A modeling method, system, device and medium for a grid-type converter

Abstract

This application discloses a modeling method, system, device, and medium for a grid-type converter, including: by dividing the GFM MMC-HVDC system into three main parts, combining the operating characteristics and modulation ratio constraints of the converter, the system differential, algebraic equation, and phasor modeling methods of the entire system are derived. While ensuring the electromechanical simulation rate of the GFM MMC-HVDC, the operating control characteristics of the GFM droop controller can be effectively retained. The method can be used for AC voltage stability analysis and reactive power dynamic response characteristic analysis, as well as for the optimal reactive power management and distribution research of the GFM MMC-HVDC. This solves the problems of traditional electromagnetic transient simulation methods in large-scale MMC-HVDC systems, such as long simulation time, high simulation platform performance requirements, and the inability of electromechanical transient simulation to fully reflect the dynamic response capability and control characteristics of the GFM.

Description

Technical Field

[0001] The present application relates to the technical field of power systems, and in particular to a modeling method, system, device, and medium for a grid-type converter. Background Art

[0002] Grid-forming (GFM) control has the potential to improve the stability and dynamic response of modular-multilevel-converter-based high voltage DC (MMC-HVDC) systems and is a key technology development direction for future large-scale HVDC systems. To study the operational control characteristics and AC system stability of GFM-based MMC-HVDC systems, accurate and rapid simulation modeling of the entire HVDC system is required.

[0003] Currently, while traditional electromagnetic transient simulation modeling methods can ensure the operational control and dynamic response characteristics of GFM, they require excessively long simulation times and place high demands on the simulation platform performance when applied to large-scale MMC-HVDC systems. On the other hand, electromechanical transient simulation analysis is essential for analyzing voltage stability and related issues. However, the simulation step size of traditional electromechanical transient methods is typically set too large, which cannot fully reflect the dynamic response capability and transient control characteristics of the GFM. Therefore, it is necessary to develop a simplified electromechanical transient modeling and rapid simulation method for large-scale GFM MMC-HVDC systems that can accurately capture the operational control characteristics and dynamic response characteristics of the GFM. Summary of the Invention

[0004] The present application provides a modeling method, system, device and medium for a grid-type converter, which are used to solve the problems of traditional electromagnetic transient simulation methods in large-scale MMC-HVDC systems, such as long simulation time, high performance requirements of the simulation platform, and the inability of electromechanical transient simulation to fully reflect the dynamic response capability and control characteristics of GFM.

[0005] In view of this, a first aspect of the present application provides a modeling method for a grid-type converter, the method comprising:

[0006] S1. Constructing a GFM MMC-HVDC system, including: a first AC power supply and a second AC power supply; the first AC power supply and the second AC power supply are interconnected via a first HB-MMC, a second HB-MMC, and a DC line;

[0007] S2. For modeling of the converter station composed of the first HB-MMC and the second HB-MMC, first derive the mathematical model of the HB-MMC regarding equivalent reactance, equivalent resistance, and equivalent capacitance based on the preset real-time capacitance of the upper and lower bridge arms of the HB-MMC and the simplified single-phase dq-axis model of the HB-MMC. Combined with the conversion relationship between the equivalent resistance and equivalent reactance on the AC and DC sides, derive the active and reactive power injected into the grid by the HB-MMC, thereby obtaining the phasor model of the HB-MMC.

[0008] S3. Modeling the controller of the GFM MMC-HVDC system, dividing the controller modeling into grid-side controller modeling and constant voltage controller modeling;

[0009] S4. For modeling the grid-side controller, first set an expression for the internal electromotive force phase angle and an expression for the phase angle difference between the internal electromotive force and the synchronous rotating coordinate system. Then, divide the grid-side controller into a voltage control link and an active power-frequency control link. Combine the dynamic models of the corresponding controllers of the voltage control link and the active power-frequency control link, and convert the mathematical model into an algebraic equation.

[0010] S5. For the modeling of the constant voltage controller, first derive the dynamic equation of the constant voltage controller based on the dual-loop control structure, and derive the dynamic equation of the DC current controller by combining the dynamic equation of the constant voltage controller. Then, assume that the grid q-axis voltage v after Park transformation is q2 Always keep it at 0, derive the power injected into the AC grid by the converter station and the AC current on the converter station side, and finally derive the equivalent capacitor voltage dynamic and DC current dynamic expressions of the constant voltage controller by combining the mathematical model and the conversion relationship;

[0011] S6. For DC line modeling, first simplify the DC line model to a series structure of reactance and resistance, derive the dynamic expression of the current on the DC line, then apply circuit laws to obtain the corresponding expression of the DC current flowing out of the converter station and the DC line current. Finally, combine the algebraic equations to solve the equations for the constant voltage controller and the converter station DC voltage. Thus, combined with steps S2 to S6, the electromechanical transient modeling of the GFM MMC-HVDC system is completed.

