A coordinated method for low voltage protection control of symmetrical unipolar high voltage direct current transmission system lines

Abstract

The present invention discloses a coordinated method for line low-voltage protection control of a symmetrical unipolar high-voltage direct current transmission system, which belongs to the technical field of high-voltage direct current transmission. The method comprises: based on a preset starting criterion, starting a current adaptive switching strategy, so that the line low-voltage protection can operate correctly when a fault occurs in the symmetrical unipolar high-voltage direct current transmission system; wherein the current adaptive switching strategy comprises: selecting the minimum value of the positive DC current on the inverter side and the negative DC current on the inverter side of the symmetrical unipolar high-voltage direct current transmission system as the inverter side controller input. The method ensures that the line low-voltage protection can operate correctly when a fault occurs in the symmetrical unipolar high-voltage direct current transmission system.

Description

Technical Field

[0001] The invention relates to a coordinated method for low-voltage protection control of a line in a symmetrical unipolar high-voltage direct current power transmission system, and belongs to the technical field of high-voltage direct current power transmission. Background Art

[0002] With the rapid growth of power supply capacity and electricity demand, the increasing shortage of resources and energy, and the urgent need for environmental protection, it is necessary to significantly increase the transmission capacity of key sections of the power grid by building a large number of new transmission lines or transforming existing transmission lines. However, due to the natural dangers of the terrain, it is extremely difficult to develop key channel resources. It is an economical and feasible solution to transform the "embedded" high-voltage direct current (HVDC) transmission system by making full use of the key transmission channels within the existing regional power grid.

[0003] Conventional UHV / UHV DC transmission systems often achieve cross-regional, long-distance, and large-capacity power transmission. In order to improve transmission reliability, UHV / UHV DC projects usually adopt a symmetrical bipolar topology in which each pole can operate independently, and the neutral points of the sending and receiving ends are connected to the grounding point outside the station through the grounding electrode lead. Compared with conventional UHV / UHV DC transmission systems, the "embedded" HVDC system located inside the regional power grid has a larger transmission capacity and a greatly shortened transmission distance. In addition, due to the location of the grounding point outside the station and related cost factors, the "embedded" HVDC is more suitable for a symmetrical monopolar topology with only the inverter side grounded inside the station.

[0004] Compared with the symmetrical bipolar topology UHV / UHV DC system, the symmetrical unipolar topology "embedded" HVDC system has significant differences in primary topology, measurement point location distribution, transmission distance, etc. If the control and protection strategy of the symmetrical bipolar UHV / UHV DC system is directly applied to the symmetrical unipolar system, there may be adaptability problems. In addition, the two poles of the symmetrical unipolar HVDC system are mutually coupled, so the fault characteristics are also very different from those of the symmetrical bipolar system.

[0005] At present, there is no research on the fault characteristics of symmetrical unipolar HVDC systems, the adaptability of control and protection strategies, etc. Therefore, in order to accelerate the construction, application and promotion of "embedded" HVDC actual projects, relevant research work is urgently needed. Summary of the invention

[0006] The object of the present invention is to provide a coordinated method for controlling line low voltage protection of a symmetrical unipolar high voltage direct current transmission system, so as to ensure that the line low voltage protection can operate correctly when a fault occurs in the symmetrical unipolar high voltage direct current transmission system.

[0007] In order to achieve the above object, the present invention provides the following technical solutions:

[0008] In a first aspect, the present invention provides a coordinated method for low voltage protection control of a symmetrical unipolar high voltage direct current transmission system line, comprising:

[0009] Based on the preset starting criteria, the starting current adaptive switching strategy enables the line low voltage protection to operate correctly when a fault occurs in the symmetrical unipolar HVDC transmission system;

[0010] Wherein, the current adaptive switching strategy includes:

[0011] The minimum value of the positive direct current on the inverter side and the negative direct current on the inverter side of the symmetrical unipolar high-voltage direct current transmission system is selected as an input of the inverter side controller.

