Stable control method for maximum power point tracking of network-constructed centralized photovoltaic inverter

Abstract

The application provides a maximum power point tracking and stable control method for a grid-constructed centralized photovoltaic inverter, comprising the following steps: if the current sampling time interval is not less than a preset sampling period, reading a current control mode, and obtaining a DC voltage change rate, a photovoltaic input power change rate and a derivative of the DC voltage to the photovoltaic input power of the grid-constructed centralized photovoltaic inverter; if a time interval from the last mode switching is greater than a preset locking time, determining a control mode switching condition according to the current control mode, and performing mode switching judgment to determine and switch to a new control mode; and determining a DC voltage reference value and a photovoltaic output power reference value through a reference value smooth transition strategy according to the new control mode and the last control mode to perform maximum power point tracking control. The application can realize grid inertia support, rapid power tracking and DC voltage stability under sudden light changes through state perception and mode smooth switching without additional energy storage devices.

Description

Technical Field

[0001] This application relates to the fields of new energy power generation and power electronics technology, specifically to a maximum power point tracking stability control method for a grid-type centralized photovoltaic inverter. Background Technology

[0002] With the construction of new power systems, grid-connected photovoltaic inverters have attracted much attention due to their ability to actively support grid voltage and frequency. Among them, virtual synchronous generator (VSG) technology, by simulating the rotor motion equation of a synchronous generator, endows the inverter with the necessary virtual inertia and damping, effectively improving the system stability under weak grid conditions.

[0003] However, existing maximum power point tracking (MPPT) strategies based on VSG power synchronization control have significant drawbacks when dealing with drastic fluctuations in solar irradiance. When solar irradiance changes abruptly, the available power of the photovoltaic array changes drastically, and traditional VSG control often leads to deterioration of system dynamic performance and even DC voltage instability. For example, in the patent "CN105552968B; Inverter control system and method based on MPPT and virtual synchronous machine characteristics", a single-stage topology, fixed-parameter traditional VSG and unconditional pure MPPT scheme are used. Relying solely on the DC bus capacitor to buffer power fluctuations, the power command jumps drastically when solar irradiance changes significantly. Coupled with the response lag caused by VSG inertia, this easily leads to deterioration of system dynamic performance and DC voltage instability.

[0004] The fundamental reason lies in the inherent contradiction between the inertial response characteristics of VSG control and the requirement for rapid power tracking at the photovoltaic source side: on the one hand, grid-connected inverters must maintain sufficient virtual inertia to provide effective grid support, which physically limits the rate of change of active power output, preventing rapid abrupt changes; on the other hand, when sudden changes in sunlight cause drastic fluctuations in photovoltaic power, the system must quickly adjust its output power to maintain instantaneous power balance on the DC side. This mutual exclusion between the requirements for dynamic response speed in "inertial support" and "rapid tracking" makes it difficult for a single fixed control framework to achieve both, and the system is highly susceptible to collapse due to DC-side power imbalance.

[0005] Therefore, how to break through the limitations of the traditional single control framework and effectively resolve the inherent contradiction between virtual inertia support and rapid source-end power tracking, so as to ensure the active support capability of the power grid while taking into account the system stability under complex operating conditions, has become a key technical problem that needs to be solved by those skilled in the art. Summary of the Invention

[0006] In view of one of the defects in the prior art, the purpose of this application is to provide a maximum power point tracking stability control method for a grid-type centralized photovoltaic inverter.

[0007] The first aspect of this application provides a maximum power point tracking stability control method for a grid-type centralized photovoltaic inverter, comprising: If the current sampling time interval is not less than the preset sampling period, read the current control mode and obtain the DC voltage change rate, photovoltaic input power change rate and the derivative of DC voltage with respect to photovoltaic input power of the grid-type centralized photovoltaic inverter. The control mode is either VSG power synchronization control mode or DC voltage synchronization control mode. If the time interval between the current and the last mode switch is greater than the preset blocking time, the control mode switching condition is determined according to the current control mode. The control mode switching condition is either an instability condition or a steady-state condition. Based on the DC voltage change rate, the photovoltaic input power change rate, the derivative of DC voltage with respect to photovoltaic input power, and the control mode switching conditions, determine and switch to a new control mode; Based on the new control mode and the previous control mode, the DC voltage reference value and the photovoltaic output power reference value are determined through a reference value smooth transition strategy, and the maximum power point tracking control is performed.

[0008] Optionally, if the current sampling time interval is not less than a preset sampling period, reading the current control mode and obtaining the DC voltage change rate, photovoltaic input power change rate, and the derivative of DC voltage with respect to photovoltaic input power of the grid-type centralized photovoltaic inverter includes: If the current sampling time interval is greater than the preset sampling period, read the current control mode; Obtain the average DC voltage and average photovoltaic input power of the grid-type centralized photovoltaic inverter within a preset sampling period since the last sampling time; Based on the average DC voltage, the average photovoltaic input power, and the preset sampling period, the rate of change of DC voltage, the rate of change of photovoltaic input power, and the derivative of DC voltage with respect to photovoltaic input power are determined.

[0009] Optionally, the instability conditions include the DC voltage change rate being less than a preset first constant, the photovoltaic input power change rate being less than a preset second constant, and the DC voltage derivative with respect to the photovoltaic input power being greater than a preset third constant. The steady-state conditions include that the absolute value of the rate of change of DC voltage is less than a preset fourth constant, and the absolute value of the rate of change of photovoltaic input power is less than a preset fifth constant, and the derivative of DC voltage with respect to photovoltaic input power is less than a preset sixth constant.

[0010] Optionally, if the time interval between the current and the last mode switch is greater than a preset locking time, the control mode switching conditions are determined based on the current control mode, including: If the time interval between the current and the last mode switch is greater than the preset blocking time, the current control mode is the VSG power synchronization control mode, and the control mode switching condition is determined to be an instability condition. If the time interval between the current and the last mode switch is greater than the preset blocking time, the current control mode is the DC voltage synchronization control mode, and the control mode switching condition is determined to be a steady-state condition.

[0011] Optionally, determining and switching to a new control mode based on the DC voltage change rate, the photovoltaic input power change rate, the derivative of DC voltage with respect to photovoltaic input power, and the control mode switching conditions includes: If the current control mode is the VSG power synchronization control mode, determine whether the grid-type centralized photovoltaic inverter meets the instability condition. If it does, determine the new control mode as the DC voltage synchronization control mode and switch to the DC voltage synchronization control mode. If the current control mode is the VSG power synchronization control mode, determine whether the grid-type centralized photovoltaic inverter meets the instability condition. If it does not meet the condition, determine the new control mode as the VSG power synchronization control mode and maintain the VSG power synchronization control mode. If the current control mode is the DC voltage synchronization control mode, determine whether the grid-type centralized photovoltaic inverter meets the steady-state condition. If it does, determine the new control mode as the VSG power synchronization control mode and switch to the VSG power synchronization control mode. If the current control mode is the DC voltage synchronization control mode, determine whether the grid-type centralized photovoltaic inverter meets the steady-state condition. If it does not meet the condition, determine the new control mode as the DC voltage synchronization control mode and maintain the DC voltage synchronization control mode.

