CN117638921A - Low-voltage fault ride-through method and system for grid-structured flexible direct current transmission - Google Patents
Low-voltage fault ride-through method and system for grid-structured flexible direct current transmission Download PDFInfo
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Abstract
The invention discloses a low-voltage fault ride-through method and system for grid-structured flexible direct current transmission, and belongs to the technical field of alternating current fault ride-through. The method of the invention comprises the following steps: when the network formation of the flexible direct current converter station is used as a receiving end for control, determining the topological structure of the network formation type flexible direct current transmission system; determining a target value of a control target according to the topological structure and the system requirement of the network-structured flexible direct current transmission system; and starting a fault judging module according to the direct current voltage fluctuation of the grid-structured flexible direct current power transmission system, judging whether the grid-structured flexible direct current power transmission system starts fault ride-through measures or not based on the fault judging module, and starting the fault ride-through measures if the direct current voltage is lower than a direct current voltage warning value. The invention can ensure the stable operation of the grid-structured flexible direct current transmission system after faults.
Description
Technical Field
The invention relates to the technical field of alternating current fault ride-through, in particular to a low-voltage fault ride-through method and system for grid-structured flexible direct current transmission.
Background
The flexible direct current transmission is voltage source converter type high-voltage direct current transmission based on a full-control type power electronic device, and compared with the conventional direct current, the flexible direct current transmission can flexibly regulate and control the active power and the reactive power, can be flexibly connected into an active or passive system, and provides a new solution for large-scale new energy source transmission and regional power grid interconnection. The traditional flexible direct networking control adopts vector control (network following control) based on a phase-locked loop, coordinate transformation is carried out by collecting the phase of grid-connected voltage, active and reactive control is realized by controlling output current, the current source characteristic is represented, and the control framework can be classified as the network following control. However, as new energy based on power electronic devices in a power grid is continuously connected, the proportion of synchronous machines in the system is gradually reduced, the short-circuit ratio is continuously reduced, the strength of the power grid is reduced, the frequency control is difficult, the voltage supporting capability is reduced, the safety and stability problems of the system are further outstanding, and when the system has extremely weak working conditions, the phase-locked loop is difficult to accurately follow the voltage of the power grid, and the problem of disturbance and instability is easy to occur.
In the prior art, simulating a swinging equation of a synchronous generator is a basic mode for realizing network construction control. However, the extraction of the control strategy is not unified at present, the network formation type control for simulating the characteristics of the synchronous generator around the swinging equation is not unified at present, the model can be generally called a virtual synchronous machine, and the analysis thought and the parameter design method of the network formation type control are also lacking. Further, some of the mesh type control simulating the characteristics of the synchronous generator in more detail is also proposed successively than the mesh type control considering the electromagnetic transient characteristics.
For the grid-structured flexible direct current transmission technology, the influence of direct current voltage fluctuation on the grid-structured flexible direct current transmission technology must be considered, and under the condition that direct current voltage fluctuation is caused by faults when other flexible direct current converter stations are connected into an alternating current power grid, how to respond the grid-structured flexible direct current converter stations, and what fault crossing technology is adopted can ensure safe and stable operation of the converter stations, and meanwhile active support of the power grid is realized, so that the grid-structured flexible direct current transmission technology is a problem which must face.
Based on verification means such as full electromagnetic transient simulation, a fault technology of the network construction type flexible direct current under multiple scene faults is researched, and key guarantee is provided for the development of the network construction type flexible direct current technology.
Disclosure of Invention
Aiming at the problems, the invention provides a low-voltage fault ride-through method for grid-structured flexible direct current transmission, which comprises the following steps:
when the network formation of the flexible direct current converter station is used as a receiving end for control, determining the topological structure of the network formation type flexible direct current transmission system;
determining a target value of a control target according to the topological structure and the system requirement of the network-structured flexible direct current transmission system;
starting a fault judging module according to the direct current voltage fluctuation of the grid-structured flexible direct current power transmission system, judging whether the grid-structured flexible direct current power transmission system starts fault ride-through measures or not based on the fault judging module, and starting the fault ride-through measures if the direct current voltage is lower than a direct current voltage warning value;
the fault ride-through measure is initiated, comprising: and determining a network-structured control structure module of the flexible direct current converter station and a parameter value of the control structure module according to the target value, and controlling the network-structured flexible direct current transmission system by using the control structure module and the parameter value of the control structure module to perform fault ride-through.
