Method and system for analyzing transient stability in fault stage of tracking-constructing network type converter series-parallel system

Abstract

The invention relates to the technical field of new energy grid-connected control, in particular to a fault stage transient stability analysis method and system for a following-constructed network type converter series-parallel system, and the method comprises the steps: enabling a constructed network type converter to be equivalent to a controlled voltage source series impedance, enabling a following network type converter to be equivalent to a controlled current source, and enabling the controlled current source to be equivalent to a controlled voltage source series impedance; the whole series-parallel system is equivalent to a scene in which double voltage sources and a single current source are jointly connected in parallel to a PCC point, and a series-parallel system model is constructed; according to the series-parallel system model, respectively representing an active power coupling term of the network-building type converter and a voltage coupling term of the network-following type converter under the condition of considering parallel connection of the network-following type converter and the network-building type converter; according to the coupling term, remodeling an active loop control structure of the network-constructing converter and a phase-locked loop synchronization structure of the network-following converter, and obtaining a transient analysis model of the series-parallel system considering the coupling term; the transient stability of the hybrid system in the power grid fault stage is analyzed through the transient analysis model, and the influence on the transient stability is effectively represented.

Description

Technical Field

[0001] This invention relates to the field of new energy grid-connected control technology, and in particular to a method and system for transient stability analysis during the fault stage of a grid-connected converter hybrid system. Background Technology

[0002] The widespread application of large-scale power electronic devices has significantly altered the dynamic characteristics of the power grid, leading to a weakening of system inertia support capabilities and a decrease in grid strength, resulting in a weak grid operation pattern dominated by power electronics. In response to the impact of large-scale renewable energy power plant integration on system stability and reliability, grid regulations have set forth certain requirements for the stable / transient operation specifications that renewable energy power plants must meet when connecting to the grid.

[0003] One of the important indicators is the low voltage ride-through performance index for new energy systems. This means that in response to different types of grid faults, new energy power plants are required to operate continuously without disconnecting from the grid while maintaining the system voltage above the minimum operating voltage curve required by the specifications. During this period, achieving transient stability during the fault phase is a prerequisite for fault ride-through in hybrid grid systems.

[0004] In existing technologies, transient stability analysis of grid-connected and grid-connected converters under grid faults still faces many challenges. For example, power coupling between different generating units in the grid-connected and grid-connected systems can cause offsets in the grid-connected function and the phase angle of the grid-connected phase-locked loop during large voltage disturbances, further increasing the difficulty of stability analysis. Furthermore, in grid-connected and grid-connected converter hybrid systems, the different control methods and parameters among different generating units make it difficult to characterize them using a single method.

[0005] The information disclosed in this background section is intended only to enhance the understanding of the general background of the invention and should not be construed as an admission or in any way implying that the information constitutes prior art known to those skilled in the art. Summary of the Invention

[0006] This invention provides a method and system for transient stability analysis during the fault stage of a hybrid system with a grid-connected converter, thereby effectively solving the problems in the background art.

[0007] To achieve the above objectives, the technical solution adopted by this invention is: a transient stability analysis method for a hybrid system with a grid-connected converter during the fault stage, comprising the following steps:

[0008] The grid-type converter is equivalent to a controlled voltage source in series impedance, the grid-type converter is equivalent to a controlled current source, and the hybrid system is equivalent to a scenario where two voltage sources and a single current source are connected in parallel at the PCC point, thus constructing a hybrid system model.

[0009] Based on the hybrid system model, the active power coupling term of the grid-type converter and the voltage coupling term of the grid-type converter are characterized respectively when considering parallel connection with the grid-type converter and the grid-type converter.

[0010] Based on the active loop control structure of the grid converter and the phase-locked loop synchronization structure of the grid converter, a transient analysis model of the hybrid system considering the coupling terms is obtained.

[0011] The transient stability of the hybrid system during the grid fault phase is analyzed using the transient analysis model.

[0012] Furthermore, the process of equating the hybrid system as a whole to a scenario where dual voltage sources and a single current source are connected in parallel at the PCC point, and constructing a hybrid system model, includes:

[0013] Construct the voltage network equations for the hybrid system;

[0014] Define the equivalent line impedance for each power generation unit;

[0015] Considering that grid-connected converters, grid-connected converters, and the power grid are connected in parallel, the equivalent admittance of the three equivalent power sources after parallel connection is defined.

