Energy storage converter virtual inertia control method based on heterogeneous SOGI-FLL

Abstract

The invention discloses an energy storage converter virtual inertia control method based on a heterogeneous second-order generalized integrator-frequency locked loop (HSOGI-FLL), and aims to solve the problems that in virtual inertia control of an existing energy storage converter, power grid angular frequency operation often needs to be depended on to provide control input, and noise interference is easy to introduce in frequency differential operation, and implementation is complex. The invention discloses the energy storage converter virtual inertia control method based on the heterogeneous second-order generalized integrator-frequency locked loop (HSOGI-FLL). According to the method, on the basis of a typical SOGI-FLL control structure, different SOGI output signals are adopted to construct an FLL control loop, an HSOGI-FLL structure is formed, power grid angular frequency differential signals can be directly and accurately extracted, and power grid angular frequency differential operation does not need to be carried out. According to the method, noise sensitivity and implementation complexity caused by power grid angular frequency differential operation can be avoided, reliable input signals are provided for virtual inertia control of the energy storage converter, then the energy storage converter can effectively provide virtual inertia support for a power grid, and the method can be suitable for the field of grid-connected control of various energy storage converters.

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 energy storage converters based on 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 energy storage converters that need to be connected to the grid. Background Technology

[0002] The power system is gradually exhibiting a "dual high" characteristic: a high proportion of renewable energy and a high proportion of power electronic equipment. Against this backdrop, a large number of renewable energy generation units, such as wind and solar power, are being integrated into the grid via power converters. Unlike traditional synchronous generators that rely on mechanical rotating parts for energy conversion, renewable energy generation units lack the mechanical inertia of traditional synchronous generators, resulting in a lack of inertia support for the grid. This reduces the system's equivalent inertia level, thus threatening the grid's operational stability. Insufficient inertia mainly induces two types of frequency instability problems: First, the system frequency change rate continuously increases, and an excessively high system frequency change rate may trigger the sliding pole protection of traditional synchronous generators to operate or malfunction, ultimately leading to cascading failures; second, the system frequency amplitude deviation widens, and in extreme cases, frequency deviations will trigger safety protection mechanisms such as low-frequency load shedding, or even cause large-scale power outages. To maintain or improve the frequency stability of the power system, it is necessary to study the control strategies of power converters to enhance the power system's inertia support capability.

[0003] To this end, various studies have been conducted, such as the article entitled "Modeling and design of df / dt-based inertia control for power converters", Daniel Duckwitz, Boris Fischer, IEEE Journal of Emerging and Selected Topics in Power Electronics, 2017, 5(4), 1553-1564 ("Modeling and design of df / dt-based inertia control for power converters", IEEE Journal of Emerging and Selected Topics in Power Electronics, 2017, Vol. 5, No. 42, pp. 1553-1564). This article proposes a virtual inertia control strategy based on the direct differentiation of the angular frequency signal of the phase-locked loop to improve the equivalent inertia level of the system connected to the power converter. However, the frequency differentiation operation is prone to harmonic amplification and the filtering delay restricts the response speed of the virtual inertia.

[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 based on frequency-locked loop", IEEE Transactions on Smart Grid, Vol. 10, No. 5, 2019, 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 enhances the grid inertia level while avoiding the high-frequency noise problem caused by the differential operation. However, the method has limited disturbance suppression capability in test conditions where the grid has harmonics, DC components and interharmonics.

[0005] The article, titled "Inertia Simulation Method for Energy Storage Converters 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 control method for energy storage converters based on an improved SOGI-FLL. This method enhances the suppression effect of the improved SOGI-FLL on characteristic subharmonic disturbances in the power grid by embedding multiple frequency adaptive notch filters in a typical SOGI-FLL structure. However, the disturbance suppression capability of this method in test conditions where the power grid contains DC components and interharmonics still needs further improvement.

[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. 01, 2022, pp. 235-241, proposes a virtual inertia control method for energy storage converters based on an improved cascaded SOGI-FLL. This method further improves the suppression effect of the improved cascaded SOGI-FLL on characteristic subharmonics, DC components, and interharmonic disturbances contained in the power grid by introducing multiple frequency adaptive notch filters into the control loop. However, it has the drawbacks of increased system control complexity and stringent requirements on controller performance.

