Flexible DC electromechanical transient modeling method, apparatus, equipment and readable storage medium

Abstract

This application provides a method, apparatus, equipment, and readable storage medium for transient modeling of flexible DC electromechanical systems. This application can connect a flexible DC transmission system to an AC system. It can calculate the valve-side voltage reference value of the converter transformer in the flexible DC transmission system using the target voltage value of the converter bus and the reference values ​​of the d-axis and q-axis currents, maximizing the maintenance of the converter bus voltage at the target value and improving the numerical stability of the transient simulation of flexible DC electromechanical systems. Simultaneously, it can calculate the converter output current of the flexible DC transmission system based on the reference value of the valve-side voltage of the converter transformer and the actual value of the converter bus voltage, and perform limit judgment and processing on the converter output current to ensure that the converter switching devices do not experience overcurrent, thus improving equipment safety and the stability of the transient modeling of flexible DC electromechanical systems.

Description

Technical Field

[0001] This application relates to the field of DC power transmission technology, and in particular to a flexible DC electromechanical transient modeling method, apparatus, equipment and readable storage medium. Background Technology

[0002] One of the key advantages of flexible DC transmission technology is that it can achieve passive inversion and establish a stable voltage for the grid connection system. Flexible DC transmission technology includes two important application scenarios: one is to supply power to passive networks, such as supplying power to urban centers or islands through flexible DC transmission systems; the other is to send the voltage from power electronics such as wind power and photovoltaics to the grid through flexible DC transmission systems.

[0003] Flexible DC transmission systems typically employ direct current control, comprising an outer-loop controller and an inner-loop controller. When connecting a flexible DC transmission system to an active network, the outer-loop controller's control objectives are the active power, DC voltage, reactive power, and AC voltage of the flexible DC transmission system, yielding d-axis and q-axis current reference values. After obtaining these reference values, the inner-loop controller can control the valve-side voltage of the flexible DC transmission system based on the difference between the reference and actual d-axis and q-axis current values. To better study the technology of transmitting large-scale renewable energy via flexible DC transmission systems, modeling and simulation studies are needed.

[0004] Existing transient modeling methods for flexible DC transmission systems connected to active networks treat the flexible DC transmission system as a current source connected to the AC network, without considering factors such as the impedance of the converter transformer in the flexible DC transmission system; or they consider treating the flexible DC transmission system as a voltage source connected in series with the impedance of the converter transformer connected to the AC network. When applied to situations where the flexible DC transmission system is connected to an active network or is powered by a purely resistive system, these methods can basically reflect the dynamic process of the flexible DC transmission system. However, when applied to scenarios where large-scale renewable energy is transmitted via flexible DC transmission systems, the existing modeling equations suffer from serious numerical stability problems and cannot be used for modeling and simulating large-scale renewable energy transmission via flexible DC transmission systems. Summary of the Invention

[0005] This application aims to at least solve one of the above-mentioned technical defects. In view of this, this application provides a flexible DC electromechanical transient modeling method, apparatus, equipment and readable storage medium to solve the technical defect that the modeling equations in the prior art have serious numerical stability problems and cannot be used for modeling and simulation of large-scale new energy transmitted through flexible DC transmission systems.

[0006] A method for transient modeling of flexible DC electromechanical systems includes:

[0007] Connect the flexible DC transmission system to the AC system;

[0008] Based on the node voltage column vector of the AC system, the first voltage of the converter bus of the flexible DC transmission system is determined;

[0009] The first voltage is sent to the flexible DC transmission system;

[0010] Based on the preset outer loop controller model, the reference value of the control current of the flexible DC transmission system is calculated;

[0011] Based on the control current reference value of the flexible DC transmission system and the preset target voltage of the converter bus, the valve-side voltage reference value of the converter transformer of the flexible DC transmission system is determined. The preset target voltage includes the d-axis component and the q-axis component of the preset target control voltage of the converter bus, and the q-axis component of the preset target control voltage of the converter bus is 0.

[0012] Based on the reference value of the valve-side voltage of the converter transformer of the flexible DC transmission system and the first voltage, the actual valve-side voltage of the converter of the flexible DC transmission system is determined.

[0013] Based on the actual valve-side voltage of the converter in the flexible DC transmission system, the equivalent current source in the flexible DC transmission system is calculated.

[0014] Preferably, determining the actual valve-side voltage of the converter in the flexible DC transmission system based on the reference value of the valve-side voltage of the converter transformer and the first voltage includes:

[0015] Based on the valve-side voltage reference value of the converter transformer of the flexible DC transmission system and the first voltage, the first target current of the converter of the flexible DC transmission system is determined.

[0016] Determine whether the first target current exceeds a preset first threshold.

[0017] If the first target current exceeds a preset first threshold, then the first target current is set as a second target current, wherein the second target current is set according to the preset first threshold.

[0018] Based on the second target current, the actual valve-side voltage of the converter in the flexible DC transmission system is determined.

[0019] Preferably, the preset outer loop controller model creation process includes:

[0020] An outer-loop controller model is created based on a preset outer-loop control strategy, wherein the preset outer-loop control strategy is as follows:

[0021] The reference value and the actual value of the voltage of the converter bus are used as input signals;

[0022] The difference between the reference value and the actual value of the voltage of the converter bus is obtained by subtracting the reference value of the d-axis component and the reference value of the q-axis component of the converter bus voltage from the actual value of the d-axis component and the actual value of the q-axis component of the converter bus voltage, respectively.

[0023] The difference between the obtained voltage reference value and the actual voltage value of the converter bus is passed through a PI controller to obtain the control current reference value of the flexible DC transmission system. The control current reference value of the flexible DC transmission system includes d-axis and q-axis current reference values.

[0024] Preferably, the method further includes:

[0025] Based on the equivalent current source and the converter transformer reactance of the flexible DC transmission system, the node voltage column vector of the AC system is adjusted.

[0026] Preferably, the connection of the flexible DC transmission system to the AC system includes:

[0027] The flexible DC transmission system is connected to the AC system using a Norton equivalent circuit or a Thevenin equivalent circuit, wherein the Norton equivalent circuit or the Thevenin equivalent circuit includes an equivalent current source.

[0028] Preferably, before determining the first voltage of the converter bus of the flexible DC transmission system based on the node voltage column vector of the AC system, the method further includes:

[0029] Calculate the node voltage column vector of the AC system;

[0030] The formula for calculating the nodal voltage column vector of the AC system is as follows:

[0031]

[0032] in,

[0033] V represents the node voltage column vector of the AC system;

[0034] Y represents the node admittance matrix of the AC system;

[0035] I represents the column vector of node currents in the AC system.

