A method and device for virtual inertia frequency modulation on the DC side of a two-stage photovoltaic inverter

Abstract

The present application relates to photovoltaic inverter frequency control technology field, especially in kind two-stage photovoltaic inverter's direct current side virtual inertia frequency modulation method and device.The present application will frequency regulation function from the rear level inverter migration to the front level DC / DC converter, generates frequency modulation power increment instruction according to the grid frequency deviation;Based on the direct current bus voltage and the preset low limit threshold comparison result judges power reserve margin, to decide to enter frequency modulation mode or maximum power point tracking mode;Switching introduces linear decay correction compensation term, so that the power reference value is with the actual working point before switching as the initial value and smooth decay to the scheduling set value;Superimposed frequency modulation power increment and scheduling set value generate complete power reference value, adjust photovoltaic array working point response frequency deviation.The present application realizes the structural decoupling of direct current bus voltage stability and frequency support, eliminates the power impact and voltage disturbance when mode switching, improves the system frequency response performance.

Description

Technical Field

[0001] This invention relates to the field of frequency modulation control technology for photovoltaic inverters, and in particular to a method, apparatus, equipment, and computer storage medium for virtual inertial frequency modulation on the DC side of a two-stage photovoltaic inverter. Background Technology

[0002] Large-scale photovoltaic (PV) power generation and grid connection alter the frequency dynamics of the power system. In existing two-stage PV inverter control methods, there is a direct coupling conflict between the AC-side active power-frequency droop control of the downstream voltage source inverter (VSI) and the DC bus voltage regulation loop. This leads to the frequency regulation function being easily overridden by the voltage regulation correction term, resulting in compromised frequency support capability. While PV load shedding schemes can reserve reserve margins, they suffer from long-term energy losses and maximum power point estimation errors. Configuring energy storage systems significantly increases hardware costs. Therefore, existing technologies generally suffer from structural coupling conflicts between DC bus voltage stability and frequency regulation functions, a lack of reliable online assessment of PV power reserve margins in frequency regulation mode, and the potential for power surges and voltage disturbances when switching between maximum power point tracking (MPPT) and frequency regulation modes. Summary of the Invention

[0003] Therefore, the technical problem to be solved by the present invention is to overcome the structural coupling conflict between DC bus voltage stability and frequency regulation function, the difficulty in reliably judging frequency regulation reserve margin online, and the problems of power surges and voltage disturbances easily generated during mode switching in the prior art.

[0004] To address the aforementioned technical problems, this invention provides a virtual inertial frequency modulation method for the DC side of a two-stage photovoltaic inverter, comprising:

[0005] The frequency regulation control function is moved from the AC side active power loop of the downstream voltage source inverter to the upstream DC / DC converter. The upstream DC / DC converter generates frequency regulation power increment commands based on the grid frequency deviation to adjust the output power of the photovoltaic array. Based on the comparison result between the DC bus voltage and the preset lower threshold, it is determined whether the photovoltaic array has a power reserve margin. If there is a reserve margin, the front-end DC / DC converter is controlled to enter the frequency modulation mode; otherwise, it is switched to the maximum power point tracking mode. When switching from maximum power point tracking mode to frequency modulation mode, a linear attenuation correction compensation term is introduced so that the power reference value in frequency modulation mode is initialized with the actual operating point before the switch and linearly attenuates to the upper-level scheduling setting value over time. In frequency modulation mode, the frequency modulation power increment command is superimposed with the upper-level scheduling setting value to generate a complete photovoltaic power reference value. Based on the photovoltaic power reference value, the front-end DC / DC converter is controlled to adjust the operating point of the photovoltaic array in response to grid frequency deviation.

[0006] Preferably, the step of generating frequency modulation power increment commands based on the grid frequency deviation through the front-end DC / DC converter includes: The power grid angular frequency deviation is obtained, which is the difference between the rated angular frequency and the actual angular frequency of the power grid. Based on the grid angular frequency deviation, the frequency modulation power increment command is generated by a first-order inertial transfer function that characterizes the equivalent virtual inertia, equivalent damping parameters, and equivalent droop gain.

[0007] Preferably, the step of generating the frequency modulation power increment command based on the grid angular frequency deviation, using a first-order inertial transfer function characterizing the equivalent virtual inertia, equivalent damping parameters, and equivalent droop gain, includes: The grid angular frequency deviation is input into the time-domain differential equation characterizing the equivalent virtual inertia, equivalent damping parameters, and equivalent droop gain, and the frequency modulation power increment command is obtained by solving the equation. Preferably, determining whether the photovoltaic array has a power reserve margin based on the comparison result between the DC bus voltage and a preset lower threshold includes: Real-time monitoring of DC bus voltage; The DC bus voltage is compared with a preset lower threshold. When the DC bus voltage is greater than or equal to the preset low threshold, a first mode flag signal is generated to confirm that the photovoltaic array has a power reserve margin. When the DC bus voltage is less than the preset lower threshold, a second mode flag signal is generated to confirm that the power reserve margin of the photovoltaic array has been exhausted.

[0008] Preferably, the step of generating a first mode flag signal when the DC bus voltage is greater than or equal to the preset lower threshold to confirm that the photovoltaic array has a power reserve margin includes: When the DC bus voltage is greater than or equal to the preset low threshold, a mode flag signal with a value of 1 is generated to control the front-end DC / DC converter to enter frequency modulation mode. The step of generating a second mode flag signal when the DC bus voltage is less than the preset low threshold to confirm that the power reserve margin of the photovoltaic array has been exhausted includes: When the DC bus voltage is less than the preset lower threshold, a mode flag signal with a value of 0 is generated to control the front-end DC / DC converter to switch to maximum power point tracking mode.

[0009] Preferably, the step of introducing a linear attenuation correction compensation term to make the power reference value in frequency modulation mode take the actual operating point before the switch as the initial value and linearly attenuate over time to the upper-level scheduling setting value includes: At the moment of switching from maximum power point tracking mode to frequency modulation mode, the actual operating power value of the front-end DC / DC converter in maximum power point tracking mode is obtained; Based on the difference between the actual operating power value and the upper-level scheduling setting value, a linear attenuation correction compensation term is generated. The compensation term is used to make the power reference value in frequency modulation mode take the actual operating power value as the initial value. The linear attenuation correction compensation term is superimposed on the upper-level scheduling setting value to obtain the power reference value in frequency modulation mode, so that the power reference value starts from the actual operating power value and linearly attenuates over time to the upper-level scheduling setting value.

