A method, medium and device for regulating a light storage inverter

Abstract

The application discloses a kind of light storage inverter regulation methods, medium and equipment, it is related to inverter technical field;Method steps: the operation data of light storage inverter is collected, and current working condition is identified;When identifying light storage inverter is in weak source with load condition, the power gap between the power demand of single-phase load and the available power of internal source is determined;The coupling between load power consumption and grid power is released, and the power gap is evenly distributed to three-phase power grid;Under the safety constraint of equipment, the grid power of idle phase and / or inverter bridge arm redundant power is aggregated and transferred to the heavy load phase carrying single-phase load.The medium and equipment are used to implement the above method.The application can realize the decoupling of load single-phase asymmetric power consumption and grid three-phase symmetric balanced power taking in weak internal source or sourceless with load scene, suppress three-phase imbalance from the source, and improve the single-phase load power supply reliability of light storage inverter.

Description

Technical Field

[0001] This application relates to the field of inverter technology, and in particular to a method, medium and device for controlling a photovoltaic-storage inverter. Background Technology

[0002] Currently, the industry's technical solutions for inverter three-phase imbalance mitigation and phase-to-phase power optimization mainly fall into two categories. One type of solution relies on the effective output of photovoltaic power generation. Based on the grid's three-phase voltage deviation and preset power thresholds, it redistributes power across phases under grid-connected power generation conditions, achieving grid voltage balance and improving photovoltaic absorption efficiency by adjusting the three-phase output power. The other type of solution relies on external load regulators and distribution area balancing equipment to perform secondary transfer and correction of existing three-phase unbalanced loads, representing passive post-implementation mitigation; or it relies on the active power support of energy storage batteries to achieve harmonic suppression, voltage fine-tuning, and small-amplitude imbalance compensation under equipment load conditions.

[0003] However, the aforementioned existing technical solutions have the following technical defects in practical use: (1) Existing phase-to-phase power regulation and three-phase imbalance compensation technologies all rely heavily on the sufficient active power output of photovoltaic and energy storage as the basis for regulation. When the internal power of photovoltaic and energy storage in the system is limited and cannot cover the power demand of single-phase loads, or when the three-phase output of the internal power itself is unbalanced, the traditional balancing regulation capability will decrease significantly. Under extreme passive conditions such as no light at night and complete depletion of energy storage, the existing regulation function will directly fail. At this time, single-phase loads can only rely on the independent power supply of single-phase grid, which is very easy to cause single-phase load concentration and three-phase current imbalance. Long-term operation will continuously deteriorate the power quality of the distribution area, which is a common technical shortcoming in the industry.

[0004] (2) Traditional inverter control logic generally follows the matching mechanism of "the phase connected to the load is the same as the phase supplied to the power grid", and the phase sequence of the load power consumption is highly coupled with the phase sequence of the power grid power intake. In residential and industrial low-voltage distribution areas, the random and concentrated connection of single-phase loads is very common, which will cause the power grid to be overdrawn for a long time. Existing technologies can only make small compensations after the fact, and cannot suppress the generation of unbalanced power from the root. The stubborn power quality problems such as long-term accumulated phase imbalance, increased line loss, and voltage drift in the distribution area can never be cured.

[0005] (3) Currently, all inverter imbalance control functions in the industry are based on local load power consumption as the starting premise and only participate in grid regulation when the equipment is under load. When the equipment is idle and there is no local load input, the control function automatically goes into hibernation and does not participate in any grid optimization. However, in reality, low-voltage distribution areas generally have inherent three-phase imbalance caused by uneven line impedance and inconsistent upstream load distribution. This type of passive imbalance problem persists during the idle period of the equipment and cannot be covered by existing technology, resulting in a significant time blind spot in grid management.

[0006] (4) When a single phase of the inverter is heavily loaded and the other two phases are lightly loaded or unloaded, the inverter arm margin and corresponding grid capacity of the two idle phases are idle for a long time. The existing technology does not make reasonable scheduling and utilization of this part of the redundant resources, which not only wastes equipment resources and grid capacity, but also cannot adapt to the short-term overload power demand of single-phase load within the safe range of equipment, resulting in poor equipment load adaptability and scenario compatibility. Summary of the Invention

[0007] One objective of this application is to provide a photovoltaic-storage inverter control method that can solve at least one of the defects in the above-mentioned background art.

[0008] Another objective of this application is to provide a computer-readable storage medium for implementing the above-described photovoltaic-storage inverter control method.

[0009] Another object of this application is to provide an electronic device for implementing the above-described photovoltaic-storage inverter control method.

[0010] To achieve at least one of the above objectives, one aspect of this application provides a photovoltaic-storage inverter control method, comprising the following steps: collecting operating data of the photovoltaic-storage inverter and identifying the current operating condition; when the photovoltaic-storage inverter is identified as being in a weak-source load condition with insufficient or no internal power supply and a locally connected single-phase load, determining the power gap between the power demand of the single-phase load and the available internal power supply; decoupling the load power consumption from the grid power supply and evenly distributing the power gap to the three-phase grid; and, under equipment safety constraints, aggregating the grid power and / or the redundant power of the inverter bridge arm in the idle phase and transferring it to the heavily loaded phase carrying the single-phase load.

[0011] Preferably, the specific process of aggregating the grid power and / or redundant power of the inverter bridge arm in the idle phase and transferring it to the heavily loaded phase carrying the single-phase load is as follows: Based on the power demand of the single-phase load and the power taken from the three-phase grid after allocation, an AC side power reference for each phase inverter bridge arm is generated; the inverter bridge arm of the idle phase is controlled to operate in rectification mode, while the heavily loaded phase is controlled to operate in inverter mode; the power absorbed by the idle phase from the three-phase grid and the internal available power are aggregated on the shared DC bus and then output to the single-phase load through the inverter bridge arm of the heavily loaded phase.

[0012] Preferably, the specific process of supplying power to a single-phase load under equipment safety constraints is as follows: determine the transferable power margin of each phase according to the equipment safety boundary of each phase inverter arm; generate the initial cross-phase transfer power command of the idle phase according to the power gap; when the initial cross-phase transfer power command of an idle phase exceeds the transferable power margin of that phase, limit the phase to obtain the limited cross-phase transfer power command and the unmet power; redistribute the unmet power to the remaining idle phases until the power gap is met or all the inverter arms of the idle phases reach their equipment safety boundaries.

[0013] Preferably, the equipment safety constraints include at least one of phase current constraints, power device junction temperature constraints, cumulative thermal damage constraints, DC bus voltage constraints, equipment temperature constraints, and grid capacity constraints; based on the boundary values ​​given for each constraint, the maximum transferable power margin corresponding to each constraint is calculated; the minimum value among the maximum transferable power margins corresponding to all constraint items is taken as the transferable power margin.

