CN112115660A - Bridge arm equivalent circuit, high-voltage direct-current transmission system and simulation method thereof - Google Patents
Bridge arm equivalent circuit, high-voltage direct-current transmission system and simulation method thereof Download PDFInfo
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Abstract
The invention provides a bridge arm equivalent circuit, a high-voltage direct-current transmission system and a simulation method thereof, wherein the bridge arm equivalent circuit comprises two half-bridge structures and a controllable voltage source; one end of each of the two half-bridge structures is connected with a common point A, the other end of each of the two half-bridge structures is connected with a common point B, the positive electrode of the controllable voltage source is connected with the common point A, and the negative electrode of the controllable voltage source is connected with the common point B; the two half-bridge structures comprise turn-off device modules, the equivalence of submodules with different topological structures is realized by controlling the turn-on or turn-off of the turn-off device modules, the half-bridge structures have universality, compatible MMC comprises a pre-charging mode, a normal mode and a fault mode, the simulation of a high-voltage direct-current power transmission system based on the MMC in different operation modes is realized, the complete decoupling of the submodules and bridge arm electricity is realized through a bridge arm equivalent circuit model, the scale of an admittance matrix to be solved in the simulation process is remarkably reduced, and the simulation speed is high.
Description
Technical Field
The invention relates to the technical field of power system simulation, in particular to a bridge arm equivalent circuit, a high-voltage direct-current power transmission system and a simulation method thereof.
Background
Modular Multilevel Converters (MMC) have become the most attractive topology of multilevel converters in voltage source converter based high voltage direct current (VSC-HVDC) transmission systems. MMC's characteristics include: 1) modularization and easy expansibility, and any voltage level can be achieved by stacking a larger number of sub-modules (SM) without increasing the complexity of topology and control strategy; 2) the reliability can be improved by utilizing the inherent fault-tolerant capability; 3) high efficiency, especially suitable for high power systems; 4) the output waveform with high quality improves the quality of output electric energy, thereby realizing the grid connection without a filter and a step-up transformer and reducing the cost. With the increase of the number of MMC-HVDC systems embedded in an alternating current power grid, the performance of the current power system, including stability, reliability, capacity and efficiency, can be remarkably improved. However, developing efficient and accurate models suitable for large-scale power system analysis, modeling and simulation is a key technical problem that limits the application of MMCs in power systems. Due to the diversity of MMC sub-module structures and the fact that a large number of semiconductor devices are contained in MMC-HVDC, time-consuming and low-efficiency accurate switch models are not suitable for analysis, modeling and simulation of large-scale MMC-HVDC systems.
At present, a high-voltage direct-current power transmission system based on an MMC is generally simulated through a Thevenin Equivalent Model (TEM), the Thevenin equivalent model is a model which is accurate and has high simulation speed, and information of the on-off state and the capacitance voltage of a submodule at each simulation moment can be acquired, so that the behavior characteristics of a current converter under the conditions of faults and locking can be simulated accurately, hardware-in-loop test can be performed on a valve base control system, but the expandability of the Thevenin equivalent model is poor, when the topology of the submodules is changed, the Thevenin equivalent model needs to be programmed and modeled again aiming at each submodule structure, and the universality is poor.
Disclosure of Invention
In order to overcome the defect of poor universality in the prior art, the invention provides a bridge arm equivalent circuit, which comprises two half-bridge structures and a controllable voltage source;
one end of each of the two half-bridge structures is connected with a common point A, the other end of each of the two half-bridge structures is connected with a common point B, the positive electrode of the controllable voltage source is connected with the common point A, and the negative electrode of the controllable voltage source is connected with the common point B;
the two half-bridge structures comprise turn-off device modules, and the equivalence of the sub-modules with different topological structures is realized by controlling the turn-on or turn-off of the turn-off device modules.