[0010] Preferably, the step of superimposing the frequency modulation power increment command with the upper-level scheduling setting value to generate a complete photovoltaic power reference value includes: The frequency modulation power increment command is summed with the upper-level scheduling setting value after linear attenuation correction compensation term to obtain a complete photovoltaic power reference value. The upper-level scheduling setting value after linear attenuation correction compensation term is equal to the actual operating power value in maximum power point tracking mode at the moment of switching, and linearly attenuates to the upper-level scheduling setting value over time.

[0011] The present invention also provides a virtual inertial frequency modulation device for the DC side of a two-stage photovoltaic inverter, comprising: The frequency response migration module is used to migrate the frequency regulation control function from the AC side active power loop of the downstream voltage source inverter to the upstream DC / DC converter. The upstream DC / DC converter generates frequency modulation power increment commands based on the grid frequency deviation to adjust the output power of the photovoltaic array. The mode switching judgment module is used to determine whether the photovoltaic array has a power reserve margin based on the comparison result between the DC bus voltage and the preset low threshold. If there is a reserve margin, the module controls the front-end DC / DC converter to enter the frequency modulation mode; otherwise, it switches to the maximum power point tracking mode. The bumpless switching module is used to introduce a linear attenuation correction compensation term when switching from maximum power point tracking mode to frequency modulation mode, so that the power reference value in frequency modulation mode is based on the actual operating point before the switch and linearly attenuates to the upper-level scheduling setting value over time. The power reference generation module is used to superimpose the frequency modulation power increment command with the upper-level scheduling setting value in frequency modulation mode to generate a complete photovoltaic power reference value, and control the front-end DC / DC converter to adjust the operating point of the photovoltaic array based on the photovoltaic power reference value in response to grid frequency deviation.

[0012] The present invention also provides a virtual inertial frequency modulation device for the DC side of a two-stage photovoltaic inverter, comprising: Memory, used to store computer programs; A processor is used to implement the steps of the above-described method for virtual inertial frequency modulation on the DC side of a two-stage photovoltaic inverter when executing the computer program.

[0013] The present invention also provides a computer-readable storage medium storing a computer program, which, when executed by a processor, implements the steps of the above-described method for virtual inertial frequency modulation on the DC side of a two-stage photovoltaic inverter.

[0014] The technical solution of the present invention has the following advantages compared with the prior art: The DC-side virtual inertial frequency regulation method for a two-stage photovoltaic inverter described in this invention achieves structural decoupling of DC bus voltage stabilization and frequency support functions by migrating the frequency regulation control function from the downstream VSI to the upstream DC / DC converter, thus eliminating coupling conflicts between the AC-side frequency regulation and DC voltage regulation loops. Simultaneously, by determining the power reserve margin based on the comparison between the DC bus voltage and a preset lower threshold, online estimation of the photovoltaic maximum power point is eliminated, reducing control complexity. Furthermore, a linear attenuation correction compensation term is introduced during mode switching, allowing the power reference value to start from the actual operating point before switching and smoothly attenuate to the scheduling setpoint. This effectively suppresses power surges and DC bus voltage disturbances, achieving seamless switching between maximum power point tracking mode and frequency regulation mode. This significantly improves the operational stability, dynamic response performance, and control flexibility of the photovoltaic grid-connected system during frequency support. Attached Figure Description

[0015] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings, wherein: Figure 1 This is a flowchart illustrating the implementation of a virtual inertial frequency modulation method for the DC side of a two-stage photovoltaic inverter provided by the present invention. Figure 2 This is a schematic diagram of the system's basic topology; Figure 3 A schematic diagram of the basic structure (including seamless switching structure) of dual-mode control for frequency modulation control / maximum power point tracking; Figure 4 Schematic diagrams of system phase trajectories under different control modes; Figure 5 For equivalent droop gain A schematic diagram of isoclinals as the values ​​change; Figure 6 For equivalent droop gain A schematic diagram of the system phase trajectory when the values ​​change; Figure 7 A schematic diagram of the simulation results for power command tracking in frequency modulation control mode. Figure 8 This is a schematic diagram of the simulation results for traditional maximum power point tracking; Figure 9 This is a schematic diagram of the simulation results for frequency modulation control; Figure 10 This is a structural block diagram of a virtual inertial frequency modulation device on the DC side of a two-stage photovoltaic inverter, provided in an embodiment of the present invention. Detailed Implementation

[0016] The core of this invention is to provide a method, device, equipment, and computer storage medium for virtual inertial frequency modulation on the DC side of a two-stage photovoltaic inverter, which effectively solves the coupling conflict between DC bus voltage stability and frequency regulation function in the prior art, realizes seamless switching between frequency regulation and maximum power point tracking mode, and improves the frequency support capability and operational stability of the photovoltaic grid-connected system.

[0017] To enable those skilled in the art to better understand the present invention, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. Obviously, the described embodiments are merely some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0018] Please refer to Figure 1. Figure 1 The flowchart illustrates the implementation of a virtual inertial frequency modulation method for the DC side of a two-stage photovoltaic inverter provided by this invention; the specific operation steps are as follows: S101: The frequency regulation control function is moved from the AC side active power loop of the downstream voltage source inverter to the upstream DC / DC converter. The upstream DC / DC converter generates frequency regulation power increment commands based on the grid frequency deviation to adjust the output power of the photovoltaic array. In a two-stage photovoltaic inverter, the frequency regulation control function is migrated from the AC-side active power loop of the downstream voltage source inverter to the upstream DC / DC converter. This upstream converter generates a frequency regulation power increment command based on the grid frequency deviation to adjust the output power of the photovoltaic array. Specifically, this method breaks the limitation of traditional control architectures where only the downstream inverter responds to grid frequency changes, explicitly granting the upstream DC / DC converter the control freedom of frequency response. The upstream DC / DC converter detects the deviation between the grid angular frequency and the rated angular frequency, calculates and generates a frequency regulation power increment command in real time based on a preset frequency regulation control law. This command is used to dynamically adjust the operating point of the photovoltaic array, thereby changing its active power injected into the DC bus. The generation of this frequency regulation power increment command is based on an equivalent simulation of the dynamic characteristics of a synchronous generator governor, making the frequency-power response characteristics of the upstream DC / DC converter correspond to the second-order dynamic behavior of the synchronous generator governor, thus constructing a frequency response mechanism with virtual inertia and damping characteristics on the DC side. By migrating the frequency modulation function from the AC-side active power loop of the preceding DC / DC converter to the preceding DC / DC converter itself, structural decoupling between DC bus voltage stabilization control and frequency support functions is achieved. The subsequent voltage source inverter focuses on maintaining DC bus voltage stability and AC-side synchronous control, eliminating the coupling conflict between the AC-side frequency modulation and DC voltage regulation loops. As one implementation, this frequency modulation power increment command can be generated by the following control law: ,in For the angular frequency deviation of the power grid, , , These are equivalent virtual inertia, equivalent damping parameters, and equivalent droop gain, respectively. By independently tuning these parameters, the frequency regulation technology requirements of different power grids can be flexibly adapted.

