A photovoltaic power generation grid-connected system transient synchronization stability control method and system

Abstract

The present application relates to photovoltaic power generation grid-connected system technical field, provide a kind of photovoltaic power generation grid-connected system transient synchronous stability control method and system, comprising: obtaining rated grid voltage amplitude and grid voltage amplitude during fault, calculate to obtain drop depth coefficient;Obtain DC bus voltage and its reference value, through DC voltage outer ring, obtain the rated current amplitude of grid-connected inverter, combine drop depth coefficient, based on grid-connected guide, generate reactive current reference value and positive sequence active current reference value, through current inner ring and sinusoidal pulse width modulation method, obtain current command, act on photovoltaic power generation grid-connected system;When drop depth coefficient is less than mode switching threshold, the phase-locked loop of photovoltaic power generation grid-connected system works in two-order high-precision tracking paradigm;When drop depth coefficient is greater than mode switching threshold, phase-locked loop switches to one-order global stability paradigm.Fundamentally overcome the instability risk of traditional two-order phase-locked loop under strong disturbance, significantly improve synchronous reliability.

Description

Technical Field

[0001] This invention belongs to the technical field of photovoltaic power generation grid-connected systems, and particularly relates to a transient synchronization and stability control method and system for photovoltaic power generation grid-connected systems. Background Technology

[0002] The statements in this section are merely background information related to the present invention and do not necessarily constitute prior art.

[0003] With the continuous increase in the penetration rate of new energy sources, low-voltage ride-through capability has become a mandatory requirement for grid-connected new energy equipment. For photovoltaic power generation grid-connected systems, maintaining the synchronous stability of the phase-locked loop during faults is the core of meeting the low-voltage ride-through requirement.

[0004] Existing solutions can be mainly divided into three categories: Phase-locked loop enhancement: The core idea is to optimize performance within the basic control framework of traditional phase-locked loop (SRF-PLL). Typical implementations include optimizing the proportional and integral parameters of the PI (proportional-integral) regulator, adopting advanced topologies such as SOGI-PLL (second-order generalized integrator phase-locked loop) and DPLL (digital phase-locked loop), and improving the anti-disturbance capability of phase tracking through parameter adjustment or structural improvement. Outer loop auxiliary control: Synchronization stability is ensured by adding auxiliary algorithms outside the phase-locked loop. Typical methods include using the "power freeze" algorithm to fix the active / reactive power command during the fault period and introducing the "active damping" algorithm to suppress system oscillation. Grid-based control: The core is to change the operating logic of the converter from "following the grid" to "building the grid". A typical technology is virtual synchronous machine (VSG) control, which achieves grid-connected control by simulating the rotor dynamics characteristics of a synchronous generator.

[0005] Limitations of existing solutions: The phase-locked loop (PLL) enhancement method only improves upon its inherent second-order nonlinear framework. Under strong disturbances such as deep voltage drops, the upper limit of the stability domain is low, and the effect is limited. Outer-loop auxiliary control methods (such as "power freeze") often require sacrificing the active power support capability during faults, which violates the requirement of modern power grids for "active support" of new energy equipment; while methods such as "active damping" are complex to design and their performance is sensitive to changes in system parameters (such as grid impedance). When the grid operating conditions change over a wide range, the robustness of maintaining stability faces challenges. The grid-based control method fundamentally changes the operating logic of converters from "grid following" to "grid construction," making it no longer suitable for typical grid-following scenarios such as photovoltaic power plants that must operate in maximum power point tracking mode, and introducing new stability issues. Summary of the Invention

