CN114069683B - Method and device for determining steady-state operation characteristics of MMC converter station and computer equipment - Google Patents

Method and device for determining steady-state operation characteristics of MMC converter station and computer equipment Download PDF

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CN114069683B
CN114069683B CN202111360540.7A CN202111360540A CN114069683B CN 114069683 B CN114069683 B CN 114069683B CN 202111360540 A CN202111360540 A CN 202111360540A CN 114069683 B CN114069683 B CN 114069683B
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converter station
mmc converter
voltage
current
mmc
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CN114069683A (en
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严喜林
梁宁
张怿宁
国建宝
张楠
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Maintenance and Test Center of Extra High Voltage Power Transmission Co
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Maintenance and Test Center of Extra High Voltage Power Transmission Co
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/36—Arrangements for transfer of electric power between ac networks via a high-tension dc link
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
    • H02J2203/20—Simulating, e g planning, reliability check, modelling or computer assisted design [CAD]
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/60—Arrangements for transfer of electric power between AC networks or generators via a high voltage DC link [HVCD]

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Dc-Dc Converters (AREA)
  • Supply And Distribution Of Alternating Current (AREA)

Abstract

The application relates to a method and a device for determining steady-state operation characteristics of an MMC converter station and computer equipment. The method comprises the following steps: independently solving a mathematical model of each target MMC converter station; calculating direct current of the reference MMC converter station; judging whether the convergence parameters meet the convergence conditions or not; if not, carrying out iterative computation until the convergence parameter meets the convergence condition; solving a mathematical model of the reference MMC converter station according to the direct-current voltage or direct-current of the reference MMC converter station under the condition that the convergence parameter meets the convergence condition, and determining steady-state operation characteristics of the reference MMC converter station according to each voltage state variable and each current state variable of the reference MMC converter station; and determining the steady-state operation characteristic of each target MMC converter station according to each voltage state variable and each current state variable of each target MMC converter station under the condition that the convergence parameters meet the convergence conditions. By adopting the method, the calculation complexity of the steady-state operation characteristics of the MMC converter station can be reduced, and the complexity of modifying the mathematical model can be reduced.

Description

Method and device for determining steady-state operation characteristics of MMC converter station and computer equipment
Technical Field
The present application relates to the field of flexible direct current transmission technology, and in particular, to a method, an apparatus, a computer device, a storage medium, and a computer program product for determining steady state operation characteristics of an MMC converter station.
Background
The flexible direct current transmission network based on MMC (Modular Multilevel Converter) and the modularized multi-level converter is developed from a two-end flexible direct current transmission system, has the technical advantages of MMC and the characteristics of flexibility and reliability of a multi-end direct current transmission network, and becomes one of research hot spots in the field of direct current transmission.
In a flexible direct current transmission network based on MMC, steady state characteristic calculation of an MMC converter station is a basis and an important link of system design, and has important significance for safe and stable operation of the system.
A steady state characteristic calculation method of a traditional flexible direct current power transmission network combines an MMC converter station model and a multi-terminal direct current circuit network model to carry out once unified solution. However, the steady state characteristics of the flexible direct current transmission network with a plurality of MMC converter stations are calculated at one time, the workload can be increased sharply along with the order of the square course of the MMC converter station model, and the calculation is very difficult.
Disclosure of Invention
Based on this, it is necessary to provide a method, a device and a computer device for determining steady-state operation characteristics of an MMC converter station in view of the above technical problems.
In a first aspect, the present application provides a method for determining steady-state operating characteristics of an MMC converter station, the method being applied to a flexible dc power grid for dc voltage sag control, the flexible dc power grid comprising a reference MMC converter station and a plurality of target MMC converter stations, the method comprising:
according to the direct-current voltage of each target MMC converter station, independently solving a mathematical model of each target MMC converter station to obtain direct-current, each voltage state variable and each current state variable of each target MMC converter station;
calculating the direct current of the reference MMC converter station according to the direct current of each target MMC converter station;
judging whether the convergence parameter meets the convergence condition, wherein the convergence parameter is the difference between the direct current of the reference MMC converter station and the direct current of the reference MMC converter station determined by the previous iterative calculation; if not, updating the direct current voltage of the reference MMC converter station, updating the direct current voltage of each target MMC converter station according to the updated direct current voltage of the reference MMC converter station and the node impedance matrix of the flexible direct current transmission network, returning to the step of independently solving the mathematical model of each target MMC converter station according to the direct current voltage of each target MMC converter station, and performing iterative calculation until convergence parameters meet convergence conditions;
Solving a mathematical model of the reference MMC converter station according to the direct-current voltage or direct-current of the reference MMC converter station under the condition that the convergence parameter meets the convergence condition so as to acquire each voltage state variable and each current state variable of the reference MMC converter station, and determining the steady-state operation characteristic of the reference MMC converter station according to each voltage state variable and each current state variable of the reference MMC converter station;
and determining the steady-state operation characteristic of each target MMC converter station according to each voltage state variable and each current state variable of each target MMC converter station under the condition that the convergence parameters meet the convergence conditions.
In one embodiment, the step of updating the dc voltage of the reference MMC converter station comprises:
acquiring a power reference value corresponding to a reference MMC converter station; the power reference value is a power reference value for direct current droop control;
and updating the direct-current voltage of the reference MMC converter station according to the power reference value and the direct-current voltage of the reference MMC converter station calculated in the iteration.
In one embodiment, the step of updating the dc voltage of the reference MMC converter station according to the power reference value and the dc voltage of the reference MMC converter station calculated in this iteration includes:
if the power reference value is a direct current power reference value, updating the direct current voltage of the reference MMC converter station according to the following expression:
wherein ,for updated reference MMC converter station DC voltage, P dcref Is a direct current power reference value, < >>For the direct voltage of the reference MMC converter station of this iterative calculation, < >>The direct current of the reference MMC converter station calculated for the iteration is calculated, k is the iteration number, and r is a correction coefficient (O is less than or equal to 1);
if the power reference value is an ac side active power reference value, updating the dc voltage of the reference MMC converter station according to the following expression:
wherein ,for updated reference MMC converter station DC voltage, P acref Is the active power reference value of the alternating current side, P s Is equivalent resistance loss power of an alternating current system, P a Power is lost for bridge arm resistance, < >>For the direct voltage of the reference MMC converter station of this iterative calculation, < >>And (3) the direct current of the reference MMC converter station calculated for the iteration is calculated, k is the iteration number, and r is a correction coefficient (r is more than 0 and less than or equal to 1).
In one embodiment, before the step of independently solving the mathematical model of each target MMC converter station according to the dc voltage of each target MMC converter station, the method comprises:
acquiring a direct-current voltage of a preset reference MMC converter station; the dc voltage of each target MMC converter station is equal to the dc voltage of the reference MMC converter station.