[0012] Optionally, the mathematical model includes:

[0013]

[0014] Where, is the average value of the sum of the capacitor voltages on the six bridge arms of HB-MMC, v d 、v q are the d-axis and q-axis components of the grid voltage respectively, 、 、 is the equivalent reactance, equivalent resistance and equivalent capacitance of the DC side of HB-MMC, 、 is the equivalent reactance and equivalent resistance of the AC side of HB-MMC, m a 、m b and m c The difference between the capacitance ratio of the upper bridge arm and the lower bridge arm of HB-MMC is half, m d 、m q m a 、m b and m c The d and q axis components, ω s is the rotation frequency of the coordinate system used for Parker transformation, is the voltage on the equivalent capacitor of HB-MMC, is the voltage of the HB-MMC DC port, is the DC side current of HB-MMC, is the d-axis component of the HB-MMC AC side current, is the q-axis component of the AC side current of HB-MMC.

[0015] Optionally, the conversion relationship includes:

[0016]

[0017] Where R arm , L arm 、R f , L f are the sum of the bridge arm resistance, bridge arm capacitance, filter resistance and transformer short-circuit resistance, and filter inductance and transformer leakage inductance, respectively. N is the number of sub-modules in each bridge arm.

[0018] Optionally, the expressions of active and reactive power injected into the grid by the HB-MMC include:

[0019]

[0020] Where p inj and q inj are the active and reactive powers injected into the grid by HB-MMC respectively.

[0021] Optionally, the expression of the algebraic equation includes:

[0022]

[0023] Where, , The angle to use for the Pike transform on the mesh side.

[0024] Optionally, the dynamic expressions of the equivalent capacitor voltage and DC current of the constant voltage controller are respectively:

[0025]

[0026] Where, is the equivalent capacitor voltage of the constant voltage controller, i dc2 is the DC current of the constant voltage controller.

[0027] Optionally, the constant voltage controller and the converter station DC voltage equation include:

[0028]

[0029] Where, 、 are the resistance and reactance of the DC line, It is the DC current from the grid side to the grid side.

[0030] A second aspect of the present application provides a modeling system for a grid-type converter, the system comprising:

[0031] A construction unit for constructing a GFM MMC-HVDC system, comprising: a first AC power supply and a second AC power supply; the first AC power supply and the second AC power supply are interconnected via a first HB-MMC, a second HB-MMC, and a DC line;

[0032] A first modeling unit is configured to model a converter station composed of the first HB-MMC and the second HB-MMC. The first modeling unit derives a mathematical model of the HB-MMC regarding equivalent reactance, equivalent resistance, and equivalent capacitance based on preset real-time capacitances of the upper and lower bridge arms of the HB-MMC and a simplified single-phase dq-axis model of the HB-MMC. The mathematical model is then combined with a conversion relationship between equivalent resistance and equivalent reactance on the AC and DC sides to derive active and reactive power injected into the power grid by the HB-MMC, thereby obtaining a phasor model of the HB-MMC.

[0033] A division unit, configured to model the controller of the GFM MMC-HVDC system, dividing the controller modeling into grid-side controller modeling and constant voltage controller modeling;

[0034] A second modeling unit is configured to model the grid-side controller by first setting an expression for the internal electromotive force phase angle and an expression for the phase angle difference between the internal electromotive force and the synchronous rotating coordinate system, then dividing the grid-type controller into a voltage control link and an active power-frequency control link, and converting the mathematical model into an algebraic equation by combining the dynamic models of the controllers corresponding to the voltage control link and the active power-frequency control link;

[0035] A third modeling unit is used to model a constant voltage controller. First, a dynamic equation of the constant voltage controller is derived based on the dual-loop control structure. The dynamic equation of the DC current controller is derived by combining the dynamic equation of the constant voltage controller. Then, the q-axis voltage vq2 of the power grid after the Park transformation is always maintained at 0. The power injected into the AC power grid by the converter station and the AC current on the converter station side are derived. Finally, the equivalent capacitor voltage dynamic and DC current dynamic expressions of the constant voltage controller are derived by combining the mathematical model and the conversion relationship.

