Impedance self-adaption-based dual-mode switching control method, device and equipment for flexible direct output of new energy power generation cluster

Abstract

The invention provides a dual-mode switching control method, device and equipment for flexible direct output of a new energy power generation cluster based on impedance self-adaption, relates to the field of new energy power generation, and aims to control an inverter to be switched between a network following mode and a network constructing mode. Comprising the following steps: setting an initial mode of inverter operation and model switching boundary values # imgabs0 # and # imgabs1 #; obtaining the equivalent impedance # imgabs2 # of the flexible direct current system after the inverter operates in the following network mode; whether # imgabs3 # is met or not is determined; if yes, re-executing the operation of the inverter in the following network type mode to obtain the equivalent impedance # imgabs4 #; if not, the inverter is controlled to be switched from a network-following mode to a network-constructing mode; obtaining the equivalent impedance # imgabs5 # of the flexible direct current system after the inverter operates in the network construction mode; whether # imgabs6 # is met or not is determined; if yes, the inverter is executed again to operate in the network construction mode, and then the equivalent impedance # imgabs7 # of the flexible direct current system is obtained; if not, the inverter is controlled to be switched from a network construction type mode to a network following type mode; and re-executing the operation of the inverter in the following network mode to obtain the equivalent impedance # imgabs8 # of the flexible direct current system, and controlling the inverter to continue to operate.

Description

Technical Field

[0001] The embodiments of the present invention relate to the field of renewable energy power generation, and in particular to a dual-mode switching control method, device and equipment for a renewable energy power generation cluster based on impedance adaptation and transmitted via flexible direct current. Background Art

[0002] In recent years, the access of large-scale renewable energy power generation clusters has made the penetration rate of renewable energy power generation higher and higher. Flexible DC transmission technology can not only realize independent control of active power and reactive power, but also supply power to weak systems and isolated islands. It has been widely used in long-distance centralized transmission of large-scale renewable energy power generation clusters. However, the introduction of flexible DC transmission system has changed the impedance characteristics of the AC system on the renewable energy side, causing the impedance of the AC system connected to the renewable energy power generation grid-connected system to fluctuate within a certain range (equivalent to the fluctuation of the short-circuit ratio SCR), which has brought challenges to the stable and efficient operation of the renewable energy power generation grid-connected system.

[0003] At present, in response to the problem that the introduction of flexible direct current transmission has led to changes in system impedance characteristics, causing instability in the entire grid-connected system, related technologies have proposed an additional damping controller to improve system stability. Since this method focuses on the flexible direct current transmission system itself, and for the grid-connected system that introduces the flexible direct current transmission system, the new energy power generation cluster is no longer connected to an infinite power grid, but is approximately connected to a power grid with variable impedance. Therefore, the stability of the system also depends on the inverter control mode in the new energy power generation cluster.

[0004] However, when the grid impedance fluctuates greatly, the stability margin and control bandwidth of the inverter operating in a single grid-connected mode will be significantly reduced, and the output power will fluctuate with the change of the AC side frequency of the flexible DC transmission system, resulting in the inability of the grid-connected system to operate stably and related problems of the flexible DC transmission system being locked. Summary of the invention

[0005] Based on the above technical problems, the embodiments of the present invention provide a dual-mode switching control method, device and equipment for a new energy power generation cluster based on impedance adaptation through flexible direct current transmission, which aims to control the inverter to switch between the grid-following type and the grid-building type grid-connected mode according to the equivalent impedance change of the flexible direct current transmission system, thereby realizing the stable operation of the inverter within a relatively large equivalent impedance change range.

[0006] A first aspect of an embodiment of the present invention provides a dual-mode switching control method for a new energy power generation cluster based on impedance adaptation through flexible direct current transmission, the method comprising: The initial operation mode of the inverter is set to the grid-following mode, and the equivalent impedance boundary value of the flexible direct current system when the inverter switches from the grid-following mode to the grid-building mode is set to , the equivalent impedance boundary value of the flexible direct current system when the inverter switches from the grid-forming mode to the grid-following mode is set to ; Control the inverter to operate in the grid-following mode, and after the inverter operates in the grid-following mode, start impedance identification to obtain the equivalent impedance of the flexible direct current system ; Determine whether ; In satisfying In the case of the above, the steps are executed again to control the inverter to operate in the grid-following mode. After the inverter operates in the grid-following mode, impedance identification is started to obtain the equivalent impedance of the flexible direct current system. ; In dissatisfaction In the case of a power outage, controlling the inverter to switch from the grid-following mode to the grid-building mode; Control the inverter to operate in the grid-forming mode, and after the inverter operates in the grid-forming mode, start impedance identification to obtain the equivalent impedance of the flexible direct current system. ; Determine whether ; In satisfying In the case of the above, the steps are executed again to control the inverter to operate in the grid-forming mode. After the inverter operates in the grid-forming mode, impedance identification is started to obtain the equivalent impedance of the flexible DC system. ; In dissatisfaction In the case of a power outage, controlling the inverter to switch from the grid-building mode to the grid-following mode; Re-execute the steps to control the inverter to operate in the grid-following mode, and after the inverter operates in the grid-following mode, start impedance identification to obtain the equivalent impedance of the flexible direct current system , controlling the inverter to continue operating.

[0007] A second aspect of an embodiment of the present invention provides a dual-mode switching control device for a new energy power generation cluster based on impedance self-adaptation and transmitted via flexible direct current, the device comprising: The initial setting module is used to set the initial operation mode of the inverter to the grid-following mode, and to set the flexible direct current system equivalent impedance boundary value when the inverter switches from the grid-following mode to the grid-building mode to , the equivalent impedance boundary value of the flexible direct current system when the inverter switches from the grid-forming mode to the grid-following mode is set to ; The first control module is used to control the inverter to operate in the grid-following mode, and after the inverter operates in the grid-following mode, start impedance identification to obtain the equivalent impedance of the flexible direct current system ; The first determination module is used to determine whether ; The second control module is used to meet the In the case of the above, the steps are executed again to control the inverter to operate in the grid-following mode. After the inverter operates in the grid-following mode, impedance identification is started to obtain the equivalent impedance of the flexible direct current system. ; The first switching module is used for In the case of a power outage, controlling the inverter to switch from the grid-following mode to the grid-building mode; The third control module is used to control the inverter to operate in the grid-forming mode, and after the inverter operates in the grid-forming mode, start impedance identification to obtain the equivalent impedance of the flexible direct current system ; The second determination module is used to determine whether ; The fourth control module is used to meet the In the case of the above, the steps are executed again to control the inverter to operate in the grid-forming mode. After the inverter operates in the grid-forming mode, impedance identification is started to obtain the equivalent impedance of the flexible DC system. ; The second switching module is used to In the case of a power outage, controlling the inverter to switch from the grid-building mode to the grid-following mode; A fifth control module is used to re-execute the steps to control the inverter to operate in the grid-following mode, and after the inverter operates in the grid-following mode, start impedance identification to obtain the equivalent impedance of the flexible direct current system. , controlling the inverter to continue operating.

[0008] A third aspect of an embodiment of the present invention provides an electronic device, comprising: a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein when the computer program is executed by the processor, a dual-mode switching control method for a new energy power generation cluster based on impedance adaptation and transmitted via flexible direct current is implemented as described in the first aspect of an embodiment of the present invention.

[0009] In the dual-mode switching control method for a new energy power generation cluster based on impedance adaptation and sent through flexible direct current provided in an embodiment of the present invention, the initial operation mode of the inverter is set to the grid-following mode, and the inverter is controlled to operate in the grid-following mode. After the inverter operates in the grid-following mode, impedance identification is started to obtain the equivalent impedance of the flexible direct current system. ; Determine whether In satisfying In the case of the above, re-execute the steps to control the inverter to operate in the grid-following mode. After the inverter operates in the grid-following mode, start the impedance identification and obtain the equivalent impedance of the flexible DC system. ; in dissatisfaction In the case of , the inverter is controlled to switch from the grid-following mode to the grid-building mode; the inverter is controlled to operate in the grid-building mode, and after the inverter operates in the grid-building mode, impedance identification is started to obtain the equivalent impedance of the flexible DC system ; Determine whether In satisfying In the case of the above, re-execute the steps to control the inverter to operate in the grid-forming mode. After the inverter operates in the grid-forming mode, start the impedance identification and obtain the equivalent impedance of the flexible DC system. ; in dissatisfaction In the case of , the inverter is controlled to switch from the grid-building mode to the grid-following mode; the inverter is controlled to operate in the grid-following mode, and after the inverter operates in the grid-following mode, the steps are re-executed to control the inverter to operate in the grid-following mode, and after the inverter operates in the grid-following mode, impedance identification is started to obtain the equivalent impedance of the flexible DC system. , control the inverter to continue running.