[0012] Optionally, the step of determining the DC voltage reference value and the photovoltaic output power reference value through a reference value smooth transition strategy based on the new control mode and the previous control mode, and performing maximum power point tracking control, includes: If the new control mode is the same as the previous control mode (VSG power synchronization control mode), and the time interval between two consecutive updates of the photovoltaic output power reference value is greater than a preset time threshold, and the derivative of the DC voltage with respect to the photovoltaic input power is greater than zero, then the control is executed. , The preset step size is used until the derivative of the DC voltage with respect to the photovoltaic input is not greater than zero, and the reference value of the photovoltaic output power is determined. The reference value of the DC voltage is the actual value of the DC voltage. If the new control mode is the same as the previous control mode (VSG power synchronization control mode), and the time interval between two consecutive updates of the photovoltaic output power reference value is greater than a preset time threshold, and the derivative of the DC voltage with respect to the photovoltaic input is not greater than zero, then the control is executed. , The preset step size is used until the derivative of the DC voltage with respect to the photovoltaic input power is greater than zero, and then the reference value of the photovoltaic output power is determined. The reference value of the DC voltage is the actual value of the DC voltage. If the new control mode is different from the previous control mode, the new control mode is the VSG power synchronization control mode, and the photovoltaic output power reference value is determined to be the actual photovoltaic output power value, and the DC voltage reference value is determined to be the actual DC voltage value.

[0013] Optionally, the reference value smooth transition strategy means using the actual value of photovoltaic output power as the reference value of photovoltaic output power for transition; The step of determining the DC voltage reference value and photovoltaic output power reference value through a reference value smooth transition strategy based on the new control mode and the previous control mode, and performing maximum power point tracking control, further includes: If the new control mode is the same as the previous control mode, which is the DC voltage synchronous control mode, the photovoltaic output power reference value is determined to be zero, and the DC voltage reference value is the preset DC voltage value. If the new control mode is different from the previous control mode, the new control mode is the DC voltage synchronization control mode, the DC voltage reference value is determined to be the preset DC voltage value, and the photovoltaic output power reference value is zero.

[0014] A second aspect of this application provides a maximum power point tracking stability control system for a grid-type centralized photovoltaic inverter, comprising: The sampling module is used to read the current control mode and obtain the DC voltage change rate, photovoltaic input power change rate and DC voltage derivative with respect to photovoltaic input power of the grid-type centralized photovoltaic inverter if the current sampling time interval is not less than the preset sampling period. The control mode is either VSG power synchronization control mode or DC voltage synchronization control mode. The control mode switching condition determination module is used to determine the control mode switching condition based on the current control mode if the time interval between the current and the last mode switching is greater than the preset blocking time. The control mode switching condition is either an instability condition or a steady-state condition. The control mode switching module is used to determine and switch to a new control mode based on the DC voltage change rate, the photovoltaic input power change rate, the derivative of DC voltage with respect to photovoltaic input power, and the control mode switching conditions. The maximum power point tracking control module is used to determine the DC voltage reference value and the photovoltaic output power reference value through a reference value smooth transition strategy based on the new control mode and the previous control mode, and to perform maximum power point tracking control.

[0015] A third aspect of this application provides a non-transitory computer-readable storage medium having a computer program stored thereon that, when executed by a processor, implements the steps of any of the methods provided in the first aspect of this application.

[0016] A fourth aspect of this application provides an electronic device comprising: A memory on which computer programs are stored; A processor for executing the computer program in the memory to implement the steps of any of the methods provided in the first aspect of this application.

[0017] The maximum power point tracking (MPPT) stability control method for grid-type centralized photovoltaic (PV) inverters disclosed in this application obtains multi-dimensional state variables such as the rate of change of DC voltage, the rate of change of PV input power, and the derivative of DC voltage with respect to PV input power by reading the current control mode. Combined with the lockout time and instability / steady-state conditions, it achieves adaptive switching between VSG power synchronization and DC voltage synchronization control modes. Simultaneously, a smooth transition strategy using a reference value is employed to smoothly determine the tracking reference value. This allows the inverter to operate in VSG power synchronization control mode when illumination is stable to provide inertia and frequency support, and to smoothly switch to DC voltage synchronization control mode during sudden changes in illumination to prevent DC-side instability and achieve rapid power point tracking. Once steady-state is reached, it automatically switches back to VSG power synchronization control mode. Without the need for additional energy storage devices, this method achieves stable control and MPPT of the grid-type centralized PV inverter under varying illumination conditions through state perception and smooth mode switching.

[0018] Other technical effects resulting from the additional features will be further illustrated in the corresponding embodiments. Attached Figure Description

[0019] Other features, objects, and advantages of this application will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings: Figure 1 This is a flowchart illustrating a maximum power point tracking stability control method for a grid-type centralized photovoltaic inverter according to an exemplary embodiment.

[0020] Figure 2 This is a schematic diagram illustrating a control mode determination logic according to an exemplary embodiment.

[0021] Figure 3 This is a schematic diagram illustrating a control mode switching condition according to an exemplary embodiment.

[0022] Figure 4 This is a schematic diagram illustrating the algorithm flow for maximum power point tracking stability control of a grid-type centralized photovoltaic inverter according to an exemplary embodiment.

[0023] Figure 5 This is a schematic diagram illustrating a maximum power point tracking stability control strategy for a grid-type centralized photovoltaic inverter according to an exemplary embodiment.

[0024] Figure 6 This is a schematic diagram of a virtual synchronous machine control structure according to an exemplary embodiment.

[0025] Figure 7 This is a schematic diagram of a DC voltage synchronization control structure according to an exemplary embodiment.

[0026] Figure 8 This is a schematic diagram of a reactive power control and primary voltage regulation control structure according to an exemplary embodiment.

[0027] Figure 9 This is a simulation diagram illustrating a conventional control strategy under operating condition 1 according to an exemplary embodiment.

[0028] Figure 10 This is a simulation diagram illustrating a maximum power point tracking stability control method for a grid-type centralized photovoltaic inverter under operating condition 1, according to an exemplary embodiment.

[0029] Figure 11 This is a simulation diagram illustrating a conventional control strategy under operating condition 2 according to an exemplary embodiment.

[0030] Figure 12 This is a simulation diagram illustrating a maximum power point tracking stability control method for a grid-type centralized photovoltaic inverter under operating condition 2, according to an exemplary embodiment.

[0031] Figure 13 This is a schematic flowchart illustrating a maximum power point tracking stability control system for a grid-type centralized photovoltaic inverter according to an exemplary embodiment. Detailed Implementation

[0032] The present application will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present application, but do not limit the present application in any way. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the present application. These all fall within the protection scope of the present application.