[0036] The fourth modeling unit is used to model the DC line. First, the DC line model is simplified into a series structure of reactance and resistance, and the dynamic expression of the current on the DC line is derived. Then, the circuit law is applied to obtain the corresponding expression of the DC current flowing out of the converter station and the DC line current. Finally, combined with the algebraic equation, the constant voltage controller and the converter station DC voltage equation are solved, thereby combining the first to fourth modeling units to complete the electromechanical transient modeling of the GFM MMC-HVDC system.

[0037] A third aspect of the present application provides a modeling device for a grid-type converter, the device comprising a processor and a memory:

[0038] The memory is used to store program code and transmit the program code to the processor;

[0039] The processor is configured to execute the steps of the modeling method for the grid-connected converter as described in the first aspect according to the instructions in the program code.

[0040] In a fourth aspect, the present application provides a computer-readable storage medium, which is used to store program code, and the program code is used to execute the modeling method of the grid-type converter described in the first aspect.

[0041] It can be seen from the above technical solutions that this application has the following advantages:

[0042] 1) This application proposes a modeling method for a grid-type converter in a grid-type flexible direct current transmission system. The GFM MMC-HVDC system is divided into three main parts. Combining the operating characteristics and modulation ratio constraints of the converter, the system differential, algebraic equation, and phasor modeling methods of the entire system are derived. While ensuring the electromechanical simulation rate of the GFM MMC-HVDC, the operating control characteristics of the GFM droop controller can be effectively retained. This method can be used for AC voltage stability analysis and reactive power dynamic response characteristic analysis, as well as for the optimal reactive power management and distribution of the GFM MMC-HVDC.

[0043] 2) The method involved in this application is simple to implement. Only a small modification of the controller model of the existing electromechanical transient simulation model is required to achieve modeling of networked controls such as virtual synchronization control and droop control.

[0044] 3) The flexible direct current transmission system based on grid-type control involved in this application can adopt not only the two-terminal system structure involved in this application, but also other multi-terminal system structures. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 This is a flow chart of a modeling method for a grid-type converter provided in an embodiment of the present application;

[0046] Figure 2 This is a structural diagram of a two-terminal MMC-HVDC system provided in an embodiment of the present application;

[0047] Figure 3 This is a structural diagram of the HB-MMC converter provided in the embodiments of the present application;

[0048] Figure 4 This is a block diagram of the GFM active power-frequency droop control structure provided in an embodiment of the present application;

[0049] Figure 5 This is a structural diagram of a modeling system for a grid-type converter provided in an embodiment of the present application. DETAILED DESCRIPTION

[0050] In order to help those skilled in the art better understand the present invention, the following will provide a clear and complete description of the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of this application.

[0051] See also Figure 1 , a modeling method for a grid-type converter provided in an embodiment of the present application includes:

[0052] Step 101: construct a GFM MMC-HVDC system, including: a first AC power supply and a second AC power supply; the first AC power supply and the second AC power supply are interconnected through a first HB-MMC, a second HB-MMC, and a DC line.

[0053] It should be noted that, when constructing a two-terminal MMC-HVDC system using GFM, the system includes: a first AC power source ( Figure 2 The AC power supply shown is 1) and ( Figure 2The AC power supply 2 shown in the figure is connected to the half-bridge modular multilevel converter (HB-MMC) HB-MMC 1 (as shown in the figure). Figure 2 AC-DC module shown), DC line, HB-MMC 2 (as shown Figure 2 The DC-AC modules shown in the figure are interconnected. Figure 2 shown.

[0054] Step 102: For modeling of the converter station composed of the first HB-MMC and the second HB-MMC, first, based on the preset real-time capacitance of the upper and lower bridge arms of the HB-MMC and the simplified single-phase dq-axis model of the HB-MMC, a mathematical model of the equivalent reactance, equivalent resistance, and equivalent capacitance of the HB-MMC is derived. In combination with the conversion relationship between the equivalent resistance and equivalent reactance on the AC and DC sides, the active and reactive power injected into the grid by the HB-MMC is derived, thereby obtaining a phasor model of the HB-MMC.

[0055] It should be noted that, in specific implementation, step 102 includes:

[0056] Step 1021: First, construct a phasor model of the converter station using the HB-MMC (hereinafter referred to as MMC) topology in the GFM MMC-HVDC system, such as Figure 3 shown.

