Grid-forming converter and control method and control device thereof

Abstract

This application relates to a grid-connected converter and its control method and device, applied to a grid-connected converter comprising multiple power units, including power units with DC sides connected to energy storage units and power units with DC sides connected to new energy generation units; the AC sides of each of the multiple power units are connected in parallel to the power grid, and the control strategy of at least one power unit is grid-connected control. The method includes: acquiring grid strength parameters; determining a control strategy switching mode based on the grid strength parameters; when the control strategy switching mode belongs to a target category switching mode, determining a target power unit from the multiple power units for which the control strategy switching mode applies; the target category switching mode instructs the power unit to switch between grid-connected control and grid-connected control; and switching the control strategy of the target power unit according to the control strategy switching mode. This method can improve the frequency support capability and power fluctuation smoothing effect of the new energy system.

Description

Technical Field

[0001] This application relates to the field of power electronics technology, and in particular to a grid-type converter and its control method and control device. Background Technology

[0002] As the proportion of fluctuating renewable energy sources such as wind and solar power in the power system continues to increase, the randomness and intermittency of their power generation pose a continuous challenge to the system's power balance. Currently, these renewable energy power plants generally adopt grid-connected control methods. However, with the formation of a pattern where "high proportion of renewable energy" and "high proportion of power electronic equipment" coexist in the power grid, the shortcomings of grid-connected units—weak disturbance rejection capability and insufficient voltage support capability—are becoming increasingly prominent, restricting the stability of system voltage and frequency, thus limiting the further large-scale grid connection of renewable energy. To improve stability, grid-connected control technology has been proposed to replace traditional grid-connected control technology, which can enhance the voltage support capability of the units and improve grid connection characteristics. However, wind or solar power systems that only adopt grid-connected control still find it difficult to provide effective frequency support when the grid frequency drops, and cannot solve their own power fluctuation problems.

[0003] Therefore, how to effectively improve the frequency support capability and power fluctuation smoothing effect of new energy systems remains a technical problem that needs to be further solved. Summary of the Invention

[0004] Therefore, it is necessary to provide a grid-type converter and its control method and device to address the above-mentioned technical problems, which can improve the frequency support capability and power fluctuation smoothing effect of the new energy system.

[0005] Firstly, this application provides a grid-connected converter control method applied to a grid-connected converter. The grid-connected converter includes multiple power units, including power units connected to energy storage units on their DC sides and power units connected to new energy generation units on their DC sides. The AC sides of each of the multiple power units are connected in parallel to the power grid, and the control strategy for at least one of the power units is grid-connected control. The method includes:

[0006] Obtain power grid strength parameters; these parameters reflect the strength of the power grid.

[0007] Based on the power grid strength parameters, determine the control strategy switching mode;

[0008] When the control strategy switching mode belongs to the target category switching mode, the target power unit applicable to the control strategy switching mode is determined from the plurality of power units; the target category switching mode indicates that the control strategy of the power unit switches between grid-based control and network-based control.

[0009] According to the control strategy switching mode, the control strategy of the target power unit is switched.

[0010] In one embodiment, the target category switching mode includes a first switching mode and a second switching mode, wherein the first switching mode indicates that the control strategy of the power unit switches from grid-following control to grid-building control, and the second switching mode indicates that the control strategy of the power unit switches from grid-building control to grid-following control.

[0011] When the control strategy switching mode belongs to the target category switching mode, determining the target power unit applicable to the control strategy switching mode from the plurality of power units includes:

[0012] When the control strategy switching mode is the first switching mode, candidate power units with grid-based control strategy are determined from the plurality of power units, and a target power unit is selected from the candidate power units according to a preset first selection strategy; the first selection strategy indicates that power units connected to the energy storage unit on the DC side are preferentially selected.

[0013] When the control strategy switching mode is the second switching mode, candidate power units with grid-type control strategy are determined from the plurality of power units, and target power units are selected from the candidate power units according to the preset second selection strategy; the second selection strategy indicates that power units connected to new energy power generation units on the DC side are preferentially selected.

[0014] In one embodiment, the new energy power generation unit includes a photovoltaic power generation unit and a wind power generation unit; the first selection strategy indicates that the power unit connected to the energy storage unit on the DC side is selected first, then the power unit connected to the wind power generation unit on the DC side is selected, and finally the power unit connected to the photovoltaic power generation unit on the DC side is selected; the second selection strategy indicates that the power unit connected to the photovoltaic power generation unit on the DC side is selected first, then the power unit connected to the wind power generation unit on the DC side is selected, and finally the power unit connected to the energy storage unit on the DC side is selected.

[0015] In one embodiment, when the control strategy switching mode is the third switching mode, the control strategies of the plurality of power units remain unchanged.

[0016] The third switching mode is different from the switching mode of the target category.

[0017] In one embodiment, the grid strength parameter is the grid short-circuit ratio, and the step of determining the control strategy switching mode based on the grid strength parameter includes:

[0018] When the grid short-circuit ratio is lower than the preset first short-circuit ratio threshold, the control strategy switching mode is determined to be the first switching mode;

[0019] When the grid short-circuit ratio is higher than a preset second short-circuit ratio threshold, the control strategy switching mode is determined to be the second switching mode; the second short-circuit ratio threshold is greater than the first short-circuit ratio threshold.