[0033] The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature.

[0034] In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0035] The terms "comprising" and "having," and any variations thereof, in the embodiments of this application are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or device that includes a series of steps or units is not limited to the steps or units listed, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to such processes, methods, products, or devices.

[0036] Existing technologies primarily employ maximum power point tracking (MPPT) strategies based on virtual synchronous generator (VSG) power synchronization control. These strategies use simulated rotor motion equations to impart virtual inertia to the inverter, thus supporting the grid. However, a drawback is that the VSG's inertia response limits the rate of change of active power, fundamentally contradicting the requirement for rapid source-side power tracking during sudden changes in solar illumination. This makes it difficult for a single control framework to simultaneously address grid support and dynamic response, easily leading to dynamic performance degradation or even DC voltage instability during severe solar illumination fluctuations. To address these issues, this application provides a method for stable MPPT control of a grid-connected centralized photovoltaic inverter, resolving these problems.

[0037] Figure 1 This is a flowchart illustrating a maximum power point tracking stability control method for a grid-type centralized photovoltaic inverter according to an exemplary embodiment.

[0038] Reference Figure 1 As shown in one embodiment of this application, a maximum power point tracking stability control method for a grid-type centralized photovoltaic inverter is provided, which can employ S11 to S14.

[0039] S11. If the current sampling time interval is not less than the preset sampling period, read the current control mode and obtain the DC voltage change rate, photovoltaic input power change rate, and the derivative of DC voltage with respect to photovoltaic input power of the grid-type centralized photovoltaic inverter.

[0040] Specifically, the control mode is either VSG power synchronization control mode or DC voltage synchronization control mode.

[0041] S12, If the time interval between the current and the last mode switch is greater than the preset interlocking time, determine the control mode switching conditions according to the current control mode.

[0042] Specifically, the control mode switching condition is either an instability condition or a steady-state condition.

[0043] S13. Based on the DC voltage change rate, the photovoltaic input power change rate, the derivative of DC voltage with respect to photovoltaic input power, and the control mode switching conditions, determine and switch to a new control mode.

[0044] S14, based on the new control mode and the previous control mode, determine the DC voltage reference value and the photovoltaic output power reference value through the reference value smooth transition strategy, and perform maximum power point tracking control.

[0045] Based on the above steps S11 to S14, during the period when the inverter system is operating normally and the lighting conditions are relatively stable, the VSG power synchronization control mode with a large virtual inertia is adopted to give full play to the active support capability of the grid-type centralized photovoltaic inverter for the power grid.

[0046] When there are significant and rapid changes in sunlight and the DC side is at risk of instability, the control mode is switched to DC voltage synchronous control mode. This mode utilizes the advantages of matching control to directly adjust the DC voltage and fast power tracking to quickly stabilize the DC bus and enable the photovoltaic array to quickly adapt to the maximum power point in the new environment.

[0047] Once the inverter system returns to steady-state operation and the lighting conditions stabilize again, it will automatically and smoothly switch back to the VSG power synchronization control mode to provide inertial support to the grid again.

[0048] By adopting a hybrid control strategy that switches grid-type centralized photovoltaic inverters on demand, the system can balance the inertia characteristics required for grid support and the rapid power point tracking capability required for sudden changes in sunlight, even without the assistance of energy storage devices.

[0049] The embodiments described above in this application obtain multi-dimensional state variables such as the rate of change of DC voltage, the rate of change of photovoltaic input power, and the derivative of DC voltage with respect to photovoltaic input power by reading the current control mode. Combined with the lockout time and instability / steady-state conditions, adaptive switching between VSG power synchronization and DC voltage synchronization control modes is achieved. At the same time, a reference value smooth transition strategy is adopted to smoothly determine the tracking reference value. This enables operation in VSG power synchronization control mode to provide inertia and frequency support when the illumination is stable, and smooth switching to DC voltage synchronization control mode when the illumination changes abruptly to prevent DC-side instability and achieve rapid power point tracking. After reaching a steady state, it automatically switches back to VSG power synchronization control mode. Without the need for additional energy storage equipment, stable control and maximum power point tracking of the grid-type centralized photovoltaic inverter under full illumination variation can be achieved through state perception and smooth mode switching.

[0050] Figure 2 This is a schematic diagram illustrating a control mode determination logic according to an exemplary embodiment.

[0051] Reference Figure 2 As shown, key state quantities are collected at fixed intervals to provide accurate basis for judging the risk of sudden changes in light intensity and realizing mode switching. In some specific embodiments of this application, for S11, if the current sampling time interval is not less than the preset sampling period, the current control mode is read and the DC voltage change rate, photovoltaic input power change rate and DC voltage derivative with respect to photovoltaic input power of the grid-type centralized photovoltaic inverter are obtained. This can be achieved by using S111 to S113.

[0052] S111, If ​​the current sampling time interval is greater than the preset sampling period, read the current control mode.

[0053] Specifically, if ,in, Indicates the current sampling time interval. This indicates the preset sampling period and reads the current control mode as either VSG power synchronization control mode or DC voltage synchronization control mode.

[0054] S112, obtain the average DC voltage and average photovoltaic input power of the grid-type centralized photovoltaic inverter within a preset sampling period since the last sampling time.

[0055] Specifically, obtain the time since the last sampling time. DC voltage of the internal grid-type centralized photovoltaic inverter Average value and photovoltaic input power average value.

[0056] S113, based on the average DC voltage, the average photovoltaic input power, and the preset sampling period, determine the DC voltage change rate, the photovoltaic input power change rate, and the derivative of DC voltage with respect to photovoltaic input power.

[0057] Specifically, the rate of change of DC voltage is expressed as The rate of change of photovoltaic input power is expressed as The derivative of DC voltage with respect to photovoltaic input power is: .

[0058] In this embodiment, the DC voltage change rate, the photovoltaic input power change rate, and the derivative of DC voltage with respect to photovoltaic input power are used as the basis for determining the switching of control modes for grid-type centralized photovoltaic inverters.

[0059] The fundamental purpose of control mode switching is to address the problem of rapid DC voltage drops and the operating point slipping into the unstable region on the left side of the PV curve of the photovoltaic array under conditions such as sudden drops in sunlight, ultimately leading to system instability. Therefore, the design of the switching criteria needs to consider two requirements simultaneously: first, the ability to quickly identify anomalies within a limited time window before instability occurs; and second, the ability to accurately distinguish between genuine instability risks and voltage fluctuations during the normal maximum power point (MPTT) search process, avoiding erroneous switching. This requires that the criterion's characteristic quantities reflect the essential characteristics of the instability process from different dimensions, rather than relying on a single indicator.