[0057] Set the sum of the capacitance ratios of the upper and lower bridge arms during MMC modulation to 1, and use m a 、m b and m c Representing half of the difference between the real-time capacitance ratio of the upper bridge arm and the lower bridge arm, we can obtain:

[0058]

[0059] Among them, m lj and m uj Respectively represent the proportion of capacitance used in the upper and lower bridge arms of each phase.

[0060] Step 1022: Combining step 1021 with the MMC single-phase dq axis simplified model, the mathematical model of the MMC is shown in formula (2).

[0061]

[0062] in, is the average value of the sum of the capacitor voltages on the six bridge arms of the MMC, v d 、v q are the d-axis and q-axis components of the grid voltage, 、 、 is the equivalent reactance, resistance and capacitance of the DC side of MMC, 、 is the equivalent reactance and resistance of the AC side of the MMC, m d 、m q They are m a 、m b and m c The d and q axis components, ω s is the rotation frequency of the coordinate system used for the Parker transformation, which is generally taken as the power frequency.

[0063] The equivalent resistance and reactance on the AC and DC sides have the conversion relationship shown in formula (3).

[0064]

[0065] Among them, R arm , L arm 、R f , L f are the sum of the bridge arm resistance, bridge arm capacitance, filter resistance and transformer short-circuit resistance, and filter inductance and transformer leakage inductance, respectively. N is the number of sub-modules in each bridge arm.

[0066] Step 1023: Combine steps 101 to 1022, and the active and reactive power p injected into the grid by the MMC inj and q inj It can be modeled by formula (4).

[0067]

[0068] Based on this, the simplified MMC can be equivalent to Figure 3 The phasor model shown.

[0069] Step 103 : For the modeling of the controller of the GFM MMC-HVDC system, the controller modeling is divided into the modeling of the grid-side controller and the constant voltage controller.

[0070] It should be noted that the controller phasor model of the GFM MMC-HVDC system is constructed, including: a constant voltage controller and a grid-side controller adopted in this patent.

[0071] Step 104: For the modeling of the grid-side controller, first set the expression of the internal electromotive force phase angle and the expression of the phase angle difference with the synchronous rotating coordinate system. Then, divide the grid-side controller into a voltage control link and an active power-frequency control link. Combine the dynamic models of the corresponding controllers of the voltage control link and the active power-frequency control link, and convert the mathematical model into an algebraic equation.

[0072] It should be noted that, in specific implementation, step 104 includes:

[0073] Step 1041: For the active power-frequency droop controller, Figure 4 As shown, the phase angle used by the GFM to control the modulation wave is generated by the internal phase angle controller, and m a 、m b With m c It is three-phase symmetrical, so set:

[0074]

[0075] Step 1042: The Parker transformation on the network side adopts a synchronous rotating coordinate system, and its angle is , and introduce , then m d and m q As shown in formula (6):

[0076]

[0077] Step 1043: The GFM droop controller is divided into a voltage control section and a power control section.

[0078] In the voltage control link, a PI controller is used to control the grid voltage, and its controller dynamic model is shown in (7) and (8).

[0079]

[0080] Among them, E p The line electromotive force generated by the controller, V ref is the line voltage reference value of the VSC grid-connected node.

[0081] The original equation of the power control link in the GFM droop controller is shown in (9).

[0082]

[0083] Among them, P ref is the reference value of the power injected into the grid, D f is the droop coefficient. In general, ω ref is the synchronization angular frequency

[0084] Step 1044: According to step 1043, formula (9) can be rewritten as The dynamic equation of is shown in Equation (10).

[0085]

[0086] Step 1045: According to the MMC working in the linear modulation region in step 1021 and formula (2) in step 1022, the electromotive force amplitude in each phase is equivalent to: However, it is difficult to measure the voltage on the equivalent capacitor during actual modulation. , only the DC port voltage v can be used to determine the modulation ratio dc Approximately, so m can be determined by formula (11),

[0087]

[0088] Step 1046: In the electromechanical transient model, the current dynamic process is ignored, so the part of equation (2) in step 1022 can be converted into an algebraic equation.

[0089]

[0090] The subscript "1" indicates that the parameter is the corresponding parameter on the network side.

[0091] Step 105: For the modeling of the constant voltage controller, first derive the dynamic equation of the constant voltage controller based on the dual-loop control structure, and derive the dynamic equation of the DC current controller by combining the dynamic equation of the constant voltage controller. Then, assume that the grid q-axis voltage v after Park transformation is q2 Always keep it at 0, derive the power injected into the AC grid by the converter station and the AC current on the converter station side, and finally derive the equivalent capacitor voltage dynamic and DC current dynamic expressions of the constant voltage controller by combining the mathematical model and conversion relationship.

