Grid-connected converter and switching method and device of grid following control mode and grid construction control mode of grid-connected converter

Abstract

The invention provides a grid-connected converter and a switching method and device for a grid following control mode and a grid construction control mode thereof, and the method comprises the steps: obtaining a power grid voltage and a power grid state parameter in each control period; when the power grid voltage deviates from the steady-state setting, determining the state characteristics of the power grid according to the power grid state parameters; determining a target switching mode according to the state characteristics; switching a control mode of a target power module in the plurality of power modules according to the target switching mode; wherein the plurality of power modules are connected in parallel and belong to the same grid-connected converter, or each power module belongs to different converters; the target switching mode is switching from the network following type control to the network construction type control or switching from the network construction type control to the network following type control. In the switching method provided by the invention, the converter adaptively adjusts the control mode of the governed power module, so that the converter is easier to adapt to a complex and changeable power grid.

Description

Technical Field

[0001] This invention relates to the field of converter control technology, and in particular to a grid-connected converter and a method and apparatus for switching between grid-connected and grid-connected control modes. Background Technology

[0002] With the development of new energy power generation technologies, represented by wind power, the capacity of a single wind turbine unit is getting larger and larger. In order to meet the ever-increasing capacity demand and improve the reliability and flexibility of the system, the converter often needs to adopt a topology structure of parallel power modules and multiple units in parallel.

[0003] Currently, most new energy sources and their supporting converters are grid-connected controlled. Grid-connected power systems rely on the stable operation of the main power grid, with voltage and frequency determined by the grid, lacking independent regulation capabilities. As their proportion increases, the power grid faces problems such as insufficient system inertia support, low short-circuit ratios, and weak disturbance rejection capabilities, leading to grid-connected stability issues like wideband oscillations, which have constrained the further large-scale development of new energy. Grid-connected control converters, on the other hand, can give new energy units strong adaptability to weak grids, effectively improving grid inertia damping characteristics and actively providing voltage and frequency support to the system. However, under strong grid conditions, grid impedance fluctuations may cause oscillations or power control instability, affecting operational reliability. Summary of the Invention

[0004] This invention provides a grid-connected converter and a method and apparatus for switching its grid-connected and grid-connected control modes. The converter adaptively adjusts the control mode of the power modules under its jurisdiction, making it easier for the converter to adapt to complex and ever-changing power grid environments and operational requirements, thereby improving the stability, adaptability and support capabilities of new energy units connected to the grid.

[0005] According to a first aspect of the present invention, a method for switching between grid-connected and grid-connected control modes of a grid-connected converter is provided. The grid-connected converter includes a power module, and the switching method includes:

[0006] In each control cycle, acquire grid voltage and grid state parameters;

[0007] When the grid voltage deviates from the steady-state setting, the grid state characteristics are determined based on the grid state parameters;

[0008] Based on the state characteristics, determine the target switching method; the target switching method is to switch from network-following control to network-building control, or from network-building control to network-following control.

[0009] The control mode of the target power module among multiple power modules is switched according to the target switching method; multiple power modules are connected in parallel and belong to the same grid-connected converter, or each power module belongs to a different converter, and the control mode of each power module is either grid-connected control or grid-connected control.

[0010] In one possible implementation, the grid state parameters include one or more of the voltage harmonic content or voltage imbalance, as well as grid strength and power angle; the state characteristics include the corresponding indicators for each grid state parameter.

[0011] Based on the power grid state parameters, determine the state characteristics of the power grid, including:

[0012] When the grid strength is lower than the set threshold range corresponding to the weak grid, the corresponding weak grid flag in the state characteristics is set to 1; when the grid strength is lower than the set threshold range corresponding to the weak grid, the corresponding weak grid flag in the state characteristics is set to 0; when the grid strength is within the set threshold range corresponding to the weak grid, the corresponding weak grid flag in the state characteristics remains unchanged.

[0013] When the power angle is higher than the power angle set threshold range, the corresponding power angle large flag in the state feature is set to 1; when the power angle is lower than the power angle set threshold range, the corresponding power angle large flag in the state feature is set to 0; when the power angle is within the power angle set threshold range, the corresponding power angle large flag in the state feature remains unchanged.

[0014] If the power grid status parameters include voltage harmonic content, when the voltage harmonic content is higher than the set threshold range, the corresponding harmonic content high flag in the status characteristics is set to 1; when the voltage harmonic content is lower than the set threshold range, the corresponding harmonic content high flag in the status characteristics is set to 0; when the voltage harmonic content is within the set threshold range, the corresponding harmonic content high flag in the status characteristics remains unchanged.

[0015] If the grid state parameters include voltage imbalance, when the voltage imbalance is higher than the voltage imbalance set threshold range, the corresponding high imbalance flag in the state characteristics is set to 1; when the voltage imbalance is lower than the voltage imbalance set threshold range, the corresponding high imbalance flag in the state characteristics is set to 0; when the voltage imbalance is within the voltage imbalance set threshold range, the corresponding high imbalance flag in the state characteristics remains unchanged.

[0016] In one possible implementation, the target switching method is determined based on state characteristics, including:

[0017] When the power grid weak flag or power angle large flag in the status characteristics is 1, and the status characteristics also include at least one other flag that is 1, the target switching mode is determined to be switching from grid-following control to grid-building control.

[0018] When at least two power modules are currently in grid-based control mode, if the weak grid flag and large power angle flag in the state characteristics are both 0, and the state characteristics also include at least one flag that is 0, then the target switching mode is determined to be switching from grid-based control to grid-following control.

[0019] In one possible implementation, the control mode of the target power module among multiple power modules is switched according to the target switching method, including:

[0020] When the number of candidate power modules currently using grid-based control is 1 among multiple power modules, the candidate power module is determined as the target power module; the control mode of the target power module is switched to grid-based control.

[0021] When the number of candidate power modules currently using grid-based control is greater than 1, the power module with smaller active power and / or smaller operating current among the candidate power modules is identified as the target power module; the control mode of the target power module is switched to grid-based control.

[0022] When the number of candidate power modules currently using grid-type control is greater than 1 among multiple power modules, the power module with larger active power and / or larger operating current among the candidate power modules is determined as the target power module; the control mode of the target power module is switched to grid-type control.