One of the turn-off modules of the half-bridge configuration comprises a first turn-off module and a second turn-off module;
wherein the turn-off modules of the other half-bridge configuration comprise a third turn-off module and a fourth turn-off module;
the first turn-off module comprises a turn-off capable device S1 and a diode D1 in anti-parallel with the turn-off capable device S1;
the second turn-off module comprises a turn-off capable device S2 and a diode D2 in anti-parallel with the turn-off capable device S2;
the third turn-off module comprises a turn-off capable device S3 and a diode D3 in anti-parallel with the turn-off capable device S3;
the fourth turn-off module includes a turn-off device S4 and a diode D4 connected in anti-parallel with the turn-off device S4.
The midpoint between the turn-off device S1 and the turn-off device S2 is the positive terminal of the bridge arm equivalent circuit, and the midpoint between the turn-off device S3 and the turn-off device S4 is the negative terminal of the bridge arm equivalent circuit.
The collectors of the turn-off capable device S1 and the turn-off capable device S3 are connected to a common point a, the emitters of the turn-off capable device S2 and the turn-off capable device S4 are connected to a common point B, the emitter of the turn-off capable device S1 is connected to the collector of the turn-off capable device S2, and the emitter of the turn-off capable device S3 is connected to the collector of the turn-off capable device S4.
In another aspect, the present invention provides a high voltage dc transmission system, comprising two MMCs and a dc bus;
the alternating current sides of the two MMCs are respectively connected with corresponding alternating current systems, and the direct current sides of the two MMCs are connected through a direct current bus;
the MMC is an H-bridge structure, and the bridge arm of the H-bridge structure adopts the bridge arm equivalent circuit of any one of claims 1 to 4.
The states of the turn-off devices in the bridge arm equivalent circuit are determined based on the operation mode of the MMC neutron module;
and the voltage of the controllable voltage source in the bridge arm equivalent circuit is obtained by accumulating the equivalent capacitance values of the sub-modules.
The sub-modules comprise a unipolar sub-module and a bipolar sub-module;
the unipolar submodule comprises a half-bridge submodule, a unipolar full-bridge submodule, a clamping bimodule module and a three-level cross connection submodule;
the bipolar sub-modules comprise a bipolar full-bridge sub-module and a five-level cross-connection sub-module.
The operation modes include a pre-charge mode, a normal mode and a fault mode, and the pre-charge mode includes an uncontrollable pre-charge mode and a controllable pre-charge mode.
When the MMC is in an uncontrollable pre-charging mode, a turn-off device S1, a turn-off device S2 and a turn-off device S3 in a corresponding topological structure of the half-bridge sub-module are turned off, the turn-off device S4 is turned on, and a turn-off device S1-a turn-off device S4 in a corresponding topological structure of the unipolar full-bridge sub-module, the clamping dual sub-module, the three-level cross-connection sub-module, the bipolar full-bridge sub-module and the five-level cross-connection sub-module is turned off;
when the MMC is in a controllable pre-charging mode, a turn-off device S1, a turn-off device S2 and a turn-off device S3 in the corresponding topological structures of the half-bridge submodule, the unipolar full-bridge submodule, the clamping double-submodule, the three-level cross-connection submodule, the bipolar full-bridge submodule and the five-level cross-connection submodule are all turned off, and the turn-off device S4 is turned on;
when the MMC is in a normal mode, a turn-off device S1 and a turn-off device S4 in a corresponding topological structure of the half-bridge submodule, the unipolar full-bridge submodule, the clamping submodule and the three-level cross-connection submodule are all turned on, the turn-off device S2 and the turn-off device S3 are all turned off, a turn-off device S1 and a turn-off device S4 in a corresponding topological structure of the bipolar full-bridge submodule and the five-level cross-connection submodule are all turned on, the turn-off device S2 and the turn-off device S3 are both turned off, or the turn-off device S1 and the turn-off device S4 are both turned off, and the turn-off device S2 and the turn-off device S3 are both turned on;
when the MMC is in a fault mode, all turn-off devices S1-S3 in the topology structure corresponding to the half-bridge submodule are turned off, all turn-off devices S4 are turned on, and all turn-off devices S1-S4 in the topology structure corresponding to the unipolar full-bridge submodule, the clamping double-submodule, the three-level cross-connection submodule, the bipolar full-bridge submodule and the five-level cross-connection submodule are turned off.