[0020] If the grid short-circuit ratio is not lower than the first short-circuit ratio threshold and not higher than the second short-circuit ratio threshold, then the control strategy switching mode is determined to be the third switching mode.

[0021] In one embodiment, the power unit connected to the new energy power generation unit on the DC side has an active power command of MPPT power command; the power unit connected to the energy storage unit on the DC side has an active power command that is allocated based on the total target active power command of the grid-type converter, wherein the total target active power command is the sum of the dispatch power command and the fluctuation suppression power command.

[0022] The scheduling power command is a power command issued by the upper-level control system of the system to which the grid-type converter is connected.

[0023] The fluctuation suppression power command is the product of the target power deviation and the fluctuation power smoothing coefficient; the target power deviation is the deviation between the average value of the historical output active power of the grid-type converter and the current output active power.

[0024] In one embodiment, the reactive power command for each power unit is obtained by allocating based on the total reactive power command of the grid-type converter; the total reactive power command is the sum of the reactive power command and the reactive power compensation command issued by the host computer to the grid-type converter.

[0025] The reactive power compensation command is determined based on the grid connection point voltage deviation and voltage droop control coefficient of the grid-connected converter. The grid connection point voltage deviation is the deviation between the grid connection point voltage command and the grid connection point voltage amplitude of the grid-connected converter.

[0026] In one embodiment, the power unit is a power branch module or a sub-converter. The power branch module includes a power device, a DC capacitor, and an AC-side inductor. The sub-converter includes a power device, a DC capacitor, and an AC-side filter. The AC-side filter includes an AC-side inductor and an AC-side capacitor.

[0027] Secondly, this application also provides a grid-connected converter control device, applied to a grid-connected converter. The grid-connected converter includes multiple power units, including power units with DC sides connected to energy storage units and power units with DC sides connected to new energy generation units. The AC sides of each of the multiple power units are connected in parallel to the power grid, and the control strategy for at least one of the power units is grid-connected control. The device includes:

[0028] An acquisition module is used to acquire power grid strength parameters; the power grid strength parameters reflect the strength of the power grid.

[0029] The switching mode determination module is used to determine the control strategy switching mode based on the power grid strength parameters.

[0030] The power unit selection module is used to determine, from the plurality of power units, a target power unit for which the control strategy switching mode applies when the control strategy switching mode belongs to the target category switching mode; the target category switching mode indicates that the control strategy of the power unit switches between grid-based control and network-based control.

[0031] The control strategy switching module is used to switch the control strategy of the target power unit according to the control strategy switching mode.

[0032] Thirdly, this application also provides a grid-connected converter, including a control unit and multiple power units. The multiple power units include power units connected to an energy storage unit on their DC side, and power units connected to a new energy generation unit on their DC side. The AC sides of each of the multiple power units are connected in parallel to the power grid, and the control strategy for at least one of the power units is grid-connected control. The multiple power units are used for power conversion, and the control unit is used to execute the following steps:

[0033] Obtain power grid strength parameters; these parameters reflect the strength of the power grid.

[0034] Based on the power grid strength parameters, determine the control strategy switching mode;

[0035] When the control strategy switching mode belongs to the target category switching mode, the target power unit applicable to the control strategy switching mode is determined from the plurality of power units; the target category switching mode indicates that the control strategy of the power unit switches between grid-based control and network-based control.

[0036] According to the control strategy switching mode, the control strategy of the target power unit is switched.

[0037] The aforementioned grid-connected converter and its control method and device, because the grid-connected converter includes multiple power units, each of which is connected to the grid via parallel AC side connections. Furthermore, some of these power units are connected to the power units of the new energy generation unit, while others are connected to the energy storage unit. This modular parallel connection offers high flexibility and scalability. The energy storage unit also helps to smooth power fluctuations in the grid-connected converter's output power within the new energy system. Moreover, since the grid strength parameter reflects the strength of the grid, the control strategy switching mode is determined based on the grid strength parameter, and the control strategy for the target power unit in the grid-connected converter is controlled. Switching between grid-connected control and grid-connected control enhances the unit's adaptability to complex grid access environments while providing reliable voltage and frequency support for the system. In summary, while ensuring the operational flexibility of the grid-connected converter, it improves the frequency support capability and power fluctuation smoothing effect of the new energy system. Attached Figure Description

[0038] To more clearly illustrate the technical solutions in the embodiments of this application or related technologies, the drawings used in the description of the embodiments of this application or related technologies will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0039] Figure 1 This is a flowchart illustrating a grid-type converter control method in one embodiment;

[0040] Figure 2 This is a schematic diagram of the topology and control framework of a grid-type converter in one embodiment;

[0041] Figure 3 This is a control block diagram for any power unit in one embodiment when the control strategy is grid-type control.

[0042] Figure 4 The block diagram for active and reactive power control when the control strategy for any power unit in one embodiment is a grid-type control;

[0043] Figure 5 The block diagram for AC voltage and grid-side current control when the control strategy for any power unit in one embodiment is grid-type control;

[0044] Figure 6 This is a schematic diagram illustrating the power command generation principle when the power unit's DC side is connected to the energy storage unit in one embodiment.