[0023] In one possible implementation, grid strength is represented by the grid short-circuit ratio and / or the penetration rate of new energy sources;

[0024] When the grid strength is below the set threshold range corresponding to a weak grid, the grid weakness flag in the state characteristics is set to 1; when the grid strength is above the set threshold range corresponding to a weak grid, the corresponding grid weakness flag in the state characteristics is set to 0; when the grid strength is within the set threshold range corresponding to a weak grid, the corresponding grid weakness flag in the state characteristics remains unchanged, including:

[0025] If the grid strength is represented by the grid short-circuit ratio, then when the grid short-circuit ratio is lower than the short-circuit ratio set threshold range corresponding to the weak grid, the grid weak flag in the state characteristics is set to 1; when the grid short-circuit ratio is higher than the short-circuit ratio set threshold range corresponding to the weak grid, the corresponding grid weak flag in the state characteristics is set to 0; when the grid short-circuit ratio is within the set threshold range corresponding to the weak grid, the corresponding grid weak flag in the state characteristics remains unchanged.

[0026] If the grid strength is represented by the penetration rate of new energy sources, then when the penetration rate of new energy sources is higher than the threshold range of the penetration rate corresponding to the weak grid, the grid weakness flag in the state characteristics is set to 1; when the penetration rate of new energy sources is lower than the threshold range of the penetration rate corresponding to the weak grid, the corresponding grid weakness flag in the state characteristics is set to 0; when the penetration rate of new energy sources is within the threshold range of the penetration rate corresponding to the weak grid, the corresponding grid weakness flag in the state characteristics remains unchanged.

[0027] If grid strength is represented by the grid short-circuit ratio and the penetration rate of new energy sources, then when the grid short-circuit ratio is lower than the short-circuit ratio threshold range corresponding to a weak grid, and / or the penetration rate of new energy sources is higher than the penetration rate threshold range corresponding to a weak grid, the grid weakness flag in the state characteristics is set to 1; when the grid short-circuit ratio is higher than the short-circuit ratio threshold range corresponding to a weak grid, and the penetration rate of new energy sources is lower than the penetration rate threshold range corresponding to a weak grid, the grid weakness flag in the state characteristics is set to 0; when the grid short-circuit ratio is within the short-circuit ratio threshold range corresponding to a weak grid, and the penetration rate of new energy sources is within the penetration rate threshold range corresponding to a weak grid, the grid weakness flag in the state characteristics remains unchanged.

[0028] In one possible implementation, the power command for each power module is P. iref =k Pi P ref Where i = 1, 2, ..., n; n is the number of power modules, and the weighting coefficient k Pi ∈(0,1), P ref This is the total active power command for the converter;

[0029] The reactive power command for each power module is Q. iref =k Qi Q ref Where i = 1, 2, ..., n; n is the number of power modules, and the weighting coefficient k Qi ∈(0,1), Q ref This is the total reactive power command for multiple power modules.

[0030] In one possible implementation, the total active power command of the multiple power modules is P. ref =P set +k fdrop (ω0-ω g ), where P set To set the active power command, k fdrop ω is the primary frequency regulation coefficient, ω0 is the rated frequency of the power grid, ω g This refers to the actual frequency of the power grid.

[0031] The total reactive power command for multiple power modules is Q. ref=Q set +k udrop (U ref -U pcc ), where Q set To set the reactive power command, k udrop U is the droop coefficient. ref For the converter grid connection point voltage command, U pcc This represents the voltage amplitude at the grid connection point.

[0032] According to a second aspect of the present invention, a switching device for grid-connected converter control modes of grid connection and grid construction is provided, applied to a grid-connected converter, the grid-connected converter including a power module, the switching device comprising:

[0033] The acquisition module is used to acquire grid voltage and grid status parameters in each control cycle;

[0034] The determination module is used to determine the state characteristics of the power grid based on the power grid state parameters when the power grid voltage deviates from the steady-state setting; it is also used to determine the target switching mode based on the state characteristics; the target switching mode is to switch from grid-following control to grid-building control, or from grid-building control to grid-following control.

[0035] The switching module is used to switch the control mode of the target power module among multiple power modules according to the target switching method; the multiple power modules are connected in parallel and belong to the same grid-connected converter, or each power module belongs to a different converter, and the control mode of each power module is grid-following control or grid-connected control.

[0036] In one possible implementation, the grid state parameters include one or more of the voltage harmonic content or voltage imbalance, as well as grid strength and power angle; the state characteristics include the corresponding indicators for each grid state parameter.

[0037] The module is specifically used for:

[0038] When the grid strength is lower than the set threshold range corresponding to the weak grid, the corresponding weak grid flag in the state characteristics is set to 1; when the grid strength is lower than the set threshold range corresponding to the weak grid, the corresponding weak grid flag in the state characteristics is set to 0; when the grid strength is within the set threshold range corresponding to the weak grid, the corresponding weak grid flag in the state characteristics remains unchanged.

[0039] When the power angle is higher than the power angle set threshold range, the corresponding power angle large flag in the status feature is set to 1; when the power angle is lower than the power angle set threshold range, the corresponding power angle large flag in the status feature is set to 0; when the power angle is within the power angle set threshold range, the corresponding power angle large flag in the status feature remains unchanged.

[0040] If the power grid status parameters include voltage harmonic content, when the voltage harmonic content is higher than the set threshold range, the corresponding harmonic content high flag in the status characteristics is set to 1; when the voltage harmonic content is lower than the set threshold range, the corresponding harmonic content high flag in the status characteristics is set to 0; when the voltage harmonic content is within the set threshold range, the corresponding harmonic content high flag in the status characteristics remains unchanged.

[0041] If the grid state parameters include voltage imbalance, when the voltage imbalance is higher than the voltage imbalance set threshold range, the corresponding high imbalance flag in the state characteristics is set to 1; when the voltage imbalance is lower than the voltage imbalance set threshold range, the corresponding high imbalance flag in the state characteristics is set to 0; when the voltage imbalance is within the voltage imbalance set threshold range, the corresponding high imbalance flag in the state characteristics remains unchanged.

[0042] According to a third aspect of the present invention, a grid-connected converter is provided, the grid-connected converter including a control unit, the control unit being configured to execute a method for switching between grid-connected and grid-connected control modes of the grid-connected converter in the first aspect of the present invention or any possible implementation thereof.