[0019] This technical step achieves structural decoupling of DC bus voltage stabilization and frequency support functions by migrating the frequency regulation function to the front-end DC / DC converter. It eliminates the coupling conflict between the traditional AC-side frequency regulation and DC voltage regulation loops, ensures the independent stability margin of each control loop, and enables the photovoltaic power station to actively adjust the injected power according to the grid frequency deviation, thereby improving the frequency response flexibility and support capability of the system.

[0020] S102: Based on the comparison result between the DC bus voltage and the preset lower threshold, determine whether the photovoltaic array has a power reserve margin, and control the front-end DC / DC converter to enter the frequency modulation mode when there is a reserve margin; otherwise, switch to the maximum power point tracking mode. This method determines whether a photovoltaic (PV) array has sufficient power reserve margin for frequency regulation by detecting the DC bus voltage and comparing it with a preset lower threshold. Specifically, it utilizes the inherent physical relationship between the DC bus voltage and the PV array's power reserve margin, transforming the PV array's power reserve status into a simple threshold judgment based on the directly measurable electrical quantity, the DC bus voltage. When the DC bus voltage is not lower than the preset lower threshold, it indicates that the PV array is currently operating at a load shedding point and has available power reserve margin. In this case, the upstream DC / DC converter is controlled to enter frequency regulation mode, enabling it to actively adjust the PV array's output power according to the grid frequency deviation and participate in the system's primary frequency regulation. Conversely, when the DC bus voltage is lower than the preset lower threshold, it indicates that the PV array's power reserve margin has been exhausted. The system autonomously exits frequency regulation mode and switches to maximum power point tracking (MPPT) mode to restore tracking of the PV array's maximum power point, thereby maintaining the system's power balance. As one implementation, this mode switching criterion can specifically be achieved by comparing the DC bus voltage with the set lower threshold. To achieve, when When it is confirmed that there is a reserve margin and the frequency modulation mode is entered, Then switch to maximum power point tracking mode.

[0021] This technical step simplifies the complex online estimation problem of photovoltaic reserve margin to a simple threshold judgment of DC bus voltage, significantly reducing the complexity and computational overhead of the control algorithm. It does not rely on accurate online estimation of the photovoltaic maximum power point under the current irradiance and temperature conditions, thereby improving the reliability and robustness of the judgment, and realizing autonomous and smooth switching between frequency modulation mode and maximum power point tracking mode.

[0022] S103: When switching from maximum power point tracking mode to frequency modulation mode, a linear attenuation correction compensation term is introduced to make the power reference value in frequency modulation mode take the actual operating point before the switch as the initial value, and linearly attenuate to the upper-level scheduling setting value over time. During the switch from maximum power point tracking (MPPT) mode to frequency modulation (FM) mode, a smooth transition mechanism based on the consistency of the operating point is introduced to suppress power surges and electrical disturbances caused by sudden changes in the control reference value. The core of this mechanism is that, at the instant of switching, the power reference value in FM mode is initialized to the actual operating point at the end of the MPPT mode before switching, rather than jumping directly to the target value set by the upper-level scheduler, thus eliminating abrupt changes in the reference value. Based on this, a correction compensation term that decays linearly over time is introduced. This compensation term uses the power deviation at the time of switching as its initial amplitude and gradually decreases to zero according to a preset decay time constant, ensuring that the power reference value in FM mode smoothly and continuously transitions from the initial actual operating point to the upper-level scheduler setting. This correction compensation term dynamically adjusts the power reference value during the transition, ensuring its trajectory is continuous and without sudden changes, and completely disappears during steady-state operation, without continuously affecting the steady-state characteristics of FM mode. As one implementation method, this linear decay correction compensation term can be expressed as: ,in, The decay time constant determines the decay rate of the compensation term. This represents the actual operating power before the switchover. The settings are configured for the upper-level scheduling. Through the above mechanism, seamless switching between the two operating modes is achieved, ensuring a smooth transition of system electrical quantities.

[0023] This technical step effectively eliminates the power reference step during mode switching by introducing an initialization and linear attenuation correction compensation mechanism based on the consistency of the operating point, avoiding the power surge and DC bus voltage disturbance caused by it. It significantly improves the dynamic stability and operational continuity of the system when switching between different operating modes, and ensures the reliability and stability of the system during frequency regulation.

[0024] S104: In frequency modulation mode, the frequency modulation power increment command is superimposed with the upper-level scheduling setting value to generate a complete photovoltaic power reference value, and the operating point of the photovoltaic array is adjusted by the front-end DC / DC converter based on the photovoltaic power reference value to respond to the grid frequency deviation.

[0025] The physical topology of the two-stage photovoltaic inverter system involved in this invention is as follows: Figure 2 As shown, the system consists of the following core components cascaded in sequence: a photovoltaic array, a front-end boost DC / DC converter, a DC bus capacitor (Cdc), a rear-end three-phase voltage source inverter (VSI), and a filter.

[0026] The photovoltaic array converts solar energy into DC power, and its output voltage is boosted by the front-stage Boost converter to a suitable DC bus voltage level for the subsequent inverter. The DC bus capacitor Cdc is connected between the output of the front-stage converter and the DC input of the subsequent inverter, serving as an intermediate energy storage stage to decouple power fluctuations between the front and rear stages and stabilize the DC bus voltage. The subsequent three-phase VSI inverts the DC bus voltage into a three-phase AC voltage, which is then filtered and injected into the AC grid.