[0006] To address the technical problems mentioned above, this invention provides a transient synchronization and stability control method and system for a photovoltaic power generation grid-connected system. Instead of being limited to optimizing local parameters of the phase-locked loop (PLL), it dynamically switches the PLL's dynamic paradigm, enabling it to operate in a first-order mode with global stability during grid faults. This fundamentally overcomes the instability risk of traditional second-order PLLs under strong disturbances and significantly improves synchronization reliability.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: The first aspect of the present invention provides a transient synchronization and stability control method for a photovoltaic power generation grid-connected system, comprising: Obtain the rated grid voltage amplitude and the grid voltage amplitude during the fault, and calculate the voltage drop depth coefficient; The DC bus voltage and its reference value are obtained. The rated current amplitude of the grid-connected inverter is obtained through the DC voltage outer loop. Combined with the drop depth coefficient, the reactive current reference value and the positive sequence active current reference value are generated based on the grid connection guidelines. The current command is obtained through the current inner loop and the sinusoidal pulse width modulation method and applied to the photovoltaic power generation grid-connected system. When the drop depth coefficient is less than the mode switching threshold, the phase-locked loop of the photovoltaic power generation grid-connected system operates in the second-order high-precision tracking paradigm; when the drop depth coefficient is greater than the mode switching threshold, the phase-locked loop of the photovoltaic power generation grid-connected system switches to the first-order global stability paradigm.

[0008] Furthermore, it also includes: when the drop depth coefficient remains below a recovery threshold and exceeds a set delay, the phase-locked loop recovers the second-order high-precision tracking paradigm.

[0009] Furthermore, when the drop depth coefficient is less than the mode switching threshold, the current controller executes the maximum power point tracking command, and the photovoltaic power generation grid-connected system operates at unity power factor; When the voltage drop factor is greater than the mode switching threshold, the current reference command switches to a mode that primarily provides reactive current support, based on the grid voltage drop depth and in accordance with the grid connection guidelines.

[0010] Furthermore, the drop depth coefficient is ;in, The rated grid voltage amplitude, This represents the voltage amplitude of the power grid during the fault.

[0011] Furthermore, based on the SRF-PLL structure, the phase-locked loop introduces a multiplier controlled by the mode switching coefficient in the integration path.

[0012] A second aspect of the present invention provides a transient synchronization and stability control system for a photovoltaic power generation grid-connected system, comprising: The drop depth coefficient calculation module is configured to: obtain the rated grid voltage amplitude and the grid voltage amplitude during the fault, and calculate the drop depth coefficient; The current command generation module is configured to: obtain the DC bus voltage and its reference value; obtain the rated current amplitude of the grid-connected inverter through the DC voltage outer loop; generate reactive current reference value and positive sequence active current reference value based on the grid connection guidelines by combining the drop depth coefficient; and obtain the current command through the current inner loop and the sinusoidal pulse width modulation method, which is then applied to the photovoltaic power generation grid-connected system. The phase-locked loop (PLL) module is configured such that when the drop depth coefficient is less than the mode switching threshold, the PLL of the photovoltaic power generation grid-connected system operates in the second-order high-precision tracking paradigm; when the drop depth coefficient is greater than the mode switching threshold, the PLL of the photovoltaic power generation grid-connected system switches to the first-order global stability paradigm.

[0013] Furthermore, it also includes: when the drop depth coefficient remains below a recovery threshold and exceeds a set delay, the phase-locked loop recovers the second-order high-precision tracking paradigm.

[0014] Furthermore, when the drop depth coefficient is less than the mode switching threshold, the current controller executes the maximum power point tracking command, and the photovoltaic power generation grid-connected system operates at unity power factor; When the voltage drop factor is greater than the mode switching threshold, the current reference command switches to a mode that primarily provides reactive current support, based on the grid voltage drop depth and in accordance with the grid connection guidelines.

[0015] Furthermore, the drop depth coefficient is ;in, The rated grid voltage amplitude, This represents the voltage amplitude of the power grid during the fault.

[0016] Furthermore, based on the SRF-PLL structure, the phase-locked loop introduces a multiplier controlled by the mode switching coefficient in the integration path.

[0017] Compared with the prior art, the beneficial effects of the present invention are: This invention is no longer limited to the local parameter optimization of the phase-locked loop (PLL). Instead, it dynamically switches the dynamic paradigm of the PLL, enabling it to operate in a first-order mode with global stability during grid faults. This fundamentally overcomes the instability risk of traditional second-order PLLs under strong disturbances and significantly improves synchronization reliability.