In one embodiment, the voltage state variables of the reference MMC converter station include a series sub-module equivalent capacitor voltage direct current component, a series sub-module equivalent capacitor voltage fundamental frequency component, and a series sub-module equivalent capacitor voltage double frequency component; the current state variables of the reference MMC converter station comprise an MMC alternating current side current fundamental frequency component, an MMC internal circulation direct current component and an MMC internal circulation double frequency component;
A step of determining steady state operating characteristics of the reference MMC converter station from the voltage state variables and the current state variables of the reference MMC converter station, comprising:
solving the extreme value of the equivalent capacitance voltage of the series sub-module according to the direct current component of the equivalent capacitance voltage of the series sub-module, the fundamental frequency component of the equivalent capacitance voltage of the series sub-module and the frequency doubling component of the equivalent capacitance voltage of the series sub-module; solving an MMC alternating-current side current extremum according to the MMC alternating-current side current fundamental frequency component; and solving a bridge arm current extremum according to the MMC alternating-current side current fundamental frequency component, the MMC internal circulation direct-current component and the MMC internal circulation double-frequency component.
In one embodiment, the step of determining whether the convergence parameter meets the convergence condition includes:
if the convergence parameter is smaller than the threshold value, meeting the convergence condition;
if the convergence parameter is greater than or equal to the threshold value, the convergence condition is not satisfied.
In a second aspect, the application also provides a device for determining steady-state operation characteristics of an MMC converter station, and the device is applied to a flexible direct current power transmission network for direct current droop control; the flexible direct current power transmission network comprises a reference MMC converter station and a plurality of target MMC converter stations; the device comprises:
the mathematical model solving module is used for independently solving the mathematical model of each target MMC converter station according to the direct-current voltage of each target MMC converter station so as to acquire the direct-current, each voltage state variable and each current state variable of each target MMC converter station; the method is further used for solving a mathematical model of the reference MMC converter station according to the direct-current voltage or direct-current of the reference MMC converter station under the condition that the convergence parameter meets the convergence condition so as to acquire all voltage state variables and all current state variables of the reference MMC converter station;
The direct current acquisition module is used for calculating direct current of the reference MMC converter station according to the direct current of each target MMC converter station;
the convergence judging module is used for judging whether convergence parameters meet convergence conditions, wherein the convergence parameters are the difference between the direct current of the reference MMC converter station and the direct current of the reference MMC converter station determined by the previous iterative computation; if not, updating the direct current voltage of the reference MMC converter station, updating the direct current voltage of each target MMC converter station according to the updated direct current voltage of the reference MMC converter station and the node impedance matrix of the flexible direct current transmission network, returning to the step of independently solving the mathematical model of each target MMC converter station according to the direct current voltage of each target MMC converter station, and performing iterative calculation until convergence parameters meet convergence conditions;
the steady-state operation characteristic calculation module is used for determining steady-state operation characteristics of the reference MMC converter station according to each voltage state variable and each current state variable of the reference MMC converter station; and the method is also used for determining the steady-state operation characteristic of the target MMC converter station according to each voltage state variable and each current state variable of the target MMC converter station under the condition that the convergence parameter meets the convergence condition.
In a third aspect, the application also provides a computer device comprising a memory storing a computer program and a processor implementing the steps of the method of any one of claims 1 to 6 when the computer program is executed by the processor.
In a fourth aspect, the application also provides a computer-readable storage medium having stored thereon a computer program which, when executed by a processor, implements the steps of the method of any of claims 1 to 6.
In a fifth aspect, the application also provides a computer program product comprising a computer program which, when executed by a processor, implements the steps of the method of any of claims 1 to 6.
One of the above technical solutions has the following advantages and beneficial effects:
according to the direct-current voltage of each target MMC converter station, the mathematical model of each target MMC converter station is independently solved, so that the direct-current, each voltage state variable and each current state variable of each target MMC converter station are obtained, and the mathematical models of each target MMC converter station can be prevented from being combined to carry out unified solving. And calculating the direct current of the reference MMC converter station according to the direct current of each target MMC converter station, so that the direct current of each MMC converter station can be balanced. Whether the convergence condition is met or not can be judged according to the difference between the direct current of the reference MMC converter station and the direct current of the reference MMC converter station determined by the last iterative calculation; if not, updating the direct current voltage of the reference MMC converter station, updating the direct current voltage of each target MMC converter station according to the updated direct current voltage of the reference MMC converter station and the node impedance matrix of the flexible direct current transmission network, returning to the step of independently solving the mathematical model of each target MMC converter station according to the direct current voltage of each target MMC converter station, and performing iterative calculation until convergence parameters meet convergence conditions; therefore, when the iterative computation converges, the voltage state variable and the current state variable of each target MMC converter station can be obtained; the mathematical model of the reference MMC converter station can be solved according to the direct-current voltage or direct-current of the reference MMC converter station under the condition that the convergence parameter meets the convergence condition, so that each voltage state variable and each current state variable of the reference MMC converter station are obtained, and the steady-state operation characteristic of the reference MMC converter station is determined according to each voltage state variable and each current state variable of the reference MMC converter station; determining steady-state operation characteristics of each target MMC converter station according to each voltage state variable and each current state variable of each target MMC converter station under the condition that the convergence parameters meet convergence conditions; therefore, steady-state operation characteristics of each MMC converter station (including reference MMC converter stations and target MMC converter stations) under the condition of convergence of iterative computation can be obtained through independent solution, order computation of a simultaneous mathematical model is reduced, complexity of computation of steady-state operation characteristics of the MMC converter stations is reduced, modification of voltage state variables or current state variables of a single MMC converter station can be limited in the range of a mathematical model of the MMC converter station, and complexity of modification of the mathematical model is reduced.
Drawings
FIG. 1 is a flow chart of a method for determining steady state operating characteristics of an MMC converter station in one embodiment;
FIG. 2 is a flowchart illustrating steps of a method for determining steady-state operating characteristics of an MMC converter station according to one embodiment;
FIG. 3 is a flowchart illustrating steps for updating the DC voltage of a reference MMC converter station according to one embodiment;
fig. 4 is a schematic flow chart illustrating a method for determining steady-state operation characteristics of an MMC converter station according to an embodiment;
fig. 5 is a block diagram illustrating a configuration of a device for determining steady-state operation characteristics of an MMC converter station according to an embodiment;
fig. 6 is an internal structural diagram of a computer device in one embodiment.