[0043] This invention provides a method and apparatus for switching the grid-connected converter's control modes between grid-connected and grid-connected modes. For power modules in a grid-connected converter, when the grid voltage deviates from the steady-state setting, the grid's state characteristics are determined based on grid state parameters. A target switching mode is determined based on these grid state characteristics. The control mode of the target power module among multiple power modules is switched according to the target switching mode; that is, the target converter is switched from grid-connected control to grid-connected control, or vice versa. By adaptively adjusting the control mode of the power modules under its jurisdiction, the converter can more easily adapt to complex and variable grid environments and operational requirements, improving the stability, adaptability, and support of new energy units connected to the grid. Furthermore, multiple power modules can be connected in parallel, belonging to the same grid-connected converter, or each power module can belong to different converters. In other words, the method and apparatus provided by this invention are applicable to multiple parallel converters as well as converters including multiple parallel power modules, demonstrating broad applicability. Attached Figure Description

[0044] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0045] Figure 1A schematic diagram of a control mode switching system structure for multiple grid-connected converters connected in parallel, provided in an embodiment of the present invention;

[0046] Figure 2 This is a schematic diagram of a control mode switching system for a grid-connected converter with multiple power modules connected in parallel, provided by an embodiment of the present invention.

[0047] Figure 3 A schematic flowchart illustrating a method for switching between grid-connected converter control modes and grid-connected control modes provided in an embodiment of the present invention;

[0048] Figure 4 A schematic flowchart of another method for switching between grid-connected converter control modes and grid-connected control modes is provided for an embodiment of the present invention;

[0049] Figure 5 A schematic flowchart of another method for switching between grid-connected converter control modes and grid-connected control modes is provided for an embodiment of the present invention;

[0050] Figure 6 A schematic diagram of the control loop structure for determining the active power command of each power module in a method for switching between grid-connected converter and grid-connected control modes provided in an embodiment of the present invention.

[0051] Figure 7 A schematic diagram of the control loop structure for determining the reactive power command of each power module in a method for switching between grid-connected converter and grid-connected control modes provided in an embodiment of the present invention.

[0052] Figure 8 A schematic diagram of the control loop structure for determining the total active power command and total reactive power command of multiple power modules in a method for switching between grid-connected converter and grid-connected control modes provided in an embodiment of the present invention.

[0053] Figure 9 This is a schematic diagram of the structure of a switching device for grid-connected converter control modes of grid connection and grid construction provided in an embodiment of the present invention. Detailed Implementation

[0054] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0055] Converter: An electrical device that changes the voltage, frequency, number of phases, and other electrical quantities or characteristics of a power supply system. It includes rectifiers (AC to DC), inverters (DC to AC), AC converters, and DC converters. New energy power generation is connected to the grid via converters; grid-connected converters include generator-side converters and grid-side converters.

[0056] Voltage harmonic content: Voltage harmonic content refers to the proportion of each harmonic voltage to the fundamental voltage in a non-sinusoidal periodic AC voltage, usually expressed as a percentage or total harmonic distortion rate.

[0057] Voltage imbalance: Voltage imbalance refers to the degree of difference in the amplitude or phase of three-phase voltage in a power system, usually expressed as a percentage.

[0058] Power angle: is the phase angle at which the excitation electromotive force of a synchronous generator leads the terminal voltage. It is used to evaluate the stable operation and stability margin of the generator.

[0059] Short-circuit ratio: This refers to the system's short-circuit capacity divided by the equipment capacity. A high short-circuit ratio indicates that the equipment is connected to a strong system, meaning that switching the equipment on or off has a relatively small impact on the system. The short-circuit ratio is positively correlated with grid strength.

[0060] Renewable energy penetration rate: This represents the proportion of renewable energy generation in the total power generation of the power system, reflecting the capacity of renewable energy to support the power grid and its absorption level. The renewable energy penetration rate is negatively correlated with grid strength.

[0061] Example 1

[0062] This invention provides a system for switching between grid-connected and grid-connected control modes of a grid-connected converter. The system structure is as follows: Figure 1 As shown, the system includes a power grid, multiple power modules belonging to multiple grid-connected converters, a converter control unit, and a feeder side. The power grid and the feeder side are connected via a DC bus. The feeder side consists of an energy storage unit, a photovoltaic generator set, and / or a wind turbine generator set. The number of power modules is the same as the number of grid-connected converters. The generator-side converters of these multiple grid-connected converters are connected to the same energy storage unit or the same generator set. The converter control unit controls the control modes of power modules 1 to n based on grid state parameters.

[0063] This invention also provides another system for switching between grid-connected converter control modes of grid connection and grid construction, the system structure of which is as follows: Figure 2 As shown, the system includes a power grid, power modules 1 to n belonging to the same grid-connected converter, a converter control unit, and a power feeder side. The power grid and the power feeder side are connected via a DC bus. The power feeder side consists of an energy storage unit, a photovoltaic generator set, and / or a wind turbine generator set. The converter control unit controls the control modes of power modules 1 to n based on grid status parameters.

[0064] in:

[0065] u g : Power grid voltage;

[0066] Z g : Power grid impedance;

[0067] TS: Transformer;

[0068] i g : Mains current;

[0069] u o1 : The grid connection point voltage of the grid-connected converter to which power module 1 belongs;

[0070] u on : The grid connection point voltage of the grid-connected converter to which power module n belongs;

[0071] C f1 : AC filter capacitor of the grid-connected converter to which power module 1 belongs;

[0072] C fn : The AC filter capacitor of the grid-connected converter to which power module n belongs;

[0073] L pfc1 : The filter inductor of power module 1;

[0074] L pfcn : The filter inductor of power module n;

[0075] i L1 : Inductor current of power module 1;

[0076] i Ln : Inductor current of power module n;

[0077] e1: Output voltage of power module 1;

[0078] e n : Output voltage of power module n;

[0079] C dc DC-side capacitor;

[0080] C f : AC filter capacitor of grid-connected converter;

[0081] u o : Grid connection point voltage of the grid-connected converter.

[0082] This invention also provides a method for switching control modes of grid-connected and grid-connected converters, applicable to... Figure 1 and Figure 2 The converter control unit in the system shown is, for example Figure 3As shown, the following steps may be included:

[0083] S310 acquires grid voltage and grid status parameters in each control cycle.

[0084] The method provided in this invention can be used to control either a single grid-connected converter comprising multiple power modules or multiple grid-connected converters comprising a single power module. Multiple power modules can be connected in parallel and belong to the same grid-connected converter, or each power module can belong to a different converter.

[0085] In each control cycle, the grid voltage and grid status parameters are detected, or the grid voltage and grid status parameters detected by other devices are received.

[0086] S320 determines the state characteristics of the power grid based on the power grid state parameters when the grid voltage deviates from the steady-state setting.

[0087] The steady-state setting is based on the pre-defined voltage and frequency values ​​of the power grid when it is in a stable and healthy operating state. When the voltage amplitude and / or frequency deviate from the steady-state setting, the control mode of the power modules is switched. When the voltage amplitude and frequency do not deviate from the steady-state setting, the control mode of each power module remains unchanged.

[0088] State characteristics represent the operating state of the power grid.