[0010] According to the dual-mode switching control method of the embodiment based on impedance self-adaptation of the new energy power generation cluster through flexible direct current transmission, according to the flexible direct current system equivalent impedance of the flexible direct current transmission system , and controls the inverter to switch between the grid-following and grid-building grid-connected modes, thereby achieving stable operation of the inverter within a relatively large equivalent impedance change range. Therefore, the inverter dual-mode switching control method based on this embodiment solves the problem that when the inverter in the new energy power generation cluster adopts a single grid-following or grid-building grid-connected mode under different equivalent impedance conditions when connected to the flexible direct current transmission system, the inverter can only stably operate within a relatively small equivalent impedance change range. This further solves the problem that the new energy power generation grid-connected system may not be able to operate stably when the change of the control mode of the flexible direct current transmission system causes the impedance of the grid at the equivalent grid connection point to change when the new energy power generation cluster is sent out through the flexible direct current transmission system. Compared with the prior art, the present invention has the following beneficial effects: (1) Solved the limitation of single mode: For the scenario where large-scale renewable energy power generation stations are connected to the grid through flexible direct current transmission system (flexible direct current transmission), the existing solutions mainly adopt a single "grid-following" or "grid-building" control mode, and usually deal with the system oscillation instability problem by optimizing the control parameters of power electronic devices or improving the impedance reshaping method of the control strategy. However, these solutions do not involve the dynamic switching method between the "grid-following" and "grid-building" modes. The present invention innovatively proposes a dual-mode switching control strategy, which effectively fills this technical gap.

[0011] (2) Overcoming complex coupling problems: This invention successfully addresses the complex coupling problems in the photovoltaic base flexible direct current transmission system composed of "grid-following" and "grid-building" inverters. Under the conditions of a high-penetration new energy grid, by introducing a dual-mode adaptive switching control strategy, the operational stability of new energy grid connection is guaranteed, and the utilization rate of new energy power generation is maximized, achieving a comprehensive optimization of stability and economy.

[0012] (3) Achieve efficient oscillation suppression: By adopting the "grid-following / grid-building" dual-mode adaptive switching control, the present invention transforms the power oscillation problem of large-scale renewable energy power generation sites caused by grid impedance changes into a control mode switching problem. This method is simple and efficient, can significantly suppress oscillation phenomena, and improve the reliability and economy of system operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments of the present invention will be briefly introduced below. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative labor.

[0014] Figure 1 It is a flowchart of the steps of a dual-mode switching control method for a new energy power generation cluster based on impedance self-adaptation and sent through flexible direct current according to an embodiment of the present invention; Figure 2 It is a schematic diagram of a topological structure when a single-phase inverter is connected to a flexible direct current transmission system model and an equivalent schematic diagram proposed in an embodiment of the present invention; Figure 3 A block diagram of a method for measuring equivalent impedance of a flexible direct current system based on non-characteristic harmonic injection according to an embodiment of the present invention; Figure 4 is a schematic diagram of a control structure of an inverter operating in a grid-following mode according to an embodiment of the present invention; Figure 5is a schematic diagram of a control structure of an inverter operating in a grid-forming mode according to an embodiment of the present invention; Figure 6 A schematic diagram of a switching method between a following-network mode and a building-network mode based on an impedance hysteresis loop according to an embodiment of the present invention; Figure 7 It is a schematic diagram of an impedance small signal model structure of an inverter operating in a grid-following mode connected to an equivalent flexible DC system shown in an embodiment of the present invention; Figure 8 It is an overall flow chart of a dual-mode control method for a new energy power generation cluster based on impedance self-adaptation and transmitted through flexible direct current according to an embodiment of the present invention; Fig. 9 It is a structural block diagram of a dual-mode switching control device based on impedance self-adaptation for a renewable energy power generation cluster via flexible direct current transmission provided by an embodiment of the present invention; Fig.10 It is a schematic diagram of an electronic device shown in an embodiment of the present invention. DETAILED DESCRIPTION

[0015] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0016] As mentioned above, the introduction of flexible DC transmission leads to the change of system impedance characteristics, causing the instability of the entire grid-connected system. Related technologies have proposed additional damping controllers to improve system stability: for example, by improving the control structure of flexible DC transmission and adding additional harmonic current loops, the equivalent impedance is indirectly changed, and additional damping control is used to improve the stability of the system. However, this related technology focuses on the flexible DC transmission system itself, while for the grid-connected system that introduces the flexible DC transmission system, the new energy power generation cluster is no longer connected to an infinite power grid, but is approximately connected to a power grid with variable impedance. Therefore, the stability of the system also depends on the inverter control mode in the new energy power generation cluster.

[0017] Based on this, the related technologies propose methods such as adaptively adjusting the control loop parameters according to the size of the impedance and increasing the virtual impedance to ensure that the inverter has sufficient control bandwidth and stability margin, thereby ensuring that the inverter can operate stably when the impedance changes. For example, in order to solve the problem that the grid voltage proportional feedforward in a weak power grid will greatly reduce the stability margin of the inverter, or even make it unstable, the related technology 1 proposes a method based on grid impedance detection to adjust the voltage of the feedforward compensation, and modify the parameters of the regulator to improve the grid adaptability of the inverter control; the related technology 2 improves the adaptability of the inverter to the weak power grid by increasing the virtual impedance of the inverter. The applicable scenario of these related technologies is that the inverters in the new energy power generation cluster work in the grid-following control mode, but the control changes of the flexible direct current transmission will cause large fluctuations in impedance. At this time, the stability margin and control bandwidth of the grid-following inverter are significantly reduced, and the new energy power generation cluster will not be able to operate normally and stably.

[0018] Based on this, some related technologies propose to make the inverters in the new energy power generation cluster work in a grid-type control mode based on droop control to achieve stable control of the inverter grid connection. For example, it is considered that the inverter works in a grid-type control mode with lower output impedance when connected to a weak grid, which can make the inverter better adapt to the weak grid with large grid impedance. However, if the inverters in the new energy cluster adopt a single grid-type grid connection mode, there are shortcomings: in order to increase the inertia of the system, the flexible DC transmission system generally also adopts a grid-type control mode to provide a frequency reference for the AC system of the new energy power generation cluster. At this time, the interaction of the two grid-type systems may cause the frequency of the AC system to jump and cause system oscillation; when the equivalent impedance of the connected flexible DC transmission system decreases, that is, the equivalent SCR increases, its output power will fluctuate with the change of the frequency of the AC side of the flexible DC transmission system, and may even oscillate.

[0019] In summary, the related technology has at least the following problems: 1) When analyzing the scenario of renewable energy power generation clusters being sent out through flexible direct current transmission, the focus is placed on the flexible direct current transmission system itself, which severs the connection between the renewable energy power generation cluster and the flexible direct current transmission system. It is assumed that the system on the renewable energy power generation cluster side is stable. However, the renewable energy power generation cluster is no longer connected to an infinite power grid, but to a power grid with variable impedance characteristics, which affects the stability of the renewable energy power generation cluster. 2) In response to the situation where the impedance fluctuation of the grid-connected system is caused by the flexible DC transmission system, only a solution is given for the new energy power generation cluster working in a single grid-connected control mode. However, the single grid-connected control mode is only applicable to the situation with a small impedance variation range. In the case of a large range, both modes have shortcomings.

[0020] Therefore, in order to at least partially solve one or more of the above problems and other potential problems, the embodiment of the present invention proposes a dual-mode switching control method for a new energy power generation cluster through flexible direct current transmission based on impedance adaptation when the new energy power generation cluster is connected to the flexible direct current transmission system and connected to the grid, in view of the fact that a single grid-following or grid-forming mode can only stably operate in a small range of fluctuations in the equivalent impedance of the flexible direct current transmission system. By switching between the grid-following and grid-forming modes, the inverter can be stably operated in a wider range of changes in the equivalent impedance of the flexible direct current transmission system. The dual-mode control method for a new energy power generation cluster through flexible direct current transmission based on impedance adaptation is proposed. Further, in order to ensure stability during switching, the switching between modes adopts a switching method based on impedance hysteresis; and when the inverter does not switch modes, that is, when the inverter operates in a single grid-following or grid-forming mode, the voltage of the feedforward compensation or the controller parameters of the inverter are adaptively adjusted according to the equivalent impedance of the flexible direct current system, so as to further improve the adaptability of the inverter to the equivalent impedance of the flexible direct current system.

[0021] Please refer to Figure 1 , Figure 1 This is a flowchart of the steps of a dual-mode switching control method for a new energy power generation cluster based on impedance adaptation and sent through flexible direct current according to an embodiment of the present invention. In this embodiment, the new energy power generation cluster refers to a new energy power generation system composed of n inverters with the same structure, and the inverters in the new energy power generation cluster are all controlled by the method proposed in this embodiment; the flexible direct current transmission system refers to a VSC-HVDC system using V / F control.

[0022] like Figure 2 As shown, Figure 2 1 is a schematic diagram of a topological structure when a single-phase inverter is connected to a flexible DC transmission system model and an equivalent schematic diagram proposed in an embodiment of the present invention. Figure 2 In the inverter topology, the DC side filter capacitor , single-phase full-bridge inverter circuit, LC filter, DC side filter capacitor The two ends of the single-phase full-bridge inverter circuit are respectively connected to the two input ends, the output end of the single-phase full-bridge inverter circuit is connected to the input end of the LC filter, and the output end of the LC filter is connected to other inverters and equivalent impedance in the cluster through the common coupling point PCC. The flexible DC transmission system is connected.

[0023] like Figure 1 As shown, the dual-mode switching control method for a new energy power generation cluster based on impedance adaptation and transmitted via flexible direct current provided in this embodiment comprises at least the following steps: Step S11: Setting the initial operation mode of the inverter to the grid-following mode, and setting the flexible direct current system equivalent impedance boundary value for switching the inverter from the grid-following mode to the grid-building mode to , the equivalent impedance boundary value of the flexible direct current system when the inverter switches from the grid-forming mode to the grid-following mode is set to .