[0012] In combination with the first aspect, further, the start criterion is:

[0013] i dp2 +i dn2 >Δ

[0014] Among them, i dp2 is the positive pole measured current on the inverter side of the symmetrical unipolar HVDC transmission system, i dn2 is the measured current of the negative pole of the inverter side of the symmetrical unipolar HVDC transmission system, and Δ is the preset starting criterion constant;

[0015] When the starting criterion is met, the starting current adaptive switching strategy is implemented.

[0016] In combination with the first aspect, further, the symmetrical unipolar high-voltage direct current transmission system comprises a rectifier side and an inverter side; the rectifier side and the inverter side both comprise a direct current line (1), two smoothing reactors (2) connected to both sides of the direct current line (1), and two converter valves (3) connected between the two smoothing reactors (2), wherein one converter valve (3) is connected to a YY-type converter transformer (4), one converter valve (3) is connected to a Y△-type converter transformer (5), the YY-type converter transformer (4) and the Y△-type converter transformer (5) are both connected to an alternating current system (7) and an alternating current filter (6), and the YY-type converter transformer (4) and the Y△-type converter transformer (5) are both grounded; the rectifier side and the inverter side are symmetrically connected via the direct current line (1); and the inverter side is grounded within the station.

[0017] In combination with the first aspect, further, the fault of the symmetrical unipolar high voltage direct current transmission system includes a high resistance grounding fault occurring in the positive direct current line and a high resistance grounding fault occurring in the negative direct current line;

[0018] When a high-resistance grounding fault occurs in the positive DC line of the symmetrical monopolar high-voltage direct current transmission system, the positive DC current on the inverter side is less than the negative DC current on the inverter side, and the positive DC current on the inverter side is selected as the inverter side controller input. The inverter side controller input and the rectifier side controller input are distributed in different loops, so that the current value of the fault branch is controlled to 0.1 times the rated current value, and then the DC line voltage value is controlled below the line low voltage protection setting value, so that the line low voltage protection can operate correctly;

[0019] When a high-resistance grounding fault occurs in the negative DC line of the symmetrical unipolar high-voltage direct current transmission system, the positive DC current on the inverter side is greater than the negative DC current on the inverter side, and the negative DC current on the inverter side is selected as the inverter side controller input. The inverter side controller input and the rectifier side controller input are distributed in different loops, thereby controlling the current value of the fault branch to 0.1 times the rated current value, and then controlling the DC line voltage value to below the line low voltage protection setting, so that the line low voltage protection can operate correctly.

[0020] In a second aspect, the present invention provides a symmetrical unipolar high voltage direct current transmission system line low voltage protection control coordination device, comprising:

[0021] Startup module: used to start the current adaptive switching strategy based on the preset startup criteria, so that the line low voltage protection can operate correctly when a fault occurs in the symmetrical unipolar high-voltage direct current transmission system;

[0022] Wherein, the current adaptive switching strategy includes:

[0023] The minimum value of the positive direct current on the inverter side and the negative direct current on the inverter side of the symmetrical unipolar high-voltage direct current transmission system is selected as an input of the inverter side controller.

[0024] In combination with the second aspect, further, the startup module includes:

[0025] A collection unit: used for collecting the measured current of the positive pole on the inverter side and the measured current of the negative pole on the inverter side of the symmetrical monopolar high voltage direct current transmission system;

[0026] A judgment unit: used to judge whether a preset start criterion is established or not according to the measured current of the positive pole of the inverter side and the measured current of the negative pole of the inverter side of the symmetrical monopolar high voltage direct current transmission system, and if the preset start criterion is established, output a current adaptive switching signal;

[0027] A switching unit is used to start the current adaptive switching strategy according to the current adaptive switching signal. In combination with the second aspect, further, the start criterion is:

[0028] i dp2 +i dn2 >Δ

[0029] Among them, i dp2 is the positive pole measured current on the inverter side of the symmetrical unipolar HVDC transmission system, i dn2 is the measured current of the negative pole of the inverter side of the symmetrical unipolar HVDC transmission system, and Δ is the preset starting criterion constant;

[0030] When the starting criterion is met, the starting current adaptive switching strategy is implemented.