[0092] It should be noted that, in specific implementation, step 105 includes:

[0093] Step 1051: For the constant voltage controller, the classic double-loop control structure is used to control i d Realize the control of DC voltage, control i q Therefore, the dynamic equations of the constant voltage controller are shown in (15) and (16).

[0094]

[0095] in, is the d-axis current command value of the grid-side VSC, is the DC voltage command value, v dc2 is the DC terminal voltage between the controller and the MMC converter, k p1 and k i1 are the PI controller parameters.

[0096] Step 1052, combined with step 1051, the dynamics of the DC current controller are shown in equations (17) and (18).

[0097]

[0098] Among them, Qref Inject reactive power command value into AC side, is the q-axis current command value.

[0099] Step 1053: When modeling the DC voltage controller, the relatively fast phase-locked loop dynamics can be ignored. That is, after the Park transformation, the grid q-axis voltage vq2 always remains at 0. Furthermore, since the dynamic response time of the current inner loop control is fast, it can be ignored to simplify the simulation model. Based on this, the power injected into the AC grid by the converter station can be written as:

[0100]

[0101] The AC current on the converter station side is:

[0102]

[0103] Step 1054, combined with step 1053 and step 1022, also ignores the two current inner loop dynamic processes. Based on this, the equivalent capacitor voltage dynamics and DC current dynamics of the DC voltage controller can be obtained as shown in equations (21) and (22), respectively:

[0104]

[0105] Step 106: For DC line modeling, first simplify the DC line model to a series structure of reactance and resistance, derive the dynamic expression of the current on the DC line, then apply circuit laws to obtain the corresponding expression between the DC current flowing out of the converter station and the DC line current. Finally, combine algebraic equations to solve the equations for the constant voltage controller and the DC voltage of the converter station. Combining steps 102 to 106, the electromechanical transient modeling of the GFM MMC-HVDC system is completed.

[0106] It should be noted that, in specific implementation, step 106 includes:

[0107] Step 1061: Model the DC line. Since MMC-HVDC systems typically have higher voltage levels and use overhead transmission lines, the DC line model can be simplified to a series structure of reactance and resistance, ignoring the ground capacitance. Therefore, the current dynamics on the DC line are shown in Equation (23):

[0108]

[0109] Among them, i line is the DC current from the grid side to the grid side, R line and L line are the resistance and reactance of the DC line, respectively, because the DC line capacitance is neglected.

[0110] Step 1062, combined with step 1061, all the DC current flowing out of the converter station flows to the DC line, so the following relationship exists:

[0111]

[0112] In addition, note that L line 、 and The currents on the φ are the same, so these three dynamics are not independent and can be organized into a unified dynamic equation (25).

[0113]

[0114] Step 1063: Combine step 1046 (13), step 1061 (23) and step 1062 (24), and introduce the total DC line inductance L Σ and the total resistance R Σ , the constant voltage controller and converter station DC voltage equation can be solved as shown in Equation (27).

[0115]

[0116] Step 1064, combined with steps 1021 to 1063, can obtain the overall modeling method of the GFM MMC-HVDC system, which is essentially a set of differential algebraic equations, where equation (4) needs to replace the corresponding quantities with quantities containing the subscript "1".

[0117] It should be noted that in existing phasor simulation models, when performing Park transformation on the grid-side voltage, a coordinate system that makes the q-axis voltage equal to 0 is generally not selected, but a synchronously rotating coordinate system is selected.

[0118] Assuming that the synchronous rotating coordinate system is selected, the dq axis voltage components on the grid side are v d_syn2 、v q_syn2 , the conversion of voltage quantities in the two coordinate systems can be obtained by formula (28).

[0119]

[0120] Among them, the grid voltage v d_syn2 、v q_syn2 These are the algebraic quantities that already exist in the existing electromechanical modeling of power systems. Therefore, when calculating Equation (19) in step 1053, it is necessary to first use Equation (28) to transform the coordinate system of these quantities.

[0121] In addition, it should be noted during initialization that the active power at the sending end is unknown due to the fixed DC voltage control and the loss of the DC system. Therefore, it is necessary to solve the initial value of the proposed phasor model and the system power flow equation simultaneously.