[0016] Furthermore, the voltage network equation is as follows:

[0017]

[0018] In the formula, I GFL I GFM and I g These represent the vector currents injected into the PCC point by the grid-connected converter GFLC, the grid-connected converter GFMC, and the grid, respectively. pcc U GFM and U g These represent the voltages at the PCC point, the GFMC of the grid-connected converter, and the grid, respectively. GFM Y GFL and Y g These are the line admittance of grid-connected converters, grid-connected converters, and the power grid, respectively.

[0019] Furthermore, the equivalent impedance of the lines of each power generation unit is:

[0020]

[0021] In the formula, Z GFM Z GFL and Z g These are the equivalent line impedances of the grid-connected converter, the grid-connected converter, and the power grid, respectively. GFM θ GFL and θ gThese are the phase angles of the grid-connected converter, the grid-connected converter, and the power grid, respectively.

[0022] Furthermore, the equivalent admittance is:

[0023]

[0024] In the formula, θ0, θ G θ g and θ L Equivalent admittances Y0 and Y1 are respectively G Y g and Y L Admittance angle, Y0, Y G Y g and Y L Equivalent admittances Y0 and Y1 are respectively G Y g and Y L The magnitude of Y0 is the total admittance of GFMC connected in parallel with the grid admittance. G It is the parallel value of the admittances of GFMC and GFLC, Y g It is the grid admittance, Y L It is the parallel value of GFLC and grid admittance.

[0025] Furthermore, the description of the active power coupling term of the grid-type converter and the voltage coupling term of the grid-type converter, respectively considering parallel connection with the grid-type converter, includes the following steps:

[0026] Based on the hybrid system model, the output power of the grid-type converter is obtained when the hybrid system is operating normally in the power grid, considering the grid connection condition with the grid-type converter, and is used as the voltage source characteristic.

[0027] Considering the active power coupling terms between the grid-connected converter and the grid-connected converter when connected to the grid;

[0028] Based on the hybrid system model, the output current and internal potential of the grid-connected converter are obtained, and the output current is used as a controlled current source.

[0029] The projection of the internal potential of the grid converter onto the dq axis of a rotating coordinate system with the internal potential of the grid converter as the reference is obtained to obtain the grid converter terminal voltage coupling terms generated during grid converter operation and the grid converter terminal voltage coupling terms generated during grid operation.

[0030] Furthermore, the active power coupling term between the grid-connected converter and the grid-connected converter is as follows:

[0031]

[0032] Gs =Rel(1 / (Z) GFM ∠θ GFM +Z g ∠θ g ));

[0033] G g =1 / Z g ∠θ g ,

[0034] In the formula, Gs is the equivalent conductance after the GFMC is connected in parallel with the grid, Gg is the real part of the grid equivalent admittance, used to calculate the power coupling term between the GFMC and GFLC, Zg is the magnitude of the grid-side impedance, and P... couple For active power coupling terms, U GFM For the internal potential of the grid-type converter, I GFL For the vector current injected into the PCC point of the grid-connected converter GFLC, δ GFM The power angle of a grid-connected converter is referenced to the phase angle of an ideal power grid; θ0, θ G θ g and θ L The equivalent admittances Y0 and Y in the hybrid system model are respectively G Y g and Y L The admittance angle, δ GFL The power angle of the grid-type converter is referenced to the ideal grid phase angle. Z is the equivalent impedance angle of the grid converter; GFM and Z g These are the line equivalent impedances of the grid-type converter and the power grid, respectively.

[0035] Furthermore, the voltage coupling term of the grid-connected converter generated during operation and the voltage coupling term of the grid-connected converter generated during grid operation are calculated by the following formula:

[0036]

[0037] In the formula, Y0 is the total admittance of GFMC and grid admittance in parallel, Y G It is the parallel value of the admittances of GFMC and GFLC, Y g It is the grid admittance, Y L It is the parallel value of GFLC and grid admittance, where Ug is the equivalent voltage source of the grid; Y G U GFM cos(δ GFM +θ G -δ GFL ) and Y G U GFM sin(δ GFM +θ G -δGFL This refers to the voltage coupling term between the grid-connected converter and the grid-connected converter terminal voltage generated during grid-connected converter operation; -Y g U g cos(δ GFL -θ g ) and -Y g U g sin(δ GFL -θ g ) represents the voltage coupling term at the generator terminals of the grid-connected converter generated during grid operation; U GFL_d U GFL_q For the internal potential U of the grid-type converter GFM The internal potential U of the grid-connected converter GFL The projection onto the dq axis of a rotating coordinate system based on .