[0031] In a third aspect, the present invention provides a symmetrical monopolar high voltage direct current transmission system line low voltage protection control coordination system, comprising:

[0032] Storage medium: used to store computer programs;

[0033] Processor: used to execute the computer program to implement the steps of any method described in the first aspect.

[0034] In a fourth aspect, the present invention provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of any one of the methods described in the first aspect.

[0035] In a fifth aspect, the present invention provides a computer program product, comprising a computer program, which, when executed by a processor, implements the steps of any one of the methods described in the first aspect.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] The coordinated method for line low-voltage protection control of a symmetrical unipolar high-voltage direct current transmission system provided by the present invention determines whether to start the current adaptive switching strategy based on a starting criterion. If the starting criterion is established, the minimum value of the positive DC current on the inverter side and the negative DC current on the inverter side of the symmetrical unipolar high-voltage direct current transmission system is selected as the input of the inverter side controller to ensure that the DC line voltage value can be controlled below the line low-voltage protection set value, so that the line low-voltage protection can correctly exit the action, and optimizes the "embedded" symmetrical unipolar high-voltage direct current transmission system line low-voltage protection control coordinated strategy to cope with line faults with higher resistance transition resistors. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 2 is a schematic diagram comparing the topologies of symmetrical bipolar and symmetrical monopolar HVDC systems provided in an embodiment of the present invention;

[0039] Figure 2 is a schematic diagram of a positive line fault in a symmetrical monopolar HVDC system provided by an embodiment of the present invention;

[0040] Figure 3is a schematic diagram of a negative line fault in a symmetrical monopolar HVDC system provided by an embodiment of the present invention;

[0041] Figure 4 It is a simulated waveform diagram of positive and negative current and voltage on the inverter side when a positive DC line has a high-resistance grounding fault provided by an embodiment of the present invention;

[0042] Figure 5 It is a simulated waveform diagram of the positive and negative current and voltage on the inverter side when a positive DC line has a high-resistance grounding fault under the starting current adaptive switching strategy provided by an embodiment of the present invention;

[0043] In the figure, 1. DC line; 2. Smoothing reactor; 3. Converter valve; 4. YY type converter transformer; 5. Y△ type converter transformer; 6. AC filter; 7. AC system; 8. Fault point; 9. Transition resistor. DETAILED DESCRIPTION

[0044] The technical solution of the present application is further described in detail below in conjunction with specific implementation methods.

[0045] The embodiments of the present application are described in detail below, and examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements with the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present application, and should not be construed as limitations on the present application. In the absence of conflict, the embodiments of the present application and the technical features in the embodiments may be combined with each other.

[0046] Embodiment 1:

[0047] The present embodiment provides a coordinated method for low-voltage protection control of a symmetrical monopolar high-voltage direct current transmission system line, which can be applied to a terminal and can be executed by a coordinated device for low-voltage protection control of a symmetrical monopolar high-voltage direct current transmission system line. The device can be implemented by software and / or hardware, and the device can be integrated in a terminal, for example: any tablet computer or computer device with communication function.

[0048] The coordinated method for low voltage protection control of symmetrical unipolar high voltage direct current transmission system lines provided in this embodiment specifically comprises the following steps:

[0049] Step 1: Based on the preset starting criteria, the starting current adaptive switching strategy is adopted so that the line low voltage protection can operate correctly when a fault occurs in the symmetrical unipolar HVDC transmission system.

[0050] In this embodiment, the start criterion is:

[0051] i dp2 +i dn2 >Δ

[0052] Among them, i dp2 is the positive pole measured current on the inverter side of the symmetrical unipolar HVDC transmission system, i dn2 is the negative pole measured current on the inverter side of the symmetrical unipolar HVDC transmission system, Δ is the preset starting criterion constant; when the starting criterion is met, the starting current adaptive switching strategy is adopted.