[0036] Preferably, the calculation formula for determining the valve-side voltage reference value of the converter transformer of the flexible DC transmission system based on the control current reference value of the flexible DC transmission system and the preset target voltage of the converter bus includes:

[0037] U dref +jU qref =(U sdref +jU sqref )+(I dref +jI qref )*(R+jX)

[0038] in,

[0039] The direction of current flow from the converter to the converter bus in the flexible DC transmission system is considered positive.

[0040] U dref The d-axis reference value represents the voltage on the valve side of the converter transformer in a flexible DC transmission system.

[0041] U qref The q-axis reference value represents the valve-side voltage of the converter transformer in a flexible DC transmission system.

[0042] R represents the resistance of the converter transformer in the flexible DC transmission system;

[0043] X represents the reactance of the converter transformer in the flexible DC transmission system;

[0044] U sdref This represents the d-axis reference value of the converter bus voltage in a flexible DC transmission system.

[0045] U sqref This represents the q-axis reference value of the converter bus voltage in a flexible DC transmission system.

[0046] I dref This represents the d-axis reference value for the control current of the flexible DC transmission system.

[0047] I qref This represents the q-axis reference value for the control current of the flexible DC transmission system.

[0048] A flexible DC electromechanical transient modeling device, comprising:

[0049] The first setup unit is used to connect the flexible DC transmission system to the AC system;

[0050] The first voltage calculation unit is used to determine the first voltage of the converter bus of the flexible DC transmission system based on the node voltage column vector of the AC system.

[0051] A transmitting unit is configured to transmit the first voltage to the flexible DC transmission system;

[0052] The second voltage calculation unit is used to calculate the control current reference value of the flexible DC transmission system based on the preset outer loop controller model.

[0053] The third voltage calculation unit is used to determine the valve-side voltage reference value of the converter transformer of the flexible DC transmission system based on the control current reference value of the flexible DC transmission system and the preset target voltage of the converter bus. The preset target voltage includes the d-axis component and the q-axis component of the preset target control voltage of the converter bus, and the q-axis component of the preset target control voltage of the converter bus is 0.

[0054] The fourth voltage calculation unit is used to determine the actual valve-side voltage of the converter of the flexible DC transmission system based on the reference value of the valve-side voltage of the converter transformer of the flexible DC transmission system and the first voltage.

[0055] The current source calculation unit is used to calculate the equivalent current source in the flexible DC transmission system based on the actual valve-side voltage of the converter in the flexible DC transmission system.

[0056] A flexible DC electromechanical transient modeling device includes: one or more processors, and a memory;

[0057] The memory stores computer-readable instructions, which, when executed by the one or more processors, implement the steps of the flexible DC electromechanical transient modeling method as described above.

[0058] A readable storage medium storing computer-readable instructions, which, when executed by one or more processors, cause the one or more processors to perform the steps of the flexible DC electromechanical transient modeling method as described in any of the foregoing descriptions.

[0059] As can be seen from the above-described technical solutions, when it is necessary to conduct modeling and simulation studies on large-scale new energy transmission scenarios via flexible DC transmission, the method provided in this application embodiment can connect the flexible DC transmission system to an AC system. When the flexible DC transmission system is connected to the AC system, the flexible DC transmission system can serve as the power network of the AC system, and the first voltage of the converter bus of the flexible DC transmission system is determined based on the node voltage column vector of the AC system. After determining the first voltage of the converter bus of the flexible DC transmission system, the first voltage can be sent to the flexible DC transmission system, and the control current reference value of the flexible DC transmission system can be calculated based on the preset outer loop controller model. Thus, the control current reference value of the flexible DC transmission system and the preset outer loop controller model can be used to calculate the control current reference value of the flexible DC transmission system. Given a target voltage for the converter bus, a reference value for the valve-side voltage of the converter transformer in the flexible DC transmission system is determined. This target voltage includes the d-axis and q-axis components of a preset target control voltage for the converter bus, with the q-axis component being 0. After determining the reference value for the valve-side voltage of the converter transformer in the flexible DC transmission system, the actual valve-side voltage of the converter in the flexible DC transmission system can be determined based on this reference value and the first voltage. After determining the reference value for the valve-side voltage of the converter in the flexible DC transmission system, the equivalent current source in the flexible DC transmission system can be calculated based on the actual valve-side voltage of the converter.

[0060] The method provided in this application embodiment can connect a flexible DC transmission system to an AC system. It can calculate the valve-side voltage reference value of the converter transformer of the flexible DC transmission system using the target voltage value of the converter bus and the reference values ​​of the d-axis and q-axis currents, thereby maximizing the maintenance of the voltage of the converter bus of the flexible DC transmission system at the target value and improving the numerical stability of the transient simulation of flexible DC electromechanical systems. Attached Figure Description

[0061] To more clearly illustrate the technical solutions in the embodiments of this application 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 of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0062] Figure 1 This is a schematic diagram illustrating the Vf control principle of a flexible DC transmission system as an example of an embodiment of this application;

[0063] Figure 2This is a schematic diagram of the voltage amplitude variation curve of the converter bus of a flexible DC transmission system, as exemplified by an embodiment of this application.

[0064] Figure 3 A flowchart illustrating a method for implementing transient modeling of flexible DC electromechanical systems is provided in this application embodiment;

[0065] Figure 4 This is a schematic diagram illustrating a flexible DC transmission system supplying power to a passive system, as exemplified by an embodiment of this application.

[0066] Figure 5 This is a control block diagram of the outer loop controller of a flexible DC transmission system, as exemplified by an embodiment of this application.

[0067] Figure 6 This is a control block diagram of an inner loop controller for a flexible DC transmission system, as exemplified by an embodiment of this application.

[0068] Figure 7 This is a schematic diagram illustrating the principle of a flexible DC electromechanical transient model for accessing an active network, as exemplified by an embodiment of this application.

[0069] Figure 8 This is a schematic diagram illustrating the principle of a flexible DC electromechanical transient model for accessing a passive network, as exemplified by an embodiment of this application.

[0070] Figure 9 This is a schematic diagram of a flexible DC electromechanical transient modeling device as an example of an embodiment of this application;

[0071] Figure 10 This is a hardware structure block diagram of a flexible DC electromechanical transient modeling device disclosed in an embodiment of this application. Detailed Implementation

[0072] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0073] In practical applications, when a flexible DC transmission system is connected to a network without AC power, the flexible DC transmission system needs to establish a constant voltage amplitude and frequency for the connected system. Flexible DC transmission systems generally use a Vf control strategy to achieve this control objective. Here, Vf control strategy refers to a voltage-frequency conversion control strategy. Figure 1 A schematic diagram illustrating the Vf control principle of a flexible DC transmission system is provided.