Wherein the target value comprises:
the method comprises the following steps of flexibly and directly transmitting a per unit value of an active power command value, flexibly and directly transmitting a per unit value of a reactive power command value, flexibly and directly outputting a per unit value of a direct current voltage command value, flexibly and directly accessing a per unit value of a node voltage command value and rated angular speed of a virtual synchronous machine.
Wherein the DC voltage warning value is 0.9 per unit value of the DC voltage.
Wherein the method further comprises:
setting a DC voltage safety value;
and after fault ride-through, if the direct current voltage is higher than the direct current voltage safety value, exiting the fault ride-through measure.
The safety value of the direct current voltage is 1.0 per unit value of the direct current voltage.
Wherein controlling the structural module parameter values comprises:
a fixed modulation ratio specified value and a damping coefficient command value.
Wherein, control structure module includes: a fault ride-through module;
the fault ride-through module comprises: a fixed modulation ratio sub-module and a damping coefficient switching sub-module;
the fixed modulation ratio submodule is used for switching a fixed modulation ratio appointed value, and controlling the network-structured flexible direct current transmission system in a low-voltage mode to establish a steady state after the fault of the network-structured flexible direct current transmission system is cleared;
the damping coefficient switching submodule is used for switching damping coefficient command values so as to increase the damping coefficient command values;
the fixed modulation ratio appointed value and the damping coefficient command value meet the corresponding relation with the target value.
In yet another aspect, a low voltage fault ride-through system for grid-tied flexible dc power transmission includes:
the method comprises the steps of establishing a topology unit, wherein the topology unit is used for determining the topology structure of a grid-structured flexible direct current transmission system when the grid-structured flexible direct current converter station is used as a receiving end for control;
the target value determining unit is used for determining a target value of a control target according to the topological structure and the system requirements of the grid-structured flexible direct current transmission system;
the control unit is used for starting a fault judging module according to the direct-current voltage fluctuation of the grid-structured flexible direct-current power transmission system, judging whether the grid-structured flexible direct-current power transmission system starts fault ride-through measures or not based on the fault judging module, and starting the fault ride-through measures if the direct-current voltage is lower than a direct-current voltage warning value;
the fault ride-through measure is initiated, comprising: and determining a network-structured control structure module of the flexible direct current converter station and a parameter value of the control structure module according to the target value, and controlling the network-structured flexible direct current transmission system by using the control structure module and the parameter value of the control structure module to perform fault ride-through.
Wherein the target value comprises:
the method comprises the following steps of flexibly and directly transmitting a per unit value of an active power command value, flexibly and directly transmitting a per unit value of a reactive power command value, flexibly and directly outputting a per unit value of a direct current voltage command value, flexibly and directly accessing a per unit value of a node voltage command value and rated angular speed of a virtual synchronous machine.
Wherein the DC voltage warning value is 0.9 per unit value of the DC voltage.
Wherein the control unit is further configured to:
setting a DC voltage safety value;
and after fault ride-through, if the direct current voltage is higher than the direct current voltage safety value, exiting the fault ride-through measure.
The safety value of the direct current voltage is 1.0 per unit value of the direct current voltage.
Wherein controlling the structural module parameter values comprises:
a fixed modulation ratio specified value and a damping coefficient command value.
Wherein, control structure module includes: a fault ride-through module;
the fault ride-through module comprises: a fixed modulation ratio sub-module and a damping coefficient switching sub-module;
the fixed modulation ratio submodule is used for switching a fixed modulation ratio appointed value, and controlling the network-structured flexible direct current transmission system in a low-voltage mode to establish a steady state after the fault of the network-structured flexible direct current transmission system is cleared;
the damping coefficient switching submodule is used for switching damping coefficient command values so as to increase the damping coefficient command values;
the fixed modulation ratio appointed value and the damping coefficient command value meet the corresponding relation with the target value.
In yet another aspect, the present invention also provides a computing device comprising: one or more processors;
a processor for executing one or more programs;
the method as described above is implemented when the one or more programs are executed by the one or more processors.
In yet another aspect, the present invention also provides a computer readable storage medium having stored thereon a computer program which, when executed, implements a method as described above.
