Method for realizing virtual inertia of net-following converter based on embedded heterogeneous SOGI-FLL

Abstract

The application discloses a virtual inertia implementation method of a grid-following type converter based on an embedded heterogeneous second order generalized integrator-based frequency locked loop (HSOGI-FLL), the implementation method embeds a second order generalized integrator into a control loop of the HSOGI-FLL to form an embedded HSOGI-FLL (EHSOGI-FLL), directly uses the EHSOGI-FLL to accurately evaluate a grid angle frequency differential signal, and applies the grid angle frequency differential signal to a virtual inertia implementation method of the grid-following type converter, so that the harmonic interference problem caused by the grid angle frequency differential operation can be effectively avoided, the influence of characteristic harmonics, a direct current component and an inter-harmonic disturbance contained in a grid voltage on the virtual inertia response performance of the grid-following type converter can be effectively suppressed, and the virtual inertia implementation method can be applicable to the grid-following type converter grid-connected control field in power electronic technology.

Description

Technical Field

[0001] This invention relates to the field of renewable energy grid-connected control technology, and in particular to a method for realizing virtual inertia of grid-connected converters based on embedded heterogeneous SOGI-FLL. This method is suitable for high-proportion renewable energy access to the power system, can simulate the inertia response characteristics of synchronous generators, and provides fast and reliable inertia support for the power grid. It is especially suitable for various grid-connected converters that need to be connected to the grid. Background Technology

[0002] With the deepening development of my country's "carbon peaking and carbon neutrality" goals, the construction of a new power system has been accelerated, and the power system is gradually showing characteristics of a high proportion of renewable energy and a high proportion of power electronic equipment. Against this backdrop, renewable energy power generation units such as wind power and photovoltaics mainly achieve grid connection through power converters. Unlike traditional synchronous generators that rely on mechanical rotating parts to provide inertia, renewable energy power generation units lack mechanical inertia and cannot effectively participate in grid angular frequency regulation, leading to a decline in the inertia level and operational stability of the power system. Weakened inertia support capacity easily leads to frequency instability problems such as excessively high frequency change rate and excessively large frequency amplitude deviation. On the one hand, an excessively high frequency change rate can easily trigger malfunctions of 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 and induce large-scale power outages in the power grid.

[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 constructs an FLL control loop using different SOGI output signals, forming a heterogeneous second-order generalized integrator-based frequency lock loop (HLL). The HSOGI-FLL method for detecting the differential angular frequency signal of the power grid has better dynamic response performance than SOGI-FLL in detecting the differential angular frequency signal of the power grid. However, like SOGI-FLL, HSOGI-FLL also has limited disturbance suppression capability under non-ideal power grid conditions, and HSOGI-FLL has not been applied to the virtual inertia realization method of grid-connected converters.

[0004] The article, 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 Grid, 2019, 10(5), 4918-4927 ("Frequency derivative-based virtual inertia control strategy for grid-connected power converters based on frequency-locked loop", IEEE Smart Grid Journal, 2019, Vol. 10, No. 5, pp. 4918-4927), proposes a virtual inertia control algorithm for grid-connected power converters based on SOGI-FLL. By associating the gain coefficient with the active power reference value, it can improve the grid inertia level while avoiding the high-frequency noise problem caused by the differential operation. However, this method has limited disturbance suppression capability in grid conditions with harmonics, DC components and interharmonics and high harmonic content in grid current.

[0005] The article, titled "Virtual Inertia Control Strategy Based on Improved Frequency Differential Operation," published in *Automation of Electric Power Systems*, Vol. 44, No. 20, 2020, pp. 94-102, proposes introducing a front-end cascaded 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 under distorted grid conditions containing characteristic subharmonics and interharmonics still needs further optimization.