[0045] Figure 7 This is a schematic diagram illustrating the reactive power command generation principle of a power unit in one embodiment.

[0046] Figure 8 This is a structural block diagram of a grid-type converter control device in one embodiment. Detailed Implementation

[0047] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0048] It should be noted that the term "multiple" as used in this application refers to two or more. The term "comprising" and any variations thereof as used in this application are intended to cover non-exclusive inclusion. The terms "first," "second," etc., as used in this application can be used to describe various elements, but these elements are not limited by these terms; these terms are only used to distinguish the first element from the second element.

[0049] In one exemplary embodiment, such as Figure 1 As shown, a grid-type converter control method is provided. This embodiment illustrates the application of this method to a grid-type converter. The grid-type converter includes multiple power units, including power units connected to energy storage units on the DC side and power units connected to new energy power generation units on the DC side. The AC sides of the multiple power units are connected in parallel to the power grid, and the control strategy of at least one power unit is grid-type control.

[0050] The grid-type converter comprises two parts: a power circuit and a control system. The power circuit can consist of multiple power units used for power conversion. The control system includes a control unit that can execute a grid-type converter control method. The number of power units is no less than two. In one embodiment, the power unit is a power branch module or a sub-converter. The power branch module includes power devices, a DC capacitor, and an AC-side inductor. The sub-converter includes power devices, a DC capacitor, and an AC-side filter. The AC-side filter includes an AC-side inductor and an AC-side capacitor. The power devices and DC capacitor can form a PWM (Pulse-Width Modulation) rectifier bridge.

[0051] The control strategy for each power unit can be either grid-based control or grid-following control, meaning it can operate in either grid-based or grid-following mode. When the power unit is a power branch module, the number of power branch modules must be no less than two, and at least one power branch module must operate in grid-based mode. When the power unit is a sub-converter, the number of sub-converters must be no less than two, and at least one sub-converter must operate in grid-based mode.

[0052] Among multiple power units, at least one power unit has its DC side connected to an energy storage unit, and at least one power unit has its DC side connected to a new energy power generation unit. The new energy power generation unit can be a photovoltaic power generation unit or a wind power generation unit. Each power unit can be connected to one of the energy storage unit, photovoltaic power generation unit, or wind power generation unit. Multiple power units operate in parallel and are connected to the grid connection point of the grid-connected converter.

[0053] Taking a sub-converter as an example, the topology and control framework diagram of a grid-type converter can be shown as follows: Figure 2 As shown. Among them, the grid-type converter may include... Individual converter, The input to the control system is a positive integer greater than 1, and is the grid-connected point voltage of the grid-connected converter. Grid-connected current of grid-type converters , The grid-side current of the individual converter , DC side voltage of the power module of the individual converter The output of the control system is Power module drive signal of individual converter . Figure 2 middle, It can represent the grid voltage. It can represent the power grid impedance. Can represent Each sub-converter's AC-side filter capacitor Can represent Each of the individual converters has its own AC-side filter inductor. Can represent The AC side voltage of each individual converter Can represent The DC side voltage of each sub-converter.

[0054] In this embodiment, the method includes the following steps 110 to 140:

[0055] Step 110: Obtain the power grid strength parameters; the power grid strength parameters reflect the strength of the power grid.

[0056] Among them, the grid strength parameter can be the grid short-circuit ratio. The grid short-circuit ratio can be monitored by the grid-type converter itself, or it can be monitored by other equipment in the renewable energy power station where the grid-type converter is located and then sent to the grid-type converter.

[0057] For example, the control unit of the grid-connected converter can acquire grid strength parameters in each control cycle. Steps 110 to 140 can be executed in each control cycle.

[0058] Step 120: Determine the control strategy switching mode based on the power grid strength parameters.

[0059] The control strategy switching mode can be a first switching mode, a second switching mode, or a third switching mode. The first switching mode indicates that the control strategy of the power unit switches from grid-following control to grid-building control; the second switching mode indicates that the control strategy of the power unit switches from grid-building control to grid-following control; and the third switching mode indicates that the control strategy of the power unit remains unchanged.

[0060] For example, step 120 includes: when the grid short-circuit ratio is lower than a preset first short-circuit ratio threshold, the control strategy switching mode is determined to be a first switching mode; when the grid short-circuit ratio is higher than a preset second short-circuit ratio threshold, the control strategy switching mode is determined to be a second switching mode; the second short-circuit ratio threshold is greater than the first short-circuit ratio threshold; when the grid short-circuit ratio is not lower than the first short-circuit ratio threshold and not higher than the second short-circuit ratio threshold, the control strategy switching mode is determined to be a third switching mode.