[0024] Step S12: Control the inverter to operate in the grid-following mode. After the inverter operates in the grid-following mode, start impedance identification to obtain the equivalent impedance of the flexible DC system. .

[0025] In this embodiment, after the inverter operates in the grid-following mode, the impedance identification algorithm is used to start the impedance identification to obtain the equivalent impedance of the flexible DC system. ; Step S13: Determine whether .

[0026] Step S14: When the In the case of the above, the steps are executed again to control the inverter to operate in the grid-following mode. After the inverter operates in the grid-following mode, impedance identification is started to obtain the current equivalent impedance of the flexible direct current system. .

[0027] In this embodiment, the judgment condition Is it satisfied? If satisfied , then return to step S12, and re-execute the above step S12: control the inverter to operate in the grid-following mode, and after the inverter operates in the grid-following mode, start impedance identification to obtain the equivalent impedance of the flexible DC system .

[0028] Step S15: If the In this case, the inverter is controlled to switch from the grid-following mode to the grid-building mode.

[0029] In this embodiment, if the , controlling the inverter to switch from the grid-following mode to the grid-building mode.

[0030] Step S16: Control the inverter to operate in the grid-forming mode. After the inverter operates in the grid-forming mode, start impedance identification to obtain the equivalent impedance of the flexible DC system. .

[0031] In this embodiment, after controlling the inverter to switch from the grid-following mode to the grid-forming mode, the inverter is controlled to operate in the grid-forming mode, and after the inverter operates in the grid-forming mode, the impedance identification algorithm is started to perform impedance identification to obtain the current equivalent impedance of the flexible direct current system. .

[0032] Step S17: Determine whether .

[0033] Step S18: When the In the case of the above, the steps are executed again to control the inverter to operate in the grid-forming mode. After the inverter operates in the grid-forming mode, impedance identification is started to obtain the equivalent impedance of the flexible DC system. .

[0034] In this embodiment, the judgment condition Is it satisfied? If satisfied , then return to step S16, and re-execute the above step S16: control the inverter to operate in the grid-forming mode, and after the inverter operates in the grid-forming mode, start impedance identification to obtain the equivalent impedance of the flexible DC system .

[0035] Step S19: If the In this case, the inverter is controlled to switch from the grid-building mode to the grid-following mode.

[0036] In this embodiment, if the , control the inverter to switch from grid-building mode to grid-following mode.

[0037] Step S110: re-execute step S111 to control the inverter to operate in the grid-following mode. After the inverter operates in the grid-following mode, impedance identification is started to obtain the equivalent impedance of the flexible DC system. , controlling the inverter to continue operating.

[0038] In this embodiment, after the inverter is controlled to switch from the grid-building mode to the grid-following mode, the process returns to step S12 and the above step S12 is re-executed: the inverter is controlled to operate in the grid-following mode, and after the inverter operates in the grid-following mode, impedance identification is started to obtain the equivalent impedance of the flexible DC system. , to control the inverter to continue running.

[0039] In this embodiment, according to the flexible direct current system equivalent impedance of the flexible direct current transmission system The inverter is controlled to switch between the grid-following and grid-forming grid-connected modes according to the changes in the impedance, thereby achieving stable operation of the inverter within a relatively large equivalent impedance change range. Therefore, the inverter dual-mode switching control method based on this embodiment solves the problem that when the inverter in the new energy power generation cluster adopts a single grid-following or grid-forming grid-connected mode under different equivalent impedance conditions when connected to the flexible direct current transmission system, the inverter can only stably operate within a relatively small equivalent impedance change range. This further solves the problem that the new energy power generation grid-connected system may not be able to operate stably when the change in the control mode of the flexible direct current transmission system causes the grid impedance of its equivalent grid-connected point to change when the new energy power generation cluster is sent out through the flexible direct current transmission system.

[0040] In combination with the above embodiments, in one implementation, the present invention further provides a dual-mode switching control method for a new energy power generation cluster based on impedance adaptation through flexible direct current transmission. In the method, the "controlling the inverter to switch from the grid-following mode to the grid-forming mode" in the above step S15 may specifically include steps S21 to S27: Step S21: Collecting the inductor current on the bridge arm side And the filter capacitor voltage , the filter capacitor voltage The grid connection point voltage phase angle is obtained by phase locking using a software phase-locked loop SOGI-SPLL based on a second-order generalized integrator and grid voltage amplitude ; Use the second-order generalized integrator SOGI to respectively convert the inductor current on the bridge arm side and the filter capacitor voltage Transformed into a two-phase stationary vertical coordinate system The amount of and ;pass Coordinate transformation transforms the two-phase stationary vertical coordinate system The amount of and Transformed to the two-phase synchronous rotating coordinate system dq, the dq component of the inductor current on the bridge arm side is obtained and the dq component of the filter capacitor voltage .

[0041] Step S22: According to the dq component of the inductor current on the bridge arm side and the filter capacitor voltage dq component , respectively, to obtain the average active power and average reactive power .

[0042] In this embodiment, according to the dq component of the bridge arm side inductor current obtained in step S21 and the dq component of the filter capacitor voltage , the average active power is obtained by the active power calculation equation and the reactive power calculation equation and average reactive power .

[0043] The active power calculation equation is: ; The reactive power calculation equation is: ; in, is the time constant of the first-order low-pass filter, s is the Laplace operator.

[0044] Step S23: According to the average active power , get the output angular frequency of the inverter , the output angular frequency The output phase angle of the inverter is obtained by integration .

[0045] In this embodiment, the average active power output by the inverter obtained in step S22 is , the output angular frequency of the inverter is obtained through the active power-frequency droop control equation , the output angular frequency The output phase angle of the inverter is obtained by integration .

[0046] The active power-frequency droop control equation is: ; in, The inverter is given an active power command The rated angular frequency corresponding to is the active power droop coefficient.

[0047] Step S24: According to the grid connection point voltage phase angle , and the output phase angle of the inverter , get the phase synchronization signal , and the phase synchronization signal Superimposed on the inverter output angular frequency superior.

[0048] In this embodiment, the grid connection point voltage phase angle obtained in step S21 is , and the output phase angle of the inverter obtained in step S23 , the phase synchronization signal is obtained by the phase synchronization algorithm equation , and the phase synchronization signal Superimposed on the inverter output angular frequency superior.

[0049] The phase synchronization algorithm equation is: ; in, is the phase integral coefficient of the phase synchronization algorithm equation, s is the Laplace operator.

[0050] Step S25: According to the average reactive power output by the inverter , obtain the reference value of the dq component of the filter capacitor voltage of the inverter .

[0051] In this embodiment, the average reactive power output by the inverter obtained in step S22 is , the reference value of the inverter filter capacitor voltage dq component is obtained through the reactive power-amplitude droop control equation .

[0052] The reactive power-amplitude droop control equation is: ; in, The inverter is given a reactive power command The rated output voltage corresponding to the time, n is the reactive power droop coefficient.

[0053] Step S26: According to the voltage amplitude of the grid connection point , and the reference value of the dq component of the filter capacitor voltage of the inverter , obtain the amplitude synchronization signal , and the amplitude synchronization signal Superimposed on the filter capacitor voltage dq component reference value superior.

[0054] In this embodiment, the grid connection point voltage amplitude obtained in step S21 is , and the reference value of the dq component of the inverter filter capacitor voltage obtained in step S25 , the amplitude synchronization signal is obtained by the amplitude synchronization algorithm equation , and the amplitude synchronization signal Added to the reference value of the dq component of the filter capacitor voltage superior.

[0055] The amplitude synchronization algorithm equation is: ; in, is the amplitude integral coefficient of the amplitude synchronization algorithm equation, s is the Laplace operator.

[0056] Step S27: First complete the grid connection point voltage phase angle The output phase angle of the inverter phase synchronization, and then complete the grid connection point voltage amplitude The reference value of the filter capacitor voltage dq component The amplitude of is synchronized to complete the switching from the following network mode to the building network mode.

[0057] In this embodiment, the grid connection point voltage phase angle is first completed according to step S24. The output phase angle of the inverter Phase synchronization, and then complete the grid voltage amplitude according to step S26 The reference value of the dq component of the filter capacitor voltage The amplitude of the signal is synchronized to complete the soft switching from the following network mode to the building network mode.

[0058] In combination with the above embodiments, the present invention also provides a dual-mode switching control method for a new energy power generation cluster based on impedance adaptation through flexible direct current transmission. In this embodiment, when the inverter switches from a grid-forming mode to a grid-following mode, a dual-mode soft switching controller based on controller synchronous mapping operation is triggered, and the controller is composed of an execution controller and a mapping controller.

[0059] In the method, the “controlling the inverter to switch from the grid-forming mode to the grid-following mode” in the above step S19 may specifically include steps S31 to S37: Step S31: Collecting DC side filter capacitance Voltage on .

[0060] Step S32: According to the DC side filter capacitor Voltage on , get the inductor current command signal .

[0061] In this embodiment, the DC side filter capacitor obtained in step S31 Voltage on , the inductor current command signal is obtained through the DC voltage control equation .

[0062] The DC voltage control equation is: ; in, is the proportional control coefficient, is the integral control coefficient, is the DC side filter capacitor voltage command given to the inverter, s is the Laplace operator.