[0014] Preferably, under weak source load conditions, the specific process for power regulation of the heavily loaded phase is as follows: Based on the real-time current, power demand, and junction temperature of the heavily loaded phase, combined with the available internal power, calculate the grid imbalance, equipment load rate, internal power margin, and thermal margin respectively; construct a comprehensive classification index based on the normalized grid imbalance, equipment load rate, internal power margin, and thermal margin; when the comprehensive classification index is less than the first boundary threshold, no power transfer is performed on the idle phase; when the comprehensive classification index is between the first and second boundary thresholds, compensation is performed on the heavily loaded phase through reactive power and / or active power; when the comprehensive classification index is between the second and third boundary thresholds, power transfer is controlled on the idle phase; when the comprehensive classification index is greater than the third boundary threshold, while controlling the power transfer on the idle phase, the short-term overload capacity of the heavily loaded phase is invoked; when the thermal margin exceeds the constraint value, the idle phase is controlled to exit power transfer, and the heavily loaded phase is deloaded or unloaded; wherein, the calculation expression for the comprehensive classification index S is: ; In the formula, , , , These represent the normalized grid imbalance, equipment load factor, internal power margin, and thermal margin, respectively. , , , These represent the weight coefficients for each item.

[0015] Preferably, the operating conditions of the photovoltaic-storage inverter also include an active load operating condition with sufficient internal power and a locally connected single-phase load, and a passive no-load operating condition with no internal power and no load. The process of identifying each operating condition of the photovoltaic-storage inverter is as follows: obtaining the photovoltaic output status, remaining energy storage capacity, load operating condition, and equipment operating stress; converting the photovoltaic output status into available photovoltaic power, the remaining energy storage capacity into available energy storage discharge power, and the equipment operating stress into an equipment stress derating factor; and generating the internal available power by fusing the available photovoltaic power, available energy storage discharge power, and equipment stress derating factor; converting the load operating condition into the load equivalent power; and generating the internal available power by fusing the internal available power and the load equivalent power. The power difference ratio is used to calculate the internal power margin ratio; load presence threshold, internal availability threshold, and surplus threshold are set; when the equivalent load power is less than the load presence threshold and the internal available power is less than the internal availability threshold, it is determined to be a passive no-load condition, and no-load static correction is performed; when the equivalent load power is greater than or equal to the load presence threshold, the internal available power is greater than or equal to the internal availability threshold, and the internal power margin ratio is greater than or equal to the surplus threshold, it is determined to be an active load condition, and the internal power directly supplies power to the single-phase load; when the equivalent load power is greater than or equal to the load presence threshold, and the internal available power is less than the internal availability threshold or the internal power margin ratio is less than zero, it is determined to be a weak source load condition.

[0016] Preferably, the process of switching between active load and weak load conditions for the photovoltaic-storage inverter is as follows: A pre-switching stage is set where the internal power margin ratio is between zero and a sufficient threshold. During this stage, the power supply ratio is calculated using the difference between the sufficient threshold and the internal power margin ratio. Based on the product of the power supply ratio and the power demand of the single-phase load, the total power output from the three-phase grid is calculated and evenly distributed across the three-phase grid. When switching from active load to weak load conditions, the inverter switches to weak load conditions after the pre-switching stage. When switching from weak load to active load conditions, if the internal power margin ratio is greater than or equal to a preset hysteresis threshold greater than zero, the photovoltaic-storage inverter exits the weak load condition and enters the pre-switching stage. If the internal power margin ratio is greater than or equal to the sum of the sufficient threshold and the hysteresis threshold, the photovoltaic-storage inverter exits the pre-switching stage and enters the active load condition.

[0017] Preferably, the specific process of performing static polarization correction under passive no-load conditions is as follows: In the no-load standby state of the photovoltaic-storage inverter, a small current at the grid connection point is acquired as the excitation current; based on the obtained excitation current, a grid connection point voltage equation is constructed regarding the upstream background voltage, excitation current, and line impedance; the grid connection point voltage equation is converted into a linear regression form, and a recursive least squares algorithm is used to identify relevant parameters online to obtain the line impedance and upstream background voltage of each phase; the absolute value of the difference between the upstream background voltage of each phase and the average upstream background voltage is calculated, and the maximum absolute value of the difference is compared with the average upstream background voltage. The ratio of the voltage to the upstream background voltage is used as a static imbalance index; the absolute value of the difference between the voltage of each phase at the grid connection point and the corresponding upstream background voltage is calculated, and the ratio of the maximum absolute value of the difference to the average upstream background voltage is used as a dynamic imbalance index; voltage compensation and imbalance correction of the offset phase are performed only when the static imbalance index is greater than or equal to the preset static imbalance threshold and the dynamic imbalance index is less than the preset dynamic imbalance threshold; when the dynamic imbalance index is greater than or equal to the dynamic imbalance threshold, it is determined to be a dynamic imbalance caused by upstream load fluctuations, and compensation is not triggered temporarily.

[0018] Another aspect of this application provides a computer-readable storage medium storing a computer program; when the computer program is executed by a processor, it implements the above-described photovoltaic-storage inverter control method.

[0019] Another aspect of this application provides an electronic device, including a processor and a memory; the memory is used to store a computer program, and the processor is used to execute the computer program to implement the above-described photovoltaic-storage inverter control method.

[0020] Compared with the prior art, the beneficial effects of this application are as follows: (1) Under the condition of weak source load, this application decouples the load power consumption and the grid power consumption and distributes the power gap equally to the three-phase grid, thereby realizing the single-phase unbalanced power consumption on the load side and the three-phase symmetrical balanced power consumption on the grid side, thereby suppressing the three-phase imbalance from the source, improving the power quality of the low-voltage distribution area, and avoiding the phase imbalance caused by single-phase concentrated power consumption.

[0021] (2) This application controls the power transmission path inside the photovoltaic-storage inverter to aggregate the grid power and / or the redundant power of the inverter arm in the idle phase and transfer it to the heavy-load phase that carries the single-phase load. Under the equipment safety constraints, it supplies power to the single-phase load, thereby making full use of the idle phase resources and the redundancy of the arm, improving the power supply reliability of the single-phase load and the utilization rate of equipment resources. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of a traditional photovoltaic-storage inverter architecture. Figure 2 This is a schematic diagram of the working steps of this application; Figure 3 This is a schematic diagram of the architecture of a specific example of this application.

[0023] In the diagram: 10 photovoltaic array, 20 photovoltaic-energy storage inverter, 201 DC / DC unit, 202 DC / AC unit, 203 bidirectional DC / DC unit, 30 three-phase power grid, 40 energy storage battery, and 50 single-phase load. Detailed Implementation

[0024] The present application will now be further described in conjunction with specific embodiments. It should be noted that, in the description of this specification, the use of terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicates that the specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms should not be construed as necessarily referring to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. In addition, those skilled in the art can combine and integrate the different embodiments or examples described in this specification.