[0027] In frequency regulation mode, the front-end DC / DC converter needs to generate a complete photovoltaic power reference value based on the grid frequency deviation and the scheduling instructions from the upper-level energy management system. This reference value is then used to precisely adjust the operating point of the photovoltaic array, thereby achieving dynamic response of active power. Specifically, this photovoltaic power reference value consists of two parts: one is the active power setpoint issued by the upper-level controller, which represents the baseline power level that the photovoltaic array should output under normal operating conditions, typically corresponding to a pre-load shedding operating point to reserve a certain power regulation margin; the other part is the frequency regulation power increment instruction generated in real time based on the grid frequency deviation, reflecting the system's proactive response to frequency changes. By superimposing these two parts, a comprehensive power reference value that simultaneously considers steady-state scheduling objectives and dynamic frequency support requirements can be obtained. Subsequently, this power reference value is converted into a corresponding voltage reference value and input into the closed-loop control loop of the front-end DC / DC converter. By adjusting the converter's duty cycle, precise control of the photovoltaic array's operating point voltage or current is achieved, thereby changing its output power to follow the comprehensive power reference value. As one implementation, the frequency modulation power increment command can be generated by a second-order transfer function simulating the dynamics of a synchronous generator governor, the expression of which is: ,in For the angular frequency deviation of the power grid, , , These are the equivalent virtual inertia, equivalent damping parameter, and equivalent droop gain, respectively. Through this control law, the front-end converter can dynamically and continuously adjust the power injection of the photovoltaic array according to the magnitude and rate of change of the frequency deviation, thereby providing the grid with equivalent inertia and primary frequency regulation support.

[0028] This technical step integrates upper-level dispatch commands and frequency response commands, achieving an organic unity between steady-state power output and dynamic frequency regulation functions of photovoltaic power plants. This enables the front-end DC / DC converter to always adjust with the dispatch-set benchmark operating point as a reference when responding to grid frequency deviations. This ensures that while providing frequency support, the system can still follow the power allocation strategy of the upper-level energy management system, thereby improving the control flexibility and coordination of the photovoltaic grid-connected system under complex operating conditions.

[0029] Based on the above embodiments, in some embodiments, the step of generating frequency modulation power increment commands through the front-end DC / DC converter according to the grid frequency deviation includes: The power grid angular frequency deviation is obtained, which is the difference between the rated angular frequency and the actual angular frequency of the power grid. Based on the grid angular frequency deviation, the frequency modulation power increment command is generated by a first-order inertial transfer function that characterizes the equivalent virtual inertia, equivalent damping parameters, and equivalent droop gain.

[0030] Furthermore, the step of generating the frequency modulation power increment command based on the grid angular frequency deviation, using a first-order inertial transfer function characterizing the equivalent virtual inertia, equivalent damping parameters, and equivalent droop gain, includes: The grid angular frequency deviation is input into the time-domain differential equation characterizing the equivalent virtual inertia, equivalent damping parameters, and equivalent droop gain, and the frequency modulation power increment command is obtained by solving the equation. In this embodiment, the specific implementation of generating the frequency modulation power increment command based on the grid frequency deviation through the front-end DC / DC converter in step S101 is as follows. First, the grid angular frequency deviation is obtained, which is defined as the difference between the rated angular frequency and the actual grid angular frequency, i.e. ,in The rated angular frequency, This represents the actual angular frequency of the power grid. This deviation value serves as the input signal for the subsequent control law, reflecting the degree to which the grid frequency deviates from its rated value. Subsequently, based on the acquired grid angular frequency deviation, a frequency modulation power increment command is generated through a first-order inertial transfer function. The expression for this first-order inertial transfer function is as follows: ,in For equivalent virtual inertia, For equivalent damping parameters, This is the equivalent droop gain. The transfer function is equivalent to the differential equation in the time domain. By solving this differential equation, the frequency modulation power increment command can be obtained in real time. The sign of this command is determined by the sign of the grid angular frequency deviation; specifically, when the grid frequency drops, causing... When it is positive, the frequency modulation power increment command A negative value indicates that the front-end DC / DC converter needs to reduce the constraint on the photovoltaic (PV) operating point, allowing the PV array to output more active power to support frequency recovery. Conversely, when the grid frequency rises, the frequency modulation power increment command is positive, indicating that the constraint on the PV operating point needs to be increased, reducing the PV injected power. Through this process, the front-end DC / DC converter can generate precise frequency modulation power increment commands based on the grid frequency deviation, thereby achieving active adjustment of the PV array's output power.

[0031] The beneficial effect of this specific implementation is that, by designing the frequency regulation control law as a first-order inertial transfer function, the frequency-power response characteristics of the front-end DC / DC converter are precisely equivalent to the second-order dynamic characteristics of the synchronous generator speed governor, thus achieving a faithful reproduction of the primary frequency regulation characteristics of the synchronous generator. Simultaneously, the equivalent virtual inertia... Equivalent damping parameters and equivalent droop gain The three parameters can be set independently, which can flexibly adapt to the frequency regulation technology requirements of different power grids, thus improving the adaptability and configurability of the control system.

[0032] Based on the above embodiments, in some embodiments, determining whether the photovoltaic array has a power reserve margin based on the comparison result of the DC bus voltage and the preset lower threshold includes: Real-time monitoring of DC bus voltage; The DC bus voltage is compared with a preset lower threshold. When the DC bus voltage is greater than or equal to the preset low threshold, a first mode flag signal is generated to confirm that the photovoltaic array has a power reserve margin. When the DC bus voltage is less than the preset lower threshold, a second mode flag signal is generated to confirm that the power reserve margin of the photovoltaic array has been exhausted.

[0033] Further, the step of generating a first mode flag signal when the DC bus voltage is greater than or equal to the preset lower threshold to confirm that the photovoltaic array has a power reserve margin includes: When the DC bus voltage is greater than or equal to the preset low threshold, a mode flag signal with a value of 1 is generated to control the front-end DC / DC converter to enter frequency modulation mode. The step of generating a second mode flag signal when the DC bus voltage is less than the preset low threshold to confirm that the power reserve margin of the photovoltaic array has been exhausted includes: When the DC bus voltage is less than the preset lower threshold, a mode flag signal with a value of 0 is generated to control the front-end DC / DC converter to switch to maximum power point tracking mode.