In another aspect, the present invention further provides a simulation method for a high voltage dc transmission system, including:
acquiring operation parameters of a high-voltage direct-current transmission system;
simulating the high-voltage direct-current power transmission system based on the operation parameters;
the high-voltage direct-current transmission system comprises two MMCs and a direct-current bus;
the alternating current sides of the two MMCs are respectively connected with corresponding alternating current systems, and the direct current sides of the two MMCs are connected through a direct current bus;
the MMC is an H-bridge structure, and bridge arms of the H-bridge structure adopt bridge arm equivalent circuits.
The simulating of the pre-established high voltage direct current transmission system based on the operating parameters comprises:
calculating a capacitance voltage value of the sub-module based on the sub-module equivalent capacitance value;
and simulating the high-voltage direct-current power transmission system based on the capacitance voltage value and the operation parameters of the sub-modules.
The calculating of the capacitance voltage value of the sub-module based on the sub-module equivalent capacitance value includes:
solving a dynamic differential equation based on the sub-module equivalent capacitance values
Obtaining a capacitance voltage value of the sub-module, wherein C is an equivalent capacitance value of the sub-module, icFor the current flowing through the sub-module capacitance, vcThe value of the capacitor voltage of the submodule.
The determination of the current flowing through the sub-module capacitor comprises:
when the MMC is in a normal mode or a controllable pre-charging mode, the current i of the sub-module capacitorc＝SSMiarmWherein i isarmFor bridge arm current, SSMFor the switching state of the submodule, when the submodule is switched in, SSMTaking 1, when the submodule is cut off, SSMTaking 0;
when the MMC is in a fault mode or an uncontrollable pre-charging mode, the current of the capacitor in the half-bridge sub-module
The current i of the capacitor in the unipolar full-bridge submodule, the three-level cross-connection submodule, the bipolar full-bridge submodule and the five-level cross-connection submodulec＝|iarmCurrent of capacitor in clamping dual sub-module
The operating parameters comprise rated power, rated voltage of an alternating current side, rated voltage of a direct current side, rated current and system frequency of the high-voltage direct current transmission system.
The technical scheme provided by the invention has the following beneficial effects:
the bridge arm equivalent circuit provided by the invention comprises two half-bridge structures and a controllable voltage source; one end of each of the two half-bridge structures is connected with a common point A, the other end of each of the two half-bridge structures is connected with a common point B, the positive electrode of the controllable voltage source is connected with the common point A, and the negative electrode of the controllable voltage source is connected with the common point B; the two half-bridge structures comprise turn-off device modules, the equivalence of sub-modules with different topological structures is realized by controlling the turn-on or turn-off of the turn-off device modules, and the half-bridge structures have universality;
according to the MMC-based high-voltage direct-current power transmission system simulation method, the operation parameters of the high-voltage direct-current power transmission system are obtained, the high-voltage direct-current power transmission system is simulated based on the operation parameters, the high-voltage direct-current power transmission system is constructed based on the MMC, the MMC is constructed based on a bridge arm equivalent circuit, the bridge arm equivalent circuit is constructed to be compatible with various sub-module topological structures, and therefore the simulation method is universal;
according to the technical scheme provided by the invention, when the topological structure of the sub-module is changed, the bridge arm equivalent circuit does not need to be reconstructed;
the technical scheme provided by the method is compatible with the MMC and comprises a pre-charging mode, a normal mode and a fault mode, wherein the pre-charging mode comprises a plurality of operation modes of an uncontrollable pre-charging mode and a controllable pre-charging mode, and simulation of the MMC-based high-voltage direct-current power transmission system under different operation modes is realized;
the method adopts the bridge arm equivalent circuit model to construct the high-voltage direct-current power transmission system, realizes complete decoupling of the sub-modules and the bridge arm electricity through the bridge arm equivalent circuit model, obviously reduces the scale of the admittance matrix to be solved in the simulation process, and has high simulation speed.