[0007] As can be seen from the above, among the existing virtual inertia control methods for energy storage converters based on the detection of grid angular frequency differential signals, the SOGI-FLL control method based on the gradient descent (GD) algorithm is often used. However, most studies focus on the optimization or improvement of typical SOGI-FLL control loops, such as adding notch filters or cascading SOGI at the front end to improve the anti-interference capability of SOGI-FLL. Research on grid angular frequency differential signal detection methods based on different GD algorithms is still rare. Summary of the Invention

[0008] To overcome the limitations of various technical solutions presented in the background art, this invention addresses the problem of increased deviations in system frequency change rate and frequency amplitude caused by the reduction in equivalent inertia of renewable energy grid-connected systems. It provides a virtual inertia control method for energy storage converters based on heterogeneous SOGI-FLL (HSOGI-FLL). This method, based on a typical SOGI-FLL control structure, constructs an FLL control loop using different SOGI output signals to form an HSOGI-FLL structure. This allows for direct and accurate extraction of the grid angular frequency differential signal without the need for grid angular frequency differential calculations. This invention avoids the noise sensitivity and implementation complexity caused by grid angular frequency differential calculations, providing a reliable input signal for the virtual inertia control of the energy storage converter, thereby enabling the energy storage converter to effectively provide virtual inertia support to the grid.

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

[0010] A virtual inertia control method for an energy storage converter based on heterogeneous SOGI-FLL includes the following steps:

[0011] Step 1: First, collect the inductor current i on the bridge arm side of the energy storage 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 bridge arm side of the energy storage converter is obtained by a single synchronous rotating coordinate transformation with the 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 ugb 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 Then, the α-axis orthogonal output component U after grid voltage filtering is obtained through the second-order generalized integrator control equation. αd with u αq β-axis quadrature 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 αβ component U of the grid voltage obtained in step 2 gα U gβ Filtered output component U αd U βd U αa with U βa And the angular frequency command ω given by the energy storage 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 energy storage converter is obtained by using the virtual inertia control equations, along with the active power command P0 of the energy storage converter and the inertia time constant H. 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 energy storage 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 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 power grid phase angle θ obtained in step 1 g The three-phase bridge arm voltage control signal U is obtained through single synchronous rotating coordinate inverse transformation. a U b U c Then, the three-phase bridge arm voltage control signal U a U b U c Generate SVPWM control signals for the inverter bridge switching transistors of the energy storage 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 second-order generalized integrator in step 2 is:

[0021]

[0022]

[0023] In the formula, 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.

[0024] Preferably, the frequency-locked loop control equation in step 3 is:

[0025]

[0026] Phase angle θ of grid voltage g The calculation formula used is:

[0027]

[0028] In the formula, λ is the integral coefficient of the second-order generalized integrator, and s is the Laplace operator.

[0029] Preferably, the virtual inertia control equation in step 4 is:

[0030]

[0031] Preferably, the reference active current I in step 5 dref The calculation formula used is:

[0032]

[0033] Reference reactive current Iqref The calculation formula used is:

[0034] I qref =0.

[0035] Preferably, the current control equation in step 6 is:

[0036]

[0037] In the formula, k pc k is the proportionality coefficient of the current loop. ic is the integral coefficient of the current loop, and s is the Laplace operator.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] This invention discloses a virtual inertia control method for energy storage converters based on heterogeneous SOGI-FLL (HSOGI-FLL). This method, based on a typical SOGI-FLL control structure, constructs an FLL control loop using different SOGI output signals to form an HSOGI-FLL structure. This allows for direct and accurate extraction of the grid angular frequency differential signal without the need for grid angular frequency differentiation calculations. This invention avoids the noise sensitivity and implementation complexity caused by grid angular frequency differentiation calculations, providing a reliable input signal for the virtual inertia control of the energy storage converter. This enables the energy storage converter to effectively provide virtual inertia support to the grid, and is applicable to various grid-connected control applications for energy storage converters. Attached Figure Description

[0040] Figure 1 This is a topology diagram of the energy storage converter according to an embodiment of the present invention.

[0041] Figure 2 This is a structural diagram of a second-order generalized integrator according to an embodiment of the present invention.