[0034] In this embodiment, step S102 determines whether the photovoltaic array has a power reserve margin based on the comparison result between the DC bus voltage and a preset low threshold, and controls the operating mode of the front-end DC / DC converter accordingly. The specific implementation process is as follows: First, the system collects the voltage signal across the DC bus capacitor in real time through a voltage detection unit; this signal is the instantaneous value of the DC bus voltage. Then, the real-time detected DC bus voltage value is compared with a preset low threshold. This preset low threshold is a fixed voltage reference value, and its physical meaning corresponds to the critical level of the DC bus voltage when the photovoltaic array's power reserve margin is exhausted. When the comparison result shows that the DC bus voltage is greater than or equal to the preset low threshold, it indicates that the current photovoltaic array has sufficient power reserve margin. The system generates a mode flag signal with a value of 1, which serves as the first mode flag signal, confirming that the photovoltaic array has a power reserve margin and controlling the front-end DC / DC converter to enter frequency modulation mode. Conversely, when the comparison result shows that the DC bus voltage is less than the preset lower threshold, it indicates that the power reserve margin of the photovoltaic array has been exhausted. The system generates a mode flag signal with a value of 0, which serves as the second mode flag signal to confirm that the power reserve margin of the photovoltaic array has been exhausted and to control the front-end DC / DC converter to switch to maximum power point tracking (MPPT) mode. In MPPT mode, the front-end DC / DC converter uses a perturbation observation method to track the maximum power point voltage of the photovoltaic array in real time and uses this voltage as a reference value to directly control the operating point of the photovoltaic array, thereby restoring the tracking of the maximum power point and maintaining the system power balance. Through the simple comparison logic based on the DC bus voltage and the preset lower threshold, the system can accurately determine the power reserve margin status of the photovoltaic array and achieve autonomous switching between frequency modulation mode and maximum power point tracking mode without the need for a complex online maximum power point estimation algorithm.

[0035] This specific implementation significantly reduces the complexity and computational overhead of the control algorithm by transforming the determination of the photovoltaic array's power reserve margin into a simple threshold comparison of the DC bus voltage. It does not rely on online estimation of the maximum power point under current illumination and temperature conditions, thereby improving the reliability of the judgment and the simplicity of engineering implementation.

[0036] Based on the above embodiments, in some embodiments, the step of introducing a linear attenuation correction compensation term to make the power reference value in frequency modulation mode take the actual operating point before the switch as the initial value and linearly attenuate over time to the upper-level scheduling setting value includes: At the moment of switching from maximum power point tracking mode to frequency modulation mode, the actual operating power value of the front-end DC / DC converter in maximum power point tracking mode is obtained; Based on the difference between the actual operating power value and the upper-level scheduling setting value, a linear attenuation correction compensation term is generated. The compensation term is used to make the power reference value in frequency modulation mode take the actual operating power value as the initial value. The linear attenuation correction compensation term is superimposed on the upper-level scheduling setting value to obtain the power reference value in frequency modulation mode, so that the power reference value starts from the actual operating power value and linearly attenuates over time to the upper-level scheduling setting value.

[0037] In this embodiment, the bumpless switching process from maximum power point tracking mode to frequency modulation mode involved in step S103 is achieved by introducing a linear attenuation correction compensation term. Specifically, at the moment of switching, i.e., the DC bus voltage... Restore to the preset low threshold The above are the trigger mode flag signals. At the instant the value changes from 0 to 1, the system first obtains the actual operating power value of the preceding DC / DC converter at the end of the maximum power point tracking mode. This is the actual operating power value. The initial state for switching is directly derived from the actual output power of the photovoltaic array under the current illumination and temperature conditions in maximum power point tracking mode. Subsequently, based on this actual operating power value... Active power setpoint issued by the upper-level controller The difference between them generates a linear attenuation correction compensation term. The specific mathematical expression of this compensation term is as follows: ,in The preset decay time constant determines the rate at which the compensation term decays from its initial value to zero. The initial value of this compensation term at the moment of switching is equal to the actual operating power value. With upper-level scheduling settings The difference, then over time Decrease linearly until time elapses. The decay then becomes zero. Finally, this linear decay correction compensation term is compared with the upper-level scheduling setting value. The values ​​are superimposed to obtain the complete power reference value in frequency modulation mode. This power reference value is equal to the actual operating power value in maximum power point tracking mode at the moment of switching. This ensures the continuity of the power reference before and after the switch, avoiding a step jump; subsequently, the power reference value decays linearly over time, eventually converging completely to the upper-level scheduling setpoint. This ensures that the power reference in frequency modulation mode is not continuously affected by the compensation term during steady-state operation, thus guaranteeing the accuracy of the steady-state frequency modulation characteristics. The output result of this correction compensation term... This will be used as the frequency modulation power increment command in subsequent step S104. One of the inputs is superimposed to form a complete photovoltaic power reference value. .

[0038] This specific implementation introduces a linear attenuation correction compensation term, which enables seamless switching from maximum power point tracking mode to frequency modulation mode. It effectively eliminates power surges and DC bus voltage disturbances that may be caused by power reference value jumps during switching, ensuring a smooth transition of electrical quantities when the system switches between different operating modes, and improving the continuity and reliability of system operation.

[0039] Based on the above embodiments, in some embodiments, the step of superimposing the frequency modulation power increment command with the upper-level scheduling setting value to generate a complete photovoltaic power reference value includes: The frequency modulation power increment command is summed with the upper-level scheduling setting value after linear attenuation correction compensation term to obtain the complete photovoltaic power reference value. The upper-level scheduling setting value after linear attenuation correction compensation term is equal to the actual operating power value in maximum power point tracking mode at the moment of switching, and linearly attenuates to the upper-level scheduling setting value over time.

[0040] The specific implementation method for generating a complete photovoltaic power reference value is as follows. First, in frequency regulation mode, the core control function of the front-end DC / DC converter is to comprehensively generate a complete photovoltaic power reference value. This reference value needs to simultaneously reflect the scheduling intention of the upper-level energy management system and the frequency regulation requirements based on the grid frequency deviation. Specifically, the active power setpoint issued by the upper-level controller, i.e., the pre-load shedding operating point, serves as the upper-level scheduling setpoint. The input is sent to the control loop. Simultaneously, based on the grid angular frequency deviation in step S101... Generated frequency modulation power increment command It also serves as another input. To ensure a smooth transition when switching from maximum power point tracking mode to frequency modulation mode, this upper-level scheduling setting... It is not used directly, but first corrected by a linear attenuation correction term. This compensation term initializes the power reference value in frequency modulation mode to the actual operating point at the end of the maximum power point tracking phase before the switch, at the instant of switching. Subsequently, the compensation term is based on a time constant. The setting is linearly decayed to zero, thus obtaining the corrected upper-level scheduling setting. Its mathematical expression is: Subsequently, in the adder, the corrected upper-level scheduling setting value is added. With the frequency-modulated power increment command generated in real time by the frequency response control law The summation operation is performed to output the complete photovoltaic power reference value. This complete photovoltaic power reference value As the input to the control loop of the preceding DC / DC converter, it is ultimately converted into a photovoltaic-side voltage reference value. The front-end converter controls the photovoltaic side voltage via a PI controller. Perform closed-loop regulation to drive the duty cycle of the Boost converter. This allows for precise adjustment of the photovoltaic array's operating point, enabling its output power to respond to grid frequency deviations and achieve frequency support.