[0063] Step S33: The inductor current command signal as an execution control variable.

[0064] Step S34: Collecting filter capacitor voltage , using the second-order generalized integrator SOGI to convert the filter capacitor voltage Transformed into a two-phase stationary vertical coordinate system The amount of ,pass Coordinate transformation transforms the two-phase stationary vertical coordinate system The amount of Transformed to the two-phase synchronous rotating coordinate system dq, the dq component of the filter capacitor voltage is obtained and .

[0065] Step S35: According to the dq component of the filter capacitor voltage and , set the reference value of the filter capacitor voltage dq component and the filter capacitor voltage dq component Equal, set the reference value of the filter capacitor voltage dq component and the filter capacitor voltage dq component Equal, get the dq component output value and , and and as mapping control variables.

[0066] In this embodiment, the dq component of the filter capacitor voltage obtained in step S34 and , set the reference value of the filter capacitor voltage dq component and the dq component of the filter capacitor voltage Equal, set the reference value of the filter capacitor voltage dq component and the dq component of the filter capacitor voltage Equal, get the dq component output value of the filter capacitor voltage control equation and , and and as mapping control variables.

[0067] The filter capacitor voltage control equation includes: ; in, is the proportional control coefficient, is the integral control coefficient, s is the Laplace operator, and , .

[0068] Step S36: Execute the control variable according to the and , and the mapping control variables and , complete the mapping control variables To the execution control variable The transition, and the completion of the mapping control variables To the execution control variable transition.

[0069] In this embodiment, the execution control variable obtained in step S33 and , and the mapping control variable obtained in step S35 and , the mapping control variables are completed through the numerical slow-start control equation To execution control variables transition, and complete the mapping control variables To execution control variables transition.

[0070] The numerical slow-start control equation is: ; in, To map control variables and To the execution control variable and The slow-down time, and are the step values ​​given for the numerical ramp-up control, and , .

[0071] Step S37: When the mapping control variable and are numerically equal to the execution control variables and When the network-building mode is switched to the network-following mode, the switching is completed.

[0072] In this embodiment, when the mapping control variable and are numerically equal to the execution control variables and , the value slow-down ends, completing the soft switch from the network-building mode to the network-following mode.

[0073] Among them, step S31 to step S33 are the execution controller outputting the execution control variables, and step S34 to step S35 are the mapping controller outputting the mapping control variables.

[0074] In combination with the above embodiments, in one implementation, the present invention also provides a dual-mode switching control method for a new energy power generation cluster based on impedance adaptation via flexible direct current transmission. Figure 3 As shown, Figure 3 FIG. 1 is a block diagram of a method for measuring equivalent impedance of a flexible direct current system based on non-characteristic harmonic injection according to an embodiment of the present invention. Figure 3 The main steps of the impedance identification algorithm are as follows, that is, the above-mentioned "starting impedance identification to obtain the equivalent impedance of the flexible direct current system" may specifically include steps S41 to S46: Step S41: injecting a non-characteristic subharmonic current with a frequency of 75 Hz at the point of common coupling PCC.

[0075] Step S42: Collecting the filter capacitor voltage at the common coupling point PCC and the current on the flexible DC transmission system side .

[0076] Step S43: The filter capacitor voltage is respectively analyzed by fast Fourier transform (FFT). and the current on the flexible DC transmission system side Analyze and obtain the amplitude of the voltage component at 75Hz frequency , the phase of the voltage component at 75Hz frequency , the amplitude of the current component at 75Hz frequency , the phase of the current component at 75Hz frequency .

[0077] In this embodiment, the filter capacitor voltage is respectively calculated by the fast Fourier transform algorithm FFT. and the current on the flexible DC transmission system side Analyze and obtain the amplitude of the voltage component at 75Hz frequency , the phase of the voltage component at 75Hz frequency , the amplitude of the current component at 75Hz frequency , the phase of the current component at 75Hz frequency .

[0078] Step S44: Based on the amplitude of the voltage component at 75 Hz and the amplitude of the current component at 75Hz , the amplitude of the equivalent impedance of the flexible DC system at a frequency of 75Hz is obtained ; According to the phase of the voltage component at 75Hz frequency and the phase of the current component at 75Hz , the phase of the equivalent impedance of the flexible DC system at 75Hz is obtained .

[0079] In this embodiment, the first formula can be used to calculate the amplitude of the voltage component at a frequency of 75 Hz: and the amplitude of the current component at 75Hz , the amplitude of the equivalent impedance of the flexible DC system at a frequency of 75Hz is obtained ; and through the first formula, according to the phase of the voltage component at 75Hz frequency and the phase of the current component at 75Hz , the phase of the equivalent impedance of the flexible DC system at 75Hz is obtained .

[0080] The first formula is: .

[0081] Step S45: According to the amplitude of the equivalent impedance of the flexible direct current system at the frequency of 75 Hz The phase of the equivalent impedance of the flexible DC system at 75Hz , the resistive component of the equivalent impedance of the flexible DC system is obtained and emotional weight .

[0082] In this embodiment, according to the amplitude of the equivalent impedance of the flexible DC system at a frequency of 75 Hz The phase of the equivalent impedance of the flexible DC system at 75Hz , the resistive component of the equivalent impedance of the flexible DC system is obtained by the second formula and emotional weight .

[0083] The second formula is: .

[0084] Step S46: Based at least on the resistive component of the equivalent impedance of the flexible DC system and the perceptual component , the equivalent impedance of the flexible DC system is obtained .

[0085] In this embodiment, at least the resistive component of the equivalent impedance of the flexible DC system and emotional weight , and the equivalent impedance of the flexible DC system is obtained In one example, the equivalent impedance of the flexible DC system is : , s is the Laplace operator.

[0086] In combination with the above embodiments, in one implementation, the present invention also provides a dual-mode switching control method for a new energy power generation cluster based on impedance adaptation via flexible direct current transmission. Figure 4 As shown, Figure 4 FIG. 1 is a schematic diagram of a control structure of an inverter operating in a grid-following mode according to an embodiment of the present invention. Figure 4 , the main steps of the control method for the inverter to operate in the grid-following mode are as follows, that is, in this embodiment, the above steps of "controlling the inverter to operate in the grid-following mode" may specifically include steps S51 to S56: Step S51: Collecting DC side filter capacitor Voltage on , Flexible DC transmission system side current , bridge arm side inductor current And the filter capacitor voltage , the filter capacitor voltage The grid connection point voltage phase angle is obtained by phase locking using a software phase-locked loop SOGI-SPLL based on a second-order generalized integrator ; Use the second-order generalized integrator SOGI to convert the bridge arm side inductor current Transformed into a two-phase stationary vertical coordinate system The amount of and ,pass Coordinate transformation transforms the two-phase stationary vertical coordinate system The amount of and The components transformed to the two-phase synchronous rotating coordinate system dq and .

[0087] Step S52: According to the DC side filter capacitor Voltage on , get the inductor current command signal .

[0088] In this embodiment, the DC side filter capacitor obtained in step S51 Voltage on , the inductor current command signal is obtained through the DC voltage control equation .

[0089] The DC voltage control equation is: ; in, is the proportional control coefficient, is the integral control coefficient, is the DC side filter capacitor voltage command given to the inverter, s is the Laplace operator.

[0090] Step S53: According to the dq component of the inductor current on the bridge arm side and , and the inductor current command signal , get the control signal and .

[0091] In this embodiment, the dq component of the inductor current on the bridge arm side obtained in step S51 and , and the inductor current command signal obtained in step S52 , the control signal is obtained through the inductor current inner loop control equation and .

[0092] The inner loop control equation of the inductor current is: ; in, is the proportional control coefficient, is the integral control coefficient, s is the Laplace operator.

[0093] Step S54: according to the current on the flexible DC transmission system side and the filter capacitor voltage , and the equivalent impedance of the flexible DC system , and voltage feed forward is obtained .

[0094] In this embodiment, the current on the flexible DC transmission system side obtained in step S51 and filter capacitor voltage , and the equivalent impedance of the flexible DC system obtained by the impedance identification algorithm , the voltage feedforward is obtained by the third formula The third formula is: .

[0095] Step S55: adaptively adjusting the voltage of the feedforward compensation according to the equivalent impedance of the flexible DC system, improving the stability margin of the inverter in the grid-following mode, and enhancing the adaptability of the inverter to different equivalent impedances of the flexible DC system.

[0096] Step S56: According to the control signal and ,pass The coordinates of the control signal and Transform to a two-phase stationary vertical coordinate system The amount of control under and ; Take the two-phase stationary vertical coordinate system The amount of control under With the voltage feed forward The inverter bridge arm voltage control signal is obtained by adding them together, and the switching signal of the inverter power device is generated by SPWM modulation, and the opening and closing of the inverter power device is controlled by the driving protection circuit.