Detailed Description
The flexible direct current transmission network based on the MMC is developed from two-end flexible direct current transmission networks, has the technical advantages of the MMC and the characteristics of flexibility and reliability of the multi-end direct current transmission network, and becomes one of research hot spots in the field of direct current transmission. The steady state operation characteristic calculation of the flexible direct current transmission network based on the MMC is a basis and an important link of system design, and has important significance for safe and stable operation of the system. The steady-state operation characteristic calculation of the flexible direct-current power transmission network based on the MMC is to determine the steady-state operation characteristic of each MMC converter station, and the premise is to obtain the steady-state value of each voltage state variable of each MMC converter station and the steady-state value of each current state variable of each MMC converter station. Wherein each voltage state variable reflects a voltage relationship between elements of the MMC converter station and each current state variable reflects a current relationship between elements of the MMC converter station. Each of the voltage state variable and the current state variable corresponds to a respective nonlinear differential equation, and the steady state value of the state variable can be solved by zeroing the differential term of the differential equation. In order to solve the steady-state operation characteristic of the whole flexible direct current transmission network, the traditional method needs to combine the nonlinear equations of the mathematical models of a plurality of MMC converter stations and the nonlinear equations of the mathematical models of the multi-terminal direct current circuit network to perform once unified solving. For small systems with a limited number of state variables, this approach can be easily solved by the fsolve function in Matlab. However, for a flexible direct current transmission network comprising a plurality of MMC converter stations, at least the following problems exist: (1) The number of state variables is excessive, resulting in a large increase in computational burden. Each MMC converter station has at least 22 state variables under balanced conditions and at least 38 state variables under unbalanced conditions, and if the frequency-dependent parametric model of the dc line is considered, the number of state variables of the whole flexible dc transmission network increases considerably. The workload of solving all nonlinear equations at one time increases sharply along with the order of the equation, so that it is very difficult to solve the steady state values of the state variables of the flexible direct current power transmission network comprising a plurality of MMC converter stations at one time; (2) Modifying the fsive function of a flexible direct current transmission network comprising a plurality of MMC converter stations is cumbersome. If a state variable needs to be added or deleted in the fsive function of the entire flexible dc power transmission network, all state variables following the modified state variable have to be renumbered. The more state variables of the fsive function of the flexible direct current transmission network, the more advanced the state variables are modified, the greater the recoding effort.
The present application will be described in further detail with reference to the drawings and examples, in order to make the objects, technical solutions and advantages of the present application more apparent. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the application.
In one embodiment, as shown in fig. 1, a method for determining steady-state operation characteristics of an MMC converter station is provided, where this embodiment is applied to a terminal for illustration, it is understood that the method may also be applied to a server, and may also be applied to a system including a terminal and a server, and implemented through interaction between the terminal and the server. In this embodiment, the method is applied to a flexible direct current power transmission network, and in particular, the method can be applied to a flexible direct current power transmission network with direct current sag control; a flexible direct current power transmission network comprising a reference MMC converter station and a plurality of target MMC converter stations, the method comprising the steps of:
step S102, according to the DC voltage of each target MMC converter station, the mathematical model of each target MMC converter station is independently solved to obtain the DC current, each voltage state variable and each current state variable of each target MMC converter station.
Specifically, referring to an MMC converter station as a reference point, the MMC converter station is configured to balance direct current injected into a flexible direct current power transmission network by each MMC converter station; the target MMC converter station is other MMC converter stations except the reference MMC converter station in the flexible direct current transmission network. The control mode of the MMC converter station (including the reference MMC converter station and the target MMC converter station) is constant power control (P-Q control) or direct current voltage droop control. The mathematical model of the MMC converter station is a fSOve function corresponding to a P-Q controlled converter station or a fSOve function corresponding to a converter station with direct current droop control. Each voltage state variable reflects a voltage relationship between elements of the MMC converter station and each current state variable reflects a current relationship between elements of the MMC converter station.
And obtaining the direct-current voltage of each target MMC converter station according to the direct-current voltage of the reference MMC converter station. For each target MMC converter station, solving a mathematical model corresponding to the target MMC converter station according to the direct-current voltage of the target MMC converter station, and obtaining direct-current injected into the flexible direct-current power transmission network by the target MMC converter station, each voltage state variable of the target MMC converter station and each current state variable of the target MMC converter station by solving the mathematical model of the target MMC converter station.
Step S104, calculating the direct current of the reference MMC converter station according to the direct current of each target MMC converter station.
Specifically, the sum of the direct currents injected into the flexible direct current transmission network by each MMC converter station (including the target MMC converter station and the reference MMC converter station) is zero. And determining the direct current of the reference MMC converter station by using the kirchhoff current law and the direct current of each target MMC converter station obtained according to the previous step.
Step S106, judging whether the convergence parameter meets the convergence condition, wherein the convergence parameter is the difference between the direct current of the reference MMC converter station and the direct current of the reference MMC converter station determined by the previous iterative computation; if not, updating the direct current voltage of the reference MMC converter station, updating the direct current voltage of each target MMC converter station according to the updated direct current voltage of the reference MMC converter station and the node impedance matrix of the flexible direct current transmission network, returning to the step of independently solving the mathematical model of each target MMC converter station according to the direct current voltage of each target MMC converter station, and performing iterative calculation until the convergence parameters meet the convergence conditions.
Specifically, the direct current of the reference MMC converter station is calculated from the direct current of each target MMC converter station. And judging whether the convergence parameter meets the convergence condition or not according to the difference between the direct currents of the reference MMC converter stations in the two adjacent iterative calculations, if not, updating the direct current voltage of the reference MMC converter stations, updating the direct current voltage of each target MMC converter station according to the updated direct current voltage of the reference MMC converter stations, the direct current of each target MMC converter station calculated in the iteration and the node impedance matrix of the flexible direct current transmission network, and returning to the step S102 for iterative calculation until the convergence parameter meets the convergence condition, namely, iterating the step S102, the step S104 and the step S106 until the iteration is ended after the iterative calculation converges. It will be appreciated that the updated dc voltage of the reference MMC converter station is the new one of the reference MMC converter stations calculated in one iteration. It can be further understood that various data obtained after the last step of judging whether the convergence parameter satisfies the convergence condition and before the current step of judging whether the convergence parameter satisfies the convergence condition are data of the current iterative calculation.
Step S108, solving a mathematical model of the reference MMC converter station according to the direct-current voltage or the direct-current of the reference MMC converter station under the condition that the convergence parameter meets the convergence condition so as to acquire each voltage state variable and each current state variable of the reference MMC converter station, and determining the steady-state operation characteristic of the reference MMC converter station according to each voltage state variable and each current state variable of the reference MMC converter station.
Specifically, if in step S106, it is determined that the convergence parameter satisfies the convergence condition, the dc voltage of the reference MMC converter station after the last iteration calculation update is the dc voltage of the reference MMC converter station when the convergence parameter satisfies the convergence condition, and the dc current of the reference MMC converter station obtained by the current iteration calculation is the dc current of the reference MMC converter station when the convergence parameter satisfies the convergence condition. And solving a mathematical model of the reference MMC converter station according to the direct-current voltage or the direct-current of the reference MMC converter station under the condition that the convergence parameter meets the convergence condition, so as to obtain each voltage state variable and each current state variable of the reference MMC converter station. And solving the values related to the steady-state operation characteristics in the voltage state variables of the reference MMC converter station and solving the values related to the steady-state operation characteristics in the current state variables of the reference MMC converter station to determine the steady-state operation characteristics of the reference MMC converter station.
Step S110, determining a steady-state operation characteristic of each target MMC converter station according to each voltage state variable and each current state variable of each target MMC converter station when the convergence parameter satisfies the convergence condition.
Specifically, if it is determined in step S106 that the convergence parameter satisfies the convergence condition, in the step of this iterative calculation, each voltage state variable and each current state variable of each target MMC converter station obtained by solving the mathematical model of each target MMC converter station are each voltage state variable and each current state variable of each target MMC converter station when the convergence parameter satisfies the convergence condition. For each target MMC converter station, solving a value related to the steady-state operating characteristic in each voltage state variable of the target MMC converter station and solving a value related to the steady-state operating characteristic in each current state variable of the target MMC converter station to determine the steady-state operating characteristic of the target MMC converter station.