[0038] The present invention also includes a transient stability analysis system for a hybrid system with a grid-connected converter during a fault phase, using the method described above, wherein the system comprises:

[0039] The equivalent modeling unit is used to convert the grid-type converter into a controlled voltage source series impedance, the grid-type converter into a controlled current source, and the hybrid system into a scenario where two voltage sources and a single current source are connected in parallel at the PCC point, so as to build a hybrid system model.

[0040] The coupling derivation unit is used to characterize, based on the hybrid system model, the active power coupling term of the grid-type converter and the voltage coupling term of the grid-type converter, respectively, when considering parallel connection of the grid-type converter and the grid-type converter.

[0041] The reshaping unit is used to reshape the active loop control structure of the grid-type converter and the phase-locked loop synchronization structure of the grid-type converter according to the coupling terms, so as to obtain the transient analysis model of the hybrid system taking into account the coupling terms.

[0042] The analysis unit is used to analyze the transient stability of the hybrid system during the grid fault phase using the transient analysis model.

[0043] The present invention also includes a computer device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor, when executing the computer program, implements the method as described above.

[0044] The present invention also includes a storage medium having a computer program stored thereon, which, when executed by a processor, implements the method as described above.

[0045] The beneficial effects of this invention are as follows: By introducing the power coupling term and voltage coupling term of the grid-connected converter, the active power coupling term of the grid-connected converter and the voltage coupling term of the grid-connected converter are respectively characterized when considering the parallel connection of the grid-connected converter and the grid-connected converter. This effectively characterizes the influence of the key control parameters of the grid-connected converter and the grid-connected converter on the transient stability of the hybrid system through the coupling relationship. Based on the coupling term, the active power loop control structure of the grid-connected converter and the phase-locked loop synchronization structure of the grid-connected converter are reshaped to obtain the transient analysis model of the hybrid system considering the coupling term. Thus, a tool for analyzing the transient stability of the grid-connected converter hybrid system under grid fault conditions is provided. Attached Figure Description

[0046] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0047] Figure 1 This is a flowchart of the method in Example 1;

[0048] Figure 2 This is a schematic diagram of the system structure in Example 1;

[0049] Figure 3 This is a flowchart of the method in Example 2;

[0050] Figure 4 This is the equivalent circuit diagram of the hybrid system of the grid-type converter in Example 2;

[0051] Figure 5 Example 2 is a grid-type converter active power loop control structure that includes power coupling terms;

[0052] Figure 6 Example 2 shows the phase-locked loop control structure for a grid-connected converter that includes voltage coupling terms;

[0053] Figure 7 This is a schematic diagram of the structure of the computer device of the present invention. Detailed Implementation

[0054] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0055] Example 1:

[0056] like Figure 1As shown: A transient stability analysis method for a hybrid system with a grid-connected converter during the fault stage, comprising the following steps:

[0057] The grid-type converter is equivalent to a controlled voltage source in series impedance, the grid-type converter is equivalent to a controlled current source, and the hybrid system is equivalent to a scenario where two voltage sources and a single current source are connected in parallel at the PCC point, thus constructing a hybrid system model.

[0058] Based on the hybrid system model, the active power coupling term of the grid-type converter and the voltage coupling term of the grid-type converter are characterized respectively when considering parallel connection with the grid-type converter and the grid-type converter.

[0059] Based on the active loop control structure of the grid converter and the phase-locked loop synchronization structure of the grid converter, a transient analysis model of the hybrid system considering the coupling terms is obtained.

[0060] The transient stability of the hybrid system during the grid fault phase is analyzed using a transient analysis model.

[0061] By introducing the power and voltage coupling terms of the grid-connected converter, the active power coupling term of the grid-connected converter and the voltage coupling term of the grid-connected converter are characterized respectively when considering the parallel connection of the grid-connected converter and the grid-connected converter. This effectively characterizes the impact of the key control parameters of the grid-connected converter and the grid-connected converter on the transient stability of the hybrid system through the coupling relationship. Based on the coupling terms, the active power loop control structure of the grid-connected converter and the phase-locked loop synchronization structure of the grid-connected converter are reshaped to obtain the transient analysis model of the hybrid system considering the coupling terms. This provides an analytical tool for the transient stability of the grid-connected converter hybrid system under grid fault conditions.

[0062] In this embodiment, the hybrid system is equivalent to a scenario where two voltage sources and a single current source are connected in parallel at the PCC point. A hybrid system model is constructed, including:

[0063] Construct the voltage network equations for the hybrid system;

[0064] Define the equivalent line impedance for each power generation unit;

[0065] Considering that grid-connected converters, grid-connected converters, and the power grid are connected in parallel, the equivalent admittance of the three equivalent power sources after parallel connection is defined.