[0089] S330 determines the target switching method based on the state characteristics.

[0090] Each power module is controlled in either grid-following or grid-building mode. The target switching method is to switch from grid-following control to grid-building control, or from grid-building control to grid-following control.

[0091] S340 switches the control mode of the target power module among multiple power modules according to the target switching method.

[0092] For multiple power modules, at least one power module whose control mode will be switched is identified. This at least one power module is designated as the target power module. The control mode of the target power module is switched from grid-following control to grid-building control, or vice versa, so that the power grid's operating state returns to a steady-state setting and adapts to the power grid's variable environment and operating requirements.

[0093] This invention provides a grid-connected converter and a method for switching its grid-following and grid-connecting control modes. When the grid voltage deviates from the steady-state setting, the grid state characteristics are determined based on grid state parameters. A target switching mode is determined based on these grid state characteristics. The control mode of the target power module among multiple power modules is switched according to the target switching mode; that is, the target converter is switched from grid-following control to grid-connecting control, or vice versa. By adaptively adjusting the control mode of the power modules under its jurisdiction, the converter can more easily adapt to complex and variable grid environments and operational requirements, improving the stability, adaptability, and support of new energy units connected to the grid. Moreover, multiple power modules can be connected in parallel, belonging to the same grid-connected converter, or each power module can belong to a different converter. In other words, the method and apparatus provided by this invention are applicable to multiple parallel converters as well as converters including multiple parallel power modules, demonstrating broad applicability.

[0094] Example 2

[0095] In one embodiment, the power grid state parameters include one or more of voltage harmonic content or voltage imbalance, as well as power grid strength and power angle; the state characteristics include the corresponding indicators for each power grid state parameter.

[0096] S310: In each control cycle, acquire grid voltage and grid status parameters.

[0097] Using existing parameter acquisition methods, obtain various parameters from the grid voltage and grid state parameters.

[0098] like Figure 4 As shown, when the amplitude and / or frequency of the grid voltage deviate from the steady-state setting, step S320 is executed; when the amplitude and frequency of the grid voltage do not deviate from the steady-state setting, the control mode of each power module remains unchanged.

[0099] S320: Determining the state characteristics of the power grid based on power grid state parameters may include the following steps:

[0100] S321, when the grid strength is lower than the set threshold range corresponding to the weak grid, set the corresponding weak grid flag in the state characteristics to 1; when the grid strength is higher than the set threshold range corresponding to the weak grid, set the corresponding weak grid flag in the state characteristics to 0; when the grid strength is within the set threshold range corresponding to the weak grid, keep the corresponding weak grid flag in the state characteristics unchanged.

[0101] A weak power grid indicator of 1 indicates a weak power grid; a weak power grid indicator of 0 indicates a strong power grid.

[0102] In one example, grid strength is represented by the grid short-circuit ratio and / or renewable energy penetration rate; S321: When the grid strength is lower than the set threshold range corresponding to a weak grid, the grid weakness flag in the state characteristics is set to 1; when the grid strength is higher than the set threshold range corresponding to a weak grid, the corresponding grid weakness flag in the state characteristics is set to 0; when the grid strength is within the set threshold range corresponding to a weak grid, the corresponding grid weakness flag in the state characteristics remains unchanged, including the following steps:

[0103] S3211, if the grid strength is represented by the grid short-circuit ratio, then when the grid short-circuit ratio is lower than the short-circuit ratio set threshold range corresponding to the weak grid, the grid weak flag in the state characteristics is set to 1; when the grid short-circuit ratio is higher than the short-circuit ratio set threshold range corresponding to the weak grid, the corresponding grid weak flag in the state characteristics is set to 0; when the grid short-circuit ratio is within the set threshold range corresponding to the weak grid, the corresponding grid weak flag in the state characteristics remains unchanged.

[0104] The short-circuit ratio setting threshold range is [K] 1L K 1H ], K 1L＜ K 1H When the power grid short-circuit ratio is less than K 1L When the grid is weak, set the corresponding grid weakness flag in the state characteristics to 1; when the grid short-circuit ratio is greater than K 1H When the grid is in a certain state, the corresponding grid weakness flag in the state characteristics is set to 0; when the grid short-circuit ratio is in [K], the corresponding grid weakness flag in the state characteristics is set to 0. 1L K 1H During this period, the corresponding weak grid flags in the state characteristics remain unchanged.

[0105] S3212, if the grid strength includes the penetration rate of new energy sources, then when the penetration rate of new energy sources is higher than the threshold range of the penetration rate corresponding to the weak grid, the grid weakness flag in the state characteristics is set to 1; when the penetration rate of new energy sources is lower than the threshold range of the penetration rate corresponding to the weak grid, the corresponding grid weakness flag in the state characteristics is set to 0; when the penetration rate of new energy sources is within the threshold range of the penetration rate corresponding to the weak grid, the corresponding grid weakness flag in the state characteristics remains unchanged.

[0106] The penetration rate threshold range is set to [K]. 2L K 2H ], K 2L＜ K 2H When the penetration rate of new energy is greater than K 2H When the power grid weakness flag in the state characteristics is set to 1, the corresponding flag will be set to 1; when the penetration rate of new energy sources is less than K... 1L When the power grid weakness flag in the state characteristics is set to 0, the corresponding flag in the state characteristics is set to 0; when the penetration rate of new energy sources is within [K... 2L K 2H During this period, the corresponding weak grid flags in the state characteristics remain unchanged.

[0107] S3213, if grid strength includes grid short-circuit ratio and renewable energy penetration rate, then when the grid short-circuit ratio is lower than the short-circuit ratio set threshold range corresponding to a weak grid, and / or the renewable energy penetration rate is higher than the penetration rate set threshold range corresponding to a weak grid, the grid weakness flag in the state characteristics is set to 1; when the grid short-circuit ratio is higher than the short-circuit ratio set threshold range corresponding to a weak grid, and the renewable energy penetration rate is lower than the penetration rate set threshold range corresponding to a weak grid, the grid weakness flag in the state characteristics is set to 0; when the grid short-circuit ratio is within the short-circuit ratio set threshold range corresponding to a weak grid, and the renewable energy penetration rate is within the penetration rate set threshold range corresponding to a weak grid, the grid weakness flag in the state characteristics remains unchanged.

[0108] S322, when the power angle is higher than the power angle set threshold range, set the corresponding power angle large flag in the status feature to 1; when the power angle is lower than the power angle set threshold range, set the corresponding power angle large flag in the status feature to 0; when the power angle is within the power angle set threshold range, keep the corresponding power angle large flag in the status feature unchanged.