In the method for determining the steady-state operation characteristics of the MMC converter stations, according to the direct-current voltage of each target MMC converter station, the mathematical model of each target MMC converter station is independently solved to obtain the direct-current, each voltage state variable and each current state variable of each target MMC converter station; therefore, the mathematical model of each target MMC converter station can be prevented from being combined to carry out unified solution. Calculating the direct current of the reference MMC converter station according to the direct current of each target MMC converter station; thereby balancing the direct current of each MMC converter station. Whether the convergence condition is met or not can be judged according to the difference between the direct current of the reference MMC converter station and the direct current of the reference MMC converter station determined by the last iterative calculation; if not, updating the direct current voltage of the reference MMC converter station, updating the direct current voltage of each target MMC converter station according to the updated direct current voltage of the reference MMC converter station and the node impedance matrix of the flexible direct current transmission network, returning to the step of independently solving the mathematical model of each target MMC converter station according to the direct current voltage of each target MMC converter station, and performing iterative calculation until convergence parameters meet convergence conditions; therefore, when the iterative computation converges, the voltage state variable and the current state variable of each target MMC converter station can be obtained; the mathematical model of the reference MMC converter station can be solved according to the direct-current voltage or direct-current of the reference MMC converter station under the condition that the convergence parameter meets the convergence condition, so that each voltage state variable and each current state variable of the reference MMC converter station are obtained, and the steady-state operation characteristic of the reference MMC converter station is determined according to each voltage state variable and each current state variable of the reference MMC converter station; determining steady-state operation characteristics of each target MMC converter station according to each voltage state variable and each current state variable of each target MMC converter station under the condition that the convergence parameters meet convergence conditions; therefore, steady-state operation characteristics of each MMC converter station (including reference MMC converter stations and target MMC converter stations) under the condition of convergence of iterative computation can be obtained through independent solution, order computation of a simultaneous mathematical model is reduced, complexity of computation of steady-state operation characteristics of the MMC converter stations is reduced, modification of voltage state variables or current state variables of a single MMC converter station can be limited in the range of a mathematical model of the MMC converter station, and complexity of modification of the mathematical model is reduced.
In a specific example, as shown in fig. 2, the method for determining steady-state operation characteristics of an MMC converter station includes the following specific steps:
step S201, according to the direct current voltage of each target MMC converter station, independently solving the mathematical model of each target MMC converter station to obtain the direct current, each voltage state variable and each current state variable of each target MMC converter station;
step S202, calculating the direct current of the reference MMC converter station according to the direct current of each target MMC converter station;
step S203, judging whether the convergence parameter meets the convergence condition;
in step S203, if the convergence parameter does not meet the convergence condition, step S204 and step S205 are executed;
step S204, updating the direct current voltage of the reference MMC converter station;
step S205, updating direct current of each target MMC converter station according to the updated direct current voltage of the reference MMC converter station and the node impedance matrix of the flexible direct current power transmission network;
after executing step S205, S201 is continued to be executed;
in step S203, if the convergence parameter satisfies the convergence condition, step S206, step S207 and step S208 are performed;
step S206, solving a mathematical model of the reference MMC converter station according to the direct-current voltage or the direct-current of the reference MMC converter station so as to acquire each voltage state variable and each current state variable of the reference MMC converter station;
Step S207, determining steady-state operation characteristics of the reference MMC converter station according to the voltage state variables and the current state variables of the reference MMC converter station;
step S208, determining the steady-state operation characteristics of each target MMC converter station according to each voltage state variable and each current state variable of each target MMC converter station.
In one embodiment, as shown in fig. 3, the step of updating the dc voltage of the reference MMC converter station includes:
step S302, a power reference value corresponding to a reference MMC converter station is acquired.
The power reference value is a power reference value for direct current droop control.
Specifically, the control mode of the target MMC converter station is constant power control (P-Q control) or direct current droop control, and the control mode of the reference MMC converter station is direct current droop control. The updating of the dc voltage of the reference MMC converter station depends on the power reference value of the voltage droop control, and thus the power reference value corresponding to the reference MMC converter station needs to be obtained.
Step S304, updating the direct current voltage of the reference MMC converter station according to the power reference value and the direct current voltage of the reference MMC converter station calculated in the iteration.
It can be understood that the direct current voltage of the reference MMC converter station calculated in this iteration is the direct current voltage of the reference MMC converter station updated in the previous iteration.
Specifically, the direct current voltage of the reference MMC converter station after updating is obtained by calculating according to the power reference value corresponding to the direct current droop control of the MMC converter station and the direct current voltage of the reference MMC converter station calculated in the iteration, and the direct current voltage of the reference MMC converter station after updating is used as the direct current voltage of the reference MMC converter station calculated in the new iteration.
In this embodiment, according to the power reference value of the direct current droop control, the direct current voltage of the reference MMC converter station can be effectively and accurately updated, and the error of the updated direct current voltage of the MMC converter station is reduced.
In one embodiment, the step of updating the dc voltage of the reference MMC converter station according to the power reference value and the dc voltage of the reference MMC converter station calculated in this iteration includes:
if the power reference value is a direct current power reference value, updating the direct current voltage of the reference MMC converter station according to the following expression:
if the power reference value is an ac side active power reference value, updating the dc voltage of the reference MMC converter station according to the following expression:
in particular, the updating of the dc voltage of the reference MMC converter station depends on whether the power reference of the voltage droop control is a dc power reference or an ac side active power reference.
If the power reference value is a direct current power reference value, updating the direct current voltage of the reference MMC converter station according to the following expression:
can make
Then
wherein ,
P dcref is a direct current power reference value, P ref For a given power reference value, K dc For sag factor, U dcref Is a direct-current voltage reference value, k is the iteration number,for reference of the DC voltage of the MMC converter station in this iteration, deltau dc For DC voltage conversion quantity, < >>For reference of the direct current of the MMC converter station in this iteration, < > for>For the updated reference MMC converter station DC voltage, r is a correction coefficient (r is more than 0 and less than or equal to 1), and the value of r should be small enough to ensure iteration convergence.
If the power reference value is an ac side active power reference value, updating the dc voltage of the reference MMC converter station according to the following expression:
order the
Then
At the same time have
P dcref ＝P acref ±P s ±P a
If the reference MMC converter station is a rectifying station, then
P dcref ＝P acref -P s -P a
I.e.
If the reference MMC converter station is an inversion station, then
P dcref ＝P acref +P s +P a
I.e.
wherein ,
P dcref is a direct current power reference value, P acref Is the active power reference value of the alternating current side, P s Is equivalent resistance loss power of an alternating current system, R s Is equivalent resistance of an alternating current system, i 1d and i1q The d-axis component and the q-axis component of the fundamental frequency of the alternating side-phase current, P a I is bridge arm resistance loss power 0 I is the direct current component of the internal circulation 2d and i2q The frequency-doubled d-axis component and the q-axis component of the internal circulation, respectively.