[0018] This invention ensures extremely high synchronization reliability during fault periods and provides full reactive current support to the grid in accordance with grid connection guidelines, without increasing hardware costs. It is easy to implement on existing photovoltaic power generation grid connection system platforms, combining high efficiency and economy, significantly improving the reliability of low voltage ride-through, and ensuring the safe and stable operation of the power grid. Attached Figure Description

[0019] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0020] Figure 1 This is a schematic diagram of the topology and basic control method of a photovoltaic power generation grid-connected system according to Embodiment 1 of the present invention; Figure 2 This is a schematic diagram of the current reference value generation strategy in Embodiment 1 of the present invention; Figure 3 This is a comparison diagram of a conventional phase-locked loop and a dynamic paradigm-switching phase-locked loop according to Embodiment 1 of the present invention; Figure 4 This is a flowchart of the low voltage ride-through control according to Embodiment 1 of the present invention. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0022] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0023] Example 1 This embodiment provides a transient synchronization and stability control method for a photovoltaic power generation grid-connected system.

[0024] Traditional phase-locked loops (PLLs) are limited by their second-order nonlinear dynamic characteristics, making them prone to synchronization instability under large disturbances such as severe grid voltage drops, which can lead to grid disconnection of renewable energy generation equipment. This problem is particularly pronounced in weak grid environments with a high proportion of renewable energy connected to the grid. Existing solutions mostly focus on adjusting the original PLL framework, failing to fundamentally avoid such transient instability problems. To address this, this embodiment proposes a dynamic paradigm switching mechanism that, without altering the original architecture of the photovoltaic grid-connected system, enables the PLL to possess global deterministic stability during transient processes such as grid faults, thereby fundamentally improving the low-voltage ride-through reliability of grid-connected converters in high-voltage power systems.

[0025] This embodiment provides a transient synchronization and stability control method for a photovoltaic power generation grid-connected system, based on a mode switching mechanism, and oriented towards high-voltage and high-efficiency power systems.

[0026] This embodiment provides a transient synchronous stability control method for a photovoltaic power generation grid-connected system, which enables the phase-locked loop to dynamically reconstruct its own dynamic order.

[0027] This embodiment provides a transient synchronous stability control method for a photovoltaic power generation grid-connected system, which enables the photovoltaic power generation grid-connected system to maintain high-precision phase tracking during normal operation; and when a grid voltage drop fault sufficient to threaten stability is detected, it can automatically and reliably switch to a first-order synchronous operation mode with global stability properties.

[0028] This embodiment provides a transient synchronous stability control method for a photovoltaic power generation grid-connected system, which aims to avoid instability risks from the dynamics level of the photovoltaic power generation grid-connected system and ensure reliable convergence of the photovoltaic power generation grid-connected system state after a large disturbance, provided that the theoretical equilibrium point exists. This provides a new technical solution for low voltage ride-through.

[0029] This embodiment provides a transient synchronization stability control method for a photovoltaic power generation grid-connected system. By dynamically reconstructing the dynamic order of the phase-locked loop, it can achieve global deterministic stability under strong disturbances, fundamentally avoiding the risk of synchronization instability and ensuring the reliability of low voltage ride-through.

[0030] 1. Overall topology and control architecture of photovoltaic power generation grid connection (photovoltaic power generation converter) system.

[0031] Models of photovoltaic power generation converter systems, such as Figure 1 As shown, the photovoltaic power generation converter system includes a photovoltaic array, a boost DC / DC converter, a two-level three-phase inverter (DC / AC), and a filter impedance Z. f (by the filter inductor L) f and filter parasitic resistance r f Composition), power grid impedance Z g (by grid-side inductor L) g and grid-side resistance r g Composition), DC bus capacitor C dc ;in, V represents the output angle of the phase-locked loop. DC The DC bus voltage can also be expressed as U. pv I pv I is the output current of the photovoltaic array. pv I calculated based on the Maximum Power Point Tracking (MPPT) algorithm pv Reference value, U dc U is the DC bus voltage. dc i is the reference value for the DC bus voltage. abc The three-phase alternating current flowing through the line, and These are the direct-axis and quadrature-axis components of the three-phase alternating current IABC in a synchronous rotating coordinate system. and yes and Reference value, and V represents the direct given values ​​of the active and reactive components of the current, respectively. oabc V is the three-phase AC voltage output from the converter port. PCCabc V is the three-phase AC voltage at the common coupling point PCC. gabc This is the voltage of the three-phase AC power grid.