[0109] A value of 1 indicates a large angle of attack, while a value of 0 indicates a small angle of attack.

[0110] The power angle setting threshold range is [K] 5L K 5H ], K 5L＜ K 5H When the angle of force is greater than K 5L When the power angle is large, set the corresponding power angle flag in the state characteristics to 1; when the power angle is less than K... 5H When the power angle is within [K], set the corresponding power angle flag in the state characteristics to 0; when the power angle is within [K], 5L K 5H During this period, the corresponding large power angle marker in the state characteristics remains unchanged.

[0111] S323, If the power grid status parameters include voltage harmonic content, when the voltage harmonic content is higher than the harmonic content set threshold range, the corresponding harmonic content high flag in the status characteristics is set to 1; when the voltage harmonic content is lower than the harmonic content set threshold range, the corresponding harmonic content high flag in the status characteristics is set to 0; when the voltage harmonic content is within the harmonic content set threshold range, the corresponding harmonic content high flag in the status characteristics remains unchanged.

[0112] A value of 1 indicates a high voltage harmonic content, while a value of 0 indicates a low voltage harmonic content.

[0113] The harmonic content threshold range is set to [K]. 3L K 3H ], K 3L＜ K 3H When the voltage harmonic content is greater than K 3LWhen the voltage harmonic content is less than K, the corresponding harmonic content flag in the state characteristics is set to 1; when the voltage harmonic content is less than K... 3H When the voltage harmonic content is within [K], the corresponding harmonic content flag in the state characteristics is set to 0; when the voltage harmonic content is within [K], the corresponding harmonic content flag in the state characteristics is set to 0. 3L K 3H When the voltage imbalance is within the set threshold range, the corresponding high harmonic content flag in the state characteristics remains unchanged. S324, If the grid state parameters include voltage imbalance, when the voltage imbalance is higher than the set threshold range, the corresponding high imbalance flag in the state characteristics is set to 1; when the voltage imbalance is lower than the set threshold range, the corresponding high imbalance flag in the state characteristics is set to 0; when the voltage imbalance is within the set threshold range, the corresponding high imbalance flag in the state characteristics remains unchanged.

[0114] A high imbalance indicator of 1 indicates a high voltage imbalance, while a high imbalance indicator of 0 indicates a low voltage imbalance.

[0115] The voltage imbalance setting threshold range is [K]. 4L K 4H ], K 4L＜ K 4H When the voltage imbalance is greater than K 4L When the voltage imbalance is less than K, set the corresponding high imbalance flag in the state characteristics to 1; 4H When the voltage imbalance is within [K], the corresponding high imbalance flag in the state characteristics is set to 0; when the voltage imbalance is within [K], the high imbalance flag in the state characteristics is set to 0. 4L K 4H Within a given timeframe, the corresponding high imbalance indicator in the state characteristics remains unchanged.

[0116] The threshold ranges for the weak power grid, harmonic content, voltage imbalance, and power angle are all set based on relevant regulations or actual needs.

[0117] The method for switching between grid-connected converter control modes and grid-connected control modes provided in this embodiment of the invention uses one or more of the following: voltage harmonic content, voltage imbalance, or power angle, as well as grid strength, to measure the operating status of the power grid, thereby reflecting the operating status of the power grid more accurately from multiple perspectives.

[0118] Example 3

[0119] In one embodiment, based on Embodiment 2, S330: Determining the target switching method according to the state characteristics may include the following steps:

[0120] S331, when the power grid weak flag or power angle large flag in the state characteristics is 1, and the state characteristics also include at least one flag that is 1, the target switching mode is determined to be switching from grid-following control to grid-building control.

[0121] If the grid state parameters include voltage harmonic content, voltage imbalance, power angle, and grid strength, such as Figure 5 As shown, if the power module's grid weakness flag is 1 or the power angle large flag is 1, and either the harmonic content large flag or the imbalance high flag is 1, then the target switching mode is determined to be switching from grid-following control to grid-forming control.

[0122] In other words, when the power grid strength is weak or the power angle is large, and at least one of the following conditions occurs: high harmonic content or high imbalance, the target switching mode is determined to be switching from grid-following control to grid-building control.

[0123] S332, when at least two power modules are currently in grid-type control mode, if the grid weakness flag and the power angle large flag in the state characteristics are both 0, and the state characteristics also include at least one flag bit 0, then the target switching mode is determined to be switching from grid-type control to grid-following control.

[0124] If the grid state parameters include voltage harmonic content, voltage imbalance, power angle, and grid strength, such as Figure 5 As shown, if the weak grid indicator is 0 and the large power angle indicator is 0, and the large harmonic content indicator is 0 and / or the high imbalance indicator is 0, then the target switching mode is determined to be switching from grid-based control to grid-following control.

[0125] In other words, when at least two power modules are currently in grid-based control mode, the grid strength is strong and the power angle is small, and the harmonic content and / or the imbalance is low, the target switching mode is determined to be switching from grid-based control to grid-following control.

[0126] In one embodiment, when the target switching mode is from network-based control to network-following control, and the number of power modules in network-based control mode is less than a, the control mode of each power module remains unchanged, where a is an integer greater than 0.

[0127] Specifically, 'a' can be 1. If only one of the multiple power modules is currently in grid-type control mode, while the other power modules are in grid-following control mode, and the grid weakness flag and power angle large flag in the state characteristics are both 0, and the state characteristics also include at least one flag that is 0, then the control mode of any power module will not be switched during this control cycle. In other words, the control mode of at least one power module will be retained as grid-type control.

[0128] The method for switching between grid-connected converter control modes and grid-connected control modes provided in this embodiment of the invention determines the target switching mode based on the operating status of the power grid, which facilitates subsequent switching of control modes.

[0129] Example 4

[0130] In one embodiment, S340: Switching the control mode of the target power module among multiple power modules according to the target switching method may include the following steps:

[0131] S341, when the number of candidate power modules currently using grid-type control among multiple power modules is 1, the candidate power module is determined as the target power module; the control mode of the target power module is switched to grid-type control.

[0132] S342, when the number of candidate power modules currently using grid-based control is greater than 1 among multiple power modules, the power module with smaller active power and / or smaller operating current among the candidate power modules is determined as the target power module; the control mode of the target power module is switched to grid-based control.

[0133] S343, when the number of candidate power modules currently using grid-type control is greater than 1 among multiple power modules, the power module with larger active power and / or larger operating current among the candidate power modules is determined as the target power module; the control mode of the target power module is switched to grid-type control.