[0097] In combination with the above embodiments, in one implementation, the present invention also provides a dual-mode switching control method for a new energy power generation cluster based on impedance adaptation via flexible direct current transmission. Figure 5 As shown, Figure 5 FIG. 1 is a schematic diagram of a control structure of an inverter operating in a grid-forming mode according to an embodiment of the present invention. When the inverter switches from the grid-following mode to the grid-forming mode, Figure 5 Switch in and Close, start the phase synchronization algorithm and the amplitude synchronization algorithm, the main steps of the phase synchronization algorithm and the amplitude synchronization algorithm are as described in step S21 to step S27. Figure 5 When the inverter is operating in grid-forming mode, disconnect the switch and , and the main steps of the inverter control method in the grid-forming mode are as follows, that is, in the method, the "controlling the inverter to operate in the grid-forming mode" in the above steps may specifically include steps S61 to S69: Step S61: Collecting the inductor current on the bridge arm side , Flexible DC transmission system side current and filter capacitor voltage , the filter capacitor voltage The grid connection point voltage phase angle is obtained by phase locking using a software phase-locked loop SOGI-SPLL based on a second-order generalized integrator and grid voltage amplitude ; Use the second-order generalized integrator SOGI to respectively convert the inductor current on the bridge arm side and the filter capacitor voltage Transformed into a two-phase stationary vertical coordinate system The amount of and ;pass Coordinate transformation transforms the two-phase stationary vertical coordinate system The amount of and The dq component of the inductor current on the bridge arm side transformed to the two-phase synchronous rotating coordinate system dq and the dq component of the filter capacitor voltage .

[0098] Step S62: According to the dq component of the inductor current on the bridge arm side and the filter capacitor voltage dq component , the average active power is obtained by the active power calculation equation and the reactive power calculation equation and average reactive power .in, The active power calculation equation is: ; The reactive power calculation equation is: ; in, is the time constant of the first-order low-pass filter, s is the Laplace operator.

[0099] Step S63: Calculate the average active power output by the inverter , get the output angular frequency of the inverter , the output angular frequency The output phase angle of the inverter is obtained by integration .

[0100] In this embodiment, the average active power output by the inverter obtained in step S62 is , the output angular frequency of the inverter is obtained through the active power-frequency droop control equation , the output angular frequency The output phase angle of the inverter is obtained by integration .

[0101] The active power-frequency droop control equation is: ; in, The inverter is given an active power command The rated angular frequency corresponding to is the active power droop coefficient.

[0102] Step S64: According to the average reactive power output by the inverter , obtain the reference value of the dq component of the filter capacitor voltage of the inverter .

[0103] In this embodiment, the average reactive power output by the inverter obtained in step S62 is , the reference value of the inverter filter capacitor voltage dq component is obtained through the reactive power-amplitude droop control equation .

[0104] The reactive power-amplitude droop control equation is: ; in, The inverter is given a reactive power command The rated output voltage corresponding to the time, n is the reactive power droop coefficient.

[0105] Step S65: According to the dq component of the filter capacitor voltage , and the reference value of the filter capacitor voltage dq component , get the inductor current command signal .

[0106] In this embodiment, the dq component of the filter capacitor voltage obtained in step S61 , and the reference value of the filter capacitor voltage dq component obtained in step S64 , the inductor current command signal is obtained through the filter capacitor voltage control equation .

[0107] The filter capacitor voltage control equation is: ; in, is the proportional control coefficient, is the integral control coefficient, s is the Laplace operator.

[0108] Step S66: According to the dq component of the inductor current on the bridge arm side , and the inductor current command signal , get the control signal and .

[0109] In this embodiment, the dq component of the inductor current on the bridge arm side obtained in step S61 , and the inductor current command signal obtained in step S65 , the control signal is obtained through the inductor current inner loop control equation and .

[0110] The inner loop control equation of the inductor current is: ; in, is the proportional control coefficient, is the integral control coefficient, s is the Laplace operator.

[0111] Step S67: according to the current on the flexible DC transmission system side and the filter capacitor voltage , and the equivalent impedance of the flexible DC system , and voltage feed forward is obtained .

[0112] In this embodiment, the current on the flexible DC transmission system side obtained in step S61 can be and filter capacitor voltage , and the equivalent impedance of the flexible DC system obtained by the impedance identification algorithm , the voltage feedforward is obtained by the third formula The third formula is: .

[0113] Step S68: Adaptively adjust the voltage of the feedforward compensation according to the equivalent impedance of the flexible DC system to improve the stability margin of the inverter in the grid-following mode, so as to enhance the adaptability of the inverter to different equivalent impedances of DC systems.

[0114] Step S69: According to the control signal and ,pass The coordinates of the control signal and Transform to a two-phase stationary vertical coordinate system The amount of control under and ; Take the two-phase stationary vertical coordinate system The amount of control under With the voltage feed forward The inverter bridge arm voltage control signal is obtained by adding them together, and the switching signal of the inverter power device is generated by SPWM modulation, and the opening and closing of the inverter power device is controlled by the driving protection circuit.

[0115] In this embodiment, when the inverter does not perform mode switching, that is, only operates in a single grid-forming or grid-following mode, the voltage of the feedforward compensation or the controller parameters of the inverter can be adaptively adjusted according to the equivalent impedance to further improve the impedance adaptability of the inverter.

[0116] like Figure 6 As shown, Figure 6 The schematic diagram of the switching method between the grid-following mode and the grid-forming mode based on impedance hysteresis is shown in an embodiment of the present invention. To ensure the stability during switching, the switching between the grid-connected modes adopts the switching method based on impedance hysteresis: the equivalent impedance boundary value of the flexible direct current system when the inverter grid-following mode switches to the grid-forming mode is set to The equivalent impedance boundary value of the flexible DC system switching from the grid-building mode to the grid-following mode is .

[0117] In combination with the above embodiments, in one implementation, the present invention also provides a dual-mode switching control method for a new energy generation cluster based on impedance adaptation and transmitted through flexible direct current. In this method, ; ; in, The maximum flexible direct current system equivalent impedance for the inverter to maintain stable operation in the grid-following mode and have a phase margin of 30°; is the hysteresis coefficient, The numerical control is .

[0118] In this embodiment, an impedance hysteresis-based switching method is used to achieve switching between the inverter's grid-following and grid-building modes, thereby achieving soft switching between the two modes and improving the stability when switching between the grid-following and grid-building modes.

[0119] In combination with the above embodiments, in one implementation, the present invention also provides a dual-mode switching control method for a new energy power generation cluster based on impedance adaptation via flexible direct current transmission. Figure 7 As shown, Figure 7 It is a schematic diagram of an impedance small signal model structure in which an inverter operating in a grid-following mode is connected to an equivalent flexible DC system, shown in an embodiment of the present invention.

[0120] according to Figure 7 , the inverter in the grid-following mode is equivalent to an ideal grid-following mode through the Norton circuit model. With an output impedance In parallel, and with the equivalent impedance The variable flexible DC transmission system is connected; thus, it can be obtained: ; in, is the output impedance of the inverter in the grid-following mode, is the variable equivalent impedance of the flexible DC system, is the AC side voltage of the flexible DC system, is the AC side current of the flexible DC system, It is an equivalent ideal network type; According to the above formula, the inverter can operate stably only if the following conditions are met: When the inverter is off-grid, the AC side voltage of the flexible DC system Stable; when the variable equivalent impedance When it is 0, the inverter is equivalent to an ideal grid type Stability can be achieved by properly designing the closed-loop parameters. Therefore, the inverter stability depends on the variable equivalent impedance And the output impedance of the inverter in grid-following mode Ratio Whether the Nyquist criterion is met; according to Whether the Nyquist criterion is met, the maximum flexible DC system equivalent impedance that the inverter can operate stably in the grid-following mode with a 30° phase margin can be obtained. , the main steps are as follows, that is, in this method, in addition to the above steps, steps S71 to S73 may also be included: Step S71: gradually increase the variable equivalent impedance The value of the variable equivalent impedance is plotted Next The Nyquist curve of Step S72: Obtain the following two conditions: The target Nyquist curve: Condition 1: does not surround the point (-1, j0); Condition 2: is tangent to a circle with (-1, j0) as the center and 0.5 as the radius; where j is an imaginary unit; Step S73: The target Nyquist curve indicates that the inverter operates stably in the grid-following mode and has a phase margin of 30°. As the maximum flexible direct current system equivalent impedance .

[0121] like Figure 8 As shown, Figure 8 FIG. 1 is a general flow chart of a dual-mode control method for a renewable energy power generation cluster based on impedance adaptation and transmitted through flexible direct current according to an embodiment of the present invention. Figure 8 The method comprises the following steps: step 1, setting the initial mode and the switching boundary value; setting the initial mode of the inverter operation to the grid-following mode; setting the flexible direct current system equivalent impedance boundary value for switching the inverter from the grid-following mode to the grid-forming mode to The equivalent impedance boundary value of the flexible DC system switching from the grid-building mode to the grid-following mode is , whose expressions are: ; ;in, The maximum flexible DC system equivalent impedance that allows the inverter to maintain stable operation in grid-following mode and have a 30° phase margin; is the hysteresis coefficient, and its value is controlled at ; Step 2, after the inverter runs in the grid-following mode, start the impedance identification algorithm to obtain the equivalent impedance of the flexible DC system ; Step 3, judge the conditions Is it satisfied? If yes, return to step 2, otherwise go to step 4; in step 4, the inverter switches from the grid-following mode to the grid-forming mode; in step 5, after the inverter switched in step 4 runs in the grid-forming mode, start the impedance identification algorithm to obtain the grid impedance ; Step 6, judge the conditions Is it satisfied? If so, return to step 5, otherwise go to step 7; Step 7, the inverter switches from the grid-building mode to the grid-following mode; Step 8, after the inverter switched in step 7 runs in the grid-following mode, return to step 2 to continue running.