[0006] The article, titled "Virtual Inertia Control Technology Based on Improved Cascaded SOGI-FLL", published in the Journal of Energiae Solaris Sinica, Vol. 43, No. 1, 2022, pp. 235-241, proposes a virtual inertia simulation method based on an improved cascaded SOGI-FLL. This method involves adding multiple frequency adaptive notch filters to the cascaded SOGI-FLL, which improves the suppression of characteristic subharmonics and DC component disturbances and enhances the control performance of the virtual inertia response. However, the introduction of multiple frequency adaptive notch filters increases the complexity of the control structure and is highly dependent on the accuracy of frequency detection.

[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 method for realizing the virtual inertia of a grid-connected converter based on an embedded heterogeneous second-order generalized integrator-based frequency locked loop (HSOGI-FLL). This method embeds the second-order generalized integrator into the control loop of the HSOGI-FLL to form an embedded HSOGI-FLL. HSOGI-FLL (EHSOGI-FLL) directly utilizes EHSOGI-FLL to accurately evaluate the differential signal of the grid angular frequency and applies it to the virtual inertia realization method of grid-connected converters. This effectively avoids harmonic interference problems caused by grid angular frequency differential calculations and effectively suppresses the impact of characteristic subharmonics, DC components, and interharmonic disturbances contained in the grid voltage on the virtual inertia response performance of grid-connected converters. This allows grid-connected converters to effectively provide virtual inertia support for the grid while ensuring grid-connected current quality.

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

[0010] A method for implementing virtual inertia in a grid-connected converter based on embedded 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. la i lb i lc and grid voltage u ga u gb u gc 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. ld I lq and the dq component of the grid voltage U gd U gq Then, the voltage amplitude U of the grid phase voltage is obtained through the voltage amplitude calculation equation. g ;

[0012] Step 2, based on the grid voltage u obtained in Step 1 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. gαu gβ The output component u after grid voltage filtering is obtained by the control equation of the preceding second-order generalized integrator. gα1 u gβ1 Then, through the control equations of the subsequent second-order generalized integrator, the α-axis orthogonal output component u after grid voltage filtering is obtained. αd with u αq β-axis orthogonal output component u βd with u βq and intermediate output component u αa with u βa ;

[0013] Step 3, based on the amplitude U of the grid phase voltage obtained in Step 1 g The filtered output component u obtained in step 2 gα1 u gβ1 u αa with u βa 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 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 ;

[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 ld I lq 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 Uq ;

[0017] Step 7, first according to 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.

[0018] Preferably, the amplitude U of the grid phase voltage in step 1 g The calculation formula used is:

[0019]

[0020] Preferably, the control equation for the preceding second-order generalized integrator in step 2 is:

[0021]

[0022] The control equation for the second-order generalized integrator is:

[0023]

[0024] In the formula, ω g denoted as ω0, k2 is the gain coefficient of the first-stage second-order generalized integrator, k1 is the gain coefficient of the second-stage second-order generalized integrator, and s is the Laplace operator.

[0025] Preferably, the frequency-locked loop control equation in step 3 is:

[0026]

[0027] Phase angle θ of grid voltage g The calculation formula used is:

[0028]

[0029] In the formula, λ is the integral coefficient of the second-order generalized integrator, and s is the Laplace operator.

[0030] Preferably, the virtual inertia control equation in step 4 is:

[0031]

[0032] Preferably, the reference active current I in step 5 dref The calculation formula used is:

[0033]

[0034] Reference reactive current I qref The calculation formula used is:

[0035] I qref =0.

[0036] Preferably, the current control equation in step 6 is:

[0037]

[0038] 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.

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] This invention discloses a method for realizing the virtual inertia of a grid-connected converter based on an embedded heterogeneous second-order generalized integrator-based frequency locked loop (HSOGI-FLL). This method embeds the second-order generalized integrator into the control loop of the HSOGI-FLL to form an embedded HSOGI-FLL (EHSOGI-FLL). The EHSOGI-FLL is directly used to accurately evaluate the differential signal of the grid angular frequency, and the differential signal of the grid angular frequency is applied to the virtual inertia realization method of the grid-connected converter. This invention can effectively avoid harmonic interference caused by the differential operation of the grid angular frequency, and can effectively suppress the influence of characteristic subharmonics, DC components and interharmonic disturbances contained in the grid voltage on the virtual inertia response performance of the grid-connected converter. It provides a reliable input signal for the realization of the virtual inertia of the grid-connected converter, so that the grid-connected converter can effectively provide virtual inertia support for the grid and ensure the grid-connected current quality. It can be applied to the grid-connected control of grid-connected converters in power electronics technology. Attached Figure Description

[0041] Figure 1 This is a topology diagram of a grid-type converter according to an embodiment of the present invention.