[0053] In this embodiment, the current adaptive switching strategy specifically includes:

[0054] The minimum value of the positive DC current on the inverter side and the negative DC current on the inverter side of the symmetrical unipolar high voltage direct current transmission system is selected as the input of the inverter side controller.

[0055] In this embodiment, Figure 2 As shown, the symmetrical unipolar high-voltage direct current transmission system includes a rectifier side and an inverter side; the rectifier side and the inverter side both include a DC line 1, two smoothing reactors 2 connected to both sides of the DC line 1, and two converter valves 3 connected between the two smoothing reactors 2, wherein one converter valve 3 is connected to a YY-type converter transformer 4, and one converter valve 3 is connected to a Y△-type converter transformer 5, and both the YY-type converter transformer 4 and the Y△-type converter transformer 5 are connected to an AC system 7 and an AC filter 6, and both the YY-type converter transformer 4 and the Y△-type converter transformer 5 are grounded; the rectifier side and the inverter side are symmetrically connected through the DC line 1, and a number of towers are also connected between the DC lines 1; the inverter side is grounded in the station.

[0056] In this embodiment, the faults of the symmetrical monopolar high voltage direct current transmission system include a high resistance grounding fault occurring in the positive direct current line and a high resistance grounding fault occurring in the negative direct current line.

[0057] like Figure 2 As shown in the figure, when a high-resistance grounding fault occurs in the positive DC line of the symmetrical unipolar HVDC transmission system, the positive DC current on the inverter side is smaller than the negative DC current on the inverter side, and the positive DC current on the inverter side is selected as the inverter side controller input. The inverter side controller input and the rectifier side controller input are distributed in different circuits, so that the current value of the fault branch (the current difference between the two circuits) is controlled at 0.1 times the rated current value, and then the DC line voltage value (the resistance of the transition resistor multiplied by the current value of the fault branch) is controlled below the line low voltage protection setting, so that the line low voltage protection can operate correctly.

[0058] like Figure 3As shown in the figure, when a high-resistance grounding fault occurs in the negative DC line of the symmetrical unipolar HVDC transmission system, the positive DC current on the inverter side is greater than the negative DC current on the inverter side, and the negative DC current on the inverter side is selected as the inverter side controller input. The inverter side controller input and the rectifier side controller input are distributed in different circuits, so that the current value of the fault branch (the current difference between the two circuits) is controlled at 0.1 times the rated current value, and then the DC line voltage value (the resistance of the transition resistor multiplied by the current value of the fault branch) is controlled below the line low voltage protection setting value, so that the line low voltage protection can operate correctly.

[0059] like Figure 1 The figure shows a topology comparison diagram of a symmetrical bipolar (taking a unipolar single 12-pulse converter valve as an example) and a symmetrical unipolar HVDC (high voltage direct current transmission) system. Figure 1 In the figure, (a) is a symmetrical bipolar HVDC system, and (b) is a symmetrical unipolar HVDC system. The bipolar of the symmetrical bipolar HVDC system is completely independent, and the DC voltage and current control objects are the voltage between the high voltage side and the neutral point side of the converter outlet, and the current on the neutral point side of the converter outlet. The bipolar of the symmetrical unipolar HVDC system is coupled together. If the control object setting of the symmetrical bipolar HVDC is used as a reference, the DC voltage and current control objects are the voltage between the positive and negative poles of the converter, and the negative pole outlet current of the converter.

[0060] In the case of non-converter internal grounding fault, the outlet currents on the high-voltage side and the neutral point side of the symmetrical bipolar HVDC system converter are always equal, so it makes no difference to use any point current as the control object. However, in the symmetrical unipolar HVDC system, the midpoint of the inverter side converter is grounded. When a grounding fault occurs on the DC side, the neutral point current will no longer be equal to zero, which will cause the positive and negative currents of the inverter side converter to no longer be equal. If a certain point current is still used as the control object, it may affect the performance of the control system.