[0122] This embodiment provides a dual-mode control method for a new energy power generation cluster via flexible direct current transmission based on impedance self-adaptation, so as to solve the problem in the related technology that when a new energy power generation cluster is connected to the grid under different flexible direct current system equivalent impedance conditions in a scenario of flexible direct current transmission, a single grid-following or grid-forming mode can only operate stably within a smaller range of change of the flexible direct current system equivalent impedance. By switching between grid-connected modes, the stable operating range of the inverter under different flexible direct current system equivalent impedance conditions is expanded. Therefore, in the scenario of new energy power generation cluster being transmitted via a flexible direct current transmission system, the inverter in the cluster adopts a dual-mode switching control method based on impedance self-adaptation to improve the stability of the new energy power generation grid-connected system.

[0123] It should be noted that, for the sake of simplicity, the method embodiments are described as a series of action combinations, but those skilled in the art should be aware that the embodiments of the present invention are not limited by the order of the actions described, because according to the embodiments of the present invention, certain steps can be performed in other orders or simultaneously. Secondly, those skilled in the art should also be aware that the embodiments described in the specification are all preferred embodiments, and the actions involved are not necessarily required by the embodiments of the present invention.

[0124] Based on the same inventive concept, an embodiment of the present invention provides a dual-mode switching control device for a renewable energy power generation cluster based on impedance adaptation and transmitted through flexible direct current. Fig. 9 , Fig. 9 This is a structural block diagram of a dual-mode switching control device based on impedance adaptive transmission of a renewable energy power generation cluster through flexible direct current transmission provided by an embodiment of the present invention. Fig. 9 As shown, the dual-mode switching control device of the embodiment based on impedance self-adaptation for the new energy power generation cluster via flexible direct current transmission may include: The initial setting module is used to set the initial operation mode of the inverter to the grid-following mode, and to set the flexible direct current system equivalent impedance boundary value when the inverter switches from the grid-following mode to the grid-building mode to , the equivalent impedance boundary value of the flexible direct current system when the inverter switches from the grid-forming mode to the grid-following mode is set to ; The first control module is used to control the inverter to operate in the grid-following mode, and after the inverter operates in the grid-following mode, start impedance identification to obtain the equivalent impedance of the flexible direct current system ; The first determination module is used to determine whether ; The second control module is used to meet the In the case of the above, the steps are executed again to control the inverter to operate in the grid-following mode. After the inverter operates in the grid-following mode, impedance identification is started to obtain the equivalent impedance of the flexible direct current system. ; The first switching module is used for In the case of a power outage, controlling the inverter to switch from the grid-following mode to the grid-building mode; The third control module is used to control the inverter to operate in the grid-forming mode, and after the inverter operates in the grid-forming mode, start impedance identification to obtain the equivalent impedance of the flexible direct current system ; The second determination module is used to determine whether ; The fourth control module is used to meet the In the case of the above, the steps are executed again to control the inverter to operate in the grid-forming mode. After the inverter operates in the grid-forming mode, impedance identification is started to obtain the equivalent impedance of the flexible DC system. ; The second switching module is used to In the case of a power outage, controlling the inverter to switch from the grid-building mode to the grid-following mode; A fifth control module is used to re-execute the steps to control the inverter to operate in the grid-following mode, and after the inverter operates in the grid-following mode, start impedance identification to obtain the equivalent impedance of the flexible direct current system. , controlling the inverter to continue operating.

[0125] Optionally, the first switching module includes: The first acquisition module is used to collect the inductor current on the bridge arm side And the filter capacitor voltage , the filter capacitor voltage The grid connection point voltage phase angle is obtained by phase locking using a software phase-locked loop SOGI-SPLL based on a second-order generalized integrator and grid voltage amplitude ; Use the second-order generalized integrator SOGI to respectively convert the inductor current on the bridge arm side and the filter capacitor voltage Transformed into a two-phase stationary vertical coordinate system The amount of and ;pass Coordinate transformation transforms the two-phase stationary vertical coordinate system The amount of and Transformed to the two-phase synchronous rotating coordinate system dq, the dq component of the inductor current on the bridge arm side is obtained and the dq component of the filter capacitor voltage ; The third determining module is used to determine the dq component of the inductor current on the bridge arm side according to the and the filter capacitor voltage dq component , respectively, to obtain the average active power and average reactive power ; The fourth determining module is used to determine the average active power according to the average active power , get the output angular frequency of the inverter , the output angular frequency The output phase angle of the inverter is obtained by integration ; The fifth determining module is used to determine the phase angle of the grid connection point voltage according to the grid connection point voltage phase angle. , and the output phase angle of the inverter , get the phase synchronization signal , and the phase synchronization signal Superimposed on the inverter output angular frequency superior; The sixth determining module is used to determine the average reactive power output by the inverter. , obtain the reference value of the dq component of the filter capacitor voltage of the inverter ; The seventh determination module is used to determine the voltage amplitude of the grid connection point according to the voltage amplitude of the grid connection point. , and the reference value of the dq component of the filter capacitor voltage of the inverter , obtain the amplitude synchronization signal , and the amplitude synchronization signal Superimposed on the filter capacitor voltage dq component reference value superior; The first synchronization module is used to first complete the grid connection point voltage phase angle The output phase angle of the inverter phase synchronization, and then complete the grid connection point voltage amplitude The reference value of the filter capacitor voltage dq component The amplitude of is synchronized to complete the switching from the following network mode to the building network mode.

[0126] Optionally, the second switching module includes: The second acquisition module is used to collect the DC side filter capacitor Voltage on ; The first obtaining module is used to obtain the DC side filter capacitor according to the DC side filter capacitor. Voltage on , get the inductor current command signal ; An eighth determination module is used to convert the inductor current command signal as executive control variables; The third acquisition module is used to collect the filter capacitor voltage , using the second-order generalized integrator SOGI to convert the filter capacitor voltage Transformed into a two-phase stationary vertical coordinate system The amount of ,pass Coordinate transformation transforms the two-phase stationary vertical coordinate system The amount of Transformed to the two-phase synchronous rotating coordinate system dq, the dq component of the filter capacitor voltage is obtained and ; The first setting module is used to set the filter capacitor voltage dq component according to the filter capacitor voltage dq component and , set the reference value of the filter capacitor voltage dq component and the filter capacitor voltage dq component Equal, set the reference value of the filter capacitor voltage dq component and the filter capacitor voltage dq component Equal, get the dq component output value and , and and as mapping control variables; A first transition module is used to execute the control variable according to the and , and the mapping control variables and , complete the mapping control variables To the execution control variable The transition, and the completion of the mapping control variables To the execution control variable transition; Switching submodule, used when the mapping control variable and are numerically equal to the execution control variables and When the network-building mode is switched to the network-following mode, the switching is completed.

[0127] Optionally, the first control module includes: A marking module is used to inject non-characteristic subharmonic current with a frequency of 75 Hz at the common coupling point PCC; The fourth acquisition module is used to collect the filter capacitor voltage at the common coupling point PCC. and the current on the flexible DC transmission system side ; The first analysis module is used to analyze the filter capacitor voltage by fast Fourier transform FFT. and the current on the flexible DC transmission system side Analyze and obtain the amplitude of the voltage component at 75Hz frequency , the phase of the voltage component at 75Hz frequency , the amplitude of the current component at 75Hz frequency , the phase of the current component at 75Hz frequency ; The fourth acquisition module is used to collect the amplitude of the voltage component at a frequency of 75 Hz. and the amplitude of the current component at 75Hz , the amplitude of the equivalent impedance of the flexible DC system at a frequency of 75Hz is obtained ; According to the phase of the voltage component at 75Hz frequency and the phase of the current component at 75Hz , the phase of the equivalent impedance of the flexible DC system at 75Hz is obtained ;

[0128] The second acquisition module is used to obtain the amplitude of the equivalent impedance of the flexible direct current system at the frequency of 75 Hz. The phase of the equivalent impedance of the flexible DC system at 75Hz , and obtain the resistive component of the equivalent impedance of the flexible DC system and emotional weight ; The third obtaining module is used to obtain the resistive component of the equivalent impedance of the flexible direct current system at least based on and the perceptual component , the equivalent impedance of the flexible DC system is obtained .

[0129] Optionally, the first control module includes: The fifth acquisition module is used to collect the DC side filter capacitor Voltage on , Flexible DC transmission system side current , bridge arm side inductor current And the filter capacitor voltage , the filter capacitor voltage The grid connection point voltage phase angle is obtained by phase locking using a software phase-locked loop SOGI-SPLL based on a second-order generalized integrator ; Use the second-order generalized integrator SOGI to convert the bridge arm side inductor current Transformed into a two-phase stationary vertical coordinate system The amount of and ,pass Coordinate transformation transforms the two-phase stationary vertical coordinate system The amount of and The components transformed to the two-phase synchronous rotating coordinate system dq and ; The fourth obtaining module is used to obtain the DC side filter capacitor according to the DC side filter capacitor. Voltage on , get the inductor current command signal ; The fifth obtaining module is used to obtain the dq components of the inductor current on the bridge arm side according to the dq components of the inductor current on the bridge arm side and , and the inductor current command signal , get the control signal and ; The sixth obtaining module is used to obtain the current of the flexible direct current transmission system according to the current and the filter capacitor voltage , and the equivalent impedance of the flexible DC system , and voltage feed forward is obtained ; A first improving module is used to adaptively adjust the voltage of the feedforward compensation according to the equivalent impedance of the flexible DC system, so as to improve the stability margin of the inverter in the grid-following mode, so as to enhance the adaptability of the inverter to different equivalent impedances of the flexible DC system; The first control submodule is used to control the and ,pass The coordinates of the control signal and Transform to a two-phase stationary vertical coordinate system The amount of control under and ; Take the two-phase stationary vertical coordinate system The amount of control under With the voltage feed forward The inverter bridge arm voltage control signal is obtained by adding them together, and the switching signal of the inverter power device is generated by SPWM modulation, and the opening and closing of the inverter power device is controlled by the driving protection circuit.