[0061] Specifically, when the grid short-circuit ratio is lower than a preset first short-circuit ratio threshold, it indicates that the grid is in a weak grid state. The first short-circuit ratio threshold can be the short-circuit ratio threshold corresponding to a weak grid. In this case, the operating mode switching flag of the grid-type converter can be set to 1 to set the control strategy switching mode to the first switching mode. When the grid short-circuit ratio is higher than a preset second short-circuit ratio threshold, it indicates that the grid is in a strong grid state. The second short-circuit ratio threshold can be the short-circuit ratio threshold corresponding to a strong grid. In this case, the operating mode switching flag of the grid-type converter can be set to -1 to set the control strategy switching mode to the second switching mode. When the grid short-circuit ratio is neither lower than the first short-circuit ratio threshold nor higher than the second short-circuit ratio threshold, the operating mode switching flag of the grid-type converter can be set to 0 to set the control strategy switching mode to the third switching mode.

[0062] Step 130: When the control strategy switching mode belongs to the target category switching mode, the target power unit for which the control strategy switching mode applies is determined from multiple power units; the target category switching mode indicates that the control strategy of the power unit switches between network-type control and network-type control.

[0063] The target category switching modes include a first switching mode and a second switching mode.

[0064] For example, step 130 may include: when the control strategy switching mode is a first switching mode, determining candidate power units with grid-type control as the control strategy from multiple power units, and selecting a target power unit from the candidate power units according to a preset first selection strategy; the first selection strategy indicates that power units connected to the energy storage unit on the DC side should be selected preferentially; when the control strategy switching mode is a second switching mode, determining candidate power units with grid-type control as the control strategy from multiple power units, and selecting a target power unit from the candidate power units according to a preset second selection strategy; the second selection strategy indicates that power units connected to the new energy power generation unit on the DC side should be selected preferentially.

[0065] Specifically, when the control strategy switching mode is the first switching mode (indicating that the control strategy of a power unit switches from grid-following control to network-building control), the candidate power unit is the power unit among multiple power units whose control strategy is determined to be grid-following control, and the target power unit is the power unit selected from the candidate power units according to the first selection strategy. It can be understood that if there is no power unit among the multiple power units with a grid-following control strategy, the control strategies of the multiple power units can remain unchanged.

[0066] When the control strategy switching mode is the second switching mode (indicating that the control strategy of a power unit is switched from network-based control to grid-based control), the candidate power unit is the power unit among multiple power units whose control strategy is determined to be network-based control, and the target power unit is the power unit selected from the candidate power units according to the second selection strategy. It can be understood that when there is only one power unit among multiple power units with a network-based control strategy, the control strategies of the multiple power units can remain unchanged; that is, at least one power unit must retain its network-based control strategy.

[0067] The number of candidate power units can be one or more, and the number of target power units can be one.

[0068] In one embodiment, the new energy power generation unit includes a photovoltaic power generation unit and a wind power generation unit; a first selection strategy indicates that the power unit connected to the energy storage unit on the DC side is selected first, followed by the power unit connected to the wind power generation unit on the DC side, and finally the power unit connected to the photovoltaic power generation unit on the DC side; a second selection strategy indicates that the power unit connected to the photovoltaic power generation unit on the DC side is selected first, followed by the power unit connected to the wind power generation unit on the DC side, and finally the power unit connected to the energy storage unit on the DC side.

[0069] Among them, energy storage units have advantages such as high controllability, fast response speed, and strong overload capacity, and have relatively high grid support capacity. Wind power generation units are partially controllable, have moderate response speed, and are limited by natural conditions, so their grid support capacity is lower than that of energy storage units. Photovoltaic power generation units have poor controllability, limited response speed, and weak overload capacity, so their grid support capacity is lower than that of wind power generation units.

[0070] In this embodiment, when the control strategy switching mode is the first switching mode, it indicates that the power grid is in a weak grid state, and the control strategy of the power unit needs to be switched from grid-following control to grid-building control. At this time, the target power unit is selected according to the first selection strategy. Combined with the control strategy of the target power unit in the subsequent switching, the grid can be supported in a timely and effective manner, improving system security. When the control strategy switching mode is the second switching mode, it indicates that the power grid is in a strong grid state, and the control strategy of the power unit can be switched from grid-building control to grid-following control. At this time, the target power unit is selected according to the second selection strategy. Combined with the control strategy of the target power unit in the subsequent switching, grid-building resources can be released in a timely manner, improving resource utilization. In this way, the selection strategy takes into account the physical characteristics of various resources, can better utilize wind power and photovoltaic resources, and can achieve a balance between system stability and economy.

[0071] Step 140: Switch the control strategy of the target power unit according to the control strategy switching mode.

[0072] For example, when the control strategy switching mode is the first switching mode, the control unit of the grid-type converter can control the control strategy of the target power unit to switch from grid-following control to grid-type control; when the control strategy switching mode is the second switching mode, the control unit of the grid-type converter can control the control strategy of the target power unit to switch from grid-type control to grid-following control.

[0073] In the aforementioned grid-connected converter control method, multiple power units are connected to the grid via parallel AC side connections. Some of these power units are connected to the power units of the renewable energy generation unit, while others are connected to the energy storage unit. This modular parallel connection offers high flexibility and scalability. Furthermore, the energy storage unit helps to smooth power fluctuations in the grid-connected converter's output power within the renewable energy system. Since the grid strength parameter reflects the strength of the grid, the control strategy switching mode is determined based on this parameter, and the control strategy for the target power unit in the grid-connected converter is controlled. Switching between grid-connected and grid-connected control enhances the unit's adaptability to complex grid access environments while providing reliable voltage and frequency support for the system. In summary, this method improves the frequency support capability and power fluctuation mitigation effect of the renewable energy system while ensuring the operational flexibility of the grid-connected converter.