[0060] The first characteristic quantity for judgment is the rate of change of DC voltage. A rapid drop in DC voltage is the most significant and direct sign that an inverter system is about to become unstable. Traditional VSG power synchronization control takes output power as the direct control object. Regardless of whether the DC voltage change originates from changes in the external environment or a failure of the control strategy itself, the VSG power synchronization control structure lacks a direct sensing and rapid response channel for the DC voltage. The DC voltage can only indirectly affect the power reference value through the MPPT algorithm, and then be slowly adjusted through the inertia link of the active power loop. This characteristic determines that the VSG power synchronization control mode cannot respond promptly and effectively to rapid drops in DC voltage. Therefore, using the rate of change of DC voltage as one of the switching criteria can directly capture this inherent blind spot of VSG power synchronization control.

[0061] The second criterion characteristic is the derivative of DC voltage with respect to photovoltaic input power. Relying solely on the rate of change of DC voltage carries the risk of misjudgment: During the normal MPPT search process, when the inverter system adjusts towards the maximum power point with large step sizes, the DC voltage may also drop rapidly. However, at this time, the operating point is approaching the maximum power point from the right side of the PV curve, and the inverter system is still within a controllable and stable region. However, once the operating point crosses the maximum power point and enters the unstable region on the left, the output characteristics of the photovoltaic array will undergo a qualitative change. Analysis of photovoltaic characteristics shows that the incremental conductance in the left region of the PV curve is negative, and the change direction of the photovoltaic input power is opposite to that of the DC voltage. Therefore, by using the voltage-power derivative as the second criterion characteristic quantity, we can essentially distinguish between two voltage drop processes that are similar in state but have completely different properties: "normally approaching the maximum power point" and "crossing the maximum power point and entering the unstable region".

[0062] The third criterion characteristic is the rate of change of photovoltaic input power. A sudden drop in solar illumination directly impacts the inverter by causing a rapid decrease in input power. Introducing the rate of change of input power as an auxiliary criterion allows for the early detection of abnormal changes in photovoltaic power before a significant drop in DC voltage, providing early warning information for switching decisions. Simultaneously, and The combination of direction and amplitude helps to distinguish between "power decrease caused by sudden changes in illumination" and "power fluctuation caused by grid-side disturbances". This manifests as a rapid decrease in both photovoltaic input power and DC voltage in the same direction. The main manifestation is fluctuations in AC output power, while the impact on photovoltaic input power is limited.

[0063] Reference Figure 2 As shown, mode indicates the current control mode: To avoid over-frequency sampling, reduce the system's computational burden, and ensure the accuracy of the state variable change rate calculation, in some specific embodiments of this application, for S11, if the current sampling time interval is not less than the preset sampling period, the current control mode is read, and the DC voltage change rate, photovoltaic input power change rate, and the derivative of DC voltage with respect to photovoltaic input power of the grid-type centralized photovoltaic inverter are obtained, S114 can also be used.

[0064] S114. If the current sampling time interval is not greater than the preset sampling period, then there is no need to read the current control mode and the average DC voltage and average photovoltaic input power of the grid-type centralized photovoltaic inverter, and wait for the sampling time interval to be greater than the preset sampling period.

[0065] The embodiments described above in this application construct a mode switching criterion that balances speed and accuracy by collecting and calculating three multi-dimensional feature quantities: the rate of change of DC voltage, the rate of change of photovoltaic input power, and the derivative of DC voltage with respect to photovoltaic input power at a fixed sampling period. This criterion can both use the rate of change of DC voltage and the rate of change of input power to provide timely warning of anomalies caused by sudden changes in illumination before instability occurs, and effectively distinguish the essential difference between normal MPPT search and entering the unstable region on the left side of the PV curve by using the voltage-power derivative, thus avoiding false switching. This allows for accurate identification of real instability risks under conditions without energy storage, ensuring smooth switching of control modes and stable system operation.

[0066] Figure 3 This is a schematic diagram illustrating a control mode switching condition according to an exemplary embodiment.

[0067] Reference Figure 3 As shown, in order to determine the control mode switching conditions, in some specific embodiments of this application, for S12, if the time interval between the current and the last mode switching is greater than the preset locking time, the control mode switching conditions are determined according to the current control mode, which can be done by: S121 to S122.

[0068] S121, If ​​the time interval between the current and the last mode switch is greater than the preset blocking time, the current control mode is VSG power synchronization control mode, and the control mode switching condition is determined to be instability condition.

[0069] Specifically, after the control mode is switched to the DC voltage synchronization control mode, a certain period of lockout is required to prevent frequent switching of control mode during transient fluctuations. Therefore, the lockout time is set.

[0070] The preset locking time is T lock The last time the mode was switched was t change , t Indicates the current time.

[0071] For example, the preset locking time can be set to T lock =0.5s.

[0072] The instability conditions include the DC voltage change rate being less than a preset first constant, the photovoltaic input power change rate being less than a preset second constant, and the DC voltage derivative with respect to the photovoltaic input power being greater than a preset third constant.

[0073] Specifically, the preset first constant is expressed as: The preset second constant is expressed as The preset third constant is expressed as .

[0074] The instability condition is: in, This represents the rate of change of DC voltage. Indicates the rate of change of photovoltaic input power. This represents the derivative of DC voltage with respect to photovoltaic input power.

[0075] S122, If the time interval between the current and the last mode switch is greater than the preset blocking time, the current control mode is DC voltage synchronization control mode, and the control mode switching condition is determined to be a steady-state condition.

[0076] The steady-state conditions include that the absolute value of the rate of change of DC voltage is less than a preset fourth constant, and the absolute value of the rate of change of photovoltaic input power is less than a preset fifth constant, and the derivative of DC voltage with respect to photovoltaic input power is less than a preset sixth constant.

[0077] Specifically, the preset fourth constant is: The preset fifth constant is The preset sixth constant is .

[0078] The steady-state condition is: in, Represents the absolute value of the rate of change of DC voltage. It represents the absolute value of the rate of change of photovoltaic input power.

[0079] Specifically, steps S121 and S122 are parallel, and one of them must be performed.

[0080] In some specific embodiments of this application, if the time interval between the current time and the last mode switch is not greater than the preset blocking time, in order to prevent frequent switching of control modes during transient fluctuations, the mode switching is stopped until the time interval between the current time and the last mode switch is greater than the preset blocking time.

[0081] The embodiments described above in this application, by setting control mode switching conditions differently according to the current mode after the lockout time ends, detect instability to trigger protection in VSG power synchronization control mode, and detect steady state to restore normal control in DC voltage synchronization control mode, realizes bidirectional adaptive switching logic. This not only avoids malfunctions and frequent oscillations during transient processes, but also ensures that the inverter system can respond in time when a fault occurs and automatically return to the optimal operating state after recovery. This significantly improves the stability, reliability and dynamic adaptability of the grid-connected photovoltaic inverter control strategy.

[0082] Reference Figure 3 As shown, in order to achieve dynamic judgment and control mode switching, in some specific embodiments of this application, for S13, the new control mode is determined and switched to according to the DC voltage change rate, the photovoltaic input power change rate, the derivative of DC voltage with respect to photovoltaic input power and the control mode switching conditions, which can be implemented as S131 to S134.