[0061] After a ground fault occurs in the positive DC line, the entire symmetrical unipolar topology DC system is also divided into two loops, such as Figure 2 In this fault condition, the current control object I dn1 and I dn2 Both are located in loop 1, and loop 2 has no current control object, which causes the steady-state characteristics under this fault condition to be significantly different from those of conventional DC.

[0062] Steady-state characteristic analysis of positive line fault in symmetrical unipolar system. If a low-resistance transition resistance fault occurs, the voltage U F Lower than U dp2 , due to the unidirectional conductivity of the thyristor, the current in loop 2 will be equal to zero. At the same time, the inverter side is in fixed turn-off angle control, and the negative pole U dn1Keep in -U N The positive voltage drops to near 0, and the inter-electrode voltage on the rectifier side is approximately equal to U N , so loop 1 will operate in VDCOL constant current control mode. At this time, the DC system will satisfy the expression:

[0063]

[0064] Therefore, U dp1 Will follow R g When R g The resistance is large enough, U dp1 Not less than 0.75U N When the condition is met, loop 1 will operate in constant current control mode, and the current command value is I N At this point, the DC system will satisfy the expression:

[0065]

[0066] If R g The resistance value continues to increase, U F Will be higher than U dp2 , the current in loop 2 is no longer zero. In this case, the DC system will satisfy the expression:

[0067]

[0068] Therefore, the positive output voltage of the rectifier side is calculated as:

[0069]

[0070] Substituting typical control parameters of the “embedded” HVDC system, the DC line position (0≤R L1 ≤R L ) occurs with transition resistance (R g ≤200Ω) in the case of a ground fault, the positive DC port voltage on the rectifier side. g When it is less than 32Ω, loop 1 is in VDCOL constant current control mode, and loop 2 has no current; when R g When the voltage is between 32Ω and 65Ω, loop 1 is in constant current control mode, and loop 2 has no current. In the above two stages, the DC voltage will increase with the R g Finally, when R g When it exceeds 65Ω, current starts to flow in loop 2, and the DC voltage is basically maintained at around 198kV.

[0071] In R g When the resistance value exceeds 25Ω, the line main protection is difficult to operate correctly. The DC voltage U dp1If the voltage is higher than the line low voltage protection action setting of 70kV, the low voltage backup protection will refuse to operate. In other words, in this fault situation, the line low voltage protection loses the ability to serve as a backup protection to deal with high resistance faults.

[0072] The control object of the symmetrical unipolar HVDC system is different from that of the conventional symmetrical bipolar system. This results in that although the line low voltage protection can operate correctly when a grounding fault with transition resistance occurs in the negative line, the line low voltage protection may fail to operate when a grounding fault with transition resistance occurs in the positive line. Therefore, it is necessary to adjust the control strategy of the symmetrical unipolar HVDC system to ensure that the line low voltage protection can operate correctly when a DC line fault occurs.

[0073] Considering the case of a negative line fault, because the controller inputs the fault pole current, the two loops formed after the fault can control the current separately. Based on this idea, when a positive pole fault occurs, a strategy can be adopted to switch the negative pole current input by the controller to the positive pole current.

[0074] When a DC line fault occurs on one pole, the loop current formed by the faulty pole on the inverter side must be smaller than the loop current of the non-faulty pole. Using this feature, the startup criterion is proposed as follows:

[0075] i dp2 +i dn2 >Δ

[0076] When the startup criteria are met, it means that the DC line may have a fault, and the smaller value of the positive and negative currents of the inverter side converter is selected as the controller input. After this strategy is adopted, when a fault occurs in the positive line, the system can use the inverter side positive converter output current as the controller input, so that loops 1 and 2 can enter the constant current control mode, thereby reducing the fault branch current I F Controlled to 0.1pu, ensuring that the line low voltage protection can operate correctly when a low resistance fault occurs.