[0074] In an exemplary embodiment, the above-described grid-type converter control method further includes: when the control strategy switching mode is the third switching mode, the control strategies of the multiple power units remain unchanged; wherein the third switching mode is different from the switching mode of the target category.

[0075] Specifically, when the control strategy switching mode is the third switching mode, it reflects that the power grid is between a weak grid state and a strong grid state. The third switching mode indicates that the control strategy of the power unit remains unchanged.

[0076] In an exemplary embodiment, the control block diagram for any power unit when the control strategy is grid-based control can be as follows: Figure 3 As shown, the control system of the grid converter can be configured according to... Figure 3 The control block diagram shown generates the first... Drive signal for each power unit This switches the control strategy of the power unit to the grid-following strategy, i.e., it operates in grid-following mode.

[0077] in, Figure 3 The meanings of the symbols in the Chinese text are as follows: It can represent the grid connection point voltage of a grid-connected converter. It can represent the first The grid-side current of each power unit , They can represent the first, second, and third parts respectively. The measured values ​​of active power and reactive power output by each power unit. , They can represent the first one respectively. Active power command and reactive power command for each power unit This can represent an active power regulator under grid-type control. This can represent a reactive power regulator under grid-type control. , They can represent the first one respectively. The d-axis and q-axis command values ​​of the grid-side current of each power unit. It can represent the phase angle of the network operation (usually the output of a phase-locked loop). , It can represent the first The d-axis and q-axis components of the grid-side current of each power unit. This can represent a current regulator under grid-type control. , The d-axis and q-axis components of the grid-connected voltage of the grid-connected converter can be represented respectively. , They can represent the first one respectively. The d-axis command value and q-axis command value of the power unit's output voltage. , This can represent the output voltage of the power unit. Axis command values ​​and Axis command value.

[0078] In an exemplary embodiment, when the control strategy for any power unit is a grid-type control, the active and reactive power control block diagrams can be as follows: Figure 4 As shown, the control block diagram for AC voltage and grid-side current when the control strategy for any power unit is grid-based control can be represented as follows: Figure 5 As shown, the control system of the grid converter can be configured according to... Figure 4 as well as Figure 5 The control block diagram shown generates the first... Drive signal for each power unit This switches the control strategy of the power unit to the network construction strategy, i.e., it operates in network construction mode.

[0079] in, Figure 4 The meanings of the symbols in the Chinese text are as follows: It can represent the grid connection point voltage of a grid-connected converter. It can represent the first The grid-side current of each power unit , They can represent the first one respectively. The measured values ​​of active power and reactive power output by each power unit. , They can represent the first one respectively. Active power command and reactive power command for each power unit It can represent virtual moment of inertia. It can represent the damping coefficient. It can represent the rated angular frequency. It can represent the amount of angular frequency adjustment. It can represent the angular frequency of the network. It can represent the first The phase angle of the network operation of each power unit (usually the output of the network power loop). This can represent the reactive power regulator in the grid configuration mode. It can represent the grid connection point voltage command for grid-connected converters. It can represent the first The virtual internal potential of each power unit.

[0080] Figure 5 middle, It can represent the first The virtual internal potential of each power unit It can represent the grid connection point voltage of a grid-connected converter. It can represent the first The phase angle of the network operation of each power unit (usually the output of the network power loop). , The d-axis and q-axis components of the grid-connected voltage of the grid-connected converter can be represented respectively. This can represent a voltage regulator in a grid configuration mode. , They can represent the first one respectively. The d-axis and q-axis command values ​​of the grid-side current of each power unit. It can represent the first The grid-side current of each power unit , It can represent the first The d-axis and q-axis components of the grid-side current of each power unit. This can represent the current regulator in grid configuration mode. , They can represent the first one respectively. The d-axis command value and q-axis command value of the power unit's output voltage. , This can represent the output voltage of the power unit. Axis command values ​​and Axis command value.

[0081] In an exemplary embodiment, the power unit connected to the new energy power generation unit on the DC side has an active power command that is an MPPT power command; the power unit connected to the energy storage unit on the DC side has an active power command that is allocated based on the total target active power command of the grid-connected converter, and the total target active power command is the sum of the dispatch power command and the fluctuation suppression power command; wherein, the dispatch power command is the power command issued by the upper-level control system of the system to which the grid-connected converter is connected; the fluctuation suppression power command is the product of the target power deviation and the fluctuation power smoothing coefficient; the target power deviation is the deviation between the average value of the historical output active power of the grid-connected converter and the current output active power.