Compared with the prior art, the invention has the beneficial effects that:
the invention provides a low-voltage fault ride-through method for grid-structured flexible direct current transmission, which comprises the following steps: when the network formation of the flexible direct current converter station is used as a receiving end for control, determining the topological structure of the network formation type flexible direct current transmission system; determining a target value of a control target according to the topological structure and the system requirement of the network-structured flexible direct current transmission system; starting a fault judging module according to the direct current voltage fluctuation of the grid-structured flexible direct current power transmission system, judging whether the grid-structured flexible direct current power transmission system starts fault ride-through measures or not based on the fault judging module, and starting the fault ride-through measures if the direct current voltage is lower than a direct current voltage warning value; the fault ride-through measure is initiated, comprising: and determining a network-structured control structure module of the flexible direct current converter station and a parameter value of the control structure module according to the target value, and controlling the network-structured flexible direct current transmission system by using the control structure module and the parameter value of the control structure module to perform fault ride-through. The invention can ensure the stable operation of the grid-structured flexible direct current transmission system after faults.
Drawings
FIG. 1 is a flow chart of the method of the present invention;
FIG. 2 is a diagram of a controller according to an embodiment of the method of the present invention;
FIG. 3 is a block diagram of a fixed modulation ratio module according to an embodiment of the method of the present invention;
FIG. 4 is a diagram showing a damping coefficient switching control structure according to an embodiment of the method of the present invention;
FIG. 5 is a schematic diagram of a simulation circuit according to an embodiment of the method of the present invention;
FIG. 6 is a graph of the MMC output AC voltage during a fault in an embodiment of the method of the present invention;
FIG. 7 is a graph of Vdref during failure for an embodiment of the method of the present invention;
FIG. 8 is a graph of a fault period Vqref for an embodiment of the method of the present invention;
FIG. 9 is a graph of Idref during failure for an embodiment of the method of the present invention;
FIG. 10 is a graph of a period of failure Iqref for an embodiment of the method of the present invention;
FIG. 11 is a graph of DC voltage during a fault in an embodiment of the method of the present invention;
FIG. 12 is a graph of ac voltage during a fault in an embodiment of the method of the present invention;
FIG. 13 is a graph of active power during a fault in an embodiment of the method of the present invention;
FIG. 14 is a graph of reactive power during a fault of an embodiment of the method of the present invention;
fig. 15 is a block diagram of the system of the present invention.
Detailed Description
The exemplary embodiments of the present invention will now be described with reference to the accompanying drawings, however, the present invention may be embodied in many different forms and is not limited to the examples described herein, which are provided to fully and completely disclose the present invention and fully convey the scope of the invention to those skilled in the art. The terminology used in the exemplary embodiments illustrated in the accompanying drawings is not intended to be limiting of the invention. In the drawings, like elements/components are referred to by like reference numerals.
Unless otherwise indicated, terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art. In addition, it will be understood that terms defined in commonly used dictionaries should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense.
Example 1:
the invention provides a low-voltage fault ride-through method for grid-structured flexible direct current transmission, which is shown in fig. 1 and comprises the following steps:
step 1, when a network structure of a flexible direct current converter station is used as a receiving end for control, determining a topological structure of the network structure flexible direct current transmission system;
step 2, determining a target value of a control target according to the topological structure and the system requirement of the grid-structured flexible direct current transmission system;
step 3, starting a fault judging module according to the direct-current voltage fluctuation of the grid-structured flexible direct-current power transmission system, judging whether the grid-structured flexible direct-current power transmission system starts fault ride-through measures or not based on the fault judging module, and starting the fault ride-through measures if the direct-current voltage is lower than a direct-current voltage warning value;
the fault ride-through measure is initiated, comprising: and determining a network-structured control structure module of the flexible direct current converter station and a parameter value of the control structure module according to the target value, and controlling the network-structured flexible direct current transmission system by using the control structure module and the parameter value of the control structure module to perform fault ride-through.
Wherein the target value comprises:
the method comprises the following steps of flexibly and directly transmitting a per unit value of an active power command value, flexibly and directly transmitting a per unit value of a reactive power command value, flexibly and directly outputting a per unit value of a direct current voltage command value, flexibly and directly accessing a per unit value of a node voltage command value and rated angular speed of a virtual synchronous machine.