[0032] The photovoltaic array achieves maximum power point tracking (MPPT) through a DC / DC converter operating in Boost mode, outputting a stable DC voltage U. dc To ensure that the efficiency of new energy power generation is maximized.

[0033] The current I output by the photovoltaic array pv Its reference value I pv The error signal is used as input, enters the DC-side current loop, and after passing through the PI regulator of the current loop, it outputs a PWM switching signal used to control the DC / DC converter.

[0034] In a DC / DC converter, PWM (Pulse Width Modulation) compares the analog control signal output from the error amplifier with a fixed-frequency triangular wave (or sawtooth wave) to generate a switching drive pulse with a constant frequency and a duty cycle that changes linearly with the control signal. By adjusting the duty cycle, the on and off times of the power switching transistors are controlled, thereby changing the energy storage and release balance of the inductor or transformer, and achieving precise and efficient regulation of the output voltage or current.

[0035] Based on the circuit topology constraints, the mathematical model of the photovoltaic grid-connected inverter in the synchronous rotating coordinate system can be obtained as follows: ; In the formula, variables with subscripts d and q represent the coordinate axis components of the rotating vector of the electrical quantity in the original stationary coordinate system in the synchronously rotating coordinate system; L eq Represents the total inductance of the circuit, r eq This represents the total resistance of the circuit. It is the rotational angular frequency of the synchronous rotating coordinate system; and These are the direct-axis and quadrature-axis components of the three-phase alternating current IABC in the synchronous rotating coordinate system; and These are the direct-axis and quadrature-axis components of the three-phase AC voltage output from the converter port in a synchronous rotating coordinate system; and These represent the direct and quadrature components of the three-phase AC grid voltage in a synchronous rotating coordinate system, respectively.

[0036] A feedforward decoupling control strategy is adopted, and the control rules are designed as follows: ; In the formula, and These represent the proportional gain and integral gain of the inner-loop PI controller for AC current measurement, respectively. It is the grid voltage vector The rotational angular frequency, and yes and Reference value; and The reference value of the modulated wave in the synchronous rotating coordinate system is used to generate the six switching signals of the converter after being modulated by the sinusoidal pulse width modulation strategy (SPWM).

[0037] 2. Photovoltaic low voltage ride-through control method.

[0038] The grid connection guideline GB / T 19964—2012 stipulates that when a grid voltage dip fault occurs, the photovoltaic power station should inject a certain amount of reactive current into the grid according to the depth of the dip to support the grid's rapid recovery from the fault. Therefore, this guideline establishes the principle that photovoltaic power stations must provide reactive current support when the grid voltage dips.

[0039] This embodiment is based on the grid connection principle, such as Figure 2 As shown, a more direct and effective current reference value generation strategy is adopted to ensure that the grid is provided with rapid and sufficient reactive power support during faults.

[0040] The fault addressed in this embodiment is a symmetrical fault; therefore, there is no need to consider the suppression of negative sequence components.

[0041] (1) Sample the DC bus voltage value U dc Compared with reference value U dc The difference is used as a voltage error signal and sent to the DC voltage outer loop regulator for closed-loop regulation. The output of the regulator is the rated current amplitude setpoint of the grid-connected inverter. .

[0042] The controller used in the outer loop of the DC voltage is a PI regulator, with the output... The calculation formula is: I max =(U dc -U dc ) (K pdc +K idc / s); where K pdc K is the proportional gain of the PI regulator in the outer loop of the DC voltage circuit. idc It is the integral gain.

[0043] (2) Reference current decision.

[0044] Specifically, the voltage sag factor defined in this embodiment is: ; in, The rated grid voltage amplitude, This represents the voltage amplitude of the power grid during the fault.