[0122] Based on this, the above is the entire model of the GFM MMC-HVDC system involved in this application. The model can be integrated into existing phasor simulation software for analysis and research on system stability.

[0123] The above is a modeling method of a grid-type converter provided in an embodiment of the present application, and the following is a modeling system of a grid-type converter provided in an embodiment of the present application.

[0124] See also Figure 5 , a modeling system for a grid-type converter provided in an embodiment of the present application includes:

[0125] The construction unit 201 is used to construct a GFM MMC-HVDC system, including: a first AC power supply and a second AC power supply; the first AC power supply and the second AC power supply are interconnected through a first HB-MMC, a second HB-MMC and a DC line.

[0126] The first modeling unit 202 is used to model the converter station composed of the first HB-MMC and the second HB-MMC. First, based on the preset real-time capacitance of the upper and lower bridge arms of the HB-MMC and the simplified single-phase dq-axis model of the HB-MMC, a mathematical model of the equivalent reactance, equivalent resistance and equivalent capacitance of the HB-MMC is derived. In combination with the conversion relationship between the equivalent resistance and the equivalent reactance on the AC and DC sides, the active and reactive power injected into the power grid by the HB-MMC is derived, thereby obtaining a phasor model of the HB-MMC.

[0127] The division unit 203 is used for modeling the controller of the GFM MMC-HVDC system, and divides the controller modeling into the grid-side controller modeling and the constant voltage controller modeling.

[0128] The second modeling unit 204 is used to model the grid-side controller. First, the expression of the internal electromotive force phase angle and the expression of the phase angle difference with the synchronous rotating coordinate system are set. Then, the grid-type controller is divided into a voltage control link and an active power-frequency control link. Combined with the dynamic models of the controllers corresponding to the voltage control link and the active power-frequency control link, the mathematical model is converted into an algebraic equation.

[0129] The third modeling unit 205 is used to model the constant voltage controller. First, the dynamic equation of the constant voltage controller is derived based on the dual-loop control structure. The dynamic equation of the DC current controller is derived by combining the dynamic equation of the constant voltage controller. Then, it is assumed that the q-axis voltage vq2 of the power grid after Park transformation is always kept at 0. The power injected into the AC power grid by the converter station and the AC current on the converter station side are derived. Finally, the equivalent capacitor voltage dynamic and DC current dynamic expressions of the constant voltage controller are derived by combining the mathematical model and the conversion relationship.

[0130] The fourth modeling unit 206 is used to model the DC line. First, the DC line model is simplified to a series structure of reactance and resistance, and the dynamic expression of the current on the DC line is derived. Then, the circuit law is applied to obtain the corresponding expression of the DC current flowing out of the converter station and the DC line current. Finally, combined with algebraic equations, the constant voltage controller and the converter station DC voltage equation are solved. Thus, the electromechanical transient modeling of the GFM MMC-HVDC system is completed by combining the first to fourth modeling units.

[0131] Furthermore, an embodiment of the present application also provides a modeling device for a grid-type converter, the device including a processor and a memory:

[0132] The memory is used to store program code and transmit the program code to the processor;

[0133] The processor is configured to execute the steps of the modeling method for a grid-type converter as described in the above method embodiment according to the instructions in the program code.

[0134] Furthermore, a computer-readable storage medium is provided in an embodiment of the present application. The computer-readable storage medium is used to store program code, and the program code is used to execute the modeling method of the grid-connected converter described in the above method embodiment.

[0135] Those skilled in the art will clearly understand that, for the convenience and brevity of description, the specific working processes of the above-described systems and units can refer to the corresponding processes in the aforementioned method embodiments and will not be repeated here.

[0136] The terms "first," "second," "third," "fourth," and the like (if any) in the specification of the present application and the accompanying drawings are used to distinguish similar objects and are not necessarily used to describe a particular order or precedence. It should be understood that the terms used in this manner are interchangeable where appropriate, so that the embodiments of the present application described herein can, for example, be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having," and any variations thereof, are intended to cover non-exclusive inclusions. For example, a process, method, system, product, or apparatus comprising a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units that are not explicitly listed or that are inherent to such process, method, product, or apparatus.

[0137] It should be understood that in this application, "at least one (item)" means one or more, and "plurality" means two or more. "And / or" is used to describe the association relationship of associated objects, indicating that three relationships can exist. For example, "A and / or B" can mean: only A exists, only B exists, and A and B exist at the same time, where A and B can be singular or plural. The character " / " generally indicates that the previous and next associated objects are in an "or" relationship. "At least one of the following items" or similar expressions refers to any combination of these items, including any combination of single or plural items. For example, at least one of a, b or c can mean: a, b, c, "a and b", "a and c", "b and c", or "a and b and c", where a, b, c can be single or plural.