[0042] Figure 2This is a structural diagram of a second-order generalized integrator according to an embodiment of the present invention.

[0043] Figure 3 This is a control structure diagram of an embedded heterogeneous second-order generalized integrator-frequency-locked loop according to an embodiment of the present invention.

[0044] Figure 4 This is a small-signal model diagram of an embedded heterogeneous second-order generalized integrator-frequency-locked loop according to an embodiment of the present invention.

[0045] Figure 5 A schematic diagram of coordinate transformation and modulation in an embodiment of the present invention.

[0046] Figure 6 This is a diagram of the virtual inertia control structure according to an embodiment of the present invention.

[0047] Figure 7 This is a comparison of simulation waveforms before and after the application of this invention to a grid converter. Detailed Implementation

[0048] The following detailed embodiments will be further described in conjunction with the above-mentioned figures, as follows:

[0049] Please see Figure 1 The present invention proposes a method for realizing virtual inertia of a grid-connected converter based on an embedded heterogeneous SOGI-FLL, comprising the following steps:

[0050] Step 1: First, collect the inductor current i on the bridge arm side of the grid converter. la i lb i lc and grid voltage u ga u gb u gc 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. ld I lq and the dq component of the grid voltage U gd U gq Then, the voltage amplitude U of the grid phase voltage is obtained through the voltage amplitude calculation equation. g ;

[0051] Among them, the amplitude U of the grid phase voltage g The calculation formula used is:

[0052]

[0053] Step 2, based on the grid voltage u obtained in Step 1 ga u gb u gcThe 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 output component u after grid voltage filtering is obtained by the control equation of the preceding second-order generalized integrator. gα1 u gβ1 Then, through the control equations of the subsequent second-order generalized integrator, the α-axis orthogonal output component u after grid voltage filtering is obtained. αd with u aq β-axis orthogonal output component u βd with u βq and intermediate output component u αa with u βa ;

[0054] The control equation for the first-stage second-order generalized integrator is:

[0055]

[0056] The control equation for the second-order generalized integrator is:

[0057]

[0058] In the formula, ω g denoted as ω0, k2 is the gain coefficient of the first-stage second-order generalized integrator, k1 is the gain coefficient of the second-stage second-order generalized integrator, and s is the Laplace operator.

[0059] 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.

[0060] Step 3, based on the amplitude U of the grid phase voltage obtained in Step 1 g The filtered output component u obtained in step 2 gα1 u gβ1 u αa with u βa 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 ;

[0061] The frequency-locked loop control equation is as follows:

[0062]

[0063] Phase angle θ of grid voltage g The calculation formula used is:

[0064]

[0065] In the formula, λ is the integral coefficient of the second-order generalized integrator, and s is the Laplace operator.

[0066] Based on the above control, the control structure diagram and small-signal model diagram of the embedded heterogeneous second-order generalized integrator-frequency-locked loop of this invention 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.

[0067] 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 ;

[0068] The virtual inertia control equation is as follows:

[0069]

[0070] 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.

[0071] 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 ;

[0072] Among them, the reference active current I dref The calculation formula used is:

[0073]

[0074] Reference reactive current I qref The calculation formula used is:

[0075] I qref =0.

[0076] Step 6, based on the reference active current I obtained in Step 5 dref Reference reactive current I qrefAnd the dq component I of the bridge arm side inductor current in step 1 ld I lq 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 ;

[0077] The current control equation is as follows:

[0078]

[0079] In the formula, k pc k is the proportionality coefficient of the current loop. lc is the integral coefficient of the current loop, L is the filter inductance on the bridge arm side, and s is the Laplace operator.