[0066] The voltage network equation is:

[0067]

[0068] In the formula, I GFL I GFM and I gThese represent the vector currents injected into the PCC point by the grid-connected converter GFLC, the grid-connected converter GFMC, and the grid, respectively. pcc U GFM and U g These represent the voltages at the PCC point, the GFMC of the grid-connected converter, and the grid, respectively. GFM Y GFL and Y g These are the line admittance of grid-connected converters, grid-connected converters, and the power grid, respectively.

[0069] The equivalent impedance of the lines for each power generation unit is as follows:

[0070]

[0071] In the formula, Z GFM Z GFL and Z g These are the equivalent line impedances of the grid-connected converter, the grid-connected converter, and the power grid, respectively. GFM θ GFL and θ g These are the phase angles of the grid-connected converter, the grid-connected converter, and the power grid, respectively.

[0072] The equivalent admittance is:

[0073]

[0074] In the formula, θ0, θ G θ g and θ L Equivalent admittances Y0 and Y1 are respectively G Y g and Y L Admittance angle, Y0, Y G Y g and Y L Equivalent admittances Y0 and Y1 are respectively G Y g and Y L The magnitude of Y0 is the total admittance of GFMC connected in parallel with the grid admittance. G It is the parallel value of the admittances of GFMC and GFLC, Y g It is the grid admittance, Y L It is the parallel value of GFLC and grid admittance.

[0075] In this embodiment, the active power coupling term of the grid-connected converter and the voltage coupling term of the grid-connected converter are characterized when considering parallel connection with the grid-connected converter and the grid-connected converter, respectively, including the following steps:

[0076] Based on the hybrid system model, when the hybrid system is operating normally in the power grid, considering the grid connection of the grid converter, the output power of the grid converter is used as a voltage source characteristic to support the system inertia and voltage stability.

[0077] Considering the active power coupling terms between the grid-connected converter and the grid-connected converter when connected to the grid;

[0078] Based on the hybrid system model, the output current and internal potential of the grid-connected converter are obtained, and the output current is used as a controlled current source to achieve accurate power point tracking.

[0079] The projection of the internal potential of the grid converter onto the dq axis of a rotating coordinate system with the internal potential of the grid converter as the reference is obtained to obtain the grid converter terminal voltage coupling terms generated during grid converter operation and the grid converter terminal voltage coupling terms generated during grid operation.

[0080] The active power coupling terms between grid-connected converters and interconnected converters are as follows:

[0081]

[0082] G s =Rel(1 / (Z) GFM ∠θ GFM +Z g ∠θ g ));

[0083] G g =1 / Z g ∠θ g ,

[0084] In the formula, Gs is the equivalent conductance after the GFMC is connected in parallel with the grid, Gg is the real part of the grid equivalent admittance, used to calculate the power coupling term between the GFMC and GFLC, Zg is the magnitude of the grid-side impedance, and P... couple For active power coupling terms, U GFM For the internal potential of the grid-type converter, I GFL For the vector current injected into the PCC point of the grid-connected converter GFLC, δ GFM The power angle of a grid-connected converter is referenced to the phase angle of an ideal power grid; θ0, θ G θ g and θ L The equivalent admittances Y0 and Y in the hybrid system model are respectively G Y g and Y L The admittance angle, δ GFL The power angle of the grid-type converter is referenced to the ideal grid phase angle. Z is the equivalent impedance angle of the grid converter;GFM and Z g These are the line equivalent impedances of the grid-type converter and the power grid, respectively.

[0085] The voltage coupling terms of the grid-connected converter terminals generated during grid-connected converter operation and the voltage coupling terms of the grid-connected converter terminals generated during grid operation are calculated by the following formula:

[0086]

[0087] In the formula, Y0 is the total admittance of GFMC and grid admittance in parallel, Y G It is the parallel value of the admittances of GFMC and GFLC, Y g It is the grid admittance, Y L It is the parallel value of GFLC and grid admittance, where Ug is the equivalent voltage source of the grid; Y G U GFM cos(δ GFM +θ G -δ GFL ) and Y G U GFM sin(δ GFM +θ G -δ GFL This refers to the voltage coupling term between the grid-connected converter and the grid-connected converter terminal voltage generated during grid-connected converter operation; -Y g U g cos(δ GFL -θ g ) and -Y g U g sin(δ GFL -θ g ) represents the voltage coupling term at the generator terminals of the grid-connected converter generated during grid operation; U GFL_d U GFL_q For the internal potential U of the grid-type converter GFM The internal potential U of the grid-connected converter GFL The projection onto the dq axis of a rotating coordinate system based on .