[0045] Based on typical requirements in engineering practice, photovoltaic power generation converter systems follow the rule of "providing an additional 2% of the rated reactive current for every 1% voltage drop," with the injected reactive current reference value... Calculate using the following formula: ; in, This is the rated current amplitude of the grid-connected inverter, which is also its maximum allowable output current amplitude. Therefore, it can be seen that when no voltage dip occurs, the photovoltaic power generation converter system operates in unity power factor mode; when a voltage dip occurs, the reactive current reference is given according to the above formula, where when the dip depth is not less than 50%, then it is calculated according to... Provides full reactive current.

[0046] Meanwhile, to ensure reactive power output and avoid device overcurrent, the positive sequence active current reference value is... Appropriate restrictions need to be imposed: ; Based on the above formula and the grid connection guideline that "photovoltaic power generation converter systems should follow the rule that 'for every 1% drop in voltage, an additional 2% of the rated reactive current should be provided,'" it can be seen that in k... sag When the reactive current is not greater than 50%, there is a reactive current reference value i. q1 =-2k sag I max Then, based on mathematical relationships, the reference value i of the positive sequence active current can be obtained. d1 Similarly, in k sag When it is greater than 50%, the reactive current reference value i q2 =-I max Similarly, the positive-sequence active current reference value i can be calculated.d2 .

[0047] In this embodiment, With the three-phase alternating current i flowing through the line abc The reactive current is obtained through abc-dq coordinate transformation. and positive sequence active current , and reactive current reference value and positive sequence active current reference value Together, current commands are obtained through the inner current loop and sinusoidal pulse width modulation (SPWM).

[0048] The current command generation strategy and the subsequent dynamic paradigm switching phase-locked loop work together to form a complete low-voltage ride-through solution.

[0049] 3. Control logic and specific implementation of dynamic paradigm switching phase-locked loop (dual-mode phase-locked loop).

[0050] The overall control structure of the photovoltaic power generation grid-connected system in this embodiment is as follows: Figure 2 As shown, its core innovation lies in the structural modification of the phase-locked loop unit. By dynamically reconstructing its dynamic order, a significant improvement in synchronization stability during low-voltage ride-through is achieved, as detailed below: (1) Fault detection and mode switching logic: The photovoltaic power generation grid-connected system monitors the grid voltage status in real time (i.e., the grid voltage amplitude V). g ), and calculate its drop depth coefficient. The mode switching logic is based on a preset mode switching threshold. Make a judgment: when When the photovoltaic power generation grid-connected system determines that a serious fault has occurred in the power grid that is sufficient to threaten synchronization stability, it immediately sets the mode switching coefficient. The phase-locked loop switches to a first-order global stability paradigm; when When the power grid is determined to be in a normal or slightly disturbed state, a mode switching coefficient is set. The phase-locked loop operates in a second-order high-precision tracking paradigm; Fault clearing (when) After the grid voltage remains below a recovery threshold for an extended period (and exceeds a set delay) and stabilizes, the photovoltaic grid-connected system will switch modes. Switching back from 0 to 1, this hysteresis logic effectively prevents repeated switching near the threshold, improving engineering practicality.

[0051] (2) Specific implementation and system dynamics of dynamic paradigm switching: like Figure 3As shown, the phase-locked loop in this embodiment, based on the traditional SRF-PLL structure, introduces a mode switching coefficient into its integration path. The controlled multiplier fundamentally alters the dynamic equations of a grid-connected photovoltaic power generation system.

[0052] when When =1 (normal mode), the phase-locked loop integral path is unobstructed, and the system behaves as a second-order nonlinear system. This second-order nonlinear system has a finite attraction domain near the stable equilibrium point. Under large disturbances, the state of the photovoltaic grid-connected system may be pushed out of this region, causing the trajectory to diverge and resulting in loss of synchronization.