[0138] In the several embodiments provided in this application, it should be understood that the disclosed systems, devices and methods can be implemented in other ways. For example, the device embodiments described above are merely schematic. For example, the division of the units is merely a logical function division. In actual implementation, there may be other division methods, such as multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be an indirect coupling or communication connection through some interfaces, devices or units, which can be electrical, mechanical or other forms.

[0139] The units described as separate components may or may not be physically separate, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed across multiple network units. Some or all of these units may be selected to achieve the purpose of this embodiment according to actual needs.

[0140] In addition, the functional units in the various embodiments of the present application may be integrated into a single processing unit, or each unit may exist physically separately, or two or more units may be integrated into a single unit. The aforementioned integrated units may be implemented in the form of hardware or software functional units.

[0141] If the integrated unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present application, or the part that contributes to the prior art, or all or part of the technical solution can be embodied in the form of a software product. The computer software product is stored in a storage medium and includes several instructions for enabling a computer device (which can be a personal computer, server, or network device, etc.) to execute all or part of the steps of the method described in each embodiment of the present application. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (full name: Read-Only Memory, English abbreviation: ROM), random access memory (full name: Random Access Memory, English abbreviation: RAM), disk or optical disk, and other media that can store program code.

[0142] As described above, the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A modeling method for a grid-type converter, characterized in that: include: S1. Constructing a GFM MMC-HVDC system, including: a first AC power supply and a second AC power supply; the first AC power supply and the second AC power supply are interconnected via a first HB-MMC, a second HB-MMC, and a DC line; S2. For modeling of the converter station composed of the first HB-MMC and the second HB-MMC, first derive the mathematical model of the HB-MMC regarding equivalent reactance, equivalent resistance, and equivalent capacitance based on the preset real-time capacitance of the upper and lower bridge arms of the HB-MMC and the simplified single-phase dq-axis model of the HB-MMC. Combined with the conversion relationship between the equivalent resistance and equivalent reactance on the AC and DC sides, derive the active and reactive power injected into the grid by the HB-MMC, thereby obtaining the phasor model of the HB-MMC. S3. Modeling the controller of the GFM MMC-HVDC system, dividing the controller modeling into grid-side controller modeling and constant voltage controller modeling; S4. For modeling the grid-side controller, first set an expression for the internal electromotive force phase angle and an expression for the phase angle difference between the internal electromotive force and the synchronous rotating coordinate system. Then, divide the grid-side controller into a voltage control link and an active power-frequency control link. Combine the dynamic models of the corresponding controllers of the voltage control link and the active power-frequency control link, and convert the mathematical model into an algebraic equation. S5. For the modeling of the constant voltage controller, first derive the dynamic equation of the constant voltage controller based on the dual-loop control structure, and derive the dynamic equation of the DC current controller by combining the dynamic equation of the constant voltage controller. Then, assume that the grid q-axis voltage v after Park transformation is q2 Always keep it at 0, derive the power injected into the AC grid by the converter station and the AC current on the converter station side, and finally derive the equivalent capacitor voltage dynamic and DC current dynamic expressions of the constant voltage controller by combining the mathematical model and the conversion relationship; S6. For DC line modeling, first simplify the DC line model to a series structure of reactance and resistance, derive the dynamic expression of the current on the DC line, then apply circuit laws to obtain the corresponding expression of the DC current flowing out of the converter station and the DC line current, and finally solve the algebraic equation to obtain the constant voltage controller and the converter station DC voltage equation, thereby combining steps S2 to S6 to complete the electromechanical transient modeling of the GFM MMC-HVDC system; The constant voltage controller and the converter station DC voltage equation include: ； ； Where, 、 are the resistance and reactance of the DC line, is the DC current from the grid side to the grid side, 、 is the total inductance and resistance of the DC link.

2. The modeling method of the grid-type converter according to claim 1, characterized in that: The mathematical model includes: ； ； ； ； Where, is the average value of the sum of the capacitor voltages on the six bridge arms of HB-MMC, v d 、v q are the d-axis and q-axis components of the grid voltage respectively, 、 、 is the equivalent reactance, equivalent resistance and equivalent capacitance of the DC side of HB-MMC, 、 is the equivalent reactance and equivalent resistance of the AC side of HB-MMC, m a 、m b and m c The difference between the capacitance ratio of the upper bridge arm and the lower bridge arm of HB-MMC is half, m d 、m q m a 、m b and m c The d and q axis components, ω s is the rotation frequency of the coordinate system used for Parker transformation, is the voltage of the HB-MMC DC port, is the DC side current of HB-MMC, is the d-axis component of the HB-MMC AC side current, is the q-axis component of the AC side current of HB-MMC.