[0088] like Figure 2 As shown, this embodiment also includes a transient stability analysis system for a grid-connected converter hybrid system during the fault phase, using the method described above. The system includes:

[0089] The equivalent modeling unit is used to convert the grid-type converter into a controlled voltage source series impedance, the grid-type converter into a controlled current source, and the hybrid system into a scenario where two voltage sources and a single current source are connected in parallel at the PCC point, so as to build a hybrid system model.

[0090] The coupling derivation unit is used to characterize the active power coupling term of the grid-type converter and the voltage coupling term of the grid-type converter, respectively, considering the parallel connection of the grid-type converter and the grid-type converter, based on the hybrid system model.

[0091] The reshaping unit is used to reshape the active loop control structure of the grid-type converter and the phase-locked loop synchronization structure of the grid-type converter according to the coupling terms, so as to obtain the transient analysis model of the hybrid system taking into account the coupling terms.

[0092] The analysis unit is used to analyze the transient stability of the hybrid system during the grid fault phase using a transient analysis model.

[0093] Example 2:

[0094] like Figure 3 As shown, this embodiment includes a transient stability analysis method for a hybrid system with grid-connected converters during grid fault phases. The method includes: equivalently aggregating the grid-connected main circuit of the actual hybrid system into a dual-machine parallel grid-connected system; equivalently representing the grid-connected converter as a controlled voltage source series impedance; equivalently representing the grid-connected converter as a controlled current source; and equivalently representing the entire system as a scenario where dual voltage sources and a single current source are connected in parallel at the PCC point. Then, based on the hybrid system model, the transient stability analysis method considering the grid-connected converter is characterized. When converters are connected in parallel, the active and reactive currents injected into them generate active power coupling terms for the grid-type converters, and the active power loop control structure of the grid-type converters is reshaped based on these coupling terms. Secondly, based on the hybrid system model, the voltage coupling terms generated by the grid-type converters in the case of parallel grid-type converters are characterized, and the phase-locked loop synchronization structure of the grid-type converters is reshaped based on these coupling terms. Finally, a transient analysis model of the hybrid system of grid-type converters taking into account the coupling terms is obtained.

[0095] The specific steps are as follows:

[0096] S1. The actual grid-connected main circuit of the hybrid system of grid-connected converters is equivalently aggregated into a dual-machine parallel grid-connected system. The power grid is equivalent to a voltage source in series with the grid impedance. The external characteristics of the grid-connected converter can be equivalent to a controlled voltage source in series with the impedance, and the external characteristics of the grid-connected converter are equivalent to a controlled current source. The overall system is equivalent to a scenario where two voltage sources and a single current source are connected in parallel at the PCC point. The equivalent network structure of the hybrid system of grid-connected converters is as follows: Figure 4 As shown.

[0097] Figure 4 In the middle, δ GFM δ is the power angle of a grid-connected converter with reference to the phase angle of an ideal power grid. GFL The power angle of the grid-type converter is referenced to the ideal grid phase angle. To match the equivalent impedance angle of the grid converter, YGFM Y GFL and Y g These are the line admittance of grid-connected converters, grid-connected converters, and the power grid, respectively.

[0098] Combination Figure 4 The voltage network equations for the hybrid system of grid-connected converters are obtained as follows:

[0099]

[0100] Among them, I GFL I GFM and I g These are the vector currents injected into the PCC point by the GFLC, GFMC, and the grid, respectively.

[0101] Based on the impedance expression Z = Z∠θ = 1 / Y, the equivalent line impedance of each power generation unit is defined as follows:

[0102]

[0103] In a hybrid system, since the GFMC, GFLC, and power grid are connected in parallel, the following equivalent admittance is defined to express the equivalent admittance after the parallel connection of the three equivalent power sources, for the purpose of analysis below:

[0104]

[0105] Where, θ0, θ G θ g and θ L Equivalent admittances Y0 and Y1 are respectively G Y g and Y L The admittance angle.