[0041] This specific implementation introduces a linear attenuation correction compensation term to modify the upper-level scheduling setting value, ensuring the continuity of the power reference value during mode switching, eliminating power surges, and ensuring that the power reference value completely converges to the scheduling setting value during steady-state operation without affecting the steady-state frequency modulation characteristics. This achieves smooth integration and precise tracking of the frequency modulation function and the upper-level scheduling command.

[0042] Based on the above embodiments, this embodiment will describe in detail the complete implementation of a virtual inertial frequency modulation method for the DC side of a two-stage photovoltaic inverter. The physical topology of the system upon which this method relies consists of a photovoltaic array, a front-stage boost DC / DC converter, a DC bus capacitor, a rear-stage three-phase voltage source inverter, and a filter cascaded sequentially. The photovoltaic array converts solar energy into DC power, and its output voltage is boosted by the front-stage boost converter to a DC bus voltage level suitable for the rear-stage inverter. The DC bus capacitor is connected between the output of the front-stage converter and the DC input of the rear-stage inverter, serving as an intermediate energy storage link, decoupling power fluctuations between the front and rear stages and stabilizing the DC bus voltage. The rear-stage three-phase VSI inverts the DC bus voltage into a three-phase AC voltage, which is then injected into the AC grid after passing through a filter.

[0043] In this embodiment, the frequency regulation control function is explicitly migrated from the AC-side active power loop of the downstream VSI to the upstream DC / DC converter. The upstream DC / DC converter generates a frequency modulation power increment command based on the grid frequency deviation to adjust the output power of the photovoltaic array. Specifically, the grid angular frequency deviation is first obtained, which is the difference between the rated angular frequency and the actual grid angular frequency, i.e. Based on the grid angular frequency deviation, a frequency modulation power increment command is generated using a first-order inertial transfer function, which is as follows: ,in For equivalent virtual inertia, For equivalent damping parameters, This represents the equivalent droop gain. The negative sign indicates that when the grid frequency decreases, the frequency regulation power increment command increases, the front-end converter reduces the constraint on the photovoltaic operating point, and releases additional active power to support frequency recovery. In the time domain, this transfer function is equivalent to the differential equation... The form of this equation corresponds exactly to the equation of the synchronous generator governor, where Determines the frequency modulation response speed. Determines the stability of the response. The steady-state frequency modulation amplitude is determined by three parameters that can be tuned independently.

[0044] To ensure compatibility with the scheduling commands of the upper-level energy management system, the complete photovoltaic power reference value in frequency regulation mode is synthesized from the active power setpoint issued by the upper-level controller and the frequency regulation power increment command. Specifically, the complete photovoltaic power reference value... ,in Set up a point for upper-level scheduling. This is a frequency modulation power increment command. When... hour, , This reduction allows the photovoltaic array to inject more active power into the grid under current illumination conditions. In the upstream DC / DC converter control loop, this power reference value is ultimately converted into a photovoltaic-side voltage reference value. The pre-converter controls the output via a PI controller. Perform closed-loop regulation to drive the duty cycle of the Boost converter. This enables precise adjustment of the photovoltaic array's operating point. The basic DC-side control structure is as follows: Figure 3 As shown.

[0045] This embodiment utilizes the inherent physical relationship between the DC bus voltage and the photovoltaic array's power reserve margin as the basis for determining the switching between frequency regulation mode and maximum power point tracking mode. The physical mechanism is as follows: when a reserve margin exists, the photovoltaic array is at its unloaded operating point. Driven by frequency regulation mode, it increases power output, and there is still a power surplus to support the DC bus capacitor voltage, thus... Not lower than the minimum setting value When the reserve margin is exhausted, the photovoltaic array has reached its maximum power point. If the power demand of the downstream VSI exceeds the maximum available power, the DC bus capacitor will continue to discharge. Descending to Nearby. Based on this, the pattern flag signal The generation logic is defined as: when hour, After confirming that the photovoltaic array has sufficient reserve margin, the system enters frequency regulation mode; when hour, This indicates that the reserve margin has been exhausted, and the system switches to maximum power point tracking mode, using the perturbation observation method to resume tracking of the maximum power point.

[0046] When switching from maximum power point tracking mode to frequency modulation mode, this embodiment introduces a linear attenuation correction compensation term to achieve a smooth transition. Specifically, at the switching time... Obtain the actual operating power value of the front-end DC / DC converter in maximum power point tracking mode. Based on this actual operating power value and the upper-level scheduling setting value. The difference is used to generate a linear attenuation correction compensation term. ,in The time constant is the decay time constant. The physical meaning of this correction mechanism is that at the moment of switching, the frequency modulation mode power reference value is initialized with the actual operating point at the end of the maximum power point tracking phase, rather than jumping directly to the upper-level scheduling setting, thus eliminating the power reference step at the moment of switching; subsequently, the compensation term uses the time constant... Linear decay to zero ensures that the power reference fully converges to the dispatch setpoint during steady-state operation. Integrating the frequency regulation power increment, the complete photovoltaic power reference in frequency regulation mode is synthesized as follows: ,in It is generated in real time by the frequency response control law.

[0047] To gain a deeper understanding of the impact mechanism of DC-side frequency modulation mode on the dynamic frequency characteristics of the system, a reduced-order analysis model is established under a single-machine infinite bus system configuration. Considering the stable operation of the downstream VSI in grid-following mode, singular perturbation theory is used to dynamically fold the fast-timescale current inner loop and phase-locked loop into a slow manifold. The dynamic frequency of the system is determined by the power angle deviation. Angular frequency deviation DC-side frequency modulation output power increment Three state variables dominate. A third-order nonlinear state-space model is obtained by simultaneously solving the kinematic identities, the power grid inertia equations, and the frequency regulator equations. When the frequency regulation time constant... At that time, the frequency modulation state variable rapidly converges to its quasi-static manifold. ,in This is the equivalent droop gain. Substituting this into the equation yields a closed two-dimensional autonomous system. Comparing the corresponding equations for the maximum power point tracking mode, it can be seen that the frequency modulation mode reduces the system's equivalent damping from... Upgraded to Enhanced amplitude and equivalent droop gain Positive correlation. The improvement in equivalent damping is reflected in the phase plane as a faster convergence of the frequency trajectory to the equilibrium point, and an effective reduction in the extreme values ​​of frequency deviation, such as... Figure 4 As shown.