[0077] When the positive DC line midpoint has 0Ω, 20Ω and 100Ω transition resistance faults, the positive and negative current simulation waveforms on the inverter side are as follows: Figure 4 The simulation results show that when a metallic or low-resistance ground fault occurs, the current flowing through Figure 2 The current Idp2 of loop 2 is 0, and the current difference between the two sides of the positive DC line (i.e., the fault branch current) is large. However, due to the low resistance of the transition resistor, the voltage of the positive line during the fault steady state is relatively low, below the line low voltage protection setting. As the transition resistor value increases to 100Ω, loop 2 begins to flow current, the fault branch current is close to 1.8kA, and the positive line voltage is maintained at 180kV, which is higher than the line low voltage protection setting of 70kV, and the protection will refuse to operate.

[0078] When the bipolar DC current adaptive switching control strategy is adopted, when the positive DC line midpoint has a 0Ω, 20Ω and 100Ω transition resistance fault, the positive and negative current simulation waveforms on the inverter side are as follows: Figure 5 The simulation results show that since the positive and negative poles of the inverter side converter use the same trigger angle, the negative pole voltage cannot be maintained near the rated value. Figure 2 The difference between loop 1 current Idp1 and loop 2 current Idp2 (i.e., fault branch current) is always maintained at about 0.3kA, so the positive line voltage can be maintained at a low level during the fault steady-state period. The positive line voltage in the three fault steady-state conditions is all below 70kV, and the line low voltage protection can operate correctly.

[0079] The coordinated control method for line low-voltage protection of a symmetrical unipolar HVDC transmission system provided in this embodiment determines whether to start the current adaptive switching strategy based on a starting criterion. If the starting criterion is established, the minimum value of the positive DC current on the inverter side and the negative DC current on the inverter side of the symmetrical unipolar HVDC transmission system is selected as the input of the inverter side controller to ensure that the DC line voltage value can be controlled below the line low-voltage protection setting value, so that the line low-voltage protection can correctly exit the action, and optimizes the "embedded" symmetrical unipolar HVDC transmission system line low-voltage protection control coordinated strategy to cope with line faults with higher resistance transition resistors.

[0080] Embodiment 2:

[0081] This embodiment provides a symmetrical unipolar high voltage direct current transmission system line low voltage protection control coordination device, including:

[0082] Startup module: used to start the current adaptive switching strategy based on the preset startup criteria, so that the line low voltage protection can operate correctly when a fault occurs in the symmetrical unipolar high-voltage direct current transmission system;

[0083] Among them, the current adaptive switching strategy includes:

[0084] The minimum value of the positive DC current on the inverter side and the negative DC current on the inverter side of the symmetrical unipolar high voltage direct current transmission system is selected as the input of the inverter side controller.

[0085] In this embodiment, the startup module includes:

[0086] Acquisition unit: used to collect the positive pole measurement current and negative pole measurement current of the inverter side of the symmetrical monopolar high voltage direct current transmission system;

[0087] A judgment unit: used to judge whether a preset start criterion is established or not according to the measured current of the positive pole on the inverter side and the measured current of the negative pole on the inverter side of the symmetrical unipolar high voltage direct current transmission system, and output a current adaptive switching signal if the preset start criterion is established;

[0088] Switching unit: used to start the current adaptive switching strategy according to the current adaptive switching signal.

[0089] In this embodiment, the start criterion is:

[0090] i dp2 +i dn2 >Δ

[0091] Among them, i dp2 is the positive pole measured current on the inverter side of the symmetrical unipolar HVDC transmission system, i dn2 is the negative pole measured current on the inverter side of the symmetrical unipolar HVDC transmission system, Δ is the preset starting criterion constant; when the starting criterion is met, the starting current adaptive switching strategy is adopted.

[0092] The symmetrical unipolar high-voltage direct current transmission system line low-voltage protection control coordination device provided in the embodiment of the present application can execute the symmetrical unipolar high-voltage direct current transmission system line low-voltage protection control coordination method provided in Example 1 of the present application, and has the corresponding functional modules and beneficial effects of the execution method.