[0025] In the description of this application, it should be noted that the directional terms such as "center", "lateral", "longitudinal", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", and "counterclockwise" indicate the orientation and positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. They should not be construed as limiting the specific protection scope of this application.

[0026] It should be noted that the terms "first," "second," etc., in the specification and claims of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence.

[0027] In this application, unless otherwise expressly specified and limited, the terms "installation," "connection," "joining," and "fixing," etc., should be interpreted broadly. For example, they can refer to a connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0028] In this application, unless otherwise expressly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature being directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature being directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0029] The terms “comprising” and “having”, and any variations thereof, in the specification and claims 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 necessarily limited to those steps or units that are explicitly listed, but may include other steps or units that are not explicitly listed or that are inherent to such process, method, product, or device.

[0030] To facilitate understanding of the technical solution of this application, a simple description of the traditional photovoltaic-storage inverter architecture will be provided below.

[0031] like Figure 1 As shown, a traditional photovoltaic-storage inverter architecture includes a photovoltaic array 10, a photovoltaic-storage inverter 20, an energy storage battery 40, and a single-phase load 50. The photovoltaic array 10 and the energy storage battery 40 are both connected to the DC side of the photovoltaic-storage inverter 20, the AC side of the photovoltaic-storage inverter 20 is connected to the three-phase power grid 30, and the single-phase load 50 is also connected to the AC side of the photovoltaic-storage inverter 20.

[0032] Specifically, the photovoltaic-storage inverter 20 includes a DC / DC unit 201, a DC / AC unit 202, and a bidirectional DC / DC unit 203. The photovoltaic array 10 is connected to the DC-side bus of the DC / AC unit 202 via the DC / DC unit 201, and the energy storage battery 40 is connected to the DC-side bus of the DC / AC unit 202 via the bidirectional DC / DC unit 203. That is, the DC / DC unit 201 and the bidirectional DC / DC unit 203 are connected in parallel on the DC side of the DC / AC unit 202. The AC side of the DC / AC unit 202 is connected to the three-phase power grid 30 and the single-phase load 50.

[0033] When the photovoltaic-storage inverter 20 is operating, if the photovoltaic array 10 and / or the energy storage battery 40 supply power to the single-phase load 50, the photovoltaic-storage inverter 20 is in an internal power supply state. If the photovoltaic array 10 and / or the energy storage battery 40 supply insufficient power to the single-phase load 50 at night or in other insufficient light scenarios, the single-phase load 50 can be supplied by drawing power from the three-phase grid 30, and the photovoltaic-storage inverter 20 is in a mixed power supply state. If the photovoltaic array 10 and / or the energy storage battery 40 has no output power, the single-phase load 50 is completely supplied by the three-phase grid 30, and the photovoltaic-storage inverter 20 is in a state without internal power supply.

[0034] Based on the above architecture, one aspect of this application provides a method for controlling a photovoltaic-storage inverter, such as... Figure 2 and Figure 3 As shown, one preferred embodiment includes the following steps: S100: Collects operating data from the photovoltaic-storage inverter 20 and identifies the current operating condition.

[0035] It should be understood that the operating data of the photovoltaic-storage inverter 20 refers to all state and electrical quantities that can be collected during the operation of the inverter 20, including but not limited to: photovoltaic output voltage, photovoltaic output current, available photovoltaic power, energy storage state of charge, available energy storage discharge power, voltage of the three-phase grid 30, three-phase grid-connected current, grid-connected point voltage, current of the single-phase load 50, power of the single-phase load 50, DC bus voltage, current of each phase bridge arm, junction temperature of power devices, heat sink temperature, equipment temperature, etc. The operating data can be obtained through the inverter's built-in voltage sampling circuit, current sampling circuit, temperature sampling circuit, and communication interface. The sampling frequency can be consistent with the inverter's control cycle, for example, a control cycle of 100 microseconds to 1 millisecond.

[0036] This step involves collecting and preprocessing the operating data of the photovoltaic-energy storage inverter 20. Preprocessing includes anomaly removal and data alignment, among other things. The specific preprocessing methods are well-known to those skilled in the art and will not be described in detail here. The preprocessed operating data allows for the identification of the current operating condition of the photovoltaic-energy storage inverter 20, facilitating the execution of corresponding power regulation.

[0037] S200: When the photovoltaic-storage inverter 20 is identified as being in a weak load condition with insufficient or no internal power support and a locally connected single-phase load 50, the power gap between the power demand of the single-phase load 50 and the available power of the internal power source is determined.

[0038] It should be understood that "internal power" refers to the active power provided by the photovoltaic array 10 and / or energy storage battery 40 in the photovoltaic-energy storage inverter 20. Under weak power supply conditions, the photovoltaic output may be low, the remaining energy storage capacity may be limited, or even there may be no output from either the photovoltaic array or the energy storage, requiring grid intervention for power supply. The power deficit refers to the portion of the single-phase load 50 whose power demand exceeds the available internal power.

[0039] S300: Decouples the load power consumption from the grid power supply and evenly distributes the power gap to the three-phase grid 30.

[0040] It should be understood that in traditional control systems, the load's power consumption and the grid's power intake are strongly coupled, meaning that the grid primarily draws power from the phase from which the load is connected. This can lead to concentrated current in the load's phase, resulting in a three-phase current imbalance. Decoupling this strong coupling means no longer aligning the load's connected phase with the grid's power intake phase, but rather drawing the load's required power from the three-phase grid in a balanced manner, ensuring that the grid's three-phase power intake current remains symmetrical or nearly symmetrical.

[0041] S400: Under equipment safety constraints, the grid power and / or inverter arm redundant power of the idle phase are aggregated and transferred to the heavy-load phase carrying the single-phase load 50.

[0042] It should be understood that an idle phase refers to a phase that is not connected to a single-phase load or has a light load, and its inverter arm has available power margin. This step can absorb electrical energy from the grid through the inverter arm of the idle phase and feed it back to the shared DC bus, or feed the redundant power of the inverter arm of the idle phase back to the shared DC bus. The inverter arm of the heavily loaded phase can absorb electrical energy from the shared DC bus and output it to the load, thereby forming a cross-phase power transfer path.

[0043] Understandably, this application, under the condition of weak source load, decouples the load power consumption from the grid power supply and distributes the power gap evenly to the three-phase grid 30, thereby achieving single-phase unbalanced power consumption on the load side and three-phase symmetrical power supply on the grid side, thus suppressing three-phase imbalance from the source, improving the power quality of the low-voltage distribution area, and avoiding phase imbalance caused by single-phase concentrated power supply.