[0074] I am Figure 1 middle:

[0075] U sdref This is represented as a reference value for the d-axis component of the converter bus voltage;

[0076] U sd This represents the actual value of the d-axis component of the converter bus voltage;

[0077] U sqref This represents the reference value for the q-axis component of the converter bus voltage;

[0078] U sq This represents the actual value of the q-axis component of the converter bus voltage;

[0079] I sdref Indicates the reference value of the d-axis component of the control current;

[0080] I sqref This represents the reference value for the q-axis component of the control current.

[0081] k ud T ud k uq And T uq These represent the control parameters of the PI controller.

[0082] In Vf control mode, the flexible DC transmission system has two control objectives: first, to control the frequency of the passive network to the rated frequency; and second, to control the voltage amplitude of the converter bus to remain constant. Generally, the frequency at which the flexible DC transmission system connects to a grid without AC power is a given value; therefore, the electrical angle is a fixed value, and the control system does not require a phase-locked loop (PLL).

[0083] The formula for calculating the electrical angle is:

[0084] θ=ω0t

[0085] Furthermore, since the electrical angle is given and the rotation speed of the dq coordinate system remains constant, to maintain a constant voltage and frequency, it is only necessary to control the actual value of the d-axis component of the converter bus voltage to a preset target voltage value, which means the actual value of the q-axis component of the converter bus voltage is 0, i.e.:

[0086] U sd =U m ;

[0087] U sq =0

[0088] in,

[0089] U m This indicates the preset target voltage value.

[0090] For flexible DC transmission systems connected to active networks, they are generally treated as controlled current sources connected to the AC grid in electromechanical transient modeling.

[0091] Existing transient modeling methods for flexible DC electromechanical systems connected to active networks generally treat the flexible DC transmission system as a current source connected to the AC network without considering factors such as the impedance of the converter transformer in the flexible DC transmission system; or treat the flexible DC transmission system as a voltage source connected in series with the impedance of the converter transformer connected to the AC network.

[0092] When applied to situations where flexible DC transmission systems are connected to active networks or when they are powered by purely resistive forces, the existing modeling equations can basically reflect the dynamic process of the flexible DC transmission system. However, when applied to scenarios where large-scale new energy sources are transmitted through flexible DC transmission systems, the existing modeling equations have serious numerical stability problems and are prone to situations where the system voltage remains constant during fault-free simulations.

[0093] as follows Figure 2 As shown, Figure 2 The example illustrates the voltage amplitude variation curve of the converter bus in a flexible DC transmission system, derived from... Figure 2 It can be known that:

[0094] The simulation lasted 1 second and no faults or other disturbances were set. Ideally, the simulation result of the voltage amplitude variation curve of the converter bus of the flexible DC transmission system should be a straight line with basically no fluctuations. However, from... Figure 2 It can be seen that before 0.2 seconds, the voltage amplitude of the converter bus of the flexible DC transmission system remains constant, but after 0.3 seconds, the voltage of the converter bus gradually oscillates and diverges, and the simulation results of the voltage amplitude of the converter bus of the flexible DC transmission system are no longer accurate. Therefore, the existing method is no longer suitable for modeling and simulating large-scale renewable energy transmission via flexible DC transmission systems.

[0095] Given that most current flexible DC electromechanical transient modeling schemes are ill-suited to complex and ever-changing operational requirements, this applicant has developed a flexible DC electromechanical transient modeling scheme. This scheme can connect the flexible DC transmission system to the AC system. It can calculate the valve-side voltage reference value of the converter transformer in the flexible DC transmission system using the target voltage value of the converter bus and the d-axis and q-axis current reference values, maximizing the maintenance of the converter bus voltage at the target value and improving the numerical stability of the flexible DC electromechanical transient simulation. Simultaneously, it can calculate the converter output current based on the valve-side voltage reference value of the converter transformer and the actual converter bus voltage, and perform limit judgment and processing on the converter output current to ensure that the converter switching devices do not experience overcurrent, thus improving equipment safety and the stability of the flexible DC electromechanical transient modeling.

[0096] The methods provided in this application can be used in a variety of general-purpose or special-purpose computing device environments or configurations. For example: personal computers, server computers, handheld or portable devices, tablet devices, multiprocessor devices, distributed computing environments including any of the above devices, etc.

[0097] This application provides a flexible DC electromechanical transient modeling method, which can be applied to various simulation systems and various computer terminals or smart terminals. The executing entity can be the processor or server of the computer terminal or smart terminal.

[0098] The following is combined Figure 3 , Figure 4 , Figure 5 , Figure 6 , Figure 7 and Figure 8 The following is a flowchart of the flexible DC electromechanical temporary modeling method provided in the embodiments of this application. Figure 3 As shown, the process may include the following steps:

[0099] Step S101: Connect the flexible DC transmission system to the AC system.

[0100] Specifically, in practical applications, flexible DC transmission systems can supply power to passive systems.

[0101] Figure 4 A schematic diagram illustrating a flexible DC transmission system supplying power to a passive system is provided.

[0102] like Figure 4 As shown:

[0103] AC1 is an active network;

[0104] AC2 is a passive system;

[0105] The flexible DC transmission system can obtain power from AC1 to supply power to AC2.

[0106] exist Figure 4 In the right-side flexible DC transmission system: the left node of R2+L2 is the valve side of the converter transformer, and the right node is the grid side of the converter transformer.

[0107] Flexible DC transmission systems can generally employ direct current control and may include an outer loop controller and an inner loop controller.

[0108] When a flexible DC transmission system is connected to an active network, the control targets of the outer loop controller can be active power, DC voltage, reactive power, AC voltage, etc., from which the d-axis and q-axis current reference values ​​of the flexible DC transmission system can be obtained. The inner loop controller can control the valve-side voltage of the converter transformer based on the difference between the d-axis and q-axis current reference values ​​and the actual values.

[0109] Among them, the control frame of the outer loop controller of the flexible DC transmission system Figure 1 Prajna Figure 5 As shown.

[0110] like Figure 5 As shown:

[0111] P s It can represent the actual value of active power at the converter bus;

[0112] P sref It can represent the reference value of active power at the converter bus;

[0113] Q s It can represent the actual value of reactive power at the converter bus;

[0114] Q sref It can represent the reference value of reactive power at the converter bus;

[0115] U dc It can represent the actual value of the converter's DC voltage;

[0116] U dcref It can represent the reference value of the converter's DC voltage;

[0117] U ac It can represent the actual value of the converter's DC voltage;

[0118] U acref It can represent the reference value of the converter's DC voltage;

[0119] I sdrefand I sqref These can represent the reference values ​​for the d-axis component and the q-axis component of the control current, respectively.

[0120] K and T can represent the control parameters of the PI controller.

[0121] U sd It can represent the d-axis component of the grid-side voltage of the converter transformer;

[0122] U sq It can represent the q-axis component of the grid-side voltage of the converter transformer;

[0123] U d It can represent the d-axis component of the valve-side voltage of the converter transformer;

[0124] U q It can represent the q-axis component of the valve-side voltage of a converter transformer.