[0082] MPPT stands for Maximum Power Point Tracking. The upper-level control system can be a microgrid controller, a renewable energy power plant controller, or others. Figure 6 This is a schematic diagram illustrating the power command generation principle when the power unit's DC side is connected to the energy storage unit. Figure 6 middle, It can represent the grid connection point voltage of a grid-connected converter. It can represent the grid connection point current of a grid-connected converter. It can represent a power scheduling command. This can represent the current output active power of the grid-type converter. It can represent the average value of the historical active power output of a grid-type converter. It can represent the fluctuation power suppression coefficient. It can represent a power command for fluctuation suppression. This can represent the total target active power command for a grid-type converter. It can represent the number of power modules (not less than 1) connected to the energy storage unit on the DC side in a grid-type converter. It can represent the active power command of the power unit connected to the energy storage unit on the DC side.

[0083] When the DC side of the power module is connected to an energy storage unit, its active power command can be obtained by equation (1). The total target active power command can be the sum of the scheduling power command and the fluctuation suppression power command. The active power command of the power module can be the total target active power command divided by the number of such power modules.

[0084] Equation (1)

[0085] Fluctuation suppression power command The fluctuation power mitigation coefficient can be obtained from equation (2). The value ranges from 0 to 1, specifically greater than 0 and not greater than 1. This represents the average value of historically output active power. The methods for obtaining this include, but are not limited to, the sliding window averaging method. Current output active power. The grid connection point voltage of the grid-connected converter can be determined by... and grid connection point current Calculated.

[0086] Equation (2)

[0087] In an exemplary embodiment, the reactive power command for each power unit is obtained by allocating the total reactive power command of the grid-connected converter; the total reactive power command is the sum of the reactive power command and the reactive power compensation command issued by the host computer to the grid-connected converter; wherein, the reactive power compensation command is determined according to the grid-connected converter's grid-connected point voltage deviation and voltage droop control coefficient, and the grid-connected point voltage deviation is the deviation between the grid-connected point voltage command and the grid-connected point voltage amplitude of the grid-connected converter.

[0088] in, Figure 7 This is a schematic diagram illustrating the principle of reactive power command generation for a power unit. Figure 7 middle, It can represent the reactive power command issued by the host computer to the grid-type converter. It can represent the grid connection point voltage of a grid-connected converter. It can represent the voltage amplitude at the grid connection point. It can represent the grid connection point voltage command for grid-connected converters. It can represent the voltage control deviation (the value is the deviation between the grid connection point voltage command and the grid connection point voltage amplitude). It can represent the voltage droop control coefficient. It can represent the voltage droop control quantity. It can represent the total reactive power command of a grid-type converter. This can represent the reactive power command weighting coefficient of the power unit. It can represent the first Reactive power command for each power unit.

[0089] No. Reactive power command for each power unit ( =1, 2, …, , (Number of power units in parallel), weighting factor ∈(0,1), , The weighting coefficients of each power unit can be the same or different. The reactive power command for each power unit... It is based on their respective weighting coefficients. Total reactive power command for grid-type converters The total reactive power command for the grid-type converter is obtained through allocation. , It can be used as a voltage droop control variable.

[0090] It should be understood that although the steps in the flowcharts of the embodiments described above are shown sequentially according to the arrows, these steps are not necessarily executed in the order indicated by the arrows. Unless explicitly stated herein, there is no strict order restriction on the execution of these steps, and they can be executed in other orders. Moreover, at least some steps in the flowcharts of the embodiments described above may include multiple steps or multiple stages. These steps or stages are not necessarily completed at the same time, but can be executed at different times. The execution order of these steps or stages is not necessarily sequential, but can be performed alternately or in turn with other steps or at least some of the steps or stages in other steps. It is understood that the steps in different embodiments can be freely combined as needed, and all non-contradictory solutions formed by such combinations are within the scope of protection of this application.

[0091] Based on the same inventive concept, this application also provides a grid-type converter control device for implementing the grid-type converter control method described above. The solution provided by this device is similar to the solution described in the above method; therefore, the specific limitations in one or more embodiments of the grid-type converter control device provided below can be found in the limitations of the grid-type converter control method described above, and will not be repeated here.

[0092] In one exemplary embodiment, such as Figure 8 As shown, a grid-connected converter control device 800 is provided, applied to a grid-connected converter. The grid-connected converter includes multiple power units, including power units connected to energy storage units on the DC side and power units connected to new energy generation units on the DC side. The AC sides of each of the multiple power units are connected in parallel to the power grid, and the control strategy of at least one power unit is grid-connected control. The grid-connected converter control device 800 includes: an acquisition module 810, a switching mode determination module 820, a power unit selection module 830, and a control strategy switching module 840, wherein:

[0093] The acquisition module 810 is used to acquire power grid strength parameters; the power grid strength parameters reflect the strength of the power grid.

[0094] The switching mode determination module 820 is used to determine the control strategy switching mode based on the power grid strength parameters.

[0095] The power unit selection module 830 is used to determine the target power unit from multiple power units when the control strategy switching mode belongs to the target category switching mode; the target category switching mode indicates that the control strategy of the power unit switches between network control and grid-based control.

[0096] The control strategy switching module 840 is used to switch the control strategy of the target power unit according to the control strategy switching mode.