[0044] Meanwhile, by controlling the power transmission path inside the photovoltaic-storage inverter 20, the grid power and / or inverter arm redundancy power of the idle phase are aggregated and transferred to the heavy-load phase carrying the single-phase load 50, and the single-phase load 50 is powered under the equipment safety constraints, thereby making full use of the idle phase resources and the arm redundancy capability, improving the power supply reliability of the single-phase load 50 and the equipment resource utilization rate.

[0045] It is important to understand that the operating conditions of the photovoltaic-storage inverter 20 include not only the weak-source load condition, but also the active load condition with sufficient internal power and a locally connected single-phase load of 50, and the passive no-load condition with no internal power and no load. The power regulation methods for different operating conditions of the photovoltaic-storage inverter 20 are different; therefore, it is necessary to identify the real-time operating conditions of the photovoltaic-storage inverter 20. To this end, the technical solution of this application provides an operating condition identification mechanism, which will be described in detail below for ease of understanding.

[0046] In a specific embodiment, the process of identifying the various operating conditions of the photovoltaic-storage inverter 20 during step S100 is as follows: S110: Obtain photovoltaic output status, remaining energy storage capacity, load operating conditions, and equipment operating stress.

[0047] It should be understood that the photovoltaic output status refers to the real-time output status and output capacity of the photovoltaic array 10 under current illumination, temperature, and operating point conditions. The remaining energy storage capacity refers to the current remaining usable energy of the energy storage battery 40 and its ability to discharge externally. The load operating condition refers to the connection status, power demand, and operating characteristics of the single-phase load 50 on the AC output side of the photovoltaic-energy storage inverter. The equipment operating stress refers to the electrical and thermal stresses currently borne by the photovoltaic-energy storage inverter, reflecting the equipment's safety margin and derating requirements.

[0048] S120: Converts photovoltaic output status into photovoltaic available power, converts remaining energy storage capacity into energy storage available discharge power, converts equipment operating stress into equipment stress derating factor, and generates internal available power by integrating photovoltaic available power, energy storage available discharge power and equipment stress derating factor, and converts load operating conditions into load equivalent power.

[0049] Specifically, the estimation of available photovoltaic power is affected by the MPPT operating point and may not be the maximum available power under the current illumination. It can be obtained by periodic open-circuit scanning and real-time operating point correction. The specific acquisition process is well known to those skilled in the art, so it will not be described in detail here.

[0050] The calculation of the available discharge power of the energy storage is affected by the state of charge, temperature and discharge rate of the energy storage battery 40. The specific calculation process is known to those skilled in the art, so it will not be described in detail here.

[0051] The calculation of the equipment stress derating factor includes the following process: First, the junction temperature of each phase power device is estimated. The specific calculation expression is as follows: .

[0052] .

[0053] .

[0054] .

[0055] In the formula, This represents the junction temperature of the power device in phase i, where i = {A, B, C}; Indicates ambient temperature. This represents the equivalent thermal resistance of the inverter bridge arm in phase i. This represents the power device loss in phase i; This represents the conduction loss of the power device in phase i. This represents the switching loss of the power device in phase i. This represents the operating current of phase i. This represents the equivalent resistance of the power device in phase i when it is turned on. This indicates the duty cycle of phase i. Indicates the switching frequency. and These represent turning energy on and off, respectively. Indicates the DC bus voltage. This represents the reference voltage, which can be 50% of the rated voltage. This represents the reference current, which can be 50% of the rated current.

[0056] Then, the heat margin coefficient is calculated, and the specific calculation expression is as follows: .

[0057] In the formula, This represents the heat margin coefficient of phase i. This indicates the maximum junction temperature of the power device, typically 150℃. This indicates the reference junction temperature, which is typically 25℃.

[0058] Then, the current margin coefficient is calculated, and the specific calculation expression is as follows: .

[0059] In the formula, This represents the current margin coefficient for phase i. Indicates the rated current.

[0060] Finally, the minimum value among the corresponding thermal margin coefficient and current margin coefficient is taken as the equipment stress derating coefficient; and the equipment stress derating coefficient is limited to the range of [0, 1]. When the equipment stress derating coefficient is 1, it means that the equipment stress is sufficient and there is no derating; when the equipment stress derating coefficient is 0, it means that the equipment stress has reached the limit and power output is prohibited.

[0061] The formula for calculating the available internal power is: .

[0062] In the formula, Indicates the available power from the internal source. This represents the stress derating factor of the equipment. Indicates the available power of photovoltaics. This indicates the available discharge power of the stored energy.

[0063] For the calculation of the load equivalent power, since the equipment is only connected to a single-phase load 50, the power required by the single-phase load 50 is the load equivalent power. In order to avoid misjudgment of the operating condition due to load power measurement noise, the load equivalent power can be filtered by a first-order low-pass filter.

[0064] S130: Calculate the internal power margin ratio based on the ratio of the difference between the internal available power and the load equivalent power.

[0065] Specifically, the formula for calculating the internal power margin ratio is as follows: .

[0066] In the formula, Indicates the internal power margin ratio. This indicates the equivalent power of the load.

[0067] S140: Set the load presence threshold, internal availability threshold, and abundance threshold.

[0068] It should be understood that the specific values ​​of the load presence threshold, the intrinsic availability threshold, and the abundance threshold can be determined by those skilled in the art based on their actual needs. For example, the load presence threshold can be 0.2kW, the intrinsic availability threshold can be 0.5kW, and the abundance threshold can range from 0.8 to 1.

[0069] S150: When the equivalent power of the load is less than the load existence threshold and the available power of the internal source is less than the internal source availability threshold, it is determined to be a passive no-load condition and no-load static correction is performed; when the equivalent power of the load is greater than or equal to the load existence threshold, the available power of the internal source is greater than or equal to the internal source availability threshold, and the internal source power margin ratio is greater than or equal to the surplus threshold, it is determined to be an active load condition and the internal source directly supplies power to the single-phase load 50; when the equivalent power of the load is greater than or equal to the load existence threshold and the available power of the internal source is less than the internal source availability threshold or the internal source power margin ratio is less than zero, it is determined to be a weak source load condition.

[0070] In a specific example, the load availability threshold can be set to 0.2kW, the internal power availability threshold to 0.5kW, and the margin threshold to 1. If both the available photovoltaic power and the available energy storage discharge power are 0, and the local single-phase load 50 is 9kW, since the equivalent load power is greater than 0.2kW and the internal power availability is less than 0.5kW, the photovoltaic-energy storage inverter 20 is determined to be in a weak power supply condition. If the sum of the available photovoltaic power and the available energy storage discharge power is 20kW, and the local single-phase load 50 is 9kW, since the equivalent load power is greater than 0.2kW, the internal power availability is greater than 0.5kW, and the internal power margin ratio M = (20-9) / 9 ≈ 1.22 > 1, the photovoltaic-energy storage inverter 20 is determined to be in an active power supply condition. If the sum of the available photovoltaic power and the available energy storage discharge power is 3kW, and the local single-phase load 50 is 9kW, since the equivalent power of the load is greater than 0.2kW, the internal power margin ratio M=(3-9) / 9≈-0.67<0, it is determined that the photovoltaic-energy storage inverter 20 is currently in a weak source load condition.