[0048] exist In the phase plane, the slope of the phase trajectory is determined by the following formula: The isoclinal line with zero slope satisfies , Increasing the inclination level causes the isotropic curve to contract towards the origin, reducing the peak deviation of the constrained frequency trajectory. This verifies the effect of the frequency modulation mode on suppressing frequency drop extremes. Figure 5As shown. Integrating the phase trajectory over the interval from the initial state of the disturbance to the frequency extremum allows for rigorous quantization. Quantitative impact on frequency drop extremes: The right-hand integral term in frequency modulation mode ( The value is more negative than that of the MPPT mode, proving that the frequency drop extreme value is smaller under the same initial disturbance conditions in the FM mode, and The larger the value, the more significant the inhibitory effect. For example... Figure 6 As shown.

[0049] A complete two-stage photovoltaic inverter system simulation model was built in the MATLAB / Simulink environment and implemented according to the system topology and control strategy. The first simulation scenario verifies the ability of the DC-side frequency regulation mode to track the upper-level dispatched active power reference value under dynamic illumination conditions. The system operates in a combined grid-connected and grid-frequency regulation mode. During the simulation, the upper-level controller sends out stepped power reference values, while the illumination intensity changes in a piecewise linear fashion. Figure 7 As shown, simulation results demonstrate that the DC-side controller achieves well-damped transient responses to each reference step, with negligible steady-state tracking error, unaffected by changes in illumination, and the DC bus voltage consistently remains near its rated value. The second simulation scenario, under a photovoltaic-storage islanded microgrid configuration, compares the system response differences between the proposed DC-side frequency regulation mode and the traditional maximum power point tracking mode during sudden load shedding frequency events. Constantly disconnecting a set of high-power loads introduces significant active power surplus disturbances. In traditional maximum power point tracking (MPPT) mode, such as... Figure 8 As shown, the photovoltaic converter maintains maximum power injection throughout the entire frequency event, does not respond to frequency deviations, and all power surplus is independently absorbed by the energy storage converter. The system frequency peak deviation reaches [value missing]. The maximum power absorption required by the energy storage converter is In the proposed frequency modulation mode, such as Figure 9 As shown, after a frequency drop event occurs, the frequency modulation control law detects the frequency rise deviation and generates a positive frequency modulation power increment command. This drives the upstream DC / DC converter to actively reduce the photovoltaic injection power, working in conjunction with the energy storage converter to absorb the power surplus. The system frequency peak deviation is compressed to [a specific value]. The power absorbed by the energy storage converter is reduced to This effectively reduces the instantaneous power load pressure on the energy storage system.

[0050] In summary, this embodiment achieves structural decoupling of DC bus voltage stability and frequency support functions by explicitly migrating the frequency modulation control degree of freedom from the AC-side active power loop of the downstream VSI to the upstream DC / DC converter. Utilizing the inherent physical correlation between the DC bus voltage and the photovoltaic array power reserve margin, a dual-mode switching criterion for FR / MPPT based on the DC bus voltage and a set lower threshold is established, eliminating the need for additional online maximum power point estimation. By introducing a state pre-initialization mechanism based on operating point consistency and a linear attenuation correction compensation term, seamless switching between FR and MPPT operating modes is achieved, suppressing power surges and DC bus voltage disturbances during switching.

[0051] Please refer to Figure 10 , Figure 10 This invention provides a structural block diagram of a virtual inertial frequency modulation device for the DC side of a two-stage photovoltaic inverter; the specific device may include: The frequency response migration module 100 is used to migrate the frequency regulation control function from the AC side active power loop of the downstream voltage source inverter to the upstream DC / DC converter. The upstream DC / DC converter generates frequency regulation power increment commands based on the grid frequency deviation to adjust the output power of the photovoltaic array. The mode switching judgment module 200 is used to determine whether the photovoltaic array has a power reserve margin based on the comparison result between the DC bus voltage and the preset low threshold, and to control the front-end DC / DC converter to enter the frequency modulation mode when there is a reserve margin, otherwise switch to the maximum power point tracking mode. The bumpless switching module 300 is used to introduce a linear attenuation correction compensation term when switching from maximum power point tracking mode to frequency modulation mode, so that the power reference value in frequency modulation mode is based on the actual operating point before the switch and linearly attenuates to the upper-level scheduling setting value over time. The power reference generation module 400 is used to superimpose the frequency modulation power increment command with the upper-level scheduling setting value in frequency modulation mode to generate a complete photovoltaic power reference value, and control the front-end DC / DC converter to adjust the operating point of the photovoltaic array based on the photovoltaic power reference value in response to grid frequency deviation.

[0052] The DC-side virtual inertial frequency modulation device of the two-stage photovoltaic inverter in this embodiment is used to implement the aforementioned DC-side virtual inertial frequency modulation method of the two-stage photovoltaic inverter. Therefore, the specific implementation of the DC-side virtual inertial frequency modulation device of the two-stage photovoltaic inverter can be found in the embodiment section of the DC-side virtual inertial frequency modulation method of the two-stage photovoltaic inverter described above. For example, the frequency response migration module 100, the mode switching judgment module 200, the disturbance-free switching module 300, and the power reference generation module 400 are respectively used to implement steps S101, S102, S103, and S104 in the aforementioned DC-side virtual inertial frequency modulation method of the two-stage photovoltaic inverter. Therefore, its specific implementation can be referred to the description of the corresponding embodiments, which will not be repeated here.

[0053] A specific embodiment of the present invention also provides a DC-side virtual inertial frequency modulation device for a two-stage photovoltaic inverter, comprising: a memory for storing a computer program; and a processor for executing the computer program to implement the steps of the aforementioned DC-side virtual inertial frequency modulation method for a two-stage photovoltaic inverter.

[0054] A specific embodiment of the present invention also provides a computer-readable storage medium storing a computer program, which, when executed by a processor, implements the steps of the above-described method for virtual inertial frequency modulation on the DC side of a two-stage photovoltaic inverter.