[0080] 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.

[0081] 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.

[0082] 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.

[0083] Example

[0084] To verify the control effect of the proposed method for realizing virtual inertia of grid-connected converters based on embedded heterogeneous SOGI-FLL, the proposed method for realizing virtual inertia of grid-connected converters based on embedded heterogeneous SOGI-FLL (hereinafter referred to as EHSOGI-FLL) is compared with an existing method for realizing virtual inertia of grid-connected converters based on SOGI-FLL. The SOGI-FLL implementation 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 subharmonics, DC components and interharmonic disturbance signals in the grid voltage. g / dt detection performance.

[0085] First, the relevant parameters are set. In this embodiment, the relevant parameter settings in the virtual inertia implementation method of the grid-connected converter based on embedded heterogeneous SOGI-FLL of the present invention are as follows:

[0086] 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 open-loop transfer function between the phase error signal and the detected phase can be obtained as follows: Based on G1(s), the symmetric optimality method is used to design k1 and k2. The standard open-loop transfer function of the closed-loop control system is: Correspondingly, ω p kp With k i For control parameters; ω p =b 2 k i / k p Let be an open-loop pole, where b is a positive number. According to G... o (s) yields the equation PM=-tan -1 (ω c / ω p )+tan -1 (k p ω c / k i ), where PM is the system phase margin; ω c This is the cutoff angular frequency. If the condition is met... At that time, PM has a maximum value, that is, PM max =tan -1 [(b 2 -1) / 2b]. At this time, according to ω c The equation, |G o (jω c )|=1 and PM max The expression can be used to obtain the expression k. p =ω c k i =ω c 2 / b,ω p =bω c Then the control parameter expression for EHSOGI-FLL is k1 = 2ω c / ω0、k2=2bω c / ω0、λ=2ω c 2 Based on the expression for the control parameter G1(s), the characteristic polynomial of the system's closed-loop transfer function can be written as follows: It can be observed that the damping coefficient ζ of the system is determined by the control parameter b. Similarly, ζ is set to... Therefore, the expression for b is This corresponds to PM = 45. It's worth noting that, for ease of parameter design, let ω... c The natural angular frequency ω of the SOGI-FLL system n If we keep it consistent, then we have ω c =ω n That is, the parameter values ​​of EHSOGI-FLL can be set to k1 = 0.752, k2 = 1.815 and λ = 11559 respectively; in addition, in order to maintain consistency with the control parameters of EHSOGI-FLL, the gain coefficient k1 and integral coefficient λ of SOGI-FLL can also be set to k1 = 0.752 and λ = 11559 respectively.

[0087] Based on the above parameter settings, simulation comparison tests were conducted, as follows:

[0088] The simulation 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 its original state in 1.0s; Operating condition 2: Injecting 5th and 7th characteristic harmonic components with an amplitude of 0.01pu into the standard grid voltage; Operating condition 3: Based on operating condition 1, introducing a DC bias with an amplitude of 0.01pu into phase A of the grid voltage; Operating condition 4: Mixing an interharmonic component with an amplitude of 0.01pu and a frequency of 5Hz into the standard grid voltage. Based on the above operating conditions, the following is obtained: Figure 7 The simulation test comparison charts shown in the figures are as follows: SOGI-FLL represents the existing grid angular frequency differential signal detection method based on a second-order generalized integrator-frequency-locked loop, and EHSOGI-FLL represents the grid angular frequency differential signal detection method based on an embedded heterogeneous second-order generalized integrator-frequency-locked loop proposed in this invention. That is, the dashed line represents the SOGI-FLL simulation waveform before the application of this invention, specifically the dynamic response simulation waveform of the grid angular frequency differential signal detected after using the existing second-order generalized integrator-phase-locked loop method. The solid line represents the EHSOGI-FLL simulation waveform after the application of this invention, specifically the dynamic response simulation waveform of the grid angular frequency differential signal detected after using the embedded heterogeneous second-order generalized integrator-frequency-locked loop proposed in this invention.

