequency differentiation calculations, avoiding the noise sensitivity and implementation complexity caused by grid angular frequency differentiation calculations. Furthermore, the overshoot of the grid angular frequency differential signal corresponding to the MHSOGI-FLL proposed in this invention is 4.78%, which is less than the 4.88% corresponding to the existing SOGI-FLL. Therefore, the MHSOGI-FLL proposed in this invention is effective when the grid angular frequency signal is 6.28 rad / s. 2 It can accurately detect the angular frequency differential signal during the rate increase and has a smaller overshoot.

[0097] As observed in 7(b), the existing SOGI-FLL output grid angular frequency differential signal contains significant ripple. Because its basic structure lacks frequency selective suppression capability for harmonics, harmonic components are directly coupled into the grid angular frequency differential signal detection stage. The MHSOGI-FLL proposed in this invention, by connecting multiple SOGI modules in parallel and utilizing a harmonic decoupling network to decouple each harmonic, can effectively filter out harmonics in distorted grids. Therefore, the MHSOGI-FLL proposed in this invention exhibits superior performance compared to existing SOGI-FLLs when dealing with grid disturbances containing characteristic harmonics, providing a reliable input signal for the virtual inertia control of grid-connected converters. This enables grid-connected converters to effectively provide virtual inertia support to the grid while ensuring grid-connected current quality.

[0098] Depend on Figure 8 (a) It can be observed that the grid angular frequency signal is 6.28 rad / s 2 During the rate increase, both the MHSOGI-FLL proposed in this invention and the existing SOGI-FLL can accurately detect the differential signal of the grid angular frequency without performing grid angular frequency differentiation calculations, avoiding the noise sensitivity and implementation complexity caused by grid angular frequency differentiation calculations. Furthermore, the overshoot of the grid angular frequency differential signal corresponding to the MHSOGI-FLL proposed in this invention is 4.93%, which is less than the 4.90% corresponding to the existing SOGI-FLL. Therefore, the MHSOGI-FLL proposed in this invention is effective when the grid angular frequency signal is 6.28 rad / s. 2 It can accurately detect the angular frequency differential signal during the rate increase and has a smaller overshoot.

[0099] As observed in 8(b), the existing SOGI-FLL output grid angular frequency differential signal contains significant ripple. Due to its basic structure's lack of frequency selective suppression capability for harmonics, harmonic components are directly coupled into the grid angular frequency differential signal detection stage. The MHSOGI-FLL proposed in this invention, by connecting multiple SOGI modules in parallel and utilizing a harmonic decoupling network to decouple each harmonic, can effectively filter out harmonics in distorted grids. The MHSOGI-FLL proposed in this invention exhibits superior performance compared to existing SOGI-FLLs when dealing with grid disturbances containing characteristic harmonics, providing a reliable input signal for the virtual inertia control of grid-connected converters. This enables grid-connected converters to effectively provide virtual inertia support to the grid while ensuring grid-connected current quality.

[0100] Depend on Figure 8 (a) and Figure 7 As can be seen from the comparison of the results in (a), in this embodiment... Figure 8 (a) Experimental test results and Figure 7 The simulation test results in (a) show a one-to-one correspondence. Both results indicate that, compared with the existing SOGI-FLL, the MHSOGI-FLL proposed in this invention can also achieve accurate detection of the grid angular frequency signal and has a smaller overshoot.

[0101] And again Figure 8 (b) and Figure 7 After comparing the results in (b), it is not difficult to see that in this embodiment... Figure 8 (b) Experimental test results and Figure 7 (b) The simulation test comparison results show a one-to-one correspondence. Both results fully demonstrate that, compared with the existing SOGI-FLL, the MHSOGI-FLL proposed in this invention can effectively filter out harmonics in the distorted power grid when dealing with the power grid containing characteristic subharmonic disturbances. Therefore, compared with the existing SOGI-FLL, the MHSOGI-FLL proposed in this invention has a better control effect.

[0102] The above description is a detailed description of the preferred embodiments of the present invention. However, the embodiments are not intended to limit the scope of the patent application of the present invention. All equivalent changes or modifications made under the technical spirit of the present invention should fall within the patent scope covered by the present invention.