Drawings
FIG. 1 is a diagram of an equivalent circuit of a bridge arm according to an embodiment of the present invention;
fig. 2 is a block diagram of an MMC-based hvdc transmission system in an embodiment of the present invention;
FIG. 3 is a diagram of an MMC topology in an embodiment of the present invention;
fig. 4 is a flowchart of a simulation method of an MMC-based hvdc transmission system in an embodiment of the present invention.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings.
Example 1
Embodiment 1 of the present invention provides a bridge arm equivalent circuit, as shown in fig. 1, where in fig. 1, iarmFor bridge arm current, VarmThe bridge arm equivalent circuit provided by the embodiment 1 of the invention comprises two half-bridge structures and a controllable voltage source;
one end of each of the two half-bridge structures is connected with a common point A, the other end of each of the two half-bridge structures is connected with a common point B, the positive electrode of the controllable voltage source is connected with the common point A, and the negative electrode of the controllable voltage source is connected with the common point B;
the two half-bridge structures comprise turn-off device modules, and the equivalence of the sub-modules with different topological structures is realized by controlling the turn-on or turn-off of the turn-off device modules.
One of the turn-off modules of the half-bridge configuration comprises a first turn-off module and a second turn-off module;
wherein the turn-off modules of the other half-bridge configuration comprise a third turn-off module and a fourth turn-off module;
the first turn-off module includes a turn-off capable device S1 and a diode D1 connected in anti-parallel with the turn-off capable device S1;
the second turn-off module includes a turn-off capable device S2 and a diode D2 connected in anti-parallel with the turn-off capable device S2;
the third turn-off module includes a turn-off capable device S3 and a diode D3 connected in anti-parallel with the turn-off capable device S3;
the fourth turn-off module includes a turn-off capable device S4 and a diode D4 connected in anti-parallel with the turn-off capable device S4.
The midpoint between the turn-off device S1 and the turn-off device S2 is the positive terminal of the bridge arm equivalent circuit, and the midpoint between the turn-off device S3 and the turn-off device S4 is the negative terminal of the bridge arm equivalent circuit.
The collectors of the turn-off capable device S1 and the turn-off capable device S3 are connected to a common point a, the emitters of the turn-off capable device S2 and the turn-off capable device S4 are connected to a common point B, the emitter of the turn-off capable device S1 is connected to the collector of the turn-off capable device S2, and the emitter of the turn-off capable device S3 is connected to the collector of the turn-off capable device S4.
Example 2
Embodiment 2 of the present invention provides a high-voltage direct-current power transmission system, as shown in fig. 2, including two MMCs (i.e., MMC1 and MMC2 in fig. 2) and a direct-current bus;
the respective interchange side of two MMCs connects corresponding AC system respectively, and respective direct current side passes through the direct current bus connection, and the AC system that MMC1 corresponds is connected to the interchange side of MMC1 promptly, and the direct current side of MMC1 passes through the direct current bus connection MMC 2's direct current side, and the AC system that MMC2 corresponds is connected to the interchange side of MMC 2.
MMC is H-bridge structure, as shown in FIG. 3, SM1-SMNIs a submodule, RarmIs a bridge arm resistance, LarmIs bridge arm inductance, VdcFor the direct-current side voltage of the MMC, the MMC comprises a plurality of bridge arms, each bridge arm comprises a plurality of serially connected sub-modules, and the bridge arms adopt the bridge arm equivalent circuit provided by embodiment 1 of the invention.
The states of the turn-off devices in the bridge arm equivalent circuit are determined based on the operation mode of the MMC neutron module;
the voltage of the controllable voltage source in the bridge arm equivalent circuit is obtained by accumulating equivalent capacitance values of the sub-modules.