[0097] In an exemplary embodiment, the target category switching mode includes a first switching mode and a second switching mode. The first switching mode indicates that the control strategy of the power unit switches from grid-following control to grid-building control, and the second switching mode indicates that the control strategy of the power unit switches from grid-building control to grid-following control. The power unit selection module 830 is further configured to, when the control strategy switching mode is the first switching mode, determine candidate power units with grid-following control from a plurality of power units, and select a target power unit from the candidate power units according to a preset first selection strategy. The first selection strategy indicates that power units connected to the energy storage unit on the DC side should be selected preferentially. When the control strategy switching mode is the second switching mode, determine candidate power units with grid-building control from a plurality of power units, and select a target power unit from the candidate power units according to a preset second selection strategy. The second selection strategy indicates that power units connected to the new energy power generation unit on the DC side should be selected preferentially.

[0098] In an exemplary embodiment, the new energy power generation unit includes a photovoltaic power generation unit and a wind power generation unit; a first selection strategy indicates that the power unit connected to the energy storage unit on the DC side is selected first, then the power unit connected to the wind power generation unit on the DC side is selected second, and finally the power unit connected to the photovoltaic power generation unit on the DC side is selected last; a second selection strategy indicates that the power unit connected to the photovoltaic power generation unit on the DC side is selected first, then the power unit connected to the wind power generation unit on the DC side is selected last, and finally the power unit connected to the energy storage unit on the DC side is selected last.

[0099] In an exemplary embodiment, the control strategy switching module 840 is further configured to maintain the control strategy of each of the multiple power units unchanged when the control strategy switching mode is the third switching mode; wherein the third switching mode is different from the switching mode of the target category.

[0100] In an exemplary embodiment, the grid strength parameter is the grid short-circuit ratio. The switching mode determination module 820 is further configured to determine the control strategy switching mode as a first switching mode when the grid short-circuit ratio is lower than a preset first short-circuit ratio threshold; determine the control strategy switching mode as a second switching mode when the grid short-circuit ratio is higher than a preset second short-circuit ratio threshold; the second short-circuit ratio threshold is greater than the first short-circuit ratio threshold; and determine the control strategy switching mode as a third switching mode when the grid short-circuit ratio is neither lower than the first short-circuit ratio threshold nor higher than the second short-circuit ratio threshold.

[0101] In an exemplary embodiment, the power unit connected to the new energy power generation unit on the DC side has an active power command that is an MPPT power command; the power unit connected to the energy storage unit on the DC side has an active power command that is allocated based on the total target active power command of the grid-connected converter, and the total target active power command is the sum of the dispatch power command and the fluctuation suppression power command; wherein, the dispatch power command is the power command issued by the upper-level control system of the system to which the grid-connected converter is connected; the fluctuation suppression power command is the product of the target power deviation and the fluctuation power smoothing coefficient; the target power deviation is the deviation between the average value of the historical output active power of the grid-connected converter and the current output active power.

[0102] In an exemplary embodiment, the reactive power command for each power unit is obtained by allocating the total reactive power command of the grid-connected converter; the total reactive power command is the sum of the reactive power command and the reactive power compensation command issued by the host computer to the grid-connected converter; wherein, the reactive power compensation command is determined according to the grid-connected converter's grid-connected point voltage deviation and voltage droop control coefficient, and the grid-connected point voltage deviation is the deviation between the grid-connected point voltage command and the grid-connected point voltage amplitude of the grid-connected converter.

[0103] In an exemplary embodiment, the power unit is a power branch module or a sub-converter. The power branch module includes a power device, a DC capacitor, and an AC-side inductor. The sub-converter includes a power device, a DC capacitor, and an AC-side filter. The AC-side filter includes an AC-side inductor and an AC-side capacitor.

[0104] Each module in the aforementioned grid-type converter control device can be implemented entirely or partially through software, hardware, or a combination thereof. These modules can be embedded in the processor of the grid-type converter control unit in hardware form or independent of it, or they can be stored in the memory of the grid-type converter control unit in software form, so that the processor can call and execute the corresponding operations of each module.

[0105] In an exemplary embodiment, a grid-type converter is provided, including a control unit and multiple power units. The multiple power units include power units with DC sides connected to energy storage units and power units with DC sides connected to new energy power generation units. The AC sides of the multiple power units are connected in parallel and then connected to the power grid, and the control strategy of at least one power unit is grid-type control. The multiple power units are used to perform power conversion, and the control unit is used to execute the steps in the above method embodiments.

[0106] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this application.

[0107] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of this patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this application should be determined by the appended claims.

Claims

1. A control method for a grid-type converter, characterized in that, The method is applied to a grid-connected converter, which includes multiple power units, including power units connected to energy storage units on their DC sides and power units connected to new energy generation units on their DC sides; the AC sides of each of the multiple power units are connected in parallel to the power grid, and the control strategy of at least one of the power units is grid-connected control. The method includes: Obtain power grid strength parameters; these parameters reflect the strength of the power grid. Based on the power grid strength parameters, determine the control strategy switching mode; When the control strategy switching mode belongs to the target category switching mode, the target power unit applicable to the control strategy switching mode is determined from the plurality of power units; the target category switching mode indicates that the control strategy of the power unit switches between grid-based control and network-based control. According to the control strategy switching mode, the control strategy of the target power unit is switched.