Wherein the DC voltage warning value is 0.9 per unit value of the DC voltage.
Wherein the method further comprises:
setting a DC voltage safety value;
and after fault ride-through, if the direct current voltage is higher than the direct current voltage safety value, exiting the fault ride-through measure.
The safety value of the direct current voltage is 1.0 per unit value of the direct current voltage.
Wherein controlling the structural module parameter values comprises:
a fixed modulation ratio specified value and a damping coefficient command value.
Wherein, control structure module includes: a fault ride-through module;
the fault ride-through module comprises: a fixed modulation ratio sub-module and a damping coefficient switching sub-module;
the fixed modulation ratio submodule is used for switching a fixed modulation ratio appointed value, and controlling the network-structured flexible direct current transmission system in a low-voltage mode to establish a steady state after the fault of the network-structured flexible direct current transmission system is cleared;
the damping coefficient switching submodule is used for switching damping coefficient command values so as to increase the damping coefficient command values;
the fixed modulation ratio appointed value and the damping coefficient command value meet the corresponding relation with the target value.
The invention is further illustrated by the following examples:
step 1: the topology structure of the flexible direct current converter station network control is determined, and the controller structure related to the invention is shown in fig. 2.
The values in the control structure diagram are as follows:
P ref an active power command value (per unit value) for soft direct transmission;
p is the active power (per unit value) of the soft direct transmission;
Q ref a reactive power command value (per unit value) for soft direct transmission;
q is reactive power (per unit value) of the soft direct transmission;
P p is a power control scaling factor;
V dcref a direct-current voltage command value (per unit value) for soft direct output;
V dc a direct current voltage (per unit value) which is a soft direct current output;
U n a node voltage command value (per unit value) for soft direct access;
L v is a virtual impedance;
d is a damping coefficient;
j is moment of inertia (kg. Square meter);
D LIM is a damping coefficient during failure;
J LIM moment of inertia (kg square meter) during failure;
ω is virtual synchronous machine angular velocity (radian/sec);
ω n rated angular velocity (radian/second) for a virtual synchronous machine;
V d、q the dq axis voltage (per unit value) at the flexible-to-straight interface;
V dref、qref the voltage command value (per unit value) of the dq axis at the flexible-direct interface;
I d、q outputting dq-axis current (per unit value) for the MMC;
I dref、qref outputting a dq-axis current command value (per unit value) for the MMC;
the inner ring structure of the controller is consistent with that of a conventional soft-direct controller, wherein each variable of the voltage ring satisfies the formula (1), and each variable of the current ring satisfies the formula (2).
Wherein k is p1 And k i1 Respectively a voltage loop proportion coefficient and an integral coefficient, k p2 And k i2 The current loop ratio coefficient and the integral coefficient are respectively. D and J satisfy virtual synchronous machine rotor mechanical equation (3).
The remaining electrical parameters are determined based on the actual electrical system.
Step 2: determining a control target value P according to system requirements ref 、Q ref 、V dcref 、U n 、ω n 。
Step 3: determining the structure and parameters of a network-structured control fault ride-through module of the receiving end flexible direct current converter station:
(1) And a fault judging module: judging whether to start fault ride-through measures through fluctuation of direct current voltage
a. Setting a DC voltage warning value V dcdanger . When the DC voltage is lower than 0.9 per unit value, the system is judged to be in fault, and the DC voltage warning value V dcdanger And setting the fault crossing module to 0.9, and starting the fault crossing module.
b. Setting a DC voltage safety value V dcsafe . When the DC voltage is recovered to 1.0 per unit value, the system is judged to be fault clearing, and the DC voltage safety value V dcsafe And setting to 1.0, and exiting the fault traversing module.
(2) And a fault ride-through module: the device comprises a fixed modulation ratio module and a damping coefficient switching module.
a. And a fixed modulation ratio module: the block diagram is shown in fig. 3. When the DC voltage drops to a low value, the controller actively reduces the amplitude of the output AC voltage by a mode of fixed modulation ratio, and the voltage command value V sdref Decline, I dref The amplitude of the pulse is in a normal range and cannot enter an out-of-control state due to amplitude limiting, so that a guarantee is provided for steady state establishment after fault clearing.
b. Damping coefficient switching module: d (D) LIM The block diagram is shown in fig. 4, which is obtained by the formula (4).