[0071] Understandably, this embodiment achieves accurate identification of active load, weak load, and passive no-load operating conditions by collecting four types of parameters: photovoltaic, energy storage, load, and equipment stress, and calculating the internal available power, load equivalent power, and internal power margin ratio. Based on the identification of real-time operating conditions, the photovoltaic-energy storage inverter 20 can automatically select direct internal power supply, inter-phase power mutual assistance, or no-load static correction according to the actual operating conditions, realizing adaptive operation under all operating conditions and improving the equipment's scenario adaptability.

[0072] In a specific embodiment, when executing step S400, the specific process of transferring the power of the idle phase to the heavily loaded phase when the photovoltaic-storage inverter 20 is in a weak source load condition is as follows: S410: Based on the power demand of the single-phase load 50 and the power output of the three-phase power grid 30 after allocation, generate the AC side power reference for each phase inverter arm.

[0073] Specifically, for the heavily loaded phase, the AC power reference is the difference between the load power and the power drawn from the grid; for the idle phase, the AC power reference is the negative power drawn from the grid, representing the power absorbed from the grid.

[0074] S420: Controls the idle phase inverter arm to operate in rectification mode, and simultaneously controls the heavy-load phase to operate in inverter mode.

[0075] S430: The power absorbed by the idle phase from the three-phase grid 30 and the internal available power are aggregated on the shared DC bus and then output to the single-phase load 50 through the inverter arm of the heavily loaded phase.

[0076] In a specific example, such as Figure 3As shown, assuming the single-phase load 50 requires 9kW of power and has 0kW of internal available power, the single-phase power drawn by the three-phase grid 30 after power gap equalization is 3kW. For the heavily loaded phase, its AC side power reference is 6kW, and for the idle phase, its AC side power reference is -3kW. At this time, the controller of the photovoltaic-storage inverter 20 can control the heavily loaded phase to operate in inverter mode, outputting 6kW; at the same time, it can control the idle phase to operate in rectification mode, each absorbing 3kW of power from the grid and feeding it back to the DC bus. The DC bus aggregates the 6kW fed back from the idle phase with the 0kW of internal available power and supplies it to the heavily loaded phase to output 6kW. Combined with the 3kW drawn from the grid by the heavily loaded phase, this provides a total of 9kW power to the single-phase load 50.

[0077] It is understood that this embodiment, by clearly defining the generation method of the AC side power reference for each phase arm and the rectification / inverter state control, enables the cross-phase power mutual assistance logic under weak source load conditions to be directly embedded into the existing three-phase photovoltaic-storage inverter 20 control software. Without adding additional hardware, it can achieve the directional transfer of grid power from idle phases to heavily loaded phases, improve equipment resource utilization, and maintain stable power supply to single-phase loads and balanced three-phase grid power intake under weak source load conditions.

[0078] It is important to note that during the actual operation of the photovoltaic-storage inverter 20, the current margin, junction temperature margin, and DC bus voltage margin of each phase inverter arm are not entirely the same. Simply sharing the power deficit may lead to overcurrent or overtemperature in a certain idle phase arm. Therefore, in the technical solution of this application, power transfer limiting and redistribution need to be performed under equipment safety constraints. For ease of understanding, this will be described in detail below.

[0079] In a specific embodiment, when performing step S400, the specific process of supplying power to the single-phase load 50 under the device safety constraints is as follows: S401: Determine the transferable power margin of each phase based on the equipment safety boundary of each phase inverter arm.

[0080] Specifically, equipment safety constraints include phase current constraints, power device junction temperature constraints, cumulative thermal damage constraints, DC bus voltage constraints, equipment temperature constraints, and grid capacity constraints. The corresponding equipment safety boundaries are the maximum phase current, the maximum junction temperature of the power device, the upper limit of cumulative thermal damage, the upper and lower limits of the DC bus voltage, the upper limit of the equipment temperature, and the upper limit of the grid capacity, respectively. Based on the boundary values ​​given for each constraint, the maximum transferable power margin corresponding to each constraint can be calculated. The specific calculation process is well known to those skilled in the art and will not be described in detail here. The minimum value among the maximum transferable power margins corresponding to all constraint items is taken as the transferable power margin.

[0081] S402: Generates the initial cross-phase transfer power command for the idle phase based on the power gap.

[0082] Specifically, the initial cross-phase transfer power command is the ratio of the power gap to the number of idle phases.

[0083] S403: When the initial interphase transfer power command of an idle phase exceeds the transferable power margin of that phase, the phase is limited to obtain the limited interphase transfer power command and the unmet power.

[0084] S404: Distribute unmet power to the remaining idle phases until the power gap is met or all idle phase inverter arms reach their equipment safety boundaries.

[0085] In a specific example, the power deficit can be set to 4kW, with one idle phase having a transferable power margin of 1.5kW and the other idle phase having a transferable power margin of 2.2kW. The initial cross-phase transfer power command for both idle phases is 2kW. Since the initial cross-phase transfer power command for one idle phase exceeds its transferable power margin, this phase needs to be limited. The limited cross-phase transfer power command is 1.5kW, corresponding to a shortfall of 0.5kW. At this point, the other idle phase still has a remaining transferable power margin of 0.2kW, which can transfer the shortfall to this idle phase, bringing its cross-phase power to the safety boundary of 2.2kW, preventing further transfer. For the remaining 0.3kW of shortfall, the controller can either control the heavily loaded phase for a short-term overload or reduce the load on a single phase, depending on the actual needs.

[0086] It is understood that this embodiment calculates the transferable power margin of each phase and limits and redistributes the initial interphase transfer power command to ensure that the interphase power exchange process is always within the equipment safety boundary. This not only makes full use of the idle phase redundancy resources, but also avoids inverter arm overcurrent, overtemperature, or DC bus voltage exceeding the limit due to power transfer, thereby improving the safety and reliability of equipment operation under weak source load conditions.

[0087] It is important to understand that during the actual operation of the photovoltaic-storage inverter 20, the grid imbalance, equipment load rate, internal power margin, and thermal margin of the heavily loaded phase are constantly changing. If cross-phase power transfer is directly performed throughout the entire weak-source load condition, it may lead to unnecessary power scheduling or increased equipment stress. Therefore, the technical solution of this application can adopt different levels of control strategies according to the actual situation of the weak-source load condition. For ease of understanding, a detailed description will follow.