[0125] Control frame of the inner loop controller of the flexible DC transmission system Figure 1 Prajna Figure 6 As shown,

[0126] like Figure 6 As shown:

[0127] I sd and I sdref The actual and reference values ​​of the d-axis component of the control current can be represented separately.

[0128] I sq and I sqref These can represent the actual and reference values ​​of the q-axis component of the control current, respectively.

[0129] U sd and U sq These can represent the actual values ​​of the d-axis and q-axis components of the converter bus voltage, respectively.

[0130] U dref and U qref It can represent the reference values ​​of the d-axis and q-axis components of the valve-side voltage of the converter transformer;

[0131] ω can represent the rated angular velocity, where,

[0132] ω = 2 * 50 * π;

[0133] L can represent the inductance of the converter transformer.

[0134] Therefore, when it is necessary to conduct modeling and simulation studies on large-scale new energy transmission scenarios via flexible DC, the flexible DC transmission system can be connected to the AC system so that the relevant parameters of the flexible DC transmission system can be set according to the relevant parameters of the AC system.

[0135] The flexible DC transmission system can be connected to the AC system using an equivalent circuit, wherein the equivalent circuit may include an equivalent current source; such as Figure 7 As shown, Figure 7 An example is provided: a schematic diagram illustrating the principle of a flexible DC electromechanical transient model connected to an active network; Figure 8 A schematic diagram illustrating the principle of a flexible DC electromechanical transient model connected to a passive network is provided.

[0136] in, Figure 8 middle:

[0137] R can represent the equivalent resistance of the converter transformer in a flexible DC transmission system;

[0138] X can represent the equivalent reactance of the converter transformer in a flexible DC transmission system;

[0139] Ieq can represent the equivalent current source of an equivalent circuit;

[0140] like Figure 7 and Figure 8 The flexible DC transmission system can be simulated as an equivalent circuit, and the equivalent circuit is connected to the AC system. The equivalent circuit includes an equivalent current source, and the current of the equivalent current source is set with reference to the control current reference value of the flexible DC transmission system.

[0141] For example, the flexible DC transmission system can be connected to the AC system using Norton equivalent circuits or Thevenin equivalent circuits.

[0142] The Norton equivalent circuit or Thevenin equivalent circuit may include an equivalent current source.

[0143] The essence of Norton's equivalent circuit is to equate the two-end network to a generator with internal resistance. That is, any two-end network can be represented by a generator with internal resistance after equivalent transformation, which is equivalent to the calculation of physical quantities outside the two-end network.

[0144] For the Norton equivalent circuit, the two-end network can be equivalent to a current source connected in parallel with an internal resistor; the calculation of voltage and current for the external circuit is completely equivalent.

[0145] It is worth noting that the "equivalence" in the equivalent circuit refers to equivalence from the perspective of the external network, not from the perspective of the internal network. Secondly, short-circuiting or disconnecting the external load simplifies the structure of the equivalent circuit, thus simplifying the calculations. Therefore, using the Norton equivalent circuit to connect the flexible DC transmission system to the AC system simplifies the calculation methods for the relevant parameters of both the flexible DC transmission system and the AC system.

[0146] Furthermore, since the equivalent circuit is generally composed of a controlled current source and a reactance connected in parallel, the reactance can be the reactance of the converter transformer, and the controlled current source can be obtained through calculation, which can help improve the numerical stability of the transient simulation of flexible DC electromechanical systems.

[0147] Step S102: Determine the first voltage of the converter bus of the flexible DC transmission system based on the node voltage column vector of the AC system.

[0148] Specifically, as described above, the method provided in this application embodiment can be used to connect the flexible DC transmission system to the AC system when modeling and simulating large-scale new energy transmission scenarios via flexible DC transmission. The flexible DC transmission system is connected to the AC system through an equivalent circuit. After connecting the flexible DC transmission system to the AC system, it is necessary to set the relevant parameters of the flexible DC transmission system. Thus, the relevant parameters of the flexible DC transmission system can be set according to the relevant parameters of the AC system.

[0149] For example, the first voltage of the converter bus of the flexible DC transmission system can be determined based on the node voltage column vector of the AC system, so that the voltage of the converter bus of the flexible DC transmission system can be set based on the first voltage.

[0150] The first voltage can be the actual voltage of the converter bus.

[0151] The first voltage can be set with reference to the node voltage column vector of the AC system.

[0152] Step S103: Send the first voltage to the flexible DC transmission system.

[0153] Specifically, as described above, the method provided in this application embodiment can determine the first voltage of the converter bus of the flexible DC transmission system based on the node voltage column vector of the AC system. After determining the first voltage, the first voltage can be sent to the flexible DC transmission system so that the voltage of the converter bus of the flexible DC transmission system can be set according to the first voltage.

[0154] Step S104: Calculate the reference value of the control current of the flexible DC transmission system based on the preset outer loop controller model.

[0155] Specifically, after connecting the flexible DC transmission system to the AC system, in addition to setting the voltage of the converter bus of the flexible DC transmission system, it is also necessary to set the reference value of the control current of the flexible DC transmission system. Since the flexible DC transmission system is controlled by an outer loop controller, the reference value of the control current of the flexible DC transmission system can be calculated based on a preset outer loop controller model, so that the reference value of the valve-side voltage of the converter transformer of the flexible DC transmission system can be determined based on the reference value of the control current of the flexible DC transmission system.

[0156] The control current reference value of the flexible DC transmission system may include the d-axis current reference value and the q-axis current reference value.

[0157] The preset outer loop controller model can be referenced. Figure 5 The control framework setup for the outer loop controller is shown.

[0158] in,

[0159] The preset outer loop controller model can be created based on the preset outer loop control strategy.

[0160] The preset outer loop control strategy can be set as follows:

[0161] The reference value and the actual value of the converter bus voltage can be used as the input signals for the outer loop controller model;

[0162] The difference between the reference value and the actual value of the voltage d-axis component of the converter bus can be obtained by subtracting the reference value and the actual value of the voltage d-axis component of the converter bus.

[0163] The difference between the obtained voltage reference value and the actual voltage value of the converter bus can be passed through a PI controller to obtain the control current reference value of the flexible DC transmission system. The control current reference value of the flexible DC transmission system includes d-axis and q-axis current reference values.

[0164] Step S105: Based on the control current reference value of the flexible DC transmission system and the preset target voltage of the converter bus, determine the valve-side voltage reference value of the converter transformer of the flexible DC transmission system. The preset target voltage includes the d-axis component and the q-axis component of the preset target control voltage of the converter bus, and the q-axis component of the preset target control voltage of the converter bus is 0.