[0042] Figure 3 This is a control structure diagram of a heterogeneous second-order generalized integrator-frequency-locked loop according to an embodiment of the present invention.

[0043] Figure 4 This is a diagram of the virtual inertia control structure according to an embodiment of the present invention.

[0044] Figure 5 This is a comparison of simulation waveforms of the energy storage converter before and after adopting this invention. Detailed Implementation

[0045] The following detailed embodiments will be further described in conjunction with the above-mentioned figures, as follows:

[0046] The energy storage converter topology used in this invention is as follows: Figure 1 As shown, the relevant parameter settings in this embodiment are as follows: DC bus voltage U of the energy storage converter dc The voltage is 600V, the effective value of the output AC line voltage is 380V / 50Hz, the rated capacity is 100kVA, the filter inductance on the bridge arm side of the energy storage converter is L=0.56mH, the filter capacitor of the energy storage converter is C=90uF, and the isolation transformer is a 100kVA 270V / 400V Dyn11 type transformer.

[0047] Please see Figure 1 The present invention proposes a virtual inertia control method for energy storage converters based on heterogeneous SOGI-FLL, comprising the following steps:

[0048] Step 1: First, collect the inductor current i on the bridge arm side of the energy storage 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 bridge arm side of the energy storage converter is obtained by a single synchronous rotating coordinate transformation with the 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 ;

[0049] Among them, the amplitude U of the grid phase voltage g The calculation formula used is:

[0050]

[0051] Step 2, based on the grid voltage u obtained in Step 1 ga u gb u gc ,like Figure 3 As shown, 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 Then, the α-axis orthogonal output component U after grid voltage filtering is obtained through the second-order generalized integrator control equation. αd with u αq β-axis quadrature output component U βd with U βq and intermediate output component U αa with U βa ;

[0052] The control equation for the second-order generalized integrator is as follows:

[0053]

[0054] In the formula, 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.

[0055] In this embodiment, the transfer function between the input and output signals of the second-order generalized integrator is a typical second-order system. The response performance of the second-order generalized integrator is mainly determined by k; that is, the larger k is, the faster its dynamic response speed and the weaker its harmonic suppression capability, and vice versa. Therefore, k is set to... To find the optimal compromise between its response speed and harmonic suppression capability.

[0056] 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.

[0057] Step 3, based on the amplitude U of the grid phase voltage obtained in Step 1 g The αβ component U of the grid voltage obtained in step 2 gα U gβ Filtered output component U αd U βd U αa with U βa And the angular frequency command ω given by the energy storage 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 ;

[0058] The frequency-locked loop control equation is as follows:

[0059]

[0060] Phase angle θ of grid voltage g The calculation formula used is:

[0061]

[0062] In the formula, λ is the integral coefficient of the second-order generalized integrator, and s is the Laplace operator.

[0063] In this embodiment, the angular frequency of the energy storage converter is the angular frequency corresponding to a rated frequency of 50Hz, i.e., ω. ref = 314.1593 rad / s, amplitude U of the grid phase voltage gThe value corresponding to a rated voltage of 380V is used, i.e., U g =311V, the recommended system damping coefficient ζ is set to To optimally balance the system's overshoot and settling time, and since λ can be expressed in terms of k and ζ, we can obtain... Then λ = 12337.

[0064] Based on the above control, the control structure diagram of the heterogeneous second-order generalized integrator-frequency-locked loop of this invention can be obtained, as shown in the figure below. Figure 3 As shown.

[0065] 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 energy storage converter is obtained by using the virtual inertia control equations, along with the active power command P0 of the energy storage converter and the inertia time constant H. ref ;

[0066] The virtual inertia control equation is as follows:

[0067]

[0068] The inertia time constant of the energy storage 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.

[0069] 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 energy storage converter is obtained through the current calculation equation. dref and reference reactive current I qref ;

[0070] Among them, the reference active current I dref The calculation formula used is:

[0071]

[0072] Reference reactive current I qref The calculation formula used is:

[0073] I qref =0.

[0074] 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 The control signal U is obtained through the current control equation.d U q ;

[0075] The current control equation is as follows:

[0076]

[0077] In the formula, k pc k is the proportionality coefficient of the current loop. ic is the integral coefficient of the current loop, and s is the Laplace operator.

[0078] 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.