Claims

1. A virtual inertia control method for a grid-connected converter based on a parallel heterogeneous SOGI-FLL, characterized in that, The main steps are as follows: Step 1: First, collect the inductor current i on the bridge arm side of the grid converter. 1a i 1b i 1c and grid voltage u ga u gb u gc The αβ component u of the grid voltage is obtained by transforming from a three-phase stationary coordinate system to a two-phase stationary coordinate system. gα u gβ The α-axis and β-axis components u of the grid voltage after decoupling are obtained through the harmonic decoupling network control equations. gαi u gβi (i = 1, 2, ..., n), and then the α-axis orthogonal output component u after grid voltage filtering is obtained by the second-order generalized integrator control equation. αdi with u aqi (i = 1, 2, ..., n), β-axis orthogonal output component u βdi with u βqi (i = 1, 2, ..., n) and intermediate output components u αai with u βai (i = 1, 2, ..., n); Step 2, based on the bridge arm side inductor current i obtained in Step 1 1a i 1b i 1c and the α-axis and β-axis components u after decoupling from the grid voltage gα1 u gβ1 After the grid voltage phase angle θ g The dq component I of the inductor current on the arm side of the grid-type converter is obtained by a single synchronous rotating coordinate transformation with orientation reference. 1d I 1q With the decoupled dq component U gd U gq Then, the voltage amplitude U of the grid phase voltage is obtained through the voltage amplitude calculation equation. g ; Step 3, based on the filtered output component u obtained in Step 1 gα1 u gβ1 u αa1 u βa1 u αd1 u βd1 The amplitude U of the grid phase voltage obtained in step 2 g And the angular frequency command ω given by the grid converter. ref The angular frequency ω of the power grid is obtained through the frequency-locked loop control equation. g and the differential signal dω of angular frequency g / dt, representing the angular frequency ω of the power grid. g The phase angle θ of the grid voltage is obtained through integration. g ; Step 4, based on the differential signal dω of the power grid angular frequency obtained in Step 3. g The reference active power P of the grid-connected converter is obtained by using the virtual inertia control equations, along with the active power command P0 and the inertia time constant H of the grid-connected converter. ref ; Step 5, based on the d-axis component U of the grid voltage obtained in Step 1 gd and the reference active power P obtained in step 4 ref The reference active current I of the grid-type converter is obtained through the current calculation equation. dref and reference reactive current I qref ; Step 6, based on the reference active current I obtained in Step 5 dref Reference reactive current I qref And the dq component I of the bridge arm side inductor current in step 1 1d I 1q dq component of grid voltage U gd U gq And the angular frequency ω of the power grid in step 3 g The control signal U is obtained through the current control equation. d U q ; Step 7, first according to the control signal U obtained in step 6 d U q and the grid voltage phase angle θ obtained in step 3 g After the grid voltage phase angle θ g The three-phase bridge arm voltage control signal U is obtained by inverse transformation of the single synchronous rotating coordinates with the orientation reference. a U b U c Then, the three-phase bridge arm voltage control signal U a U b U c The SVPWM modulation stage generates the drive signal for the inverter bridge switching transistors of the grid converter.

2. The virtual inertia control method for grid-connected converters based on parallel heterogeneous SOGI-FLL as described in claim 1, characterized in that, The control equations for the harmonic decoupling network in step 1 are as follows: The control equation for the second-order generalized integrator is: in: In the formula, n is a positive integer, i and j are both positive integers from 1 to n, and ω g ω is the angular frequency of the power grid, k is the gain coefficient of the second-order generalized integrator, and s is the Laplace operator.

3. The virtual inertia control method for grid-connected converters based on parallel heterogeneous SOGI-FLL as described in claim 1, characterized in that, The amplitude U of the grid phase voltage in step 2 g The calculation formula used is:

4. The virtual inertia control method for grid-connected converters based on parallel heterogeneous SOGI-FLL as described in claim 1, characterized in that, The frequency-locked loop control equation in step 3 is: Phase angle θ of grid voltage g The calculation equation used is: In the formula, λ is the integral coefficient of the second-order generalized integrator, and s is the Laplace operator.

5. The virtual inertia control method for grid-connected converters based on parallel heterogeneous SOGI-FLL according to claim 1, characterized in that, The virtual inertia control equation in step 4 is:

6. The virtual inertia control method for grid-connected converters based on parallel heterogeneous SOGI-FLL as described in claim 1, characterized in that, The reference active current I in step 5 dref The calculation formula used is: Reference reactive current I qref The calculation formula used is: s I qref ＝0。 7. The virtual inertia control method for grid-connected converters based on parallel heterogeneous SOGI-FLL as described in claim 1, characterized in that, The current control equation in step 6 is: In the formula, k pc k is the proportionality coefficient of the current loop. ic is the integral coefficient of the current loop, L is the filter inductance on the bridge arm side, and s is the Laplace operator.

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