[0088] In a specific embodiment, the specific process of power regulation of the heavily loaded phase under weak source load conditions is as follows: (1) Based on the real-time current, power demand and junction temperature of the heavy-load phase, and combined with the available internal power, calculate the grid imbalance, equipment load rate, internal power margin and thermal margin respectively.

[0089] It should be noted that the specific calculation process for grid imbalance, equipment load rate, internal power margin and thermal margin is well known to those skilled in the art, and therefore will not be elaborated in detail here.

[0090] (2) Based on the normalized power grid imbalance, equipment load rate, internal power margin and heat margin, construct a comprehensive classification index.

[0091] It should be understood that the normalization of grid imbalance, equipment load rate, internal power margin, and heat margin can be calculated by comparing each of these parameters to its corresponding upper limit value. The expression for calculating the comprehensive grading index S is as follows: ; In the formula, , , , These represent the normalized grid imbalance, equipment load factor, internal power margin, and thermal margin, respectively. , , , These represent the weighting coefficients for each item. The specific values ​​can be selected by those skilled in the art based on their actual needs, for example... , , , .

[0092] (3.1) When the comprehensive classification index is less than the first boundary threshold, power transfer is not performed on the idle phase.

[0093] Specifically, when the comprehensive classification index is less than the first boundary threshold, it indicates that the grid imbalance is low, the equipment load rate is low, the internal margin is sufficient, and the thermal margin is sufficient. At this time, there is no need to perform interphase power transfer, and each phase inverter arm only maintains the small current required for grid synchronization.

[0094] (3.2) When the comprehensive classification index is between the first boundary threshold and the second boundary threshold, the heavy-load phase is compensated by reactive power and / or active power.

[0095] Specifically, when the comprehensive grading index is between the first and second boundary thresholds, it indicates a slight imbalance in the power grid or a slightly high load rate, but sufficient equipment stress. In this case, voltage compensation for the heavily loaded phases is preferentially achieved by injecting reactive current; only when the reactive compensation capacity is insufficient is a small amount of active current introduced, with the upper limit of the active current constrained by no-load losses or low losses.

[0096] (3.3) When the comprehensive classification index is between the second boundary threshold and the third boundary threshold, control the idle phase to perform power transfer.

[0097] Specifically, when the comprehensive classification index is between the second boundary threshold and the third boundary threshold, it indicates that the power grid imbalance is obvious, the load rate is high, or the internal margin is insufficient. At this time, the idle phase can be controlled to perform power transfer in accordance with the above-mentioned content, which will not be repeated here.

[0098] (3.4) When the comprehensive classification index is greater than the third boundary threshold, while controlling the idle phase to perform power transfer, the short-term overload capacity of the heavy-load phase is called.

[0099] Specifically, when the comprehensive classification index is greater than the third boundary threshold, it indicates that the power grid is seriously unbalanced, or the load rate is close to the rated value, or the internal source is seriously insufficient, or the thermal margin is tight but the protection is not triggered. At this time, within the equipment safety boundary, the heavily loaded phase can be allowed to undergo short-term overload to maximize the power supply capacity of a single-phase load.

[0100] (3.5) When the thermal margin exceeds the constraint value, control the idle phase to exit power transfer and unload or unload the heavy-load phase.

[0101] Specifically, when the thermal margin exceeds the constraint value, the thermal constraint is triggered, or the inverter protection state is triggered, or the load power exceeds the equipment's safe upper limit. At this time, the idle phase needs to exit power transfer first to reduce thermal stress, while controlling the single-phase load 50 to partially unload or reduce load according to load priority. After the thermal margin of the idle phase is reduced to a safe value, it is then controlled to perform power transfer after load reduction or unloading.

[0102] It is understandable that this embodiment constructs a comprehensive hierarchical index S to integrate grid imbalance, equipment load rate, internal power margin, and thermal margin into the control decision, thereby achieving hierarchical execution of power control for heavily loaded phases under weak source load conditions. This avoids unnecessary power transfer during mild imbalances and promptly utilizes idle phase redundancy resources and short-term overload capacity during severe imbalances, balancing grid management effectiveness, load power supply reliability, and equipment operational safety.

[0103] It is important to understand that during the actual operation of the photovoltaic-storage inverter 20, its internal available power and load power will continuously change. This necessitates the inverter 20 to switch between weak-source load conditions and active load conditions. Direct switching could lead to frequent control mode jumps and power surges. Therefore, the technical solution of this application provides a method for balancing operating conditions, which will be described in detail below for ease of understanding.

[0104] In a specific embodiment, the process of switching the photovoltaic-storage inverter 20 between active load mode and weak load mode is as follows: (1) A pre-switching phase is set where the internal power margin ratio is between zero and the surplus threshold. During this phase, the energy supply ratio coefficient is calculated based on the difference between the surplus threshold and the internal power margin ratio. The specific calculation expression is as follows: .

[0105] In the formula, K represents the energy supply ratio coefficient. Indicates the abundance threshold, This indicates the internal power margin ratio.

[0106] (2) Calculate the total power consumption of the three-phase power grid 30 by multiplying the power consumption ratio coefficient with the power demand of the single-phase load 50, and distribute the total power consumption evenly to the three-phase power grid 30.

[0107] (3) When switching from active load condition to weak load condition, the switch is made to weak load condition after a pre-switching stage.

[0108] (4) When switching from weak source load condition to active load condition, if the internal power margin ratio is greater than or equal to the preset hysteresis threshold greater than zero, the photovoltaic-storage inverter 20 exits the weak source load condition and enters the pre-switching stage; if the internal power margin ratio is greater than or equal to the sum of the sufficiency threshold and the hysteresis threshold, the photovoltaic-storage inverter 20 exits the pre-switching stage and enters the active load condition.

[0109] It should be understood that the specific value of the hysteresis threshold can be set according to the actual needs of those skilled in the art, for example, the value can be 10% to 20% of the sufficiency threshold.

[0110] In a specific example, let the power margin threshold be 1 and the hysteresis threshold be 0.2. If the load's power demand is 9kW, and the internal power margin ratio of the photovoltaic-storage inverter 20 is 0.8, it is in the pre-switching stage. Calculate the power supply ratio coefficient K = (1-0.8) / 1 = 0.2. Then, the total power taken from the three-phase grid 30 is 9 × 0.2 = 1.8kW, that is, each phase of the three-phase grid 30 takes 0.6kW. At this time, the internal power source can provide 7.2kW of surplus power to the single-phase load 50.

[0111] When the internal power margin ratio drops below 0, it enters the weak-source load mode, at which point the power demand of the single-phase load 50 is entirely supplied by the three-phase grid 30. When the internal power margin ratio increases to 0.1, since it is less than the hysteresis threshold, the photovoltaic-storage inverter 20 is still in the weak-source load mode. When the internal power margin ratio increases again to above 0.2, since it is greater than the hysteresis threshold, the photovoltaic-storage inverter 20 can enter the pre-switching stage and partially draw power from the three-phase grid 30. When the internal power margin ratio increases again to above 1.2, the photovoltaic-storage inverter 20 exits the pre-switching stage and enters the active load mode, at which point it supplies power to the single-phase load 50 entirely through internal power.