The submodules comprise unipolar submodules and bipolar submodules;
the unipolar submodule comprises a Half-bridge submodule (Half-bridge SM), a unipolar full-bridge submodule (UFB), a clamping submodule (Clamp-double SM) and a three-level cross-connection submodule (namely 3 LCC);
the bipolar sub-modules include a bipolar Full-bridge sub-module (Full-bridge SM) and a Five-level cross-connected sub-module (Five-level cross-connected SM).
The operation modes include a pre-charge mode, a normal mode and a fault mode, and the pre-charge mode includes an uncontrollable pre-charge mode and a controllable pre-charge mode.
When the MMC is in an uncontrollable pre-charging mode, a turn-off device S1, a turn-off device S2 and a turn-off device S3 in a corresponding topological structure of the half-bridge sub-module are turned off, the turn-off device S4 is turned on, and a turn-off device S1-a turn-off device S4 in a corresponding topological structure of the unipolar full-bridge sub-module, the clamping dual sub-module, the three-level cross-connection sub-module, the bipolar full-bridge sub-module and the five-level cross-connection sub-module is turned off;
when the MMC is in a controllable pre-charging mode, a turn-off device S1, a turn-off device S2 and a turn-off device S3 in the corresponding topological structures of the half-bridge submodule, the unipolar full-bridge submodule, the clamping double-submodule, the three-level cross-connection submodule, the bipolar full-bridge submodule and the five-level cross-connection submodule are all turned off, and the turn-off device S4 is turned on;
when the MMC is in a normal mode, a turn-off device S1 and a turn-off device S4 in a corresponding topological structure of the half-bridge submodule, the unipolar full-bridge submodule, the clamping submodule and the three-level cross-connection submodule are all turned on, the turn-off device S2 and the turn-off device S3 are all turned off, a turn-off device S1 and a turn-off device S4 in a corresponding topological structure of the bipolar full-bridge submodule and the five-level cross-connection submodule are all turned on, the turn-off device S2 and the turn-off device S3 are both turned off, or the turn-off device S1 and the turn-off device S4 are both turned off, and the turn-off device S2 and the turn-off device S3 are both turned on;
when the MMC is in a fault mode, all turn-off devices S1-S3 in the topology structure corresponding to the half-bridge submodule are turned off, all turn-off devices S4 are turned on, and all turn-off devices S1-S4 in the topology structure corresponding to the unipolar full-bridge submodule, the clamping double-submodule, the three-level cross-connection submodule, the bipolar full-bridge submodule and the five-level cross-connection submodule are turned off.
The specific state of the turn-off device in the topology corresponding to the MMC operating mode is shown in table 1:
TABLE 1
Example 3
Embodiment 3 of the present invention provides a simulation method for a high-voltage direct-current power transmission system, where a specific flowchart is shown in fig. 4, and the specific process is as follows:
s101: acquiring operation parameters of a high-voltage direct-current transmission system;
s102: simulating the high-voltage direct-current transmission system provided by the embodiment 2 of the invention based on the operation parameters;
the high-voltage direct-current transmission system comprises two MMCs and a direct-current bus;
the alternating current sides of the two MMCs are respectively connected with corresponding alternating current systems, and the direct current sides of the two MMCs are connected through a direct current bus;
the MMC is an H-bridge structure, and a bridge arm of the H-bridge structure employs the bridge arm Equivalent Circuit (ECM) provided in embodiment 1 of the present invention.
Simulating a pre-established high voltage direct current transmission system based on the operating parameters, comprising:
calculating a capacitance voltage value of the sub-module based on the sub-module equivalent capacitance value;
and simulating the high-voltage direct-current power transmission system based on the capacitance voltage value and the operation parameters of the sub-modules.
The calculating of the capacitance voltage value of the sub-module based on the sub-module equivalent capacitance value includes:
solving a dynamic differential equation based on the sub-module equivalent capacitance values
Obtaining a capacitance voltage value of the sub-module, wherein C is an equivalent capacitance value of the sub-module, icFor passing through sub-module capacitanceCurrent, vcThe value of the capacitor voltage of the submodule.