[0079] 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 The three-phase bridge arm voltage control signal U is obtained through single synchronous rotating coordinate inverse transformation. a U b U c Then, the three-phase bridge arm voltage control signal U a U b U c Generate SVPWM control signals for the inverter bridge switching transistors of the energy storage converter.

[0080] Based on the above control, the control structure diagram of the virtual inertia of this invention can be obtained, as shown in the figure below. Figure 4 As shown.

[0081] Example

[0082] To verify the control effect of the proposed virtual inertia control method for energy storage converters based on heterogeneous SOGI-FLL, the proposed virtual inertia control method for energy storage converters based on heterogeneous SOGI-FLL (hereinafter referred to as HSOGI-FLL) is compared with the existing typical SOGI-FLL (hereinafter referred to as SOGI-FLL) virtual inertia control method. 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 J, Zhang R, Li H, 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 Transactions on Smart Grids, Vol. 10, No. 5, 2019, pp. 4918-4927) provides a simulation comparison, mainly comparing the detection of the differential signal dω of the grid angular frequency under the condition of grid angular frequency rise. g The dynamic response performance of / dt.

[0083] Based on the above parameter settings, simulation comparison tests were conducted, as follows:

[0084] The simulation test conditions were set as follows: the three-phase grid voltage was a standard sinusoidal waveform, and the angular frequency of the three-phase grid voltage was 6.28 rad / s at 0.5s. 2 The rate increases and returns to its original state after 1.0 s. Based on the above operating conditions, the following is obtained: Figure 5 The simulation test comparison diagrams shown in the diagrams are as follows: SOGI-FLL represents the existing typical second-order generalized integrator-frequency-locked loop (PLL) method for detecting the angular frequency differential signal, while HSOGI-FLL represents the heterogeneous second-order generalized integrator-frequency-locked loop (PLL) method proposed in this invention. Specifically, the dotted line representing SOGI-FLL is the simulation waveform diagram before using this invention, and specifically, it is the dynamic response simulation waveform diagram of the detected angular frequency differential signal after using the existing typical second-order generalized integrator-PLL method. The dashed line representing HSOGI-FLL is the simulation waveform diagram after using this invention, and specifically, it is the dynamic response simulation waveform diagram of the detected angular frequency differential signal after using the heterogeneous second-order generalized integrator-frequency-locked loop proposed in this invention.

[0085] according to Figure 5 It can be observed that at a grid angular frequency of 6.28 rad / s 2During the rate increase, both the proposed HSOGI-FLL and the existing SOGI-FLL can accurately detect the grid angular frequency differential signal without performing grid angular frequency differential calculations. This avoids the noise sensitivity and implementation complexity caused by grid angular frequency differential calculations, providing a reliable input signal for the virtual inertia control of the energy storage converter, thereby enabling the energy storage converter to effectively provide virtual inertia support for the grid.

[0086] 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 an energy storage converter based on 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 energy storage 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 bridge arm side of the energy storage converter is obtained by a single synchronous rotating coordinate transformation with the 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. ga U gβ Then, the α-axis orthogonal output component U after grid voltage filtering is obtained through the second-order generalized integrator control equation. αd with U aq β-axis quadrature 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 αβ component U of the grid voltage obtained in step 2 ga U gβ Filtered output component U αd U βd U αa with U βa And the angular frequency command ω given by the energy storage 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 / dt and the active power command P of the energy storage converter o The inertia time constant H is used to obtain the reference active power P of the energy storage converter through the virtual inertia control equation. 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 energy storage 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 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 power grid phase angle θ obtained in step 1 g The three-phase bridge arm voltage control signal U is obtained through single synchronous rotating coordinate inverse transformation. a U b U c Then, the three-phase bridge arm voltage control signal U a U b U c Generate SVPWM control signals for the inverter bridge switching transistors of the energy storage converter.

2. The virtual inertia control method for energy storage converters based on 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 virtual inertia control method for energy storage converters based on heterogeneous SOGI-FLL according to claim 1, characterized in that, The control equation for the second-order generalized integrator in step 2 is: In the formula, 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.

4. The virtual inertia control method for energy storage converters based on 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 virtual inertia control method for energy storage converters based on 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 energy storage converters based on 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 virtual inertia control method for energy storage converters based on 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, and s is the Laplace operator.

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