[0134] The method for switching between grid-connected converter control modes and grid-connected control modes provided in this embodiment of the invention also takes into account the operating modes of other power modules when switching the control modes of power modules, so as to avoid negative impacts on the power grid after the switch.

[0135] Example 5

[0136] In one embodiment, the power command for each power module is P. iref =k Pi P ref Where i = 1, 2, ..., n; n is the number of power modules, and the weighting coefficient k Pi ∈(0,1), P ref This is the total active power command for the converter;

[0137] The reactive power command for each power module is Q. iref =k Qi Q ref Where i = 1, 2, ..., n; n is the number of power modules, and the weighting coefficient k Qi ∈(0,1), Q ref This is the total reactive power command for multiple power modules.

[0138] The converter control unit includes an active power distribution module and a reactive power distribution module, as follows: Figure 6 He Ru Figure 7 As shown, active and reactive power are allocated to each power module.

[0139] The grid-connected converter switching mode between grid connection and grid construction control provided in this embodiment of the invention allocates power to multiple power modules and controls the power output of each power module to the grid to meet the power demand of the grid.

[0140] Example 6

[0141] In one embodiment, the total active power command of the multiple power modules is P. ref =P set +k fdrop (ω0-ω g ), where P set To set the active power command, k fdrop ω is the primary frequency regulation coefficient, ω0 is the rated frequency of the power grid, ω g This refers to the actual frequency of the power grid.

[0142] The total reactive power command for the power module is Q. ref =Q set +k udrop (U ref -U pcc ), where Q set To set the reactive power command, k udrop U is the droop coefficient. ref For the converter grid connection point voltage command, U pcc This represents the voltage amplitude at the grid connection point.

[0143] The converter control unit includes, for example: Figure 8 The circuit structure shown adjusts the total active power command and total reactive power command of multiple power modules.

[0144] The method for switching between grid-connected converter control modes and grid-connected control modes provided in this embodiment of the invention adjusts the total active power command and total reactive power command of multiple power modules to meet the power demand of the power grid.

[0145] Example 7

[0146] This invention also provides a switching device for grid-connected converter control modes of grid connection and grid integration, applied to a grid-connected converter, the grid-connected converter including a power module, and the switching device including:

[0147] The acquisition module is used to acquire grid voltage and grid status parameters in each control cycle;

[0148] The determination module is used to determine the state characteristics of the power grid based on the power grid state parameters when the power grid voltage deviates from the steady-state setting; it is also used to determine the target switching mode based on the state characteristics; the target switching mode is to switch from grid-following control to grid-building control, or from grid-building control to grid-following control.

[0149] The switching module is used to switch the control mode of the target power module among multiple power modules according to the target switching method; multiple power modules are connected in parallel and belong to the same grid-connected converter, or each power module belongs to a different converter; the control mode of each power module is either grid-following control or grid-connected control.

[0150] This invention provides a grid-connected converter and a switching device for its grid-following and grid-connecting control modes. For power modules in the grid-connected converter, when the grid voltage deviates from the steady-state setting, the state characteristics of the grid are determined based on grid state parameters. Based on these grid state characteristics, a target switching mode is determined. The control mode of the target power module among multiple power modules is switched according to the target switching mode; that is, the target converter is switched from grid-following control to grid-connecting control, or vice versa. By adaptively adjusting the control mode of the power modules under its jurisdiction, the converter can more easily adapt to complex and variable grid environments and operational requirements, improving the stability, adaptability, and support of new energy units connected to the grid. Furthermore, multiple power modules can be connected in parallel, belonging to the same grid-connected converter, or each power module can belong to different converters. In other words, the method and device provided by this invention are applicable to multiple parallel converters as well as converters including multiple parallel power modules, demonstrating broad applicability.

[0151] Example 8

[0152] In one embodiment, the power grid state parameters include one or more of voltage harmonic content or voltage imbalance, as well as power grid strength and power angle; the state characteristics include the corresponding indicators for each power grid state parameter.

[0153] The module is specifically used for:

[0154] When the grid strength is lower than the set threshold range corresponding to the weak grid, the corresponding weak grid flag in the state characteristics is set to 1; when the grid strength is lower than the set threshold range corresponding to the weak grid, the corresponding weak grid flag in the state characteristics is set to 0; when the grid strength is within the set threshold range corresponding to the weak grid, the corresponding weak grid flag in the state characteristics remains unchanged.

[0155] When the power angle is higher than the power angle set threshold range, the corresponding power angle large flag in the status feature is set to 1; when the power angle is lower than the power angle set threshold range, the corresponding power angle large flag in the status feature is set to 0; when the power angle is within the power angle set threshold range, the corresponding power angle large flag in the status feature remains unchanged.

[0156] If the power grid status parameters include voltage harmonic content, when the voltage harmonic content is higher than the set threshold range, the corresponding harmonic content high flag in the status characteristics is set to 1; when the voltage harmonic content is lower than the set threshold range, the corresponding harmonic content high flag in the status characteristics is set to 0; when the voltage harmonic content is within the set threshold range, the corresponding harmonic content high flag in the status characteristics remains unchanged.

[0157] If the grid state parameters include voltage imbalance, when the voltage imbalance is higher than the voltage imbalance set threshold range, the corresponding high imbalance flag in the state characteristics is set to 1; when the voltage imbalance is lower than the voltage imbalance set threshold range, the corresponding high imbalance flag in the state characteristics is set to 0; when the voltage imbalance is within the voltage imbalance set threshold range, the corresponding high imbalance flag in the state characteristics remains unchanged.

[0158] The grid-connected converter switching mode between grid connection and grid construction control provided in this embodiment of the invention uses one or more of the following parameters: voltage harmonic content, voltage imbalance, or power angle, as well as grid strength, to measure the grid's operating status, thus reflecting the grid's operating status more accurately from multiple perspectives.

[0159] The grid-connected converter grid-following and grid-connection control mode switching device provided in this embodiment belongs to the same inventive concept as the grid-connected converter grid-following and grid-connection control mode switching method provided in the above embodiments of the present invention. It can execute the grid-connected converter grid-following and grid-connection control mode switching method provided in any of the above embodiments of the present invention, and has the corresponding functional modules and beneficial effects for performing the switching of grid-connected converter grid-following and grid-connection control modes. Technical details not described in detail in this embodiment can be found in the specific processing content of the adaptive grid voltage change converter control method provided in the above embodiments of the present invention, and will not be repeated here.