Further, according to the updated direct current voltage of the reference MMC converter station and the node impedance matrix of the flexible direct current transmission network, updating the direct current voltage of each target MMC converter station according to the following expression:
wherein, the left side of the equation is the direct current voltage, Z, of each updated target MMC converter station dc Is a node impedance matrix of the flexible direct current transmission network,direct current of each target MMC converter station calculated in the iteration mode>And the updated direct current voltage of the reference MMC converter station.
In one embodiment, before the step of independently solving the mathematical model of each target MMC converter station from the dc voltage of each target MMC converter station, it comprises:
acquiring a direct-current voltage of a preset reference MMC converter station; the dc voltage of each target MMC converter station is equal to the dc voltage of the reference MMC converter station.
Specifically, during initial calculation, a preset direct current voltage of the reference MMC converter station is obtained, and the direct current voltage of the target MMC converter station is enabled to be equal to the direct current voltage of the reference MMC converter station. It will be appreciated that the initial computation is when an iterative computation has not been entered.
In one embodiment, the voltage state variables of the reference MMC converter station include a series sub-module equivalent capacitor voltage direct current component, a series sub-module equivalent capacitor voltage fundamental frequency component, and a series sub-module equivalent capacitor voltage double frequency component; the current state variables of the reference MMC converter station comprise an MMC alternating current side current fundamental frequency component, an MMC internal circulation direct current component and an MMC internal circulation double frequency component;
A step of determining steady state operating characteristics of the reference MMC converter station from the voltage state variables and the current state variables of the reference MMC converter station, comprising:
solving the extreme value of the equivalent capacitance voltage of the series sub-module according to the direct current component of the equivalent capacitance voltage of the series sub-module, the fundamental frequency component of the equivalent capacitance voltage of the series sub-module and the frequency doubling component of the equivalent capacitance voltage of the series sub-module; solving an MMC alternating-current side current extremum according to the MMC alternating-current side current fundamental frequency component; and solving a bridge arm current extremum according to the MMC alternating-current side current fundamental frequency component, the MMC internal circulation direct-current component and the MMC internal circulation double-frequency component. Specifically, solving a mathematical model of the reference MMC converter station to obtain each voltage state variable and each current state variable of the reference MMC converter station; the voltage state variables of the reference MMC converter station comprise a series submodule equivalent capacitor voltage direct current component, a series submodule equivalent capacitor voltage fundamental frequency component and a series submodule equivalent capacitor voltage double frequency component; the current state variables of the reference MMC converter station comprise an MMC alternating current side current fundamental frequency component, an MMC internal circulation direct current component and an MMC internal circulation double frequency component; the extremum of each electrical quantity of the reference MMC converter station can be solved by a point-by-point scanning method. In this way, the extreme value of the equivalent capacitance voltage of the series sub-module of the reference MMC converter station is solved according to the direct current component, the fundamental frequency component and the frequency doubling component of the equivalent capacitance voltage of the series sub-module of the reference MMC converter station; solving an MMC alternating-current side current extremum of the reference MMC converter station according to an MMC alternating-current side current fundamental frequency component of the reference MMC converter station; according to the MMC alternating current side current fundamental frequency component, the MMC internal circulation direct current component and the MMC internal circulation frequency doubling component of the reference MMC converter station, the bridge arm current extremum of the reference MMC converter station is solved, and the steady-state operation characteristic of the reference MMC converter station can be obtained.
Further, according to the method for solving the extremum of each electric quantity of the reference MMC converter station, the extremum of each electric quantity of each target MMC converter station is independently solved, and the steady-state operation characteristic of each target MMC converter station can be obtained.
In one embodiment, the step of determining whether the convergence parameter satisfies the convergence condition includes:
if the convergence parameter is smaller than the threshold value, meeting the convergence condition;
if the convergence parameter is greater than or equal to the threshold, the convergence condition is not satisfied.
Specifically, the difference between the direct currents of the reference MMC converter stations calculated in two adjacent iterations should be within the allowable error range, that is, the convergence parameter is smaller than the threshold value, and the iteration calculation converges at this time. Judging whether a convergence condition is satisfied according to the following expression:
wherein ,for the convergence parameter ε is the minimum allowable error, i.e. the threshold, +.>For the direct current of reference MMC converter station of this iterative calculation, < >>And (3) the direct current of the reference MMC converter station calculated for the last iteration.
In a specific embodiment, as shown in fig. 4, the method for determining steady-state operation characteristics of an MMC converter station includes the following steps:
step S401, obtaining a direct current voltage of a preset reference MMC converter station; the dc voltage of each target MMC converter station is equal to the dc voltage of the reference MMC converter station.
Step S402, according to the direct current voltage of each target MMC converter station, independently solving the mathematical model of each target MMC converter station to obtain the direct current, each voltage state variable and each current state variable of each target MMC converter station;
step S403, calculating the direct current of the reference MMC converter station according to the direct current of each target MMC converter station by using kirchhoff current law;
step S404, judging whether the convergence parameter meets the convergence condition, wherein the convergence parameter is the difference between the direct current of the reference MMC converter station and the direct current of the reference MMC converter station determined by the previous iterative computation;
step S405, if the convergence parameter is greater than or equal to the threshold value, obtaining a power reference value corresponding to the reference MMC converter station; the power reference value is a power reference value for direct current droop control; if the power reference value is a dc power reference value, the dc voltage of the reference MMC converter station is updated according to the following expression (1):
wherein ,for updated reference MMC converter station DC voltage, P dcref Is a direct current power reference value, < >>For the direct voltage of the reference MMC converter station of this iterative calculation, < >>The direct current of the reference MMC converter station calculated for the iteration is calculated, k is the iteration number, and r is a correction coefficient (r is more than 0 and less than or equal to 1);
If the power reference value is an ac side active power reference value, updating the dc voltage of the reference MMC converter station according to the following expression (2):
wherein ,for updated reference MMC converter station DC voltage, P acref Is the active power reference value of the alternating current side, P s Is equivalent resistance loss power of an alternating current system, P a Power is lost for bridge arm resistance, < >>For the direct voltage of the reference MMC converter station of this iterative calculation, < >>And (3) the direct current of the reference MMC converter station calculated for the iteration is calculated, k is the iteration number, and r is a correction coefficient (r is more than 0 and less than or equal to 1).
Step S406, updating the direct current voltage of each target MMC converter station according to the updated direct current voltage of the reference MMC converter station and the node impedance matrix of the flexible direct current transmission network, and returning to the step of independently solving the mathematical model of each target MMC converter station according to the direct current voltage of each target MMC converter station so as to perform iterative computation until the convergence parameter is smaller than the threshold value;
step S407, solving a mathematical model of the reference MMC converter station according to the direct current voltage or the direct current of the reference MMC converter station under the condition that the convergence parameter meets the convergence condition, so as to obtain each voltage state variable and each current state variable of the reference MMC converter station, and solving an extremum of the equivalent capacitance voltage of the serial submodule of the reference MMC converter station according to the equivalent capacitance voltage direct current component, the equivalent capacitance voltage fundamental frequency component of the serial submodule and the double frequency component of the equivalent capacitance voltage of the serial submodule of the reference MMC converter station; solving an MMC alternating-current side current extremum of the reference MMC converter station according to an MMC alternating-current side current fundamental frequency component of the reference MMC converter station; according to the MMC alternating current side current fundamental frequency component, the MMC internal circulation direct current component and the MMC internal circulation frequency doubling component of the reference MMC converter station, solving a bridge arm current extremum of the reference MMC converter station.