[0106] S2. The active power loop of the grid-type converter adopts VSG control, and its external characteristics are analog synchronous generator (SG). Therefore, the mathematical model of its external characteristics is expressed as follows:

[0107]

[0108] Based on equation (1) and the inverter power output formula, the output power of the grid-connected converter under the condition of grid connection when the system is operating normally in the power grid is as follows:

[0109]

[0110] Among them, G s =Rel(1 / (Z) GFM ∠θ GFM +Z g ∠θg )), G g =1 / Z g ∠θ g According to the formula, when the power grid is operating normally, the active power output of the grid-connected converter is mainly determined by the internal electromotive force U of the grid-connected converter. GFM Decision. Considering grid connection with a grid-connected converter, there will be an active power coupling term P between the grid-connected converter and the grid-connected converter. couple ,Right now

[0111]

[0112] Combining equation (8), we obtain the reshaped active power loop of the grid-type converter, including power coupling terms, when the power grid is operating normally, as shown in equation (8). Figure 5 As shown, this active power loop is coupled through the active power coupling term P. couple Characterized by the control parameters of the grid-connected converter (such as I) GFL , and δ GFL The impact on the active power loop of grid-type converters.

[0113] S3. The grid-connected converter achieves synchronous operation with the power grid through a phase-locked loop. When a power grid fault occurs, the grid-connected converter directly adjusts the output current via a PI controller in the dq coordinate system. The output current I of the grid-connected converter is obtained according to equation (1). GFL The expression is as follows:

[0114] I GFL =(Y GFM +Y g )U pcc -Y GFM U GFM -Y g U g (9)

[0115] Furthermore, based on equation (9), the expression for the internal potential of the grid-connected converter is as follows:

[0116]

[0117] To specifically express the magnitude and phase angle of the voltage, current, and admittance of each unit, equation (10) is changed to a polynomial form of magnitude multiplied by phase angle as follows:

[0118]

[0119] Combining equation (11), the internal potential U of the grid-type converter is obtained. GFM The internal potential U of the grid-connected converter GFL The projection U on the dq axis of the rotating coordinate system based on the reference GFL_d UGFL_q The q-axis components are as follows:

[0120]

[0121] Among them, Y G U GFM cos(δ GFM +θ G -δ GFL ) and Y G U GFM sin(δ GFM +θ G -δ GFL The term -Y represents the voltage coupling between the grid-connected converter terminals and the grid-connected converter during operation. g U g cos(δ GFL -θ g ) and -Y g U g sin(δ GFL -θ g This refers to the voltage coupling term of the grid-connected converter terminal voltage generated during grid operation. The output of the grid-connected converter in a hybrid system can include three parts: the first part is the voltage drop caused by the output current of the grid-connected converter at the line impedance; the second part is the synchronization coupling term generated by the output voltage of the grid-connected converter; and the third part is the coupling synchronization term generated by the output voltage of the grid.

[0122] Taking into account the power angle δ of the grid-type converter GFM and line impedance voltage drop Y G U GFM The combined effect on the q-axis projection U of the internal potential of the grid-connected converter GFL_q After the coupling effect occurs, the reshaped phase-locked loop control structure of the grid converter, which includes voltage coupling terms, is as follows: Figure 6 As shown.

[0123] By introducing the power and voltage coupling terms of the grid-connected converter, the influence of the key control parameters of the grid-connected and grid-connected converters on the transient stability of the hybrid system through the coupling relationship is effectively characterized, providing an analytical tool for the transient stability of the grid-connected converter hybrid system under grid fault conditions.

[0124] Please see Figure 7 The diagram shows a structural schematic of a computer device provided in an embodiment of this application. An embodiment of this application provides a computer device 400, including a processor 410 and a memory 420. The memory 420 stores a computer program executable by the processor 410. When the computer program is executed by the processor 410, it performs the method described above.

[0125] This application embodiment also provides a storage medium 430, on which a computer program is stored, and the computer program is executed by a processor 410 to perform the above method.

[0126] The storage medium 430 can be implemented by any type of volatile or non-volatile storage device or a combination thereof, such as Static Random Access Memory (SRAM), Electrically Erasable Programmable Read-Only Memory (EEPROM), Erasable Programmable Read Only Memory (EPROM), Programmable Red-Only Memory (PROM), Read-Only Memory (ROM), magnetic storage, flash memory, magnetic disk, or optical disk.

[0127] In the description of this invention, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. "A plurality of" means two or more, unless otherwise explicitly specified.

[0128] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0129] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Furthermore, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0130] Any process or method description in the flowchart or otherwise herein can be understood as representing a module, segment, or portion of code comprising one or more executable instructions for implementing a particular logical function or process, and the scope of the preferred embodiments of the invention includes additional implementations in which functions may be performed not in the order shown or discussed, including substantially simultaneously or in reverse order depending on the functions involved, as will be understood by those skilled in the art to which embodiments of the invention pertain.