[0130] Optionally, the third control module includes: The sixth acquisition module is used to collect the inductor current on the bridge arm side , Flexible DC transmission system side current and filter capacitor voltage , the filter capacitor voltage The grid connection point voltage phase angle is obtained by phase locking using a software phase-locked loop SOGI-SPLL based on a second-order generalized integrator and grid voltage amplitude ; Use the second-order generalized integrator SOGI to respectively convert the inductor current on the bridge arm side and the filter capacitor voltage Transformed into a two-phase stationary vertical coordinate system The amount of and ;pass Coordinate transformation transforms the two-phase stationary vertical coordinate system The amount of and The dq component of the inductor current on the bridge arm side transformed to the two-phase synchronous rotating coordinate system dq and the dq component of the filter capacitor voltage ; The seventh obtaining module is used to obtain the dq component of the inductor current on the bridge arm side according to the and the filter capacitor voltage dq component , respectively, to obtain the average active power and average reactive power ; An eighth acquisition module is used to obtain the average active power output by the inverter. , get the output angular frequency of the inverter , the output angular frequency The output phase angle of the inverter is obtained by integration ; The ninth acquisition module is used to obtain the average reactive power output by the inverter. , obtain the reference value of the dq component of the filter capacitor voltage of the inverter ; The tenth obtaining module is used to obtain the voltage dq component of the filter capacitor according to the filter capacitor voltage dq component , and the reference value of the filter capacitor voltage dq component , get the inductor current command signal ; The eleventh obtaining module is used to obtain the dq component of the inductor current on the bridge arm side according to the , and the inductor current command signal , get the control signal and ; The twelfth obtaining module is used to obtain the current of the flexible direct current transmission system side according to the and the filter capacitor voltage , and the equivalent impedance of the flexible DC system , and voltage feed forward is obtained ; The second improving module is used to adaptively adjust the voltage of the feedforward compensation according to the equivalent impedance of the flexible DC system, so as to improve the stability margin of the inverter in the grid-forming mode, so as to enhance the adaptability of the inverter to different equivalent impedances of DC systems; The second control submodule is used to control the and ,pass The coordinates of the control signal and Transform to a two-phase stationary vertical coordinate system The amount of control under and ; Take the two-phase stationary vertical coordinate system The amount of control under With the voltage feed forward The inverter bridge arm voltage control signal is obtained by adding them together, and the switching signal of the inverter power device is generated by SPWM modulation, and the opening and closing of the inverter power device is controlled by the driving protection circuit.

[0131] Optionally, ; ; in, The maximum flexible direct current system equivalent impedance for the inverter to maintain stable operation in the grid-following mode and have a phase margin of 30°; is the hysteresis coefficient, The numerical control is .

[0132] Optionally, the device further comprises: Curve determination module for gradually increasing the variable equivalent impedance The value of the variable equivalent impedance is plotted Next The Nyquist curve of The curve acquisition module is used to obtain the curves that meet the following two conditions: The target Nyquist curve is: Condition 1: not enclosing the point (-1, j0); Condition 2: tangent to a circle with (-1, j0) as the center and 0.5 as the radius; where j is an imaginary unit; The maximum equivalent impedance determination module is used for the target Nyquist curve to indicate that the inverter operates stably in the grid-following mode and has a 30° phase margin, and the variable equivalent impedance corresponding to the target Nyquist curve is As the maximum flexible direct current system equivalent impedance .

[0133] Based on the same inventive concept, another embodiment of the present invention provides an electronic device, such as Fig.10 shown. Fig.10 The present invention is a schematic diagram of an electronic device shown in an embodiment of the present invention. The electronic device includes a memory, a processor, and a computer program stored in the memory and executable on the processor, and when the processor executes, the steps in the dual-mode switching control method for a new energy power generation cluster based on impedance adaptation and transmitted through flexible direct current are implemented as described in any of the above embodiments of the present invention.

[0134] As for the device embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and the relevant parts can refer to the partial description of the method embodiment. Each embodiment in this specification is described in a progressive manner, and each embodiment focuses on the differences from other embodiments, and the same and similar parts between the embodiments can be referred to each other.

[0135] The above is a detailed introduction to the dual-mode switching control method, device and equipment for a new energy power generation cluster based on impedance adaptation and flexible direct current transmission provided by the present invention. Specific examples are used in this article to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea; at the same time, for general technical personnel in this field, according to the idea of ​​the present invention, there will be changes in the specific implementation method and application scope. In summary, the content of this specification should not be understood as a limitation on the present invention.

Claims

1. A dual-mode switching control method for a renewable energy power generation cluster based on impedance adaptation via flexible direct current transmission, characterized in that: The method comprises: The initial operation mode of the inverter is set to the grid-following mode, and the equivalent impedance boundary value of the flexible direct current system when the inverter switches from the grid-following mode to the grid-building mode is set to , the equivalent impedance boundary value of the flexible direct current system when the inverter switches from the grid-forming mode to the grid-following mode is set to ; Control the inverter to operate in the grid-following mode, and after the inverter operates in the grid-following mode, start impedance identification to obtain the equivalent impedance of the flexible direct current system ; Determine whether ; In satisfying In the case of the above, the steps are executed again to control the inverter to operate in the grid-following mode. After the inverter operates in the grid-following mode, impedance identification is started to obtain the equivalent impedance of the flexible direct current system. ; In dissatisfaction In the case of a power outage, controlling the inverter to switch from the grid-following mode to the grid-building mode; Control the inverter to operate in the grid-forming mode, and after the inverter operates in the grid-forming mode, start impedance identification to obtain the equivalent impedance of the flexible direct current system. ; Determine whether ; In satisfying In the case of the above, the steps are executed again to control the inverter to operate in the grid-forming mode. After the inverter operates in the grid-forming mode, impedance identification is started to obtain the equivalent impedance of the flexible DC system. ; In dissatisfaction In the case of a power outage, controlling the inverter to switch from the grid-building mode to the grid-following mode; Re-execute the steps to control the inverter to operate in the grid-following mode, and after the inverter operates in the grid-following mode, start impedance identification to obtain the equivalent impedance of the flexible direct current system , controlling the inverter to continue operating.

2. The dual-mode switching control method for flexible direct current transmission of a renewable energy power generation cluster based on impedance adaptation according to claim 1 is characterized in that: Controlling the inverter to switch from the grid-following mode to the grid-building mode includes: Collect the inductor current on the bridge arm side And the filter capacitor voltage , the filter capacitor voltage The grid connection point voltage phase angle is obtained by phase locking using a software phase-locked loop SOGI-SPLL based on a second-order generalized integrator and grid voltage amplitude ; Use the second-order generalized integrator SOGI to respectively convert the inductor current on the bridge arm side and the filter capacitor voltage Transformed into a two-phase stationary vertical coordinate system The amount of and ;pass Coordinate transformation transforms the two-phase stationary vertical coordinate system The amount of and Transformed to the two-phase synchronous rotating coordinate system dq, the dq component of the inductor current on the bridge arm side is obtained and the dq component of the filter capacitor voltage ; According to the dq component of the inductor current on the bridge arm side and the filter capacitor voltage dq component , respectively, to obtain the average active power and average reactive power ; According to the average active power , get the output angular frequency of the inverter , the output angular frequency The output phase angle of the inverter is obtained by integration ; According to the grid connection point voltage phase angle , and the output phase angle of the inverter , get the phase synchronization signal , and the phase synchronization signal Superimposed on the inverter output angular frequency superior; According to the average reactive power output by the inverter , obtain the reference value of the dq component of the filter capacitor voltage of the inverter ; According to the voltage amplitude of the grid connection point , and the reference value of the dq component of the filter capacitor voltage of the inverter , obtain the amplitude synchronization signal , and the amplitude synchronization signal Superimposed on the filter capacitor voltage dq component reference value superior; First complete the grid connection point voltage phase angle The output phase angle of the inverter phase synchronization, and then complete the grid connection point voltage amplitude The reference value of the filter capacitor voltage dq component The amplitude of is synchronized to complete the switching from the following network mode to the building network mode.