[0083] S131, if the current control mode is VSG power synchronization control mode, determine whether the grid-type centralized photovoltaic inverter meets the instability condition. If it does, determine the new control mode as DC voltage synchronization control mode and switch to DC voltage synchronization control mode.

[0084] Specifically, a grid-type centralized photovoltaic inverter meets the instability conditions, namely, the rate of change of DC voltage is less than a preset first constant, the rate of change of photovoltaic input power is less than a preset second constant, and the derivative of DC voltage with respect to photovoltaic input power is greater than a preset third constant, indicating instability, and switches from VSG power synchronization control mode to DC voltage synchronization control mode.

[0085] S132, if the current control mode is VSG power synchronization control mode, determine whether the grid-type centralized photovoltaic inverter meets the instability conditions. If not, determine the new control mode as VSG power synchronization control mode and maintain the VSG power synchronization control mode.

[0086] Specifically, if a grid-type centralized photovoltaic inverter does not meet the instability conditions, that is, if any one or more of the following conditions are not met: the rate of change of DC voltage is less than a preset first constant, the rate of change of photovoltaic input power is less than a preset second constant, or the derivative of DC voltage with respect to photovoltaic input power is greater than a preset third constant, it indicates that it is not instable and maintains the VSG power synchronization control mode.

[0087] S133, if the current control mode is DC voltage synchronization control mode, determine whether the grid-type centralized photovoltaic inverter meets the steady-state conditions. If it does, determine the new control mode as VSG power synchronization control mode and switch to VSG power synchronization control mode.

[0088] Specifically, a grid-type centralized photovoltaic inverter meets the steady-state conditions, namely, the absolute value of the DC voltage change rate is less than a preset fourth constant, the absolute value of the photovoltaic input power change rate is less than a preset fifth constant, and the derivative of the DC voltage with respect to the photovoltaic input power is less than a preset sixth constant, indicating that a steady state has been reached, and the inverter switches from the DC voltage synchronous control mode to the VSG power synchronous control mode.

[0089] S134. If the current control mode is DC voltage synchronous control mode, determine whether the grid-type centralized photovoltaic inverter meets the steady-state conditions. If not, determine the new control mode as DC voltage synchronous control mode and maintain the DC voltage synchronous control mode.

[0090] Specifically, if a grid-type centralized photovoltaic inverter does not meet the steady-state conditions, that is, if any one or more of the following conditions are not met: the absolute value of the DC voltage change rate is less than the preset fourth constant, the absolute value of the photovoltaic input power change rate is less than the preset fifth constant, or the derivative of the DC voltage with respect to the photovoltaic input power is less than the preset sixth constant, it indicates that steady state has not been reached, and the DC voltage synchronous control mode is maintained.

[0091] The steps S131 to S134 above are parallel steps, and you can choose to execute any one of them.

[0092] The embodiments described above in this application construct precise instability and steady-state criteria by comprehensively considering multi-dimensional state variables such as the rate of change of DC voltage, the rate of change of photovoltaic input power, and the derivatives of the rate of change of DC voltage and the rate of change of photovoltaic input power. This enables bidirectional adaptive seamless switching between VSG power synchronization control and DC voltage synchronization control modes. It can quickly identify instability risks and switch to DC voltage synchronization mode to maintain system stability under disturbances such as sudden changes in illumination. It can also accurately determine steady-state conditions and automatically return to VSG mode after the operating conditions recover to ensure grid-connected performance. This effectively avoids frequent switching or response lag caused by misjudgment of a single indicator, and significantly improves the dynamic stability, control reliability, and operating efficiency of grid-connected centralized photovoltaic inverters under complex operating conditions.

[0093] Figure 4 This is a schematic diagram illustrating the algorithm flow for maximum power point tracking stability control of a grid-type centralized photovoltaic inverter according to an exemplary embodiment.

[0094] Reference Figure 4 As shown, in order to ensure the transient stability of the inverter system while achieving smooth tracking of the maximum power point, in some specific embodiments of this application, for S14, the DC voltage reference value and the photovoltaic output power reference value are determined by a reference value smooth transition strategy according to the new control mode and the previous control mode, and the maximum power point tracking control is performed. This can be achieved by using S141 to S145.

[0095] S141, if the new control mode is the same as the previous control mode (VSG power synchronization control mode), and the time interval between two consecutive updates of the photovoltaic output power reference value is greater than a preset time threshold, and the derivative of the DC voltage with respect to the photovoltaic input power is greater than zero, then execute... , This indicates the preset step size, which is used until the derivative of the DC voltage with respect to the photovoltaic input is not greater than zero, thus determining the reference value of the photovoltaic output power. The reference value of the DC voltage is the actual value of the DC voltage.

[0096] The time interval between two consecutive updates of the photovoltaic output power reference value is: The preset time threshold can be set to 0.1s, and the preset time threshold can be adjusted adaptively according to specific needs.

[0097] That is, step S141 above needs to satisfy... .

[0098] The preset step size can be adaptively set according to specific needs.

[0099] The DC voltage reference value is the actual DC voltage value, i.e. ,in, This represents the actual value of the DC voltage.

[0100] S142, if the new control mode is the same as the previous control mode (VSG power synchronization control mode), and the time interval between two consecutive updates of the photovoltaic output power reference value is greater than a preset time threshold, and the derivative of the DC voltage with respect to the photovoltaic input is not greater than zero, then execute. , This indicates the preset step size, which is maintained until the derivative of the DC voltage with respect to the photovoltaic input power is greater than zero, thus determining the reference value of the photovoltaic output power. The reference value of the DC voltage is the actual value of the DC voltage.

[0101] Specifically, step S142 above needs to satisfy... .

[0102] The DC voltage reference value is the actual DC voltage value, i.e. ,in, This represents the actual value of the DC voltage.

[0103] S143, if the new control mode is different from the previous control mode, the new control mode is the VSG power synchronization control mode, and the photovoltaic output power reference value is determined to be the actual photovoltaic output power value, and the DC voltage reference value is determined to be the actual DC voltage value.

[0104] In some specific embodiments of this application, the reference to smooth transition strategy means using the actual value of photovoltaic output power as a reference value for photovoltaic output power during the transition.

[0105] The DC voltage reference value is the actual DC voltage value, i.e. ,in, This represents the actual value of the DC voltage.

[0106] In some specific embodiments of this application, for S14, the DC voltage reference value and the photovoltaic output power reference value are determined by a reference value smooth transition strategy according to the new control mode and the previous control mode, and the maximum power point tracking control is performed. S144 to S145 can also be used.

[0107] S144, if the new control mode is the same as the previous control mode, which is the DC voltage synchronous control mode, the photovoltaic output power reference value is determined to be zero, and the DC voltage reference value is the preset DC voltage value.

[0108] Specifically, ,in, This indicates the preset DC voltage value.

[0109] S145, if the new control mode is different from the previous control mode, the new control mode is the DC voltage synchronous control mode, the DC voltage reference value is determined to be the preset DC voltage value, and the photovoltaic output power reference value is zero.