Determination of the current flowing through the sub-module capacitance, comprising:
when the MMC is in a normal mode or a controllable pre-charging mode, the current i of the sub-module capacitorc＝SSMiarmWherein i isarmFor bridge arm current, SSMFor the switching state of the submodule, when the submodule is switched in, SSMTaking 1, when the submodule is cut off, SSMTaking 0;
when the MMC is in a fault mode or an uncontrollable pre-charging mode, the current of the capacitor in the half-bridge sub-module
Current i of capacitor in polar full-bridge submodule, three-level cross-connection submodule, bipolar full-bridge submodule and five-level cross-connection submodulec＝|iarmCurrent of capacitor in clamping dual sub-module
That is, for the clamped bimodule, when the bridge arm current is positive, the two half bridges SM are connected in series, and the current of the capacitor is | iarmL, |; when the arm current is negative, two HB SM are connected in parallel, and the two capacitors share the bridge arm current, so that the current of the capacitor is 0.5| iarm|。
The operating parameters include rated power, rated voltage on the ac side, rated voltage on the dc side, rated current and system frequency of the hvdc transmission system.
The computer used for simulating the high-voltage direct-current transmission system in embodiment 3 of the present invention is configured with a Microsoft Windows 10 operating system, a 2.60GHz Intel Core i7-6700HQ CPU, and an 8GB RAM.
The parameters of the high-voltage direct-current transmission system are shown in table 2:
TABLE 2
In order to verify the accuracy of the equivalent circuit of the bridge arm, an HVDC system based on HB-MMC, an HVDC system based on FB-MMC and an HVDC system based on mixed MMC are respectively built in embodiment 3 of the invention, and the obtained simulation result of the equivalent circuit of the bridge arm is compared with the simulation result of the accurate switch model. By comparing the bridge arm current, the capacitance voltage of the MMC and the direct current, the bridge arm equivalent circuit provided by the embodiment 3 of the invention has a result consistent with an accurate switch model, the simulation result can accurately reflect the dynamic characteristics inside and outside the MMC, and the topological structure and the running state of various MMC sub-module circuits can be considered. When the bridge arm equivalent circuit and the accurate switch model both adopt 10us simulation step lengths, errors of all simulation results of the bridge arm equivalent circuit relative to the accurate switch model are not more than five per thousand.
In addition, for the MMC with a bipolar structure, in case of a direct short circuit fault, it can work in a STATCOM mode to provide reactive power for the grid. For such an operation mode, the bridge arm equivalent circuit provided in embodiment 3 of the present invention may still be subjected to simulation, and the simulation result is consistent with the accurate switch model.
In order to verify the simulation efficiency of the proposed bridge arm equivalent circuit, the simulation time of comparing the MMC-HVDC switch model based on different sub-module topologies and the bridge arm equivalent circuit in embodiment 3 of the invention is shown in table 3.
TABLE 3
From the test result, the bridge arm equivalent circuit can effectively shorten the simulation time and improve the simulation speed and efficiency.
In addition, the simulation time of the detailed bridge arm equivalent circuit and the simplified bridge arm equivalent circuit of the MMC-HVDC system with different levels is shown in table 4, the simulation time of the detailed bridge arm equivalent circuit is increased along with the increase of the level number, and the simplified bridge arm equivalent circuit still keeps short simulation time. From the results, the proposed bridge arm equivalent circuit can efficiently simulate various MMC converters with complex structures.
TABLE 4
For convenience of description, each part of the above-described apparatus is separately described as being functionally divided into various modules or units. Of course, the functionality of the various modules or units may be implemented in the same one or more pieces of software or hardware when implementing the present application.
As will be appreciated by one skilled in the art, embodiments of the present application may be provided as a method, system, or computer program product. Accordingly, the present application may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present application may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein.