[0093] Embodiment 3:

[0094] This embodiment provides a symmetrical unipolar high voltage direct current transmission system line low voltage protection control coordination system, including:

[0095] Storage medium: used to store computer programs;

[0096] Processor: used to execute computer programs to implement the steps of the method in Example 1.

[0097] Embodiment 4:

[0098] This embodiment provides a computer-readable storage medium on which a computer program is stored. When the computer program is executed by a processor, the steps of the method in Embodiment 1 are implemented.

[0099] Embodiment 5:

[0100] This embodiment provides a computer program product, including a computer program, which implements the steps of the method in Embodiment 1 when executed by a processor.

[0101] Those skilled in the art will appreciate that the embodiments of the present application may be provided as methods, systems, or computer program products. Therefore, the present application may adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment in combination with software and hardware. Moreover, the present application may adopt the form of a computer program product implemented in one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) that include computer-usable program code.

[0102] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0103] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0104] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0105] The above are only preferred implementations of the present application. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present application. These improvements and modifications should also be regarded as the scope of protection of the present application.

Claims

1. A coordinated method for low voltage protection control of symmetrical unipolar high voltage direct current transmission system lines, characterized in that: include: Based on the preset starting criteria, the starting current adaptive switching strategy enables the line low voltage protection to operate correctly when a fault occurs in the symmetrical unipolar HVDC transmission system; Wherein, the current adaptive switching strategy includes: Selecting the minimum value of the inverter-side positive DC current and the inverter-side negative DC current of the symmetrical unipolar high-voltage direct current transmission system as an inverter-side controller input; The symmetrical unipolar high-voltage direct current transmission system comprises a rectifier side and an inverter side; the rectifier side and the inverter side both comprise a direct current line (1), two smoothing reactors (2) connected to both sides of the direct current line (1), and two converter valves (3) connected between the two smoothing reactors (2), wherein one converter valve (3) is connected to a YY-type converter transformer (4), one converter valve (3) is connected to a Y△-type converter transformer (5), the YY-type converter transformer (4) and the Y△-type converter transformer (5) are both connected to an alternating current system (7) and an alternating current filter (6), and the YY-type converter transformer (4) and the Y△-type converter transformer (5) are both grounded; the rectifier side and the inverter side are symmetrically connected via the direct current line (1); the inverter side is grounded in the station; The faults of the symmetrical unipolar high-voltage direct current transmission system include a high-resistance grounding fault occurring in the positive direct current line and a high-resistance grounding fault occurring in the negative direct current line; When a high-resistance grounding fault occurs in the positive DC line of the symmetrical monopolar high-voltage direct current transmission system, the positive DC current on the inverter side is less than the negative DC current on the inverter side, and the positive DC current on the inverter side is selected as the inverter side controller input. The inverter side controller input and the rectifier side controller input are distributed in different loops, so that the current value of the fault branch is controlled to 0.1 times the rated current value, and then the DC line voltage value is controlled below the line low voltage protection setting value, so that the line low voltage protection can operate correctly; When a high-resistance grounding fault occurs in the negative DC line of the symmetrical unipolar high-voltage direct current transmission system, the positive DC current on the inverter side is greater than the negative DC current on the inverter side, and the negative DC current on the inverter side is selected as the inverter side controller input. The inverter side controller input and the rectifier side controller input are distributed in different loops, thereby controlling the current value of the fault branch to 0.1 times the rated current value, and then controlling the DC line voltage value to below the line low voltage protection setting, so that the line low voltage protection can operate correctly.

2. The coordinated method for low voltage protection control of symmetrical unipolar high voltage direct current transmission system lines according to claim 1, characterized in that: The start criterion is: ； in, The positive pole current is measured on the inverter side of a symmetrical unipolar HVDC transmission system. The negative pole current is measured on the inverter side of a symmetrical unipolar HVDC transmission system. Set the value for the preset start criterion; When the starting criterion is met, the starting current adaptive switching strategy is implemented.