According to the formula (3), the amplitude of the damping coefficient influences the power change speed, and the larger the damping coefficient is, the smaller the power change is in the range where the steady state can be established, the more stable the system is, so that the damping coefficient can be increased during the fault period to reduce the power angle change, and the power angle instability is prevented.
Step 4: and (5) completing fault ride-through.
In the east-west flexible direct current asynchronous networking scheme of a certain province, the networking flexible direct current PSMOdel simulation platform is adopted for simulation modeling, a control chart is built according to the step 1, and parameters are determined according to the steps 2-3, wherein the parameter values are shown in the table 1.
TABLE 1
When the network-structured converter station is used as a receiving end, the model is shown in fig. 5, and the simulation test working conditions are as follows: at the moment of 6.0s, a three-phase metallic ground short circuit fault occurs on the alternating current side of the constant direct current voltage station, and the duration of the fault is 100ms. The model was simulated for 10s using a 50 μs step size.
The waveforms of the electrical information (per unit value) and the control variable at the receiving end when no measures are taken and the measures according to the invention are taken are shown in fig. 6 to 14.
As is clear from the waveform diagrams, when a three-phase short circuit occurs in a dc voltage converter station which is defined as a receiving end, the problem that the dc voltage is low for a long time, the cross-circuit voltage oscillates, and the d-axis component of the controller is out of control is generated by the modulation ratio during the fault. After the fault is cleared, the direct current voltage is restored and stabilized within 0.5s after the fault is cleared by adopting the fault crossing measures, the alternating current voltage is restored and stabilized within 0.3s, the alternating current voltage basically has no oscillation, and when no measures are taken, the direct current voltage and the alternating current voltage can both be restored and stabilized within 2s, and the alternating current voltage oscillates at 0.02 per unit value, so that the restoring speed is obviously accelerated after the fault is cleared by adopting measures compared with the situation when no measures are taken, the oscillation degree is obviously reduced, and the transient characteristics of various electric quantities are obviously improved.
Under the condition that the grid-structured converter station is used as a receiving end, if the fixed direct-current voltage converter station has an alternating-current short-circuit fault, the fault ride-through measures can effectively improve the speed of recovering the steady state after the fault is cleared, and reduce the oscillation caused by low voltage.
Example 2:
as shown in fig. 15, a low-voltage fault ride-through system 200 for grid-formation flexible dc power transmission includes:
a topology unit 201 is established, which is used for determining the topology structure of the grid-structured flexible direct current transmission system when the grid-structured flexible direct current converter station is used as a receiving end for control;
a target value determining unit 202, configured to determine a target value of a control target according to the topology structure and a system requirement of the grid-structured flexible direct current power transmission system;
the control unit 203 is configured to start a fault discrimination module according to dc voltage fluctuation of the grid-configured flexible dc power transmission system, determine whether the grid-configured flexible dc power transmission system starts a fault ride-through measure based on the fault discrimination module, and if the dc voltage is lower than a dc voltage warning value, start the fault ride-through measure;
the fault ride-through measure is initiated, comprising: and determining a network-structured control structure module of the flexible direct current converter station and a parameter value of the control structure module according to the target value, and controlling the network-structured flexible direct current transmission system by using the control structure module and the parameter value of the control structure module to perform fault ride-through.
Wherein the target value comprises:
the method comprises the following steps of flexibly and directly transmitting a per unit value of an active power command value, flexibly and directly transmitting a per unit value of a reactive power command value, flexibly and directly outputting a per unit value of a direct current voltage command value, flexibly and directly accessing a per unit value of a node voltage command value and rated angular speed of a virtual synchronous machine.
Wherein the DC voltage warning value is 0.9 per unit value of the DC voltage.
Wherein the control unit 203 is further configured to:
setting a DC voltage safety value;
and after fault ride-through, if the direct current voltage is higher than the direct current voltage safety value, exiting the fault ride-through measure.
The safety value of the direct current voltage is 1.0 per unit value of the direct current voltage.
Wherein controlling the structural module parameter values comprises:
a fixed modulation ratio specified value and a damping coefficient command value.