Step S408, according to the voltage state variables and the current state variables of each target MMC converter station under the condition that the convergence parameters meet the convergence conditions, and according to the direct current component, the fundamental frequency component and the frequency doubling component of the equivalent capacitance voltage of the series sub-module of each target MMC converter station, the extremum of the equivalent capacitance voltage of the series sub-module of each target MMC converter station is solved; solving MMC alternating current side current extremum of each target MMC converter station according to MMC alternating current side current fundamental frequency components of each target MMC converter station; and solving bridge arm current extremum of each target MMC converter station according to the MMC alternating current side current fundamental frequency component, the MMC internal circulation direct current component and the MMC internal circulation double frequency component of each target MMC converter station.
It should be understood that, although the steps in the flowcharts related to the embodiments described above are sequentially shown as indicated by arrows, these steps are not necessarily sequentially performed in the order indicated by the arrows. The steps are not strictly limited to the order of execution unless explicitly recited herein, and the steps may be executed in other orders. Moreover, at least some of the steps in the flowcharts described in the above embodiments may include a plurality of steps or a plurality of stages, which are not necessarily performed at the same time, but may be performed at different times, and the order of the steps or stages is not necessarily performed sequentially, but may be performed alternately or alternately with at least some of the other steps or stages.
Based on the same inventive concept, the embodiment of the application also provides a device for determining the steady-state operation characteristics of the MMC converter station, which is used for realizing the method for determining the steady-state operation characteristics of the MMC converter station. The implementation of the solution provided by the device is similar to the implementation described in the above method, so the specific limitation in the embodiments of the device for determining the steady-state operation characteristics of one or more MMC converter stations provided below may be referred to the limitation of the method for determining the steady-state operation characteristics of an MMC converter station hereinabove, and will not be repeated here.
In one embodiment, as shown in fig. 5, the present application further provides a device for determining steady-state operation characteristics of an MMC converter station, where the device is applied to a flexible dc power transmission network for dc voltage sag control; the flexible direct current power transmission network comprises a reference MMC converter station and a plurality of target MMC converter stations; the device comprises: a mathematical model solving module 510, a direct current obtaining module 520, a convergence judging module 530, and a steady-state operation characteristic calculating module 540, wherein:
the mathematical model solving module 510 is configured to independently solve a mathematical model of each target MMC converter station according to a dc voltage of each target MMC converter station, so as to obtain a dc current, each voltage state variable, and each current state variable of each target MMC converter station; the method is further used for solving a mathematical model of the reference MMC converter station according to the direct-current voltage or direct-current of the reference MMC converter station under the condition that the convergence parameter meets the convergence condition so as to acquire all voltage state variables and all current state variables of the reference MMC converter station;
The direct current obtaining module 520 is configured to calculate a direct current of the reference MMC converter station according to the direct current of each target MMC converter station;
the convergence judging module 530 is configured to judge whether a convergence parameter meets a convergence condition, where the convergence parameter is a difference between a direct current of the reference MMC converter station and a direct current of the reference MMC converter station determined by a previous iterative calculation; if not, updating the direct current voltage of the reference MMC converter station, updating the direct current voltage of each target MMC converter station according to the updated direct current voltage of the reference MMC converter station and the node impedance matrix of the flexible direct current transmission network, returning to the step of independently solving the mathematical model of each target MMC converter station according to the direct current voltage of each target MMC converter station, and performing iterative calculation until convergence parameters meet convergence conditions;
a steady state operating characteristic calculation module 540 for determining a steady state operating characteristic of the reference MMC converter station according to each voltage state variable and each current state variable of the reference MMC converter station; and the method is also used for determining the steady-state operation characteristic of the target MMC converter station according to each voltage state variable and each current state variable of the target MMC converter station under the condition that the convergence parameter meets the convergence condition.
In one embodiment, the convergence judging module 530 includes a dc voltage updating unit for acquiring a power reference value corresponding to a reference MMC converter station; the power reference value is a power reference value for direct current droop control; and updating the direct-current voltage of the reference MMC converter station according to the power reference value and the direct-current voltage of the reference MMC converter station calculated in the iteration.
In one embodiment, the dc voltage updating unit includes an expression selecting unit for updating the dc voltage of the reference MMC converter station according to the following expression if the power reference value is the dc power reference value:
wherein ,for updated reference MMC converter station DC voltage, P dcref Is a direct current power reference value, < >>For the direct voltage of the reference MMC converter station of this iterative calculation, < >>The direct current of the reference MMC converter station calculated for the iteration is calculated, k is the iteration number, and r is a correction coefficient (r is more than 0 and less than or equal to 1);
if the power reference value is an ac side active power reference value, updating the dc voltage of the reference MMC converter station according to the following expression:
wherein ,for updated reference MMC converter station DC voltage, P acref Is the active power reference value of the alternating current side, P s Is equivalent resistance loss power of an alternating current system, P a Power is lost for bridge arm resistance, < >>For this iterationCalculated direct voltage of reference MMC converter station, < >>And (3) the direct current of the reference MMC converter station calculated for the iteration is calculated, k is the iteration number, and r is a correction coefficient (r is more than 0 and less than or equal to 1).
In one embodiment, the device further comprises a preset direct current voltage acquisition module,
the method comprises the steps of obtaining direct-current voltage of a preset reference MMC converter station; the dc voltage of each target MMC converter station is equal to the dc voltage of the reference MMC converter station.
In one embodiment, the voltage state variables of the reference MMC converter station include voltage state variables of the reference MMC converter station including a series sub-module equivalent capacitance voltage direct current component, a series sub-module equivalent capacitance voltage fundamental frequency component, and a series sub-module equivalent capacitance voltage double frequency component; the current state variables of the reference MMC converter station comprise an MMC alternating current side current fundamental frequency component, an MMC internal circulation direct current component and an MMC internal circulation double frequency component;
the steady state operating characteristic calculation module 540 includes a reference station characteristic determination unit, wherein,
the reference station characteristic determining unit is used for solving the extremum of the equivalent capacitance voltage of the series submodule according to the direct current component of the equivalent capacitance voltage of the series submodule, the fundamental frequency component of the equivalent capacitance voltage of the series submodule and the frequency doubling component of the equivalent capacitance voltage of the series submodule; solving an MMC alternating-current side current extremum according to the MMC alternating-current side current fundamental frequency component; and solving a bridge arm current extremum according to the MMC alternating-current side current fundamental frequency component, the MMC internal circulation direct-current component and the MMC internal circulation double-frequency component.
In one embodiment, the convergence determination module 530 includes a threshold comparison unit;
the threshold comparison unit is used for judging that if the convergence parameter is smaller than the threshold value, the convergence condition is met; if the convergence parameter is greater than or equal to the threshold value, the convergence condition is not satisfied.