[0160] Example 9

[0161] This invention also provides a grid-connected converter, which includes a control unit. The control unit is used to execute the switching method for grid-connected and grid-connected control modes of the grid-connected converter provided in any of the above embodiments of this invention. The control unit has corresponding functional modules and beneficial effects for executing the switching method for grid-connected and grid-connected control modes. Technical details not described in detail in this embodiment can be found in the specific processing content of the switching method for grid-connected and grid-connected control modes of the grid-connected converter provided in the above embodiments of this invention, and will not be repeated here.

[0162] For the foregoing method embodiments, in order to simplify the description, they are all described as a series of actions. However, those skilled in the art should understand that the present invention is not limited to the described order of actions, because according to the present invention, some steps can be performed in other orders or simultaneously. Furthermore, those skilled in the art should also understand that the embodiments described in the specification are preferred embodiments, and the actions and modules involved are not necessarily essential to the present invention.

[0163] It should be noted that the various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For apparatus embodiments, since they are basically similar to method embodiments, the description is relatively simple; relevant parts can be referred to the descriptions in the method embodiments.

[0164] The steps in the methods of the various embodiments of the present invention can be adjusted, merged, or deleted in order according to actual needs, and the technical features described in the various embodiments can be replaced or combined.

[0165] The modules and sub-modules in the various embodiments of the present invention can be merged, divided, and deleted according to actual needs.

[0166] In the embodiments provided by this invention, it should be understood that the disclosed terminals, devices, and methods can be implemented in other ways. For example, the terminal embodiments described above are merely illustrative. For instance, the division of modules or sub-modules is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple sub-modules or modules may be combined or integrated into another module, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be an indirect coupling or communication connection through some interfaces, devices, or modules, and may be electrical, mechanical, or other forms.

[0167] The modules or submodules described as separate components may or may not be physically separate. The components that constitute a module or submodule may or may not be physical modules or submodules; that is, they may be located in one place or distributed across multiple network modules or submodules. Some or all of the modules or submodules can be selected to achieve the purpose of this embodiment's solution, depending on actual needs.

[0168] Furthermore, the functional modules or sub-modules in the various embodiments of the present invention can be integrated into one processing module, or each module or sub-module can exist physically separately, or two or more modules or sub-modules can be integrated into one module. The integrated modules or sub-modules described above can be implemented in hardware or in the form of software functional modules or sub-modules.

[0169] Those skilled in the art will further recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of both. To clearly illustrate the interchangeability of hardware and software, the components and steps of the various examples have been generally described in terms of functionality in the foregoing description. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementations should not be considered beyond the scope of this invention.

[0170] The steps of the methods or algorithms described in conjunction with the embodiments disclosed herein can be implemented directly by hardware, a software unit executed by a processor, or a combination of both. The software unit can be located in random access memory (RAM), main memory, read-only memory (ROM), electrically programmable ROM, electrically erasable programmable ROM, registers, hard disk, removable disk, CD-ROM, or any other form of storage medium known in the art.

[0171] Finally, it should be noted that in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes the element.

[0172] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for switching between grid-connected converter control modes and grid-connected control modes, characterized in that, The grid-connected converter includes a power module, and the switching method includes: In each control cycle, acquire grid voltage and grid state parameters; When the grid voltage deviates from the steady-state setting, the grid state characteristics are determined based on the grid state parameters; Based on the aforementioned state characteristics, the target switching mode is determined; the target switching mode is either switching from network-following control to network-building control, or switching from network-building control to network-following control. The control mode of the target power module among the multiple power modules is switched according to the target switching method; the multiple power modules are connected in parallel and belong to the same grid-connected converter, or each power module belongs to a different converter, and the control mode of each power module is grid-following control or grid-connected control.

2. The method for switching between grid-connected converter control modes and grid-connected control modes according to claim 1, characterized in that, The power grid state parameters include one or more of the following: voltage harmonic content or voltage imbalance, as well as power grid strength and power angle; the state characteristics include the corresponding indicators for each power grid state parameter. Based on the power grid state parameters, the state characteristics of the power grid are determined, including: When the power grid strength is lower than the set threshold range corresponding to a weak power grid, the corresponding weak power grid flag in the state characteristics is set to 1; When the power grid strength is higher than the set threshold range corresponding to the weak power grid, the corresponding weak power grid flag in the state characteristics is set to 0; when the power grid strength is within the set threshold range corresponding to the weak power grid, the corresponding weak power grid flag in the state characteristics remains unchanged. When the power angle is higher than the power angle set threshold range, the corresponding power angle large flag in the state feature is set to 1; when the power angle is lower than the power angle set threshold range, the corresponding power angle large flag in the state feature is set to 0; when the power angle is within the power angle set threshold range, the corresponding power angle large flag in the state feature remains unchanged. If the power grid state parameters include voltage harmonic content, when the voltage harmonic content is higher than the harmonic content set threshold range, the corresponding harmonic content high flag in the state characteristics is set to 1; when the voltage harmonic content is lower than the harmonic content set threshold range, the corresponding harmonic content high flag in the state characteristics is set to 0; when the voltage harmonic content is within the harmonic content set threshold range, the corresponding harmonic content high flag in the state characteristics remains unchanged. If the power grid state parameters include voltage imbalance, when the voltage imbalance is higher than the voltage imbalance set threshold range, the corresponding high imbalance flag in the state characteristics is set to 1; when the voltage imbalance is lower than the voltage imbalance set threshold range, the corresponding high imbalance flag in the state characteristics is set to 0; when the voltage imbalance is within the voltage imbalance set threshold range, the corresponding high imbalance flag in the state characteristics remains unchanged.

3. The method for switching between grid-connected converter control modes and grid-connected control modes according to claim 2, characterized in that, Based on the aforementioned state characteristics, the target switching method is determined, including: When the grid weakness flag or power angle large flag in the status characteristics is 1, and the status characteristics also include at least one flag that is 1, the target switching mode is determined to be switching from grid-following control to grid-building control. When at least two power modules are currently in grid-based control mode, if the weak grid flag and large power angle flag in the state characteristics are both 0, and the state characteristics also include at least one flag that is 0, then the target switching mode is determined to be switching from grid-based control to grid-following control.

4. The method for switching between grid-connected converter and grid-connected control modes according to any one of claims 1-3, characterized in that, The step of switching the control mode of the target power module among the plurality of power modules according to the target switching method includes: When the number of candidate power modules currently using grid-based control among the plurality of power modules is 1, the candidate power module is determined as the target power module; the control mode of the target power module is switched to grid-based control. When the number of candidate power modules currently using grid-based control is greater than 1 among the multiple power modules, the power module with smaller active power and / or smaller operating current among the candidate power modules is determined as the target power module; the control mode of the target power module is switched to grid-based control; When the number of candidate power modules currently using grid-based control is greater than 1 among the multiple power modules, the power module with larger active power and / or larger operating current among the candidate power modules is determined as the target power module; the control mode of the target power module is switched to grid-based control.