[0053] when When the phase-locked loop integral path is cut off (fault mode), the whole system degenerates into a first-order system. Theoretical analysis shows that, under the condition that a stable equilibrium point exists, the phase trajectory of this first-order system has global convergence characteristics. That is, no matter what the initial state is, the photovoltaic grid-connected system will be attracted to the unique stable equilibrium point, thus achieving global deterministic stability during the fault period.

[0054] (3) Co-operational workflow with low voltage ride-through control: like Figure 4 As shown, the complete collaborative workflow of this embodiment is as follows, divided into three cases: (A) Normal operation: The power grid is in good condition. ), =1, the phase-locked loop operates in second-order high-precision tracking mode (mode 1), providing accurate phase for current control. Since no faults occur at this time, the system is necessarily stable. At the same time, the current controller executes the maximum power point tracking command, and the photovoltaic power generation grid-connected system operates with unity power factor. (B) Fault Trace: When a critical fault is detected ( The photovoltaic power generation grid-connected system immediately executes the following in parallel: [Settings] =0, the phase-locked loop switches to the first-order global stability mode (mode 2) to fundamentally avoid the risk of loss of synchronization; the current reference command switches to the mode that mainly provides reactive current support according to the grid voltage drop depth and the grid connection guidelines, actively supporting the grid voltage.

[0055] (C) Fault Recovery: Once the fault is cleared and the grid voltage stabilizes, the photovoltaic power generation grid-connected system will perform the following in parallel: Reset to 1, the phase-locked loop returns to its original second-order high-precision mode; the current command switches back to the normal maximum power point tracking mode.

[0056] When β=1, v PCCq The PI regulator generates an angular change law signal (dotδ), which is then compared with the grid angular frequency. The sums are fed into an integrator to generate θ. pll ; When β=0, the integral term of the PI controller is removed, and it becomes a proportional controller. At this time, v PCCq The proportional regulator generates an angular change law signal (dotδ), which is added to the grid angular frequency w0 and then sent to the integrator to generate θ. pll .

[0057] Specifically, for a typical phase-locked loop, the three-phase voltage V is first transformed using coordinate transformation (abc-dq). PCCabc Convert to direct axis component v PCCd and cross-axis component v PCCq Then the proportionality coefficient K was adopted. ppll and integral coefficient K ipll The PI controller, composed of an integral element, controls the input quantity v. PCCq Adjustments are made to the output frequency deviation dotδ (i.e., This frequency deviation is different from the rated frequency. The summation yields the angular frequency of the synchronously rotating coordinate system. The phase angle θ is then obtained through integration. pll This type of phase-locked loop has a simple structure and fixed parameters, and can achieve stable phase-locking under ideal power grid conditions, but it is extremely prone to instability under large disturbance fault scenarios such as power grid voltage drops. Specifically, the core topological difference between the dual-mode phase-locked loop and the traditional PI-type phase-locked loop lies in the integration path of the PI regulator (i.e., the integral coefficient K). ipll Previously, a switching gain β was added to control the on / off state of the integrator. The operating mode of the phase-locked loop can be dynamically adjusted by switching the value of β. Under normal operating conditions, β=1, the phase-locked loop integral path is fully conductive, and its topology is completely consistent with that of a traditional PI-type phase-locked loop, enabling high-precision tracking of the grid phase. From the perspective of the control loop transmission mechanism, the output of the PI regulator is the output angular velocity of the phase-locked loop. Synchronous angular velocity with the power grid The difference, i.e., the rate of change of the work angle δ, is dotδ=ω pll ω0, the rate of change of this angle is integrated to obtain the sine value (sin( )), and then compared with the grid voltage amplitude V g This forms a gain element, which is then connected to ω, representing the active component. pll L g i d and r representing the reactive component g i q The combined effect yields the q-axis voltage v at the grid connection point. PCCqAnd use it as the net input of the phase-locked loop. Thus, in normal mode, the photovoltaic power generation grid-connected system containing the phase-locked loop can be equivalent to a second-order nonlinear system. This second-order nonlinear system has only a limited range of attraction domains near the stable equilibrium point. When a significant voltage drop fault is detected in the power grid, β quickly switches from 1 to 0, and the phase-locked loop integrator is directly disabled, reducing the original second-order nonlinear system to a first-order system. The attraction domain of the stable equilibrium point is greatly expanded. From a physical perspective, cutting off the integrator during a severe fault is equivalent to significantly reducing the "acceleration" effect of the system, which can effectively improve the stability margin of the system. Ultimately, the dual-mode phase-locked loop has significantly better low-voltage fault ride-through capability and transient synchronization stability than traditional phase-locked loops.