The respective modules in the above-described determination means of the steady-state operating characteristics of the MMC converter station may be implemented wholly or partly in software, hardware and combinations thereof. The above modules may be embedded in hardware or may be independent of a processor in the computer device, or may be stored in software in a memory in the computer device, so that the processor may call and execute operations corresponding to the above modules.
In one embodiment, a computer device is provided, which may be a terminal, and the internal structure of which may be as shown in fig. 6. The computer device includes a processor, a memory, a communication interface, a display screen, and an input device connected by a system bus. Wherein the processor of the computer device is configured to provide computing and control capabilities. The memory of the computer device includes a non-volatile storage medium and an internal memory. The non-volatile storage medium stores an operating system and a computer program. The internal memory provides an environment for the operation of the operating system and computer programs in the non-volatile storage media. The communication interface of the computer device is used for carrying out wired or wireless communication with an external terminal, and the wireless mode can be realized through WIFI, a mobile cellular network, NFC (near field communication) or other technologies. The computer program, when executed by a processor, implements a method of determining steady state operating characteristics of an MMC converter station. The display screen of the computer equipment can be a liquid crystal display screen or an electronic ink display screen, and the input device of the computer equipment can be a touch layer covered on the display screen, can also be keys, a track ball or a touch pad arranged on the shell of the computer equipment, and can also be an external keyboard, a touch pad or a mouse and the like.
It will be appreciated by those skilled in the art that the structure shown in FIG. 5 is merely a block diagram of some of the structures associated with the present inventive arrangements and is not limiting of the computer device to which the present inventive arrangements may be applied, and that a particular computer device may include more or fewer components than shown, or may combine some of the components, or have a different arrangement of components.
In an embodiment, there is also provided a computer device comprising a memory and a processor, the memory having stored therein a computer program, the processor implementing the steps of the method embodiments described above when the computer program is executed.
In one embodiment, a computer-readable storage medium is provided, on which a computer program is stored which, when executed by a processor, carries out the steps of the method embodiments described above.
In an embodiment, a computer program product is provided, comprising a computer program which, when executed by a processor, implements the steps of the method embodiments described above.
Those skilled in the art will appreciate that implementing all or part of the above described methods may be accomplished by way of a computer program stored on a non-transitory computer readable storage medium, which when executed, may comprise the steps of the embodiments of the methods described above. Any reference to memory, database, or other medium used in embodiments provided herein may include at least one of non-volatile and volatile memory. The nonvolatile Memory may include Read-Only Memory (ROM), magnetic tape, floppy disk, flash Memory, optical Memory, high density embedded nonvolatile Memory, resistive random access Memory (ReRAM), magnetic random access Memory (Magnetoresistive Random Access Memory, MRAM), ferroelectric Memory (Ferroelectric Random Access Memory, FRAM), phase change Memory (Phase Change Memory, PCM), graphene Memory, and the like. Volatile memory can include random access memory (Random Access Memory, RAM) or external cache memory, and the like. By way of illustration, and not limitation, RAM can be in the form of a variety of forms, such as static random access memory (Static Random Access Memory, SRAM) or dynamic random access memory (Dynamic Random Access Memory, DRAM), and the like. The databases referred to in the embodiments provided herein may include at least one of a relational database and a non-relational database. The non-relational database may include, but is not limited to, a blockchain-based distributed database, and the like. The processor referred to in the embodiments provided in the present application may be a general-purpose processor, a central processing unit, a graphics processor, a digital signal processor, a programmable logic unit, a data processing logic unit based on quantum computing, or the like, but is not limited thereto.
The technical features of the above embodiments may be arbitrarily combined, and all possible combinations of the technical features in the above embodiments are not described for brevity of description, however, as long as there is no contradiction between the combinations of the technical features, they should be considered as the scope of the description.
The foregoing examples illustrate only a few embodiments of the application and are described in detail herein without thereby limiting the scope of the application. It should be noted that it will be apparent to those skilled in the art that several variations and modifications can be made without departing from the spirit of the application, which are all within the scope of the application. Accordingly, the scope of the application should be assessed as that of the appended claims.

Claims (10)

1. A method of determining steady state operating characteristics of an MMC converter station, the method being applied to a flexible dc power grid for dc voltage sag control, the flexible dc power grid including a reference MMC converter station and a plurality of target MMC converter stations, the method comprising:
according to the direct-current voltage of each target MMC converter station, independently solving a mathematical model of each target MMC converter station to obtain direct-current, each voltage state variable and each current state variable of each target MMC converter station;
Calculating the direct current of the reference MMC converter station according to the direct current of each target MMC converter station;
judging whether a convergence parameter meets a convergence condition, wherein the convergence parameter is the difference between the direct current of the reference MMC converter station and the direct current of the reference MMC converter station determined by the previous iterative calculation; if not, updating the direct current voltage of the reference MMC converter station, updating the direct current voltage of each target MMC converter station according to the updated direct current voltage of the reference MMC converter station and the node impedance matrix of the flexible direct current transmission network, returning to the step of independently solving the mathematical model of each target MMC converter station according to the direct current voltage of each target MMC converter station, and performing iterative calculation until the convergence parameters meet convergence conditions;
solving a mathematical model of the reference MMC converter station according to the direct-current voltage or direct-current of the reference MMC converter station under the condition that the convergence parameter meets the convergence condition so as to acquire each voltage state variable and each current state variable of the reference MMC converter station, and determining the steady-state operation characteristic of the reference MMC converter station according to each voltage state variable and each current state variable of the reference MMC converter station;
Determining steady-state operation characteristics of each target MMC converter station according to each voltage state variable and each current state variable of each target MMC converter station under the condition that the convergence parameters meet convergence conditions;
the step of updating the direct voltage of the reference MMC converter station comprises:
acquiring a power reference value corresponding to the reference MMC converter station; the power reference value is a power reference value for direct current droop control;
if the power reference value is a direct current power reference value, updating the direct current voltage of the reference MMC converter station according to the following expression:
wherein ,for updated reference MMC converter station DC voltage, P dcref Is a direct current power reference value, < >>For the direct voltage of the reference MMC converter station of this iterative calculation, < >>For this timeIterative calculation's reference MMC converter station's direct current, k are iteration number, r are correction factor (0<r≤1)；
If the power reference value is an ac side active power reference value, updating the dc voltage of the reference MMC converter station according to the following expression:
wherein ,for the updated reference MMC converter station DC voltage, pacref is the AC side active power reference value, P s Is equivalent resistance loss power of an alternating current system, P a Power is lost for bridge arm resistance, < >>For the direct voltage of the reference MMC converter station of this iterative calculation, < >>For the direct current of the reference MMC converter station calculated in the iteration, K is the iteration number, r is the correction coefficient, and 0<r≤1。
2. The method according to claim 1, characterized in that before the step of independently solving the mathematical model of each target MMC converter station from the dc voltage of each target MMC converter station, it comprises:
acquiring a preset direct-current voltage of the reference MMC converter station; the direct current voltage of each target MMC converter station is equal to the direct current voltage of the reference MMC converter station.