[0089] Depend on Figure 7 (a) It can be observed that the grid angular frequency signal is 6.28 rad / s 2 During the rate increase, the overshoot of the angular frequency differential signal corresponding to the EHSOGI-FLL proposed in this invention is 1.82%, which is much smaller than the 4.88% corresponding to SOGI-FLL. At steady state, the angular frequency differential signals of both are at 6.28 rad / s. 2 The presence of minor fluctuations indicates that both methods can accurately detect the differential signal of the power grid angular frequency without requiring differential calculations, thus avoiding the noise sensitivity and implementation complexity associated with these calculations. According to 7(b), the maximum value of the differential angular frequency signal corresponding to the EHSOGI-FLL proposed in this invention is approximately 10.86 rad / s. 2 It is much smaller than the 122.89 rad / s corresponding to SOGI-FLL. 2 . Figure 7(c) The comparison results show that the response curve of the EHSOGI-FLL proposed in this invention has no ripple under operating condition 3, its stability is better than SOGI-FLL, and it can accurately detect the differential signal of the grid angular frequency. Figure 7 (d) It can be seen that the maximum value of the angular frequency differential signal corresponding to the EHSOGI-FLL proposed in this invention is approximately 2.92 rad / s. 2 It is much smaller than the 64.44 rad / s corresponding to SOGI-FLL. 2 .Will Figure 7 (a)- Figure 7 After comparing the results in (d), it is easy to see that the EHSOGI-FLL proposed in this invention has superior performance compared with SOGI-FLL in dealing with disturbances in the power grid, including harmonics, DC components and interharmonics. It provides a reliable input signal for the virtual inertia control of grid-connected converters, thereby enabling grid-connected converters to effectively provide virtual inertia support for the power grid and ensure the quality of grid-connected current.

[0090] 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 method for realizing virtual inertia of a grid-connected converter based on embedded 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. la i lb i lc and grid voltage u ga u gb u gc 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. ld I lq and the dq component of the grid voltage U gd U gq Then, the voltage amplitude U of the grid phase voltage is obtained through the voltage amplitude calculation equation. g ; Step 2, based on the grid voltage u obtained in Step 1 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 output component u after grid voltage filtering is obtained by the control equation of the preceding second-order generalized integrator. gα1 u gβ1 Then, through the control equations of the subsequent second-order generalized integrator, the α-axis orthogonal output component u after grid voltage filtering is obtained. αd with u αq β-axis orthogonal output component u βd with u βq and intermediate output component u αa with u βa ; Step 3, based on the amplitude U of the grid phase voltage obtained in Step 1 g The filtered output component u obtained in step 2 gα1 u gβ1 u αa with u βa 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 ld I lq 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 method for realizing virtual inertia of a grid-connected converter based on embedded heterogeneous SOGI-FLL according to claim 1, characterized in that, The amplitude U of the grid phase voltage in step 1 g The calculation formula used is:

3. The method for realizing virtual inertia of a grid-connected converter based on embedded heterogeneous SOGI-FLL according to claim 1, characterized in that, The control equation for the preceding second-order generalized integrator in step 2 is: The control equation for the second-order generalized integrator is: In the formula, ω g denoted as ω0, k2 is the gain coefficient of the first-stage second-order generalized integrator, k1 is the gain coefficient of the second-stage second-order generalized integrator, and s is the Laplace operator.

4. The method for realizing virtual inertia of a grid-connected converter based on embedded heterogeneous SOGI-FLL according to 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 method for realizing virtual inertia of a grid-connected converter based on embedded heterogeneous SOGI-FLL according to claim 1, characterized in that, The virtual inertia control equation in step 4 is:

6. The method for realizing virtual inertia of a grid-connected converter based on embedded heterogeneous SOGI-FLL according to 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: I qref ＝0。 7. The method for realizing virtual inertia of a grid-connected converter based on embedded heterogeneous SOGI-FLL according to 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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