[0131] The logic and / or steps represented in the flowchart or otherwise described herein, for example, can be considered as a ordered list of executable instructions for implementing logical functions, and can be embodied in any computer-readable medium for use by, or in conjunction with, an instruction execution system, apparatus, or device (such as a computer-based system, a processor-included system, or other system that can fetch and execute instructions from, an instruction execution system, apparatus, or device). For the purposes of this specification, "computer-readable medium" can be any means that can contain, store, communicate, propagate, or transmit programs for use by, or in conjunction with, an instruction execution system, apparatus, or device. More specific examples (a non-exhaustive list) of computer-readable media include: an electrical connection having one or more wires (electronic device), a portable computer disk drive (magnetic device), random access memory (RAM), read-only memory (ROM), erasable and editable read-only memory (EPROM or flash memory), fiber optic devices, and portable optical disc read-only memory (CDROM). Alternatively, the computer-readable medium may be paper or other suitable media on which the program can be printed, since the program can be obtained electronically, for example, by optically scanning the paper or other medium, followed by editing, interpreting, or otherwise processing as necessary, and then stored in a computer memory.

[0132] It should be understood that various parts of the present invention can be implemented in hardware, software, firmware, or a combination thereof. In the above embodiments, multiple steps or methods can be implemented in software or firmware stored in memory and executed by a suitable instruction execution system. For example, if implemented in hardware, as in another embodiment, it can be implemented using any one or a combination of the following techniques known in the art: discrete logic circuits having logic gates for implementing logical functions on data signals, application-specific integrated circuits (ASICs) having suitable combinational logic gates, programmable gate arrays (PGAs), field-programmable gate arrays (FPGAs), etc.

[0133] Those skilled in the art will understand that all or part of the steps of the methods in the above embodiments can be implemented by a program instructing related hardware. The program can be stored in a computer-readable storage medium, and when executed, the program includes one or a combination of the steps of the method embodiments.