[0058] This embodiment provides a transient synchronous stability control method for a photovoltaic power generation grid-connected system, which realizes a transformation in the concept of stability control: it is no longer limited to the local parameter optimization of the phase-locked loop, but fundamentally expands the stability boundary by dynamically reconstructing its dynamic order, effectively solving the synchronous instability problem of traditional second-order phase-locked loops under strong disturbances of symmetrical voltage drops.

[0059] This embodiment provides a transient synchronization and stability control method for a photovoltaic power generation grid-connected system. During fault periods (when the grid voltage drops), it can ensure extremely high synchronization reliability (the converter maintains stable synchronization) and provide full reactive current support to the grid in accordance with the grid connection guidelines. It does not require additional hardware costs, is easy to implement on existing photovoltaic power generation grid-connected system platforms, and combines high efficiency and economy. It significantly improves the reliability of low voltage ride-through and ensures the safe and stable operation of the grid.

[0060] This embodiment provides a transient synchronization and stability control method for a photovoltaic power generation grid-connected system. By dynamically switching the dynamic paradigm of the phase-locked loop (PLL), it enables the PLL to operate in a first-order mode with global stability during grid faults. This fundamentally overcomes the instability risk of traditional second-order PLLs under strong disturbances and significantly improves synchronization reliability.

[0061] Example 2 This embodiment provides a transient synchronization and stability control system for a photovoltaic power generation grid-connected system, including: The drop depth coefficient calculation module is configured to: obtain the rated grid voltage amplitude and the grid voltage amplitude during the fault, and calculate the drop depth coefficient; The current command generation module is configured to: obtain the DC bus voltage and its reference value; obtain the rated current amplitude of the grid-connected inverter through the DC voltage outer loop; generate reactive current reference value and positive sequence active current reference value based on the grid connection guidelines by combining the drop depth coefficient; and obtain the current command through the current inner loop and the sinusoidal pulse width modulation method, which is then applied to the photovoltaic power generation grid-connected system. The phase-locked loop (PLL) module is configured such that when the drop depth coefficient is less than the mode switching threshold, the PLL of the photovoltaic power generation grid-connected system operates in the second-order high-precision tracking paradigm; when the drop depth coefficient is greater than the mode switching threshold, the PLL of the photovoltaic power generation grid-connected system switches to the first-order global stability paradigm.

[0062] Furthermore, it also includes: when the drop depth coefficient remains below a recovery threshold and exceeds a set delay, the phase-locked loop recovers the second-order high-precision tracking paradigm.

[0063] Furthermore, when the drop depth coefficient is less than the mode switching threshold, the current controller executes the maximum power point tracking command, and the photovoltaic power generation grid-connected system operates at unity power factor; When the voltage drop factor is greater than the mode switching threshold, the current reference command switches to a mode that primarily provides reactive current support, based on the grid voltage drop depth and in accordance with the grid connection guidelines.

[0064] Furthermore, the drop depth coefficient is ;in, The rated grid voltage amplitude, This represents the voltage amplitude of the power grid during the fault.

[0065] Furthermore, based on the SRF-PLL structure, the phase-locked loop introduces a multiplier controlled by the mode switching coefficient in the integration path.

[0066] It should be noted that each module in this embodiment corresponds one-to-one with each step in Embodiment 1, and their specific implementation processes are the same, so they will not be repeated here.