[0165] Specifically, as described above, the method provided in this application embodiment can determine the control current reference value of the flexible DC transmission system, based on... Figure 5 The control principle of the outer loop controller model shown shows that the valve-side voltage reference value of the converter transformer in the flexible DC transmission system is related to the control current reference value of the flexible DC transmission system. The valve-side voltage reference value of the converter transformer in the flexible DC transmission system can be set according to the control current reference value of the flexible DC transmission system.

[0166] Therefore, after determining the control current reference value of the flexible DC transmission system, the valve-side voltage reference value of the converter transformer of the flexible DC transmission system can be further determined based on the control current reference value of the flexible DC transmission system and the preset target voltage of the converter bus. The preset target voltage may include the d-axis component and the q-axis component of the preset target control voltage of the converter bus, and the q-axis component of the preset target control voltage of the converter bus can be set to 0.

[0167] The target voltage of the preset converter bus can be set according to the engineering requirements in actual application.

[0168] The calculation formula for determining the reference value of the valve-side voltage of the converter transformer in the flexible DC transmission system may include the following:

[0169] U dref +jU qref =(U sdref +jU sqref )+(I dref +jI qref )*(R+jX)

[0170] in,

[0171] The positive direction can be defined as the direction of current flow from the converter to the converter bus in the flexible DC transmission system.

[0172] U dref This can represent the d-axis reference value of the converter transformer valve-side voltage in a flexible DC transmission system.

[0173] U qref This can represent the q-axis reference value of the converter transformer valve-side voltage in a flexible DC transmission system.

[0174] R can represent the resistance of the converter transformer in a flexible DC transmission system;

[0175] X can represent the reactance of the converter transformer in a flexible DC transmission system;

[0176] U sdref It can represent the d-axis reference value of the converter bus voltage in a flexible DC transmission system;

[0177] U sqrefIt can represent the q-axis reference value of the converter bus voltage in a flexible DC transmission system;

[0178] I dref It can represent the d-axis reference value of the control current in a flexible DC transmission system;

[0179] I qref It can represent the q-axis reference value of the control current in a flexible DC transmission system.

[0180] By using the target voltage of the converter bus and the d-axis and q-axis current reference values ​​of the control current of the flexible DC transmission system to calculate the valve-side voltage reference value of the converter transformer of the flexible DC transmission system, the voltage of the converter bus can be maintained at the target value to the maximum extent, and the numerical stability of the transient simulation of flexible DC electromechanical systems can also be effectively improved.

[0181] Step S106: Determine the actual valve-side voltage of the converter of the flexible DC transmission system based on the reference value of the valve-side voltage of the converter transformer of the flexible DC transmission system and the first voltage.

[0182] Specifically, as described above, the method provided in this application embodiment can determine the valve-side voltage reference value of the converter transformer in the flexible DC transmission system and the first voltage. Figure 5 and Figure 6 As can be seen from the control principles of the outer loop controller model and the inner loop controller model shown, the actual current of the converter in the flexible DC transmission system is related to the valve-side voltage of the converter transformer and the actual voltage of the converter bus in the flexible DC transmission system. The actual current of the converter in the flexible DC transmission system can be set with reference to the valve-side voltage of the converter transformer and the actual voltage of the converter bus in the flexible DC transmission system.

[0183] Therefore, after determining the reference value of the valve-side voltage of the converter transformer of the flexible DC transmission system and the first voltage, the actual valve-side voltage of the converter of the flexible DC transmission system can be determined based on the reference value of the valve-side voltage of the converter transformer of the flexible DC transmission system and the first voltage.

[0184] Step S107: Calculate the equivalent current source in the flexible DC transmission system based on the actual valve-side voltage of the converter in the flexible DC transmission system.

[0185] Specifically, as described above, the method provided in this application embodiment can determine the actual current of the converter in the flexible DC transmission system. The flexible DC transmission system is connected to the AC system in an equivalent circuit manner, as shown above. Figure 7 or Figure 8 As shown, the equivalent circuit generally includes an equivalent current source.

[0186] The equivalent current source can be set with reference to the actual current of the converter of the flexible DC transmission system. Therefore, after determining the actual current of the converter of the flexible DC transmission system, the equivalent current source in the flexible DC transmission system can be calculated based on the actual valve-side voltage of the converter of the flexible DC transmission system.

[0187] As can be seen from the above-described technical solutions, the method provided in this application embodiment can connect a flexible DC transmission system to an AC system. The target voltage value of the converter bus of the flexible DC transmission system and the reference values ​​of the d-axis and q-axis currents can be used to calculate the reference value of the valve-side voltage of the converter transformer of the flexible DC transmission system, thereby maximizing the maintenance of the voltage of the converter bus of the flexible DC transmission system at the target value and improving the numerical stability of the transient simulation of flexible DC electromechanical systems.

[0188] As described above, the method provided in this application embodiment can determine the actual valve-side voltage of the converter in the flexible DC transmission system based on the reference value of the valve-side voltage of the converter transformer and the first voltage. The process will be described below, and it may include the following steps:

[0189] Step S201: Determine the first target current of the converter of the flexible DC transmission system based on the valve-side voltage reference value of the converter transformer of the flexible DC transmission system and the first voltage.

[0190] Specifically, as described above, the method provided in this application embodiment can determine the valve-side voltage reference value of the converter transformer of the flexible DC transmission system and the first voltage.

[0191] As described above Figure 5 and Figure 6 As shown in the control logic, the current of the converter in the flexible DC transmission system is related to the reference value of the valve-side voltage of the converter transformer in the flexible DC transmission system and the actual voltage. The actual current of the converter in the flexible DC transmission system can be set with reference to the reference value of the valve-side voltage of the converter transformer in the flexible DC transmission system and the actual voltage.

[0192] Therefore, based on the valve-side voltage reference value of the converter transformer of the flexible DC transmission system and the first voltage, the first target current of the converter of the flexible DC transmission system is determined.

[0193] The first target current of the converter in the flexible DC transmission system can represent the actual current of the converter. This first target current includes a d-axis component and a q-axis component. The first target current can be calculated using the following formula:

[0194]

[0195] in,

[0196] I d It can represent the d-axis component of the actual current flowing out of the flexible DC converter;

[0197] I q It can represent the q-axis component of the actual current flowing out of the flexible DC converter;

[0198] U dref This can represent the d-axis reference value of the converter transformer valve-side voltage in a flexible DC transmission system.

[0199] U qref This can represent the q-axis reference value of the converter transformer valve-side voltage in a flexible DC transmission system.

[0200] R can represent the resistance of the converter transformer in a flexible DC transmission system;

[0201] X can represent the reactance of the converter transformer in a flexible DC transmission system;

[0202] U sdref It can represent the d-axis reference value of the converter bus voltage in a flexible DC transmission system;

[0203] U sqref It can represent the q-axis reference value of the converter bus voltage in a flexible DC transmission system.