3. The method of claim 1, wherein the voltage state variables of the reference MMC converter station include a series sub-module equivalent capacitor voltage direct current component, a series sub-module equivalent capacitor voltage fundamental frequency component, and a series sub-module equivalent capacitor voltage double frequency component; the current state variables of the reference MMC converter station comprise an MMC alternating-current side current fundamental frequency component, an MMC internal circulation direct-current component and an MMC internal circulation frequency doubling component;
determining steady state operating characteristics of the reference MMC converter station according to the voltage state variables and the current state variables of the reference MMC converter station, including:
Solving the extremum of the equivalent capacitance voltage of the series sub-module according to the direct current component of the equivalent capacitance voltage of the series sub-module, the fundamental frequency component of the equivalent capacitance voltage of the series sub-module and the frequency doubling component of the equivalent capacitance voltage of the series sub-module; solving an MMC alternating-current side current extremum according to the MMC alternating-current side current fundamental frequency component; and solving a bridge arm current extremum according to the MMC alternating current side current fundamental frequency component, the MMC internal circulation direct current component and the MMC internal circulation double frequency component.
4. The method of claim 1, wherein the step of determining whether the convergence parameter satisfies a convergence condition comprises:
if the convergence parameter is smaller than the threshold value, the convergence condition is met;
and if the convergence parameter is greater than or equal to a threshold value, the convergence condition is not satisfied.
5. A device for determining steady-state operating characteristics of an MMC converter station, characterized in that it is applied to a flexible dc power transmission network with controlled dc sag; the flexible direct current power transmission network comprises a reference MMC converter station and a plurality of target MMC converter stations; the device comprises:
the mathematical model solving module is used for independently solving the mathematical model of each target MMC converter station according to the direct-current voltage of each target MMC converter station so as to acquire the direct-current, each voltage state variable and each current state variable of each target MMC converter station; the method is further used for solving a mathematical model of the reference MMC converter station according to the direct-current voltage or direct-current of the reference MMC converter station under the condition that the convergence parameter meets the convergence condition so as to acquire each voltage state variable and each current state variable of the reference MMC converter station;
The direct current acquisition module is used for calculating the direct current of the reference MMC converter station according to the direct current of each target MMC converter station;
the convergence judging module is used for judging whether convergence parameters meet convergence conditions, wherein the convergence parameters are the difference between the direct current of the reference MMC converter station and the direct current of the reference MMC converter station determined by the previous iterative computation; if not, updating the direct current voltage of the reference MMC converter station, updating the direct current voltage of each target MMC converter station according to the updated direct current voltage of the reference MMC converter station and the node impedance matrix of the flexible direct current transmission network, returning to the step of independently solving the mathematical model of each target MMC converter station according to the direct current voltage of each target MMC converter station, and performing iterative calculation until the convergence parameters meet convergence conditions;
the steady-state operation characteristic calculation module is used for determining the steady-state operation characteristic of the reference MMC converter station according to each voltage state variable and each current state variable of the reference MMC converter station; the method is also used for determining the steady-state operation characteristic of the target MMC converter station according to each voltage state variable and each current state variable of the target MMC converter station under the condition that the convergence parameter meets the convergence condition;
The convergence judging module comprises a direct-current voltage updating unit, wherein the direct-current voltage updating unit is used for acquiring a power reference value corresponding to the reference MMC converter station; the power reference value is a power reference value for direct current droop control;
the direct current voltage updating unit comprises an expression selecting unit, wherein the expression selecting unit is used for updating the direct current voltage of the reference MMC converter station according to the following expression if the power reference value is a direct current power reference value:
wherein ,for updated reference MMC converter station DC voltage, P dcref Is a direct current power reference value, < >>For the direct voltage of the reference MMC converter station of this iterative calculation, < >>For the reference MMC converter station direct current calculated in this iteration, k is the number of iterations, r is the correction coefficient (0<r≤1)；
If the power reference value is an ac side active power reference value, updating the dc voltage of the reference MMC converter station according to the following expression:
wherein ,for the updated reference MMC converter station DC voltage, pacref is the AC side active power reference value, P s Is equivalent resistance loss power of an alternating current system, P a Power is lost for bridge arm resistance, < >>For the direct voltage of the reference MMC converter station of this iterative calculation, < > >For the direct current of the reference MMC converter station calculated in the iteration, k is the iteration number, r is the correction coefficient, and 0<r≤1。
6. The apparatus of claim 5, further comprising a preset dc voltage acquisition module;
the preset direct-current voltage acquisition module is used for acquiring the direct-current voltage of a preset reference MMC converter station; the dc voltage of each target MMC converter station is equal to the dc voltage of the reference MMC converter station.
7. The apparatus of claim 5, wherein the voltage state variables of the reference MMC converter station include voltage state variables of the reference MMC converter station including a series sub-module equivalent capacitor voltage direct current component, a series sub-module equivalent capacitor voltage fundamental frequency component, and a series sub-module equivalent capacitor voltage double frequency component; the current state variables of the reference MMC converter station comprise an MMC alternating current side current fundamental frequency component, an MMC internal circulation direct current component and an MMC internal circulation double frequency component;
the steady-state operation characteristic calculation module includes a reference station characteristic determination unit; the reference station characteristic determining unit is used for solving the extreme value of the equivalent capacitance voltage of the serial submodule according to the direct current component of the equivalent capacitance voltage of the serial submodule, the fundamental frequency component of the equivalent capacitance voltage of the serial submodule and the frequency doubling component of the equivalent capacitance voltage of the serial submodule; solving an MMC alternating-current side current extremum according to the MMC alternating-current side current fundamental frequency component; and solving a bridge arm current extremum according to the MMC alternating-current side current fundamental frequency component, the MMC internal circulation direct-current component and the MMC internal circulation double-frequency component.
8. A computer device comprising a memory and a processor, the memory storing a computer program, characterized in that the processor implements the steps of the method of any of claims 1 to 4 when the computer program is executed.
9. A computer readable storage medium, on which a computer program is stored, characterized in that the computer program, when being executed by a processor, implements the steps of the method of any of claims 1 to 4.
10. A computer program product comprising a computer program, characterized in that the computer program, when executed by a processor, implements the steps of the method of any of claims 1 to 4.
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CN110784116A (en) * 2019-10-29 2020-02-11 国网新疆电力有限公司 Method and system for determining converter station working domain considering MMC internal dynamic constraint
CN112103998A (en) * 2020-09-09 2020-12-18 中国南方电网有限责任公司超高压输电公司检修试验中心 LCC-MMC hybrid direct current power transmission system steady state operation characteristic calculation analysis method and device

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CN103427425A (en) * 2013-08-22 2013-12-04 华北电力大学 Coordinated control device and method for MMC (modular multilevel converter) type unified power quality conditioner
CN110784116A (en) * 2019-10-29 2020-02-11 国网新疆电力有限公司 Method and system for determining converter station working domain considering MMC internal dynamic constraint
CN112103998A (en) * 2020-09-09 2020-12-18 中国南方电网有限责任公司超高压输电公司检修试验中心 LCC-MMC hybrid direct current power transmission system steady state operation characteristic calculation analysis method and device

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