3. The dual-mode switching control method for the new energy power generation cluster based on impedance adaptation through flexible direct current transmission according to claim 1 is characterized in that: Controlling the inverter to switch from the grid-building mode to the grid-following mode includes: Collect DC side filter capacitor Voltage on ; According to the DC side filter capacitor Voltage on , get the inductor current command signal ; The inductor current command signal as executive control variables; Collect filter capacitor voltage , using the second-order generalized integrator SOGI to convert the filter capacitor voltage Transformed into a two-phase stationary vertical coordinate system The amount of ,pass Coordinate transformation transforms the two-phase stationary vertical coordinate system The amount of Transformed to the two-phase synchronous rotating coordinate system dq, the dq component of the filter capacitor voltage is obtained and ; According to the dq component of the filter capacitor voltage and , set the reference value of the filter capacitor voltage dq component and the filter capacitor voltage dq component Equal, set the reference value of the filter capacitor voltage dq component and the filter capacitor voltage dq component Equal, get the dq component output value and , and and as mapping control variables; According to the execution control variables and , and the mapping control variables and , complete the mapping control variables To the execution control variable The transition, and the completion of the mapping control variables To the execution control variable transition; When the mapping control variable and are numerically equal to the execution control variables and When the network-building mode is switched to the network-following mode, the switching is completed.

4. The dual-mode switching control method for the new energy power generation cluster based on impedance adaptation through flexible direct current transmission according to claim 1 is characterized in that: Start impedance identification and get the equivalent impedance of the flexible DC system ,include: Inject non-characteristic subharmonic current with a frequency of 75 Hz at the common coupling point PCC; Collect the filter capacitor voltage at the common coupling point PCC and the current on the flexible DC transmission system side ; The filter capacitor voltage is respectively calculated by fast Fourier transform (FFT). and the current on the flexible DC transmission system side Analyze and obtain the amplitude of the voltage component at 75Hz frequency , the phase of the voltage component at 75Hz frequency , the amplitude of the current component at 75Hz frequency , the phase of the current component at 75Hz frequency ; According to the amplitude of the voltage component at 75Hz frequency and the amplitude of the current component at 75Hz , the amplitude of the equivalent impedance of the flexible DC system at a frequency of 75Hz is obtained ; According to the phase of the voltage component at 75Hz frequency and the phase of the current component at 75Hz , the phase of the equivalent impedance of the flexible DC system at 75Hz is obtained ; According to the amplitude of the equivalent impedance of the flexible DC system at 75Hz frequency The phase of the equivalent impedance of the flexible DC system at 75Hz , and obtain the resistive component of the equivalent impedance of the flexible DC system and emotional weight ; At least based on the resistive component of the equivalent impedance of the flexible DC system and the perceptual component , the equivalent impedance of the flexible DC system is obtained .

5. The dual-mode switching control method for the new energy power generation cluster based on impedance adaptation through flexible direct current transmission according to claim 1 is characterized in that: Controlling the inverter to operate in the grid-following mode includes: Collect DC side filter capacitor Voltage on , Flexible DC transmission system side current , bridge arm side inductor current And the filter capacitor voltage , the filter capacitor voltage The grid connection point voltage phase angle is obtained by phase locking using a software phase-locked loop SOGI-SPLL based on a second-order generalized integrator ; Use the second-order generalized integrator SOGI to convert the bridge arm side inductor current Transformed into a two-phase stationary vertical coordinate system The amount of and ,pass Coordinate transformation transforms the two-phase stationary vertical coordinate system The amount of and The components transformed to the two-phase synchronous rotating coordinate system dq and ; According to the DC side filter capacitor Voltage on , get the inductor current command signal ; According to the dq component of the inductor current on the bridge arm side and , and the inductor current command signal , get the control signal and ; According to the current on the flexible DC transmission system side and the filter capacitor voltage , and the equivalent impedance of the flexible DC system , and voltage feed forward is obtained ; Adaptively adjusting the voltage of the feedforward compensation according to the equivalent impedance of the flexible DC system, improving the stability margin of the inverter in the grid-following mode, so as to enhance the adaptability of the inverter to different equivalent impedances of the flexible DC system; According to the control signal and ,pass The coordinates of the control signal and Transform to a two-phase stationary vertical coordinate system The amount of control under and ; Take the two-phase stationary vertical coordinate system The amount of control under With the voltage feed forward The inverter bridge arm voltage control signal is obtained by adding them together, and the switching signal of the inverter power device is generated by SPWM modulation, and the opening and closing of the inverter power device is controlled by the driving protection circuit.

6. The dual-mode switching control method for flexible direct current transmission of a renewable energy power generation cluster based on impedance self-adaptation according to claim 1 is characterized in that: Controlling the inverter to operate in the grid-forming mode includes: Collect the inductor current on the bridge arm side , Flexible DC transmission system side current and filter capacitor voltage , the filter capacitor voltage The grid connection point voltage phase angle is obtained by phase locking using a software phase-locked loop SOGI-SPLL based on a second-order generalized integrator and grid voltage amplitude ; Use the second-order generalized integrator SOGI to respectively convert the inductor current on the bridge arm side and the filter capacitor voltage Transformed into a two-phase stationary vertical coordinate system The amount of and ;pass Coordinate transformation transforms the two-phase stationary vertical coordinate system The amount of and The dq component of the inductor current on the bridge arm side transformed to the two-phase synchronous rotating coordinate system dq and the dq component of the filter capacitor voltage ; According to the dq component of the inductor current on the bridge arm side and the filter capacitor voltage dq component , respectively, to obtain the average active power and average reactive power ; According to the average active power output by the inverter , get the output angular frequency of the inverter , the output angular frequency The output phase angle of the inverter is obtained by integration ; According to the average reactive power output by the inverter , obtain the reference value of the dq component of the filter capacitor voltage of the inverter ; According to the dq component of the filter capacitor voltage , and the reference value of the filter capacitor voltage dq component , get the inductor current command signal ; According to the dq component of the inductor current on the bridge arm side , and the inductor current command signal , get the control signal and ; According to the current on the flexible DC transmission system side and the filter capacitor voltage , and the equivalent impedance of the flexible DC system , and voltage feed forward is obtained ; Adaptively adjusting the voltage of the feedforward compensation according to the equivalent impedance of the flexible DC system, improving the stability margin of the inverter in the grid-forming mode, so as to enhance the adaptability of the inverter to different equivalent impedances of DC systems; According to the control signal and ,pass The coordinates of the control signal and Transform to a two-phase stationary vertical coordinate system The amount of control under and ; Take the two-phase stationary vertical coordinate system The amount of control under With the voltage feed forward The inverter bridge arm voltage control signal is obtained by adding them together, and the switching signal of the inverter power device is generated by SPWM modulation, and the opening and closing of the inverter power device is controlled by the driving protection circuit.

7. The dual-mode switching control method for a new energy power generation cluster based on impedance self-adaptation through flexible direct current transmission according to any one of claims 1 to 6, characterized in that: ； ； in, The maximum flexible direct current system equivalent impedance for the inverter to maintain stable operation in the grid-following mode and have a phase margin of 30°; is the hysteresis coefficient, The numerical control is .

8. The dual-mode switching control method for flexible direct current transmission of a renewable energy power generation cluster based on impedance adaptation according to claim 7 is characterized in that: The method further comprises: Gradually increase the variable equivalent impedance The value of the variable equivalent impedance is plotted Next The Nyquist curve of Get the following two conditions The target Nyquist curve is: Condition 1: Do not surround the point (-1, j0); Condition 2: Tangent to a circle with (-1, j0) as center and 0.5 as radius; Where, j is the imaginary unit; The target Nyquist curve indicates that the inverter operates stably in the grid-following mode and has a phase margin of 30°. As the maximum flexible direct current system equivalent impedance .

9. A dual-mode switching control device based on impedance self-adaptation for a renewable energy power generation cluster via flexible direct current transmission, characterized in that: The device comprises: The initial setting module is used to set the initial operation mode of the inverter to the grid-following mode, and to set the flexible direct current system equivalent impedance boundary value when the inverter switches from the grid-following mode to the grid-building mode to , the equivalent impedance boundary value of the flexible direct current system when the inverter switches from the grid-forming mode to the grid-following mode is set to ; The first control module is used to control the inverter to operate in the grid-following mode, and after the inverter operates in the grid-following mode, start impedance identification to obtain the equivalent impedance of the flexible direct current system ; The first determination module is used to determine whether ; The second control module is used to meet the In the case of the above, the steps are executed again to control the inverter to operate in the grid-following mode. After the inverter operates in the grid-following mode, impedance identification is started to obtain the equivalent impedance of the flexible direct current system. ; The first switching module is used to In the case of a power outage, controlling the inverter to switch from the grid-following mode to the grid-building mode; The third control module is used to control the inverter to operate in the grid-forming mode, and after the inverter operates in the grid-forming mode, start impedance identification to obtain the equivalent impedance of the flexible direct current system ; The second determination module is used to determine whether ; The fourth control module is used to meet the In the case of the above, the steps are executed again to control the inverter to operate in the grid-forming mode. After the inverter operates in the grid-forming mode, impedance identification is started to obtain the equivalent impedance of the flexible DC system. ; The second switching module is used to In the case of a power outage, controlling the inverter to switch from the grid-building mode to the grid-following mode; A fifth control module is used to re-execute the steps to control the inverter to operate in the grid-following mode, and after the inverter operates in the grid-following mode, start impedance identification to obtain the equivalent impedance of the flexible direct current system. , controlling the inverter to continue operating.

10. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein: When the computer program is executed by the processor, the dual-mode switching control method for a new energy power generation cluster based on impedance adaptation and transmitted via flexible direct current is implemented as described in any one of claims 1 to 8.

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