[0055] Those skilled in the art will understand that embodiments of this application can be provided as methods, systems, or computer program products. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application can take the form of a computer program product embodied on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0056] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart... Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0057] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0058] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0059] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A virtual inertial frequency modulation method for the DC side of a two-stage photovoltaic inverter, characterized in that, Includes the following steps: The frequency regulation control function is moved from the AC side active power loop of the downstream voltage source inverter to the upstream DC / DC converter. The upstream DC / DC converter generates frequency regulation power increment commands based on the grid frequency deviation to adjust the output power of the photovoltaic array. Based on the comparison result between the DC bus voltage and the preset lower threshold, it is determined whether the photovoltaic array has a power reserve margin. If there is a reserve margin, the front-end DC / DC converter is controlled to enter the frequency modulation mode; otherwise, it is switched to the maximum power point tracking mode. When switching from maximum power point tracking mode to frequency modulation mode, a linear attenuation correction compensation term is introduced so that the power reference value in frequency modulation mode is initialized with the actual operating point before the switch and linearly attenuates to the upper-level scheduling setting value over time. In frequency modulation mode, the frequency modulation power increment command is superimposed with the upper-level scheduling setting value to generate a complete photovoltaic power reference value. Based on the photovoltaic power reference value, the front-end DC / DC converter is controlled to adjust the operating point of the photovoltaic array in response to grid frequency deviation.

2. The method according to claim 1, characterized in that, The step of generating frequency modulation power increment commands based on grid frequency deviation through the front-end DC / DC converter includes: The power grid angular frequency deviation is obtained, which is the difference between the rated angular frequency and the actual angular frequency of the power grid. Based on the grid angular frequency deviation, the frequency modulation power increment command is generated by a first-order inertial transfer function that characterizes the equivalent virtual inertia, equivalent damping parameters, and equivalent droop gain.

3. The method according to claim 2, characterized in that, The generation of the frequency modulation power increment command based on the grid angular frequency deviation, using a first-order inertial transfer function characterizing the equivalent virtual inertia, equivalent damping parameters, and equivalent droop gain, includes: The grid angular frequency deviation is input into the time-domain differential equation characterizing the equivalent virtual inertia, equivalent damping parameters, and equivalent droop gain, and the frequency modulation power increment command is obtained by solving the equation.

4. The method according to claim 1, characterized in that, The determination of whether the photovoltaic array has a power reserve margin based on the comparison result between the DC bus voltage and the preset lower threshold includes: Real-time monitoring of DC bus voltage; The DC bus voltage is compared with a preset lower threshold. When the DC bus voltage is greater than or equal to the preset low threshold, a first mode flag signal is generated to confirm that the photovoltaic array has a power reserve margin. When the DC bus voltage is less than the preset lower threshold, a second mode flag signal is generated to confirm that the power reserve margin of the photovoltaic array has been exhausted.

5. The method according to claim 4, characterized in that, The step of generating a first mode flag signal when the DC bus voltage is greater than or equal to the preset lower threshold, confirming that the photovoltaic array has a power reserve margin, includes: When the DC bus voltage is greater than or equal to the preset low threshold, a mode flag signal with a value of 1 is generated to control the front-end DC / DC converter to enter frequency modulation mode. The step of generating a second mode flag signal when the DC bus voltage is less than the preset low threshold to confirm that the power reserve margin of the photovoltaic array has been exhausted includes: When the DC bus voltage is less than the preset lower threshold, a mode flag signal with a value of 0 is generated to control the front-end DC / DC converter to switch to maximum power point tracking mode.

6. The method according to claim 1, characterized in that, The step of introducing a linear attenuation correction compensation term to make the power reference value in frequency modulation mode take the actual operating point before the switch as the initial value and linearly attenuate over time to the upper-level scheduling setting value includes: At the moment of switching from maximum power point tracking mode to frequency modulation mode, the actual operating power value of the front-end DC / DC converter in maximum power point tracking mode is obtained; Based on the difference between the actual operating power value and the upper-level scheduling setting value, a linear attenuation correction compensation term is generated. The compensation term is used to make the power reference value in frequency modulation mode take the actual operating power value as the initial value. The linear attenuation correction compensation term is superimposed on the upper-level scheduling setting value to obtain the power reference value in frequency modulation mode, so that the power reference value starts from the actual operating power value and linearly attenuates over time to the upper-level scheduling setting value.

7. The method according to claim 1, characterized in that, The step of superimposing the frequency modulation power increment command with the upper-level scheduling setting value to generate a complete photovoltaic power reference value includes: The frequency modulation power increment command is summed with the upper-level scheduling setting value after linear attenuation correction compensation term to obtain the complete photovoltaic power reference value. The upper-level scheduling setting value after linear attenuation correction compensation term is equal to the actual operating power value in maximum power point tracking mode at the moment of switching, and linearly attenuates to the upper-level scheduling setting value over time.

8. A virtual inertial frequency modulation device for the DC side of a two-stage photovoltaic inverter, characterized in that, include: The frequency response migration module is used to migrate the frequency regulation control function from the AC side active power loop of the downstream voltage source inverter to the upstream DC / DC converter. The upstream DC / DC converter generates frequency modulation power increment commands based on the grid frequency deviation to adjust the output power of the photovoltaic array. The mode switching judgment module is used to determine whether the photovoltaic array has a power reserve margin based on the comparison result between the DC bus voltage and the preset low threshold. If there is a reserve margin, the module controls the front-end DC / DC converter to enter the frequency modulation mode; otherwise, it switches to the maximum power point tracking mode. The bumpless switching module is used to introduce a linear attenuation correction compensation term when switching from maximum power point tracking mode to frequency modulation mode, so that the power reference value in frequency modulation mode is based on the actual operating point before the switch and linearly attenuates to the upper-level scheduling setting value over time. The power reference generation module is used to superimpose the frequency modulation power increment command with the upper-level scheduling setting value in frequency modulation mode to generate a complete photovoltaic power reference value, and control the front-end DC / DC converter to adjust the operating point of the photovoltaic array based on the photovoltaic power reference value in response to grid frequency deviation.

9. A virtual inertial frequency modulation device for the DC side of a two-stage photovoltaic inverter, characterized in that, include: Memory, used to store computer programs; A processor, configured to execute the computer program to implement the steps of the DC-side virtual inertial frequency modulation method for a two-stage photovoltaic inverter as described in any one of claims 1 to 7.

10. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores a computer program that, when executed by a processor, implements the steps of the DC-side virtual inertial frequency modulation method for a two-stage photovoltaic inverter as described in any one of claims 1 to 7.

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