2. The method according to claim 1, characterized in that, The target category switching mode includes a first switching mode and a second switching mode. The first switching mode indicates that the control strategy of the power unit is switched from grid-following control to grid-building control, and the second switching mode indicates that the control strategy of the power unit is switched from grid-building control to grid-following control. When the control strategy switching mode belongs to the target category switching mode, determining the target power unit applicable to the control strategy switching mode from the plurality of power units includes: When the control strategy switching mode is the first switching mode, candidate power units with grid-based control strategy are determined from the plurality of power units, and a target power unit is selected from the candidate power units according to a preset first selection strategy; the first selection strategy indicates that power units connected to the energy storage unit on the DC side are preferentially selected. When the control strategy switching mode is the second switching mode, candidate power units with grid-type control strategy are determined from the plurality of power units, and target power units are selected from the candidate power units according to the preset second selection strategy; the second selection strategy indicates that power units connected to new energy power generation units on the DC side are preferentially selected.

3. The method according to claim 2, characterized in that, The new energy power generation unit includes a photovoltaic power generation unit and a wind power generation unit; the first selection strategy indicates that the power unit connected to the energy storage unit on the DC side is selected first, then the power unit connected to the wind power generation unit on the DC side is selected, and finally the power unit connected to the photovoltaic power generation unit on the DC side is selected; the second selection strategy indicates that the power unit connected to the photovoltaic power generation unit on the DC side is selected first, then the power unit connected to the wind power generation unit on the DC side is selected, and finally the power unit connected to the energy storage unit on the DC side is selected.

4. The method according to claim 2, characterized in that, The method further includes: When the control strategy switching mode is the third switching mode, the control strategies of the multiple power units remain unchanged. The third switching mode is different from the switching mode of the target category.

5. The method according to claim 4, characterized in that, The grid strength parameter is the grid short-circuit ratio. Determining the control strategy switching mode based on the grid strength parameter includes: When the grid short-circuit ratio is lower than the preset first short-circuit ratio threshold, the control strategy switching mode is determined to be the first switching mode; When the grid short-circuit ratio is higher than a preset second short-circuit ratio threshold, the control strategy switching mode is determined to be the second switching mode; the second short-circuit ratio threshold is greater than the first short-circuit ratio threshold. If the grid short-circuit ratio is not lower than the first short-circuit ratio threshold and not higher than the second short-circuit ratio threshold, then the control strategy switching mode is determined to be the third switching mode.

6. The method according to claim 1, characterized in that, The power unit connected to the new energy power generation unit on the DC side has an active power command of MPPT power command; the power unit connected to the energy storage unit on the DC side has an active power command that is allocated based on the total target active power command of the grid-type converter, and the total target active power command is the sum of the dispatch power command and the fluctuation suppression power command. The scheduling power command is a power command issued by the upper-level control system of the system to which the grid-type converter is connected. The fluctuation suppression power command is the product of the target power deviation and the fluctuation power smoothing coefficient; the target power deviation is the deviation between the average value of the historical output active power of the grid-type converter and the current output active power.

7. The method according to claim 1, characterized in that, The reactive power command for each power unit is obtained by allocating based on the total reactive power command of the grid-type converter; the total reactive power command is the sum of the reactive power command and reactive power compensation command issued by the host computer to the grid-type converter. The reactive power compensation command is determined based on the grid connection point voltage deviation and voltage droop control coefficient of the grid-connected converter. The grid connection point voltage deviation is the deviation between the grid connection point voltage command and the grid connection point voltage amplitude of the grid-connected converter.

8. The method according to any one of claims 1-7, characterized in that, The power unit is a power branch module or a sub-converter. The power branch module includes a power device, a DC capacitor, and an AC-side inductor. The sub-converter includes a power device, a DC capacitor, and an AC-side filter. The AC-side filter includes an AC-side inductor and an AC-side capacitor.

9. A grid-type converter control device, characterized in that, The device is applied to a grid-connected converter, which includes multiple power units, including power units connected to energy storage units on their DC sides and power units connected to new energy generation units on their DC sides; the AC sides of each of the multiple power units are connected in parallel to the power grid, and the control strategy of at least one of the power units is grid-connected control. The device includes: An acquisition module is used to acquire power grid strength parameters; the power grid strength parameters reflect the strength of the power grid. The switching mode determination module is used to determine the control strategy switching mode based on the power grid strength parameters. The power unit selection module is used to determine, from the plurality of power units, a target power unit for which the control strategy switching mode applies when the control strategy switching mode belongs to the target category switching mode; the target category switching mode indicates that the control strategy of the power unit switches between grid-based control and network-based control. The control strategy switching module is used to switch the control strategy of the target power unit according to the control strategy switching mode.

10. A grid-type converter, comprising a control unit and multiple power units, characterized in that, The plurality of power units include power units connected to energy storage units on the DC side, and power units connected to new energy power generation units on the DC side; the AC sides of each of the plurality of power units are connected in parallel to the power grid, and the control strategy of at least one of the power units is grid-type control; the plurality of power units are used for power conversion, and the control unit is used to execute the steps of the method according to any one of claims 1 to 8.

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