[0110] In this application, steps S144 to S145 are all parallel, and one of them may be performed.

[0111] In some specific embodiments of this application, if the new control mode is the same as the previous control mode, which is the VSG power synchronization control mode, and the time interval between two consecutive updates of the photovoltaic output power reference value is not greater than a preset time threshold, the step of determining whether the new control mode is the same as the previous control mode is returned.

[0112] The embodiments described above in this application effectively eliminate reference value abrupt changes and power surges during control mode transitions by setting differentiated reference value generation logic for different mode holding and switching scenarios and using actual values ​​as transition benchmarks during mode switching. This ensures accurate maximum power point tracking based on derivative criteria in VSG power synchronous control mode and continuity of voltage support in DC voltage synchronous control mode, thereby achieving smooth transition, stable control, and efficient energy capture of grid-connected photovoltaic inverters throughout the steady-state operation and transient switching process.

[0113] Figure 5 This is a schematic diagram illustrating a maximum power point tracking stability control strategy for a grid-type centralized photovoltaic inverter according to an exemplary embodiment.

[0114] Reference Figure 5 As shown, through the MPPT module, mode selection module, and switching switch, adaptive control and maximum power point tracking stability control of the grid-type photovoltaic inverter are achieved based on mode selection and dual-loop control. Its working principle is as follows: The MPPT module determines the current control mode and DC voltage based on the current control mode and DC voltage. Photovoltaic input power and the derivative of DC voltage with respect to photovoltaic input power Generate DC voltage reference value and photovoltaic output power reference value The mode selection module is based on DC voltage. Photovoltaic input power Determine the rate of change of DC voltage Photovoltaic input power change rate and the derivative of DC voltage with respect to photovoltaic input power Dynamically determine and output the mode signal, and control the switch (0 / 1) within the dashed box to select the VSG power synchronization control path (via... Points generation Superimposed power grid angular frequency Obtain the system angular frequency Integrate again to get the phase angle (or DC voltage synchronous control path; PI regulation is based on...) Adjusting the output together achieves stable operation and maximum power point tracking under adaptive mode switching.

[0115] Figure 6 This is a schematic diagram of a virtual synchronous machine control structure according to an exemplary embodiment.

[0116] Reference Figure 6 As shown, this application implements VSG power synchronization control mode through virtual synchronous machine control. The virtual synchronous machine control structure is a power-frequency droop control structure, with the photovoltaic output power reference value... With actual output power The deviation is taken as input and processed through a proportional-integral droop stage. (in, Indicates the droop coefficient, (representing the rated angular frequency) and inertial elements (J represents virtual moment of inertia) Generation frequency deviation This frequency deviation is superimposed on the rated angular frequency. Obtain the output angular frequency of the inverter system Then through the points process Obtain the output phase angle This allows for the simulation of the rotor motion equations and power angle characteristics of a synchronous machine, enabling autonomous adjustment of grid frequency support and active power.

[0117] Figure 7 This is a schematic diagram of a DC voltage synchronization control structure according to an exemplary embodiment.

[0118] Reference Figure 7 As shown, this application achieves DC voltage synchronization control mode through a DC voltage synchronization control structure. The DC voltage synchronization control structure is a DC voltage-frequency regulation structure, based on the actual value of the DC bus voltage. DC bus voltage reference value The deviation is taken as input, and the angular frequency deviation is generated by the PI controller. This frequency deviation is superimposed on the rated angular frequency. Obtain the output angular frequency of the inverter system Then through the points process Obtain the output phase angle This allows for the simulation of the rotor motion equations and power angle characteristics of a synchronous machine, thereby achieving grid frequency support and constant DC bus voltage.

[0119] Figure 8 This is a schematic diagram illustrating the principle of a reactive power control and primary voltage regulation control structure according to an exemplary embodiment.

[0120] Reference Figure 8As shown, the grid-type centralized photovoltaic inverter achieves autonomous voltage amplitude regulation and reactive power support through a voltage amplitude regulation structure that integrates reactive power control and primary voltage regulation, using the AC bus voltage reference value. With actual voltage The deviation is the input, which is then processed by the proportional gain. Generate reactive power regulation, which is related to the reactive power reference. and actual no-work The difference (i.e., reactive power deviation) is added together and then fed into the integral stage. ( The integral gain is used for cumulative correction, resulting in an output voltage regulation component; finally, the equivalent electromotive force of the power grid is superimposed. The final output voltage E is obtained, enabling integrated control of drooping reactive power distribution and dynamic voltage support based on voltage deviation.

[0121] This application provides a maximum power point tracking (MPPT) stability control method for a grid-type centralized photovoltaic (PV) inverter. When the illumination is stable, the inverter system operates in VSG power synchronization control mode, which can provide inertia and frequency support to the grid. When the illumination changes abruptly, it smoothly switches to DC voltage synchronization control mode, using direct DC voltage regulation to achieve rapid power point tracking and prevent DC-side instability. After the inverter system returns to steady state, it automatically switches back to VSG power synchronization control mode, thereby achieving stable control of the centralized grid-type PV inverter under full illumination variations.

[0122] The preferred features in the above embodiments can be used individually in any embodiment, or in any combination thereof, provided they do not conflict with each other. Furthermore, parts not described in detail in the embodiments can be implemented using existing technologies.

[0123] The following examples and comparative examples will be used to further illustrate this application in order to better understand the above-mentioned technical solutions. It should be understood that the following are only some examples and are not intended to limit this application.

[0124] To verify the method provided in this application, simulation experiments were conducted using simulation software.

[0125] Operating Condition 1: The initial light intensity was set to 1500 W / m2, and dropped to 800 W / m2 in 1.5s.

[0126] Figure 9 This is a simulation diagram illustrating a conventional control strategy under operating condition 1 according to an exemplary embodiment.

[0127] Figure 9 In this context, (a) represents the DC voltage and active power controlled using the traditional control strategy under operating condition 1. Figure 9(b) in the figure represents the light intensity under condition 1.

[0128] Reference Figure 9 As shown, when the traditional virtual synchronous machine control strategy is used, the DC voltage drops rapidly during sudden changes in light intensity, which in turn causes the active power of the system to drop rapidly. This leads to frequent oscillations in DC voltage and active power, resulting in system instability.

[0129] Figure 10 This is a simulation diagram illustrating a maximum power point tracking stability control method for a grid-type centralized photovoltaic inverter under operating condition 1, according to an exemplary embodiment.

[0130] Figure 10 In this context, (a) represents the DC voltage and active power controlled by the method provided in this application under operating condition 1. Figure 10 (b) in the figure represents the light intensity under condition 1.

[0131] Reference Figure 10 As shown, using the method provided in this application, after detecting a rapid drop in DC voltage, the inverter system can automatically switch to DC voltage synchronous control mode in a very short time. Both the output power and DC voltage can quickly recover to a new steady state within 0.05s. After the inverter system stabilizes, it can also automatically switch back to the VGS power synchronous control mode of the virtual synchronous generator.