[0204] Step S202: Determine whether the first target current exceeds a preset first threshold.

[0205] Specifically, in practical applications, because the current of the switching devices of the converter has a maximum limit, the d-axis component and the q-axis component of the first target current also have a maximum limit. If the first target current, including the d-axis component and the q-axis component, exceeds the maximum limit, it may damage the switching devices of the converter.

[0206] Therefore, after determining that the first target current includes both d-axis and q-axis components, it is necessary to perform a limit-crossing judgment on the first target current including both d-axis and q-axis components. Thus, after determining the first target current, it can be determined whether the first target current exceeds a preset first threshold.

[0207] The preset first threshold can be set with reference to the maximum current of the switching devices of the converter.

[0208] For example, the preset first threshold can be set to the maximum current of the switching devices of the converter.

[0209] If the first target current, including both the d-axis and q-axis components, exceeds the maximum limit, then step S203 can be executed.

[0210] Step S203: Set the first target current as the second target current, wherein the second target current is set according to the preset first threshold.

[0211] Specifically, as described above, if the first target current exceeds the maximum value of the switching devices of the converter, the equipment may be damaged. Therefore, after determining that the first target current exceeds the preset first threshold, the first target current can be set as the second target current, wherein the second target current is set according to the preset first threshold.

[0212] For example, the second target current can be set to the preset first threshold, that is, when the first target current exceeds the maximum current of the converter, the actual current of the converter can be set to the maximum current of the converter.

[0213] Step S204: Determine the actual valve-side voltage of the converter of the flexible DC transmission system based on the second target current.

[0214] Specifically, as described above, the method provided in this application embodiment can determine the actual current of the converter of the flexible DC transmission system. The actual valve-side voltage of the converter of the flexible DC transmission system is related to the actual current of the converter of the flexible DC transmission system. The actual valve-side voltage of the converter of the flexible DC transmission system can be set with reference to the actual current of the converter of the flexible DC transmission system.

[0215] Therefore, after determining the second target current, the actual valve-side voltage of the converter of the flexible DC transmission system can be determined based on the second target current.

[0216] As can be seen from the above-described technical solutions, the method provided in this application embodiment can connect a flexible DC transmission system to an AC system. It can calculate the valve-side voltage reference value of the converter transformer in the flexible DC transmission system using the target voltage value of the converter bus and the reference values ​​of the d-axis and q-axis currents, maximizing the maintenance of the converter bus voltage at the target value and improving the numerical stability of the transient simulation of flexible DC electromechanical systems. Simultaneously, it can calculate the converter output current of the flexible DC transmission system based on the reference value of the valve-side voltage of the converter transformer and the actual value of the converter bus voltage, and perform limit judgment and processing on the converter output current to ensure that the converter switching devices of the flexible DC transmission system do not experience overcurrent, which is beneficial to improving equipment safety and the stability of the transient modeling of flexible DC electromechanical systems.

[0217] In practical applications, after determining the equivalent current source of the flexible DC transmission system, the method provided in this application embodiment can further adjust the node voltage column vector of the AC system based on the equivalent current source. This process is described below and may include the following:

[0218] Based on the equivalent current source and the converter transformer reactance of the flexible DC transmission system, the node voltage column vector of the AC system is adjusted.

[0219] Specifically, as described above, the method provided in this application embodiment can determine the equivalent current source of the flexible DC transmission system based on the actual valve-side voltage of the converter of the flexible DC transmission system. The equivalent current source is related to the relevant parameters of the AC system. Therefore, after determining the equivalent current source, the node voltage column vector of the AC system can be adjusted based on the equivalent current source and the converter transformer reactance of the flexible DC transmission system to gradually adjust the relevant parameters of the flexible DC transmission system and the AC system, so that the numerical values ​​of the flexible DC electromechanical transient modeling tend to stabilize.

[0220] As can be seen from the above-described technical solution, after determining the equivalent current source of the flexible DC transmission system, the method provided in this application embodiment can further adjust the node voltage column vector of the AC system according to the equivalent current source, so as to gradually adjust the relevant parameters of the flexible DC transmission system and the AC system, so that the numerical values ​​of the flexible DC electromechanical transient modeling tend to be stable.

[0221] As described above, the method provided in this application embodiment can determine the first voltage of the converter bus of the flexible DC transmission system based on the node voltage column vector of the AC system. In practical applications, before determining the first voltage of the converter bus of the flexible DC transmission system based on the node voltage column vector of the AC system, the method provided in this application embodiment can also first calculate the node voltage column vector of the AC system so that the first voltage of the converter bus of the flexible DC transmission system can be determined based on the node voltage column vector of the AC system. This process will be described below, and may include the following:

[0222] Calculate the node voltage column vector of the AC system;

[0223] in,

[0224] The formula for calculating the node voltage column vector of the AC system may include the following:

[0225]

[0226] in,

[0227] V can represent the node voltage column vector of the AC system;

[0228] Y can represent the node admittance matrix of the AC system;

[0229] I can represent the column vector of node currents in the AC system.

[0230] As can be seen from the above-described technical solutions, before determining the first voltage of the converter bus of the flexible DC transmission system based on the node voltage column vector of the AC system, the method provided in this application embodiment can first calculate the node voltage column vector of the AC system so that the first voltage of the converter bus of the flexible DC transmission system can be determined based on the node voltage column vector of the AC system.

[0231] The flexible DC electromechanical temporary modeling device provided in the embodiments of this application is described below. The flexible DC electromechanical temporary modeling device described below and the flexible DC electromechanical temporary modeling method described above can be referred to in correspondence.

[0232] See Figure 9 , Figure 9 This is a schematic diagram of a flexible DC electromechanical temporary modeling device disclosed in an embodiment of this application.

[0233] like Figure 9 As shown, the flexible DC electromechanical temporary modeling device may include:

[0234] The first setting unit 101 is used to connect the flexible DC transmission system to the AC system;

[0235] The first voltage calculation unit 102 is used to determine the first voltage of the converter bus of the flexible DC transmission system based on the node voltage column vector of the AC system.

[0236] Transmitting unit 103 is used to transmit the first voltage to the flexible DC transmission system;

[0237] The second voltage calculation unit 104 is used to calculate the control current reference value of the flexible DC transmission system based on the preset outer loop controller model.

[0238] The third voltage calculation unit 105 is used to determine the valve-side voltage reference value of the converter transformer of the flexible DC transmission system based on the control current reference value of the flexible DC transmission system and the preset target voltage of the converter bus. The preset target voltage includes the d-axis component and the q-axis component of the preset target control voltage of the converter bus, and the q-axis component of the preset target control voltage of the converter bus is 0.

[0239] The fourth voltage calculation unit 106 is used to determine the actual valve-side voltage of the converter of the flexible DC transmission system based on the valve-side voltage reference value of the converter transformer of the flexible DC transmission system and the first voltage.