Wherein, control structure module includes: a fault ride-through module;
the fault ride-through module comprises: a fixed modulation ratio sub-module and a damping coefficient switching sub-module;
the fixed modulation ratio submodule is used for switching a fixed modulation ratio appointed value, and controlling the network-structured flexible direct current transmission system in a low-voltage mode to establish a steady state after the fault of the network-structured flexible direct current transmission system is cleared;
the damping coefficient switching submodule is used for switching damping coefficient command values so as to increase the damping coefficient command values;
the fixed modulation ratio appointed value and the damping coefficient command value meet the corresponding relation with the target value.
The invention can ensure the stable operation of the grid-structured flexible direct current transmission system after faults.
Example 3:
based on the same inventive concept, the invention also provides a computer device comprising a processor and a memory for storing a computer program comprising program instructions, the processor for executing the program instructions stored by the computer storage medium. The processor may be a central processing unit (Central Processing Unit, CPU), but may also be other general purpose processors, digital signal processors (Digital Signal Processor, DSP), application specific integrated circuits (Application SpecificIntegrated Circuit, ASIC), off-the-shelf Programmable gate arrays (FPGAs) or other Programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc., which are the computational core and control core of the terminal adapted to implement one or more instructions, in particular adapted to load and execute one or more instructions within a computer storage medium to implement the corresponding method flow or corresponding functions to implement the steps of the method in the embodiments described above.
Example 4:
based on the same inventive concept, the present invention also provides a storage medium, in particular, a computer readable storage medium (Memory), which is a Memory device in a computer device, for storing programs and data. It is understood that the computer readable storage medium herein may include both built-in storage media in a computer device and extended storage media supported by the computer device. The computer-readable storage medium provides a storage space storing an operating system of the terminal. Also stored in the memory space are one or more instructions, which may be one or more computer programs (including program code), adapted to be loaded and executed by the processor. The computer readable storage medium herein may be a high-speed RAM memory or a non-volatile memory (non-volatile memory), such as at least one magnetic disk memory. One or more instructions stored in a computer-readable storage medium may be loaded and executed by a processor to implement the steps of the methods in the above-described embodiments.
It will be appreciated by those skilled in the art that embodiments of the present invention may be provided as a method, system, or computer program product. Accordingly, the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present invention 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 scheme in the embodiment of the invention can be realized by adopting various computer languages, such as object-oriented programming language Java, an transliteration script language JavaScript and the like.
The present invention is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems) and computer program products according to embodiments of the invention. It will be understood that each flow and/or block of the flowchart illustrations and/or block diagrams, and combinations of flows and/or blocks in the flowchart illustrations 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.
While preferred embodiments of the present invention have been described, additional variations and modifications in those embodiments may occur to those skilled in the art once they learn of the basic inventive concepts. It is therefore intended that the following claims be interpreted as including the preferred embodiments and all such alterations and modifications as fall within the scope of the invention.
It will be apparent to those skilled in the art that various modifications and variations can be made to the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention also include such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.
Claims (16)
1. The low-voltage fault ride-through method for the grid-structured flexible direct current transmission is characterized by comprising the following steps of:
when the network formation of the flexible direct current converter station is used as a receiving end for control, determining the topological structure of the network formation type flexible direct current transmission system;
determining a target value of a control target according to the topological structure and the system requirement of the network-structured flexible direct current transmission system;
starting a fault judging module according to the direct current voltage fluctuation of the grid-structured flexible direct current power transmission system, judging whether the grid-structured flexible direct current power transmission system starts fault ride-through measures or not based on the fault judging module, and starting the fault ride-through measures if the direct current voltage is lower than a direct current voltage warning value;
the fault ride-through measure is initiated, comprising: and determining a network-structured control structure module of the flexible direct current converter station and a parameter value of the control structure module according to the target value, and controlling the network-structured flexible direct current transmission system by using the control structure module and the parameter value of the control structure module to perform fault ride-through.
2. The fault ride-through method according to claim 1, characterized in that the target value includes:
the method comprises the following steps of flexibly and directly transmitting a per unit value of an active power command value, flexibly and directly transmitting a per unit value of a reactive power command value, flexibly and directly outputting a per unit value of a direct current voltage command value, flexibly and directly accessing a per unit value of a node voltage command value and rated angular speed of a virtual synchronous machine.