[0112] Understandably, this embodiment, by setting a pre-switching phase and a hysteresis threshold, enables the photovoltaic-storage inverter 20 to smoothly transition between active and weak source loads, avoiding frequent control mode switching and power surges caused by fluctuations in internal power. Simultaneously, during the pre-switching phase, power is supplied jointly by the internal source and the grid, fully utilizing the internal power while ensuring the continuity of power supply to the load, thus improving system operational stability and adaptability to different operating conditions.

[0113] It is important to understand that the imbalance control function of traditional inverters typically relies on local load power consumption as a prerequisite for activation. When the equipment is in idle standby mode, the control function is dormant and cannot participate in grid management. However, low-voltage distribution areas generally suffer from inherent three-phase imbalances due to uneven line impedance and inconsistent upstream load distribution. This makes it impossible for traditional methods to perform three-phase imbalance correction when the photovoltaic-storage inverter 20 is in idle standby mode. Therefore, the technical solution of this application provides a method for grid management under passive no-load conditions, which will be described in detail below for ease of understanding.

[0114] In a specific embodiment, the specific process of performing no-load static correction under passive no-load conditions is as follows: (1) In the no-load standby state of the photovoltaic-storage inverter 20, the small current at the grid connection point is obtained as the excitation current.

[0115] It should be noted that, under no-load standby conditions, the small current source at the grid connection point of the photovoltaic-storage inverter 20 mainly consists of: the small amount of active current required for the photovoltaic-storage inverter 20 to maintain synchronization with the grid, which is usually 0.5% to 2% of the rated current; under no-load conditions, the photovoltaic-storage inverter 20 can output a small amount of reactive current for voltage support or parameter identification, which is usually 1% to 5% of the rated current.

[0116] (2) Based on the obtained excitation current, construct the grid connection point voltage equation for the upstream background voltage, excitation current and line impedance.

[0117] It should be noted that upstream background voltage refers to the voltage of the upstream equivalent voltage source of the power grid, and line impedance refers to the line impedance from the grid connection point to the upstream equivalent voltage source.

[0118] Specifically, the expression for the grid connection point voltage equation is: .

[0119] In the formula, This represents the voltage of phase i at the grid connection point at time t. This represents the upstream background voltage at time t. This represents the line equivalent impedance of phase i. This represents the excitation current at time t.

[0120] (3) The voltage equation at the grid connection point is converted into a linear regression form, and the relevant parameters are identified online using the recursive least squares algorithm to obtain the line impedance and upstream background voltage of each phase.

[0121] Specifically, the linear regression form of the grid connection point voltage equation is expressed as follows: .

[0122] ; .

[0123] In the formula, This represents the regression vector at time t. This represents the vector of parameters to be identified. This represents the measurement noise and model error at time t. and Let represent the d-axis and q-axis components of the excitation current at time t, respectively. This represents the equivalent resistance of phase i. This represents the equivalent reactance of the i-phase line.

[0124] Online identification using recursive least squares method The specific identification process is well known to those skilled in the art, and therefore will not be described in detail here.

[0125] (4) Calculate the absolute value of the difference between the upstream background voltage of each phase and the average upstream background voltage, and use the ratio of the maximum absolute value of the difference to the average upstream background voltage as the static imbalance index.

[0126] (5) Calculate the absolute value of the difference between the voltage of each phase at the grid connection point and the corresponding upstream background voltage, and use the ratio of the maximum absolute value of the difference to the average upstream background voltage as the dynamic imbalance index.

[0127] (6) Voltage compensation and imbalance correction of the offset phase are performed only when the static imbalance index is greater than or equal to the preset static imbalance threshold and the dynamic imbalance index is less than the preset dynamic imbalance threshold. When the dynamic imbalance index is greater than or equal to the dynamic imbalance threshold, it is determined to be a dynamic imbalance caused by upstream load fluctuations, and compensation is not triggered temporarily.

[0128] It should be understood that the specific values ​​of the static imbalance threshold and the dynamic imbalance threshold can be set according to the actual needs of those skilled in the art. For example, the value range of the static imbalance threshold can be 0.3% to 0.5%, and the value range of the dynamic imbalance threshold can be 1% to 3%.

[0129] Understandably, this embodiment injects a small excitation current during no-load standby, utilizes a recursive least squares algorithm to identify line impedance and upstream background voltage online, and distinguishes between static and dynamic imbalances, performing only minor compensation for inherent imbalances. Thus, the photovoltaic-storage inverter 20 can participate in grid power quality management even during no-load standby, eliminating the blind spot where traditional equipment cannot manage grid imbalances during no-load periods, achieving all-weather grid management, and avoiding erroneous compensation for dynamic imbalances caused by upstream load fluctuations, thereby improving compensation accuracy and grid adaptability.

[0130] Another aspect of this application provides a computer-readable storage medium, in a preferred embodiment of which a computer program is stored on the storage medium; when the computer program is executed by a processor, the above-described photovoltaic-storage inverter control method is implemented.

[0131] Another aspect of this application provides an electronic device, in a preferred embodiment of which includes a processor and a memory; the memory is used to store a computer program, and the processor is used to execute the computer program to implement the above-described photovoltaic-storage inverter control method.

[0132] The basic principles, main features, and advantages of this application have been described above. Those skilled in the art should understand that this application is not limited to the above embodiments. The embodiments and descriptions in the specification are merely the principles of this application. Various changes and modifications can be made to this application without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claims. The scope of protection claimed by this application is defined by the appended claims and their equivalents.

Claims

1. A method for controlling a photovoltaic-storage inverter, characterized in that, Includes the following steps: Collect operating data from the photovoltaic-storage inverter to identify the current operating condition; When the photovoltaic-storage inverter is identified as being in a weak load condition with insufficient or no internal support and a local single-phase load, the power gap between the power demand of the single-phase load and the available internal power is determined. Decouple the load power consumption from the grid power supply and distribute the power gap evenly to the three-phase grid; Under equipment safety constraints, the grid power and / or inverter arm redundant power of the idle phase are aggregated and transferred to the heavily loaded phase carrying the single-phase load.

2. The photovoltaic-storage inverter control method as described in claim 1, characterized in that, The specific process of aggregating the grid power and / or inverter arm redundant power of the idle phase and transferring it to the heavily loaded phase carrying a single-phase load is as follows: Based on the power demand of the single-phase load and the power taken from the three-phase power grid after distribution, the AC side power reference of each phase inverter arm is generated. The inverter arm of the idle phase is controlled to operate in rectification mode, while the heavily loaded phase is controlled to operate in inverter mode. The power absorbed by the idle phase from the three-phase grid and the internal available power are aggregated on the shared DC bus and then output to the single-phase load through the inverter arm of the heavily loaded phase.