3. A symmetrical unipolar high voltage direct current transmission system line low voltage protection control coordination device, characterized in that: include: Startup module: used to start the current adaptive switching strategy based on the preset startup criteria, so that the line low voltage protection can operate correctly when a fault occurs in the symmetrical unipolar high-voltage direct current transmission system; Wherein, the current adaptive switching strategy includes: Selecting the minimum value of the inverter-side positive DC current and the inverter-side negative DC current of the symmetrical unipolar high-voltage direct current transmission system as an inverter-side controller input; The symmetrical unipolar high-voltage direct current transmission system comprises a rectifier side and an inverter side; the rectifier side and the inverter side both comprise a direct current line (1), two smoothing reactors (2) connected to both sides of the direct current line (1), and two converter valves (3) connected between the two smoothing reactors (2), wherein one converter valve (3) is connected to a YY-type converter transformer (4), one converter valve (3) is connected to a Y△-type converter transformer (5), the YY-type converter transformer (4) and the Y△-type converter transformer (5) are both connected to an alternating current system (7) and an alternating current filter (6), and the YY-type converter transformer (4) and the Y△-type converter transformer (5) are both grounded; the rectifier side and the inverter side are symmetrically connected via the direct current line (1); the inverter side is grounded in the station; The faults of the symmetrical unipolar high-voltage direct current transmission system include a high-resistance grounding fault occurring in the positive direct current line and a high-resistance grounding fault occurring in the negative direct current line; When a high-resistance grounding fault occurs in the positive DC line of the symmetrical monopolar high-voltage direct current transmission system, the positive DC current on the inverter side is less than the negative DC current on the inverter side, and the positive DC current on the inverter side is selected as the inverter side controller input. The inverter side controller input and the rectifier side controller input are distributed in different loops, so that the current value of the fault branch is controlled to 0.1 times the rated current value, and then the DC line voltage value is controlled below the line low voltage protection setting value, so that the line low voltage protection can operate correctly; When a high-resistance grounding fault occurs in the negative DC line of the symmetrical unipolar high-voltage direct current transmission system, the positive DC current on the inverter side is greater than the negative DC current on the inverter side, and the negative DC current on the inverter side is selected as the inverter side controller input. The inverter side controller input and the rectifier side controller input are distributed in different loops, thereby controlling the current value of the fault branch to 0.1 times the rated current value, and then controlling the DC line voltage value to below the line low voltage protection setting, so that the line low voltage protection can operate correctly.

4. The symmetrical unipolar high voltage direct current transmission system line low voltage protection control coordination device according to claim 3, characterized in that: The startup module includes: A collection unit: used for collecting the measured current of the positive pole on the inverter side and the measured current of the negative pole on the inverter side of the symmetrical monopolar high voltage direct current transmission system; A judgment unit: used to judge whether a preset start criterion is established or not according to the measured current of the positive pole on the inverter side and the measured current of the negative pole on the inverter side of the symmetrical monopolar high voltage direct current transmission system, and if the preset start criterion is established, output a current adaptive switching signal; Switching unit: used to start the current adaptive switching strategy according to the current adaptive switching signal.

5. The symmetrical unipolar high voltage direct current transmission system line low voltage protection control coordination device according to claim 3, characterized in that: The start criterion is: ； in, The positive pole current is measured on the inverter side of a symmetrical unipolar HVDC transmission system. The negative pole current is measured on the inverter side of a symmetrical unipolar HVDC transmission system. Set the value for the preset start criterion; When the starting criterion is met, the starting current adaptive switching strategy is implemented.

6. A symmetrical unipolar high voltage direct current transmission system line low voltage protection control coordination system, characterized in that: include: Storage medium: used to store computer programs; Processor: used to execute the computer program to implement the steps of the method according to any one of claims 1 to 2.

7. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the method described in any one of claims 1 to 2 are implemented.

8. A computer program product, comprising a computer program, characterized in that When the computer program is executed by a processor, the steps of the method described in any one of claims 1 to 2 are implemented.

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