[0132] Operating Condition 2: The initial light intensity is set to 1000 W / m2, and the grid frequency drops by 0.2Hz in 1.5s-2s.

[0133] Figure 11 This is a simulation diagram illustrating a conventional control strategy under operating condition 2 according to an exemplary embodiment.

[0134] Figure 11 In this context, (a) represents the DC voltage and active power controlled using the traditional control strategy under operating condition 2. Figure 11 (b) in the figure represents the light intensity under condition 2.

[0135] Reference Figure 11 As shown, the effect of using only the VGS power synchronization control mode is that after the grid frequency drops, the VGS power synchronization control mode generates additional active power to support the grid frequency according to the primary frequency regulation droop characteristic. However, at this time, the input power of the photovoltaic array is limited by the lighting conditions and does not increase. All the additional active power comes from the discharge of the DC bus capacitor. Since the preset active power reserve margin under this condition is insufficient to cover all the additional power required for the frequency drop, the DC voltage continues to drop and eventually crosses the maximum power point of the PV curve and enters the unstable region on the left. The inverter system becomes unstable, and the output power collapses accordingly.

[0136] Figure 12 This is a simulation diagram illustrating a maximum power point tracking stability control method for a grid-type centralized photovoltaic inverter under operating condition 2, according to an exemplary embodiment.

[0137] Figure 12 In this context, (a) represents the DC voltage and active power controlled by the method provided in this application under operating condition 2. Figure 12 (b) in the diagram represents the light intensity under condition 2. Reference Figure 12 As shown, when the method provided in this application is adopted, it can react in time when the DC voltage shows a downward trend and switch to DC voltage synchronous control, thus preventing further instability.

[0138] Figure 13 This is a schematic flowchart illustrating a maximum power point tracking stability control system for a grid-type centralized photovoltaic inverter according to an exemplary embodiment.

[0139] Reference Figure 13 As shown in another embodiment of this application, a maximum power point tracking stability control system 100 for a grid-type centralized photovoltaic inverter is provided, including: a sampling module 110, a control mode switching condition determination module 120, a control mode switching module 130, and a maximum power point tracking control module 140.

[0140] The sampling module 110 is used to read the current control mode and obtain the DC voltage change rate, photovoltaic input power change rate and DC voltage derivative with respect to photovoltaic input power of the grid-type centralized photovoltaic inverter if the current sampling time interval is not less than the preset sampling period. The control mode is either VSG power synchronization control mode or DC voltage synchronization control mode. The control mode switching condition determination module 120 is used to determine the control mode switching condition based on the current control mode if the time interval between the current and the last mode switching is greater than the preset blocking time. The control mode switching condition is either an instability condition or a steady-state condition. The control mode switching module 130 is used to determine and switch to a new control mode based on the DC voltage change rate, the photovoltaic input power change rate, the derivative of DC voltage with respect to photovoltaic input power, and the control mode switching conditions. The maximum power point tracking control module 140 is used to determine the DC voltage reference value and the photovoltaic output power reference value through a reference value smooth transition strategy based on the new control mode and the previous control mode, and to perform maximum power point tracking control.

[0141] The embodiments described above in this application obtain multi-dimensional state variables such as the rate of change of DC voltage, the rate of change of photovoltaic input power, and the derivative of DC voltage with respect to photovoltaic input power by reading the current control mode. Combined with the lockout time and instability / steady-state conditions, adaptive switching between VSG power synchronization and DC voltage synchronization control modes is achieved. At the same time, a reference value smooth transition strategy is adopted to smoothly determine the tracking reference value. This enables operation in VSG power synchronization control mode to provide inertia and frequency support when the illumination is stable, and smooth switching to DC voltage synchronization control mode when the illumination changes abruptly to prevent DC-side instability and achieve rapid power point tracking. After reaching a steady state, it automatically switches back to VSG power synchronization control mode. Without the need for additional energy storage equipment, stable control and maximum power point tracking of the grid-type centralized photovoltaic inverter under full illumination variation can be achieved through state perception and smooth mode switching.

[0142] Regarding the embodiments of the above system, the specific ways in which each module performs operations have been described in detail in the embodiments of the method, and will not be elaborated here.

[0143] Based on the same technical concept, in some specific embodiments of this application, a terminal includes a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the program, it can be used to execute a maximum power point tracking stability control method for a grid-type centralized photovoltaic inverter.

[0144] Based on the same technical concept, in some specific embodiments of this application, a computer-readable storage medium is provided, on which a computer program is stored, which, when executed by a processor, can be used to perform a maximum power point tracking stability control method for a grid-type centralized photovoltaic inverter.

[0145] Optionally, the memory is used to store programs; the memory may include volatile memory, such as random-access memory (RAM), such as static random-access memory (SRAM), double data rate synchronous dynamic random-access memory (DDR SDRAM), etc.; the memory may also include non-volatile memory, such as flash memory. The memory is used to store computer programs (such as application programs and functional modules that implement the above methods), computer instructions, etc., and the aforementioned computer programs and computer instructions can be partitioned and stored in one or more memories. Furthermore, the aforementioned computer programs, computer instructions, data, etc., can be accessed by the processor.

[0146] The aforementioned computer programs, computer instructions, etc., can be stored in partitions within one or more memory locations. Furthermore, the aforementioned computer programs, computer instructions, data, etc., can be accessed by a processor.

[0147] A processor is used to execute a computer program stored in memory to implement the various steps of the methods involved in the above embodiments. For details, please refer to the relevant descriptions in the preceding method embodiments.

[0148] The processor and memory can be separate structures or integrated structures. When the processor and memory are separate structures, they can be coupled together via a bus.

[0149] 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.

[0150] 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.

[0151] 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.

[0152] 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.

[0153] The foregoing has described some specific embodiments of this application. It should be understood that this application is not limited to the specific embodiments described above, and those skilled in the art can make various modifications or variations within the scope of the claims, which do not affect the substantive content of this application. The above-described preferred features can be used in any combination without conflict.

Claims

1. A method for stable maximum power point tracking control of a grid-type centralized photovoltaic inverter, characterized in that, include: If the current sampling time interval is not less than the preset sampling period, read the current control mode and obtain the DC voltage change rate, photovoltaic input power change rate and the derivative of DC voltage with respect to photovoltaic input power of the grid-type centralized photovoltaic inverter. The control mode is either VSG power synchronization control mode or DC voltage synchronization control mode. If the time interval between the current and the last mode switch is greater than the preset blocking time, the control mode switching condition is determined according to the current control mode. The control mode switching condition is either an instability condition or a steady-state condition. Based on the DC voltage change rate, the photovoltaic input power change rate, the derivative of DC voltage with respect to photovoltaic input power, and the control mode switching conditions, determine and switch to a new control mode; Based on the new control mode and the previous control mode, the DC voltage reference value and the photovoltaic output power reference value are determined through a reference value smooth transition strategy, and the maximum power point tracking control is performed.