The present application is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the application. It will be understood that each flow and/or block of the flow diagrams and/or block diagrams, and combinations of flows and/or blocks in the flow diagrams and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
Finally, it should be noted that: the above embodiments are only intended to illustrate the technical solution of the present invention and not to limit the same, and a person of ordinary skill in the art can make modifications or equivalent substitutions to the specific embodiments of the present invention with reference to the above embodiments, and any modifications or equivalent substitutions which do not depart from the spirit and scope of the present invention are within the protection scope of the present invention as claimed in the appended claims.
Claims (14)
1. A bridge arm equivalent circuit is characterized by comprising two half-bridge structures and a controllable voltage source;
one end of each of the two half-bridge structures is connected with a common point A, the other end of each of the two half-bridge structures is connected with a common point B, the positive electrode of the controllable voltage source is connected with the common point A, and the negative electrode of the controllable voltage source is connected with the common point B;
the two half-bridge structures comprise turn-off device modules, and the equivalence of the sub-modules with different topological structures is realized by controlling the turn-on or turn-off of the turn-off device modules.
2. The bridge arm equivalent circuit according to claim 1, characterized in that one of the shut-off modules of the half-bridge configuration comprises a first shut-off module and a second shut-off module;
wherein the turn-off modules of the other half-bridge configuration comprise a third turn-off module and a fourth turn-off module;
the first turn-off module comprises a turn-off capable device S1 and a diode D1 in anti-parallel with the turn-off capable device S1;
the second turn-off module comprises a turn-off capable device S2 and a diode D2 in anti-parallel with the turn-off capable device S2;
the third turn-off module comprises a turn-off capable device S3 and a diode D3 in anti-parallel with the turn-off capable device S3;
the fourth turn-off module includes a turn-off device S4 and a diode D4 connected in anti-parallel with the turn-off device S4.
3. The bridge arm equivalent circuit of claim 2, wherein a midpoint between the turn-off device S1 and the turn-off device S2 is a positive terminal of the bridge arm equivalent circuit, and a midpoint between the turn-off device S3 and the turn-off device S4 is a negative terminal of the bridge arm equivalent circuit.
4. The bridge arm equivalent circuit according to claim 2, wherein the collectors of the turn-off devices S1 and S3 are connected to a common point a, the emitters of the turn-off devices S2 and S4 are connected to a common point B, the emitter of the turn-off device S1 is connected to the collector of the turn-off device S2, and the emitter of the turn-off device S3 is connected to the collector of the turn-off device S4.
5. A high-voltage direct-current transmission system is characterized by comprising two MMCs and a direct-current bus;
the alternating current sides of the two MMCs are respectively connected with corresponding alternating current systems, and the direct current sides of the two MMCs are connected through a direct current bus;
the MMC is an H-bridge structure, and the bridge arm of the H-bridge structure adopts the bridge arm equivalent circuit of any one of claims 1 to 4.
6. The HVDC transmission system of claim 5, wherein the states of the turn-off devices in the bridge arm equivalent circuit are each determined based on an operating mode of a sub-module in the MMC;
and the voltage of the controllable voltage source in the bridge arm equivalent circuit is obtained by accumulating the equivalent capacitance values of the sub-modules.
7. The HVDC transmission system of claim 6, wherein the sub-modules comprise a unipolar sub-module and a bipolar sub-module;
the unipolar submodule comprises a half-bridge submodule, a unipolar full-bridge submodule, a clamping bimodule module and a three-level cross connection submodule;
the bipolar sub-modules comprise a bipolar full-bridge sub-module and a five-level cross-connection sub-module.
8. The HVDC transmission system of claim 7, wherein the operating modes include a pre-charge mode, a normal mode and a fault mode, the pre-charge modes including an uncontrollable pre-charge mode and a controllable pre-charge mode.