[0240] The current source calculation unit 107 is used to calculate the equivalent current source in the flexible DC transmission system based on the actual valve-side voltage of the converter in the flexible DC transmission system.

[0241] As can be seen from the above-described technical solutions, when it is necessary to conduct modeling and simulation studies on large-scale new energy transmission via flexible DC, the device provided in this application embodiment can use the first setting unit 101 to connect the flexible DC transmission system to the AC system. When the flexible DC transmission system is connected to the AC system, the flexible DC transmission system can serve as the power network of the AC system, and the first voltage calculation unit 102 can determine the first voltage of the converter bus of the flexible DC transmission system based on the node voltage column vector of the AC system. After determining the first voltage of the converter bus of the flexible DC transmission system, the first voltage can be sent to the flexible DC transmission system using the sending unit 103, and the second voltage calculation unit 104 can calculate the control current reference value of the flexible DC transmission system based on the preset outer loop controller model. Thus, the third voltage calculation unit 105 can calculate the control current reference value of the flexible DC transmission system based on the preset outer loop controller model. Based on the reference value of the control current of the flexible DC transmission system and the preset target voltage of the converter bus, the reference value of the valve-side voltage of the converter transformer of the flexible DC transmission system is determined. The preset target voltage includes the d-axis and q-axis components of the preset target control voltage of the converter bus, with the q-axis component being 0. After determining the reference value of the valve-side voltage of the converter transformer of the flexible DC transmission system, the fourth voltage calculation unit 106 can use the reference value of the valve-side voltage of the converter transformer of the flexible DC transmission system and the first voltage to determine the actual valve-side voltage of the converter of the flexible DC transmission system. After determining the reference value of the valve-side voltage of the converter of the flexible DC transmission system, the current source calculation unit 107 can use the actual valve-side voltage of the converter of the flexible DC transmission system to calculate the equivalent current source in the flexible DC transmission system.

[0242] The method provided in this application embodiment can connect a flexible DC transmission system to an AC system. It can calculate the valve-side voltage reference value of the converter transformer of the flexible DC transmission system using the target voltage value of the converter bus and the reference values ​​of the d-axis and q-axis currents, thereby maximizing the maintenance of the voltage of the converter bus of the flexible DC transmission system at the target value and improving the numerical stability of the transient simulation of flexible DC electromechanical systems.

[0243] Further optionally, the fourth voltage calculation unit 106 described above may include:

[0244] The first target current calculation unit is used to determine the first target current of the converter of the flexible DC transmission system based on the valve side voltage reference value of the converter transformer of the flexible DC transmission system and the first voltage.

[0245] The judgment unit is used to determine whether the first target current exceeds a preset first threshold.

[0246] The second setting unit is used to set the first target current as a second target current when the execution result of the judgment unit determines that the first target current exceeds a preset first threshold, wherein the second target current is set according to the preset first threshold.

[0247] The actual valve-side voltage calculation unit is used to determine the actual valve-side voltage of the converter of the flexible DC transmission system based on the second target current.

[0248] Further optionally, the preset outer loop controller model creation process includes:

[0249] Create an outer loop controller model based on the preset outer loop control strategy;

[0250] The preset outer loop control strategy is as follows:

[0251] The reference value and the actual value of the voltage of the converter bus are used as input signals;

[0252] The difference between the reference value and the actual value of the voltage of the converter bus is obtained by subtracting the reference value of the d-axis component and the reference value of the q-axis component of the converter bus voltage from the actual value of the d-axis component and the actual value of the q-axis component of the converter bus voltage, respectively.

[0253] The difference between the obtained voltage reference value and the actual voltage value of the converter bus is passed through a PI controller to obtain the control current reference value of the flexible DC transmission system. The control current reference value of the flexible DC transmission system includes d-axis and q-axis current reference values.

[0254] Further optionally, the device may also include:

[0255] The node voltage adjustment unit is used to adjust the node voltage column vector of the AC system based on the equivalent current source and the converter transformer reactance of the flexible DC transmission system.

[0256] Further optionally, the first setting unit 101 may include:

[0257] The first setting subunit is used to connect the flexible DC transmission system to the AC system using a Norton equivalent circuit or a Thevenin equivalent circuit, wherein the Norton equivalent circuit or the Thevenin equivalent circuit includes an equivalent current source.

[0258] Further optionally, the device may also include:

[0259] A node voltage calculation unit is used to calculate the node voltage column vector of the AC system;

[0260] The formula for calculating the nodal voltage column vector of the AC system is as follows:

[0261]

[0262] in,

[0263] V can represent the node voltage column vector of the AC system;

[0264] Y can represent the node admittance matrix of the AC system;

[0265] I can represent the column vector of node currents in the AC system.

[0266] Further optionally, the calculation formula for the valve-side voltage reference value of the converter transformer in the flexible DC transmission system may include:

[0267] U dref +jU qref =(U sdref +jU sqref )+(I dref +jI qref )*(R+jX)

[0268] in,

[0269] The positive direction can be defined as the direction of current flow from the converter to the converter bus in the flexible DC transmission system.

[0270] U dref This can represent the d-axis reference value of the converter transformer valve-side voltage in a flexible DC transmission system.

[0271] U qref This can represent the q-axis reference value of the converter transformer valve-side voltage in a flexible DC transmission system.

[0272] R can represent the resistance of the converter transformer in a flexible DC transmission system;

[0273] X can represent the reactance of the converter transformer in a flexible DC transmission system;

[0274] U sdrefIt can represent the d-axis reference value of the converter bus voltage in a flexible DC transmission system;

[0275] U sqref It can represent the q-axis reference value of the converter bus voltage in a flexible DC transmission system;

[0276] I dref It can represent the d-axis reference value of the control current in a flexible DC transmission system;

[0277] I qref It can represent the q-axis reference value of the control current in a flexible DC transmission system.

[0278] The specific processing flow of each unit included in the aforementioned flexible DC electromechanical temporary modeling device can be found in the relevant introduction of the flexible DC electromechanical temporary modeling method section above, and will not be repeated here.

[0279] The flexible DC electromechanical temporary modeling device provided in this application embodiment can be applied to flexible DC electromechanical temporary modeling equipment, such as terminals: mobile phones, computers, etc. Optionally, Figure 10 The hardware structure block diagram of the flexible DC electromechanical temporary modeling device is shown, with reference to Figure 10 The hardware structure of the flexible DC electromechanical temporary modeling device may include: at least one processor 1, at least one communication interface 2, at least one memory 3, and at least one communication bus 4.

[0280] In this embodiment, the number of processor 1, communication interface 2, memory 3, and communication bus 4 is at least one, and processor 1, communication interface 2, and memory 3 communicate with each other through communication bus 4.