3. The photovoltaic-storage inverter control method as described in claim 1, characterized in that, The specific process of supplying power to a single-phase load under equipment safety constraints is as follows: The transferable power margin of each phase is determined based on the equipment safety boundary of each phase inverter arm; The initial cross-phase transfer power command for the idle phase is generated based on the power gap; When the initial cross-phase transfer power command of an idle phase exceeds the transferable power margin of that phase, the phase is limited to obtain the limited cross-phase transfer power command and the unmet power. Unmet power is redistributed to the remaining idle phases until the power gap is met or all idle phase inverter arms reach their equipment safety boundaries.

4. The photovoltaic-storage inverter control method as described in claim 3, characterized in that, Equipment safety constraints include phase current constraints, power device junction temperature constraints, cumulative thermal damage constraints, DC bus voltage constraints, equipment temperature constraints, and grid capacity constraints. Calculate the maximum transferable power margin for each constraint term based on the boundary value given for each constraint term. The minimum value among the maximum transferable power margins corresponding to all constraint terms is taken as the transferable power margin.

5. The photovoltaic-storage inverter control method as described in claim 1, characterized in that, The specific process of power regulation of the heavily loaded phase under weak source load conditions is as follows: Based on the real-time current, power demand, and junction temperature of the heavily loaded phase, and combined with the available internal power, the grid imbalance, equipment load rate, internal power margin, and thermal margin are calculated respectively. A comprehensive classification index is constructed based on the normalized grid imbalance, equipment load rate, internal power margin, and thermal margin; when the comprehensive classification index is less than the first boundary threshold, power transfer is not performed on the idle phase. When the comprehensive classification index is between the first boundary threshold and the second boundary threshold, the heavy-load phase is compensated by reactive power and / or active power. When the comprehensive classification index is between the second boundary threshold and the third boundary threshold, control the idle phase to perform power transfer; When the comprehensive classification index is greater than the third boundary threshold, while controlling the idle phase to perform power transfer, the short-term overload capacity of the heavily loaded phase is activated. When the thermal margin exceeds the constraint value, the idle phase is controlled to exit power transfer and the heavily loaded phase is deloaded or unloaded. The formula for calculating the comprehensive grading index S is as follows: ； In the formula, , , , These represent the normalized grid imbalance, equipment load factor, internal power margin, and thermal margin, respectively. , , , These represent the weight coefficients for each item.

6. The photovoltaic-storage inverter control method according to any one of claims 1-5, characterized in that, The operating conditions of the photovoltaic-storage inverter also include the active load operating condition with sufficient internal power and a locally connected single-phase load, and the passive no-load operating condition with no internal power and no load; the process of identifying each operating condition of the photovoltaic-storage inverter is as follows: Acquire photovoltaic power output status, remaining energy storage capacity, load operating conditions, and equipment operating stress; The photovoltaic output status is converted into photovoltaic available power, the remaining energy storage capacity is converted into energy storage available discharge power, the equipment operating stress is converted into equipment stress derating factor, and the internal available power is generated by merging the photovoltaic available power, energy storage available discharge power and equipment stress derating factor; the load operating condition is converted into load equivalent power. Calculate the internal power margin ratio based on the ratio of the difference between the internal available power and the load equivalent power. Set load presence threshold, internal availability threshold, and abundance threshold; When the equivalent power of the load is less than the load existence threshold and the internal available power is less than the internal availability threshold, it is determined to be a passive no-load condition, and no-load static correction is performed. When the equivalent power of the load is greater than or equal to the load existence threshold, the available power of the internal source is greater than or equal to the internal source availability threshold, and the internal source power margin ratio is greater than or equal to the surplus threshold, it is determined to be an active load condition, and the internal source directly supplies power to the single-phase load. When the equivalent power of the load is greater than or equal to the load existence threshold, and the available internal power is less than the internal availability threshold or the internal power margin ratio is less than zero, it is determined to be a weak source load condition.

7. The photovoltaic-storage inverter control method as described in claim 6, characterized in that, The process of switching between active load and weak load conditions for photovoltaic-storage inverters is as follows: A pre-switching phase is set where the internal power margin ratio is between zero and the sufficient threshold. During this phase, the energy supply ratio coefficient is calculated by the ratio of the difference between the sufficient threshold and the internal power margin ratio. The total power output of the three-phase power grid is calculated by multiplying the power supply ratio coefficient with the power demand of the single-phase load, and the total power output is evenly distributed to the three-phase power grid. When switching from active load condition to weak load condition, the switch to weak load condition is performed after a pre-switching phase. When switching from weak source load mode to active load mode, if the internal power margin ratio is greater than or equal to the preset hysteresis threshold greater than zero, the photovoltaic-storage inverter exits the weak source load mode and enters the pre-switching stage; if the internal power margin ratio is greater than or equal to the sum of the sufficiency threshold and the hysteresis threshold, the photovoltaic-storage inverter exits the pre-switching stage and enters the active load mode.

8. The photovoltaic-storage inverter control method as described in claim 6, characterized in that, The specific process of performing static correction under passive no-load conditions is as follows: In the no-load standby state of the photovoltaic-storage inverter, the small current at the grid connection point is obtained as the excitation current. Based on the obtained excitation current, construct the grid connection point voltage equation regarding the upstream background voltage, excitation current, and line impedance; The grid connection point voltage equation is converted into a linear regression form, and the relevant parameters are identified online using a recursive least squares algorithm to obtain the line impedance and upstream background voltage of each phase. Calculate the absolute value of the difference between the upstream background voltage of each phase and the average upstream background voltage, and use the ratio of the maximum absolute value of the difference to the average upstream background voltage as the static imbalance index. Calculate the absolute value of the difference between the voltage of each phase at the grid connection point and the corresponding upstream background voltage, and use the ratio of the maximum absolute value of the difference to the average upstream background voltage as a dynamic imbalance index. Voltage compensation and imbalance correction for the offset phase are performed only when the static imbalance index is greater than or equal to the preset static imbalance threshold and the dynamic imbalance index is less than the preset dynamic imbalance threshold. When the dynamic imbalance index is greater than or equal to the dynamic imbalance threshold, it is determined to be a dynamic imbalance caused by upstream load fluctuations, and compensation is not triggered temporarily.

9. An electronic device, characterized in that, It includes a processor and a memory; the memory is used to store a computer program, and the processor is used to execute the computer program to implement the photovoltaic-storage inverter control method as described in any one of claims 1-8.

10. A computer-readable storage medium, characterized in that, The storage medium stores a computer program; when the computer program is executed by a processor, it implements the photovoltaic-storage inverter control method as described in any one of claims 1-8.

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