2. The maximum power point tracking stability control method for a grid-type centralized photovoltaic inverter according to claim 1, characterized in that, If the current sampling time interval is not less than the preset sampling period, the current control mode is read, and the DC voltage change rate, photovoltaic input power change rate, and the derivative of DC voltage with respect to photovoltaic input power of the grid-type centralized photovoltaic inverter are obtained, including: If the current sampling time interval is greater than the preset sampling period, read the current control mode; Obtain the average DC voltage and average photovoltaic input power of the grid-type centralized photovoltaic inverter within a preset sampling period since the last sampling time; Based on the average DC voltage, the average photovoltaic input power, and the preset sampling period, the rate of change of DC voltage, the rate of change of photovoltaic input power, and the derivative of DC voltage with respect to photovoltaic input power are determined.

3. The maximum power point tracking stability control method for a grid-type centralized photovoltaic inverter according to claim 1, characterized in that, The instability conditions include the DC voltage change rate being less than a preset first constant, the photovoltaic input power change rate being less than a preset second constant, and the DC voltage derivative with respect to the photovoltaic input power being greater than a preset third constant. The steady-state conditions include that the absolute value of the rate of change of DC voltage is less than a preset fourth constant, and the absolute value of the rate of change of photovoltaic input power is less than a preset fifth constant, and the derivative of DC voltage with respect to photovoltaic input power is less than a preset sixth constant.

4. The maximum power point tracking stability control method for a grid-type centralized photovoltaic inverter according to claim 3, characterized in that, If the time interval between the current and last mode switch is greater than the preset locking time, the control mode switching conditions are determined based on the current control mode, including: If the time interval between the current and the last mode switch is greater than the preset blocking time, the current control mode is the VSG power synchronization control mode, and the control mode switching condition is determined to be an instability condition. If the time interval between the current and the last mode switch is greater than the preset blocking time, the current control mode is the DC voltage synchronization control mode, and the control mode switching condition is determined to be a steady-state condition.

5. The maximum power point tracking stability control method for a grid-type centralized photovoltaic inverter according to claim 4, characterized in that, The step of determining and switching to a new control mode based on the DC voltage change rate, the photovoltaic input power change rate, the derivative of DC voltage with respect to photovoltaic input power, and the control mode switching conditions includes: If the current control mode is the VSG power synchronization control mode, determine whether the grid-type centralized photovoltaic inverter meets the instability condition. If it does, determine the new control mode as the DC voltage synchronization control mode and switch to the DC voltage synchronization control mode. If the current control mode is the VSG power synchronization control mode, determine whether the grid-type centralized photovoltaic inverter meets the instability condition. If it does not meet the condition, determine the new control mode as the VSG power synchronization control mode and maintain the VSG power synchronization control mode. If the current control mode is the DC voltage synchronization control mode, determine whether the grid-type centralized photovoltaic inverter meets the steady-state condition. If it does, determine the new control mode as the VSG power synchronization control mode and switch to the VSG power synchronization control mode. If the current control mode is the DC voltage synchronization control mode, determine whether the grid-type centralized photovoltaic inverter meets the steady-state condition. If it does not meet the condition, determine the new control mode as the DC voltage synchronization control mode and maintain the DC voltage synchronization control mode.

6. The maximum power point tracking stability control method for a grid-type centralized photovoltaic inverter according to claim 5, characterized in that, The step of determining the DC voltage reference value and photovoltaic output power reference value through a reference value smooth transition strategy based on the new control mode and the previous control mode, and performing maximum power point tracking control, includes: If the new control mode is the same as the previous control mode (VSG power synchronization control mode), and the time interval between two consecutive updates of the photovoltaic output power reference value is greater than a preset time threshold, and the derivative of the DC voltage with respect to the photovoltaic input power is greater than zero, then the control is executed. , The preset step size is used until the derivative of the DC voltage with respect to the photovoltaic input is not greater than zero, and the reference value of the photovoltaic output power is determined. The reference value of the DC voltage is the actual value of the DC voltage. If the new control mode is the same as the previous control mode (VSG power synchronization control mode), and the time interval between two consecutive updates of the photovoltaic output power reference value is greater than a preset time threshold, and the derivative of the DC voltage with respect to the photovoltaic input is not greater than zero, then the control is executed. , The preset step size is used until the derivative of the DC voltage with respect to the photovoltaic input power is greater than zero, and then the reference value of the photovoltaic output power is determined. The reference value of the DC voltage is the actual value of the DC voltage. If the new control mode is different from the previous control mode, the new control mode is the VSG power synchronization control mode, and the photovoltaic output power reference value is determined to be the actual photovoltaic output power value, and the DC voltage reference value is determined to be the actual DC voltage value.

7. The maximum power point tracking stability control method for a grid-type centralized photovoltaic inverter according to claim 1, characterized in that, The reference value smooth transition strategy means using the actual value of photovoltaic output power as the reference value of photovoltaic output power for transition; The step of determining the DC voltage reference value and photovoltaic output power reference value through a reference value smooth transition strategy based on the new control mode and the previous control mode, and performing maximum power point tracking control, further includes: If the new control mode is the same as the previous control mode, which is the DC voltage synchronous control mode, the photovoltaic output power reference value is determined to be zero, and the DC voltage reference value is the preset DC voltage value. If the new control mode is different from the previous control mode, the new control mode is the DC voltage synchronization control mode, the DC voltage reference value is determined to be the preset DC voltage value, and the photovoltaic output power reference value is zero.

8. A maximum power point tracking stability control system for a grid-type centralized photovoltaic inverter, characterized in that, include: The sampling module is used to read the current control mode and obtain the DC voltage change rate, photovoltaic input power change rate and DC voltage derivative with respect to photovoltaic input power of the grid-type centralized photovoltaic inverter if the current sampling time interval is not less than the preset sampling period. The control mode is either VSG power synchronization control mode or DC voltage synchronization control mode. The control mode switching condition determination module is used to determine the control mode switching condition based on the current control mode if the time interval between the current and the last mode switching is greater than the preset blocking time. The control mode switching condition is either an instability condition or a steady-state condition. The control mode switching module is used to determine and switch to a new control mode based on the DC voltage change rate, the photovoltaic input power change rate, the derivative of DC voltage with respect to photovoltaic input power, and the control mode switching conditions. The maximum power point tracking control module is used to determine the DC voltage reference value and the photovoltaic output power reference value through a reference value smooth transition strategy based on the new control mode and the previous control mode, and to perform maximum power point tracking control.

9. A non-transitory computer-readable storage medium having a computer program stored thereon, characterized in that, When executed by a processor, the program implements the steps of the method described in any one of claims 1-7.

10. An electronic device, characterized in that, include: A memory on which computer programs are stored; A processor for executing the computer program in the memory to implement the steps of the method according to any one of claims 1-7.

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