3. The modeling method of the grid-type converter according to claim 2, characterized in that: The conversion relationship includes: ； Where R arm , L arm 、R f , L f are the sum of the bridge arm resistance, bridge arm capacitance, filter resistance and transformer short-circuit resistance, and filter inductance and transformer leakage inductance, respectively. N is the number of sub-modules in each bridge arm.

4. The modeling method of the grid-type converter according to claim 3, characterized in that: The expressions for the active and reactive power injected into the grid by the HB-MMC include: ； Where p inj and q inj are the active and reactive powers injected into the grid by HB-MMC respectively.

5. The modeling method of the grid-type converter according to claim 4, characterized in that: The expression of the algebraic equation includes: ； ； ； Where, , The angle to use for the Pike transform on the mesh side.

6. The modeling method of the grid-type converter according to claim 5, characterized in that: The dynamic expressions of the equivalent capacitor voltage and DC current of the constant voltage controller are: ； 。 7. A modeling system for a grid-type converter, characterized in that: include: A construction unit for constructing a GFM MMC-HVDC system, comprising: a first AC power supply and a second AC power supply; the first AC power supply and the second AC power supply are interconnected via a first HB-MMC, a second HB-MMC, and a DC line; A first modeling unit is configured to model a converter station composed of the first HB-MMC and the second HB-MMC. The first modeling unit derives a mathematical model of the HB-MMC regarding equivalent reactance, equivalent resistance, and equivalent capacitance based on preset real-time capacitances of the upper and lower bridge arms of the HB-MMC and a simplified single-phase dq-axis model of the HB-MMC. The mathematical model is then combined with a conversion relationship between equivalent resistance and equivalent reactance on the AC and DC sides to derive active and reactive power injected into the power grid by the HB-MMC, thereby obtaining a phasor model of the HB-MMC. A division unit, configured to model the controller of the GFM MMC-HVDC system, dividing the controller modeling into grid-side controller modeling and constant voltage controller modeling; A second modeling unit is configured to model the grid-side controller by first setting an expression for the internal electromotive force phase angle and an expression for the phase angle difference between the internal electromotive force and the synchronous rotating coordinate system, then dividing the grid-side controller into a voltage control link and an active power-frequency control link, and converting the mathematical model into an algebraic equation by combining the dynamic models of the controllers corresponding to the voltage control link and the active power-frequency control link; A third modeling unit is used to model a constant voltage controller. First, a dynamic equation of the constant voltage controller is derived based on the dual-loop control structure. The dynamic equation of the DC current controller is derived by combining the dynamic equation of the constant voltage controller. Then, the q-axis voltage vq2 of the power grid after the Park transformation is always maintained at 0. The power injected into the AC power grid by the converter station and the AC current on the converter station side are derived. Finally, the equivalent capacitor voltage dynamic and DC current dynamic expressions of the constant voltage controller are derived by combining the mathematical model and the conversion relationship. The fourth modeling unit is used to model the DC line. First, the DC line model is simplified to a series structure of reactance and resistance, and a dynamic expression of the current on the DC line is derived. Then, the circuit law is applied to obtain the corresponding expression of the DC current flowing out of the converter station and the DC line current. Finally, the algebraic equation is combined to solve the equation of the constant voltage controller and the DC voltage of the converter station. Thus, the electromechanical transient modeling of the GFM MMC-HVDC system is completed by combining the first to fourth modeling units. The constant voltage controller and the converter station DC voltage equation include: ； ； Where, 、 are the resistance and reactance of the DC line, is the DC current from the grid side to the grid side, 、 is the total inductance and resistance of the DC link.

8. A modeling device for a grid-type converter, characterized in that: The device includes a processor and a memory: The memory is used to store program code and transmit the program code to the processor; The processor is configured to execute the grid-connected converter modeling method according to any one of claims 1 to 6 according to instructions in the program code.

9. A computer-readable storage medium, characterized in that The computer-readable storage medium is used to store program code, and the program code is used to execute the modeling method of the grid-type converter according to any one of claims 1 to 6.

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