[0134] The storage medium mentioned above can be a read-only memory, a disk, or an optical disk, etc. Although embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for fault stage transient stability analysis of a grid-forming converter hybrid system, characterized in that, The method comprises the following steps: equivalent the grid-connected converter to a controlled voltage source in series with an impedance, equivalent the grid-following converter to a controlled current source, and equivalent the hybrid system as a whole to a scenario in which a double voltage source and a single current source are connected in parallel at the PCC point, to construct a hybrid system model; according to the hybrid system model, respectively represent the active power coupling term of the grid-connected converter and the voltage coupling term of the grid-following converter in the case of considering the parallel connection of the grid-following converter and the grid-connected converter; according to the coupling terms, reshape the active ring control structure of the grid-connected converter and the phase-locked loop synchronization structure of the grid-following converter, to obtain a transient analysis model of the hybrid system considering the coupling terms; analyze the transient stability of the hybrid system in the power grid fault stage through the transient analysis model. 2.The method according to claim 1, wherein, The step of constructing the hybrid system model by equivalent the hybrid system as a whole to a scenario in which a double voltage source and a single current source are connected in parallel at the PCC point comprises: constructing a voltage network equation of the hybrid system; defining line equivalent impedance of each power generation unit; considering that the grid-connected converter, the grid-following converter and the power grid are connected in parallel, defining equivalent admittance of the three kinds of equivalent power sources after parallel connection. 3.The method according to claim 2, wherein, The voltage network equation is: where I GFL , I GFM and I g are the vector currents of the grid following converter GFLC, the grid forming converter GFMC and the grid injection PCC point, respectively, U pcc , U GFM and U g are the voltages at the PCC point, the grid forming converter GFMC and the grid, respectively, Y GFM and Y g are the line admittances of the grid forming converter and the grid, respectively. 4.The method according to claim 3, wherein, The line equivalent impedance of each power generation unit is: wherein Z GFM , Z GFL and Z g are the line equivalent impedance of the grid-forming converter, the grid-following converter and the grid, respectively, Y GFL is the line admittance of the grid-following converter, and θ GFM , θ GFL and θ g are the phase angles of the grid-forming converter, the grid-following converter and the grid, respectively. 5.The method according to claim 4, wherein, The equivalent admittance is: In the formula, θ0, θ G θ g and θ L Equivalent admittances Y0 and Y1 are respectively G Y g and Y L Admittance angle, Y0, Y G Y g and Y L Equivalent admittances Y0 and Y1 are respectively G Y g and Y L The magnitude of the GFMC; Y0 is the total admittance of the GFMC connected in parallel with the grid admittance, Y G It is the parallel value of the admittances of GFMC and GFLC, Y g It is the grid admittance, Y L It is the parallel value of GFLC and grid admittance. 6.The method according to claim 1, wherein, The step of respectively representing the active power coupling term of the grid-connected converter and the voltage coupling term of the grid-following converter in the case of considering the parallel connection of the grid-following converter and the grid-connected converter comprises the following steps: according to the hybrid system model, obtaining the output power of the grid-connected converter under the condition of considering the grid-connected condition of the grid-following converter when the hybrid system is in normal operation, and taking the output power as a voltage source characteristic; considering the grid-connected condition of the grid-following converter, there is an active power coupling term between the grid-connected converter and the grid-following converter; according to the hybrid system model, obtaining the output current and internal potential of the grid-following converter, and taking the output current as a controlled current source; solving the projection of the internal potential of the grid-connected converter on the dq axis of the rotating coordinate system with the internal potential of the grid-following converter as the reference, to obtain the grid-following converter terminal voltage coupling term generated by the operation of the grid-connected converter and the grid-following converter terminal voltage coupling term generated by the operation of the power grid. 7.The method according to claim 6, wherein, The active power coupling term between the grid-connected converter and the grid-following converter is: G s = Rel(1 / (Z GFM ∠θ GFM +Z g ∠θ g )) G g = 1 / Z g ∠θ g , where Gs is the equivalent conductance of the parallel connection of GFMC and the grid, Gg is the real part of the grid equivalent admittance used to calculate the power coupling term between GFMC and GFLC, Zg is the grid-side impedance magnitude, P couple is the active power coupling term, U GFM is the internal voltage of the grid-forming converter, I GFL is the vector current injected by the grid-following converter GFLC at the PCC point, δ GFM is the power angle of the grid-forming converter referenced to the ideal grid phase angle; θ G , θ g and θ L are the admittance angles of the equivalent admittances Y G , Y g and Y L in the hybrid system model, respectively, θ GFM is the phase angle of the grid-forming converter, δ GFL is the power angle of the grid-following converter with the ideal grid phase angle as reference, is the equivalent impedance angle of the grid-following converter; Z GFM and Z g are the line equivalent impedances of the grid-forming converter and the grid, respectively. 8.The method according to claim 7, wherein, The grid-following converter terminal voltage coupling term generated by the operation of the grid-connected converter and the grid-following converter terminal voltage coupling term generated by the operation of the power grid are calculated by the following formula: where Y0is the total admittance of the parallel connection of the grid admittance and the GFMC admittance, Y G is the parallel value of the GFMC and GFLC admittances, Y g is the grid admittance, Y L is the parallel value of the GFLC and grid admittances, U g is the grid equivalent voltage source; Y G U GFM cos(δ GFM + θ G - δ GFL ) and Y G U GFM sin(δ GFM + θ G - δ GFL ) are the grid-forming converter operating generated grid-following converter machine terminal voltage coupling terms; -Y g U g cos(δ GFL - θ g ) and -Y g U g sin(δ GFL - θ g ) are the grid operating generated grid-following converter machine terminal voltage coupling terms; U GFL_d , U GFL_q is the grid-forming converter internal potential U GFM in the dq axes of the rotating coordinate system with the grid-following converter internal potential U GFL as the reference.

9. A transient stability analysis system for a hybrid system with a grid-connected converter during a fault phase, characterized in that, The system comprises: an equivalent modeling unit, configured to equivalent the grid-connected converter to a controlled voltage source in series with an impedance, equivalent the grid-following converter to a controlled current source, and equivalent the hybrid system as a whole to a scenario in which a double voltage source and a single current source are connected in parallel at the PCC point, to construct a hybrid system model; a coupling derivation unit, configured to according to the hybrid system model, respectively represent the active power coupling term of the grid-connected converter and the voltage coupling term of the grid-following converter in the case of considering the parallel connection of the grid-following converter and the grid-connected converter; a remodeling unit configured to remodel an active loop control structure of a grid-forming converter and a phase-locked loop synchronization structure of a grid-following converter according to the coupling term to obtain a transient analysis model of the hybrid system taking into account the coupling term; an analysis unit configured to analyze transient stability of the hybrid system during a power grid fault stage by using the transient analysis model.

10. A computer device comprising a memory, a processor, and a computer program stored on the memory and executable on the processor, characterized in that, The processor executes the computer program to implement the method of any one of claims 1-8.

11. A storage medium having stored thereon a computer program, characterized in that The computer program is executed by the processor to implement the method of any one of claims 1-8. The computer program is executed by the processor to implement the method of any one of claims 1-8.

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