[0067] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A transient synchronous stability control method for a photovoltaic power generation grid-connected system, characterized in that, include: Obtain the rated grid voltage amplitude and the grid voltage amplitude during the fault, and calculate the voltage drop depth coefficient; The DC bus voltage and its reference value are obtained. The rated current amplitude of the grid-connected inverter is obtained through the DC voltage outer loop. Combined with the drop depth coefficient, the reactive current reference value and the positive sequence active current reference value are generated based on the grid connection guidelines. The current command is obtained through the current inner loop and the sinusoidal pulse width modulation method and applied to the photovoltaic power generation grid-connected system. When the drop depth coefficient is less than the mode switching threshold, the phase-locked loop of the photovoltaic power generation grid-connected system operates in the second-order high-precision tracking paradigm; when the drop depth coefficient is greater than the mode switching threshold, the phase-locked loop of the photovoltaic power generation grid-connected system switches to the first-order global stability paradigm.

2. The transient synchronization and stability control method for a photovoltaic power generation grid-connected system as described in claim 1, characterized in that, Also includes: When the drop depth coefficient remains below a recovery threshold and exceeds the set delay, the phase-locked loop resumes the second-order high-precision tracking paradigm.

3. The transient synchronization and stability control method for a photovoltaic power generation grid-connected system as described in claim 1, characterized in that, When the drop depth coefficient is less than the mode switching threshold, the current controller executes the maximum power point tracking command, and the photovoltaic power generation grid-connected system operates at unity power factor; When the voltage drop factor is greater than the mode switching threshold, the current reference command switches to a mode that primarily provides reactive current support, based on the grid voltage drop depth and in accordance with the grid connection guidelines.

4. The transient synchronization and stability control method for a photovoltaic power generation grid-connected system as described in claim 1, characterized in that, The drop depth coefficient is ;in, The rated grid voltage amplitude, This represents the voltage amplitude of the power grid during the fault.

5. The transient synchronization and stability control method for a photovoltaic power generation grid-connected system as described in claim 1, characterized in that, The phase-locked loop, based on the SRF-PLL structure, introduces a multiplier controlled by mode switching coefficients in the integration path.

6. A transient synchronous stability control system for a photovoltaic power generation grid-connected system, characterized in that, include: The drop depth coefficient calculation module is configured to: obtain the rated grid voltage amplitude and the grid voltage amplitude during the fault, and calculate the drop depth coefficient; The current command generation module is configured to: obtain the DC bus voltage and its reference value; obtain the rated current amplitude of the grid-connected inverter through the DC voltage outer loop; generate reactive current reference value and positive sequence active current reference value based on the grid connection guidelines by combining the drop depth coefficient; and obtain the current command through the current inner loop and the sinusoidal pulse width modulation method, which is then applied to the photovoltaic power generation grid-connected system. The phase-locked loop (PLL) module is configured such that when the drop depth coefficient is less than the mode switching threshold, the PLL of the photovoltaic power generation grid-connected system operates in the second-order high-precision tracking paradigm; when the drop depth coefficient is greater than the mode switching threshold, the PLL of the photovoltaic power generation grid-connected system switches to the first-order global stability paradigm.

7. The transient synchronization and stability control system for a photovoltaic power generation grid-connected system as described in claim 6, characterized in that, Also includes: When the drop depth coefficient remains below a recovery threshold and exceeds the set delay, the phase-locked loop resumes the second-order high-precision tracking paradigm.

8. The transient synchronous stability control system for a photovoltaic power generation grid-connected system as described in claim 6, characterized in that, When the drop depth coefficient is less than the mode switching threshold, the current controller executes the maximum power point tracking command, and the photovoltaic power generation grid-connected system operates at unity power factor; When the voltage drop factor is greater than the mode switching threshold, the current reference command switches to a mode that primarily provides reactive current support, based on the grid voltage drop depth and in accordance with the grid connection guidelines.

9. A transient synchronous stability control system for a photovoltaic power generation grid-connected system as described in claim 6, characterized in that, The drop depth coefficient is ;in, The rated grid voltage amplitude, This represents the voltage amplitude of the power grid during the fault.

10. A transient synchronous stability control system for a photovoltaic power generation grid-connected system as described in claim 6, characterized in that, The phase-locked loop, based on the SRF-PLL structure, introduces a multiplier controlled by mode switching coefficients in the integration path.

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