[0281] Processor 1 may be a central processing unit (CPU), an application-specific integrated circuit (ASIC), or one or more integrated circuits configured to implement the embodiments of this application.

[0282] Memory 3 may include high-speed RAM, and may also include non-volatile memory, such as at least one disk storage device;

[0283] The memory stores a program, and the processor can call the program stored in the memory. The program is used to implement the various processing flows in the aforementioned terminal flexible DC electromechanical temporary modeling scheme.

[0284] This application embodiment also provides a readable storage medium that can store a program suitable for processor execution, the program being used to: implement the various processing flows of the aforementioned terminal in the flexible DC electromechanical temporary modeling scheme.

[0285] Finally, it should be noted that in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0286] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0287] The above description of the disclosed embodiments enables those skilled in the art to make or use this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Various embodiments can be combined with each other. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for transient modeling of flexible DC electromechanical systems, characterized in that, include: Connect the flexible DC transmission system to the AC system; Based on the node voltage column vector of the AC system, the first voltage of the converter bus of the flexible DC transmission system is determined; The first voltage is sent to the flexible DC transmission system; Based on the preset outer loop controller model, the reference value of the control current of the flexible DC transmission system is calculated; Based on the control current reference value of the flexible DC transmission system and the preset target voltage of the converter bus, the valve-side voltage reference value of the converter transformer of the flexible DC transmission system is determined. The preset target voltage includes the d-axis component and the q-axis component of the preset target control voltage of the converter bus, and the q-axis component of the preset target control voltage of the converter bus is 0. Based on the reference value of the valve-side voltage of the converter transformer of the flexible DC transmission system and the first voltage, the actual valve-side voltage of the converter of the flexible DC transmission system is determined. Based on the actual valve-side voltage of the converter in the flexible DC transmission system, calculate the equivalent current source in the flexible DC transmission system; The step of determining the actual valve-side voltage of the converter in the flexible DC transmission system based on the reference value of the valve-side voltage of the converter transformer and the first voltage includes: Based on the valve-side voltage reference value of the converter transformer of the flexible DC transmission system and the first voltage, the first target current of the converter of the flexible DC transmission system is determined. Determine whether the first target current exceeds a preset first threshold. If the first target current exceeds a preset first threshold, then the first target current is set as a second target current, wherein the second target current is set according to the preset first threshold. Based on the second target current, the actual valve-side voltage of the converter in the flexible DC transmission system is determined.

2. The method according to claim 1, characterized in that, The preset outer loop controller model creation process includes: Create an outer loop controller model based on the preset outer loop control strategy; The preset outer loop control strategy is as follows: The reference value and the actual value of the voltage of the converter bus are used as input signals; The difference between the reference value and the actual value of the voltage of the converter bus is obtained by subtracting the reference value of the d-axis component and the reference value of the q-axis component of the converter bus voltage from the actual value of the d-axis component and the actual value of the q-axis component of the converter bus voltage, respectively. The difference between the obtained voltage reference value and the actual voltage value of the converter bus is passed through a PI controller to obtain the control current reference value of the flexible DC transmission system. The control current reference value of the flexible DC transmission system includes d-axis and q-axis current reference values.

3. The method according to claim 1, characterized in that, The method also includes: Based on the equivalent current source and the converter transformer reactance of the flexible DC transmission system, the node voltage column vector of the AC system is adjusted.

4. The method according to claim 1, characterized in that, The connection of the flexible DC transmission system to the AC system includes: The flexible DC transmission system is connected to the AC system using a Norton equivalent circuit or a Thevenin equivalent circuit, wherein the Norton equivalent circuit or the Thevenin equivalent circuit includes an equivalent current source.

5. The method according to claim 1, characterized in that, Before determining the first voltage of the converter bus of the flexible DC transmission system based on the node voltage column vector of the AC system, the method further includes: Calculate the node voltage column vector of the AC system; The formula for calculating the nodal voltage column vector of the AC system is as follows: in, This represents the column vector of node voltages in the AC system. This represents the node admittance matrix of the AC system; This represents the column vector of node currents in the AC system.

6. The method according to any one of claims 1-5, characterized in that, The calculation formula for determining the valve-side voltage reference value of the converter transformer in the flexible DC transmission system, based on the control current reference value of the flexible DC transmission system and the preset target voltage of the converter bus, includes: in, The direction of current flow from the converter to the converter bus in the flexible DC transmission system is considered positive. The d-axis reference value represents the voltage on the valve side of the converter transformer in a flexible DC transmission system. The q-axis reference value represents the valve-side voltage of the converter transformer in a flexible DC transmission system. This represents the resistance of the converter transformer in a flexible DC transmission system. This represents the reactance of the converter transformer in a flexible DC transmission system. This represents the d-axis reference value of the converter bus voltage in a flexible DC transmission system. This represents the q-axis reference value of the converter bus voltage in a flexible DC transmission system. This represents the d-axis reference value for the control current of the flexible DC transmission system. This represents the q-axis reference value for the control current of the flexible DC transmission system.

7. A flexible DC electromechanical transient modeling device, used to implement the steps of the flexible DC electromechanical transient modeling method as described in any one of claims 1 to 6, characterized in that, include: The first setup unit is used to connect the flexible DC transmission system to the AC system; The first voltage calculation unit is used to determine the first voltage of the converter bus of the flexible DC transmission system based on the node voltage column vector of the AC system. A transmitting unit is configured to transmit the first voltage to the flexible DC transmission system; The second voltage calculation unit is used to calculate the control current reference value of the flexible DC transmission system based on the preset outer loop controller model. The third voltage calculation unit is used to determine the valve-side voltage reference value of the converter transformer of the flexible DC transmission system based on the control current reference value of the flexible DC transmission system and the preset target voltage of the converter bus. The preset target voltage includes the d-axis component and the q-axis component of the preset target control voltage of the converter bus, and the q-axis component of the preset target control voltage of the converter bus is 0. The fourth voltage calculation unit is used to determine the actual valve-side voltage of the converter of the flexible DC transmission system based on the reference value of the valve-side voltage of the converter transformer of the flexible DC transmission system and the first voltage. The current source calculation unit is used to calculate the equivalent current source in the flexible DC transmission system based on the actual valve-side voltage of the converter in the flexible DC transmission system.

8. A flexible DC electromechanical transient modeling device, characterized in that, include: One or more processors, and memory; The memory stores computer-readable instructions, which, when executed by the one or more processors, implement the steps of the flexible DC electromechanical transient modeling method as described in any one of claims 1 to 6.

9. A readable storage medium, characterized in that: The readable storage medium stores computer-readable instructions that, when executed by one or more processors, cause the one or more processors to perform the steps of the flexible DC electromechanical transient modeling method as described in any one of claims 1 to 6.

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