5. The method for switching between grid-connected converter control modes and grid-connected control modes according to claim 3, characterized in that, The grid strength is represented by the grid short-circuit ratio and / or the penetration rate of new energy sources; When the grid strength is below the set threshold range corresponding to the weak grid, the grid weakness flag in the state characteristics is set to 1; when the grid strength is above the set threshold range corresponding to the weak grid, the corresponding grid weakness flag in the state characteristics is set to 0; when the grid strength is within the set threshold range corresponding to the weak grid, the corresponding grid weakness flag in the state characteristics remains unchanged, including: If the grid strength is represented by the grid short-circuit ratio, then when the grid short-circuit ratio is lower than the short-circuit ratio set threshold range corresponding to the weak grid, the grid weak flag in the state characteristics is set to 1; when the grid short-circuit ratio is higher than the short-circuit ratio set threshold range corresponding to the weak grid, the corresponding grid weak flag in the state characteristics is set to 0; when the grid short-circuit ratio is within the set threshold range corresponding to the weak grid, the corresponding grid weak flag in the state characteristics remains unchanged. If the grid strength is represented by the penetration rate of new energy sources, then when the penetration rate of new energy sources is higher than the threshold range of the penetration rate corresponding to the weak grid, the grid weakness flag in the state characteristics is set to 1; when the penetration rate of new energy sources is lower than the threshold range of the penetration rate corresponding to the weak grid, the corresponding grid weakness flag in the state characteristics is set to 0; when the penetration rate of new energy sources is within the threshold range of the penetration rate corresponding to the weak grid, the corresponding grid weakness flag in the state characteristics remains unchanged. If grid strength is represented by the grid short-circuit ratio and the penetration rate of new energy sources, then when the grid short-circuit ratio is lower than the short-circuit ratio threshold range corresponding to a weak grid, and / or the new energy penetration rate is higher than the penetration rate threshold range corresponding to a weak grid, the grid weakness flag in the state characteristics is set to 1; when the grid short-circuit ratio is higher than the short-circuit ratio threshold range corresponding to a weak grid, and the new energy penetration rate is lower than the penetration rate threshold range corresponding to a weak grid, the grid weakness flag in the state characteristics is set to 0; when the grid short-circuit ratio is within the short-circuit ratio threshold range corresponding to a weak grid, and the new energy penetration rate is within the penetration rate threshold range corresponding to a weak grid, the grid weakness flag in the state characteristics remains unchanged.

6. The method for switching between grid-connected converter control modes and grid-connected control modes according to claim 1, characterized in that, The active power command for each power module is P. iref =k Pi P ref Where i = 1, 2, ..., n; n is the number of power modules, and the weighting coefficient k Pi ∈(0,1), P ref This is the total active power command for the converter; The reactive power command for each power module is Q. iref =k Qi Q ref Where i = 1, 2, ..., n; n is the number of power modules, and the weighting coefficient k Qi ∈(0,1), Q ref This is the total reactive power command for multiple power modules.

7. The method for switching between grid-connected converter control modes and grid-connected control modes according to claim 1, characterized in that, The total active power command of the multiple power modules is P. ref =P set +k fdrop (ω0-ω g ), where P set To set the active power command, k fdrop ω is the primary frequency regulation coefficient, ω0 is the rated frequency of the power grid, ω g This refers to the actual frequency of the power grid. The total reactive power command of the multiple power modules is Q. ref =Q set +k udrop (U ref -U pcc ), where Q set To set the reactive power command, k udrop U is the droop coefficient. ref For the converter grid connection point voltage command, U pcc This represents the voltage amplitude at the grid connection point.

8. A switching device for grid-connected converter control modes of grid connection and grid construction, characterized in that, Applied to a grid-connected converter, the grid-connected converter including a power module, the switching device includes: The acquisition module is used to acquire grid voltage and grid status parameters in each control cycle; The determination module is used to determine the state characteristics of the power grid based on the power grid state parameters when the power grid voltage deviates from the steady-state setting; it is also used to determine the target switching mode based on the state characteristics; the target switching mode is to switch from grid-following control to grid-building control, or from grid-building control to grid-following control; The switching module is used to switch the control mode of the target power module among the multiple power modules according to the target switching method; the multiple power modules are connected in parallel and belong to the same grid-connected converter, or each power module belongs to a different converter, and the control mode of each power module is grid-connected control or grid-connected control.

9. The switching device for grid-connected converter control modes according to claim 8, characterized in that, The power grid state parameters include one or more of the following: voltage harmonic content or voltage imbalance, as well as power grid strength and power angle; the state characteristics include the corresponding indicators for each power grid state parameter. The determining module is specifically used for: When the power grid strength is lower than the set threshold range corresponding to the weak power grid, the corresponding weak power grid flag in the state characteristics is set to 1; when the power grid strength is higher than the set threshold range corresponding to the weak power grid, the corresponding weak power grid flag in the state characteristics is set to 0; when the power grid strength is within the set threshold range corresponding to the weak power grid, the corresponding weak power grid flag in the state characteristics remains unchanged. When the power angle is higher than the power angle set threshold range, the corresponding power angle large flag in the state feature is set to 1; when the power angle is lower than the power angle set threshold range, the corresponding power angle large flag in the state feature is set to 0; when the power angle is within the power angle set threshold range, the corresponding power angle large flag in the state feature remains unchanged. If the power grid state parameters include voltage harmonic content, when the voltage harmonic content is higher than the harmonic content set threshold range, the corresponding harmonic content high flag in the state characteristics is set to 1; when the voltage harmonic content is lower than the harmonic content set threshold range, the corresponding harmonic content high flag in the state characteristics is set to 0; when the voltage harmonic content is within the harmonic content set threshold range, the corresponding harmonic content high flag in the state characteristics remains unchanged. If the power grid state parameters include voltage imbalance, when the voltage imbalance is higher than the voltage imbalance set threshold range, the corresponding high imbalance flag in the state characteristics is set to 1; when the voltage imbalance is lower than the voltage imbalance set threshold range, the corresponding high imbalance flag in the state characteristics is set to 0; when the voltage imbalance is within the voltage imbalance set threshold range, the corresponding high imbalance flag in the state characteristics remains unchanged.

10. A grid-connected converter, characterized in that, The grid-connected converter includes a control unit, which is used to execute the switching method of grid-connected converter control mode and grid-connected control mode as described in any one of claims 1-8.

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