3. The fault ride-through method according to claim 1, wherein the dc voltage guard value is 0.9 per unit of the dc voltage.
4. The fault ride-through method of claim 1, further comprising:
setting a DC voltage safety value;
and after fault ride-through, if the direct current voltage is higher than the direct current voltage safety value, exiting the fault ride-through measure.
5. The fault-ride-through method of claim 4, wherein the dc voltage safety value is 1.0 per unit of dc voltage.
6. The fault ride-through method of claim 1, wherein the control structure module parameter values comprise:
a fixed modulation ratio specified value and a damping coefficient command value.
7. The fault ride-through method of claim 1, wherein the control structure module comprises: a fault ride-through module;
the fault ride-through module comprises: a fixed modulation ratio sub-module and a damping coefficient switching sub-module;
the fixed modulation ratio submodule is used for switching a fixed modulation ratio appointed value, and controlling the network-structured flexible direct current transmission system in a low-voltage mode to establish a steady state after the fault of the network-structured flexible direct current transmission system is cleared;
the damping coefficient switching submodule is used for switching damping coefficient command values so as to increase the damping coefficient command values;
the fixed modulation ratio appointed value and the damping coefficient command value meet the corresponding relation with the target value.
8. A low voltage fault ride-through system for grid-structured flexible direct current transmission, the fault ride-through system comprising:
the method comprises the steps of establishing a topology unit, wherein the topology unit is used for determining the topology structure of a grid-structured flexible direct current transmission system when the grid-structured flexible direct current converter station is used as a receiving end for control;
the target value determining unit is used for determining a target value of a control target according to the topological structure and the system requirements of the grid-structured flexible direct current transmission system;
the control unit is used for starting a fault judging module according to the direct-current voltage fluctuation of the grid-structured flexible direct-current power transmission system, judging whether the grid-structured flexible direct-current power transmission system starts fault ride-through measures or not based on the fault judging module, and starting the fault ride-through measures if the direct-current voltage is lower than a direct-current voltage warning value;
the fault ride-through measure is initiated, comprising: and determining a network-structured control structure module of the flexible direct current converter station and a parameter value of the control structure module according to the target value, and controlling the network-structured flexible direct current transmission system by using the control structure module and the parameter value of the control structure module to perform fault ride-through.
9. The fault ride-through system of claim 8, wherein the target value comprises:
the method comprises the following steps of flexibly and directly transmitting a per unit value of an active power command value, flexibly and directly transmitting a per unit value of a reactive power command value, flexibly and directly outputting a per unit value of a direct current voltage command value, flexibly and directly accessing a per unit value of a node voltage command value and rated angular speed of a virtual synchronous machine.
10. The fault ride-through system of claim 8, wherein the dc voltage alert value is 0.9 per unit of dc voltage.
11. The fault ride-through system of claim 8, wherein the control unit is further configured to:
setting a DC voltage safety value;
and after fault ride-through, if the direct current voltage is higher than the direct current voltage safety value, exiting the fault ride-through measure.
12. The fault ride-through system of claim 11, wherein the dc voltage safety value is 1.0 per unit of dc voltage.
13. The fault ride-through system of claim 8, wherein the control structure module parameter values comprise:
a fixed modulation ratio specified value and a damping coefficient command value.
14. The fault ride-through system of claim 8, wherein the control structure module comprises: a fault ride-through module;
the fault ride-through module comprises: a fixed modulation ratio sub-module and a damping coefficient switching sub-module;
the fixed modulation ratio submodule is used for switching a fixed modulation ratio appointed value, and controlling the network-structured flexible direct current transmission system in a low-voltage mode to establish a steady state after the fault of the network-structured flexible direct current transmission system is cleared;
the damping coefficient switching submodule is used for switching damping coefficient command values so as to increase the damping coefficient command values;
the fixed modulation ratio appointed value and the damping coefficient command value meet the corresponding relation with the target value.
15. A computer device, comprising:
one or more processors;
a processor for executing one or more programs;
the method of any of claims 1-7 is implemented when the one or more programs are executed by the one or more processors.
16. A computer readable storage medium, characterized in that a computer program is stored thereon, which computer program, when executed, implements the method according to any of claims 1-7.
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