9. The HVDC transmission system of claim 8,
when the MMC is in an uncontrollable pre-charging mode, a turn-off device S1, a turn-off device S2 and a turn-off device S3 in a corresponding topological structure of the half-bridge sub-module are turned off, the turn-off device S4 is turned on, and a turn-off device S1-a turn-off device S4 in a corresponding topological structure of the unipolar full-bridge sub-module, the clamping dual sub-module, the three-level cross-connection sub-module, the bipolar full-bridge sub-module and the five-level cross-connection sub-module is turned off;
when the MMC is in a controllable pre-charging mode, a turn-off device S1, a turn-off device S2 and a turn-off device S3 in the corresponding topological structures of the half-bridge submodule, the unipolar full-bridge submodule, the clamping double-submodule, the three-level cross-connection submodule, the bipolar full-bridge submodule and the five-level cross-connection submodule are all turned off, and the turn-off device S4 is turned on;
when the MMC is in a normal mode, a turn-off device S1 and a turn-off device S4 in a corresponding topological structure of the half-bridge submodule, the unipolar full-bridge submodule, the clamping submodule and the three-level cross-connection submodule are all turned on, the turn-off device S2 and the turn-off device S3 are all turned off, a turn-off device S1 and a turn-off device S4 in a corresponding topological structure of the bipolar full-bridge submodule and the five-level cross-connection submodule are all turned on, the turn-off device S2 and the turn-off device S3 are both turned off, or the turn-off device S1 and the turn-off device S4 are both turned off, and the turn-off device S2 and the turn-off device S3 are both turned on;
when the MMC is in a fault mode, all turn-off devices S1-S3 in the topology structure corresponding to the half-bridge submodule are turned off, all turn-off devices S4 are turned on, and all turn-off devices S1-S4 in the topology structure corresponding to the unipolar full-bridge submodule, the clamping double-submodule, the three-level cross-connection submodule, the bipolar full-bridge submodule and the five-level cross-connection submodule are turned off.
10. A simulation method for a high voltage direct current transmission system is characterized by comprising the following steps:
acquiring operation parameters of a high-voltage direct-current transmission system;
simulating the high-voltage direct-current power transmission system based on the operation parameters;
the high-voltage direct-current transmission system comprises two MMCs and a direct-current bus;
the alternating current sides of the two MMCs are respectively connected with corresponding alternating current systems, and the direct current sides of the two MMCs are connected through a direct current bus;
the MMC is an H-bridge structure, and the bridge arm of the H-bridge structure adopts the bridge arm equivalent circuit of any one of claims 1 to 4.
11. The method of simulating an hvdc transmission system according to claim 10, wherein said simulating a pre-constructed hvdc transmission system based on said operating parameters comprises:
calculating a capacitance voltage value of the sub-module based on the sub-module equivalent capacitance value;
and simulating the high-voltage direct-current power transmission system based on the capacitance voltage value and the operation parameters of the sub-modules.
12. The method of simulating an hvdc transmission system according to claim 11, wherein said calculating a capacitance voltage value for a sub-module based on a sub-module equivalent capacitance value comprises:
solving a dynamic differential equation based on the sub-module equivalent capacitance values
Obtaining a capacitance voltage value of the sub-module, wherein C is an equivalent capacitance value of the sub-module, icFor the current flowing through the sub-module capacitance, vcThe value of the capacitor voltage of the submodule.
13. The method of simulating an hvdc transmission system according to claim 12, wherein said determining of the current flowing through the sub-module capacitor comprises:
when the MMC is in a normal mode or a controllable pre-charging mode, the current i of the sub-module capacitorc＝SSMiarmWherein i isarmFor bridge arm current, SSMFor the switching state of the submodule, when the submodule is switched in, SSMTaking 1, when the submodule is cut off, SSMTaking 0;
when the MMC is in a fault mode or an uncontrollable pre-charging mode, the current of the capacitor in the half-bridge sub-module
The current i of the capacitor in the unipolar full-bridge submodule, the three-level cross-connection submodule, the bipolar full-bridge submodule and the five-level cross-connection submodulec＝|iarmCurrent of capacitor in clamping dual sub-module
14. The method according to claim 10, characterized in that the operating parameters comprise rated power, ac side rated voltage, dc side rated voltage, rated current and system frequency of the hvdc transmission system.
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